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DOE OE Stationary Energy Storage Publications - PNNL

ES Publication 2017

  1. Lu, X, HJ Chang, JF Bonnett, NL Canfield, K Jung, VL Sprenkle, G Li. "Effect of cathode thickness on the performance of planar Na-NiCl2 battery." Journal of Power Sources 365: 456-462 (Oct. 2017).
    Abstract:Na-beta alumina batteries (NBBs) are one of the most promising technologies for renewable energy storage and grid applications. Commercial NBBs are typically constructed in tubular designs, primarily because of their ease of sealing. However, planar designs are considered superior to tubular counterparts in terms of power output, cell packing, ease of assembly, and thermal management. In this paper, the performance of planar NBBs has been evaluated at an intermediate temperature. In particular, planar Na-NiCl2 cells with different cathode loadings and thicknesses have been studied at 190°C. The effects of the cathode thickness, charging current, and discharging power output on the cell capacity and resistance have been investigated. More than 60% of theoretical cell capacity was retained with constant discharging power levels of 200, 175, and 100 mW/cm2 for 1x, 2x, and 3x cathode loadings, respectively. The cell resistance with 1x and 2x cathode loadings was dominated by ohmic resistance with discharging currents up to 105 mA/cm2, while for 3x cathode loading, it was primarily dominated by ohmic resistance with currents less than 66.67 mA/cm2 and by polarization resistance above 66.67 mA/cm2.
  2. Wu D, M Kintner-Meyer, T Yang, P Balducci. "Analytical sizing methods for behind-the-meter battery storage." Journal of Energy Storage 12: 297-304 (Aug. 2017).
    Abstract:In behind-the-meter application, battery storage system (BSS) is used to reduce a commercial or industrial customer's payment for electricity use, including energy and demand charges. The potential value of BSS in payment reduction and the optimal size can be determined by formulating and solving standard mathematical programming problems. In such mathematical programming methods, users input system information such as load profiles, energy/demand charge rates, and battery characteristics to construct a standard programming problem, which typically involves a large number of constraints and decision variables. The problems are then solved by optimization solvers to obtain numerical solutions. Such kind of methods cannot directly link the obtained optimal battery sizes to input parameters and requires case-by-case analysis. In this paper, we present an objective quantitative analysis of costs and benefits for customer-side BSS, and thereby identify key factors that affect optimal sizing. We then develop simple but effective guidelines for determining the most cost-effective battery size. The proposed analytical sizing methods are innovative, and provide engineering insights on how the optimal battery size varies with system characteristics. We illustrate the proposed methods using practical building load profile and utility rate. The obtained results are compared with the ones using mathematical programming based methods for validation.
  3. Cho SJ, MJ Uddin, PK Alaboina, SS Han, MI Nandasiri, YS Choi, E Hu, KW Nam, AM Schwarz, SK Nune, JS Cho, KH Oh, D Choi. "Exploring Lithium Deficiency in Layered Oxide Cathode for Li-Ion Battery." Advanced Sustainable Systems 1 (7) (June 2017).
    Abstract:The ever-growing demand for high capacity cathode materials is on the rise since the futuristic applications are knocking on the door. Conventional approach to developing such cathode relies on the lithium-excess materials to operate the cathode at high voltage and extract more lithium-ion. Yet, they fail to satiate the needs because of their unresolved issues upon cycling such as, for lithium manganese-rich layered oxides-their voltage fading, and for as nickel-based layered oxides-the structural transition. Here, in contrast, lithium-deficient ratio is demonstrated as a new approach to attain high capacity at high voltage for layered oxide cathodes. Rapid and cost effective lithiation of a porous hydroxide precursor with lithium deficient ratio is acted as a driving force to partially convert the layered material to spinel phase yielding in a multiphase structure (MPS) cathode material. Upon cycling, MPS reveals structural stability at high voltage and high temperature and results in fast lithium-ion diffusion by providing a distinctive solid electrolyte interface (SEI) chemistry-MPS displays minimum lithium loss in SEI and forms a thinner SEI. MPS thus offers high energy and high power applications and provides a new perspective compared to the conventional layered cathode materials denying the focus for lithium excess material.
  4. Li Y ,An Q ,Cheng Y ,Liang Y ,Ren Y ,Sun CJ ,Dong H ,Tang Z ,Li G ,Yao Y. "A high-voltage rechargeable magnesium-sodium hybrid battery." Nano Energy 34: 188-194 (April 2017).
    Abstract:Growing global demand of safe and low-cost energy storage technology triggers strong interests in novel battery concepts beyond state-of-art Li-ion batteries. Here we report a high-voltage rechargeable Mg-Na hybrid battery featuring dendrite-free deposition of Mg anode and Na-intercalation cathode as a low-cost and safe alternative to Li-ion batteries for large-scale energy storage. A prototype device using a Na3V2(PO4)3 cathode, a Mg anode, and a Mg-Na dual salt electrolyte exhibits the highest voltage (2.60 V vs. Mg) and best rate performance (86% capacity retention at 10C rate) among reported hybrid batteries. Synchrotron radiation-based X-ray absorption near edge structure (XANES), atomic-pair distribution function (PDF), and high-resolution X-ray diffraction (HRXRD) studies reveal the chemical environment and structural change of Na3V2(PO4)3 cathode during the Na ion insertion/deinsertion process. XANES study shows a clear reversible shift of vanadium K-edge and HRXRD and PDF studies reveal a reversible two-phase transformation and V-O bond length change during cycling. The energy density of the hybrid cell could be further improved by developing electrolytes with a higher salt concentration and wider electrochemical window. This work represents a significant step forward for practical safe and low-cost hybrid batteries.
  5. Chang HJ ,Lu X ,Bonnett J F,Canfield N L,Son S ,Park YC ,Jung K ,Sprenkle V L,Li G. "Development of intermediate temperature sodium nickel chloride rechargeable batteries using conventional polymer sealing technologies." Journal of Power Sources 348: 150-157 (April 2017).
    Abstract:Developing advanced and reliable electrical energy storage systems is critical to fulfill global energy demands and stimulate the growth of renewable energy resources. Sodium metal halide batteries have been under serious consideration as a low cost alternative energy storage device for stationary energy storage systems. Yet, there are number of challenges to overcome for the successful market penetration, such as high operating temperature and hermetic sealing of batteries that trigger an expensive manufacturing process. Here we demonstrate simple, economical and practical sealing technologies for Na-NiCl2 batteries operated at an intermediate temperature of 190°C. Conventional polymers are implemented in planar Na-NiCl2 batteries after a prescreening test, and their excellent compatibilities and durability are demonstrated by a stable performance of Na-NiCl2 battery for more than 300 cycles. The sealing methods developed in this work will be highly beneficial and feasible for prolonging battery cycle life and reducing manufacturing cost for Na-based batteries at elevated temperatures (<200°C).
  6. Soto F A,Yan P ,Engelhard M H,Marzouk A ,Wang C ,Liu J ,Sprenkle V L,El-Mellouhi F ,Balbuena P B,Li X. "Tuning the Solid Electrolyte Interphase for Selective Li- and Na-Ion Storage in Hard Carbon." Advanced Materials 29 (18): 1606860 (March 2017).
    Abstract:Solid-electrolyte interphase (SEI) films with controllable properties are highly desirable for improving battery performance. In this paper, a combined experimental and theoretical approach is used to study SEI films formed on hard carbon in Li- and Na-ion batteries. It is shown that a stable SEI layer can be designed by precycling an electrode in a desired Li- or Na-based electrolyte, and that ionic transport can be kinetically controlled. Selective Li- and Na-based SEI membranes are produced using Li- or Na-based electrolytes, respectively. The Na-based SEI allows easy transport of Li ions, while the Li-based SEI shuts off Na-ion transport. Na-ion storage can be manipulated by tuning the SEI layer with film-forming electrolyte additives, or by preforming an SEI layer on the electrode surface. The Na specific capacity can be controlled to < 25 mAh g-1;= 1/10 of the normal capacity (250 mAh g-1). Unusual selective/preferential transport of Li ions is demonstrated by preforming an SEI layer on the electrode surface and corroborated with a mixed electrolyte. This work may provide new guidance for preparing good ion-selective conductors using electrochemical approaches.
  7. Chang HJ ,Canfield N L,Jung K ,Sprenkle V L,Li G. "Advanced Na-NiCl2 Battery Using Nickel-Coated Graphite with Core-Shell Microarchitecture." ACS Applied Materials & Interfaces 9 (13): 11609-11614 (March 2017).
    Abstract:Stationary electric energy storage devices (rechargeable batteries) have gained increasing prominence due to great market needs, such as smoothing the fluctuation of renewable energy resources and supporting the reliability of the electric grid. With regard to raw materials availability, sodium-based batteries are better positioned than lithium batteries due to the abundant resource of sodium in Earth's crust. However, the sodium-nickel chloride (Na-NiCl2) battery, one of the most attractive stationary battery technologies, is hindered from further market penetration by its high material cost (Ni cost) and fast material degradation at its high operating temperature. Here, we demonstrate the design of a core?shell microarchitecture, nickel-coated graphite, with a graphite core to maintain electrochemically active surface area and structural integrity of the electron percolation pathway while using 40% less Ni than conventional Na-NiCl2 batteries. An initial energy density of 133 Wh/kg (at ~C/4) and energy efficiency of 94% are achieved at an intermediate temperature of 190°C.
  8. Li B, Liu, J. "Progress and directions in low-cost redox-flow batteries for large-scale energy storage." National Science Review 4 (1): 91-105 (Jan. 2017).
    Abstract:Compared to lithium-ion batteries, redox-flow batteries have attracted widespread attention for long-duration, large-scale energy-storage applications. This review focuses on current and future directions to address one of the most significant challenges in energy storage: reducing the cost of redox-flow battery systems. A high priority is developing aqueous systems with low-cost materials and high-solubility redox chemistries. Highly water-soluble inorganic redox couples are important for developing technologies that can provide high energy densities and low-cost storage. There is also great potential to rationally design organic redox molecules and fine-tune their properties for both aqueous and non-aqueous systems. While many new concepts begin to blur the boundary between traditional batteries and redox-flow batteries, breakthroughs in identifying/developing membranes and separators and in controlling side reactions on electrode surfaces also are needed.
  9. Fu S ,Zhu C ,Song J ,Engelhard M H,Li X ,Zhang P ,Xia H ,Du D ,Lin Y. "Template-directed synthesis of nitrogen- and sulfur-codoped carbon nanowire aerogels with enhanced electrocatalytic performance for oxygen reduction." Nano Research 10 (6): 1888-1895 (Dec. 2016).
    Abstract:Heteroatom doping, precise composition control, and rational morphology design are efficient strategies for producing novel nanocatalysts for the oxygen reduction reaction (ORR) in fuel cells. Herein, a cost-effective approach to synthesize nitrogen- and sulfur-codoped carbon nanowire aerogels using a hard templating method is proposed. The aerogels prepared using a combination of hydrothermal treatment and carbonization exhibit good catalytic activity for the ORR in alkaline solution. At the optimal annealing temperature and mass ratio between the nitrogen and sulfur precursors, the resultant aerogels show comparable electrocatalytic activity to that of a commercial Pt/C catalyst for the ORR. Importantly, the optimized catalyst shows much better long-term stability and satisfactory tolerance for the methanol crossover effect. These codoped aerogels are expected to have potential applications in fuel cells.
  10. Shamie J S,Liu C H,Shaw L L,Sprenkle V L. "New Mechanism for the Reduction of Vanadyl Acetylacetonate to Vanadium Acetylacetonate for Room Temperature Flow Batteries." ChemSusChem 10 (3): 533-540 (Dec. 2016).
    Abstract:In this study, a new mechanism for the reduction of vanadyl acetylacetonate, VO(acac)2, to vanadium acetylacetonate, V(acac)3, is introduced. V(acac)3 has been studied for use in redox flow batteries (RFBs) for some time; however, contamination by moisture leads to the formation of VO(acac)2. In previous work, once this transformation occurs, it is no longer reversible because there is a requirement for extreme low potentials for the reduction to occur. Here, we propose that, in the presence of excess acetylacetone (Hacac) and free protons (H+), the reduction can take place between 2.25 and 1.5 V versus Na/Na+ via a one-electron-transfer reduction. This reduction can take place in situ during discharge in a novel hybrid Na-based flow battery (HNFB) with a molten Na-Cs alloy as the anode. The in situ recovery of V(acac)3 during discharge is shown to allow the Coulombic efficiency of the HNFB to be =100% with little or no capacity decay over cycles. In addition, utilizing two-electron-transfer redox reactions (i.e., V3+/V4+ and V2+/V3+ redox couples) per V ion to increase the energy density of RFBs becomes possible owing to the in situ recovery of V(acac)3 during discharge. The concept of in situ recovery of material can lead to more advances in maintaining the cycle life of RFBs in the future.
  11. Murugesan, V, Q Luo, R Lloyd, Z Nie, X Wei, B Li, VL Sprenkle, JD Londono, M Unlu, W Wang. "Tuning the Perfluorosulfonic Acid Membrane Morphology for Vanadium Redox-Flow Batteries."ACS Applied Materials and Interfaces 8 (50): 34327-34334 (Nov. 2016).
    Abstract:The microstructure of perfluorinated sulfonic acid proton-exchange membranes such as Nafion significantly affects their transport properties and performance in a vanadium redox-flow battery (VRB). In this work, Nafion membranes with various equivalent weights ranging from 1000 to 1500 are prepared and the morphology-property-performance relationship is investigated. NMR and small-angle X-ray scattering studies revealed their composition and morphology variances, which lead to major differences in key transport properties related to proton conduction and vanadium-ion permeation. Their performances are further characterized as VRB membranes. On the basis of this understanding, a new perfluorosulfonic acid membrane is designed with optimal pore geometry and thickness, leading to higher ion selectivity and lower cost compared with the widely used Nafion 115. Excellent VRB single-cell performance (89.3% energy efficiency at 50 mA·cm-2) was achieved along with a stable cyclical capacity over prolonged cycling.
  12. Park, M, J Ryu, W Wang, J Cho. "Material design and engineering of next-generation flow-battery technologies."Nature Review Materials 2 (Nov. 2016).
    Abstract:Spatial separation of the electrolyte and electrode is the main characteristic of flow-battery technologies, which liberates them from the constraints of overall energy content and the energy/power ratio. The concept of a flowing electrolyte not only presents a cost-effective approach for large-scale energy storage, but has also recently been used to develop a wide range of new hybrid energy storage and conversion systems. The advent of flow-based lithium-ion, organic redox-active materials, metal-air cells and photoelectrochemical batteries promises new opportunities for advanced electrical energy-storage technologies. In this Review, we present a critical overview of recent progress in conventional aqueous redox-flow batteries and next-generation flow batteries, highlighting the latest innovative alternative materials. We outline their technical feasibility for use in long-term and large-scale electrical energy-storage devices, as well as the limitations that need to be overcome, providing our view of promising future research directions in the field of redox-flow batteries.
  13. Wang Y, P Yan, J Xiao, X Lu, J Zhang, VL Sprenkle. "Effect of Al2O3 on the sintering of garnet-type Li6.5La3Zr1.5Ta0.5O12."Solid State Ionics 294: 108-115 (Oct. 2016).
    Abstract:It is widely recognized that Al plays a dual role in the fabrication of garnet-type solid electrolytes, i.e., as a dopant that stabilizes the cubic structure and a sintering aid that facilitates the densification. However, the sintering effect of Al2O3 has not been well understood so far because Al is typically "unintentionally" introduced into the sample from the crucible during the fabrication process. In this study, we have investigated the sintering effect of Al on the phase composition, microstructure, and ionic conductivity of Li6.5La3Zr1.5Ta0.5O12 by using an Al-free crucible and intentionally adding various amounts of y-Al2O3. It was found that the densification of Li6.5La3Zr1.5Ta0.5O12 occurred via liquid-phase sintering, with evidence of morphology change among different compositions. Among all of the compositions, samples with 0.05mol Al per unit formula of garnet oxide (i.e., 0.3wt% Al2O3) exhibited the optimal microstructure and the highest total ionic conductivity of 5x10-4Scm-1 at room temperature.
  14. Cheng, Y, HJ Chang, H Dong, D Choi, VL Sprenkle, J Liu, Y Yao, G Li. "Rechargeable Mg-Li hybrid batteries: status and challenges."Journal of Materials Research 31 (20) :3125-3141 (Oct. 2016).
    Abstract:A magnesium-lithium (Mg-Li) hybrid battery consists of an Mg metal anode, a Li+ intercalation cathode, and a dual-salt electrolyte with both Mg2+ and Li+ ions. The demonstration of this technology has appeared in literature for few years and great advances have been achieved in terms of electrolytes, various Li cathodes, and cell architectures. Despite excellent battery performances including long cycle life, fast charge/discharge rate, and high Coulombic efficiency, the overall research of Mg-Li hybrid battery technology is still in its early stage, and also raised some debates on its practical applications. In this regard, we focus on a comprehensive overview of Mg-Li hybrid battery technologies developed in recent years. Detailed discussion of Mg-Li hybrid operating mechanism based on experimental results from literature helps to identify the current status and technical challenges for further improving the performance of Mg-Li hybrid batteries. Finally, a perspective for Mg-Li hybrid battery technologies is presented to address strategic approaches for existing technical barriers that need to be overcome in future research direction.

ES Publication 2016

  1. Choi D, C Zhu, S Fu, D Du, MH Engelhard, Y Lin. "Electrochemically Controlled Ion-exchange Property of Carbon Nanotubes/Polypyrrole Nanocomposite in Various Electrolyte Solutions." Electroanalysis 29 (3): 929-936 (Sept. 2016).
    Abstract: The electrochemically controlled ion-exchange properties of multi-wall carbon nanotube (MWNT)/electronically conductive polypyrrole (PPy) polymer composite in the various electrolyte solutions have been investigated. The ion-exchange behavior, rate and capacity of the electrochemically deposited polypyrrole with and without carbon nanotube (CNT) were compared and characterized using cyclic voltammetry (CV), chronoamperometry (CA), electrochemical quartz crystal microbalance (EQCM), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). It has been found that the presence of carbon nanotube backbone resulted in improvement in ion-exchange rate, stability of polypyrrole, and higher anion loading capacity per PPy due to higher surface area, electronic conductivity, porous structure of thin film, and thinner film thickness providing shorter diffusion path. Chronoamperometric studies show that electrically switched anion exchange could be completed more than 10 times faster than pure PPy thin film. The anion selectivity of CNT/PPy film is demonstrated using X-ray photoelectron spectroscopy (XPS).
  2. Fu, S, C Zhu, J Song, MH Engelhard, X Li, D Du, Y Lin. "Highly Ordered Mesoporous Bimetallic Phosphides as Efficient Oxygen Evolution Electrocatalysts."ACS Energy Letters 1 (4) :792-796 (Sept. 2016).
    Abstract:Oxygen evolution from water using earth-abundant transition-metal-based catalysts is of importance for the commercialization of water electrolyzers. Herein, we report a hard templating method to synthesize transition metal phosphides with uniform shape and size. By virtue of the structural feature, synergistic effects among metals, and the in situ formed active species, the as-prepared phosphides with optimized composition present enhanced electrocatalytic performance toward the oxygen evolution reaction in alkaline solution. In detail, the catalyst with optimized composition reaches a current density of 10 mA/cm2 at a potential of 1.511 V vs a reversible hydrogen electrode, which is much lower than that of a commercial RuO2 catalyst. Our work offers a new strategy to optimize the catalysts for water splitting by controlling the morphology and composition.
  3. Li X, P Yan, MH Engelhard, AJ Crawford, V Viswanathan, C Wang, J Liu, VL Sprenkle. "The importance of solid electrolyte interphase formation for long cycle stability full-cell Na-ion batteries."Nano Energy 27: 664-672 (Sept. 2016).
    Abstract:Na-ion battery, as an alternative high-efficiency and low-cost energy storage device to Li-ion battery, has attracted wide interest for electrical grid and vehicle applications. However, demonstration of a full-cell battery with high energy and long cycle life remains a significant challenge. Here, we investigated the role of solid electrolyte interphase (SEI) formation on both cathodes and anodes and revealed a potential way to achieve long-term stability for Na-ion battery full-cells. Pre-cycling of cathodes and anodes leads to preformation of SEI, and hence mitigates the consumption of Na ions in full-cells. The example full-cell of Na0.44MnO2-hard carbon with pre-cycled and capacity-matched electrodes can deliver a specific capacity of ~116 mAh/g based on Na0.44MnO2 at 1 C rate (1 C=120 mA/g). The corresponding specific energy is ~313 Wh/kg based on the cathode. Excellent cycling stability with ~77% capacity retention over 2000 cycles was demonstrated at 2 C rate. Our work represents a leap forward in Na-ion battery development.
  4. Wei X, W Duan, J Huang, L Zhang, B Li, DM Reed, W Xu, VL Sprenkle. "A High-Current, Stable Nonaqueous Organic Redox Flow Battery."ACS Energy Letters 1: 705-711 (Sept. 2016).
    Abstract:Nonaqueous redox flow batteries are promising in pursuit of high energy density storage systems owing to the broad voltage windows (>2 V) but currently are facing key challenges such as limited cyclability and rate performance. To address these technical hurdles, here we report the nonaqueous organic flow battery chemistry based on N-methylphthalimide anolyte and 2,5-di-tert-butyl-1-methoxy-4-[2'-methoxyethoxy]benzene catholyte, which harvests a theoretical cell voltage of 2.30 V. The redox flow chemistry exhibits excellent cycling stability under both cyclic voltammetry and flow cell tests upon repeated cycling. A series of Daramic and Celgard porous separators are evaluated in this organic flow battery, which enable the cells to be operated at greatly improved current densities as high as 50 mA·cm-2 compared to those of other nonaqueous flow systems. The stable cyclability and high-current operations of the organic flow battery system represent significant progress in the development of promising nonaqueous flow batteries.
  5. Li B, J Liu, Z Nie, W Wang, DM Reed, J Liu, P McGrail, VL Sprenkle. "Metal-Organic Frameworks as Highly Active Electrocatalysts for High-Energy Density, Aqueous Zinc-Polyiodide Redox Flow Batteries."Nano Letters 16 (7): 4335-4340 (June 2016).
    Abstract:The new aqueous zinc-polyiodide redox flow battery (RFB) system with highly soluble active materials as well as ambipolar and bifunctional designs demonstrated significantly enhanced energy density, which shows great potential to reduce RFB cost. However, the poor kinetic reversibility and electrochemical activity of the redox reaction of I3-/I- couples on graphite felts (GFs) electrode can result in low energy efficiency. Two nanoporous metal-organic frameworks (MOFs), MIL-125-NH2 and UiO-66-CH3, that have high surface areas when introduced to GF surfaces accelerated the I3-/I- redox reaction. The flow cell with MOF-modified GFs serving as a positive electrode showed higher energy efficiency than the pristine GFs; increases of about 6.4% and 2.7% occurred at the current density of 30 mA/cm2 for MIL-125-NH2 and UiO-66-CH3, respectively. Moreover, UiO-66-CH3 is more promising due to its excellent chemical stability in the weakly acidic electrolyte. This letter highlights a way for MOFs to be used in the field of RFBs.
  6. Cheng Y, L Luo, L Zhong, J Chen, B Li, W Wang, SX Mao, C Wang, VL Sprenkle, G Li, J Liu. "Highly Reversible Zinc-Ion Intercalation into Chevrel Phase Mo6S8 Nanocubes and Applications for Advanced Zinc-Ion Batteries."ACS Applied Materials and Interfaces 8 (22):13673-13677 (June 2016).
    Abstract:This work describes the synthesis of Chevrel phase Mo6S8 nanocubes and its application as the anode material for rechargeable Zn-ion batteries. Mo6S8 can host Zn(2+) ions reversibly in both aqueous and nonaqueous electrolytes with specific capacities around 90 mAh/g, and exhibited remarkable intercalation kinetics and cyclic stability. In addition, we assembled full cells by integrating Mo6S8 anodes with zinc-polyiodide (I(-)/I3(-))-based catholytes, and demonstrated that such full cells were also able to deliver outstanding rate performance and cyclic stability. This first demonstration of a zinc-intercalating anode could inspire the design of advanced Zn-ion batteries.
  7. Estevez L, DM Reed, Z Nie, AM Schwarz, MI Nandasiri, JP Kizewski, W Wang, EC Thomsen, J Liu, J Zhang, VL Sprenkle, B Li. "Tunable oxygen functional groups as electrocatalysts on graphite felt surfaces for all-vanadium flow batteries."ChemSusChem 9 (12): 1455-1461 (May 2016).
    Abstract:A dual oxidative approach using O2 plasma followed by treatment with H2O2 to impart oxygen functional groups onto the surface of a graphite felt electrode. When used as electrodes for an all-vanadium redox flow battery (VRB) system, the energy efficiency of the cell is enhanced by 8.2 % at a current density of 150 mA cm-2 compared with one oxidized by thermal treatment in air. More importantly, by varying the oxidative techniques, the amount and type of oxygen groups was tailored and their effects were elucidated. It was found that O-C=O groups improve the cells performance whereas the C-O and C=O groups degrade it. The reason for the increased performance was found to be a reduction in the cell overpotential after functionalization of the graphite felt electrode. This work reveals a route for functionalizing carbon electrodes to improve the performance of VRB cells. This approach can lower the cost of VRB cells and pave the way for more commercially viable stationary energy storage systems that can be used for intermittent renewable energy storage.
  8. Shen F, W Luo, J Dai, Y Yao, M Zhu, E Hitz, Y Tang, Y Chen, VL Sprenkle, X Li, L Hu. "Ultra-Thick, Low-Tortuosity, and Mesoporous Wood Carbon Anode for High-Performance Sodium-Ion Batteries."Advanced Energy Materials 6 (14) (May 2016).
    Abstract:Pyrolysis of earth-abundant wood yields to ultra-thick, low-tortuosity, and mesoporous carbon anodes for sodium-ion batteries. Such a low-tortuosity and porous structure promotes electrolyte diffusion and provides fast transport channels for Na ions, which enables a high areal capacity.
  9. Dong H, Y Li, Y Liang, G Li, CJ Sun, Y Ren, Y Lu, Y Yao. "A magnesium-sodium hybrid battery with high operating voltage."Chemical Communications 52: 8263-8266 (April 2016).
    Abstract:We report a high performance magnesium-sodium hybrid battery utilizing a magnesium-sodium dual-salt electrolyte, a magnesium anode, and a Berlin green cathode. The cell delivers an average discharge voltage of 2.2 V and a reversible capacity of 143 mA h g-1. We also demonstrate the cell with an energy density of 135 W h kg-1 and a high power density of up to 1.67 kW kg-1.
  10. Wang W, VL Sprenkle. "Energy storage: Redox flow batteries go organic."Nature Chemistry 8 (3): 204-206 (Feb. 2016).
    Abstract:Access to sustainable and affordable energy is the foundation for the economic growth and future prosperity of our society. Given the drive to also reduce the carbon footprint associated with traditional fossil-based electricity generation, renewable resources could provide a clean and sustainable energy future. However, while the amount of energy produced from renewable resources such as solar and wind is steadily increasing, and the generation costs continuously falling, it still only represents a small fraction of current energy production. One big issue is the intermittent and fluctuating nature of energy produced from renewables and this will threaten the stability of the grid when the energy share from these resources surpasses 20% of the overall energy capacity1. Electrical energy storage is a potentially cost-effective approach to solving this problem and would be beneficial for renewable energy integration, balancing the mismatch between supply and demand, as well as improving the overall reliability and efficiency of the grid.
  11. Choi D, X Li, WA Henderson, Q Huang, SK Nune, JP Lemmon, VL Sprenkle. "LiCoPO4 cathode from a CoHPO4xH2O nanoplate precursor for high voltage Li-ion batteries." Heliyon 2 (2) (Feb. 2016).
    Abstract:A highly crystalline LiCoPO4/C cathode material has been synthesized without noticeable impurities via a single step solid-state reaction using CoHPO4xH2O nanoplate as a precursor obtained by a simple precipitation route. The LiCoPO4/C cathode delivered a specific capacity of 125 mAhg-1 at a charge/discharge rate of C/10. The nanoplate precursor and final LiCoPO4/C cathode have been characterized using X-ray diffraction, thermogravimetric analysis - differential scanning calorimetry (TGA-DSC), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) and the electrochemical cycling stability has been investigated using different electrolytes, additives and separators.
  12. Cheng Y, D Choi, KS Han, KT Mueller, J Zhang, VL Sprenkle, J Liu, G Li. "Toward the design of high voltage magnesium-lithium hybrid batteries using dual-salt electrolytes." Chemical Communications 52: 5379-5382 (Feb. 2016).
    Abstract:We report a design of high voltage magnesium-lithium (Mg-Li) hybrid batteries through rational control of the electrolyte chemistry, electrode materials and cell architecture. Prototype devices with a structure of Mg-Li/LiFePO4 (LFP) and Mg-Li/LiMn2O4 (LMO) have been investigated. A Mg-Li/LFP cell using a dual-salt electrolyte 0.2 M [Mg2Cl2(DME)4][AlCl4]2 and 1.0 M LiTFSI exhibits voltages higher than 2.5 V (vs. Mg) and a high specific energy density of 246 W h kg-1 under conditions that are amenable for practical applications. The successful demonstrations reported here could be a significant step forward for practical hybrid batteries.
  13. Li G, X Lu, JY Kim, KD Meinhardt, HJ Chang, NL Canfield, VL Sprenkle. "Advanced intermediate temperature sodium-nickel chloride batteries with ultra-high energy density." Nature Communications 7:10683 (Feb. 2016).
    Abstract:Sodium-metal halide batteries have been considered as one of the more attractive technologies for stationary electrical energy storage, however, they are not used for broader applications despite their relatively well known redox system. One of the roadblocks hindering market penetration is the high operating temperature. Here we demonstrate that planar sodium-nickel chloride batteries can be operated at an intermediate temperature of 190°C with ultra-high energy density. A specific energy density of 350 Wh kg -1, higher than that of conventional tubular sodium-nickel chloride batteries (280°C), is obtained for planar sodium-nickel chloride batteries operated at 190°C over a long-term cell test (1,000 cycles), and it attributed to the slower particle growth of the cathode materials at the lower operating temperature. Results reported here demonstrate that planar sodium-nickel chloride batteries operated at an intermediate temperature could greatly benefit this traditional energy storage technology by improving battery energy density, cycle life and reducing material costs.
  14. Reed DM, EC Thomsen, B Li, W Wang, Z Nie, BJ Koeppel, VL Sprenkle. "Performance of a low cost interdigitated flow design on a 1 kW class all vanadium mixed acid redox flow battery." Journal of Power Sources 306: 24-31 (Feb. 2016).
    Abstract:Three flow designs were operated in a 3-cell 1 kW class all vanadium mixed acid redox flow battery. The influence of electrode surface area and flow rate on the coulombic, voltage, and energy efficiency and the pressure drop in the flow circuit will be discussed and correlated to the flow design. Material cost associated with each flow design will also be discussed.
  15. Liu L, X Wei, Z Nie, VL Sprenkle, W Wang. "A Total Organic Aqueous Redox Flow Battery Employing a Low Cost and Sustainable Methyl Viologen Anolyte and 4-HO-TEMPO Catholyte." Advanced Energy Materials 6(3):1-8 (Dec. 2015).
    Abstract:Increasing worldwide energy demands and rising CO2 emissions have motivated a search for new technologies to take advantage of renewables such as solar and wind energies. Redox flow batteries (RFBs) with their high power density, high energy efficiency, scalability (up to MW and MWh), and safety features are one suitable option for integrating such energy sources and overcoming their intermittency. However, resource limitation and high system costs of current RFB technologies impede wide implementation. Here, a total organic aqueous redox flow battery (OARFB) is reported, using low-cost and sustainable methyl viologen (MV, anolyte) and 4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl (4-HO-TEMPO, catholyte), and benign NaCl supporting electrolyte. The electrochemical properties of the organic redox active materials are studied using cyclic voltammetry and rotating disk electrode voltammetry. The MV/4-HO-TEMPO ARFB has an exceptionally high cell voltage, 1.25 V. Prototypes of the organic ARFB can be operated at high current densities ranging from 20 to 100 mA cm2, and deliver stable capacity for 100 cycles with nearly 100% Coulombic efficiency. The MV/4-HO-TEMPO ARFB displays attractive technical merits and thus represents a major advance in ARFBs.
  16. Lu X, G Li, JY Kim, KD Meinhardt, VL Sprenkle. "Enhanced sintering of ß"-Al2/O3/YSZ with the sintering aids of TiO2 and MnO2." Journal of Power Sources 295:167-174 (Nov. 2015).
    Abstract:ß"-Al2O3 has been the dominated choice for the electrolyte materials of sodium batteries because of its high ionic conductivity, excellent stability with the electrode materials, satisfactory mechanical strength, and low material cost. To achieve adequate electrical and mechanical performance, sintering of ß"-Al2O3 is typically carried out at temperatures above 1600°C with deliberate efforts on controlling the phase, composition, and microstructure. Here, we reported a simple method to fabricate ß"-Al2O3/YSZ electrolyte at relatively lower temperatures. With the starting material of boehmite, single phase of ß"-Al2O3 can be achieved at as low as 1200°C. It was found that TiO2 was extremely effective as a sintering aid for the densification of ß"-Al2O3 and similar behavior was observed with MnO2 for YSZ. With the addition of 2 mol% TiO2 and 5 mol% MnO2, the ß"-Al2O3/YSZ composite was able to be densified at as low as 1400°C with a fine microstructure and good electrical/mechanical performance. This study demonstrated a new approach of synthesis and sintering of ß"-Al2O3/YSZ composite, which represented a simple and low-cost method for fabrication of high-performance ß"-Al2O3/YSZ electrolyte.
  17. Wei X, G Xia, BW Kirby, EC Thomsen, B Li, Z Nie, GG Graff, J Liu, VL Sprenkle, W Wang. "An Aqueous Redox Flow Battery Based on Neutral Alkali Metal Ferri/ferrocyanide and Polysulfide Electrolytes." Journal of The Electrochemical Society 163(1):A5150-A5153 (Nov. 2015).
    Abstract:We have demonstrated a new ferri/ferrocyanide - polysulfide (Fe/S) flow battery, which employs less corrosive, relatively environmentally benign neutral alkali metal ferri/ferrocyanide and alkali metal polysulfides as the active redox couples. A cobalt nanoparticle - decorated graphite felt was used at the polysulfide side as the catalyst. Excellent electrochemical performance was successfully acquired in the Fe/S flow cells with high cell efficiencies (99% coulombic efficiency and ~74% energy efficiency) and good cycling stability over extended charge/discharge operations. The positive half-cell appears to be the performance - limiting side in the Fe/S flow battery determined by using a carbon cloth probe. The inexpensive redox materials and possibly cell part materials can lead to reduced capital cost, making the Fe/S flow battery a promising cost-effective energy storage technology candidate.
  18. Reed DM, EC Thomsen, B Li, W Wang, Z Nie, BJ Koeppel, JP Kizewski, VL Sprenkle. "Stack Developments in a kW Class All Vanadium Mixed Acid Redox Flow Battery at the Pacific Northwest National Laboratory." Journal of the Electrochemical Society 163 (1):A5211-A5219 (Nov. 2015).
    Abstract:Over the past several years, efforts have been focused on improving the performance of kW class all vanadium mixed acid redox flow battery stacks with increasing current density. The influence of the Nafion membrane resistance, an interdigitated design to reduce the pressure drop in the electrolyte circuit, the temperature of the electrolyte, and the electrode structure will be discussed and correlated to the electrical performance. Improvements to the stack energy efficiency and how those improvements translate to the overall system efficiency will also be discussed.
  19. Crawford A, V Viswanathan, D Stephenson, W Wang, EC Thomsen, DM Reed, B Li, PJ Balducci, M Kinter-Meyer, VL Sprenkle. "Comparative analysis for various redox flow batteries chemistries using a cost performance model." Journal of Power Sources 293: 388-399 (Oct. 2015).
    Abstract:The total energy storage system cost is determined by means of a robust performance-based cost model for multiple flow battery chemistries. Systems aspects such as shunt current losses, pumping losses and various flow patterns through electrodes are accounted for. The system cost minimizing objective function determines stack design by optimizing the state of charge operating range, along with current density and current-normalized flow. The model cost estimates are validated using 2-kW stack performance data for the same size electrodes and operating conditions. Using our validated tool, it has been demonstrated that an optimized all-vanadium system has an estimated system cost of < $350 kWh-1 for 4-h application. With an anticipated decrease in component costs facilitated by economies of scale from larger production volumes, coupled with performance improvements enabled by technology development, the system cost is expected to decrease to 160 kWh-1 for a 4-h application, and to $100 kWh-1 for a 10-h application. This tool has been shared with the redox flow battery community to enable cost estimation using their stack data and guide future direction.

ES Publication 2015

  1. Cosimbescu L, X Wei, M Vijayakumar, W Xu, ML Helm, SD Burton, CM Sorensen, J Liu, VL Sprenkle, W Wang. "Anion-Tunable Properties and Electrochemical Performance of Functionalized Ferrocene Compounds." Scientific Reports 5:14117 (Sept. 2015).
    Abstract:We report a series of ionically modified ferrocene compounds for hybrid lithium-organic non-aqueous redox flow batteries, based on the ferrocene/ferrocenium redox couple as the active catholyte material. Tetraalkylammonium ionic moieties were incorporated into the ferrocene structure, in order to enhance the solubility of the otherwise relatively insoluble ferrocene. The effect of various counter anions of the tetraalkylammonium ionized species appended to the ferrocene, such as bis(trifluoromethanesulfonyl)imide, hexafluorophosphate, perchlorate, tetrafluoroborate, and dicyanamide on the solubility of the ferrocene was investigated. The solution chemistry of the ferrocene species was studied, in order to understand the mechanism of solubility enhancement. Finally, the electrochemical performance of these ionized ferrocene species was evaluated and shown to have excellent cell efficiency and superior cycling stability.
  2. Lu X, ME Bowden, VL Sprenkle, J Liu. "A Low Cost, High Energy Density, and Long Cycle Life Potassium-Sulfur Battery for Grid-Scale Energy Storage." Advanced Materials 27(39):5915-5922 (Aug. 2015).
    Abstract:A potassium-sulfur battery using K+-conducting beta-alumina as the electrolyte to separate a molten potassium metal anode and a sulfur cathode is presented. The results indicate that the battery can operate at as low as 150°C with excellent performance. This study demonstrates a new type of high-performance metal-sulfur battery that is ideal for grid-scale energy-storage applications.
  3. Wei X, W Xu, J Huang, L Zhang, ED Walter, CW Lawrence, M Vijayakumar, WA Henderson, TL Liu, L Cosimbescu, B Li, VL Sprenkle, W Wang. "Radical Compatibility with Nonaqueous Electrolytes and Its Impact on an All-Organic Redox Flow Battery." Angewandte Chemie 54 (30):8684-8687 (July 2015).
    Abstract:Nonaqueous redox flow batteries hold the promise of achieving higher energy density because of the broader voltage window than aqueous systems, but their current performance is limited by low redox material concentration, cell efficiency, cycling stability, and current density. We report a new nonaqueous all-organic flow battery based on high concentrations of redox materials, which shows significant, comprehensive improvement in flow battery performance. A mechanistic electron spin resonance study reveals that the choice of supporting electrolytes greatly affects the chemical stability of the charged radical species especially the negative side radical anion, which dominates the cycling stability of these flow cells. This finding not only increases our fundamental understanding of performance degradation in flow batteries using radical-based redox species, but also offers insights toward rational electrolyte optimization for improving the cycling stability of these flow batteries.
  4. Reed DM, ED Thomsen, W Wang, Z Nie, B Li, X Wei, BJ Koeppel, VL Sprenkle. "Performance of Nafion® N115, Nafion® NR-212, and Nafion® NR-211 in a 1 kW class all vanadium mixed acid redox flow battery."Journal of Power Sources 285:425-430 (July 2015).
    Abstract:Three Nafion® membranes of similar composition but different thicknesses were operated in a 3-cell 1 kW class all vanadium mixed acid redox flow battery. The influence of current density on the charge/discharge characteristics, coulombic and energy efficiency, capacity fade, operating temperature and pressure drop in the flow circuit will be discussed and correlated to the Nafion® membrane thickness. Material costs associated with the Nafion® membranes, ease of handling the membranes, and performance impacts will also be discussed.
  5. Canfield NL, JY Kim, JF Bonnett, RL Pearson III, VL Sprenkle, J Kung. "Effects of fabrication conditions on mechanical properties and microstructure of duplex ß"-Al2O3 solid electrolyte." Materials Science and Engineering: B 197: 43-50 (July 2015).
    Abstract:Na-beta batteries are an attractive technology as a large-scale electrical energy storage for grid applications. However, additional improvements in performance and cost are needed for wide market penetration. To improve cell performance by minimizing polarizations, reduction of electrolyte thickness was attempted using a duplex structure consisting of a thin dense electrolyte layer and a porous support layer. In this paper, the effects of sintering conditions, dense electrolyte thickness, and cell orientation on the flexural strength of duplex BASEs fabricated using a vapor phase approach were investigated. It is shown that sintering at temperatures between 1500 and 1550°C results in fine grained microstructures and the highest flexural strength after conversion. Increasing thickness of the dense electrolyte has a small impact on flexural strength, while the orientation of load such that the dense electrolyte is in tension instead of compression has major effects on strength for samples with a well-sintered dense electrolyte.
  6. Kim JY, NL Canfield, JF Bonnett, VL Sprenkle, K Jung, I Hong. "A Duplex ß"-Al2O3 Solid Electrolyte Consisting of A Thin Dense Layer and A Porous Substrate."Solid State Ionics 278: 192-197 (June 2015).
    Abstract:To improve the performance of Na-beta batteries at intermediate temperatures (≤200°C) where much improved cyclability and reduced degradation can be achieved, there is a need to lower the resistance/polarization coming from BASEs while maintaining good strength. In this paper, the concept of a duplex BASE consisting of a thin dense electrolyte and a porous support was proposed as a solution to achieve low area-specific resistance while maintaining good mechanical strength. The effects of various factors including porosity, composition, and the homogeneity of ingredients on the flexural strength of duplex BASEs were examined. In summary, lower porosity, higher YSZ content in the structure, and the attrition milling of powders resulted in improved strength. The area-specific resistance measurement exhibited that the resistance of duplex BASEs was mainly originated from a dense layer. Overall, the maximum strength of 260 MPa and the ASR value of 0.31 cm2 (at 350°C) was achieved from a duplex BASE consisting of a 50 µm thick dense layer (Al2O3: YSZ = 7:3 in volume) and a 500 µm thick porous support (Al2O3: YSZ = 4:6 in volume with 19% open porosity). The effects of various factors on the properties of duplex BASEs will be explained in details.
  7. Li G, X Lu, JY Kim, V Viswanathan, KD Meinhardt, MH Engelhard, VL Sprenkle. "An Advanced Na-FeCl2 ZEBRA Battery for Stationary Energy Storage Application." Advanced Energy Materials 5(12) (June 2015).
    Abstract:In article number 1500357, Guosheng Li, Jin Y. Kim, and co-workers report a remarkably reliable Na-FeCl2 ZEBRA battery for stationary energy storage applications. The removal of surface oxide passivation layers on iron particles is critical and it is attributed to polysulfide species generated from sulfur-based additives through polysulfide reactions. The Na-FeCl2 cells presented can be assembled at the discharge state (NaCl + Fe powder) without handling highly hazardous materials such as anhydrous FeCl2 and metallic sodium.
  8. Shamie JS, C Liu, LL Shaw, VL Sprenkle. "Room Temperature, Hybrid Sodium-Based Flow Batteries with Multi-Electron Transfer Redox Reactions." Scientific Reports 5, article number 11215 (June 2015).
    Abstract:We introduce a new concept of hybrid Na-based flow batteries (HNFBs) with a molten Na alloy anode in conjunction with a flowing catholyte separated by a solid Na-ion exchange membrane for grid-scale energy storage. Such HNFBs can operate at ambient temperature, allow catholytes to have multiple electron transfer redox reactions per active ion, offer wide selection of catholyte chemistries with multiple active ions to couple with the highly negative Na alloy anode, and enable the use of both aqueous and non-aqueous catholytes. Further, the molten Na alloy anode permits the decoupled design of power and energy since a large volume of the molten Na alloy can be used with a limited ion-exchange membrane size. In this proof-of-concept study, the feasibility of multi-electron transfer redox reactions per active ion and multiple active ions for catholytes has been demonstrated. The critical barriers to mature this new HNFBs have also been explored.
  9. Wei X, B Li, W Wang. "Porous Polymeric Composite Separators for Redox Flow Batteries." Polymer Reviews 55(2):247-272 (May 2015).
    Abstract:Currently, the most commonly used membranes in redox flow batteries (RFB) are ion-exchange membranes. In particular, in all vanadium flow battery systems (VRB), perfluorinated polymers such as Nafion® are widely used, owing to their high proton conductivity and chemical stability; however, the extremely high cost of currently available membranes has limited the commercialization of VRB technology. Recently, low-cost porous polymeric composite separators (e.g., polytetrafluoroethylene [PTFE]/silica), as an alternative to traditional ion-exchange membranes, have attracted a great deal of interest because of their significantly lower cost. Porous separators prepared from various polymer materials and inorganic fillers have demonstrated comparable electrochemical performances to that of Nafion? in flow battery tests with different redox chemistries. This paper provides a review of porous separators for flow battery applications. In addition to discussions of separator material selection and preparation methods, we also emphasize the electrochemical performance of various flow battery systems, especially the capacity fade mechanism that is closely related to ion-transport across porous separator.
  10. Cheng Y, RM Stolley, KS Han, Y Shao, BW Arey, NM Washton, KT Mueller, ML Helm, VL Sprenkle, J Liu, G Li. "Highly Active Electrolytes for Rechargeable Mg Batteries Based on [Mg2(μ-Cl)2]2+ Cation Complex in Dimethoxyethane. "Physical Chemistry Chemical Physics 17: 13307-13314 (Apr. 2015).
    Abstract:A novel [Mg2(μ-Cl)2]2+ cation complex, which is highly active for reversible Mg electrodeposition, was identified for the first time in this work. This complex was found to be present in electrolytes formulated in dimethoxyethane (DME) through dehalodimerization of non-nucleophilic MgCl2 by reacting with either Mg salts (such as Mg(TFSI)2, TFSI = bis(trifluoromethane)sulfonylimide) or Lewis acid salts (such as AlEtCl2 or AlCl3). The molecular structure of the cation complex was characterized by single crystal X-ray diffraction, Raman spectroscopy and NMR. The electrolyte synthesis process was studied and rational approaches for formulating highly active electrolytes were proposed. Through control of the anions, electrolytes with an efficiency close to 100%, a wide electrochemical window (up to 3.5 V) and a high ionic conductivity (>6 mS cm-1) were obtained. The understanding of electrolyte synthesis in DME developed in this work could bring significant opportunities for the rational formulation of electrolytes of the general formula [Mg2(μ-Cl)2][anion]x for practical Mg batteries.
  11. Vijayakumar M, N Govind, B Li, X Wei, Z Nie, S Thevuthasan, VL Sprenkle, W Wang. "Aqua-vanadyl ion interaction with Nafion® membranes."Frontiers in Energy Research 3, article number 10 (March 2015).
    Abstract:Lack of comprehensive understanding about the interactions between Nafion membrane and battery electrolytes prevents the straightforward tailoring of optimal materials for redox flow battery applications. In this work, we analyzed the interaction between aqua-vanadyl cation and sulfonic sites within the pores of Nafion membranes using combined theoretical and experimental X-ray spectroscopic methods. Molecular level interactions, namely, solvent share and contact pair mechanisms are discussed based on vanadium and sulfur K-edge spectroscopic analysis.
  12. Han SD, SH Yun, O Borodin, DM Seo, RD Sommer, VG Young, WA Henderson. "Solvate Structures and Computational/Spectroscopic Characterization of LiPF6 Electrolytes."J. Phys. Chem. C 119 (16):8492-8500 (March 2015).
    Abstract:Raman spectroscopy is a powerful method for identifying ion?ion interactions, but only if the vibrational band signatures for the anion coordination modes can be accurately deciphered. The present study characterizes the PF6- anion P-F Raman symmetric stretching vibrational band for evaluating the PF6-Li+ cation interactions within LiPF6 crystalline solvates to create a characterization tool for liquid electrolytes. To facilitate this, the crystal structures for two new solvates-(G3)1:LiPF6 and (DEC)2:LiPF6 with triglyme and diethyl carbonate, respectively-are reported. DFT calculations for Li-PF6 solvates have been used to aid in the assignments of the spectroscopic signatures. The information obtained from this analysis provides key guidance about the ionic association information which may be obtained from a Raman spectroscopic evaluation of electrolytes containing the LiPF6 salt and aprotic solvents. Of particular note is the overlap of the Raman bands for both solvent-separated ion pair (SSIP) and contact ion pair (CIP) coordination in which the PF6- anions are uncoordinated or coordinated to a single Li+ cation, respectively.
  13. Li B, Z Nie, M Vijayakumar, G Li, J Liu, VL Sprenkle, W Wang. "Ambipolar zinc-polyiodide electrolyte for a high-energy density aqueous redox flow battery." Nature Communications 6 article number 6303 (Feb. 2015).
    Abstract:Redox flow batteries are receiving wide attention for electrochemical energy storage due to their unique architecture and advantages, but progress has so far been limited by their low energy density (~25Whl-1). Here we report a high-energy density aqueous zinc-polyiodide flow battery. Using the highly soluble iodide/triiodide redox couple, a discharge energy density of 167Whl-1 is demonstrated with a near-neutral 5.0 M Znl2 electrolyte. Nuclear magnetic resonance study and density functional theory-based simulation along with flow test data indicate that the addition of an alcohol (ethanol) induces ligand formation between oxygen on the hydroxyl group and the zinc ions, which expands the stable electrolyte temperature window to from -20 to 50°C, while ameliorating the zinc dendrite. With the high-energy density and its benign nature free from strong acids and corrosive components, zinc-polyiodide flow battery is a promising candidate for various energy storage applications.
  14. Wei X, W Xu, M Vijayakumar, L Cosimbescu, TL Liu, VL Sprenkle, and W Wang. "TEMPO-based Catholyte for High Energy Density Nonaqueous Redox Flow Batteries." Advanced Materials 26(45):7649-7653 (Dec 2014).
    Abstract:A TEMPO-based non-aqueous electrolyte with the TEMPO concentration as high as 2.0 M is demonstrated as a high-energy-density catholyte for redox flow battery applications. With a hybrid anode, Li|TEMPO flow cells using this electrolyte deliver an energy efficiency of ca. 70% and an impressively high energy density of 126 W h L-1.
  15. Li G, X Lu, JY Kim, MH Engelhard, JP Lemmon, and VL Sprenkle. "The Role of FeS in Initial Activation and Performance Degradation of Na-NiCl2 Batteries." Journal of Power Sources 272:398-403 (Dec 2014).
    Abstract: The role of iron sulfide (FeS) in initial cell activation and degradation in the Na-NiCl2 battery was investigated in this work. The research focused on identifying the effects of the FeS level on the electrochemical performance and morphological changes in the cathode. The x-ray photoelectron spectroscopy study along with battery tests revealed that FeS plays a critical role in initial battery activation by removing passivation layers on Ni particles. It was also found that the optimum level of FeS in the cathode resulted in minimum Ni particle growth and improved battery cycling performance. The results of electrochemical characterization indicated that sulfur species generated in situ during initial charging, such as polysulfide and sulfur, are responsible for removing the passivation layer. Consequently, the cells containing elemental sulfur in the cathode exhibited similar electrochemical behavior during initial charging compared to that of the cells containing FeS.
  16. Seo DM, T Afroz, JL Allen, PD Boyle, PC Trulove, HC DeLong, WA Henderson. "Structural Interactions within Lithium Salt Solvates: Cyclic Carbonates and Esters." J. Phys. Chem. C 118 (45): 25884-25889 (Oct. 2014).
    Abstract:Only limited information is available regarding the manner in which cyclic carbonate and ester solvents coordinate Li+ cations in electrolyte solutions for lithium batteries. One approach to gleaning significant insight into these interactions is to examine crystalline solvate structures. To this end, eight new solvate structures are reported with ethylene carbonate, y-butyrolactone, and y-valerolactone: (EC)3:LiClO4, (EC)2:LiClO4, (EC)2:LiBF4, (GBL)4:LiPF6, (GBL)1:LiClO4, (GVL)1:LiClO4, (GBL)1:LiBF4, and (GBL)1:LiCF3SO3. The crystal structure of (EC)1:LiCF3SO3 is also re-reported for comparison. These structures enable the factors that govern the manner in which the ions are coordinated and the ion/solvent packing?in the solid-state?to be scrutinized in detail.

ES Publication 2014

  1. Vijayakumar, M., Nie, Z., Walter, E., Hu, J., Liu, J., Sprenkle, V. and Wang, W. "Understanding Aqueous Electrolyte Stability through Combined Computational and Magnetic Resonance Spectroscopy: A Case Study on Vanadium Redox Flow Battery Electrolytes." ChemPlusChem doi: 10.1002/cplu.201402139 (Sept 2014).
    Abstract: Commercial sodium-sulphur or sodium-metal halide batteries typically need an operating temperature of 300-350°C, and one of the reasons is poor wettability of liquid sodium on the surface of beta alumina. Here we report an alloying strategy that can markedly improve the wetting, which allows the batteries to be operated at much lower temperatures. Our combined experimental and computational studies suggest that addition of caesium to sodium can markedly enhance the wettability. Single cells with Na-Cs alloy anodes exhibit great improvement in cycling life over those with pure sodium anodes at 175 and 150°C. The cells show good performance even at as low as 95°C. These results demonstrate that sodium-beta alumina batteries can be operated at much lower temperatures with successfully solving the wetting issue. This work also suggests a strategy to use liquid metals in advanced batteries that can avoid the intrinsic safety issues associated with dendrite formation.
  2. Han SD, O Borodin, DM Seo, ZB Zhou, WA Henderson. "Electrolyte Solvation and Ionic Association V. Acetonitrile-Lithium Bis(fluorosulfonyl)imide (LiFSI) Mixtures."Journal of the Electrochemistry Society 161 (14):A2042-A2053 (Sept. 2014).
    Abstract:Electrolytes with the salt lithium bis(fluorosulfonyl)imide (LiFSI) have been evaluated relative to comparable electrolytes with other lithium salts. Acetonitrile (AN) has been used as a model electrolyte solvent due to the simplicity of its solvation interactions (the AN molecule has only a single electron lone-pair for Li+ cation coordination). The information obtained from the thermal phase behavior, solvation/ionic association interactions, quantum chemical (QC) calculations and molecular dynamics (MD) simulations (with an APPLE&P many-body polarizable force field for the LiFSI salt) of the (AN)n-LiFSI mixtures provides detailed insight into the coordination interactions of the FSI- anions and the wide variability noted in the electrolyte transport properties (i.e., viscosity and ionic conductivity).
  3. Wei X, L Cosimbescu, W Xu, JZ Hu, M Vijayakumar, J Feng, MY Hu, X Deng, J Xiao, J Liu, VL Sprenkle, and W Wang. "Towards High Performance Nonaqueous Redox Flow Electrolyte Via Ionic Modification of Active Species." Advanced Energy Materials (1400678), doi:DOI: 10.1002/aenm.201400678 (Aug 2014).
    Abstract: Nonaqueous redox flow batteries are emerging flow-based energy storage technologies that have the potential for higher energy densities than their aqueous counterparts because of their wider voltage windows. However, their performance has lagged far behind their inherent capability due to one major limitation of low solubility of the redox species. Here, a molecular structure engineering strategy towards high performance nonaqueous electrolyte is reported with significantly increased solubility. Its performance outweighs that of the state-of-the-art nonaqueous redox flow batteries. In particular, an ionic-derivatized ferrocene compound is designed and synthesized that has more than 20 times increased solubility in the supporting electrolyte. The solvation chemistry of the modified ferrocene compound. Electrochemical cycling testing in a hybrid lithium-organic redox flow battery using the as-synthesized ionic-derivatized ferrocene as the catholyte active material demonstrates that the incorporation of the ionic-charged pendant significantly improves the system energy density. When coupled with a lithium-graphite hybrid anode, the hybrid flow battery exhibits a cell voltage of 3.49 V, energy density about 50 Wh L-1, and energy efficiency over 75%. These results reveal a generic design route towards high performance nonaqueous electrolyte by rational functionalization of the organic redox species with selective ligand.
  4. X. Lu, G. Li, J.Y. Kim, D. Mei, J.P. Lemmon, and V.L. Sprenkle, "Liquid-metal electrode to enable ultra-low temperature sodium–beta alumina batteries for renewable energy storage." Nat. Commun. 5:4578 (Aug 2014).
    Abstract: Commercial sodium–sulphur or sodium-metal halide batteries typically need an operating temperature of 300–350°C, and one of the reasons is poor wettability of liquid sodium on the surface of beta alumina. Here we report an alloying strategy that can markedly improve the wetting, which allows the batteries to be operated at much lower temperatures. Our combined experimental and computational studies suggest that addition of caesium to sodium can markedly enhance the wettability. Single cells with Na-Cs alloy anodes exhibit great improvement in cycling life over those with pure sodium anodes at 175 and 15°C. The cells show good performance even at as low as 95°C. These results demonstrate that sodium–beta alumina batteries can be operated at much lower temperatures with successfully solving the wetting issue. This work also suggests a strategy to use liquid metals in advanced batteries that can avoid the intrinsic safety issues associated with dendrite formation.
  5. Cheng Y, LR Parent, Y Shao, CM Wang, VL Sprenkle, G Li, and J Liu. "Facile Synthesis of Chevrel Phase Nanocubes and their Applications for Multivalent Energy Storage." Chemistry of Materials 26(17):4904-4907. doi:10.1021/cm502306c (Aug 2014).
    Abstract: The Chevrel phases (CPs, MxMo6T8, M=metal, T=S or Se) are capable of rapid and reversible intercalation of multivalent ions and are the most practical cathode materials for rechargeable magnesium batteries. For the first time, we report a facile method for synthesizing Mo6S8 nanoparticles and demonstrate that these nanoparticles have significantly better Mg2+ intercalation kinetics compared with microparticles. The results described in this work could inspire the synthesis of nanoscale CPs, which could substantially impact their application.
  6. Seo DM, PD Boyle, JL Allen, SD Han, E Jonsson, P Johannsson, WA Henderson. "Solvate Structures and Computational/Spectroscopic Characterization of LiBF4 Electrolytes."Journal of Physical Chemistry C 118 (32):18377-18386 (July 2014).
    Abstract:Crystal structures have been determined for both LiBF4 and HBF4 solvates: (acetonitrile)2:LiBF4, (ethylene glycol diethyl ether)1:LiBF4, (diethylene glycol diethyl ether)1:LiBF4, (tetrahydrofuran)1:LiBF4, (methyl methoxyacetate)1:LiBF4, (succinonitrile)1:LiBF4, (N,N,N',N,N-pentamethyldiethylenetriamine)1:HBF4, (N,N,N',N'-tetramethylethylenediamine)3/2:HBF4, and (phenanthroline)2:HBF4. These, as well as other known LiBF4 solvate structures, have been characterized by Raman vibrational spectroscopy to unambiguously assign the anion Raman band positions to specific forms of BF4-Li+ cation coordination. In addition, complementary DFT calculations of BF4-Li+ cation complexes have provided additional insight into the challenges associated with accurately interpreting the anion interactions from experimental Raman spectra. This information provides a crucial tool for the characterization of the ionic association interactions within electrolytes.
  7. BR Chalamala, T Soundappan, GR Fisher, MA Anstey, VV Viswanathan, ML Perry. "Redox Flow Batteries: An Engineering Perspective." Proceedings of the IEEE 102 (6): 976 - 999 (June 2014).
    Abstract:Redox flow batteries are well suited to provide modular and scalable energy storage systems for a wide range of energy storage applications. In this paper, we review the development of redox-flow-battery technology including recent advances in new redox active materials, cell designs, and systems, all from the perspective of engineers interested in applying this technology. We discuss cost, performance, and reliability metrics that are critical for deployment of large flow-battery systems. The technology, while relatively young, has the potential for significant improvement through reduced materials costs, improved energy efficiency, and significant reduction in the overall system costs.
  8. Yingwen Cheng, Yuyan Shao, Ji-Guang Zhang, Vincent L. Sprenkle, Jun Liu and Guosheng Li, "High performance batteries based on hybrid magnesium and lithium chemistry" Chem. Commun., 2014, 50, 9644-9646 (June 2014).
    Abstract: This work studied hybrid batteries assembled with a Mg metal anode, a Li+ ion intercalation cathode and a dual-salt electrolyte containing Mg2+ and Li+ ions. We show that such hybrid batteries were able to combine the advantages of Li and Mg electrochemistry. They delivered outstanding rate performance (83% capacity retention at 15 C) with superior safety and stability (B5% fade for 3000 cycles).
  9. Ran Yi, Jinkui Feng, Dongping Lu, Mikhail Gordin, Shuru Chen, Daiwon Choi, Donghai Wang, "GeOx/Reduced Graphene Oxide Composite as an Anode for Li-ion Batteries: Enhanced Capacity via Reversible Utilization of Li2O along with Improved Rate Performance" Advanced Functional Materials, 24, p.1059-1066 (Feb 2014).
    Abstract: A self-assembled GeOx/reduced graphene oxide (GeOx/RGO) composite, where GeOx nanoparticles are grown directly on reduced graphene oxide sheets, is synthesized via a facile one-step reduction approach and studied by X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy, electron energy loss spectroscopy elemental mapping, and other techniques. Electrochemical evaluation indicates that incorporation of reduced graphene oxide enhances both the rate capability and reversible capacity of GeOx, with the latter being due to the RGO enabling reversible utilization of Li2O. The composite delivers a high reversible capacity of 1600 mAh g-1 at a current density of 100 mA g-1, and still maintains a capacity of 410 mAh g-1 at a high current density of 20 A g-1. Owing to the flexible reduced graphene oxide sheets enwrapping the GeOx particles, the cycling stability of the composite is also improved significantly. To further demonstrate its feasibility in practical applications, the synthesized GeOx/RGO composite anode is successfully paired with a high voltage LiNi0.5Mn1.5O4 cathode to form a full cell, which shows good cycling and rate performance.
  10. Viswanathan VV, AJ Crawford, DE Stephenson, S Kim, W Wang, B Li, GW Coffey, EC Thomsen, GL Graff, PJ Balducci, MCW Kintner-Meyer, and VL Sprenkle. 2014. "Cost and Performance Model for Redox Flow Batteries." Journal of Power Sources, 247:1040-1051. doi:10.1016/j.jpowsour.2012.12.023 (Feb 2014).
    Abstract: A cost model is developed for all vanadium and iron-vanadium redox flow batteries. Electrochemical performance modeling is done to estimate stack performance at various power densities as a function of state of charge and operating conditions. This is supplemented with a shunt current model and a pumping loss model to estimate actual system efficiency. The operating parameters such as power density, flow rates and design parameters such as electrode aspect ratio and flow frame channel dimensions are adjusted to maximize efficiency and minimize capital costs. Detailed cost estimates are obtained from various vendors to calculate cost estimates for present, near-term and optimistic scenarios. The most cost-effective chemistries with optimum operating conditions for power or energy intensive applications are determined, providing a roadmap for battery management systems development for redox flow batteries. The main drivers for cost reduction for various chemistries are identified as a function of the energy to power ratio of the storage system.
  11. G, Li, X. Lu, J.Y. Kim, J.P. Lemmon, and V.L. Sprenkle, "Improved cycling behavior of ZEBRA battery operated at intermediate temperature of 175°C," Journal of Power Sources, 249 (2014) 414-417 (Jan. 2014).
    Abstract: Operation of the sodium-nickel chloride battery at temperatures below 200°C reduces cell degradation and improves cyclability. One of the main technical issues with operating this battery at intermediate temperatures such as 175°C is the poor wettability of molten sodium on β"?-alumina solid electrolyte (BASE), which causes reduced active area and limits charging. In order to overcome the poor wettability of molten sodium on BASE at 175°C, a Pt grid was applied on the anode side of the BASE using a screen printing technique. Cells with their active area increased by metallized BASEs exhibited deeper charging and stable cycling behavior.
  12. B Li, M Gu, Z Nie, X Wei, C Wang, V Sprenkle, and W Wang, "Nanorod Niobium Oxide as Powerful Catalysts for an All Vanadium Redox Flow Battery", Nano Letters, 2014, 14, 158-165 (Dec 2013).
    Abstract: A powerful low-cost electrocatalyst, nanorod Nb2O5, is synthesized using hydrothermal method with monoclinic phases and simultaneously deposited on the surface of graphite felt (GF) electrode in an all vanadium flow battery (VRB). Cyclic voltammetry (CV) study confirmed that Nb2O5 has catalytic effects towards redox couples of V(II)/V(III) at the negative side and V(IV)/V(V) at the positive side to facilitate the electrochemical kinetics of the vanadium redox reactions. Because of poor conductivity of Nb2O5, the performance of the Nb2O5 loaded electrodes is strongly dependent on the nanosize and uniform distribution of catalysts on GFs surfaces. Accordingly, optimal amounts of W-doped Nb2O5 nanorods with minimum agglomeration and improved distribution on GFs surfaces are established by adding water-soluble compounds containing tungsten (W) into the precursor solutions. The corresponding energy efficiency is enhanced by ~10.7% at high current density (150 as compared with one without catalysts. Flow battery cyclic performance also demonstrates the excellent stability of the as prepared Nb2O5 catalyst enhanced electrode. These results suggest that Nb2O5-based nanorods, replacing expensive noble metals, uniformly decorating GFs holds great promise as high-performance electrodes for VRB applications.
  13. G. Li, X. Lu, J.Y. Kim, J.P. Lemmon, and V.L. Sprenkle, "Cell Degradation of a Na-NiCl2 (ZEBRA) Battery," Journal of Materials Chemistry A, 47 (2013) 14935 - 14942 (Nov 2013).
    Abstract: In this work, the parameters influencing the degradation of a Na-NiCl2 (ZEBRA) battery were investigated. Planar Na-NiCl2 cells using β"?-alumina solid electrolyte (BASE) were tested with different C-rates, Ni/NaCl ratios, and capacity windows, in order to identify the key parameters for the degradation of Na-NiCl2 battery. The morphology of NaCl and Ni particles were extensively investigated after 60 cycles under various test conditions using a scanning electron microscope. A strong correlation between the particle size (NaCl and Ni) and battery degradation was observed in this work. Even though the growth of both Ni and NaCl can influence the cell degradation, our results indicate that the growth of NaCl is a dominant factor in cell degradation. The use of excess Ni seems to play a role in tolerating the negative effects of particle growth on degradation since the available active surface area of Ni particles can be still sufficient even after particle growth. For NaCl, a large cycling window was the most significant factor, of which effects were amplified with decrease in Ni/NaCl ratio.
  14. Vijayakumar M, W Wang, Z Nie, VL Sprenkle, and JZ Hu. "Elucidating the Higher Stability of Vanadium (V) Cations in Mixed Acid Based Redox Flow Battery Electrolytes." Journal of Power Sources 241:173-177. doi:10.1016/j.jpowsour.2013.04.072 (Nov 2013).
    Abstract:The Vanadium (V) cation structures in mixed acid based electrolyte solution were analysed by density functional theory (DFT) based computational modelling and 51V and 35Cl Nuclear Magnetic Resonance (NMR) spectroscopy. The Vanadium (V) cation exists as di-nuclear [V2O3Cl2.6H2O]2+ compound at higher vanadium concentrations (=1.75M). In particular, at high temperatures (>295K) this di-nuclear compound undergoes ligand exchange process with nearby solvent chlorine molecule and forms chlorine bonded [V2O3Cl2.6H2O]2+ compound. This chlorine bonded [V2O3Cl2.6H2O]2+ compound might be resistant to the de-protonation reaction which is the initial step in the precipitation reaction in Vanadium based electrolyte solutions. The combined theoretical and experimental approach reveals that formation of chlorine bonded [V2O3Cl2.6H2O]2+ compound might be central to the observed higher thermal stability of mixed acid based Vanadium (V) electrolyte solutions.
  15. B Li, Q Luo, X Wei, Z Nie, E Thomsen, B Chen, V Sprenkle, and W Wang, "Capacity Decay Mechanism of Microporous Separator-Based All-Vanadium Redox Flow Batteries and its Recovery", ChemSusChem, 2014, 7, 577-584 (Oct 2013).
    Abstract: The results of the investigation of the capacity decay mechanism of vanadium redox flow batteries with microporous separators as membranes are reported. The investigation focuses on the relationship between the electrochemical performance and electrolyte compositions at both the positive and negative half-cells. Although the concentration of total vanadium ions remains nearly constant at both sides over cycling, the net transfer of solution from one side to the other and thus the asymmetrical valance of vanadium ions caused by the subsequent disproportionate self-discharge reactions at both sides lead to capacity fading. Through in situ monitoring of the hydraulic pressure of the electrolyte during cycling at both sides, the convection was found to arise from differential hydraulic pressures at both sides of the separators and plays a dominant role in capacity decay. A capacity-stabilizing method is developed and was successfully demonstrated through the regulation of gas pressures in both electrolyte tanks.

ES Publications 2013

  1. X. Wei, Q. Luo, B. Li, Z. Nie, E. Miller, J. Chambers, V. Sprenkle, and W. Wang. "Performance Evaluation of Microporous Separator in Fe/V Redox Flow Battery." ECS Transactions 45(26):17-24. (Sept 2013).
    Abstract: The newly developed Fe/V redox flow battery has demonstrated attractive cell performance. However, the deliverable energy density is relatively low due to the reduced cell voltage. To compensate this disadvantage and compete with other redox flow battery systems, cost reduction of the Fe/V system is necessary. This paper describes evaluation of hydrocarbon-based Daramic® microporous separators for use in the Fe/V system. These separators are very inexpensive and have exceptional mechanical properties. Separator B having ion exchange capacity demonstrated excellent capacity retention capability, and exhibited energy efficiency above 65% over a broad temperature range of 5-50°C and at current densities up to 80mA/cm2. Therefore, this separator shows great potential to replace the expensive Nafion® membrane. This will drive down the capital cost and make the Fe/V system a promising low-cost energy storage technology.
  2. Soowhan Kim, Edwin Thomsen, Guanguang Xia, Zimin Nie, Jie Bao, Kurtis Recknagle, Wei Wang, Vilayanur Viswanathan, Qingtao Luo, Xiaoliang Wei, Alasdair Crawford, Greg Coffey, Gary Maupin, Vincent Sprenkle. "1 kW/1 kWh advanced vanadium redox flow battery utilizing mixed acid electrolytes". Journal of Power Sources 237 (2013) 300-309 (Sept 2013).
    Abstract: This paper reports on the recent demonstration of an advanced vanadium redox flow battery (VRFB) using a newly developed mixed acid (sulfuric and hydrochloric acid) supporting electrolyte at a kW scale. The developed prototype VRFB system is capable of delivering more than 1.1 kW in the operation range of 15~85% state of charge (SOC) at 80 mA cm-2 with an energy efficiency of 82% and energy content of 1.4 kWh. The system operated stably without any precipitation at electrolyte temperatures >45°C. At similar electrolyte temperatures, tests with a conventional sulfuric acid electrolyte suffered from precipitation after 80 cycles. By operating stably at elevated temperatures (>40°C), the mixed acid system enables significant advantages over the conventional sulfate system, namely; 1) high stack energy efficiency due to better kinetics and lower electrolyte resistance, 2) lower viscosity resulting in reduced pumping losses, 3) lower capital cost by elimination of heat exchanger, 4) higher system efficiency and 5) simplified system design and operation. Demonstration of the prototype stack with the mixed acid electrolyte has been shown to lower the cost of conventional VRFB systems for large-scale energy storage applications.
  3. W Xu, X Chen, W Wang, D Choi, F Ding, J Zheng, Z Nie, YJ Choi, J Zhang, and Z Yang. "Simply AlF3-treated Li4Ti5O12 composite anode materials for stable and ultrahigh power lithium-ion batteries."Journal of Power Sources 236 (2013), 169 -174. (Aug 2013).
    Abstract: The commercial Li4Ti5O12 (LTO) is successfully modified by AlF3 via a low temperature process. After being calcined at 400°C for 5 h, AlF3 reacts with LTO to form a composite material, which mainly consists of Al3+ and F- co-doped LTO with small amounts of anatase TiO2. Al3+ and F- co-doped LTO demon- strates ultrahigh rate capability comparing to the pristine LTO. Since the amount of the byproduct TiO2 is relatively small, the modified LTO electrodes retain the main voltage characteristics of LTO with a minor feature similar to those of anatase TiO2. The doped LTO anodes deliver slightly higher discharge capacity and maintain the excellent long-term cycling stability when compared to the pristine LTO anode. Therefore, Al3+ and F- co-doped LTO composite material synthesized at low temperature is an excellent stable and ultra-high power lithium-ion batteries.
  4. Xiaochuan Lu, Guosheng Li, Jin Y Kim, John P. Lemmon, Vincent L Sprenkle, Zhenguo Yang, "A novel low-cost sodium-zinc chloride battery." Energy & Environmental Science 6(6): 1837-1843 (Jun 2013).
    Abstract: The sodium-metal halide (ZEBRA) battery has been considered as one of the most attractive energy storage systems for stationary and transportation applications. Even though Na-NiCl2 battery has been widely investigated, there is still a need to develop a more economical system to make this technology more attractive for commercialization. In the present work, a novel low-cost Na-ZnCl2 battery with a planar β"-Al2O3 solid electrolyte (BASE) was proposed, and its electrochemical reactions and battery performance were investigated. Compared to the Na-NiCl2 chemistry, the ZnCl2-based chemistry was more complicated, in which multiple electrochemical reactions including liquid-phase formation occurred at temperatures above 253°C. During the first stage of charge, NaCl reacted with Zn to form Na in the anode and Na2ZnCl4 in the cathode. Once all the residual NaCl was consumed, further charging led to the formation of a NaCl-ZnCl2 liquid phase. At the end of charge, the liquid phase reacted with Zn to produce solid ZnCl2. To identify the effects of liquid-phase formation on electrochemical performance, button cells were assembled and tested at 280°C and 240°C. At 280°C where the liquid phase formed during cycling, cells revealed quite stable cyclability. On the other hand, more rapid increase in polarization was observed at 240°C where only solid-state electrochemical reactions occurred. SEM analysis indicated that the stable performance at 280°C was due to the suppressed growth of Zn and NaCl particles, which were generated from the liquid phase during discharge of each cycle.
  5. Dongyang Chen, Soowhan Kim, Vincent Sprenkle, Michael A. Hickner. "Composite blend polymer membranes with increased proton selectivity and lifetime for vanadium redox flow batteries". Journal of Power Sources 231 (2013) 301-306. (Jun 2013).
    Abstract: Composite membranes based on blends of sulfonated fluorinated poly(arylene ether) (SFPAE) and poly(vinylidene fluoride-co-hexafluoropropene) (P(VDF-co-HFP)) were prepared with varying P(VDF-co-HFP) content for vanadium redox flow battery (VRFB) applications. The properties of the SFPAE-P(VDF-co-HFP) blends were characterized by atomic force microscopy, differential scanning calorimetry, and Fourier transform infrared spectroscopy. The water uptake, mechanical properties, thermal properties, proton conductivity, VO2+] permeability and VRFB cell performance of the composite membranes were investigated in detail and compared to the pristine SFPAE membrane. It was found that SFPAE had good compatibility with P(VDF-co-HFP) and the incorporation of P(VDF-co-HFP) increased the mechanical properties, thermal properties, and proton selectivity of the materials effectively. An SFPAE composite membrane with 10 wt.% P(VDF-co-HFP) exhibited a 44% increase in VRFB cell lifetime as compared to a cell with a pure SFPAE membrane. Therefore, the P(VDF-co-HFP) blending approach is a facile method for producing low-cost, high-performance VRFB membranes.
  6. Bin Li, Liyu Li, Wei Wang, Zimin Nie, Baowei Chen, Xiaoliang Wei, Qingtao Luo, Zhenguo Yang, and Vincent Sprenkle. "Fe/V Redox Flow Battery Electrolyte Investigation and Optimization". Journal of Power Sources 229 (2013) 1-5. (May 2013).
    Abstract: The recently invented iron (Fe)/vanadium (V) redox flow battery (IVB) system has attracted increasing attention because of its long-term cycling stability and low-cost membrane/separator. In this paper, we describe our extensive matrix study of factors such as electrolyte composition; state of charge (SOC), and temperature that influence the stability of electrolytes in both positive and negative half-cells. During the study, an optimized electrolyte that can be operated in a temperature range from -5°C to 50°C without precipitation is identified. Fe/V flow cells using the optimized electrolyte and low-cost separator exhibit satisfactory cycling performance at different temperatures. Efficiencies, capacities, and energy densities of flow batteries at various temperatures are studied.
  7. X. Wei, Z Nie, Q Luo, B Li, V. Sprenkle, and W. Wang, "Polyvinyl Chloride/Silica Nanoporous Composite Separator for All-Vanadium Redox Flow Battery Applications." Journal of the Electrochemical Society, 160(8):A1215 - A1218, 2013. (May 2013).
    Abstract: We demonstrate application of a commercial nanoporous polyvinyl chloride (PVC)/silica separator in an all-vanadium redox flow battery (VRB) as a low-cost alternative to expensive Nafion® membranes. This hydrophilic separator is composed of silica particles enmeshed in a PVC matrix that creates unique porous structures. These nano-scale pores with an average pore size of 45nm and a porosity of 65% serve as ion transport channels that are critically important for flow battery operation. The VRB flow cell using the PVC/silica separator produces excellent electrochemical performance in a mixed-acid VRB system with average energy efficiency (EE) of 79% at the current density of 50mAcm-2. This separator affords the VRB flow cell with excellent rate capability with its EE higher than that of Nafion® membrane at current densities above 100mAcm-2. With this separator, the EE of the VRB flow cell exhibits great tolerance to temperature fluctuations in the typical operational temperature range of the mixed-acid VRB system. More importantly, the flow cell using the separator demonstrates an excellent capacity retention over cycling, which enables the VRB system to operate in the long term with minimal electrolyte maintenance.
  8. X. Wei, Z. Nie, Q. Luo, B. Li, B. Chen, K. Simmons, V. Sprenkle, W. Wang, "Nanoporous Polytetrafluoroethylene/Silica Composite Separator as a High-Performance All-Vanadium Redox Flow Battery Membrane". Advanced Energy Materials, 3, 1215-1220, 2013. (Apr 2013).
    Abstract:A novel low-cost nanoporous polytetrafluoroethylene (PTFE)/silica composite separator has been prepared and evaluated for its use in an all-vanadium redox flow battery (VRB). The separator consists of silica particles enmeshed in a PTFE fibril matrix. It possesses unique nanoporous structures with an average pore size of 38 nm and a porosity of 48%. These pores function as the ion transport channels during redox flow battery operation. This separator provides excellent electrochemical performance in the mixed-acid VRB system. The VRB using this separator delivers impressive energy efficiency, rate capability, and temperature tolerance. In addition, the flow cell using the novel separator also demonstrates an exceptional capacity retention capability over extended cycling, thus offering excellent stability for long-term operation. The characteristics of low cost, excellent electrochemical performance and proven chemical stability afford the PTFE/silica nanoporous separator great potential as a substitute for the Nafion membrane used in VRB applications.
  9. D Reed, G Coffey, E Mast, N Canfield, J Mansurov, X Lu, VL Sprenkle. "Wetting of sodium on ß-Al2O3/YSZ composites for low temperature planar sodium-metal halide batteries". Journal of Power Sources 227: 94-100 (Apr 2013).
    Abstract:Wetting of Na on ß-Al2O3/YSZ composites was investigated using the sessile drop technique. The effects of moisture and surface preparation were studied at low temperatures. Electrical conductivity of Na/ß-Al2O3/YSZ/Na cells was also investigated at low temperatures and correlated to the wetting behavior. The use of planar ß-Al2O3 substrates at low temperature with low cost polymeric seals is realized due to improved wetting at low temperature and conductivity values consistent with the literature.
  10. B. Li, M. Gu, Z. Nie, Y. Shao, Q. Luo, X. Wei, X. Li, J. Xiao, C. Wang, V. Sprenkle, and W. Wang, "Bismuth Nanoparticle Decorating Graphite Felt as a High-Performance Electrode for an All-Vanadium Redox Flow Battery". Nano Letters, 13, 1330-1335, 2013. (Feb 2013).
    Abstract: Employing electrolytes containing Bi3+, bismuth nanoparticles are synchronously electrodeposited onto the surface of a graphite-felt electrode during operation of an all-vanadium redox flow battery (VRFB). The influence of the Bi nanoparticles on the electrochemical performance of the VRFB is thoroughly investigated. It is confirmed that Bi is only present at the negative electrode and facilitates the redox reaction between V(II) and V(III). However, the Bi nanoparticles significantly improve the electrochemical performance of VRFB cells by enhancing the kinetics of the sluggish V(II)/V(III) redox reaction, especially under high power operation. The energy efficiency is increased by 11% at high current density (150 owing to faster charge transfer as compared with one without Bi. The results suggest that using Bi nanoparticles in place of noble metals offers great promise as high-performance electrodes for VRFB application.
  11. Q Luo, L Li, W Wang, Z Nie, X Wei, B Li, B Chen, Z Yang, and VL Sprenkle. "Capacity Decay and Remediation of Nafion-based All-Vanadium Redox Flow Batteries". ChemSusChem 6(2) 268-274. (Feb 2013).
    Abstract: The relationship between the electrochemical performance of vanadium redox flow batteries (VRB) and electrolyte compositions has been investigated, and the reasons for capacity decay over charge-discharge cycling have been analyzed and are discussed in this paper. The results show that the reasons for capacity fading over real charge-discharge cycling include not only the imbalanced vanadium active species, but also the asymmetrical valence of vanadium ions in positive and negative electrolytes. The asymmetrical valence of vanadium ions leads to the SOC range to decrease in positive electrolyte and increase in negative electrolyte, respectively. As a result, the higher SOC range in negative half-cells further aggravate the capacity fading by creating a higher over-potential and possible hydrogen evolution. Based on this finding, we developed two methods for restoring the lost capacity; thereby enabling long-term operation of VRBs to be achieved without the substantial loss of energy resulting from periodic remixing of electrolytes.
  12. W Wang, Q Luo, B Li, X Wei, L Li, and Z Yang. "Recent Progress in Redox Flow Battery Research and Development".Advanced Functional Materials 23 (8), 970-986.(Feb 2013).
    Abstract: With the increasing need to seamlessly integrate renewable energy with the current electricity grid, which itself is evolving into a more intelligent, efficient, and capable electrical power system, it is envisioned that energy-storage systems will play a more prominent role in bridging the gap between current technology and a clean sustainable future in grid reliability and utilization. Redox flow battery technology is a leading approach in providing a well-balanced approach for current challenges. In this paper, we review recent progress in the research and development of redox flow battery technology, including cell-level components of electrolytes, electrodes, and membranes. Our review focuses on new redox chemistries for both aqueous and non-aqueous systems.
  13. X. Lu, JP Lemmon, JY Kim, VL Sprenkle, and ZG Yang. "High Energy Density Na-S/NiCl2 Hybrid Battery." Journal of Power Sources 224 (2013) 312- 316. (Feb 2013).
    Abstract: High temperature (250-350°C) sodium-beta alumina batteries (NBBs) are attractive energy storage devices for renewable energy integration and other grid related applications. Currently, two technologies are commercially available in NBBs, e.g., sodium-sulfur (Na-S) battery and sodium-metal halide (ZEBRA) batteries. In this study, we investigated the combination of these two chemistries with a mixed cathode. In particular, the cathode of the cell consisted of molten NaAlCl4 as a catholyte and a mixture of Ni, NaCl and Na2S as active materials. During cycling, two reversible plateaus were observed in cell voltage profiles, which matched electrochemical reactions for Na-S and Na-NiCl2 redox couples. An irreversible reaction between sulfur species and Ni was identified during initial charge at 280°C, which caused a decrease in cell capacity. The final products on discharge included Na2Sn with 1< n < 3, which differed from Na2S3 found in traditional Na-S battery. Reduction of sulfur in the mixed cathode led to an increase in overall energy density over ZEBRA batteries. Despite of the initial drop in cell capacity, the mixed cathode demonstrated relatively stable cycling with more than 95% of capacity retained over 60 cycles under 10mA/cm2. Optimization of the cathode may lead to further improvements in battery performance.
  14. Wang W, D Choi, and Z Yang."Li-Ion Battery with LiFePO4 Cathode and Li4Ti5O12 Anode for Stationary Energy Storage". Metallurgical and Materials Transactions A, Physical Metallurgy and Materials Science 44A(1 Supplement): 21-25. (Jan 2013).
    Abstract: Li-ion batteries based on commercially available LiFePO4 cathode and Li4Ti5O12 anode were investigated for potential stationary energy storage applications. The full cell that operated at flat 1.85 V demonstrated stable cycling up to 200 cycles followed by a rapid fade. A Li-ion full cell with Ketjen black modified LiFePO4 cathode and an unmodified Li4Ti5O12 anode exhibited negligible fade after more than 1200 cycles with a capacity of ~130 mAh/g at C/2. The improved stability, along with its cost-effectiveness, environmental benignity, and safety, make the LiFePO4/Li4Ti5O12 combination Li-ion battery a promising option for storing renewable energy.
  15. X Lu, BW Kirby, W Xu, G Li, JY Kim, JP Lemmon, VL Sprenkle, and ZG Yang. "Advanced Intermediate-Temperature Na-S Battery." Energy & Environmental Science 6(1) (2013) 299 - 306. (Jan 2013).
    Abstract: In this study, we reported an intermediate-temperature (~150°C) sodium-sulfur (Na-S) battery. With a reduced operating temperature, this novel battery can potentially reduce the cost and safety issues associated with the conventional high-temperatures (300~350°C) Na-S battery. A dense β"-Al2O3 solid membrane and tetraglyme were utilized as the electrolyte separator and catholyte solvent in this battery. Solubility tests indicated that cathode mixture of Na2S4 and S exhibited extremely high solubility in tetraglyme (e.g., > 4.1 M for Na2S4 + 4 S). CV scans of Na2S4 in tetraglyme revealed two pairs of redox couples with peaks at around 2.22 and 1.75 V, corresponding to the redox reactions of polysulfide species. The discharge/charge profiles of the Na-S battery showed a slope region and a plateau, indicating multiple steps and cell reactions. In-situ Raman spectra during battery operation suggested that polysulfide species were formed in the sequence of Na2S5 + S → Na2S5 + Na2S4 → Na2S4 + Na2S2 during discharge and in a reverse order during charge. This battery showed dramatic improvement in rate capacity and cycling stability over room-temperature Na-S batteries, which makes it extremely attractive for renewable energy integration and other grid related applications.
  16. GS Li, XC Lu, CA Coyle, JY Kim, JP Lemmon, VL Sprenkle, and ZG Yang. "Novel ternary molten salt electrolytes for intermediate-temperature sodium/nickel chloride batteries."Journal of Power Sources 220, 193 -198. (Dec 2012).
    Abstract: The sodium-nickel chloride (ZEBRA) battery is typically operated at relatively high temperature (250~350°C) to achieve adequate electrochemical performance. Reducing the operating temperature in the range of 150 to 200°C can lead to enhanced cycle life by suppressing temperature related degradation mechanisms. The operation at these intermediate temperatures also allows for lower cost materials of construction such as elastomeric sealants and gaskets. To achieve adequate electrochemical performance at lower operating temperatures requires an overall reduction in ohmic losses associated with temperature. This includes reduction in the ohmic resistance of β"-alumina solid electrolyte (BASE) and the incorporation of low melting point molten salt as the secondary electrolyte. In present work, planar-type Na/NiCl2 cells with a thin flat BASE (600 μm) and low melting point secondary electrolyte were evaluated at reduced temperatures. Molten salts used as secondary electrolytes were fabricated by the partial replacement of NaCl in the standard secondary electrolyte (NaAlCl4) with other lower melting point alkali metal salts such as NaBr, LiCl, and LiBr. Electrochemical characterization of these ternary molten salts demonstrated improved ionic conductivity and sufficient electrochemical window at reduced temperatures. Furthermore, Na/NiCl2 cells with 50 mol% NaBr-containing secondary electrolyte exhibited reduced polarizations at 175°C compared to the cell with the standard NaAlCl4 catholyte. The cells also exhibited stable cycling performance even at 150°C.
  17. Q Luo, L Li, Z Nie, W Wang, X Wei, B Li, B Chen, Z Yang. "In-situ investigation of vanadium ion transport in redox flow battery." Journal of Power Sources 218 (2012) 15-30 (Nov 2012).
    Abstract: Flow batteries with vanadium and iron redox couples as the electroactive species were employed to investigate the transport behavior of vanadium ions in the presence of an electric field. It was shown that the electric field accelerated the positive-to-negative and reduced the negative-to-positive transport of vanadium ions in the charging process and affected the vanadium ion transport in the opposite way during discharge. In addition, a method was designed to differentiate the concentration-gradient?driven vanadium ion diffusion and electric-field?driven vanadium ion migration. A simplified mathematical model was established to simulate the vanadium ion transport in real charge-discharge operation of the flow battery. The concentration gradient diffusion coefficients and electric-migration coefficients of V2+, V3+, VO2+, and VO2+ across a NAFION® membrane were obtained by fitting the experimental data.
  18. X Wei, L Li, Q Luo, Z Nie, W Wang, B Li, GG Xia, E Millar, J Chambers, Z Yang. "Microporous separators for Fe/V redox flow batteries." (2013) Journal of Power Sources 218 (2012) 39-45 (Nov 2012).
    Abstract: The Fe/V redox flow battery has demonstrated promising performance with distinct advantages over other redox flow battery systems. Due to the less oxidative nature of the Fe(III) species, hydrocarbon-based ion exchange membranes or separators can be used. Daramic® microporous polyethylene separators were tested on Fe/V flow cells using sulfuric/chloric mixed acid-supporting electrolytes. Among them, separator C exhibited good flow cell cycling performance with satisfactory repeatability over a broad temperature range of 5-50°C. Energy efficiency (EE) of C remains around 70% at current densities of 50-80 in temperatures ranging from room temperature to 50°C. The capacity decay problem could be circumvented through hydraulic pressure balancing by means of applying different pump rates to the positive and negative electrolytes. Stable capacity and energy were obtained over 20 cycles at room temperature and 40°C. These results show that extremely low-cost separators ($1-20/m2) are applicable in the Fe/V flow battery system with acceptable energy efficiency. This represents a remarkable breakthrough: a significant reduction of the capital cost of the Fe/V flow battery system, which could further its market penetration in grid stabilization and renewable integration.
  19. W Wang, L Li, Z Nie, B Chen, Q Luo, Y Shao, X Wei, F Chen, G Xia, Z Yang. "A new hybrid redox flow battery with multiple redox couples." Journal of Power Sources 216 (2012), 99-103. (Oct 2012).
    Abstract: A redox flow battery using V4+/V5+ vs. V2+/V3+ and Fe2+/Fe3+ vs. V2+/V3+ redox couples in chloric/sulfuric mixed acid supporting electrolyte was investigated for potential stationary energy storage applications. The Fe/V hybrid redox flow cell using mixed reactant solutions and operated within a voltage window of 0.5~1.7 V demonstrated stable cycling over 100 cycles with energy efficiency ~80% and negligible capacity fading at room temperature. A 66% improvement in the energy density of the Fe/V hybrid cell was achieved compared with the previously reported Fe/V cell using only Fe2+/Fe3+ vs. V2+/V3+ redox couples.
  20. X Lu, GS Li, JY Kim, JP Lemmon, VL Sprenkle, and ZG Yang. "The effects of temperature on the electrochemical performance of sodium-nickel chloride batteries." Journal of Power Sources 215 (2012), 288-295. (Oct 2012).
    Abstract: The sodium-nickel chloride (ZEBRA) battery is typically operated at relatively high temperatures (≥ 300°C) to achieve adequate electrochemical performance. In the present study, the effects of operating temperature on the electrochemical performance of planar-type sodium-nickel chloride batteries were investigated in order to evaluate the feasibility of the battery operation at low temperatures (≥ 200°C). Electrochemical test results revealed that the battery was able to be cycled at C/3 rate at as low as 175°C despite the higher cell polarization at the reduced temperature. Overall, low operating temperature resulted in a considerable improvement in the stability of cell performance. Cell degradation was negligible at 175°C, while 55% increase in end-of-charge polarization was observed at 280°C after 60 cycles. SEM analysis indicated that the performance degradation at higher temperatures was related to the particle growth of both nickel and sodium chloride in the cathode. The cells tested at lower temperatures (e.g., 175 and 200°C), however, exhibited a sharp drop in cell voltage at the end of discharge due to the diffusion limitation, possibly caused by the limited ionic conductivity of NaAlCl4 melt or the poor wettability of sodium on the β"-Al2O3 solid electrolyte (BASE). Therefore, improvements in the ionic conductivity of a secondary electrolyte and sodium wetting as well as reduction in the ohmic resistance of BASE are required to further enhance the battery performance at low temperatures.
  21. D Stephenson, S Kim, F Chen, E Thomsen, V Viswanathan, W Wang, VL Sprenkle. "Electrochemical Model of the Fe/V Redox Flow Battery."Journal of the Electrochemical Society 159 (12): A1993-A2000 (Oct 2012).
    Abstract: A zero-dimensional electrochemical model of the Fe/V redox flow battery (RFB) is presented that can model RFB performance at low flow rates (<0.5 mL min-1 cm-2) and varied temperatures. The electrochemical model is appropriate for practical RFBs and provides good agreement with experimental data. In addition, a proposed non-ideal electrode model is introduced that accounts for higher voltage losses at low flow rates. Semi-quantitative operation strategies and electrode design guidelines can be obtained from the model. We found that ohmic losses associated with the electrolyte were dominating our electrode losses, which means operating the cell at higher temperature will reduce electrolyte ohmic losses and viscosity, thus leading to higher system efficiency. Thinner electrodes than the 4.5-mm-thick felt used in this study should reduce ohmic losses as well as pumping losses if the same space velocity is maintained. This electrochemical model can be easily incorporated into system-level and cost models, which will help in system optimization, system control, and pump selection and help avoid potential risks of large scale RFB system development.

ES Publications 2012

  1. Cao Y, L Xiao, ML Sushko, W Wang, b Schwenzer, J Xiao, Z Nie, LV Saraf, Z Yang, J Liu. "Sodium Ion Insertion in Hollow Carbon Nanowires for Battery Applications." Nano Letters 12 (7): 3783-3787 (June 2012).
    Abstract: Hollow carbon nanowires (HCNWs) were prepared through pyrolyzation of a hollow polyaniline nanowire precursor. The HCNWs used as anode material for Na-ion batteries deliver a high reversible capacity of 251 mAh g-1 and 82.2% capacity retention over 400 charge-discharge cycles between 1.2 and 0.01 V (vs Na+/Na) at a constant current of 50 mA g-1 (0.2 C). Excellent cycling stability is also observed at an even higher charge-discharge rate. A high reversible capacity of 149 mAh g-1 also can be obtained at a current rate of 500 mA g-1 (2C). The good Na-ion insertion property is attributed to the short diffusion distance in the HCNWs and the large interlayer distance (0.37 nm) between the graphitic sheets, which agrees with the interlayered distance predicted by theoretical calculations to enable Na-ion insertion in carbon materials.
  2. Wang W, W Xu, L Cosimbescu, D Choi, L Li, and Z Yang. "Anthraquinone with Tailored Structure for Nonaqueous Metal-Organic Redox Flow Battery." Chemical Communications 48(53):6669-6671. (May 2012).
    Abstract: A nonaqueous, hybrid metal-organic redox flow battery based on tailored anthraquinone structure is demonstrated to have an energy efficiency of ~82% and a specific discharge energy density similar to these of aqueous redox flow batteries, which is due to the significantly improved solubility of anthraquinone in supporting electrolytes.
  3. Wang W, Z Nie, B Chen, F Chen, Q Luo, X Wei, G Xia, M Skyllas-Kazacos, L Li, and Z Yang. "A New Fe/V Redox Flow Battery Using Sulfuric/Chloric Mixed Acid Supporting Electrolyte." Advanced Energy Materials 2(4): 487-493. (Feb. 2012).
    Abstract: A redox flow battery using Fe2+/Fe3+ and V2+/V3+ redox couples in chloric/sulfuric mixed-acid supporting electrolyte was investigated for potential stationary energy storage applications. The Fe/V redox flow cell using mixed reactant solutions operated within a voltage window of 0.5~1.35 V with a nearly 100% utilization ratio and demonstrated stable cycling over 100 cycles with energy efficiency > 80% and no capacity fading at room temperature. A 25% improvement in the discharge energy density of the Fe/V cell was achieved compared with the previous reported Fe/V cell using pure chloride-acid supporting electrolyte. Stable performance was achieved in the temperature range between 0°C and 50°C as well as using a microporous separator as the membrane. The improved electrochemical performance makes the Fe/V redox flow battery a promising option as a stationary energy storage device to enable renewable integration and stabilization of the electric grid.
  4. Zhang J, L Li, Z Nie, B Chen, M Vijayakumar, S Kim, W Wang, B Schwenzer, J Liu, and Z Yang. "Effects of additives on the stability of electrolytes for all-vanadium redox flow batteries." Journal of Applied Electrochemistry 41(10 - Special Issue S1):1215-1221. (Oct 2011).
    Abstract: The stability of the electrolytes for all-vanadium redox flow battery was investigated with ex-situ heating/cooling treatment and in situ flow-battery testing methods. The effects of inorganic and organic additives have been studied. The additives containing the ions of potassium, phosphate, and polyphosphate are not suitable stabilizing agents because of their reactions with V(V) ions, forming precipitates of KVSO6 or VOPO4. Of the chemicals studied, polyacrylic acid and its mixture with CH3SO3H are the most promising stabilizing candidates, which can stabilize all the four vanadium ions (V2+, V3+, VO2+, and VO2+) in electrolyte solutions up to 1.8 M. However, further effort is needed to obtain a stable electrolyte solution with >1.8 M V5+ at temperatures higher than 40°C.

ES Publications 2011

  1. Li L, S Kim, W Wang, M Vijayakumar, Z Nie, B Chen, J Zhang, G Xia, JZ Hu, GL Graff, J Liu, and Z Yang. "A Stable Vanadium Redox-Flow Battery with High Energy Density for Large-scale Energy Storage." Advanced Energy Materials 1(3):394-400. (March 2011).
    Abstract: The all-vanadium redox flow battery is a promising technology for large-scale renewable and grid energy storage, but is limited by the low energy density and poor stability of the vanadium electrolyte solutions. A new vanadium redox flow battery with a significant improvement over the current technology is reported in this paper. This battery uses sulfate-chloride mixed electrolytes, which are capable of dissolving 2.5 M vanadium, representing about a 70% increase in energy capacity over the current sulfate system. More importantly, the new electrolyte remains stable over a wide temperature range of -5 to 50°C, potentially eliminating the need for electrolyte temperature control in practical applications. This development would lead to a significant reduction in the cost of energy storage, thus accelerating its market penetration.
  2. Wang W, S Kim, B Chen, Z Nie, J Zhang, G Xia, L Li, and Z Yang. "A New Redox Flow Battery Using Fe/V Redox Couples in Chloride Supporting Electrolyte." Energy & Environmental Science 4(10):4068-4073. (June 2011).
    Abstract: A new redox flow battery using Fe2+/Fe3+ and V2+/V3+ redox couples in chloride-supporting electrolyte was proposed and investigated for potential stationary energy storage applications. The Fe/V redox flow cell using mixed reactant solutions operated within a voltage window of 0.5~1.35 V with a nearly 100% utilization ratio and demonstrated stable cycling with energy efficiency around 80% at room temperature. Stable performance was also achieved in the temperature range between 0°C and 50°C. The improved stability and electrochemical activity over a broader temperature range over the current technologies (such as Fe/Cr redox chemistry) potentially eliminate the necessity of external heat management and use of catalysts, making the Fe/V redox flow battery a promising option as a stationary energy storage device to enable renewable integration and stabilization of the electrical grid.
  3. Schwenzer B, S Kim, M Vijayakumar, Z Yang, J Liu. "Correlation of structural differences between Nafion/polyaniline and Nafion/polypyrrole composite membranes and observed transport properties."Journal of Membrane Science 327 (1-2): 11-19 (Apr. 2011).
    Abstract:Polyaniline/Nafion and polypyrrole/Nafion composite membranes, prepared by chemical polymerization, are studied by scanning electron microscopy, infrared and nuclear magnetic resonance spectroscopy. Differences in vanadium ion diffusion through the membranes and in the membranes' area specific resistance are linked to analytical observations that polyaniline and polypyrrole interact differently with Nafion. Polypyrrole, a weakly basic polymer, binds less strongly to the sulfonic acid groups of the Nafion membrane. Infrared spectroscopy results suggest that the hydrophobic polymer aggregates in the center of the Nafion channel rather than attaching to the hydrophilic walls containing sulfonic acid groups. This results in a drastically elevated membrane resistance and only slightly decreased vanadium ion diffusion compared to a Nafion membrane. Polyaniline, on the other hand, polymerizes along the sides of the Nafion pores and on the membrane surface, binding tightly to the sulfonic acid groups of Nafion, polyaniline's greater basicity possibly causing the difference in polymerization behavior. This leads to a more effective reduction in vanadium ion transport across the polyaniline/Nafion membranes and the increase in membrane resistance is less severe. The performance of selected polypyrrole/Nafion composite membranes is tested in a static vanadium redox cell. Increased coulombic efficiency, compared to a cell employing a pure Nafion membrane, further confirms the reduced vanadium ion transport through the composite membranes.
  4. Yang Z, J Zhang, MCW Kintner-Meyer, X Lu, D Choi, JP Lemmon, and J Liu. "Electrochemical Energy Storage for Green Grid." Chemical Reviews 111(5):3577 -3613. (March 2011).
    Abstract: Electrochemical Energy Storage (EES) is an established, valuable approach for improving the reliability and overall use of the entire power system (generation, transmission, and distribution [T&D]). Sited at various T&D stages, EES can be employed for providing many grid services, including a set of ancillary services such as (1) frequency regulation and load following (aggregated term often used is balancing services), (2) cold start services, (3) contingency reserves, and (4) energy services that shift generation from peak to off -peak periods. In addition, it can provide services to solve more localized power quality issues and reactive power support.

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