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Sandia National Laboratories Journal Articles

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Date Title Authors Publisher
2014-12

Maximizing plating density and efficiency for a negative deposition reaction in a flow battery

Abstract: Flow batteries utilizing a plating reaction as the negative reaction are limited in energy capacity by the available void area in the cell stack. Large scale energy storage applications necessitate maximizing the plating density within the flow battery. Six porous negative electrode configurations using conductive and non-conductive materials are considered for use in a hybrid flow battery. Plating results using a Cu Fe sulfate chemistry demonstrated a plating density in a carbon felt electrode (145 mAh cm-2 at 40 mA cm-2). Two layered electrode configurations were able to achieve 150 mAh cm-2 of plating density: carbon felt with non-conductive felt, and carbon felt-Daramic-carbon felt. Both electrode designs were tested with the all-iron chemistry using shallow charge/discharge cycles. The carbon felt with non-conducting felt electrode configuration maintained a voltaic efficiency of 81% over six cycles.
Hawthorne, K.
...
Wainright, J.,
Savinell, R.
Journal of Power Sources
269(10):216-224
2014-12

The Role of Excess Sodium in Sol-Gel NaSICON Synthesis and Stability

Abstract: Controlling the materials chemistry of the solid-state ion conductor NaSICON is key to realizing its potential utility in emerging sodium-based battery technologies. We describe here the influence of excess sodium on phase evolution of sol-gel synthesized NaSICON. Alkoxide-based sol-gel processing was used to produce powders of Na3Zr2PSi2O12 NaSICON with 0-2 atomic % excess sodium. Phase formation and component volatility were studied as a function of temperature. NaSICON synthesis at temperatures between 900-1100°C with up to 2% excess sodium significantly reduced the presence of zirconia, sodium phosphate, and sodium silicate secondary phases in fired NaSICON powders. Insights into the role of sodium on the phase chemistry of sol-gel processed NaSICON may inform key improvements in NaSICON development.
Bell, N.
...
Edney, C.,
Wheeler, J.,
Ingersoll, D.,
Spoerke, E.
J. Amer. Ceram. Soc.
DOI: 10.1111/jace.13167
2014-10

Characterization of Reliability in SiC Power Devices

Abstract: Power devices based on the wide-bandgap semiconductors SiC and GaN have many potential advantages compared to conventional Si-based switching devices, especially for renewable energy and smart grid applications. However, while these emerging devices have developed rapidly in recent years, many factors affecting their performance and reliability remain unknown. In this paper, we discuss some of the key results that have been obtained for both SiC- and GaN-based devices under Sandia National Lab's “post-Silicon” power electronics reliability program. State-of-the-art, commercially available 4H-SiC MOSFETs are evaluated for stability under high-temperature over-voltage and pulsed over-current conditions. The devices show maximum vulnerability under high-temperature off-state operation at high temperature. The room-temperature pulsed over-current operation results in degradation similar to that observed under high-temperature on-state DC conditions, presumably due to overheating of the device beyond its specified junction temperature. Prototype AlGaN/GaN HEMTs with ~1800 V breakdown are evaluated for stability under different bias conditions. Current collapse is observed and analyzed, and trapping components with very different time constants are found to be involved. The specific nature of degradation and recovery depends strongly upon the particular stress bias (gate vs. drain) condition applied.
Marinella, M.,
...
Hughart, D.
Flicker, J.
Atcitty, S.
Kaplar, R.
Proceedings of the 226th meeting of the Electrochemical Society
2014-10

Switching frequency optimization of a high-frequency link based energy storage system

Abstract: There is currently a big thrust for integrating renewable resources to the electric grid. With increasing variable generation the need for energy storage devices has escalated. Traditional storage devices have bulky 60 Hz transformer to provide the electrical isolation from the grid. But, with the advent of advanced magnetic materials, power electronic topologies with high frequency link transformers are being researched. These systems have high power density and can be quickly dispatched for remote installations. This paper presents the design of the energy storage system consisting of the three phase rectifier and bi-directional dual active bride converter. It presents a methodology to optimize the switching frequency of the dual active bridge converter by minimizing the volume of the transformer and the total losses in the system. Frequency dependent and independent terms are aggregated and minimized over the range of switching frequency.
Kulasekaran, S.,
...
Ayyanar, R.,
Atcitty, S.
Proceedings of the Annual Conference of the IEEE Industrial Electronics Society (IECON)
2014-07

Integrating Energy Storage Devices Into Market Management Systems

Abstract: Intuitively, the integration of energy storage technologies such as pumped hydro and batteries into vertically integrated utility and independent system operator/regional transmission operator (ISO/RTO)-scale systems should confer significant benefits to operations, ranging from mitigation of renewables generation variability to peak shaving. However, the realized benefits of such integration are highly dependent upon the environment in which the integration occurs. Further, integration of storage requires careful modeling extensions of existing market management systems (MMSs), which are currently responsible for market and reliability operations in the grid. In this paper, we outline the core issues that arise when integrating storage devices into an MMS system, ranging from high-level modeling of storage devices for purposes of unit comment and economic dispatch to the potential need for new mechanisms to more efficiently allow for storage to participate in market environments. We observe that the outcomes of cost-benefit analyses of storage integration are sensitive to system-specific details, e.g., wind penetration levels. Finally, we provide an illustrative case study showing significant positive impacts of storage integration.
Silva-Monroy, C.,
...
Watson, J.
Proceedings of the IEEE
(102):1084-1093
2014-07

Studies of Iron-Ligand Complexes for an All-Iron Flow Battery Application

Abstract: Seven organic ligands were investigated for use to coordinate reactive ions in the positive electrolyte of an all-iron flow battery. Exchange current densities, diffusion coefficients, and open circuit potentials of the ligand complexed ferric/ferrous redox couple are presented on a glassy carbon electrode. Results in a flow cell configuration suggest an ohmically controlled cell voltage and a highly distributed current distribution; the contributions from charge transfer and mass transfer are minor. The open circuit potential becomes a major factor in the selection of the complexed redox couple for determining which ligand to use in a flow battery. The iron-glycine complex was further investigated as a function of the ratio of glycine to ferric/ferrous ions and the pH of the solution. Results suggest a 1:1 glycine to iron ion electrolyte will be soluble up to 0.5 M ferric ion at a pH of 2 with a reaction potential of 468 mV vs. Ag/AgCl (0.690 vs SHE), suitable for use as a positive redox couple in the all-iron flow battery.
Hawthorne, K.,
...
Wainright, J.,
Savinell, R.
Journal of The Electrochemical Society
161(10):A1662-A1671
2014-06

Performance and Reliability Characterization of 1200 V Silicon Carbide Power JFETs at High Temperatures

Abstract: We have characterized 1200 V SiC MOSFETs as well as Junction FETs (JFETs), which do not utilize a gate oxide, at high temperatures under both static and dynamic gate bias stress conditions. SiC JFET devices demonstrate more stable VT than SiC MOSFET devices for both types of gate bias stresses at high temperatures (Fig. 1b). For static gate bias stresses, packaged JFET devices exhibited a negligible VT shift (ΔVT < 2 mV) for temperatures up to 250oC. At higher temperatures, bare JFET die demonstrated ΔVT < 10 mV up to 525oC. Further, in contrast to the SiC MOSFETs, the VT of the SiC JFETs was unaffected by dynamic gate bias stress over the test period, although the sub-threshold leakage current increased with time. In addition to monitoring VT shifts, we have calculated the change in density of SiC/SiO2 interface traps (ΔDIT) due to the application of gate stress to MOSFETs. These profiles can be extracted from I-V curves for SiC MOSFETs based on the changes in sub-threshold slope. This technique can either be used to determine ΔDIT (if body doping and gate capacitance are unknown) or absolute DIT at specific energies within the bandgap (if doping and capacitance are known).
Flicker, J.,
...
Hughart, D.,
Marinella, M.,
Atcitty, S.,
Kaplar, R.
Proceedings of the High Temperature Electronics Conference
2014-06

Trap-Related Parametric Shifts under DC Bias and Switched Operation Life Stress in Power AlGaN/GaN HEMTs

Abstract: This paper reports on trap-related shifts of the transfer curve and threshold voltage of power AlGaN/GaN HEMTs under switched bias operating life and reverse and forward DC bias stress. Opposite polarity threshold voltage shifts at room temperature under operating life and reverse bias stress conditions can be explained by means of drain current transient measurements under reverse bias stress conditions. A proposed model to explain the trapping/de-trapping behavior under different stress conditions is described and highlights the critical role of the electric field. Experimental evidence of the importance of the role of the electric field is seen in reduced parametric shift by improving the field plate design.
Khalil, S.,
...
Ray, L.,
Chen, M.,
Chu, R.,
Zehnder, D.,
Garrido, A.,
Munsi, M.,
Hughes, B.,
Boutros, K.,
Kaplar, R.,
Dickerson, J.,
DasGupta, S.,
Atcitty, S.,
Marinella, M.
Proceedings of the International Reliability Physics Symposium
2014-06

A New Technique for Trapped Charge Extraction in SiC MOSFETs from Subthreshold Characteristics

Abstract: A method for extracting interface trap density (DIT) from subthreshold I-V characteristics is used to analyze data on a SiC MOSFET stressed for thirty minutes at 175°C with a gate bias of -20 V. Without knowing the channel doping, the change in DIT can be calculated when referenced to an energy level correlated with the threshold voltage.
Hughart, D.,
...
Flicker, J.,
Atcitty, S.,
Marinella, M.,
Kaplar, R.
Proceedings of the International Reliability Physics Symposium
2014-06

Impact of Gate Stack on the Stability of Normally-Off AlGaN/GaN Power Switching HEMTs

Abstract: We have examined the response of AlGaN/GaN power switching HEMTs to electrical bias stress. Three different gate stack structures were studied. In devices containing a ~ 5 nm thick AlGaN layer in the gate stack, both positive and negative shifts in the threshold voltage were observed following high blocking voltage stress, consistent with a short initial period of electron trapping followed by a longer period of de-trapping. Correlated changes in reverse bias leakage current were also observed, although this also occurred in devices containing only residual AlGaN in the gate stack. The data have been explained by a field-enhanced emission model in which an electron trapping to de-trapping transition occurs. The exact nature of the transition is found to be sensitive to a variety of parameters including trap energy, geometry, and initial and boundary conditions.
Kaplar, R.,
...
Dickerson, J.,
DasGupta, S.,
Atcitty, S.,
Marinella, M.,
Khalil, S.,
Zehnder, D.,
Garrido, A.
Proceedings of the International Symposium on Power Semiconductor Devices
2014-06

Static and Switching characteristics of 1200 V SiC Junction Transistors with on-chip integrated Schottky rectifiers

Abstract: A comprehensive evaluation of high-temperature (up to 200°C) on-state, blocking voltage and switching operation of 1200 V-class SiC Junction Transistors (SJTs) with on-chip integrated Schottky rectifiers is presented in this paper. The SJTs feature current gains of 69 and on-resistance of 6.3 mΩ-cm2 at room-temperature. The integrated free-wheeling Schottky rectifier displays a 0.9 V knee voltage and low on-resistance of 3.3 mΩ-cm2 at 25°C. Both the SJT and integrated Schottky rectifier show purely majority carrier characteristics with a desirable positive temperature co-efficient of on-state voltage drop. The integrated devices display robust 1200 V blocking voltages with low-leakage currents and a positive temperature co-efficient of breakdown - a clear signature of avalanche multiplication. Sub-50 ns switching waveforms are observed during hard-switching with an inductive load, due to the lower parasitic inherent to the integrated devices. Promising long-term current gain stability is obtained for the latest generation of SiC SJTs.
Sundaresan, S.,
...
Jeliazkov, S.,
Issa, H.,
Grummel, B.,
Singh, R.
IEEE 26th International Symposium on Power Semiconductor Devices and ICs (ISPSD)
p. 249-252
2014-06

Evaluation of Diels Alder poly(phenylene) anion exchange membranes in all-vanadium redox flow batteries

Abstract: Quaternary ammonium functionalized Diels-Alder poly(phenylene)s (QDAPPs) with different ion exchange capacities (IECs) are examined as membranes in all-vanadium redox flow batteries. QDAPP membrane behavior is compared to a standard, Nafion 212, in measurements of cycling efficiencies, areal specific resistance (ASR), vanadium permeation and durability. The IEC of the QDAPPs clearly shows an impact on the cell ASR and vanadium crossover. The results imply a trade-off between performance, indicated by cell voltage loss at a given current density, and rate of cross-over driven capacity loss in the system. Among the membranes studied, QDAPP with moderate IEC represents the best trade-off of these factors and exhibits higher performance and lower capacity loss compared to Nafion 212. All QDAPP membranes are found to be more durable than the analogous cation exchange membrane, sulfonated DAPP (SDAPP), in V5+ solution.
Sun, C.,
...
Tang, Z.,
Belcher, C.,
Zawodzinski, T.,
Fujimoto, C.
Electrochem. Comm.
43:63-66
2014-05

Sol Gel Based Synthesis and Electrochemistry of Magnesium Vanadium Oxide: A Promising Cathode Material for Secondary Magnesium Ion Batteries

Abstract: Magnesium-ion batteries are desirable due to the high environmental abundance and low cost of magnesium metal. Preparation,characterization, and an initial electrochemical study of Mg0.1V2O5 prepared by a novel sol gel method with no high temperature post processing is presented. Cyclic voltammetry showed the material to be quasi-reversible, with improved kinetics in an acetonitrile relative to a carbonate based electrolyte. Galvanostatic test data under a C/10 discharge showed a delivered capacity >250 mAh/g over several cycles. Projecting these results to a magnesium anode battery would yield an average operating voltage ∼3.2 V with an energy density ∼800 mWh/g for the cathode material, suggesting promise of our synthesized material as a viable cathode material for secondary magnesium batteries.
Lee, S.,
...
DiLeo, R.,
Marschilok, A.,
Takeuchi, K.,
Takeuchi, E.
ECS Electrochemistry Letters
3(8):A87-A90
2014-01

Optical measurements of impurities in room-temperature ionic liquids

Abstract: The absorption spectra of 1-methylimidazole and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [EMIM][TFSI], mixtures from 0% to 20% mole fraction are reported at ultraviolet to infrared wavelengths. Quantitative measurement of 1-methylimidazole in [EMIM][TFSI] is reported using an isolated 1-methylimidazole absorption feature at 1520 cm-1. UV measurements reveal a 1-methylimidazole absorption feature at 270 nm and a 260 nm feature for [EMIM][TFSI]. Absorption at 280 nm is demonstrated to scale with 1-methylimidazole mole fraction in [EMIM][TFSI] and is used to measure 1-methylimidazole mole fractions. Absorption is shown to increase around 240 nm upon addition of 1-methylimidazole to [EMIM][TFSI], which preliminary time-dependent density functional theory (DFT) calculations identify as an intermolecular excitation between [EMIM][TFSI] and 1-methylimidazole. We report recommendations for UV and infrared detection schemes for the quantitative detection of 1-methylimidazole in [EMIM][TFSI].
Porter, J.,
...
Dreyer, C.,
Bicknase, D.,
Vyas, S.,
Maupin, M.,
Poshusta, J.,
Martin, J.
Quant. Spectr. Rad. Trans.
133:300-310
2014-01

Optical Measurements of Impurities in Room Temperature Ionic Liquids

Abstract: The absorption spectra of 1-methylimidazole and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [EMIM][TFSI], mixtures from 0% to 20% mole fraction are reported at ultraviolet to infrared wavelengths. Quantitative measurement of 1-methylimidazole in [EMIM][TFSI] is reported using an isolated 1-methylimidazole absorption feature at 1520 cm(-1). UV measurements reveal a 1-methylimidazole absorption feature at 270 nm and a 260 nm feature for [EMIM][TFSI]. Absorption at 280 nm is demonstrated to scale with 1-methylimidazole mole fraction in [EMIM][TFSI] and is used to measure 1-methylimidazole mole fractions. Absorption is shown to increase around 240 nm upon addition of 1-methylimidazole to [EMIM][TFSI], which preliminary time-dependent density functional theory (DFT) calculations identify as an intermolecular excitation between [EMIM][TFSI] and 1-methylimidazole. We report recommendations for UV and infrared detection schemes for the quantitative detection of 1-methylimidazole in [EMIM][TFSI].
Porter, J.
...
Dreyer, C.,
Bicknase, D.,
Vyas, S.,
Maupin, C.,
Poshusta, J.,
Martin, J.
J. of Quantitative Spectroscopy and Radiative Transfer
133:300-310
2014

Silicon Carbide Junction Transistors and Schottky Rectifiers optimized for 250°C operation

Abstract: Electrical performance and reliability of SiC Junction Transistors (SJTs) and Schottky rectifiers are presented. The 650 V/50 A-rated SiC SJTs feature current gains (β) up to 110 at room-temperature, 70 at 250°C, and stable breakdown characteristics. Single current pulse measurements indicate an almost invariant β up to 800 A/cm2 at 175°C - a measure of the SOA boundary for pulsed current SJT operation. Lower than 5 mA/cm2 leakage currents are measured on the SJTs at the rated blocking voltage and at 250°C. 1200 V Schottky rectifiers designed for high-temperature operation display < 3 mA/cm2 leakage currents up to 250°C. A 10x reduction in leakage current and 23% reduction in junction capacitance are observed when compared to the nearest competitor. The high-temperature Schottky rectifiers and SJTs display stable breakdown voltages and on-state characteristics after long-term HTRB stressing. A significant improvement in current gain stability is achieved by fine-tuning the fabrication process.
Sundaresan, S.,
...
Grummel, B.,
Singh, R.
MRS Proceedings
1693 mrss14-1693-dd03-08
doi:10.1557/opl.2014.531
2014

Rapidly Maturing SiC Junction Transistors featuring current gain > 130, blocking voltages up to 2700 V and stable long-term operation

Abstract: SiC npn Junction Transistors (SJTs) with current gains as high as 132, low on-resistance of 4 mΩ-cm2, and minimal emitter-size effect are demonstrated with blocking voltages > 600 V. 2400 V-class SJTs feature blocking voltages as high as 2700 V combined with on-resistance as low as 5.5 mΩ-cm2. A significant improvement in the current gain stability under long-term high current stress is achieved for the SJTs fabricated by the high gain process.
Sundaresan, S.,
...
Jeliazkov, S.,
Grummel, B.,
Singh, R.
Materials Science Forum
778-780:1001-1004
2014

Phase formation of BaTiO3 - Bi(Zn1/2Ti1/2)O3 perovskite ceramics

Abstract: Materials based on BiMO3-modified BaTiO3 have been shown to exhibit a number of attractive electrical and electromechanical properties. In addition, many of the materials in this broad family exhibit reduced sintering temperatures for densification as compared to pure BaTiO3. We report here a study of the phase evolution and sintering behavior of Bi(Zn1/2Ti1/2)O3-modified BaTiO3 materials from low-cost mixed oxide/carbonate precursor powders. By accelerating the reaction of the BaCO3 species and increasing the diffusion kinetics associated with densification, Bi(Zn1/2Ti1/2)O3 additions reduce the calcination and sintering temperatures by ~200°C compared to unmodified BaTiO3. This system provides an example of the important and often overlooked role of additives in the calcination, phase evolution, and densification processes, and provides insight into mechanisms that may be further exploited in this and other important materials systems. We are quite honored to have the opportunity to publish in a special issue dedicated to the life and work of our dear late colleague Prof. Marija Kosec. The topic of this paper is fitting as well, since the work was in large part directly inspired by her work on the importance of reactions and intermediate phases in the alkali niobate systems and heavily informed by her work on the Pb-based perovskites. Marija appreciated better than most the importance of careful processing in the formation of fine ceramics, and the global ceramics community is grateful to her for all of the lessons that she taught us—and through her papers and her students, continues to teach us.
Triamnak, N.,
...
Brennecka, G.,
Brown-Shaklee, H.,
Rodriguez, M.,
Cann, D.
J. Cer. Soc. Jpn.
122:260-266
2014

The Design and Development of a 15 kV SiC Half-Bridge Multi-Chip Power Module for Medium Voltage Applications

Abstract: In this work, the packaging design and development of a high voltage (> 15 kV), high current (120 A) silicon carbide (SiC) multi-chip power module (MCPM) will be presented. The module implements a MCPM packaging strategy which itself uses subassemblies to reduce manufacturing cost through reworkability. The use of solderless internal connections aids in reducing cost both by simplifying the assembly process as well as enabling a high level of flexibility in the manufacturing process in order to drive down costs by increasing yield. A wire bondless flip-chip die interconnection scheme has been developed in this work in parallel with a more traditional wire bonded method. Both presented approaches utilize a common set of parts with minimal differences due to the divergent portions of each interconnection scheme. Device neutrality in this design ensures that a variety of die types from any manufacturer may be housed in a number of arrangements depending on the requirements of the end-use application without requiring significant redesign effort for each new application or improvement in device technology. The SiC MCPM is constructed using high temperature capable materials, enabling operation at high junction temperatures. This leads to the ability to design a small, low profile module with low parasitic inductances and a small junction to case thermal resistance. A low module thermal resistance makes it possible to significantly reduce the size and complexity of the cooling systems, ultimately, reducing the size of the system. Thus, the novel high voltage SiC MCPM represents a significant step forward in high voltage switching applications. This paper discusses the overall mechanical design of the SiC high voltage MCPM; the three-dimensional finite-element modeling and analysis of the thermal and electrical characteristics of the high voltage power module are also presented.
Cole, Z.,
...
Stabach, J.,
Falling, G.,
Killeen, P.,
McNutt, T.,
Passmore, B.
Proceedings of the IMAPS 47th International Symposium on Microelectronics
2014

AlGaN composition dependence of the band offsets for epitaxial Gd2O3/ AlxGa1-xN (0≤x≤0.67) heterostructures

Abstract: In this work we investigated the dependence of AlGaN composition on the valence band offsets at a Gd2O3/AlGaN interface. We found that as the AlN content in the AlGaN semiconductor layer increases, the valence band offset with the gate oxide, Gd2O3, decreases. An AlGaN composition with ~67% AlN possessed virtually no valence band offset with the gate oxide and therefore shows that this is an important design criteria for the development of next generation nominally-off power electronic devices.
Ihlefeld, J.,
...
Brumbach, M.,
Allerman, A.,
Wheeler, D.,
Atcitty, S.
Applied Physics Letters
105:012102
2013-12

Computational model of a sodium-copper-iodide rechargeable battery

Abstract: This paper first derives a model to describe a class of Na-metal-halide secondary batteries, using molten sodium as the anode, NASICON as the sodium-ion-conducting separator, and copper-iodide chemistry in an aqueous electrolyte for the cathode. The model is based upon solving transient conservation equations using a Nernst-Planck-Poisson (NPP) formulation. The broad objective is to develop a predictive model that can assist the design and development of large-scale grid-storage batteries. However, the model-predicted results and discussion are focused on a laboratory-scale battery. Several examples are discussed, considering the effects of current density and catholyte molar concentrations on battery performance.
Zhu, H.,
...
Bhavaraju, S.,
Kee, R.
Electrochim. Acta
112:629-639
2013-12

Computational model of a sodium-copper-iodide rechargeable battery

Abstract: This paper first derives a model to describe a class of Na-metal-halide secondary batteries, using molten sodium as the anode, NASICON as the sodium-ion-conducting separator, and copper-iodide chemistry in an aqueous electrolyte for the cathode. The model is based upon solving transient conservation equations using a Nernst-Planck-Poisson (NPP) formulation. The broad objective is to develop a predictive model that can assist the design and development of large-scale grid-storage batteries. However, the model-predicted results and discussion are focused on a laboratory-scale battery. Several examples are discussed, considering the effects of current density and catholyte molar concentrations on battery performance.
Zhu, H.,
...
Bhavaraju, S.,
Kee, R.
Electrochmica Acta
112:629-639
2013-10

Progress in SiC MOSFET Reliability

Abstract: Bias-temperature stress experiments performed on two generations of SiC power MOSFETs from the same manufacturer show reductions in threshold voltage (VT) shift at elevated temperatures from first- to second-generation. The negative VT shift is reduced from a range of -1 V to -1.6 V to a range of -100 mV to -300 mV for temperatures from 125°C to 175°C. Plastic-packaged parts show a gate-bias-independent junction leakage current at temperatures above the rated temperature, suggesting that the plastic packaging introduces an extrinsic leakage path. Junction leakage in metal-packaged parts can be significantly reduced by applying a small negative gate bias at elevated temperatures. Switching gate bias temperature stresses show VT shifts dependent on duty cycle, with a higher duty cycle resulting in a higher rate of VT shift. Cumulative damage effects may be observed between switching gate bias stresses.
Marinella, M.,
...
Hughart, D.,
Flicker, J.,
DasGupta, S.,
Atcitty, S.,
Kaplar, R.
Proceedings of the 224th Meeting of the Electrochemical Society
2013-09

Application of Redox Non-Innocent Ligand to Non-Aqueous Flow Battery Electrolytes

Abstract: Demonstrate that electrolytes comprising redox “non-innocent” ligands, which store equivalents of charge separate from the metal center, are a new avenue for electrical energy storage.
Cappillino, P.,
...
Pratt III, H.,
Hudak, N.,
Tomson, N.,
Anderson, T.,
Anstey, M.
Adv. Energy Mater.
(4):1-4
2013-09

Application of Redox Non-Innocent Ligands to Non-Aqueous Flow Battery Electrolytes

Abstract: High energy-density, redox flow batteries (RFB) can provide cost-effective, grid-scale energy storage, facilitating the use of intermittent sources such as solar and wind power. A new electrolyte based on vanadium and redox-active ligands that stores equivalents of charge separately from the metal center is presented. Electrolytes composed of non-innocent ligands greatly enhance both the energy density and stability of non-aqueous RFBs.
Cappillino, P.,
...
Pratt III, H.,
Hudak, N.,
Tomson, N.,
Anderson, T.,
Anstey, M.
Advanced Energy Materials
2013-09

Copper Ionic Liquids: Tunable ligand and anion chemistries to control electrochemistry and deposition morphology

Abstract: A multi-technique investigation was performed on three copper-based ionic liquids to elucidate the influence of coordinating ligands and charge-balancing anions on the electrochemical properties of the materials. Galvanostatic cycling of Cu(OHCH2CH2NH2)6(BF4)2 (Cu1) in 1-butyl-3-methyl-imidazolium hexafluorophosphate gave partially reversible plating of copper that was consistent with cyclic voltammetry data (collected using an ionic liquid-based reference electrode verified with measurements of ferrocene, cobaltocene, and lithium). Scanning electron microscopy also showed pitting in the copper-coated surface of the electrode that was consistent with the stripping wave observed by cyclic voltammetry. Potentiostatic deposition in neat Cu1 showed significant dendrite formation. The substitution of the OHCH2CH2NH2 ligands of Cu1 with stronger coordinating NH(CH2CH2OH)2 in Cu(NH(CH2CH2OH)2)6(BF4)2 (Cu2) resulted in the complete suppression of both copper stripping and dendrite formation. Substitution of the BF4- anions of Cu2 with CF3SO3- in Cu(NH(CH2CH2OH)2)6(CF3SO3)2 (Cu3) shifted the copper deposition 0.1 V more negative and produced slightly larger spherical particles (1.5 μm versus 5 μm). The results suggested that while the anion composition influenced particle size, and the metal-ligand bond strength helped control particle morphology, both factors affected the electrochemical properties including the plating and stripping of copper.
Pratt III, H.,
...
Ingersoll, D.,
Hudak, N.,
McKenzie, B.,
Anderson, T.
J. Electroanal. Chem.
704:153-158
2013-08

Synthesis and characterization of a family of solvated sodium aryloxide compounds

Abstract: A family of crystallographically characterized solvated sodium alkoxides ([(solv)xNa(OR)]n) was synthesized from the reaction of sodium bis(trimethylsilyl)amide with a series of sterically varied aryl alcohols (H-OAr): 2-alkyl phenol [alkyl = methyl (oMP), iso-propyl (oPP), and tert-butyl (oBP)] or 2,6-di-alkyl phenol [alkyl = methyl (DMP), iso-propyl (DIP), and tert-butyl (DBP)]. Single crystal X-ray experiments revealed the structure of the products to be highly dependent on the ligand set employed and the solvent used (THF or py). The [(solv)xNa(OAr)]n products were identified as: [(THF)Na(μ3-oMP)]6 (1), [(THF)4Na6(μ3-oPP)4(μ4-oPP)2] (2), [(THF)Na(μ3-oBP)]4 (3)·THF, [(THF)Na(μ3-DMP)]4 (4), [(THF)2Na(μ-DIP)]2 (5), [(THF)2Na(μ-DBP)]2 (6), {[Na(μ-DPhP-ηx)]2}n (7), [(py)5Na6(μ3-oMP)4(μ4-oMP)2]2[(py)4Na6(μ3-oMP)4(μ4-oMP)2] (8), [(py)6Na4(μ3-oPP)4] (9)·py, [(py)Na(μ3-DMP)]4 (11), [(py)2Na(μ-DIP)]2 (12), [(py)4Na(DBP)] (13). Crystals could not be isolated for the Na/oBP/py (10) system but the powder was assigned the '[(py)Na(oBP)]4' structure based on the available analytical data. In addition, under similar conditions, the neo-pentoxide (ONep) derivatives were isolated and characterized as [(solv)4Na6(μ3-ONep)4(μ4-ONep)2] (solv = THF, 14; py 15). A number of complex structures (monomers, squares, cubes, fused-cubes, hexagons) were observed for this family of [(solv)xNa(OAr)]n compounds. The solution behaviors of these compounds were studied using heteronuclear 23Na NMR. A comparison of these [(solv)xA(OR)]n A = Li, Na, K, Rb, Cs structural motifs is also presented.
Boyle, T.,
...
Velazquez, A.,
Yonemoto, D.,
Alam, T.,
Moore, C.,
Rheingold, A.
Inorganica Chimica Acta
405:374-386
2013-08

A Photocapacitance Decay Technique for Interface Trap Characterization near Inversion Band in Wide Bandgap MOS Capacitors

Abstract: A technique to characterize interface traps near the minority carrier band for wide bandgap metal-oxide-semiconductor (MOS) capacitors at room temperature is presented. The method uses photogeneration of minority carriers and transient analysis of the subsequent photocapacitance decay to evaluate trap response times. The technique is demonstrated using n-type substrate 6H-SiC/SiO2 MOS capacitors to extract interface trap density (Dit) ranging in energy from 0.2 to 0.8 eV above the valence band edge (Ev) and trap cross sections from 0.4 to 0.7 eV above Ev. For the given material system, traps near Ev exhibit significant differences between n-and p-type substrate MOS capacitors.
DasGupta, S.,
...
Kaplar, R.,
Atcitty, S.,
Marinella, M.
IEEE Transactions on Electron Devices
60(8):2619
2013-07

Damping of Inter-area Oscillations using Energy Storage

Abstract: Low frequency inter-area oscillations have been identified as a significant problem in utility systems due to the potential for system damage and the resulting restrictions on power transmission over select lines. Previous research has identified real power injection by energy storage based damping control nodes as a promising approach to mitigate inter-area oscillations. In this paper, a candidate energy storage system based on UltraCapacitor technology is evaluated for damping control applications in theWestern Electric Coordinating Council (WECC), and an analytical method for ensuring proper stability margins is also presented for inclusion in a future supervisory control algorithm. Dynamic simulations of the WECC were performed to validate the expected system performance. Finally, the Nyquist stability criteria was employed to derive safe operating regions in the gain, time delay space for a simple two-area system to provide guaranteed margins of stability.
Neely, J.,
...
Byrne, R.,
Elliott, R.,
Silva-Monroy, C.,
Schoenwald, D.,
Trudnowski, D.,
Donnelly, M.
IEEE Power & Energy Society
2013-07

Performance and Reliability Characterization of 1200 V Silicon Carbide Power MOSFETs at High Temperatures

Abstract: Commercially available, 1200 V SiC power MOSFETs have been characterized under bias-temperature stress conditions. Two generations of devices from a single manufacturer were tested. For the first-generation MOSFETs, both plastic- and metal-packaged devices were evaluated, whereas for the second-generation MOSFETs, only plastic-packaged devices were tested. Threshold voltage was observed to decrease with increasing temperature in the absence of gate bias stress, as expected. Drain leakage current increased with increasing temperature above the rated temperature of 125˚C for first-generation plastic-packaged parts, with the leakage ~10× higher for the plastic-packaged parts compared to the metal-packaged parts. A negative gate voltage was shown to reduce drain leakage current for the metal-packaged parts only, suggesting a parasitic leakage path associated with the plastic packaging. The threshold voltage shift DVT was minimal for T < 125˚C. DVT increased with increasing temperature above 125˚C, and was larger for negative gate voltage bias stress, suggesting that the oxide is more sensitive to trapping of holes than trapping of electrons. DVT was insensitive to the type of package. The second-generation SiC MOSFET showed significantly less susceptibility to bias temperature stress, especially for negative gate voltage, indicating improvement in device design and/or processing in the second-generation MOSFET. Switching gate stress showed complex behavior, with a rapid initial shift in VT followed by a much slower shift. Initial testing indicates a strong dependence on duty cycle and possible influence of self-heating. More detailed study of reliability under switching conditions is needed.
Kaplar, R.,
...
Hughart, D.,
Atcitty, S.,
Flicker, J.,
DasGupta, S.,
Marinella, M.
High Temperature Electronics Network,
Oxford, UK
2013-05

Highly Li-Stuffed Garnet-Type Structured Li7+xLa3Zr2-xYxO12

Abstract: We report the synthesis, microstructure and Li ion conductivity of Li-stuffed garnet-type metal oxides, with nominal chemical formulae Li7.06La3Zr1.94Y0.06O12 and Li7.16La3Zr1.84Y0.16O12. Powder X-ray diffraction (PXRD) shows the formation of cubic garnet-type structure at 950°C (12 h in air) with cell constant of 12.974(3) Å and 12.995(2) Å for Li7.06La3Zr1.94Y0.06O12 and Li7.16La3Zr1.84Y0.16O12, respectively. The slight increase in cubic cell constant is consistent with Y-substitution for Zr in Li7La3Zr2O12. For samples sintered at 1100-1150°C, PXRD displays multi-phase mixtures, but the garnet-type structure remained the major phase. Scanning electron microscopy (SEM) studies show an average crystallite size in the range of 2-5 μm, and particle size increases with increasing sintering temperature, as anticipated. Energy dispersive spectroscopy (EDS) elemental mapping show single homogenous distribution of elements, for samples prepared at 950°C. Electrochemical AC impedance spectra exhibit mainly bulk contribution at temperatures higher than 150°C, and at low temperature, we see contributions from bulk and grain-boundary resistance. The bulk electrical conductivity of the sample was found to be comparable to those of the high temperature tetragonal Li7La3Zr2O12 phase. The electrical conductivity of Y-doped samples investigated in the present work was ~10-6 Scm-1 at 23°C with an activation energy of 0.47 eV. The lower conductivity of this Y-doped garnet was explained based on Raman spectroscopy and SEM analysis.
Hitz, G.,
...
Wachsman, E.,
Thangadurai, V.
Electrochem. Soc.
160:A1248-A1255
2013-05

Characterization and Reliability of SiC- and GaN-Based Power Transistors for Renewable Energy Applications

Abstract: Power devices based on the wide-bandgap semiconductors SiC and GaN have many potential advantages compared to conventional Si-based switching devices, especially for renewable energy and smart grid applications. However, while these emerging devices have developed rapidly in recent years, many factors affecting their performance and reliability remain unknown. In this paper, we discuss some of the key results that have been obtained for both SiC- and GaN-based devices under Sandia National Lab's “post-Silicon” power electronics reliability program. State-of-the-art, commercially available 4H-SiC MOSFETs are evaluated for stability under high-temperature over-voltage and pulsed over-current conditions. The devices show maximum vulnerability under high-temperature off-state operation at high temperature. The room-temperature pulsed over-current operation results in degradation similar to that observed under high-temperature on-state DC conditions, presumably due to overheating of the device beyond its specified junction temperature. Prototype AlGaN/GaN HEMTs with ~1800 V breakdown are evaluated for stability under different bias conditions. Current collapse is observed and analyzed, and trapping components with very different time constants are found to be involved. The specific nature of degradation and recovery depends strongly upon the particular stress bias (gate vs. drain) condition applied.
Kaplar, R.,
...
Marinella, M.,
DasGupta, S.,
Smith, M.,
Atcitty, S.,
Sun, M.,
Palacios, T.
IEEE Energy Tech,
Cleveland, OH
2013-04

Reliability Analysis and Prediction of Commercial 1200 V, 33A, 4H-SiC MOSFETs under DC and Pulsed Stress

Abstract: State-of-the-art, commercially available, 4H-SiC MOSFETs are evaluated for stability under high-temperature over-voltage and pulsed over-current conditions. The devices show maximum vulnerability under high-temperature accumulation stress, demonstrating that the gate oxide is more prone to hole trapping than to electron trapping. The power MOSFET architecture coupled with a high interface trap density enables us to predict the stability of the device through a simple evaluation of the free-wheeling diode ideality factor (h) of the unstressed device. The pulsed over-current operation results in degradation similar to electron trapping at high temperature, presumably due to overheating of the device beyond its specified junction temperature. Over-current degradation is more severe at high switching frequency.
DasGupta, S.,
...
Kaplar, R.,
Marinella, M.,
Smith, M.,
Atcitty, S.
International Reliability Physics Symposium,
Anaheim, CA
2013-03

A Polyoxometalate Flow Battery

Abstract: A redox flow battery utilizing two, three-electron polyoxometalate redox couples was investigated for use in stationary storage in either aqueous or non-aqueous conditions. The aqueous battery had coulombic efficiencies greater than 95% with relatively low capacity fading over 100 cycles. Infrared studies showed there was no decomposition of the compound under these conditions. The non-aqueous analog had a higher operating voltage but at the expense of coulombic efficiency. The spontaneous formation of these clusters by self-assembly facilitates recovery of the battery after being subjected to reversed polarity. Polyoxometalates offer a new approach to stationary storage materials because they are capable of undergoing multielectron reactions and are stable over a wide range of pH values and temperatures.
Pratt III, H.,
...
Hudak, N.,
Fang, X.,
Anderson, T.
Journal of Power Sources
2013-02

Copper ionic liquids: examining the role of the anion in determining physical and electrochemical properties

Abstract: Five new copper(II)-based ionic liquids and three crystalline compounds have been synthesized in order to further understand the role of the anion in determining their physicochemical properties. Materials were prepared with combinations of three different anions (2-ethylhexanoate (EHN), tetrafluoroborate (BF4), and triflate (OTf)) and six-coordinate Cu(II) cations. The complexes that contain at least one BF4 anion consistently displayed both the highest specific conductivity and electrochemical reversibility. The presence of one OTf anion (in combination with one EHN or BF4) facilitates the formation of crystalline materials. Single crystal X-ray diffraction studies were completed on two of the mixed anion compounds. The results show that both ethanolamine (EA) and diethanolamine (DEA) chelate to the Cu(II) centers in a highly distorted tetragonal geometry. The properties of the ionic liquid with the overall lowest viscosity and highest conductivity and electrochemical reversibility (Cu{NH2CH2CH2OH}6(BF4)2, 4) were studied as a function of temperature. The viscosity decreases with increasing temperature, but at 45 °C (over three hours) there is a loss of two EA ligands to form a more viscous four-coordinate complex. Cyclic voltammetry of 4 reveals a quasi-reversible Cu(II)/Cu(I) reduction wave that shifts to more positive potentials with increasing temperature.
Pratt III, H.,
...
Leonard, J.,
Steele, L.,
Staiger, C.,
Anderson, T.
Inorg. Chim. Acta
396:78-83
2013

Mixed addenda polyoxometalate 'solutions' for stationary energy storage

Abstract: A series of redox flow batteries utilizing mixed addenda (vanadium and tungsten), phosphorus-based polyoxometalates (A-α-PV3W9O406-, B-α-PV3W9O406−, and P2V3W15O629−) were prepared and tested.
Pratt III, H.,
...
Anderson, T.
Dalton Trans.
42:15650-15655
2013

Band offsets of La2O3 on (0001) GaN grown by reactive molecular-beam epitaxy

Abstract: In this work we studied how a candidate gate oxide material, La2O3, grows on (0001) GaN and investigated the band offsets at the oxide/semiconductor interface. We found that the oxide grows in a hexagonal symmetry (same as GaN) for the first several nanometers and transitions to a cubic symmetry as the thickness increases. This transition in symmetry is accompanied by increased oxide roughness, which leads to increased threading defect densities. The band offsets, measured for the hexagonal phase, were less than 1eV for the valence band and therefore show that while this material has many desirable properties for a gate oxide (high permittivity, lattice matching with GaN), there may be low high temperature performance owing to the limited band offset and electrical leakage.
Ihlefeld, J.,
...
Brumbach, M.,
Atcitty, S.
Applied Physics Letters
102:162903
2012-11

Dielectric Properties of BaTiO3 - Bi(Zn1/2Ti1/2)O3 - NaNbO3 Solid Solutions

Abstract: In order to develop dielectric ceramics with temperature-stable permittivity characteristics, perovskite BaTiO3-Bi(Zn1/2Ti1/2)O3-NaNbO3 ceramic solid solutions were investigated with a particular focus on effects of BaTiO3 and NaNbO3 contents on the dielectric properties of ternary compounds. Keeping the ratios of the other two constituents constant, decreasing the BaTiO3 content leads to a broadening of the temperature-dependent permittivity maximum and a decrease in the overall permittivity. For compositions of constant BaTiO3 content, replacing Bi(Zn1/2Ti1/2)O3 with NaNbO3 shifts the temperature of the maximum permittivity to lower temperatures (e.g., to −103 °C for a composition of 70BT-5BZT-25NN) while maintaining a broad permittivity peak with temperature, which for the 50BT-25BZT-25NN composition also satisfies the X9R standard. Thus, the investigation of BT-BZT-NN compounds resulted in promising dielectric properties with broad temperature ranges of high permittivity, which is of interest for advanced capacitor applications.
Raengthon, N.,
...
Brown-Shaklee, H.,
Brennecka, G.,
Cann, D.
J. Mater. Sci.
48:031401
2012-10

Secondary Battery Science: At the Confluence of Electrochemistry and Materials Engineering

Abstract: Considerations of energy density, power, and calendar life are critical to effectively develop advanced secondary systems. For next generation battery applications requiring multiple features including long life, large cycle count, high energy density and high power, new strategies are needed for the rational design of electroactive materials and electrodes. This article discusses several conceptual approaches under exploration with examples from our research group. The first approach is the systematic synthesis of materials with structures facilitating ion insertion and deinsertion at high voltage and energy density, where we control materials properties such as surface area, particle size and in particular crystallite size. A second approach is the investigation of novel electrode structures and substrates to increase energy density and capacity retention under cycling, where we have developed strategies for minimizing passive components. A third approach is investigation of catalysts for metal air batteries where the cathode active material is drawn from the air rather than carried in the battery.
Takeuchi, E.,
...
Marschilok, A.,
Takeuchi, K.
Electrochemistry
80(10):700-705
2012-07

Vanadium redox flow battery efficiency and durability studies of sulfonated Diels Alder poly(phenylene)s

Abstract: Sulfonated Diels Alder poly(phenylene) (SDAPP) was examined for vanadium redox flow battery (VRFB) use. The ion exchange capacity (IEC) was varied from 1.4, 1.6 and 2.0 meq/g in order to tune the proton conductivity and vanadium permeability. Coulombic efficiencies between 92 to 99% were observed, depending on IEC (lower IEC, higher coulombic efficiencies). In all cases the SDAPP displayed comparable energy efficiencies (88-90%) to Nafion 117 (88%) at 50 mA/cm2. Membrane durability also was dependent on IEC; SDAPP with the highest IEC lasted slightly over 50 cycles while SDAPP with the lowest IEC lasted over 400 cycles and testing was discontinued only due to time constraints. Durability screening tests were initialed with SDAPP, by soaking films in a 0.1 M V5+ and 5.0 M total SO4− 2 solution. The rate of degradation was also proportional with IEC; the 2 meq/g sample dissolved within 376 h, the 1.6 meq/g sample dissolved after 860 h, while the 1.4 meq/g sample broke apart after 1527 h.
Fujimoto, C.,
...
Soowhan, K.,
Stanis, R.,
Wei, X.,
Li, L.,
Zhenguo, Y
Electrochem. Comm.
20:48-51
2012

Linear single phase inverter model for Battery Energy Storage System evaluation and controller design

Abstract: A method for deriving a set of linear transfer functions for a single phase grid tied system is presented, which can be used to determine how small signal perturbations and transients on the utility side are translated through the inverter to the dc link, as well as assist in controller design. These transfer functions can be used by a Battery Energy Storage System (BESS) designer to predict what harmonics the battery will see in the field, without the need for expensive simulation software. With this information, battery designers will be able to design a more robust battery specifically tailored for single phase inverter applications.
Watson, L.,
...
Kimball, J.,
Atcitty, S.
Proc. Applied Power Electronics Conference and Exposition (APEC)
2012 Twenty-Seventh Annual
IEEE 10(1109):1861-1867, /apec.2012.6166075
2012

Carbide-Derived Carbon Monoliths with Hierarchical Pore Architectures

Abstract: Porous carbon materials are crucial components in catalysis, gas storage, electronics, and biochemistry. A hierarchical pore architecture in these materials is essential to achieve high surface areas combined with advanced mass transport kinetics. Widely used approaches for the generation of micro- or mesopores are activation and nanocasting. In contrast, macroporous carbon materials are primarily obtained by carbonization of polymeric precursor gels or replication of larger templates. A relatively new class of micro- and mesoporous carbon material with tunable porosity are carbide-derived carbon materials (CDCs). High-temperature chlorination of carbides leads to selective removal of metal- or semi-metal atoms and allows control over the pore size of the resulting CDCs in a sub-Angstrom range by changing synthesis conditions or the carbide precursor. These materials have been studied for applications in gas storage and as electrode materials in supercapacitors because of their high specific surface areas.
Oschatz, M.,
...
Borchardt, L.,
Thommes, M.,
Cychosz, K.,
Senkovska, I.,
Klein, N.,
Frind, R.,
Leistner, M.,
Presser, V.,
Gogotsi, Y.,
Kaskel, S.
Angewandte Chemie
51:7577-7580
2012

Tunable Young's Modulus in Carbon MEMS using Graphene-based Stiffeners

Abstract: Carbon composite micro-electromechanical systems (C-MEMS) incorporating 2 wt.% graphene stiffeners show a 65% increase in Young's modulus and 11% increase in conductivity. An improved reduced graphene oxide (iRGO), is blended into pyrolytic carbon beams prepared for resonant frequency testing. Designed around a 10:1 (length: width) aspect ratio, the linearity of wt.% iRGO in the cantilevers as a function of resonant frequencies is evaluated. The collection of the 1st through 3rd bending modes using laser Doppler velocimetery (LDV) of the graphene filled cantilevers shows an increase in frequency response with nanomaterial loading (wt.%). A model was developed using the 3-bending modes and correlated with cross sectional geometry and density to extract a Young's modulus.
Washburn, C.,
...
Lambert, T.,
Blecke, J.,
Davis, D.,
Finnegan, P.,
Hance, B.,
Strong, J.
J. Electrochem. Soc. Trans.
50(12):423-434
2012

Defect Mechanisms in High Resistivity BaTiO3 - Bi(Zn0.5Ti0.5)O3 Ceramics

Abstract: The defect mechanisms that underpin the high energy density dielectric 0.8BaTiO3-0.2Bi(Zn1/2Ti1/2)O3 were investigated. Characterization of the nominally stoichiometric composition revealed the presence of a Ti3+-related defect center, which is correlated with lower resistivities and an electrically heterogeneous microstructure. In compositions with 2 mol. % Ba-deficiency, a barium vacancy-oxygen vacancy pair Active content removed , acted as an electron-trapping site. This defect was responsible for a significant change in the transport behavior with a high resistivity and an electrically homogeneous microstructure.
Raengthon, N.,
...
DeRose, V.,
Brennecka, G.,
Cann, D.
Appl. Phys. Lett.
101:112904
2011-11

Electrical Energy Storage for the Grid: A Battery of Choices

Abstract: The increasing interest in energy storage for the grid can be attributed to multiple factors, including the capital costs of managing peak demands, the investments needed for grid reliability, and the integration of renewable energy sources. Although existing energy storage is dominated by pumped hydroelectric, there is the recognition that battery systems can offer a number of high-value opportunities, provided that lower costs can be obtained. The battery systems reviewed here include sodium-sulfur batteries that are commercially available for grid applications, redox-flow batteries that offer low cost, and lithium-ion batteries whose development for commercial electronics and electric vehicles is being applied to grid storage.
Dunn, B.,
...
Kamath, H.,
Tarascon, J.
Science
334:928-934
2011-06

Simulation and optimization of a flow battery in an area regulation application

Abstract: Flow batteries have the potential to provide ancillary grid services such as area regulation. In this paper, a hypothetical 2 MW flow battery is simulated in an area regulation application to find the optimal energy-to-power ratio that maximizes the net present value (NPV) of a 10 year project based on a range of installation costs. Financial and operational results are presented, and candidate battery chemistries are discussed. A simplified model of battery installation costs (dollars per kW h) resulted in a positive NPV for installation costs below $500 kW(-1) h(-1). For installation costs between $300 and $500 kW(-1) h(-1), an optimal energy-to-power ratio is 1.39. The traditional advantage of decoupling power and energy capacity may not be realized in area regulation; therefore hybrid flow batteries may be more appropriate. Zinc-bromine and iron-chromium chemistries might fit well with this application, along with lower-cost flow battery chemistries in the future.
Mellentine, J.,
...
Culver, W.,
Savinell, R.
Journal of Applied Electrochemistry
41(10):1167-1174
DOI: 10.1007/s10800-011-0326-8
2011-04

Experimental Deformation of Salt in Cyclic Loading, Insights from Acoustic Emission Measurements

Abstract: Compressed air energy storage (CAES) in geologic media has been proposed to help ensure reliability of renewable energy sources, for example wind and solar, by providing a means to store energy when excess energy was available, and to provide an energy source during non productive renewable energy time periods. Such a storage media may experience hourly (perhaps small) pressure swings within a geologic storage media. This implies that the storage "container," for example, a salt cavern, may experience small irregular pressure cycling.
Bauer, S.,
...
Broome, S.,
Bronowski, D.,
Rinehart, A.,
Ingraham, M.
Solution Mining Research Institute

 

Pacific Northwest National Laboratory Journal Articles

Sandia | PNNL | ORNL | Top

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Date Title Authors Publisher
2014-08

Liquid-metal electrode to enable ultra-low temperature sodium–beta alumina batteries for renewable energy storage

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 ​sodiumanodes 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.
Lu, X.,
...
Li, G.,
Kim, J.,
Mei, D.,
Lemmon, J.,
Sprenkle, V.
Nat. Commun.
5:4578 doi: 10.1038/ncomms5578
2014-02

Cost and Performance Model for Redox Flow Batteries

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.
Stephenson, D.,
...
Kim, S.,
Wang, W.,
Li, B.,
Coffey, G.,
Thomsen, E.,
Graff, G.,
Balducci, P.,
Kintner-Meyer, M.,
Sprenkle, V.
Journal of Power Sources,
247:1040-1051. doi:10.1016/j.jpowsour.2012.12.023
2014-02

GeOx/Reduced Graphene Oxide Composite as an Anode for Li-ion Batteries: Enhanced Capacity via Reversible Utilization of Li2O along with Improved Rate Performance

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.
Yi, R.,
...
Feng, J.,
Lu, D.,
Gordin, M.,
Chen, S.,
Choi, D.,
Wang, D.
Advanced Functional Materials,
24:1059-1066
2014-01

Improved cycling behavior of ZEBRA battery operated at intermediate temperature of 175°C

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 ß"-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.
Li, G.,
...
Lu, X.,
Kim, J.,
Lemmon, J.,
Sprenkle, V.
Journal of Power Sources,
249(2014):414-417
2013-12

Nanorod Niobium Oxide as Powerful Catalysts for an All Vanadium Redox Flow Battery

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 mA·cm-2) 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.
Li, B.,
...
Gu, M.,
Nie, Z.,
Wei, X.,
Wang, C.,
Sprenkle, V.,
Wang, W.
Nano Letters
2014(14):158-165
2013-11

Cell Degradation of a Na-NiCl2 (ZEBRA) Battery

Abstract: In this work, the parameters influencing the degradation of a Na-NiCl2 (ZEBRA) battery were investigated. Planar Na-NiCl2 cells using ß"-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.
Li, G.,
...
Lu, X.,
Kim, J.,
Lemmon, J.,
Sprenkle, V.
Journal of Materials Chemistry A,
47(2013):14935 - 14942
2013-10

On-Line Investigation of the Capacity-Decay Mechanism of Micro-porous Separator-Based All-Vanadium Redox Flow Batteries and Its Recovery

Abstract: In this paper, we report the results of our investigation of the capacity decay mechanism of vanadium redox flow batteries with micro-porous separators as membranes. Our investigation focused on the relationship of 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 solutions from one side to the other and thus the asymmetrical valance of vanadium ions due to 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, we found that convection arising from differential hydraulic pressures at both sides of separators plays a dominant role in capacity decay. We developed a capacity stabilizing method, and successfully demonstrated it through the regulation of gas pressures in both electrolyte tanks.
Li, B.,
...
Luo, Q.,
Wei, X.,
Nie, Z.,
Thomsen, E.,
Chen, B.,
Sprenkle, V.,
Wang, W.
ChemSusChem
2014(7):577 - 584
2013-09

Performance Evaluation of Microporous Separator in Fe/V Redox Flow Battery

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 5-50oC 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.
Wei, X.,
...
Luo, Q.,
Li, B.,
Nie, Z.,
Miller, E.,
Chambers, J.,
Sprenkle, V.,
Wang, W.
ECS Transactions
45(26):17-24
2013-09

1 kW/1 kWh advanced vanadium redox flow battery utilizing mixed acid electrolytes

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 oC. At similar electrolyte temperatures, tests with a conventional sulfuric acid electrolyte suffered from precipitation after 80 cycles. By operating stably at elevated temperatures (>40 oC), 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.
Kim, S.,
...
Thomsen, E.,
Xia, G.,
Nie, Z.,
Bao, J.,
Recknagle, K.,
Wang, W.,
Viswanathan, V.,
Luo, Q.,
Wei, X.,
Crawford, A.,
Coffey, G.,
Maupin, G.,
Sprenkle, V.
Journal of Power Sources
237(2013):300-309
2013-08

Simply AlF3-treated Li4Ti5O12 composite anode materials for stable and ultrahigh power lithium-ion batteries

Abstract: The commercial Li4Ti5O12 (LTO) is successfully modified by AlF3 via a low temperature process. After being calcined at 400 oC 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.
Xu, W.,
...
Chen, X.,
Wang, W.,
Choi, D.,
Ding, F.,
Zheng, J.,
Nie, Z.,
Choi, Y.,
Zhang, J.,
Yang, Z.
Journal of Power Sources
236(2013):169-174
2013-07

High performance batteries based on hybrid magnesium and lithium chemistry

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).
Cheng, Y.,
...
Shao, Y.,
Zhang, J.,
Sprenkle, V.,
Liu, J.,
Li, G.
Chem. Commun.,
2014(50):9644-9646
2013-06

A novel low-cost sodium-zinc chloride battery

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.
Lu, X.,
...
Li, G.,
Kim, J.,
Lemmon, J.,
Sprenkle, V.,
Yang, Z.
Energy & Environmental Science
6(6): 1837-1843
2013-06

Composite blend polymer membranes with increased proton selectivity and lifetime for vanadium redox flow batteries

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.
Chen, D.,
...
Kim, S.,
Sprenkle, V.,
Hickner, M.
Journal of Power Sources
231(2013):301-306
2013-05

Elucidating the higher stability of vanadium (V) cations in mixed acid based redox flow battery electrolytes

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.
Vijayakumar, M.,
...
Wang, W.,
Nie, Z.,
Sprenkle, V.,
Hu, J.
Journal of Power Sources
241(2013):173-177
2013-05

Polyvinyl Chloride/Silica Nanoporous Composite Separator for All-Vanadium Redox Flow Battery Applications

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.
Wei, X.,
...
Nie, Z.,
Luo, Q.,
Li, B.,
Sprenkle, V.,
Wang, W.
Journal of the Electrochemical Society
160(8):A1215-A1218
2013-05

Fe/V Redox Flow Battery Electrolyte Investigation and Optimization

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 oC to 50 oC 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.
Li, B.,
...
Li, L.,
Wang, W.,
Nie, Z.,
Chen, B.,
Wei, X.,
Luo, Q.,
Yang, Z.,
Sprenkle, V.
Journal of Power Sources
229(2013):1-5
2013-04

Nanoporous Polytetrafluoroethylene/Silica Composite Separator as a High-Performance All-Vanadium Redox Flow Battery Membrane

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 additon, 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.
Wei, X.,
...
Nie, Z.,
Luo, Q.,
Li, B.,
Chen, B.,
Simmons, K.,
Sprenkle, V.,
Wang, W.
Advanced Energy Materials
3:1215-1220
2013-02

High Energy Density Na-S/NiCl2 Hybrid Battery

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.
Lu, X.,
...
Lemmon, J.,
Kim, J.,
Sprenkle, V.,
Yang, Z.
Journal of Power Sources
224(2013):313-316
2013-02

Bismuth Nanoparticle Decorating Graphite Felt as a High-Performance Electrode for an All-Vanadium Redox Flow Battery

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 mA∙cm−2) 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.
Li, B.,
...
Gu, M.,
Nie, Z.,
Shao, Y.,
Luo, Q.,
Wei, X.,
Li, X.,
Xiao, J.,
Wang, C.,
Sprenkle, V.,
Wang, W.
Nano Letters
13:1330-1335
2013-02

Capacity Decay and Remediation of Nafion-based All-Vanadium Redox Flow Batteries

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.
Luo, Q,.
...
Li, L.,
Wang, W.,
Nie, Z.,
Wei, X.,
Li, B.,
Chen, B.,
Yang, Z.,
Sprenkle, V.
ChemSusChem
6(2):268-274
2013-02

Recent Progress in Redox Flow Battery Research and Development

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.
Wang, W.,
...
Luo, Q.,
Li, B.,
Wei, X.,
Li, L.,
Yang, Z.
Advanced Functional Materials
23(8): 970-986
2013-01

Li-Ion Battery with LiFePO4 Cathode and Li4Ti5O12 Anode for Stationary Energy Storage

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.
Wang, W.,
...
Choi, D.,
Yang, Z.
Metallurgical and Materials Transactions A,
Physical Metallurgy and Materials Science
44A(1 Supplement):21-25
2013-01

Advanced Intermediate-Temperature Na-S Battery

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.
Lu, X.,
...
Kirby, B.,
Xu, W.,
Li, G.,
Kim, J.,
Lemmon, J.,
Sprenkle, V.,
Yang, Z.
Energy & Environmental Science
6(1)(2013):299-306
2012-12

Novel ternary molten salt electrolytes for intermediate-temperature sodium/nickel chloride batteries

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.
Li, G.,
...
Lu, X.,
Coyle, C.,
Kim, J.,
Lemmon, J.,
Sprenkle, V.,
Yang, Z.
Journal of Power Sources
220(2012):193-198
2012-11

In-situ investigation of vanadium ion transport in redox flow battery

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.
Luo, Q.,
...
Li, L.,
Nie, Z.,
Wang, W.,
Wei, X.,
Li, B.,
Chen, B.,
Yang, Z.
Journal of Power Sources
218(2012):15-30
2012-11

Microporous separators for Fe/V redox flow batteries

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 mA∙cm-2 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.
Wei, X.,
...
Li, L.,
Luo, Q.,
Nie, Z.,
Wang, W.,
Li, B.,
Xia, G.,
Millar, E.,
Chambers, J.,
Yang, Z.
Journal of Power Sources
218(2012):39-45
2012-10

A new hybrid redox flow battery with multiple redox couples

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.
Wang, W.,
...
Li, L.,
Nie, Z.,
Chen, B.,
Luo, Q.,
Shao, Y.,
Wei, X.,
Chen, F.,
Xia, G.,
Yang, Z.
Journal of Power Sources
216(2012):99-103
2012-10

The effects of temperature on the electrochemical performance of sodium-nickel chloride batteries

Abstract: The sodium-nickel chloride (ZEBRA) battery is typically operated at relatively high temperatures (≥ 300ºC) 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.
Lu, X.,
...
Li, G.,
Kim, J.,
Lemmon, J.,
Sprenkle, V.,
Yang, Z.
Journal of Power Sources
215(2012):288-295
2012-05

Anthraquinone with Tailored Structure for Nonaqueous Metal-Organic Redox Flow Battery

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.
Wang, W.,
...
Xu, W.,
Cosimbescu, L.,
Choi, D.,
Li, L.,
Yang, Z.
Chemical Communications
48(53):6669-6671
2012-03

Advanced Redox Flow Batteries for Stationary Electrical Energy Storage (PNNL-21174)

Abstract: This report describes the status of advanced redox flow battery research being performed at Pacific Northwest National Laboratory for the U.S. Department of Energy's Energy Storage Systems Program. The FY12, Quarter 1 milestone was completed on time. The milestone entails completing evaluation and optimization of single cell components for the advanced all vanadium (V/V) mixed acid redox flow battery electrolyte chemistries recently developed at the Laboratory. All the single cell components to be used in future kW-scale stacks have been identified and optimized in this quarter, which include solution electrolyte, membrane; carbon felt electrode and bi-polar plate. Varied electrochemical, chemical and physical evaluations were performed to assist the component screening and optimization. The mechanisms of the battery capacity fading behavior for the all (V/V) redox flow were discovered, which allowed us to optimize the related cell operation parameters and continuously operate the system for more than 3 months without any capacity decay.
Li, L.,
...
Kim, S.,
Xia, G.,
Wang, W.,
Z Yang
Pacific Northwest National Laboratory
Richland, WA
2012-02

A New Fe/V Redox Flow Battery Using Sulfuric/Chloric Mixed Acid Supporting Electrolyte

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.
Wang, W.,
...
Nie, Z.,
Chen, B.,
Chen, F.,
Luo, Q.,
Wei, X.,
Xia, G.,
Skyllas-Kazacos, M.,
Li, L.,
Yang, Z.
Advanced Energy Materials
2(4):487-493
2011-06

A New Redox Flow Battery Using Fe/V Redox Couples in Chloride Supporting Electrolyte

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 0oC and 50oC. 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.
Wang, W.,
...
Kim, S.,
Chen, B.,
Nie, Z.,
Zhang, J.,
Xia, G.,
Li, L.,
Yang, Z.
Energy & Environmental Science
4(10):4068-4073
2011-04

Effects of additives on the stability of electrolytes for all-vanadium redox flow batteries

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.
Zhang, J.,
...
Li, L.,
Nie, Z.,
Chen, B.,
Vijayakumar, M.,
Kim, S.,
Wang, W.,
Schwenzer, B.,
Liu, J.,
Yang, Z.
Journal of Applied Electrochemistry
41(10 - Special Issue S1):1215-1221
2011-03

A Stable Vanadium Redox-Flow Battery with High Energy Density for Large-scale Energy Storage

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.
Li, L.,
...
Kim, S.,
Wang, W.,
Vijayakumar, M.,
Nie, Z.,
Chen, B.,
Zhang, J.,
Xia, G.,
Hu, J.,
Graff, G.,
Liu, J.,
Yang, Z.
Advanced Energy Materials
1(3):394-400
2011-03

Electrochemical Energy Storage for Green Grid

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.
Yang, Z.,
...
Zhang, J.,
Kintner-Meyer, M.,
Lu, X.,
Choi, D.,
Lemmon, J.,
Liu, J.
Chemical Reviews
111(5):3577-3613

 

Oak Ridge National Laboratory Journal Articles

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Title XXX

Abstract: Text.
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Last name, initials
Publisher