Basic Research Needs for Electrical Energy Storage: Report of the ...

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like wearable ECs that can be incorporated into virtually any device to provide power for portable electronics and other applications. References 1. K. Yuyama, G. Masuda, H. Yoshida, and T. Sato, “Ionic liquids containing the tetrafluoroborate anion have the best performance and stability for electric double layer capacitor applications,” Journal of Power Sources 162, 1401 (2006). 2. N. Nanbu, T. Ebina, H. Uno, S. Ishizawa, and Y. Sasaki, “Physical and electrochemical properties of quaternary ammonium bis(oxalato)borates and their application to electric double layer capacitors,” Electrochimica Acta 52, 1763 (2006). 3. A. Balducci, R. Dugas, P. L. Taberna, P. Simon, D. Plée, M. Mastragostino, and S. Passerini, “High temperature carbon-carbon supercapacitor using ionic liquid as electrolyte,” J. Power Sources 165, 922 (2007). 4. B. E. Conway, Electrochemical Supercapacitors: Scientific Fundamentals and Technological Applications, Kluwer Academic/Plenum Publishers, New York, 1999. 5. J. Chmiola, G. Yushin, Y. Gogotsi, C. Portet, P. Simon, and P. L. Taberna. “Anomalous increase in carbon capacitance at pore sizes less than 1 nanometer,” Science 313, 1760 (2006). 6. M. Herstedt, W. A. Henderson, M. Smirnov, L. Ducasse, L. Servant, D. Talaga, and J. C. Lassègues, “Conformational isomerism and phase transitions in tetraethylammonium bis(trifluoromethanesulfonyl) imide Et4NTFSI,” Journal of Molecular Structure 783, 145 (2006). 7. S. Baldelli, “Probing electric fields at the ionic liquid-electrode interface using sum frequency generation spectroscopy and electrochemistry,” Journal of Physical Chemistry 109, 13049 (2005). 46
MULTIFUNCTIONAL MATERIALS FOR PSEUDOCAPACITORS AND HYBRID DEVICES Pseudocapacitors exhibit characteristics of both electrochemical double layer capacitors (EDLCs) and batteries. They thus offer the potential to address critical performance gaps that exist between those two classes of energy storage devices. Materials that exhibit pseudocapacitance range from conducting and redox polymers to a variety of transition metal oxides. To further advance this broad class of energy storage materials, future fundamental research should focus on the design and discovery of new materials and architectures. In particular, composite architectures comprising multiple components (e.g., combinations of polymers, oxides, and/or carbon) will be required to achieve optimized energy and power density. A fundamental understanding of interfacial phenomena, including charge storage processes, will also be critical to achieve stability and high performance for pseudocapacitor materials. Background and Motivation The term “pseudocapacitance” broadly describes rapid and reversible Faradaic reactions whose discharge profiles mimic those of EDLCs. 1, 2 The classes of materials being investigated for their promising pseudocapacitance include transition metal oxides, conductive nitrides, and conducting polymers. Because pseudocapacitive mechanisms involve electron-transfer reactions and may include both bulk and interfacial processes, materials that exhibit pseudocapacitance often provide higher energy densities than materials that store charge via double layer capacitance (e.g., high-surface-area carbons). Thus, devices that incorporate pseudocapacitance charge storage functionality will bridge the performance gap that currently exists between batteries and EDLCs in terms of achieving both high energy and high power density. 3 In addition, materials that exhibit pseudocapacitance may be combined with traditional chemical energy storage (battery) or EDLC materials to produce hybrid asymmetric devices that further expand the possible energy/power performance range beyond any metrics that are achievable today. Electrical energy storage (EES) devices based on pseudocapacitance may ultimately replace conventional systems that require discrete battery and capacitor components to address the usually divergent requirements for power vs. energy density. Science Questions and Opportunities Hydrous forms of ruthenium dioxide (RuO2) currently represent the state of the art in pseudocapacitor materials exhibiting specific capacitances in excess of 700 F/g –1 (Ref. 4). However, the high cost of ruthenium (a platinum group metal) is prohibitive for any largescale application to EES. Thus, alternative materials are presently being explored, including lower-cost transition metal oxides (e.g., MnO2 and MnFe2O4) as well as a broad class of conducting and redox polymers. However, simply exploring possible new materials without understanding the fundamental issues that result in optimum performance will not result in the technology breakthroughs that are needed for future EES devices. Although the redoxbased charge storage mechanisms of pseudocapacitor materials are related to those of conventional battery materials, the pseudocapacitance phenomenon is not well understood. Because pseudocapacitance is exhibited by a broad class of materials, the operational mechanisms of particular materials, often based on highly complex and specific redox reactions, cannot be generalized to new pseudocapacitor materials as they are discovered. 47
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On the cover: The cover depicts the
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CONTENTS iii Page Figures..........
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14. Calculated and scaled Raman spe
Page 10 and 11: SEI solid electrolyte interphase Sh
Page 12 and 13: transportation and electricity dist
Page 14 and 15: time, during charge transport and t
Page 17 and 18: INTRODUCTION A modern economy depen
Page 19: developments have stimulated interd
Page 23 and 24: CHEMICAL ENERGY STORAGE Abstract Ba
Page 25 and 26: What Is a Battery? A battery contai
Page 27 and 28: Further, an understanding is needed
Page 29 and 30: computation and analysis will be ne
Page 31 and 32: charge-discharge cycles each can un
Page 33 and 34: dimensional architectures. By desig
Page 35: systems that offer high conductivit
Page 39 and 40: NOVEL DESIGNS AND STRATEGIES FOR CH
Page 41 and 42: nanostructured, high-surface-area e
Page 43 and 44: and electronic conductors. For exam
Page 45 and 46: SOLID-ELECTROLYTE INTERFACES AND IN
Page 47 and 48: Research Directions Strategies for
Page 49 and 50: Many opportunities exist for design
Page 51 and 52: CAPACITIVE ENERGY STORAGE MATERIALS
Page 53 and 54: understood at present, nor are the
Page 55 and 56: ELECTROLYTE INTERACTIONS IN CAPACIT
Page 57 and 58: Figure 12. Ions in the ionic liquid
Page 59: species dynamically at the interfac
Page 63 and 64: the functionalities described. New
Page 65 and 66: conductive architectures. 7 Templat
Page 67 and 68: RATIONAL MATERIALS DESIGN THROUGH T
Page 69 and 70: Figure 16. (Left) Sketch of a singl
Page 71 and 72: changes in performance through the
Page 73 and 74: is often more relevant for the prac
Page 75 and 76: validated against quantum-mechanica
Page 77: References 1. M. Bervas et al., “
Page 81 and 82: CROSS-CUTTING SCIENCE FOR ELECTRICA
Page 83 and 84: with theory, modeling, and simulati
Page 85 and 86: path for the preparation of metal o
Page 87 and 88: studying double layer capacity and
Page 89 and 90: An even more demanding goal is to u
Page 91: CONCLUSION
Page 94 and 95: This Report outlines substantial te
Page 96 and 97: demanding goal for theory is the de
Page 101: TECHNOLOGY AND APPLIED R&D NEEDS FO
Page 105: Electrical Energy Storage Factual D
Page 109 and 110: 2.1 TRANSPORTATION Electrical Energ
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designed with electronically contro
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Electric Energy per cycle in Wh Fig
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Capacitor range and self-discharge.
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Figure 4 shows the effects of and o
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The following applications are ways
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oversized, and load fluctuations⎯
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atteries with higher discharge rate
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3. RECHARGEABLE BATTERIES FOR ENERG
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Such failure mechanisms can be held
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The open circuit voltage (OCV) and
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Figure 10. Charge and overcharge pr
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3.4 HIGH-TEMPERATURE SODIUM BETA BA
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Batteries for Load Leveling Beta ba
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that protects from further reaction
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LiFePO4 (olivine) have been used as
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In similar metal-water batteries, t
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Lithium-air Batteries There have be
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Fig. 13. A stack of four redox flow
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the redox flow cells can be dispatc
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laboratory studies and observations
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46 Fig. 14. Equivalent circuit diag
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densities, and excellent cycle life
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system operating voltage is relativ
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52 Fig. 17. Cutaway drawing of a bi
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54 Fig. 19. Commercial large-format
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typically in 1 minute or less, whic
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58 removing impurities from the car
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PROBING ELECTRICAL ENERGY STORAGE C
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electrolytes, as demonstrated for 1
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Figure B.2. Imaging lithium in a bl
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Since most chemical reactions invol
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Workshop on Basic Research Needs El
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Breakout Sessions—Chemical Storag
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John Ferraris, University of Texas
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DISCLAIMER This report was prepared
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