Stable of higher voltage, faster charging, and longer-living lithium-ion

Stable electrolyte solution chemistries are essential for the development of higher voltage, faster charging, and longer-living lithium-ion cells as well as next-generation cell technologies (e.g., sodium-ion and lithium-air).1–4 To avoid electrolyte decomposition, many batteries in use today operate at much lower cell voltages than the capability of the electrode materials, often leaving a significant fraction of the theoretical capacity unused.5–7 In recent years, chemical additives have been used in research and commercially available cells to increase cell stability limits to higher voltages and temperatures, creating industrial and academic interest in further additive development.5,6,8–18 The potential to achieve cutting-edge performance with minimal changes to supply chains for electrolyte salts and solvents has tremendous practical appeal. However, the design of new additives for different applications still poses significant scientific challenges to which the emergence of additive blends in recent years adds further complexity.19–22Whereas the selection of new solution chemistries has traditionally followed a lengthy trial and error method, there is an increasing desire to streamline the process by applying modern calculations. High-throughput computational methods for the discovery of new compounds are by now well-developed, for example in the pharmaceutical field of drug discovery.23–25 Quantum mechanical and molecular mechanics calculations have been suggested to offer similar potential for energy storage technology research, including the development of new electrode materials26–28 and electrolyte solutions29–32 for batteries. Yet before the computational discovery of new electrolyte additives may be realized, there is a need for a greater understanding of how additives function, at a fundamental level, and how multiple additives interact in a cell to affect the measured performance.With these motivations, this work examines an illustrative binary blend, ethylene sulfate (1,3,2-dioxathiolane-2,2-dioxide, DTD) and prop-1-ene-1,3-sultone (PES). Individually, each additive increases coulombic efficiency (CE) and decreases charge end point capacity slippage.14,22,33–37 As a binary blend, the improvements to these metrics are even greater.37 Moreover, both components are part of known ternary blends, denoted PES222 (2% PES, 2% DTD, and 2% tris(trimethylsilyl)phosphite TTSPi) and PES211D (2% PES, 1% DTD, and 1% TTSPi).38 In this work, reaction pathways for the formation of an additive-derived solid-electrolyte interphase (SEI) on the negative electrode were proposed and then evaluated using density functional theory (DFT) and various experimental methods (electrochemistry, volumetric measurements, gas chromatography, X-ray photoelectron spectroscopy, isothermal microcalorimetry).


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