Stabilization of Silicon Anode By Advanced Localized High Concentration Electrolytes

Abstract

The rapid market penetration of EVs requires batteries with higher energy densities. However, graphite-based lithium-ion batteries (LIBs) has eventually reached their practical limit and an anode with higher specific capacities is required to further improve energy density of LIBs. In this regard, silicon (Si) anode has been pursued as one of the most promising anodes because it exhibits a capacity ten times as high as those of graphite. However, fast capacity fade during cycling and calendar aging limits the practical application of Si-based anodes due to its severe volume changes and continuous side reactions with electrolyte. Therefore, development of electrolytes that are stable with an electrode with large volume expansion is critical to stabilize the Si anode and enable the full potential of the Si based LIBs. In the case of graphite, a stable solid electrolyte interphase (SEI) can be formed on graphite surface because it does not experience large volume change (< 10%), so the SEI can prevent further reactions between graphite and electrolyte once it is formed. In contrast, the SEI layer formed on Si anode must be mechanically strong and withhold large volume changes (>300%). This work reports the design and performance of advanced localized high concentration electrolytes (LHCEs) for Si anode, in which robust SEI forms on the surface of Si anode and protects the Si anode from the pulverization caused by the large volume changes. As a result, the overall performance of the Si based LIBs are greatly improved by using the optimized LHCEs. The electrolytes have been tailored for different applications, including high voltage (4.45 V), high temperature (45°C) and high rate (> 2C) applications. The fundamental understandings of LHCEs and corresponding SEIs developed in this work can guide the design of new electrolytes for other anodes with large volume expansion.