Sulfonyl diimidazole to stabilize fluoroethylene carbonate-based SEI in high-voltage Li ion cells with a SiOx containing negative electrode

Abstract

Pairing nickel-rich layered oxide cathodes (e.g., LiNi0.8Mn0.1Co0.1O2 (NMC811)) with silicon-based anodes (e.g., SiOx-graphite) and simultaneously increasing the upper cut-off voltage (> 4.3 V vs. Li|Li+) offers a promising pathway to increase the energy density of LIBs. However, the instability of state-of-the-art electrolytes poses a notable challenge for high-voltage Li ion cells with SiOx-based anodes due to abrupt cell failure. This challenge originates mainly from the restricted lithium transport due to a thick solid electrolyte interphase (SEI), followed by lithium metal plating on the SiOx-Gr anode, which leads to a roll-over failure. In this study, we introduce an additive-based electrolyte designed to facilitate the formation of a stable SEI on SiOx-Gr while protecting the SEI from attack by hydrofluoric acid and PF6−. The electrolyte formulation comprises 1 M lithium hexafluorophosphate (LiPF6) dissolved in ethyl carbonate (EC) and ethyl methyl carbonate (EMC) mixture (3:7 by wt.) with 5 wt.% fluoroethylene carbonate (FEC) and 1.5 wt.% sulfonyl diimidazole show the ability to suppress roll-over behavior and retain a capacity of 92 % at 1C and 20 °C.