Trifluoromethyl-free anion for highly stable lithium metal polymer batteries

Abstract With the blooming of energy storage systems in e-mobility applications, the research activities of rechargeable lithium metal (Li°) batteries (LMBs) using solid-state electrolytes have been rekindled in recent years in light of stringent demands in terms of safety and energy density which are far beyond the capability of the contemporary lithium-ion batteries (LIBs). Lithium metal polymer (LMP) batteries utilizing solid polymer electrolytes (SPEs) are inherently safe and easy to process, thus becoming in the spotlights of solid-state lithium metal batteries (SSLMBs) technologies. However, the widely used electrolyte salts generally contain the trifluoromethyl (—CF3) group which has very low chemical and biochemical degradability, despite its strong electron-withdrawing ability which is essential for the dissolution and transport of ions in SPEs. In this work, a trifluoromethyl-free anion, bis(difluoromethanesulfonyl)imide {[N(SO2CF2H)2]−, DFSI−}, as an environmentally benign and interfacially favourable anion for high-performance SSLMB is reported. In contrast to the popular bis(trifluoromethanesulfonyl)imide anion {[N(SO2CF3)2]−, TFSI−}, the DFSI-based salt shows more rapid chemical degradation and its SPEs possess higher Li-only conductivity, significantly enhanced stability against Li° electrode, and better cell performance of LMP batteries. The results conveyed in this work may inspire the design of better SPEs, thus enabling a wider practical deployment of SSLMBs.