Cyano-reinforced in-situ polymer electrolyte enabling long-life cycling for high-voltage lithium metal batteries

Solid-state polymer electrolytes (SSPEs) are expected to improve energy density and safety characteristic of lithium metal batteries (LMBs). However, high-voltage LMBs using conventional ethylene oxide (EO)-based SSPEs suffer from poor cyclability, due to the low oxidation decomposition potential of EO segments and highly crystallinity of polymer matrix at ambient temperature. Herein, a cyano-reinforced SSPE is presented by in-situ copolymerization of 2-cyanoethyl acrylate and poly (ethylene glycol) methyl ether acrylate to improve the cyclability of high-voltage LMBs. In such SSPE, -CN with low negative electrostatic potential can preferentially and strongly interact with LiCoO2 during charging process, effectively suppressing the decomposition of EO segments. A -CN-rich and LiF-rich stable cathode electrolyte interphase (CEI) is thus formed, which further improve the compatibility of EO-based SSPE with LiCoO2 cathode. Besides, such in-situ polymerization strategy not only simplifies the preparation process but also effectively inhibits the crystallization of SSPE. As consequence, LiCoO2/Li-based batteries exhibit excellent cyclability with 80.7% capacity retention after 500 cycles at 4.4 V under 60 °C and 93.5% capacity retention after 100 cycles at 4.5 V under ambient temperature. This simple and effective cyano-reinforced design strategy sheds a milestone significance light on the rational design of EO-based SSPEs for high-voltage LMBs.