A highly salt concentrated ethylene carbonate-based self-standing copolymer electrolyte for solid-state lithium metal batteries

Abstract

CO₂-derived aliphatic polycarbonate-based solid polymer electrolytes (SPEs) with high Li salt concentrations promise notable electrochemical properties for solid-state lithium metal batteries (SSLMBs). However, adequate mechanical properties of these electrolytes for long-cycle-life batteries have rarely been obtained. In this work, we achieved long cycling of SSLMBs utilizing an electrolyte based on CO₂-derived crosslinked random poly(ethylene carbonate-co-ethylene oxide-co-allyl glycidyl ether) (CP). The CP with as high as 29% crosslinking unit ratio (CP₂₉) dissolving a high concentration of LiFSI can be obtained as a mechanically stable self-standing membrane and functions as an efficient electrolyte with a reasonable ionic conductivity. Remarkably, a Li//LiFePO₄ SSLMB with the electrolyte as the self-standing separator enabled rechargeable operation for 400 cycles at 40 °C, with a coulombic efficiency of more than 99.5%. This work will pave the way to realize long-cycle-life SSLMBs with highly concentrated crosslinked polymer electrolytes in the future.