Understanding Electrochemical Stability and Lithium Ion-Dominant Transport in Concentrated Poly(ethylene carbonate) Electrolyte

Ion-conductive solid polymer electrolytes (SPEs) are important materials for implementing safer energy storage. In the present study we show that a concentrated SPE composed of poly (ethylene carbonate) (PEC) and lithium bis(fluorosulfonyl)imide (LiFSI) has high oxidation tolerance and prevents aluminum corrosion. These properties enable cycling of a LiMn2O4, cell charged above 4 V. Battery operation above 4 V is difficult for conventional polyether electrolytes because of their poor electrochemical stability. Mechanistic studies imply that an aggregated solvation structure, in which a large portion of the carbonyl groups interact with Li ions, is correlated with the enhanced electrochemical stability. The studies suggest that relatively rigid structure of PEC induces an increase in conductivity with increasing salt concentration. The increase in conductivity enables concentrated electrolyte with reasonable conductivity and high Li transference number. The present study reveals the clear potential of concentrated SPEs based on unexplored polymers having relatively high glass transition temperature for use in high-voltage Li batteries.