–C≡N functionalizing polycarbonate-based solid-state polymer electrolyte compatible to high-voltage cathodes

Abstract

Solid-state polymer electrolytes (SPEs) capable of withstanding high voltage are considered to be key for next-generation energy storage devices with inherent safety as well as high energy density. This study involves the rational design of solid-state –C≡N functionalized P(VEC1-CEA0.3)/LiTFSI@CE SPEs and its synthesis by in-situ free radical polymerization of vinyl ethylene carbonate (VEC) and 2-cyanoethyl acrylate (CEA). In situ polymerization yields electrode/electrolyte interfaces with low interfacial resistance, forming a stable SEI layer enriched with LiF, Li3N, and RCOOLi, ensuring stable Li plating/stripping for over 1400 h. The –C≡N moiety renders the αH on the adjacent αC positively charged, thereby endowing it with the capability to anchor TFSI−. Simultaneously, the incorporation of –C≡N moiety diminishes the electron-donating ability of the C=O, C–O–C, and –C≡N functional groups, facilitating not only the ion conductivity enhancement but also a more rapid Li+ migration proved by DFT theoretical calculations and Raman spectroscopy. At room temperature, tLi+ of 0.60 for P(VEC1-CEA0.3)/LiTFSI@CE SPEs is achieved when the ionic conductivity σLi+ is 2.63 × 10−4 S cm−1 and the electrochemical window is expanded to 5.0 V. Both coin cells with high-areal-loading cathodes and the 6.5-mAh pouch cell, exhibit stable charge/discharge cycling. At 25 °C, the 4.45-V Li|P(VEC1-CEA0.3)/LiTFSI@CE|LiCoO2 battery performs stable cycling over 200 cycles at 0.2 C, with a capacity retention of 82.1%.