High-Voltage Resistance of PCL/PEO Blending Polymer-Based Solid Electrolyte for High-Temperature Lithium Metal Batteries

Polyethylene oxide (PEO) is regarded as the most promising candidate for the next generation solid polymer lithium metal batteries (LMBs). However, it suffers from low mechanical strength and limited electrochemical stability window (ESW), which restricts its application in high energy density LMBs. In this work, polycaprolactone (PCL) is chosen as the main matrix to fabricate a blending polymer-based electrolyte with PEO, which shows an improved electrochemical performance with a high lithium ion transference number of 0.65. The improvement can be attributed to the competition between ester and ether groups of different polymer chains, which can both interact with lithium ions to release more free cations. Moreover, the high-voltage resistance of PCL can broaden the electrochemical stability window to 4.8 V of PCL/PEO solid electrolyte to match LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (NCM811) cathode, and its high-temperature resistance ensure a satisfying dimensional stability for the assembled NCM811||Li cell to operate at 55 ℃, with a high initial specific capacity of 210 mAh/g and a retention of 95% within 100 cycles. This work provides a practical solution for the commercialization of high-voltage, high safety and high energy density solid lithium metal batteries for high temperature.