A 4 V Cathode Compatible, Superionic Conductive Solid Polymer Electrolyte for Solid Lithium Metal Batteries with Long Cycle Life

A highly conductive and electrochemically stable dual-salt solid polymer electrolyte (SPE) for a high-capacity cathode was developed. A phase-diagram approach was adopted to provide rational guidance for achieving a high ionic conductivity (over 1.76 mS/cm at 30 °C). The synergy of combining different salts rendered superior electrochemical stability to the SPE with an electrochemical window from 0 to 5 V (vs Li+/Li) in linear sweep voltammetry and up to 4.15 V in lithium metal batteries (LMBs). The SPE exhibited outstanding long-term stability performance in lithium plating/stripping experiments under current densities from 0.08 to 0.5 mA/cm2. The solid-state lithium metal batteries (with an LiNi0.8Co0.15Al0.05O2, NCA, cathode) exhibited initial capacities of 165 mAh/g at a rate of 0.1 C and 113 mAh/g at a rate of 1 C at 30 °C. The average Coulombic efficiency of solid-state batteries was over 99.99% in the first 1000 cycles at a rate of 1 C, and the capacity retention was 66% after 1000 cycles. In addition, the per cycle capacity fading after the initial 100 cycles was only 0.017%/cycle. The results demonstrate that the SPE is a promising candidate electrolyte for a high-energy-density solid-state lithium metal battery.