Optimization for polyethylene glycol/garnet oxide composite electrolyte membrane for solid-state batteries

Abstract

To achieve solid-state batteries with high conductivity, polymer electrolyte membranes blended with inorganic fillers are attracting greater interests. Current work is mainly focused on Li+ migration mechanism for optimized composite electrolyte membrane (CEM). Herein, 6.71 vol% (37.50 wt%) Al-doping Li7La3Zr2O12 dispersed in polyethylene glycol (PEG)-LiClO4 matrix shows the maximal ionic conductivity (∼1.56 × 10−4 S cm−1 at 45 °C) and high cycling reversibility (≥380 cycles). Garnet oxide fillers enlarge the amorphous region and electrochemical stability, and the higher amorphous level of PEG matrix enables a high Li+ dissolution and a rapid Li+ migration. Time-of-flight secondary ion mass spectrometry is employed to locate Li+ migration pathways, and the results indicate that Li+ migration depends on the amorphous phase in the CEM. Therefore, an empirical equation has been proposed to simulate the relationship of mass ratio and volume ratio of fillers. With a close connection between the CEM and two electrodes, a solid-state lithium-metal battery assembled with the NCM111 cathode delivers an average capacity of ∼108 mAh g−1 at C/25 and after 200 cycles.