Co-contribution of quenching and nanocrystallization on ionic-conductivity improvement of a composite electrolyte of polyethylene Oxide/Li7La3Zr2O12 nanofibers at 45 °C for all-solid-state Li metal batteries

Abstract Solid electrolytes have been actively researched for rechargeable lithium batteries, but low ion conductivity (σ) and the growth of lithium dendrites hinder their practical applications. This study synthesizes a composite solid electrolyte combining polyethylene oxide (PEO) with Li7La3Zr2O12 nanofibers (LLZO NFs) and quenching in liquid nitrogen. The LLZO NFs efficiently increase the σ and mechanical strength of composite polymer electrolytes (CPEs), thereby promoting the uniform deposition of lithium metal and inhibiting the growth of lithium dendrites. More importantly, the quenching markedly reduces the crystallinity of the electrolyte, which further enhances the ionic conductivity even at 30 °C. The CPEs exhibit high σ (1.09 × 10−4 S cm−1 at 30 °C) and enlarged electrochemical window (up to 5 V vs. Li/Li+). An integrated all-solid-state lithium metal battery (ASSLMBs) (labeled as LiFePO4|PEO/LLZO NFs/LiTFSI-q|Li) delivers high initial discharge capacity (138.8 mAh g−1) and excellent cycling stability (74.8% at 0.5C after 300 cycles) with remarkable capacity retention (84.0% at 1C after 200 cycles) at 45 °C. This strategy enables the promotion and application of ASSLMBs at room temperature.