Large-scale preparation of ultrathin composite polymer electrolytes with excellent mechanical properties and high thermal stability for solid-state lithium-metal batteries

Large-scale preparation of ultrathin flexible solid-state electrolytes with high performance and low cost is critical for the commercialization of solid-state lithium-metal batteries. Herein, through a rational combination of the typical scraping and hot-pressing processes to impregnate polyethylene oxide (PEO)/Li-salt (LiTFSI) electrolyte into porous poly(tetrafluoroethylene) (PTFE) matrix, an ultrathin, highly dense composite polymer electrolyte (PLP-HP) has been successfully achieved. The hot-pressing process at appropriate temperature guarantees the densely impregnating of the PEO/LiTFSI conductive networks, and the enhancement effect of PTFE matrix ensures the excellent mechanical properties and the high thermal stability of the composite electrolyte with a thickness of 14.5 μm or even lower to 6 μm. As a result, the Li//Li symmetrical cell with the 14.5 μm thick electrolyte shows a stable cycling time of more than 900 h at 60°C without growth of Li dendrites and its LiFePO4//Li full cell can stably cycle more than 500 cycles with a superhigh average coulombic efficiency of over 99.9 % at 0.5 C and 60°C. Furthermore, the full cell with the 6 μm thick electrolyte even demonstrates more superior rate performance due to its much shorter Li+ diffusion distance, which enables the battery to operate at 30°C with a reversible capacity of around 135 mAh g−1 at 0.2 C. This study offers a guidance for the large-scale and low-cost preparation of high performance ultrathin composite polymer electrolytes.