In situ formation of polymer electrolytes using a phosphazene cross-linker for high-performance lithium-ion batteries

Polymer electrolytes (PEs) have been intensively studied in lithium-ion batteries and the studies have recently focused on improving their electrochemical performances. In this study, an in situ thermal curing method is proposed to prepare polyethylene glycol-based electrolytes using a cyclic phosphazene cross-linker directly onto the lithium anode, endowing the preparation of PEs with improved ion transport across the interfaces and better electrochemical performances than those using free-standing polymer electrolytes. The buildup of the cross-linked electrolyte network by incorporating the phosphazene cross-linker endows the as-prepared PEs exhibiting excellent deformation and thermal stability, a wide electrochemical window, high ionic conductivity (3.07 × 10⁻³ S cm⁻¹) at room temperature. The in situ-formed, cross-linked electrolyte network with good elasticity and conformal attachment at the electrolyte/electrode interface achieves a high capacity (>160 mAh g⁻¹ at 0.1C rate) and a long cycle life at room temperature (0.2C rate, 93.8% at 250 cycles) in the equipped Li|LiFePO₄ cell, making this strategy a promising approach for developing the next-generation lithium-ion batteries.