The Synergy Between In Situ Gradient Polymerization and Phase Separation Enables Practical Solid-State Ni-Rich...

Solid polymer electrolytes (SPEs) have garnered significant attention due to their exceptional safety property. However, most of the previously reported SPEs cannot well match with high-loading and high-voltage cathodes due to their low ionic conductivity and limited anodic stability. Herein, a SPE with superior compatibility with high-loading Ni-rich cathodes is generated by in situ gradient polymerization of a deep eutectic electrolyte. Besides, a polymerization-induced petaloid phase separation structure enhances interfacial ion transport, resulting in a high room temperature ionic conductivity of 1.5 × 10^-3 S cm^-1. As a result, the as-assembled high-loading (19.5 mg cm^-2) NCM811||graphite full battery exhibites a high capacity retention of 85.3% after 200 cycles and outstanding rate performance (1 C). Industrial 1.2 Ah NCM811||SiO_x pouch cell demonstrates unprecefented energy density of 382 Wh kg^-1. Moreover, this SPE also exhibits significantly enhanced safety characteristics, delaying the onset temperature of heat release from 157 °C to 266 °C and thermal runaway temperature from 198 °C to 312 °C. This study provides a general and practical avenue to high-energy-density lithium-ion batteries.