Zwitterionic Polyurethane-Based Solid Polymer Electrolytes for High-Performance Solid-State Lithium Metal Batteries

Polyurethanes (PUs) have emerged as promising candidates for next-generation solid polymer electrolytes (SPEs) due to their tunable structures and excellent mechanical properties. However, their application in solid-state lithium metal batteries (SSLMBs) is hindered by insufficient ion conduction and cycling stability. Herein, we introduce a functional zwitterionic extender between hard segments in the PU chain structure, which effectively immobilizes TFSI-anions while suppresses polymer crystallization, thereby notably promoting the Li+ transport. Diverse spectroscopic techniques combined with density functional theory (DFT) calculations confirm the crucial role of the zwitterionic group in achieving overall improvement of SPEs. The engineered zwitterionic PU SPE exhibits an ionic conductivity of 1.60 & times; 10-4 S cm-1 and a high Li+ transference number of 0.65 at 60 degrees C, alongside robust mechanical strength and thermal stability. The lithium metal symmetric cell demonstrates ultralong cycling stability for 4000 h, and the Li||LFP full cell achieves a high specific capacity of 166.5 mAh g-1 with 93.1% capacity retention after 250 cycles. This work highlights the potential of zwitterionic modification for developing advanced PU-based SPEs with improved conductivity, mechanical strength, and interfacial stability for high-energy-density SSLMBs.