Solid polymer electrolytes with fragment-separated microphase for advanced Li ion transport and highly stable lithium metal batteries

Solid polymer electrolytes (SPEs) with high ionic conductivity and good interfacial compatibility are one of the main factors constraining the performance of lithium metal batteries. However, the most common PEO (Polyethylene oxide)-based SPEs always lack of considerable relaxation of PEO segments, and therefore fail to apply into practical situations. Herein a novel method to prepare fragment-separated epoxy polymer electrolytes (FSEEs) characterized with fragment-separated microphase patterns via a rigid-and flexible monomers cross-link reaction is presented to enhance the overall SPE performance. The fragment-separated microphase can separate the PEO chains in framework and improve the relaxation of PEO chains, optimize the Li+ transport, where the ionic conductivity can be up to 0.56 mS cm−1 at 25 °C. The fragment-separated Li+ transport mechanism in FSEEs also provide better interfacial compatibility than that of PEO due to the even Li+ distribution at interface. The utilization of FSEE-S in Li/Li symmetric cells demonstrated a stable voltage plateau after cycling for 2000 h. Additionally, Li/LFP batteries exhibit favorable 0.5 C performance under 45 °C, lasting over 600 h and exceeding 150 cycles. This study offers a promising approach to SPE design, which may catalyze further exploration of the role of microphase in SPE performance.