Tailoring polymer electrolyte for high-voltage solid-state Li metal batteries working at ultra-low temperatures

Abstract Stable operation of batteries at low temperatures is critical for applications in cold-climates; however, low-temperature operations are plagued by low ionic conductivity of electrolytes, slow interfacial kinetics and unstable solid–electrolyte interphases (SEIs). We report a polymer electrolyte with an ionic conductivity of 2.2⋅10− 4 S cm− 1 and an ionic transference number of 0.8 at − 20 °C; the electrolyte is synthesized by in-situ polymerizing 1,3,5-trioxane (TXE), 2-2-2-trifluoro-N, N-dimethylacetamide (FDMA), fluoroethylene carbonate (FEC) and lithium difluoro(oxalate)borate (LiDFOB). The polymer electrolyte enables a dual-layered SEI on the Li metal anode and strongly stabilizes the LiNi0.8Co0.1Mn0.1O2 cathode, thus defining fast interfacial charge-transfer at low temperatures. Consequently, the galvanic Li corrosion and the dendritic growth are suppressed, stable Li metal anode and LiNi0.8Co0.1Mn0.1O2 cathode are achieved, and the operation temperatures of polymer-based batteries are decreased to below − 30°C. From − 30°C to room temperature, the Li||LiNi0.8Co0.1Mn0.1O2 battery achieves long cycle lifetime and high capabilities. Even at − 20°C, the Li||LiNi0.8Co0.1Mn0.1O2 battery realizes > 75% (~ 151 mAh g− 1) of its room-temperature capacity, and presents stable cycling over 200 cycles. Outstandingly, the Li||LiNi0.8Co0.1Mn0.1O2 pouch cell successfully powers an electric fan at − 58.3°C.