Dual-salt poly(tetrahydrofuran) electrolyte enables quasi-solid-state lithium metal batteries to operate at −30 °C

The stable operation of solid-state lithium metal batteries at low temperatures is plagued by severe restrictions from inferior electrolyte-electrode interface compatibility and increased energy barrier for Li+ migration. Herein, we prepare a dual-salt poly(tetrahydrofuran)-based electrolyte consisting of lithium hexafluorophosphate and lithium difluoro(oxalato)borate (LiDFOB). The Li-salt anions (DFOB−) not only accelerate the ring-opening polymerization of tetrahydrofuran, but also promote the formation of highly ion-conductive and sustainable interphases on Li metal anodes without sacrificing the Li+ conductivity of electrolytes, which is favorable for Li+ transport kinetics at low temperatures. Applications of this polymer electrolyte in Li||LiFePO4 cells show 82.3% capacity retention over 1000 cycles at 30 °C and endow stable discharge capacity at −30 °C. Remarkably, the Li||LiFePO4 cells retain 52% of their room-temperature capacity at −20 °C and 0.1 C. This rational design of dual-salt polymer-based electrolytes may provide a new perspective for the stable operation of quasi-solid-state batteries at low temperatures.