Design of Polymer-in-Salt Electrolyte for Solid State Lithium Battery with Wide Working Temperature Range

The application of solid polymer electrolytes (SPEs) is a versatile strategy to increase the energy density of solid-state batteries as well as their safety. Poly(ethylene oxide) (PEO) is an appealing matrix for SPEs due to its superior lithium salt dissolution ability. However, while such PEO-based SPEs generally exhibit dramatic ionic conductivity at high temperatures (~60 °C), the ionic conductivity at room temperature (~30 °C) is not satisfactory, which severely hinders the application of SPEs at room temperature. In this work, a Polymer-In-Salt Solid Electrolyte (PISSE) with a three-dimensional frame structure was designed and fabricated with PVDF membrane as the frame and polymer-in-salt (PEO-in-Bis(trifluoromethane) sulfonimide lithium salt (LiTFSI)) as a filler (PPIS). PPIS exhibits high ionic conductivity of 4.5 × 10 -5 S m -1 and a superior lithium transference number of 0.54 at room temperature with a wide electrochemical window beyond 5.5 V. Meanwhile, it exhibits excellent mechanical property and interfacial stability, which effectively suppresses the growth of lithium dendrite even after cycling for 1000 h. The assembled LiFePO 4 /PPIS/Li solid-state battery exhibits the excellent cycling performance of 154 mAh g -1 with capacity retention of 98.8% at 0.2 C after 100 cycles at high temperature (60 °C). Especially, LiFePO 4 /PPIS/Li solid-state battery offers outstanding cycling performance of 130 mAh g -1 with capacity retention of 91.3% at 0.2 C after 100 cycles at room temperature (30 °C). In addition, LFP/PPIS/Li solid-state pouch cell displays significant safety and functional flexibility even under harsh conditions such as folding, burning, and cutting. This work provides a promising strategy for achieving lithium metal solid-state batteries with high energy density, exceptional thermal stability, and a wide working temperature range