Room Temperature Solid‐State Polymer Electrolyte in Li‐LiFePO4, Li‐S and Li‐O2 batteries

A solid polymer electrolyte is developed and employed in lithium-metal batteries of relevant interest. The material employes crystalline polyethylene glycol dimethyl ether (PEGDME), LiTFSI and LiNO3 salts, and SiO2 ceramic filler. The electrolyte shows ionic conductivity over than 10-4 S cm-1 at room temperature and approaching 10-3 S cm-1 at 60 °C, Li+ transference number exceeding 0.3, electrochemical stability from 0 to 4.4 V vs. Li+/Li, lithium stripping/deposition overvoltage below 0.08 V, and electrode/electrolyte interphase resistance of 400 Ω. Thermogravimetry indicates that the electrolyte stands up to 200 °C without significant weight loss, while FT-IR spectroscopy suggests the dissolution of the LiTFSI conducting salt in the polymer. The electrolyte is used in solid state cells with various cathodes, including olivine LiFePO4 exploiting the Li-insertion, sulfur-carbon composite operating through Li-conversion, and an oxygen electrode in which reduction and evolution reactions (i.e., ORR/OER) evolve on carbon-coated gas diffusion layer (GDL). The cells reversibly operate at the room temperature with a capacity of 140 mAh g-1 at 3.4 V for LiFePO4, 400 mAh g-1 at 2 V for sulfur electrode, and 500 mAh g-1 at 2.5 V for oxygen. The results suggest the electrolyte for application in room-temperature solid polymer cells.