Room-Temperature Solid-State Polymer Electrolyte in Li-LiFePO₄ , Li-S and Li-O₂ Batteries

A solid polymer electrolyte has been developed and employed in lithium-metal batteries of relevant interest. The material includes crystalline poly(ethylene glycol)dimethyl ether (PEGDME), LiTFSI and LiNO₃ salts, and a SiO₂ ceramic filler. The electrolyte shows ionic conductivity more than 10^-4  S cm^-1 at room temperature and approaching 10^-3  S cm^-1 at 60 °C, a 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 FTIR spectroscopy suggests that the LiTFSI conducting salt dissolves in the polymer. The electrolyte is used in solid-state cells with various cathodes, including LiFePO₄ olivine 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 a carbon-coated gas diffusion layer (GDL). The cells operate reversibly at room temperature with a capacity of 140 mA h g^-1 at 3.4 V for LiFePO₄ , 400 mA h g^-1 at 2 V for sulfur electrode, and 500 mA h g^-1 at 2.5 V for oxygen. The results suggest that the electrolyte could be applied in room-temperature solid polymer cells.