Achieving Stable Solid-State Polymer Lithium Metal Batteries by Weakening Li ⁺ –Polymer Coordination

Solution casting is one of the most traditional methods for preparing poly(ethylene oxide) (PEO)-based solid-state electrolytes. However, commonly used solvents such as acetonitrile and N,N-dimethylformamide are toxic, and there are often residual solvent molecules within the solid-state electrolytes, causing severe side reactions with Li metal anode. In this work, a safe and green mixed solvent of ethanol and water was proposed to prepare PEO-based solid-state electrolyte. The solvent molecules form hydrogen bonds with PEO, thus leading to weak Li+–polymer coordination and enabling “weak solvation” of Li+ in the solid-state electrolyte. Therefore, the solid-state electrolyte displays fast Li+ transport kinetics, and promotes the formation of a thin and uniform solid electrolyte interface layer on the Li metal anode. As a result, the Li||Li symmetric cells can stably cycle for over 3000 h. Moreover, the Li||LiFePO4 (LFP) batteries show improved rate capability and cycling stability. This work presents a low-cost and environmentally friendly strategy for solid polymer lithium metal batteries.