High Cycling Stability for Solid‐State Li Metal Batteries via Regulating Solvation Effect in Poly(Vinylidene Fluoride)‐Based Electrolytes

Abstract Solid polymer electrolytes have emerged as promising alternatives to current liquid electrolytes due to their advantages in battery safety and stability. Among various polymer electrolytes, poly(vinylidene fluoride) (PVDF)‐based electrolytes with high ionic conductivity, large mechanical strength, and excellent electrochemical and thermal stability have a great potential for practical applications. However, fundamental issues, such as how the Li ions transport in the PVDF‐based electrolytes and how the residual solvent affects the cell performance, are unclear. Here, we demonstrate that the solvation effect due to a small amount of residual N,N ‐dimethylformamide (DMF) bound into the electrolytes plays a critical role in ionic transport, interface stability, and cell performance. With the residual DMF existing in the electrolytes in a bound state not as free solvent, the ionic conduction could be realized by the Li‐ion transport among the interaction sites between the bound DMF and PVDF chains. Regulating the solvation effect in the electrolytes can make the PVDF‐based solid‐state Li metal batteries a significantly improved cycling performance at 25 °C (e. g., over 1000 cycles with a capacity retention of more than 94 %). These findings would promote the development of next‐generation Li metal batteries with high energy density and safety.