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

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.