Unraveling the Role of Residual Solvent in PVDF-Based Solid-State Electrolytes: Balance between Ionic Conductivity and Electrochemical Stability

Residual solvents play a critical role for PVDF-based solid-state electrolytes. However, the quantitative effect is not yet well understood. This work elucidates the dual-edged role of residual solvents in PVDF-based solid electrolytes, specifically their influence on ionic conductivity and electrochemical stability. PVDF-based electrolytes with different levels of <i>N</i>-methyl-2-pyrrolidone, <i>N</i>,<i>N</i>-dimethylformamide, and dimethyl sulfoxide were fabricated. The results show that a high content of residual solvent increases ionic conductivity and the Li⁺ transference number. However, it simultaneously induces severe interfacial side reactions with lithium metal, as well as shuttle effects in Li-Sulfur cells. Conversely, an excessively low content yields insufficient ionic conductivity for practical battery performance. Thus, the balance between ionic conductivity and electrochemical stability by modulating the residual solvent is demonstrated. Notably, introducing inorganic fillers Li_1.3Al_0.3Ti_1.7(PO₄)₃ into electrolyte effectively mitigates the intrinsic trade-off caused by residual solvents. This work offers practical strategies for improving the performance of solid-state batteries.