Study on the Compatibility of Ionic Liquid-Based Electrolytes with Polypropylene Separators

This study aims to optimize the separator-electrolyte system by investigating the compatibility between ionic liquid-based electrolytes and commercial separators, thereby enhancing the performance of lithium metal batteries. Three commercial polypropylene separators (PP25OO, PP3501, and PP2325) are selected and combined with a specific ionic liquid-based electrolyte (tributyl (methoxymethyl) phosphonium hexafluorophosphate. [P₄₄₄₁₀₁] [ PF₆]) to construct different separator-electrolyte systems. The lithium-ion mobility, lithium deposition behavior, and lithium metal battery performance of these systems are systematically analyzed. The results show that tlte PP3501 separator exhibits the best compatibility with the ionic liquid-based electrolyte, achieving a high lithium ion conductivity (0. 103 mS/cm) and uniform lithium deposition on the lithium metal surface. Titis promotes stable cycling of Li|LiFePO₄ batteries under high loading (LiFePO₄ active material loading of 11. 25 mg/cm₂), with an initial discharge specific capacity of 129 mA • h/g at a rate of 0. 5C (where C represents the battery charge/discharge rate). The findings provide theoretical and practical guidance for separator selection when using ionic liquids as electrolytes.