Enhanced Dendrite Resistance and Thermal Stability with Ultra-thin SiO2 Separators for Li-Metal Batteries
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Mechanical and thermal failures in polyolefin separators can lead to internal short circuits and rapid heat generation, causing thermal runaway in batteries. A method was developed to enhance polypropylene separators (PPS) with a thin, uniform SiO2 layer. This involved coating with PVDF containing double bonds, grafting with specific methacrylates, and applying SiO2 nanoparticles via immersion or casting. These modifications improved the separator's pore structure, electrolyte affinity, thermal stability, and mechanical properties. The casting method for SiO2 nanoparticles showed better capacity retention and lower impedance than unmodified PPS cells and outperformed the immersion method in long-term cycling stability. Post-cycling analysis indicated smooth lithium plating in cells modified by casting, likely due to a high lithium-ion transference number. This work provides a robust technique for developing advanced separators and underscores their importance in battery performance.