Robust Self-Composite Polyimide Separators for Long-Life Lithium-Ion Batteries

Electrospun polyimide (PI) nanofiber separators hold promise for high-performance lithium-ion batteries due to their exceptional thermal stability and affinity for electrolytes. However, their practical application is limited by inadequate mechanical integrity and large, nonuniform pores that fail to suppress lithium dendrite growth. To address these challenges, we developed a "self-composite" strategy that integrates electrospinning with non-solvent-induced phase separation (NIPS). This method produces a hierarchical self-composite polyimide (SCPI) separator, featuring a robust electrospun PI nanofiber scaffold infilled with and bonded by a NIPS-derived PI matrix. The resulting monolithic composite exhibits a 230% increase in tensile strength over a pristine electrospun membrane and a significant decrease in average pore size from the micrometer scale (∼1-5 μm) down to 200-500 nm. This uniform nanoporous structure and superior wettability effectively homogenize lithium-ion flux, enabling dendrite-free lithium plating/stripping even at a high current density of 5 mA/cm². Consequently, Li/LFP pouch cells with SCPI separators achieve outstanding long-term stability, retaining 98.75% of their initial capacity after 800 cycles at 1 C with a Coulombic efficiency exceeding 99.99%. This scalable approach offers an effective pathway to engineer advanced membrane structures for safe, high-performance, next-generation lithium batteries.