Polyimide Separators Navigating Challenges and Opportunities in Next-Generation Lithium Batteries

The development of lithium-ion batteries towards higher energy density and enhanced safety is hindered by the performance limitations of their core component: the separator. The inherent drawbacks of traditional polyolefin separators, namely poor thermal stability (pronounced melting and shrinkage at elevated temperatures) and insufficient electrolyte affinity (leading to high interfacial impedance), represent critical obstacles that must be overcome. Polyimide (PI), renowned for its exceptional thermal resistance, mechanical strength, and chemical stability, emerges as an ideal alternative material. However, transforming dense PI polymers into high-performance porous separators faces three major challenges: (i) achieving precise construction of high porosity and interconnected pore channels while maintaining excellent thermal stability; (ii) balancing high porosity with high mechanical strength and further optimizing the electrochemical interface; and (iii) overcoming the bottlenecks of high cost and scalable manufacturing to meet industrial demands. This review systematically summarizes strategies and progress in addressing these challenges. First, we analyze preparation strategies for porous structures, discussing breakthroughs achieved by nonsolvent-induced phase separation (NIPS), thermally induced phase separation (TIPS), and electrospinning methods and electrospinning methods in constructing fine structures such as nanofiber networks and vertical channels. Subsequently, we focus on performance optimization and functionalization: enhancing mechanical and thermal stability through inorganic compositing and surface armoring; optimizing ion transport and interfacial compatibility via polar modification and wettable coatings; and imparting advanced functionalities like smart responsiveness and catalytic conversion to adapt to emerging battery systems such as lithium-sulfur and lithium-metal batteries. The discussion consistently centers on the transition from laboratory research to industrial application, evaluating the practical potential of various strategies. Finally, we outline future directions, emphasizing the need to bridge the gap from material innovation to commercial application through rational design and engineering innovation, aiming to provide a clear roadmap for developing next-generation, safe, high-performance lithium battery separator solutions.