ZHANG Lei, FU Dingmi, WU Ying, ZHANG Shangshang, ZHU Gaowen, CHEN Shou, WANG Yingying
With the rapid growth of energy storage systems, electric vehicles, and portable electronic devices, the safety of lithium-ion batteries has become a critical concern. As the core functional layer between the cathode and anode, the separator directly determines the lifespan, safety boundary, and reliability of the battery. Although polyolefin-based separators remain dominant due to mature processing and cost advantages, their limitations in thermal stability, mechanical strength, wettability, and chemical compatibility hinder their application under high-energy-density and complex working conditions. The main types and performance requirements of separators were reviewed, and their failure mechanisms were categorized into five modes: thermal failure, mechanical failure, electrochemical failure, functional degradation, and multi-physics coupling. In terms of analysis, a multidimensional characterization framework-covering morphology, thermal, mechanical, electrochemical, and compositional aspects was proposed, and experimental cases were used to reveal the intrinsic correlation between separator degradation and battery safety attenuation. To mitigate failure risks, modification strategies such as ceramic coating, nanofiber reinforcement, functional interfacial layers, and flame-retardant additives were highlighted. It is further emphasized that separator research is evolving from single modifications toward multifunctional synergistic optimization, requiring thin, mechanically robust, thermally stable separators with additional properties such as flame retardancy, self-healing, and intelligent sensing. Finally, perspectives on multi-physics modeling, advanced in-situ characterization, and intelligent separator development are presented to provide guidance for next-generation high-safety, high-performance batteries.
