Safer Lithium-Ion Batteries from the Separator Aspect: Development and Future Perspectives

With the rapid development of lithium-ion batteries (LIBs), safety problems are the great obstacles that restrict large-scale applications of LIBs, especially for the high-energy-density electric vehicle industry. Developing component materials (e.g., cathode, anode, electrolyte, and separator) with high thermal stability and intrinsic safety is the ultimate solution to improve the safety of LIBs. Separators are crucial components that do not directly participate in electrochemical reactions during charging/discharging processes, but play a vital role in determining the electrochemical performance and safety of LIBs. In this review, the recent advances on traditional separators modified with ceramic materials and multifunctional separators ranging from the prevention of the thermal runaway to the flame retardant are summarized. The component-structure-performance relationship of separators and their effect on the comprehensive performance of LIBs are discussed in detail. Furthermore, the research challenges and future directions toward the advancement in separators for high-safety LIBs are also proposed.