LiFePO4 as a dual-functional coating for separators in lithium-ion batteries: A new strategy for improving capacity and safety

Lithium-ion batteries (LIBs) require separators with high performance and safety to meet the increasing demands for energy storage applications. Coating electrochemically inert ceramic materials on conventional polyolefin separators can enhance stability but comes at the cost of increased weight and decreased capacity of the battery. Herein, a novel separator coated with lithium iron phosphate (LFP), an active cathode material, is developed via a simple and scalable process. The LFP-coated separator exhibits superior thermal stability, mechanical strength, electrolyte wettability, and ionic conductivity than the conventional polyethylene (PE) separator. Moreover, the LFP coating can actively participate in the electrochemical reaction during the charge-discharge process, thus enhancing the capacity of the battery. The results show that the LFP-coated separator can increase the cell capacity by 26%, and improve the rate capability by 29% at 4 C compared with the conventional PE separator. The LFP-coated separator exhibits only 1.1% thermal shrinkage at 140 °C, a temperature even above the melting point of PE. This work introduces a new strategy for designing separators with dual functions for the next-generation LIBs with improved performance and safety.