Nanosilica-filled flame-retardant copolyester electrospun composite separators for high-performance safe lithium-ion batteries

The essential role of separators in battery safety and electrochemical performance makes it necessary to create advanced separators for next-generation energy storage systems. However, conventionally commercial polyolefin separators often have problems with poor thermal stability and insufficient electrolyte wettability, resulting in restricted battery performance and serious safety issues of lithium-ion batteries. Herein, we report a separator composed of silica (SiO 2 ) nanoparticles and intrinsically flame-retardant copolyester P(ET- co -PN) 5 electrospun nanofibers, i.e. SiO 2 @P(ET- co -PN) 5 (SP) separator. The copolyester nanofiber's three-dimensional skeleton filled with close-packed SiO 2 nanoparticles endows the separator with good mechanical performance (tensile strength of 9.8 MPa) and electrolyte wettability (electrolyte uptake of 333 %), superior heatproof and fireproof properties (no shrinkage at 250 °C, PHRR of 111.6 W/g, and THR of 9.4 kJ/g). The LiFePO 4 /SP/Li cells exhibit high capacity of 150.2 mAh/g, high average Coulombic efficiency of nearly 100 %, and impressive capacity retention close to 100 % after 220 cycles at 0.5 C. Notably, the LiFePO 4 /SP/Li cells can endure 1000 cycles at 5 C with 53 % of capacity retention and approximately 100 % of Coulombic efficiency. Moreover, it delivers an initial capacity of 148 mAh/g and retains 123.2 mAh/g over 45 cycles at 120 °C.