High performance polyimide-based separator for 4.5V high voltage LiCoO2 battery with superior safety

Polyolefin separator has poor thermal stability which leads to short circuit and thermal runaway of lithium ion batteries(LIBs) about 100 °C. Here, we used polyimide (PI) as the core material and poly(vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP) as the shell material to prepare PI/PVDF-HFP composite separator by coaxial electrospinning. Compared with Celgard 2400, the PI/PVDF-HFP separator not only demonstrates negligible thermal shrinkage at 200 °C and excellent flame retardancy, but also shows higher porosity and electrolyte uptakes as well as superior wettability, which are conducive to reduced interfacial impedance and improved ion conductivity. The 4.5 V high-voltage LiCoO2/Li cell with PI/PVDF-HFP separator exhibits an initial discharge specific capacity of 181 mAh g−1 and a capacity retention ratio of 95% after 300 cycles, and it also shows superior C-rate capability. The accelerating rate calorimetry (ARC) test manifests that the onset temperature of thermal-runaway of the 4.5 V LiCoO2/Li cell with PI/PVDF-HFP separator is 190 °C, indicating that PI/PVDF-HFP separator possesses superior safety.