Multilayer polyethylene separator with enhanced thermal properties for safe lithium-ion batteries

Separator plays an important part in battery safety and performance. Polyolefin separators are widely used in commercial LIBs owing to their excellent properties, but suffering from serious thermal shrinkage and poor electrolyte wettability. Thus, a multilayer separator (ASPESA) is developed by coating two thin layers of low-density polyethylene (LDPE) and Al2O3 on both sides of polyethylene membrane using a facile and environmentally-friendly casting technique. The ASPESA separator demonstrates a shutdown function at 120 °C and shows enhanced thermal stability under 185 °C with a small thermal shrinkage of 1%. Meanwhile, the LDPE and Al2O3 layers can improve the electrolyte wettability and electrolyte uptake (407.23%). The multilayer ASPESA separator delivers an excellent cycle performance in LiFePO4||Li cells with a discharge capacity of 144.5 mAh g-1 after 900 cycles with a high-capacity retention of 98.9% (compared with the 5th cycle). Therefore, the multilayer ASPESA separator has great utilization potential as a high safety separator in LIBs.