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

The separator plays an important part in battery safety and performance. Polyolefin separators are widely used in commercial Lithium-ion batteries (LIBs), owing to their excellent properties, but they suffer 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 a 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 to the 5th cycle). Therefore, the multilayer ASPESA separator has great utilization potential as a high-safety separator in LIBs.