Shutdown-Functionalized Poly Ethylene-Vinyl Alcohol Sulfonate Lithium and Poly (Vinyl Alcohol) Composite Lithium-Ion Battery Separator

The thermal shutdown of the separator is the crucial feature for hindering thermal runaway of lithium-ion batteries. Because the temperature within the cell continues to rise rather than drop immediately after shutdown, the separator should be capable of maintaining adequate dimensional stability up to a specific range above the shutdown temperature to prevent internal short circuits. Based on this, a composite separator with high shutdown temperature and a wider shutdown temperature window was fabricated based on the non-solvent induced phase separation process of poly ethylene-vinyl alcohol sulfonate lithium (EVOH-SO3Li) and poly (vinyl alcohol) (PVA). The scanning electron microscope, pore size analysis, and wettability test results show that the composite separator possesses a uniform micron-sized porous structure and excellent electrolyte affinity owing to the abundant hydroxyl and sulfonic acid groups. Hence, the composite separator obtains the optimized electrochemical performances. The cell assembled with the composite separator also exhibits superior discharge C-rate capacity and cycle stability. In addition, the composite separator displays a higher shutdown function of 155 °C and maintained sufficient dimensional integrity below 213 °C, which is conducive to fabrication of lithium-ion batteries with adequate security feature and ideal cycle ability.