High-safety poly(ethylene-co-vinyl acetate)/poly(ether ether ketone)/poly(ethylene-co-vinyl acetate) composite separator with the thermal shutdown feature for lithium-ion battery

The thermal safety of lithium-ion batteries (LIBs) is a major obstacle to expanding LIBs applications. High-safety separators with a thermal shutdown feature are considered the most promising and appealing thermal protection strategy for LIBs to avoid thermal runaway. Herein, a high-safety poly (ethylene-co-vinyl acetate)/poly (ether ether ketone)/poly (ethylene-co-vinyl acetate) (EVA/PEEK/EVA) composite separator is fabricated by dip-coating and thermally induced phase separation. Once the operating temperature exceeds 80 °C inadvertently (the thermal runaway onset temperature), the EVA layers of the EVA/PEEK/EVA separator are converted into barrier membranes to cut off ion transport and prevent battery reactions. Meanwhile, the PEEK substrate remains dimensionally stable even at temperatures up to 240 °C to avoid the dangers associated with thermal inertia after shutdown. Moreover, compared to the polyolefin separator (commercially available), the EVA/PEEK/EVA separator shows an increase of 42% and 77.1% in ionic conductivity and discharge capacity at the rate of 4C, respectively. Therefore, the EVA/PEEK/EVA separator can secure the LIBs without sacrificing electrochemical performance, and further expand the application of LIBs.