A Thermal-Ball-Valve Structure Separator for Highly Safe Lithium-Ion Batteries.

The separator located between the positive and negative electrodes not only provides a lithium-ion transmission channel but also prevents short circuits for direct contact of electrodes. The inferior dimension thermostability of commercial polyolefin separators intensifies the thermal runaway of batteries under abuse such as short circuits, overcharge, and so on. a polyvinylidene fluoride/polyether imide (PVDF/PEI) separator with high thermal stability in which the high thermostable PEI microspheres are evenly dispersed in the PVDF film matrix and also located in the micro holes of the PVDF film is developed. They not only function as strong skeleton that enables the rare shrink of the separator at 200 °C avoiding short circuit but also act as ball valve that blocks the lithium ion transmission channel at 150 °C interrupting the further heat aggregation. Thus, the LiNiCoMnO/Li batteries exhibit high cycle stability of 96.5% capacity retention after 100 cycles at 0.2C and 80°C. Further, the LiNiCoMnO/graphite pouch cells are constructed and deliver good safety performance without smoke release and catching fire after the nail penetration test.