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 degrees C avoiding short circuit but also act as ball valve that blocks the lithium ion transmission channel at 150 degrees C interrupting the further heat aggregation. Thus, the LiNi0.6Co0.2Mn0.2O2/Li batteries exhibit high cycle stability of 96.5% capacity retention after 100 cycles at 0.2C and 80 degrees C. Further, the LiNi0.6Co0.2Mn0.2O2/graphite pouch cells are constructed and deliver good safety performance without smoke release and catching fire after the nail penetration test. A high thermostable separator composed of PVDF and PEI is developed. The thermostable PEI microspheres are evenly dispersed in the PVDF film matrix which not only functions as a strong skeleton enabling the rare shrink of the separator at 200 oC but also acts as a ball valve shutting down the lithium-ion transmission channel at 150 oC.image