Highly dispersible silicon nitride whiskers in asymmetric porous separators for high-performance lithium-ion battery

Abstract

The separator plays a pivotal role in the safe operation of rechargeable batteries. In this work, a novel separator fabricated by incorporating Poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP) with silicon nitride (Si3N4) whiskers was reported for the first time. Compared with introducing nano powders as inorganic fillers, incorporating inorganic whiskers into polymetric substrates not only suppresses the agglomeration of fillers, but also maintains high structural stability at high temperatures by forming a concrete composite structure. Systematical comparison of “powder-in-polymer” and “whiskers-in-polymer” separators demonstrated that the whisker filler can suppress unexpected dimensional shrinkage at high temperatures and improve electrochemical stability. The composite separator with 60 wt% silicon nitride whiskers exhibits enhanced ionic conductivity of 0.884 mS/cm at 25 °C, stable coulombic efficiency, higher capacity retention rate of 97.4% after 100 cycles and high specific capacity of 103.9 mAh·g−1 at 5 C.