Comprehensive crosslinking strategy using fluorinated azide to enhance the thermal stability of ceramic-coated separators for Li-ion batteries

Abstract

Enhancing the thermal and mechanical stabilities of ceramic-coated separators (CCSs) is required for high-safety lithium-ion batteries (LIBs). As both the thickness and areal mass of ceramic coating layers (CCLs) have reduced, various strategies have been developed to overcome the limitations of conventional ceramics and polymeric binders. In this regard, we suggest a comprehensive photocrosslinking approach to form fully crosslinked CCLs using a new fluorinated azide binder that can readily react with aliphatic functional groups in any component of CCSs. When a small amount of azide binder is added to a CCL slurry consisting of Al2O3 particles and a poly (acrylic acid) (PAA) binder, short UV irradiation can lead to inter- and intramolecular crosslinking points within the polyethylene (PE) separator, between the PE separator and the PAA binder, and within the PAA binders in the CCL. Consequently, the thermal stability and the adhesive strength of crosslinked CCS (X-CCS) can be significantly improved compared to the control CCS without azide. Moreover, a LiNi0.6Co0.2Mn0.2O2/graphite cell with X-CCS exhibited a comparable cycle life to that of the PE separator and non-crosslinked CCS. Furthermore, because UV illuminators are easily added to conventional fabrication processes, this strategy is a simple but effective approach for advancing high-safety LIBs.