Bifunctional separators design for safe lithium-ion batteries : Suppressed lithium dendrites and fire retardance

Dendrite-free lithium-ion batteries (LIBs) are usually achieved by constructing an artificial SEI layer on Li anode, inevitable to be performed in harsh operating condition and bring barriers to quantity production. This issue can be relieved by designing multifunctional separators with Li deposition tunability. Herein, the MXene on a developed separator plays a crucial role in controlling the deposition configuration of Li metal and hindering the internal short circuits caused by ununiform Li dendrites growth. Furthermore, the developed separator based on the poly (vinylidene fluoride-co-hexafluoropropylene) (abbreviated as PVHF) filled by the hydroxyapatite nanowire networks (abbreviated as HAP) and decorated with MXene (denoted as M-HAP@PVHF) displays superior safety performance than the conventional polypropylene (denoted as PP) separator under the same flame-resistance testing condition. The M-HAP@PVHF separator reported in this work may help to improve the safe operation of LIBs and further enhance the cyclability of LIBs. A symmetric cell based on the M-HAP@PVHF separator delivers a stable lifespan of 700 h with an ultralow overpotential of 15.8 mV at 2 mA cm⁻¹ due to the formation of a stable solid electrolyte interfacial (SEI) layer containing LiF and uniform Li deposition. The Li/M-HAP@PVHF/LiCoO₂ full cell could maintain a stable 150-cycle lifespan with Coulombic efficiency above 95% and still deliver a 99% capacity retention (145 mAh g⁻¹).