Flame-Retardant Bilayer Separator with Multifaceted van der Waals Interaction for Lithium-Ion Batteries

Safety issues induced by a flammable organic electrolyte challenge the practical applications of high-specific energy lithium-ion batteries (LIBs). Here, we develop a robust bilayer separator by incorporating MoO3 and Al-doped Li6.75La3Zr1.75Ta0.25O12 (LLZTO). The bilayer separator is highly flame-resistive and manages to endure intense fire. Density functional calculations reveal that abundant hydrogen bonds and van der Waals forces within the bilayer separator greatly suppress the combustion with interfacial adhesion of MoO3 and LLZTO to poly(vinylidene fluoride-hexafluoropropylene). With MoO3 and LLZTO, the graphitized carbon content of the carbon residues is increased, and the formation of molybdenum fluoride (MoFx) and lanthanum fluoride (LaFx) is induced during combustion, thus suppressing heat accumulation. The bilayer separator owns a large ductility (227%) and low thermal shrinkage (5%) after annealing at 160 °C for 4 h. Based on the bilayer separator, Li/LiFePO4 cells deliver a remarkable discharge capacity of 162 mA h/g at 0.5 C with a high capacity retention of 95% after 100 cycles. This work provides a new strategy for achieving safe LIBs.