Poly(methyl methacrylate-butyl-acrylamide-styrene)/polyethylene electrospinning separator incorporated with ionic liquid for safer LiNi0.5Co0.2Mn0.3O2 cathode

To significantly improve the safety property of commercial lithium-ion batteries, replacing the flammable carbonate solvents by the ionic liquid solvents should be the convenient strategy. However, the special structure of ionic liquid resulted in its poor wettability with traditional polyolefin separators, leading to the high internal resistance and pitiful cycle stability of the assembled battery. To solve the incompatibility between ionic liquid and polyolefin separator, the poly(methyl methacrylate-butyl-acrylamide-styrene) (P(MMA-BA-AN-St)) copolymer was coated onto polyethylene (PE) separator by electrospinning technique. The contact angle between imidazole ionic liquid electrolyte and separator sharply decreased from 77.9° for PE separator to 48.4° for P(MMA-BA-AN-St)/PE separator. Meanwhile, the P(MMA-BA-AN-St)/PE separator saturated with the ionic liquid electrolyte presented the non-flammability, higher ionic conductivity of 5.5 × 10−4 S cm−1, wider oxidative decomposition potential, and improved electrochemical stability compared with the carbonate electrolyte, contributing to the better coulombic efficiency (close to 100%), capacity retention, and rate property for the high-energy–density Li/LiNi0.5Co0.2Mn0.3O2 coin cell. Thus, the developed separator provided an alternatives to match the safer ionic liquid electrolyte with 4 V cathode.