Close-packed SiO₂/poly(methyl methacrylate) binary nanoparticles-coated polyethylene separators for lithium-ion batteries

In an endeavour to improve not only the thermal shrinkage but also the electrochemical performance of separators in lithium-ion batteries, a novel composite separator is developed, i.e., a close-packed SiO₂/ poly(methyl methacrylate) (PMMA) binary nanoparticles-coated polyethylene (PE) separator. The introduction of SiO₂ nanoparticles to the coating layer effectively suppresses thermal shrinkage of the composite separator. In contrast to a SiO₂/PMMA coating layer having a film-shaped PMMA binder, the SiO₂/PMMA binary nanoparticle coating layer employs PMMA particles as a binder. As a consequence, a highly porous structure, i.e., well-connected interstitial voids, is formed between the binary SiO₂ and PMMA nanoparticles. The unique porous morphology allows favourable liquid electrolyte wettability and facile ionic conduction, which play a crucial role in improving cell performance such as the discharge capacity and the C-rate capability of the composite separator.