Facile fabrication of nanoporous composite separator membranes for lithium-ion batteries: poly(methyl methacrylate) colloidal particles-embedded nonwoven poly(ethylene terephthalate)

Highly-ordered nanoparticle arrangements have drawn substantial attention as an ideal starting template for the preparation of micro-and nanostructured porous materials. In the present study, by exploiting the concept of these unusual colloidal structures, we demonstrate facile fabrication of novel nanoporous composite separator membranes for high-safety and high-power lithium-ion batteries. This is based on the introduction of close-packed poly(methyl methacrylate) (PMMA) colloidal particle arrays to a poly(ethylene terephthalate) (PET) nonwoven support. Herein, the nanoparticle arrangement, driven by the self-assembly of PMMA colloidal particles provides a highly-ordered nanoporous structure, i.e. well-connected interstitial voids formed between the close-packed PMMA nanoparticles, in the composite separator membrane. The nonwoven PET serves as a mechanical support to mitigate the thermal shrinkage of the nonwoven composite separator membrane. Performance benefits of the nonwoven composite separator membrane, as compared to a commercialized polyethylene (PE) separator membrane, are elucidated in terms of thermal shrinkage, liquid electrolyte wettability, and ionic transport. Based on comprehensive characterization of the nonwoven composite separator membrane, the effect of the nanoporous structure on the electrochemical performance, such as self-discharge, discharge capacity, discharge C-rate capability, and cyclability of cells is investigated.