: Polyethylene (PE) separators have been the most
popular option for commercial Li-ion batteries because of their
uniform pore size, high tensile strength, low cost, and electrochemical
stability. Unfortunately, PE separators generally suffer from significant
dimensional changes at high temperatures, which frequently results in
serious safety problems. In this regard, the integration of inorganic
nanoparticles with PE separators has been considered to be a
promising approach. Here, inorganic nanoparticles with a hierarchical
pore structure were coated on a conventional polymer separator. The
resultant composite separator exhibited superior Li ion transportation
compared with separators coated with mesopore-only nanoparticles or
conventional nonporous nanoparticles. The mesopores and macropores
act synergistically to improve the electrolyte uptake and ionic
conductivity of the inorganic nanoparticles, while other positive
aspects such as their thermal and mechanical properties are still maintained.