Low-Cost Self-Assembled Oxide Separator for Rechargeable Batteries

Rechargeable battery cells having a liquid electrolyte require a separator permeable to the electrolyte between the two electrodes. Because the electrodes change their volume during charge and discharge, the porous separators are flexible polymers with an electronic energy gap E-g large enough for the Fermi levels of the two electrodes to be within it. In this work, a porous film of self-assembled SiO2 nanoparticles is developed as the separator for a Li-ion battery with a liquid electrolyte. This coating does not require the plasticity of a polymer membrane and has the required large E-g. If adsorbed water is removed from the SiO2 surface, the nanoparticles bond to one another and to an oxide cathode to form a plastic self-assembling porous layer into which the liquid electrolyte can penetrate. The Li-ion batteries with a LiCoO2 cathode coated with SiO2 as a separator show similar performance to cells with a traditional polypropylene separator and improved cyclability with a reduced volume of liquid electrolyte owing to the electrolyte wetting properties of the SiO2 nanoparticles. The SiO2 nanoparticles are easy to prepare, cheap, and environmentally friendly.