Nanoparticle-on-nanofiber hybrid membrane separators for lithium-ion batteries via combining electrospraying and electrospinning techniques

Nanoparticle-on-nanofiber hybrid membranes were prepared by electrospraying of SiO₂ dispersions and electrospinning of polyvinylidene fluoride (PVDF) solution simultaneously. The aim of this study was to design new high-performance separator membranes with superior electrochemical properties such as high C-rate performance and good thermal stability compared to polyolefin based membranes. Uniform, bead-free fibrous structure with high amount of SiO₂ nanoparticles exposed on PVDF nanofiber surfaces was observed. It was found that wettability and ionic conductivity were improved by dispersing SiO₂ nanoparticles onto PVDF nanofiber surfaces. Electrochemical properties were enhanced due to the increased surface area caused by the unique hybrid structure of SiO₂ nanoparticles and PVDF nanofibers. Compared with commercial microporous polyolefin membranes, SiO₂/PVDF hybrid membranes had larger liquid electrolyte uptake, higher electrochemical oxidation limit, and lower interfacial resistance with lithium. SiO₂/PVDF hybrid membrane separators were assembled into lithium/lithium iron phosphate cells and demonstrated high cell capacities and good cycling performance at room temperature. In addition, cells using SiO₂/PVDF hybrid membrane separators showed superior C-rate performance compared to those using commercial microporous PP membrane.