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.