Eco-Friendly Preparation of a Polyimide/Polyethylene Composite Separator and Its Application in Lithium-Ion Batteries

The surface modification of polyolefin separators for lithium-ion batteries using polymer particles has been extensively investigated to enhance their electrolyte wettability, thermal resistance, and mechanical properties. However, the traditional polymer synthesis and/or polymer-based separator modifications have mostly been carried out using harmful and expensive organic solvents. In this study, a powder-type polyimide (PI) was synthesized using water as a solvent, and then PI-particle-containing coating slurries were prepared in an aqueous dispersion medium. The coating slurries were applied on a polyethylene (PE) separator to obtain PI-particle-coated PE (PI-PE) separators. Thermal and mechanical properties were evaluated for the PI-PE separators. Electrolyte uptake, porosity, air permeability, and ionic conductivity of the separators were also evaluated. The electrochemical properties of coin cells assembled with the PI-PE separator were evaluated by charge-discharge property. Coating of PI particles improves the thermal stability and electrolyte wettability of the PE separator, and LiCoO₂/PI-PE separator/Li half-cells showed battery performance similar to that of bare PE half-cells. This work offers insights into the simple, eco-friendly preparation of a separator with excellent thermal stability, electrolyte wettability and effective ionic conductivity.