Surface Modification of Polyethylene Separator for Li-Ion Batteries via Imine Formation

Abstract

Porous polyethylene (PE) polymer film is a representative material for separators in Li-ion batteries (LIBs). Although PE separators are widely used in commercial LIBs owing to several advantages such as chemical stability, low cost, and good processability, the material still suffers from poor wettability to organic liquid electrolytes and low thermal stability. In this study, a facile surface modification method via the nucleophilic addition of amine in a solution is proposed. To improve the electrolyte wettability and thermal stability of the PE separators, a carbonyl group (C=O) was introduced onto the surface by pretreatment. Then, an imine functional group (R–N=C) was created by the conversion reaction between the carbonyl and amine groups (R-NH2) in a poly(ethylene glycol) bis(amine) solution. By including the formed imine group onto the surface, the surface-modified PE separator exhibited enhanced wettability and thermal stability. The chemical surface treatment transformed the PE separator from hydrophobic to hydrophilic, resulting in the increased ionic conductivity of the electrolyte and rate capability of the cells without any negative effect on the physical and electrochemical properties of the separator.