Enhanced Performance of Lithium-Ion Batteries Based on a Polyethylenimine-Grafted SiO₂-Modified Polypropylene Separator

Lithium battery (LIB) separators are integral components of lithium batteries, serving the crucial function of separating the positive and negative electrodes within the batteries, thereby enabling the passage of lithium ions. In general, lithium-ion battery (LIB) separators must exhibit excellent wettability, ionic conductivity, and heat resistance. In this study, commercial polypropylene (PP) separators were modified through the application of a coating comprising polyethylene imine (PEI)-functionalized silica nanoparticles. In particular, a silane coupling agent (KH560) was used to create epoxy groups on the surface of nanosilica, which was then subjected to a chemical cross-linking process with PEI through the ring-opening reaction between epoxy groups and amino groups. It was observed that the modified PP separator displayed augmented wettability, electrolyte absorption rate, and ionic conductivity, which in turn enhanced the cycling and rate performance and other electrochemical properties of the lithium-ion battery. In particular, the optimized sample (1.6 wt %) exhibited the highest specific capacity (151.1 mAh g –1 @1C,LiFePO 4 ||Li) at 1C in comparison to the unmodified commercial PP (142.5 mAh g –1 @1C,LiFePO 4 ||Li). Additionally, the modified PP separator demonstrated enhanced thermal stability in comparison to that of the pristine PP separator, thereby ensuring the stable operation of lithium-ion batteries even under extreme conditions.