Polyethylene separator grafting with polar monomer for enhancing the lithium-ion transport property

The commercial polyolefin separator plays a key role in guaranteeing the safety and is also involved in transporting ions inside the battery. However, polyolefin separator composed of C–H chains has nonpolar surface and presents worse affinity to liquid electrolyte. In this study, we firstly have activated polyethylene (PE) separator using γ-irradiation. And then the polar methyl acrylate (MA) monomer has been successfully grafted onto the surface of activated separator with induction of ultraviolet (UV). The obtained PE-g-MA separator has MA modification layer with the ester functional group. As a result, PE-g-MA separator exhibits higher lithium ion transference number of 0.49 than bare PE separator (0.29), it is believed that the enhanced interaction between PE-g-MA separator wall and solvent is beneficial to the desolvation of lithium ion. Moreover, PE-g-MA separator has lower activation energy of 52.1 kJ/mol than pristine PE separator (56.5 kJ/mol), it confirms that lithium ion is easier to migrate across the interface of electrode/PE-g-MA separator filled with liquid electrolyte. The LiCoO2/Li half cells employing PE-g-MA separator possess cycling stability and higher capacity at high current density. Therefore, the PE separator modified with polar group is expected to be applied in the high-power supply.