Role of Separator Surface Polarity in Boosting the Lithium-Ion Transport Property for a Lithium-Based Battery

The separator is a significant safety component inside the lithium-based battery. To design a higher-power-density system, a functional separator has attracted more attention. In our study, vinyl trimethoxysilane (VTMS) has been directly grafted onto a polyethylene (PE) separator by γ-irradiation. We have evaluated the performance of a PE separator grafted with VTMS (PE-g-SiH) and its basic hydrolysis separator (PE-g-SiO) in detail and have discussed the role of separator surface polarity in the ion transport process. The consequence shows that the lithium-ion transference number of the PE-g-SiO separator is 0.38, superior than 0.27 of a pure PE separator and 0.29 of a PE-g-SiH separator. It can be a reason that the LiCoO2/Li cell with a PE-g-SiO separator shows excellent cycle stability and rate performance. Furthermore, in the case of a PE-g-SiO separator, the Li/Li symmetric model possesses the lowest activation energy of 55.2 kJ mol–1, indicating that lithium ions migrate easily at the interface of electrodes and a separator filled with liquid electrolyte. It is attributed to the improved interaction between the separator wall and solvent, which is in favor of lithium-ion-selective transport. Hence, separator functionalization is expected to enhance the battery performance further.