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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 LiCoO 2 /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.

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The coating method of Al2O3 nanoparticles has been widely applied to promote the thermostability and wettability of polyolefin separators. However, the untreated Al2O3/polyethylene (PE) composite separators still need to improve the ionic conductivity (σ) and lithium‐ion transference number (tLi+). Herein, a method is found to obtain amino‐functionalized Al2O3 nanoparticles (N‐Al2O3). As a result, the cell with the N‐Al2O3/PE composite separator has improved σ (0.39 mS cm−1) and tLi+ (0.49). The LiCoO2/Li half‐cell based on N‐Al2O3/PE composite separator exhibits higher discharge capacity (125 mAh g−1) and better cycle performance under the current density of 1 C. Furthermore, the cell containing N‐Al2O3/PE composite separator has a better rate performance and the discharge capacity still maintains 75 mAh g−1 at a high rate of 4 C. This method is effective and simple to modify the PE separator with the amino‐functionalized Al2O3 nanoparticles and enhance the high rate performance of Li‐ion batteries.