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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.

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.

Commercial polyolefin separator cannot guarantee the safety of lithium-ion batteries at high temperatures due to their poor thermal stability. All kinds of nanofiber membranes with high thermal stability become the focus. In this paper, we have prepared PVDF nanofiber membrane by electrospinning method and have studied the relationship between the electrochemical performance and nanofiber morphology in detail. It is found that the morphology of PVDF is transformed from ball-like to various nanofiber with increasing the concentration of spinning solution. As a result, the PVDF nanofiber membrane (24 wt%-HP) prepared from spinning solution with the concentration of 24 wt% is composed of coarse nanofiber and fine nanofiber, which exhibits better electrochemical properties, such as cycling stability (300 cycles) and ionic conductivity (1.65 mS cm À1 ). LiCoO 2 /Li cells based on PVDF nanofiber separators have higher discharge capacity even at the current density of 5 C-rate, superior than the cells based on PE separator. It is inspiring for high-energy-density battery safety to use this PVDF nanofiber separator.