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Traditional polyolefin separators cannot guarantee safety for lithium‐ion batteries at high temperature due to their low melting point, especially for high power discharge. Therefore, it is imperative to develop separators with excellent thermal stability. In this paper, we have prepared TiO2 modified PVDF composite separators by electrospinning. When compared with commercial PE separators, this kind of composite separators show superior thermal stability at 160°C. In addition, it is found that the 0.5‐TiO2@PVDF separator exhibits excellent flame retardant and optimal tension strength. Meanwhile, the 0.5‐TiO2@PVDF separator exhibits ideal liquid electrolyte storage capacity, which improves the ionic conductivity (0.68 mS cm−1). As a result, the LiCoO2||Li cells with 0.5‐TiO2@PVDF separator have high discharge capacity retention rate at a current density of 1 C (300 cycles) and excellent rate performance (1.75 mAh at 5 C). In short, nano‐TiO2 modified PVDF separator has a great application prospect in high‐performance and high‐safety lithium‐ion batteries. [ABSTRACT FROM AUTHOR]

As various heat-resistant polymer separators come out, although they possess better thermal stability and superior affinity to liquid electrolyte than commercial polyolefin separator, the porous structure and chemical stability of these novel separators should be paid more attention. In this work, we prepare a thin polyacrylonitrile/cellulose acetate (PAN/CA) composite nanofiber separator and discuss the importance of chemical stability in the ester-based electrolyte. The addition of CA decreases the PAN/CA fiber diameter from 310 nm to 210 nm. However, CA containing a lot of ester groups is easy to be dissolved by liquid electrolyte for the property of similarity and compatibility. Hence, the obtained PAN/CA composite nanofiber separator is treated via alkaline hydrolysis process, and some ester groups are transformed to be hydroxyl groups. Noteworthily, hydroxyl-rich PAN/CA composite nanofiber separator not only remains stable in electrolyte, but also possesses an improved lithium-ion transport property for reducing concentration polarization effect. As a result, the LiCoO 2 /Li half cells employing the hydroxyl-rich composite nanofiber separator exhibits better capacity retention (118.5 mAh g−1 after 300 cycles) and superior rate performance (143.1 mAh g−1 at 3C). Therefore, this multi-functional groups decorated composite nanofiber separator with excellent chemical stability is a candidate for next-generation lithium-based battery. [Display omitted] • PAN/CA composite separator are successfully prepared by electrospinning. • PAN/CA separator possesses outstanding ionic transport property. • Li-symmetric cell with PAN/CA separator obtains a dendrite free Li deposition. • Half-cell with PAN/CA separator exhibits excellent electrochemical performance. [ABSTRACT FROM AUTHOR]

[Display omitted] • Flower-like calcium phosphate coating is successfully formed on the surface of modified PE separator. • The obtained composite separator exhibits stronger affinity to electrolyte and absorbs more liquid electrolyte. • CaP@PE separator possess an improved ionic conductivity (0.52 mS cm−1) and lithium-ion transference number (0.36). • Cell assembled with CaP@PE separator exhibits excellent cycle performance and rate performance. The organic–inorganic composite separator possesses great thermal stability and electrolyte wettability, which is normally prepared via the slurry containing binder. However, this preparation is involved with large amounts of organic solvent that is harmful to health. In this paper, we design a novel method that combines the crosslinking technology and biomimetic mineralization process to prepare a Ca 3 (PO 4) 2 inorganic coating modified polyethylene separator (CaP@PE). The obtained composite separator exhibits stronger affinity to electrolyte, and its porous coating structure can store more liquid electrolyte, thus the ionic conductivity is promoted from 0.27 mS cm−1 to 0.52 mS cm−1 and the lithium-ion transference number is increased from 0.26 to 0.36. Compared with PE separator, CaP@PE separator shows better thermal stability at high temperature. Due to the improved ionic transport performance and reduced charge transfer impedance, LiCoO 2 /Li half-cell employing CaP@PE separator displays superior cycle stability and capacity retention ability after 150 cycles at a current density of 1C. Even at a high rate of 5C (7.5 mA cm−2), the cell with CaP@PE separator still exhibits a discharge capacity of 0.80 mAh. This work provides a promising separator to optimize the electrochemical performance and safety performance in lithium-ion battery. [ABSTRACT FROM AUTHOR]

Thermally induced phase separation (TIPS) is used to prepare polyethylene (PE) micro-porous membrane, consisting of melt blending, fast cooling, stretching and extracting process, which determine the pore-structure of the PE membrane. In this study, we tried to extract PE/liquid paraffin (LP) oil membrane to obtain PE porous membrane by n-hexane (n-PE) and dichloromethane (d-PE). The n-PE membrane would shrink by 10% for extractant volatilizing, less than 15% of the d-PE membrane after the extraction. These PE membranes were applied into symmetrical cells and LiCoO 2 /Li cells. As a result, the LiCoO 2 /Li cell based on n-PE separator exhibited better capacity retention (98%) than d-PE separator (91%) after 80 cycles at a current density of 1C rate for higher ionic conductivity. And the LiCoO 2 /Li cell with d-PE separator had higher capacity at 2C and 3C, it could be attributed to stronger interaction between solvent and wall of d-PE separator with the smaller and curved pore. In addition, the method that electrochemical impedance spectroscopy (EIS) technique carried out with cyclic voltammetry (CV) and charge-discharge curves is successfully applied to monitor the variety of impedance during the cycles, which is helpful to explore the mechanism of capacity attenuation. • The effect of extraction process on electrochemical performance of PE separator was explored. • n-PE membrane exhibited better capacity retention during the cycles, while d-PE membrane had a better C-rate performance. • EIS could be applied to monitor the variety of impedance inside the cell. • The equivalent circuit of EIS results of LiCoO 2 should contain positive region, separator region and negative region. [ABSTRACT FROM AUTHOR]