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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]