Microporous polymer separators and corresponding gel electrolyte have been widely used in lithium ion batteries. This work aims to explore a safety microporous separator for lithium ion batteries by studying the distribution and stability mechanism of liquid electrolyte in this kind of separator. A comb polymer P(MMA-co-PEGMA) was synthesized and blended into poly(vinylidene fluoride) (PVDF) matrix to prepare porous separators via immersion precipitation phase inversion process. The separators then were immersed in liquid electrolyte to form lithium ion conducting gel polymer electrolyte membranes (GPEs). The influence of P(MMA-co-PEGMA) on the morphology, crystallinity, and the liquid electrolyte uptake and distribution in the porous separators was investigated. The ion conductivity increased with copolymer content and the maximum conductivity value of 3.01 x 10(-3) S cm(-1) was found at 25 degrees C in the prepared samples. The Graphite vertical bar GPE vertical bar LiFePO4 cells assembled with modified separators showed improved capacity retention at various C-rates and higher coulombic efficiency than pure PVDF separators (C) 2013 Elsevier Ltd. All rights reserved.