A polyacrylonitrile (PAN)-interpenetrating cross-linked polyoxyethylene (PEO) network (named XANE) was synthesized acting as separator and as gel polymer electrolytes simultaneously. SEM images show that the surface of the XANE membrane is nonporous, comparing to the surface of the commercial separator to be porous. This property results in excellent electrolyte uptake amount (425 wt %), and electrolyte retention for XANE membrane, significantly higher than that of commercial separator (200 wt %). The DSC result indicates that the PEO crystallinity is deteriorated by the cross-linked process and was further degraded by the interpenetration of the PAN. The XANE membrane shows significantly higher ionic conductivity (1.06–8.21 mS cm–1) than that of the commercial Celgard M824 separator (0.45–0.90 mS cm–1) ascribed to the high electrolyte retention ability of XANE (from TGA), the deteriorated PEO crystallinity (from DSC) and the good compatibility between XANE and electrode (from measuring the interfacial-resistance). For battery application, under all charge/discharge rates (from 0.1 to 3 C), the specific half-cell capacities of the cell composed of the XANE membrane are all higher than those of the aforementioned commercial separator. More specifically, the cell composed of the XANE membrane has excellent cycling stability, that is, the half-cell composed of the XANE membrane still exhibited more than 97% columbic efficiency after 100 cycles at 1 C. The above-mentioned advantageous properties and performances of the XANE membrane allow it to act as both an ionic conductor as well as a separator, so as to work as separator-free gel polymer electrolytes.