## 1 Introduction  
The development of porous polymer membranes has attracted remarkable attention in such fields as separation, energy storage, and crystallization [1, 2, 3]. Recently, much research endeavor has been dedicated to enhancing the thermal stability, wettability, and mechanical properties of membranes. Among polymers, polyvinylidene fluoride (PVDF) has been widely used in a large range of applications due to outstanding mechanical strength, excellent chemical resistance, good thermal stability, and high hydrophobicity [4, 5]. However, the copolymer of PVDF and hexafluoropropylene (PVDF-HFP), possessed higher solubility, higher hydrophobicity, greater free volume, and better mechanical strength, has been prominently emerged as a fascinating membrane material because the incorporation of HFP groups enhances the fluorine content compared with original PVDF polymer [2]. Many attempts were made to enhance the mechanical properties of polymer separators by adding nanof fillers, using cross-linkers, and employing nonwoven materials as mechanical supports [1; 2]. Numerous studies have addressed to nanofillers used for enhancing the mechanical strength and increasing the ion conductivity of a composite membrane [6; 7; 8; 9; 10; 11]. However, the uniform dispersion of nanomaterials into an organic-based polymer solution is difficult because of their high surface energy and large energy disparity compared to those of common organic solvents [6; 9]. The aggregation of the nanomaterials neutralizes any nanoscale benefits [9]. Moreover, abundant functional polar groups appearing on nanomaterials may not be electrochemically stable against the strong oxidizing and reducing environments posed by the active electrodes under charge/discharge cycles, which can interfere with the functions of the battery. An alternative approach offers a nonwoven mat employed as a thin support film [10]. Although this type of nonwoven mat can provide good mechanical strength and useful thermal shutdown properties, it causes an increment in the thickness and a reduction in the porosity of the composite separator [11; 12]. These disadvantages limit the electrochemical performance and life cycle of high-power LIBs. Moreover, in some cases, prior to use nonwoven materials in producing a composite separator, additional prerequisite complex steps are required leading to an increase in production cost [11]. Cross-linking of the polymer matrix has also been suggested to improve the mechanical and thermal stability levels of polymer electrolytes. This concept can be an effective approach to produce highly flexible and expandable gel electrolytes [13; 14; 15; 16]. However, the formation of a dense polymer phase in most cross-linked gel polymer electrolytes causes difficulty in filling with a liquid electrolyte. Moreover, it adversely affects the residual initiators on the battery compounds such as a liquid electrolyte, electrode materials, or even a polymer separator, leading to the degradation of the battery performance under cycling. To overcome the disadvantage mentioned above, we developed a unique layered configuration which offers a variety of potential benefits with which to address issues related to the mechanical integrity and electrochemical stability of gel polymer electrolytes made with a thin separator. First, such a configuration enhances the mechanical strength and flexibility of a polymer electrolyte because an interspace between the layers can alleviate large extrusions when applied with stress. Second, a stack of layers can suppress short circuits deriving from the low structural uniformity of each thin film. Third, the gap space can act as an electrolyte reservoir to facilitate high electrolyte adsorption, leading to improved battery performance. To date, strict requirements for the efficient use of energy sources accelerate the investigation in the field of storing energy [17].