| abstract |
PROBLEM TO BE SOLVED: To suppress collapse of pores on a separator surface accompanying expansion of an electrode and suppress deterioration of battery characteristics. A substrate comprising a porous film and a porous surface layer formed on at least one surface of the substrate, having a concavo-convex surface and a higher porosity than the substrate. Use a separator. The surface layer includes a first layer composed of a porous convex portion and a concave portion existing as a void, and a porous second layer formed between the first layer and the base material, Preferably, the second layer has a higher porosity than the substrate, and the first layer has a higher porosity than the second layer. In this case, the porosity of the substrate is 25% to 40%, the porosity of the first layer is 60% to 90%, and the porosity of the second layer is 40% to 65%. Is preferred. [Selection] Figure 2 |