TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The multilayer structure of micron and nano fibers: has a pore size of 1-700 nm, a porosity of greater than or equal to 45% or 45-80%, and a thickness of less than 30 mu m; and has a pore size of 1-400 nm and an average pore size of 50-200 nm, when the weight ratio between micron and nano fibers is 10:5-10:10. The web of micron fibers has a pore size of 10-700 nm, preferably 1-500 nm, and a thickness of 10-25 mu m. The web of nano fibers: has a pore size of 10-500 nm and a thickness of 1-5 mu m; and is formed by nano fibers interweaved on the web of micron fibers by electro-spinning a polymer solution. The weight ratio between the micron fibers, the nano fibers and the resin is 60-65:20:20-15. One side of the web of micron fibers is coated with a mixture solution containing the resin and is further water bathed to remove a solvent of the mixture solution to reduce the mixture layer of fibers and pore size of parts of the micron fibers of the web of micron fibers. The micron fibers are formed by materials including polyethylene terephthalate, polyethylene, or polypropylene polymer. The nano fibers are formed by materials including pitch fiber, polyacrylonitrile fiber, phenolic fiber or an ion polymer having repeat units of formulae (-CH2-CH(R1)m-) (I) and (-CH2-CH(R2)n-) (II). The resin is polyvinylidene fluoride (PVDF) dissolved in N-methyl-2-pyrrolidon, or polyacrylonitrile dissolved in dimethylacetamide. The micron fibers have a diameter of 1-10 mu m. The nano fibers have a diameter of 1-700 nm. The single fiber layer structure of micron fibers has a pore size of 1-450 nm and an average pore size of 100-350 nm. In the single fiber layer structure of micron fibers, the web of micron fibers has a thickness of 10-40 mu m. The weight ratio between the micron fibers and the resin is 10:5. In the single fiber layer structure of nano fibers, the nano fibers have a diameter of 1 nm-500 nm and an average diameter of 10-300 nm, and the web of nano fibers has a pore size of 1-500 nm, an average pore size of 100-350 nm, and a thickness of 5-40 mu m.R1 = benzenesulfonic acid;R2 = 1-methylimidazole, 2-methylpyridine, 4-methylpyridine, or monovalent group of formulae (a)-(c);R3 = amine or sulfonate;X = chloride, bromide or iodide; andm, n = numbers of repeat units, where the ratio of m/n is 1/99-99/1.