A separator for an electrochemical device, comprising: a porous polymer substrate; and a porous coating layer formed on at least one surface of the porous polymer substrate, wherein the porous coating layer comprises inorganic particles, a first polyvinylidene fluoride copolymer and a second polyvinylidene fluoride copolymer, characterised in that G' (storage modulus) and G" (loss modulus) of the first polyvinylidene fluoride copolymer undergo a reverse transition, and G' (storage modulus) and G" (loss modulus) of the second polyvinylidene fluoride copolymer undergo no reverse transition; wherein the reverse transition is a case wherein G' passes over G" value in a region of frequency of 0.5 Hz or less under the condition of a solution containing the first polyvinylidene fluoride copolymer at a solid content of 5 wt% in a solvent including N-methyl pyrrolidone and water mixed at a weight ratio of 90:10; wherein the first polyvinylidene fluoride copolymer has a weight average molecular weight of 400,000-1,000,000, and the second polyvinylidene fluoride copolymer has a weight average molecular weight of 50,000-350,000; and the weight ratio of the first polyvinylidene fluoride copolymer to the second polyvinylidene fluoride copolymer is 90:10-40:60; wherein each of the first polyvinylidene fluoride copolymer and the second polyvinylidene fluoride copolymer independently comprises a vinylidene fluoride-derived repeating unit; and at least one additional repeating unit derived from hexafluoropropylene, trichloroethylene, trifluoroethylene, tetrachloroethylene, tetrafluoroethylene or chlorotrifluoroethylene, and wherein the weight ratio of the vinylidene fluoride-derived repeating unit to the additional repeating unit in the first polyvinylidene fluoride copolymer is 99:1-90:10, and the weight ratio of the vinylidene fluoride-derived repeating unit to the additional repeating unit in the second polyvinylidene fluoride copolymer is 89:11-70:30. a porous polymer substrate; and a porous coating layer formed on at least one surface of the porous polymer substrate, wherein the porous coating layer comprises inorganic particles, a first polyvinylidene fluoride copolymer and a second polyvinylidene fluoride copolymer, characterised in that G' (storage modulus) and G" (loss modulus) of the first polyvinylidene fluoride copolymer undergo a reverse transition, and G' (storage modulus) and G" (loss modulus) of the second polyvinylidene fluoride copolymer undergo no reverse transition; wherein the reverse transition is a case wherein G' passes over G" value in a region of frequency of 0.5 Hz or less under the condition of a solution containing the first polyvinylidene fluoride copolymer at a solid content of 5 wt% in a solvent including N-methyl pyrrolidone and water mixed at a weight ratio of 90:10; wherein the first polyvinylidene fluoride copolymer has a weight average molecular weight of 400,000-1,000,000, and the second polyvinylidene fluoride copolymer has a weight average molecular weight of 50,000-350,000; and the weight ratio of the first polyvinylidene fluoride copolymer to the second polyvinylidene fluoride copolymer is 90:10-40:60; wherein each of the first polyvinylidene fluoride copolymer and the second polyvinylidene fluoride copolymer independently comprises a vinylidene fluoride-derived repeating unit; and at least one additional repeating unit derived from hexafluoropropylene, trichloroethylene, trifluoroethylene, tetrachloroethylene, tetrafluoroethylene or chlorotrifluoroethylene, and wherein the weight ratio of the vinylidene fluoride-derived repeating unit to the additional repeating unit in the first polyvinylidene fluoride copolymer is 99:1-90:10, and the weight ratio of the vinylidene fluoride-derived repeating unit to the additional repeating unit in the second polyvinylidene fluoride copolymer is 89:11-70:30.