Separator for electrochemical device and method for manufacturing the same
A separator for an electrochemical device, including a porous polymer substrate and an inorganic coating layer formed on at least one surface of the porous polymer substrate. The inorganic coating layer includes inorganic particles and a binder resin. The binder resin includes a polyvinylidene fluoride (PVdF)-based polymer having a main chain, and at least one hydrogen atom in the main chain of the PVdF-based polymer is substituted with an acrylic compound-derived functional group.
1. A separator for an electrochemical device, comprising:
a porous polymer substrate; and
an inorganic coating layer formed on at least one surface of the porous polymer substrate,
wherein the inorganic coating layer comprises inorganic particles and a binder resin,
wherein the binder resin comprises a polyvinylidene fluoride (PVdF)-based polymer having a main chain,
wherein at least one hydrogen atom in the main chain of the PVdF-based polymer is substituted with an acrylic compound-derived functional group, and
wherein the polyvinylidene fluoride (PVdF)-based polymer comprises a polymer represented by the following Chemical Formula 1, wherein each of R1 and R2 independently represents a group represented by the following Chemical Formula 2, and each of R3, R4 and R5 is independently substituted with a functional group having at least one hydrogen bound to each carbon atom, and the functional group is at least one selected from the group consisting of ester, ketone, hydroxyl, ether, carboxyl and carbonyl groups,
2. The separator for an electrochemical device according to claim 1 , wherein the main chain of the PVdF-based polymer comprises a copolymer of vinylidene fluoride with a monomer copolymerizable with vinylidene fluoride, wherein the monomer is at least one selected from: trifluoroethylene (TrFE); chlorofluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkylvinyl)etherperfluoro (1,3-dioxole); or perfluoro (2,2-dimethyl-1,3-dioxole (PDD), and wherein a substitution ratio with the monomer is 1-20 wt %.
3. The separator for an electrochemical device according to claim 1 , wherein the acrylic compound-derived functional group is derived from at least one selected from the group consisting of (meth)acrylic acid, (meth)acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-ethylhexyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, n-ethylhexyl methacrylate, 2-ethylhexyl methacrylate, hydroxyethyl methacrylate, (meth)acrylonitrile butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, lauryl (meth)acrylate, tetradecyl (meth)acrylate and dimethyl 2-methylenepentanedionate hydroxypropyl methacrylate.
4. The separator for an electrochemical device according to claim 1 , wherein the PVdF polymer comprises the acrylic compound-derived functional group at a ratio of 0.1 wt % to 5 wt % based on 100 wt % of the PVdF polymer.
5. The separator for an electrochemical device according to claim 1 , wherein the PVdF-based polymer has a weight average molecular weight of 100,000 to 600,000.
6. The separator for an electrochemical device according to claim 1 , wherein the inorganic coating layer comprises the inorganic particles in an amount of 50 wt % or more based on 100 wt % of a total weight of the inorganic particles and the binder resin.
7. The separator for an electrochemical device according to claim 1 , wherein a portion of the inorganic coating layer at a surface of the inorganic coating layer opposite the porous polymer substrate forms an electrode adhesive portion, wherein the electrode adhesive portion has a content of binder resin that is higher than a content of binder resin in the remainder of the inorganic coating layer adjacent to the porous polymer substrate.
8. The separator for an electrochemical device according to claim 1 , wherein the inorganic particles in the inorganic coating layer are bound to each other by the binder resin,
wherein the inorganic coating layer has a plurality of micropores derived from interstitial volumes formed among the inorganic particles,
wherein the inorganic coating layer has an electrode adhesive portion having a content of binder resin that is higher than the remainder of the inorganic coating layer adjacent to the porous polymer substrate, and
wherein the electrode adhesive portion is formed on a surface portion of the inorganic coating layer opposite the porous polymer substrate, and the inorganic coating layer and the electrode adhesive portion are bound integrally and indivisibly to each other.
9. The separator for an electrochemical device according to claim 7 , wherein the electrode adhesive portion is formed by a phase separation process of the binder resin, while drying the separator under a humidified condition.
10. The separator for an electrochemical device according to claim 9 , wherein the humidified condition comprises a relative humidity of 40% to 80%.
11. An electrochemical device comprising:
a negative electrode;
a positive electrode; and
a separator interposed between the negative electrode and the positive electrode,
wherein the separator is as defined in claim 1 .
12. The separator for an electrochemical device according to claim 7 , wherein the electrode adhesive portion is integral and indivisible from the remainder of the inorganic coating layer adjacent to the porous polymer substrate, and wherein the electrode adhesive portion comprises the binder resin in an amount of 70 wt % or more from a topmost portion in a thickness direction of the inorganic coating layer.
13. The separator for an electrochemical device according to claim 8 , wherein the electrode adhesive portion comprises the binder resin in an amount of 70 wt % or more from a topmost portion in a thickness direction of the inorganic coating layer.