Stainless steel pouch film for the secondary battery

Abstract

The present invention relates to a stainless steel pouch film for a secondary battery.

Description

Technology Field

[0001] The present invention relates to a stainless steel pouch film for a secondary battery. Background Technology

[0003] Due to their excellent energy density and output characteristics, lithium-ion rechargeable batteries are widely used in devices or components such as mobile phones, laptop computers, tablets, power tools, and electric vehicles. In particular, they are frequently used in mobile phones and other mobile devices where miniaturization and lightweight properties are required. Conventionally, aluminum alloys have been used for the packaging materials of these batteries due to their lightweight properties, formability, and economic advantages.

[0004] Recently, based on various advantages such as high energy density and excellent output, the use and application of secondary batteries are expanding explosively, ranging from IT devices to key components for power supply in electric vehicles. As pouch films serve as outer materials encasing the electrode group and electrolyte of these secondary batteries, they must satisfy required characteristics such as adhesion between layers composed of metal thin films and polymers, thermal fusion strength, electrolyte resistance, airtightness, moisture permeability, and moldability.

[0005] Pouch films are largely composed of an outer layer, a metal barrier layer, and an inner sealant layer. The metal barrier layer is required to provide barrier properties against water vapor or other gases, resistance to electrolytes, and moldability. Materials such as aluminum (Al) or aluminum alloys are used for the metal barrier layer; while aluminum is currently the most widely used, the development of new materials is still required.

[0006] In order to protect the electrode assembly from subsequent impact, such an aluminum pouch film for a secondary battery forms an outer resin layer using a polymer resin, etc. on an aluminum thin film, and forms an inner resin layer using a polyolefin, etc. on the other side of the aluminum thin film.

[0007] However, secondary batteries using the aluminum pouch film described above may be damaged for various reasons in various environments. Typically, automobiles are used for extended periods while exposed to diverse environments, requiring protection of the battery from high temperatures, high humidity, and mechanical shock. In automobiles, heat is generated from external sources and during the charging and discharging of high-capacity batteries; this heat can cause microscopic pinholes or internal damage to the pouch film, leading to cracks in the internal adhesive layer and exposing the aluminum layer to the electrolyte. The aluminum layer exposed to the electrolyte in this manner can undergo a chemical reaction with oxygen or moisture in the electrolyte that has penetrated or diffused into the battery, resulting in corrosion. This leads to the generation of corrosive gases, causing a swelling phenomenon that expands the interior of the battery, which presents a significant problem.

[0008] In addition, while the use of secondary batteries as power sources for electric and hybrid vehicles is rapidly expanding, due to the nature of automobiles being constantly exposed to moisture in various natural environments, if a small amount of moisture enters and accumulates inside the battery over a long period, it is predicted that there will be a risk of fire or explosion caused by internal chemical reactions along with a degradation of battery performance. Therefore, it will be necessary to provide improved gas barrier performance, different from conventional methods, to the exterior materials of batteries exposed for such long periods. More specifically, when LiPF6 reacts with water and oxygen to generate hydrofluoric acid (HF), a corrosive gas, it may react with aluminum to cause a rapid exothermic reaction. Furthermore, if it is adsorbed onto the aluminum surface through a secondary reaction and penetrates into the tissue, the brittleness of the tissue increases, causing cracks in the pouch film even with a micro-impact. This leakage of the electrolyte can lead to a reaction between lithium and the atmosphere, resulting in ignition.

[0009] Therefore, in order to solve the aforementioned problems, technology for pouch films using stainless steel (Steel Use Stainless, SUS) instead of aluminum is being researched. Prior art literature

[0010] KR 10-1628993 B1, "Stainless steel pouch film for secondary batteries, packaging material including the same, and secondary battery including the same" The problem to be solved

[0011] The present invention aims to provide a stainless steel pouch film for a secondary battery that not only exhibits excellent corrosion resistance and chemical resistance even when the battery is exposed to external physical or chemical shock or stress, but also has excellent bonding and adhesion strength with the adhesive layer inside the pouch. means of solving the problem

[0013] In order to achieve the above objective,

[0014] The present invention comprises a stainless steel layer in which at least one of a first surface and a second surface is chromate and corona treated;

[0015] An outer resin layer formed on the first surface of the above stainless steel layer;

[0016] It includes an internal resin layer formed on the second surface of the above stainless steel layer;

[0017] The above outer resin layer provides a stainless steel pouch film for a secondary battery comprising polyethylene terephthalate. Effects of the invention

[0019] The stainless steel pouch film for a secondary battery according to the present invention has the advantage of excellent corrosion resistance and chemical resistance even when the battery is exposed to physical or chemical shock or stress from the outside, as well as the ability to suppress crack formation in the adhesive layer inside the pouch and prevent delamination as at least one of the first surface and the second surface of the stainless steel layer is treated with chromate and corona. Specific details for implementing the invention

[0021] The present invention will be described in more detail below.

[0023] The present invention comprises a stainless steel layer in which at least one of a first surface and a second surface is chromate and corona treated;

[0024] An outer resin layer formed on the first surface of the above stainless steel layer;

[0025] It includes an internal resin layer formed on the second surface of the above stainless steel layer,

[0026] The above-described outer resin layer relates to a stainless steel pouch film for a secondary battery comprising polyethylene terephthalate.

[0028] Hereinafter, each component of the stainless steel pouch film for a secondary battery according to the present invention will be described in detail.

[0030] stainless steel layer

[0031] In the stainless steel pouch film for a secondary battery according to the present invention, the grade of stainless steel constituting the stainless steel layer may include one grade selected from the group consisting of austenitic, ferritic, and martensitic types, but is not limited thereto. The ferritic and martensitic grades have significantly lower corrosion resistance compared to the austenitic grade and possess magnetism. Magnetism can affect the environment of finished devices using secondary batteries utilizing the stainless steel pouch film, such as the use of magnets or wireless charging. Therefore, in exemplary embodiments of the present invention, it may be most preferable to use an austenitic grade as the stainless steel.

[0032] Examples of steel grades may include SUS304, SUS430, and SUS316, etc. In addition, the type of surface finish of the stainless steel is not particularly limited, and examples of the type may include BA, 2B, 2D, No.4, and HL, etc.

[0033] In an exemplary embodiment, 304, 304L, 304J1, 316, and 316L, which have excellent corrosion resistance and machinability, may be used.

[0034] Preferably, the thickness of the stainless steel layer is 20 to 60 μm, and the total thickness of the pouch film using this is in the range of 110 to 160 μm.

[0035] When the thickness of the stainless steel layer is 60㎛ or more, the rolling process is easy, but the formability as an exterior material for batteries is significantly reduced, making it difficult to apply. From this perspective, it is desirable for the thickness of the stainless steel layer for exterior materials to be between 20 and 60㎛. Formability is nearly equivalent for thicknesses exceeding 40㎛ up to 60㎛, while steel with a thickness of less than 20㎛ is very difficult to roll and difficult to apply to mass production due to a sharp increase in manufacturing costs.

[0036] In the present invention, the thickness of the stainless steel layer can be appropriately set according to the weight, strength, processing depth, etc. required as a battery casing. From the perspective of reducing the weight of the battery casing, it is preferable for the stainless steel layer to be thinner. However, as the thickness of the layer becomes thinner, strength and processability decrease, and manufacturing costs increase. Considering the strength and processing depth of the battery casing generally required, it is preferable for the thickness of the stainless steel layer to be 20 to 150 μm. In addition, from the perspective of securing strength as a battery casing, it is preferable for the thickness of the stainless steel layer to be 40 to 60 μm.

[0037] Preferably, the weight ratio of each component included in the stainless steel layer is 0.02 to 0.1 wt% carbon, 0.1 to 1.0 wt% silicon, 10 to 30 wt% chromium, and 0.05 to 0.3 wt% nickel. In addition, among the mechanical properties, the yield strength is 100 N / mm² 2 , tensile strength is 200N / mm 2 And if the elongation is 20% or less, formability deteriorates when manufactured into pouch film, and there is a high possibility of pinholes and microcracks occurring, and also the yield strength is 300 N / mm 2 , tensile strength is 700N / mm 2 When the elongation is 60% or higher, formability improves when producing pouch films; however, forming stress remains in the stainless steel after forming. After a certain period, due to residual stress within the material, wrinkles occur at the contact surfaces and vertices of the formed surfaces at room temperature, which may lead to fatigue failure. To prevent such degradation of material properties, the yield strength is set to a range of 100 to 300 N / mm² as a range of mechanical properties. 2 , tensile strength is 200 to 700 N / mm 2 It is preferable that the elongation rate be 20 to 60%.

[0039] In addition, at least one of the first surface and the second surface of the stainless steel layer of the present invention may be chromate and corona treated, and preferably, the first surface and the second surface may be chromate and corona treated.

[0040] The above chromate treatment is a type of chemical conversion coating treatment in which a thin insoluble chromate (chromate) film containing chromium components is formed on one or more of the first and second surfaces of the stainless steel layer. To this end, the stainless steel layer is coated with chromium ions (Cr 3+It is immersed in an aqueous solution containing ) and then chromium ions undergo an oxidation reaction to form insoluble chromium oxide on one or more of the first and second surfaces of the stainless steel layer, thereby forming a chromate film. That is, one or more of the first and second surfaces of the stainless steel layer of the present invention may have a chromate film containing chromium formed thereon.

[0041] Specifically, chromate treatment refers to treatment with a liquid containing chromate anhydride, chromate, dichromate, chromate, or dichromate. Chromate treatment may include elements such as Co, Fe, Ni, Mo, Zn, Ta, Cu, Al, P, W, Sn, As, and Ti (any form such as metal, alloy, oxide, nitride, sulfide, etc.). Examples of aqueous solutions containing chromium ions include aqueous solutions of chromate anhydride or potassium dichromate, and may additionally contain zinc ions.

[0042] The above corona treatment may be performed after chromatizing one or more of the first surface and the second surface of the stainless steel layer, preferably after chromatizing the first surface and the second surface.

[0043] The above corona treatment may be carried out by a method known in the industry, and by corona treating, the roughness of one or more of the first surface and the second surface of the chromate-treated stainless steel can be improved, thereby improving the mechanical bonding strength of the stainless steel pouch film for secondary batteries.

[0045] outer resin layer

[0046] In the stainless steel pouch film for a secondary battery according to the present invention, since the outer resin layer corresponds to the part that comes into direct contact with the hardware, it is preferable that the resin be an insulating resin. Accordingly, the resin used as the outer resin layer may be polyethylene terephthalate.

[0047] In addition, in addition to the polyethylene terephthalate mentioned above, it may further include polyester resins such as polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, copolymer polyester, and polycarbonate, or may further include polyamide resin, polyimide resin, and copolymer of polyamide and polyimide, and preferably may further include copolymer of polyamide and polyimide.

[0048] Specifically, the above copolymer polyesters include polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polyethylene isophthalate, polycarbonate, copolymer polyesters based on repeating units of ethylene terephthalate, copolymer polyesters based on repeating units of butylene terephthalate, etc. In addition, copolymer polyesters based on ethylene terephthalate as the main repeating unit include, specifically, copolymer polyesters polymerized with ethylene isophthalate based on ethylene terephthalate as the main repeating unit, polyethylene (terephthalate / isophthalate), polyethylene (terephthalate / adipate), polyethylene (terephthalate / sodium sulfoisophthalate), polyethylene (terephthalate / sodium isophthalate), polyethylene (terephthalate / phenyl-dicarboxylate), polyethylene (terephthalate / decanedicarboxylate), etc.

[0049] In addition, copolymer polyesters based on butylene terephthalate as the main repeating unit include, specifically, copolymer polyesters polymerized with butylene isophthalate based on butylene terephthalate as the main repeating unit, polybutylene (terephthalate / adipate), polybutylene (terephthalate / sebacate), polybutylene (terephthalate / decandicarboxylate), polybutylene naphthalate, etc. These polyesters may be used individually or in combination of two or more types.

[0050] The above outer resin layer may comprise polyamideimide, inorganic particles, and an amide slip agent.

[0051] By including the above-mentioned inorganic particles and amide slip agent, the slip properties, processability, and moldability of the stainless steel pouch film for secondary batteries can be improved.

[0052] The above inorganic particles may be one or more selected from the group consisting of spherical silicon beads, silica gel, and spherical alumina silica, and preferably may be spherical silicon beads.

[0053] In addition, the above amide slip agent may be erucamide, but is not limited thereto.

[0054] In the above outer resin layer, if the concentration of inorganic particles is less than 50 ppm or the concentration of the amide slip agent is less than 50 ppm, the slip agent cannot be saturated inside the resin layer and cannot migrate to the outside of the resin layer over time, thus failing to reduce the friction coefficient of the surface. Conversely, if the concentration of inorganic particles exceeds 400 ppm or the concentration of the amide slip agent exceeds 400 ppm, the concentration of the slip agent migrating to the surface of the resin layer is excessive, contaminating the rolls of the equipment during the production of the pouch film and causing defects in the appearance of the pouch film. Therefore, as for the concentration of the slip agent, the inorganic particles may be included at 50 to 400 ppm and the amide slip agent at 50 to 400 ppm.

[0056] Internal resin layer

[0057] In the stainless steel pouch film for a secondary battery according to the present invention, the internal resin layer may be formed such that at least one of the first surface and the second surface is formed on the second surface of the stainless steel layer that has been chromate and corona treated.

[0058] The above-mentioned inner resin layer is not specifically limited in type as long as it is used in the industry, and may be selected from the group consisting of polyolefin-based materials such as polyethylene, polypropylene, and polybutylene; ethylene copolymer; propylene copolymer; polyester-based materials; polyamide-based materials; polycarbonate-based materials; fluorine-based materials; silicone-based materials; acrylic-based materials; ethylene-propylene-diene-monomer rubber (EPDM); and mixtures thereof. Preferably, a polyolefin-based resin or a mixed resin of polybutadiene and polyolefin may be used.

[0059] Specific examples of the above polyolefins include polyethylenes such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, and linear low-density polyethylene; polypropylenes such as homopolypropylene, block copolymers of polypropylene (e.g., block copolymers of propylene and ethylene), and random copolymers of polypropylene (e.g., random copolymers of propylene and ethylene); and ternary copolymers of ethylene-butene-propylene. Among these, polyethylene and polypropylene are preferably examples.

[0060] When a polyolefin such as polyethylene or polypropylene or a copolymer thereof is used in the inner resin layer, it is desirable because it not only possesses physical properties required for packaging materials for secondary batteries, such as good heat sealability, moisture resistance, and heat resistance, but also has excellent processability such as lamination. Considering moldability, insulation, and electrolyte resistance, the thickness of the inner resin layer is preferably 20 to 100 μm, and more preferably 30 to 80 μm. If the above range is not satisfied, problems may arise in which moldability, insulation, and electrolyte resistance decrease.

[0062] adhesive layer

[0063] The stainless steel pouch film for a secondary battery according to the present invention may have a first adhesive layer laminated between an outer resin layer and a stainless steel layer that has at least one of a first surface and a second surface chromate-treated, and a second adhesive layer laminated between an inner resin layer and a stainless steel layer that has at least one of the first surface and a second surface chromate-treated.

[0065] 1st adhesive layer

[0066] The first adhesive layer is a layer that enhances the adhesion between the stainless steel layer and the outer resin layer. The first adhesive layer is formed by an adhesive resin capable of bonding the outer resin layer and the stainless steel layer. The adhesive resin used to form the first adhesive layer may be a two-component curing adhesive resin or a one-component curing adhesive resin. In addition, the adhesive mechanism of the adhesive resin used to form the first adhesive layer is not particularly limited and may be any of the following: a chemical reaction type, a solvent volatilization type, a heat melting type, a hot pressing type, etc.

[0067] Adhesive resins that can be used to form the first adhesive layer may include polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polyethylene isophthalate, polycarbonate, copolymer polyester, etc.; polyether resins; polyurethane resins; epoxy resins; phenolic resins; polyamide resins such as nylon 6, nylon 66, nylon 12, copolymer polyamide, etc.; polyolefin resins such as polyolefin, acid-modified polyolefin, metal-modified polyolefin, etc.; polyvinyl acetate resins; cellulose resins; (meth)acrylic resins; polyimide resins; amino resins such as urea resin, melamine resin, etc.; rubbers such as chloroprene rubber, nitrile rubber, styrene-butadiene rubber, etc.; silicone resins; or fluoroethylene propylene copolymers, etc. The above adhesive resin may be used as a single type or as a mixture of two or more types.

[0068] When two or more types of resins are used as the above adhesive resin, the combination is not particularly limited, but examples include a mixed resin of polyamide and acid-modified polyolefin, a mixed resin of polyamide and metal-modified polyolefin, a mixed resin of polyamide and polyester, a mixed resin of polyester and acid-modified polyolefin, and a mixed resin of polyester and metal-modified polyolefin. Among these, in order to effectively suppress delamination by suppressing the decrease in lamination strength between the substrate layer and the metal layer, and to have excellent ductility, durability under high humidity conditions, suppression of sagging, and suppression of deterioration during heat sealing, it is preferable to use a polyurethane-based two-component curing adhesive resin; or a mixed resin of polyamide, polyester, or a modified polyolefin mixed with these.

[0069] In addition, as a known adhesive material, examples include a polyurethane-based adhesive containing a main component comprising a polyol such as a polyester polyol, a polyether polyol, an acrylic polyol, or a carbonate polyol, and a curing agent comprising a difunctional or higher isocyanate compound. A polyurethane-based resin is formed by applying the curing agent to the main component.

[0070] First, polyols may be used as components of the adhesive. Examples of polyol compounds used in urethane-type adhesives include polyester polyols, polyester polyurethane polyols, polyether polyols, and polyether polyurethane polyols. The hydroxyl group equivalents and weight-average molecular weights of these polyol compounds are not particularly limited as long as they ultimately satisfy the above properties in relation to the combined isocyanate-based compound, but examples include a hydroxyl group equivalent (units / mol) of 0.5 to 2.5, preferably 0.7 to 1.9, and a weight-average molecular weight of 500 to 120000, preferably 1000 to 80000. Among these polyol compounds, polyester polyols, polyester polyurethane polyols, and polyether polyurethane polyols are preferably used. These polyol compounds may be used as a single type, or two or more types may be used in combination.

[0071] As the above polyester polyol, it is possible to use a material obtained by reacting at least one polybasic acid with at least one diol. Examples of polybasic acids include aliphatic dibasic acids such as succinic acid, glutaric acid, adipic acid, pimetic acid, souveric acid, azelaic acid, sebacic acid, and brasylic acid, and aromatic dibasic acids such as isophthalic acid, terephthalic acid, and naphthalene dicarboxylic acid. Examples of diols include aliphatic diols such as ethylene glycol, propylene glycol, butanediol, neopentyl glycol, methylpentanediol, hexanediol, heptanediol, octanediol, nonanediol, decanediol, and dodecanediol, alicyclic diols such as cyclohexanediol and hydrogenated xylylene glycol, and aromatic diols such as xylylene glycol.

[0072] In addition, as a polyester polyol, examples include polyester urethane polyols in which the hydroxyl groups at both ends of the polyester polyol are extended using an adduct, biuret, or isocyanurate body containing an isocyanate compound or at least one isocyanate compound. Examples of isocyanate compounds include 2,4- or 2,6-tolylene diisocyanate, xylylene isocyanate, 4,4'-diphenylmethane diisocyanate, methylene diisocyanate, isopropylene diisocyanate, lysine diisocyanate, 2,2,4- or 2,4,4-trimethylhexamethylene diisocyanate, 1,6-hexamethylene diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, isopropylidene dicyclohexyl-4,4'-diisocyanate, etc.

[0073] Examples of the above acrylic polyols include copolymers with poly(meth)acrylic acid as the main component. As the copolymer in question, starting with hydroxyl group-containing monomers such as 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate, alkyl (meth)acrylate-based monomers in which the alkyl group is a methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, t-butyl group, 2-ethylhexyl group, or cyclohexyl group, or (meth)acrylamide, N-alkyl (meth)acrylamide, N,N-dialkyl (meth)acrylamide (in which the alkyl group is a methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, t-butyl group, 2-ethylhexyl group, cyclohexyl group, etc.), N-alkoxy (meth)acrylamide, N,N-dialkoxy (meth)acrylamide (in which the alkoxy group is, Examples of materials obtained by copolymerizing monomers containing amide groups such as methoxy groups, ethoxy groups, butoxy groups, isobutoxy groups, etc.), N-methylol (meth)acrylamide, N-phenyl (meth)acrylamide, glycidyl group-containing monomers such as glycidyl (meth)acrylate, allyl glycidyl ether, silane-containing monomers such as (meth)acryloxypropyl trimethoxysilane, (meth)acryloxypropyl triethoxysilane, and isocyanate group-containing monomers such as (meth)acryloxypropyl isocyanate. As the carbonate polyol, it is possible to use a material obtained by reacting a carbonate compound with a diol. As the carbonate compound, dimethyl carbonate, diphenyl carbonate, ethylene carbonate, etc. may be used. As the above diol, aliphatic diols such as ethylene glycol, propylene glycol, butanediol, neopentyl glycol, methylpentanediol, hexanediol, heptanediol, octanediol, nonanediol, decanediol, dodecanediol, etc., alicyclic diols such as cyclohexanediol, hydrogenated xylylene glycol, aromatic diols such as xylylene glycol, etc. may be used.

[0074] In addition, it is possible to use a polycarbonate urethane polyol in which the terminal hydroxyl groups of the above carbonate polyol are extended by the isocyanate compound described above.

[0075] Next, isocyanate can be cited as a component of the above adhesive.

[0076] Examples of isocyanate-based compounds used in the above-mentioned urethane-type adhesive include polyisocyanates, their adducts, their isocyanurate modifieds, their carbodiimide modifieds, their allophanate modifieds, their biuret modifieds, etc. Specifically, the above-mentioned polyisocyanates include aromatic diisocyanates such as diphenylmethane diisocyanate (MDI), polyphenylmethane diisocyanate (polymeric MDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI), bis(4-isocyanatecyclohexyl)methane (H12MDI), isophorone diisocyanate (IPDI), 1,5-naphthalene diisocyanate (1,5-NDI), 3,3'-dimethyl-4,4'-diphenylene diisocyanate (TODI), and xylene diisocyanate (XDI); Examples include aliphatic diisocyanates such as tramethylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, and isophorone diisocyanate; and alicyclic diisocyanates such as 4,4'-methylenebis(cyclohexyl isocyanate) and isophorone diisocyanate. Specifically, the above adducts may be polyisocyanates to which trimethylolpropane, glycol, etc., are added. Among these isocyanate-based compounds, preferably polyisocyanates and their adducts; more preferably aromatic diisocyanates, their adducts, and their isocyanurate modifieds; even more preferably MDI, polymeric MDI, TDI, their adducts, and their isocyanurate modifieds; particularly preferably, MDI adducts, TDI adducts, polymeric MDI, and TDI isocyanurate modifieds. These isocyanate compounds may be used individually or in combination of two or more types.

[0077] As for the isocyanate compound with two or more functional groups used as the curing agent, it is possible to use an isocyanate compound of the type used as a chain extender, and, although repeated, a single isocyanate compound selected from 2,4- or 2,6-tolylene diisocyanate, xylylene isocyanate, 4,4'-diphenylmethane diisocyanate, methylene diisocyanate, isopropylene diisocyanate, lysine diisocyanate, 2,2,4- or 2,4,4-trimethylhexamethylene diisocyanate, 1,6-hexamethylene diisocyanate, methylcyclohexane diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, isopropylidene dicyclohexyl-4,4'-diisocyanate, etc., or at least one isocyanate selected from the above isocyanate compounds. Examples of compounds include adducts, biurets, and isocyanurates.

[0078] The amount of the above-mentioned curing agent is preferably 1 to 100 parts by weight per 100 parts by weight of the main component, and more preferably 5 to 50 parts by weight. If it is less than 1 part by weight, there is a risk that performance in terms of adhesion or electrolyte resistance will not be exhibited. If it is more than 100 parts by weight, an excess of isocyanate groups will be present, and there is a risk that the residue of unreacted material will affect the adhesive film quality or the hardness.

[0079] In addition to the above-mentioned polyurethane-based adhesive, it is also possible to incorporate carbodiimide compounds, oxazoline compounds, epoxy compounds, phosphorus compounds, silane coupling agents, etc., to promote adhesion.

[0080] The above carbodiimide compounds include N,N'-di-o-toluyl carbodiimide, N,N'-diphenyl carbodiimide, N,N'-di-2,6-dimethylphenyl carbodiimide, N,N'-bis(2,6-diisopropylphenyl)carbodiimide, N,N'-dioctyldecyl carbodiimide, N-triyl-N'-cyclohexyl carbodiimide, N,N'-di-2,2-di-t-butylphenyl carbodiimide, N-triyl-N'-phenyl carbodiimide, N,N'-di-p-nitrophenyl carbodiimide, N,N'-di-p-aminophenyl carbodiimide, N,N'-di-p-hydroxyphenyl carbodiimide, N,N'-di-cyclohexyl carbodiimide, and Examples include N,N'-di-p-toluyl carbodiimide. Examples of the above oxazolin compounds include monooxazolin compounds such as 2-oxazolin, 2-methyl-2-oxazolin, 2-phenyl-2-oxazolin, 2,5-dimethyl-2-oxazolin, and 2,4-diphenyl-2-oxazolin, and dioxazolin compounds such as 2,2'-(1,3-phenylene)-bis(2-oxazolin), 2,2'-(1,2-ethylene)-bis(2-oxazolin), 2,2'-(1,4-butylene)-bis(2-oxazolin), and 2,2'-(1,4-phenylene)-bis(2-oxazolin).

[0081] The above epoxy compounds include: diglycidyl ethers of aliphatic diols such as 1,6-hexanediol, neopentyl glycol, and polyalkylene glycol; polyglycidyl ethers of aliphatic polyols such as sorbitol, sorbitan, polyglycerol, pentaerythritol, diglycerol, glycerol, and trimethylolpropane; polyglycidyl ethers of alicyclic polyols such as cyclohexanedimethanol; diglycidyl esters or polyglycidyl esters of aliphatic or aromatic polycarboxylic acids such as terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, trimellitic acid, adipic acid, and sebacic acid; resorcinol; bis-(p-hydroxyphenyl)methane; 2,2-bis-(p-hydroxyphenyl)propane; and tris-(p-hydroxyphenyl)methane. Examples include diglycidyl ethers or polyglycidyl ethers of polyvalent phenols such as 1,1,2,2-tetrakis(p-hydroxyphenyl)ethane, N-glycidyl derivatives of amines such as N,N'-diglycidylaniline, N,N,N-diglycidyltoluidine, N,N,N',N'-tetraglycidyl-bis-(p-aminophenyl)methane, triglycidyl derivatives of aminophenols, triglycidyl tris(2-hydroxyethyl)isocyanurate, triglycidyl isocyanurate, orthocresol-type epoxy, phenol novolak-type epoxy resin, etc.

[0082] The above phosphorus-containing compounds include tris(2,4-di-t-butylphenyl)phosphite, tetrakis(2,4-di-t-butylphenyl)-4,4'-biphenylenephosphonite, bis(2,4-di-t-butylphenyl)pentaerythritol-di-phosphite, bis(2,6-di-t-butyl-4-methylphenyl)pentaerythritol-di-phosphite, 2,2-methylenebis(4,6-di-t-butylphenyl)octylphosphite, 4,4'-butylidene-bis(3-methyl-6-t-butylphenyl-di-tridecyl)phosphite, 1,1,3-tris(2-methyl-4-ditridecylphosphite-5-t-butylphenyl)butane, tris(mixed mono- and di-nonylphenyl)phosphite, Examples include tris(nonylphenyl)phosphite, 4,4'-isopropylidene bis(phenyl-dialkylphosphite), etc.

[0083] As the above silane coupling agent, it is possible to use various silane coupling agents such as vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, γ-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-chloropropylmethoxysilane, vinyltrichlorosilane, γ-mercaptopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane.

[0084] As an adhesive used to form a first adhesive layer satisfying the physical properties of a stainless steel pouch film for a secondary battery according to the present invention, preferably, a urethane-type adhesive comprising at least one polyol compound selected from the group consisting of polyester polyol, polyester polyurethane polyol, polyether polyol, and polyether polyurethane polyol, and at least one isocyanate-based compound selected from the group consisting of aromatic diisocyanate, its adduct, and its isocyanurate modified body; more preferably, a urethane-type adhesive comprising at least one polyol compound selected from the group consisting of polyester polyol, polyester polyurethane polyol, polyether polyol, and polyether polyurethane polyol, and at least one isocyanate-based compound selected from the group consisting of MDI, polymeric MDI, TDI, their adducts, and their isocyanurate modified bodies.

[0085] In addition, in an adhesive comprising a polyol compound (main component) and an isocyanate-based compound (curing agent), the ratio thereof is appropriately set according to the physical properties to be provided in the adhesive layer, but for example, the ratio of isocyanate groups of the isocyanate-based compound to 1 mole of hydroxyl groups of the polyol compound may be 1 to 30 moles, preferably 3 to 20 moles.

[0086] The thickness of the first adhesive layer is preferably 2 to 10 μm, and more preferably 3 to 5 μm, considering the adhesion with the outer resin layer and the thickness after molding. If the thickness is less than 2 μm, the adhesion is poor, and if it exceeds 10 μm, problems such as cracking may occur.

[0088] Second adhesive layer

[0089] The second adhesive layer mentioned above is a layer that enhances the adhesion between the inner resin layer and the stainless steel layer.

[0090] In the stainless steel pouch film for a secondary battery according to the present invention, the second adhesive layer may be polyurethane, heat-sealable olefin resin, acid-modified polyolefin resin, or epoxy resin. Specific examples of the second adhesive layer may include maleic anhydride polypropylene (MAHPP).

[0091] Examples of the above heat-sealable olefin-based resins include polyethylene, ethylene-α-olefin copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-acrylic acid ester copolymer, ethylene-methacrylic acid ester copolymer, ethylene-vinyl acetate copolymer, ionomers, polypropylene, maleic anhydride-modified polypropylene, ethylene-propylene copolymer, and propylene-1-butene-ethylene copolymer, and preferably, it may include one or more olefin-based resins selected from the group consisting of polypropylene, ethylene-propylene copolymer, and propylene-1-butene-ethylene copolymer.

[0092] The above acid-modified polyolefin resin is a polymer modified by graft polymerization of a polyolefin with an unsaturated carboxylic acid, etc. Specifically, polyolefins that undergo acid modification include polyethylenes such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, and linear low-density polyethylene; crystalline or amorphous polypropylenes such as homopolypropylene, block copolymers of polypropylene (e.g., block copolymers of propylene and ethylene), and random copolymers of polypropylene (e.g., random copolymers of propylene and ethylene); and ethylene-butene-propylene terpolymers. In terms of heat resistance, preferably polyolefins having at least propylene as a constituent monomer, more preferably ethylene-butene-propylene terpolymers and propylene-ethylene random copolymers may be cited. Examples of unsaturated carboxylic acids used for modification include maleic acid, acrylic acid, itaconic acid, crotonic acid, maleic anhydride, itaconic anhydride, etc. Among these unsaturated carboxylic acids, maleic acid and maleic anhydride are preferably used. One or a combination of two or more acid-modified polyolefins may be used.

[0093] Considering the adhesion with the inner layer and the thickness after molding, the second adhesive layer is preferably 2 to 10 μm thick, and more preferably 3 to 5 μm thick. If the thickness is less than 2 μm, the adhesion is poor, and if it exceeds 5 μm, problems such as cracking may occur.

[0094] When an internal resin layer is laminated on one side of the second adhesive layer and a stainless steel layer is laminated on the other side, there are no specific limitations, but preferably, the lamination can be performed using a dry lamination method, a heat lamination method, or an extrusion lamination method.

[0096] Method for manufacturing stainless steel pouch film for secondary batteries

[0097] The stainless steel pouch film for a secondary battery according to the present invention is,

[0098] a) Step of preparing the stainless steel layer;

[0099] b) a step of chromatizing at least one of the first surface and the second surface of the stainless steel layer with an aqueous solution containing chromium ions (Cr3+);

[0100] c) a step of corona treating one or more of the chromate-treated first surface and second surface;

[0101] d) a step of forming an external resin layer on the first surface of the stainless steel layer; and

[0102] e) It may be manufactured by a method including the step of forming an internal resin layer on the second surface of the stainless steel layer, and the external resin layer may include polyethylene terephthalate.

[0104] a) Step of preparing the stainless steel layer

[0105] The above stainless steel layer may be the same as the stainless steel layer described above.

[0107] b) At least one of the first surface and the second surface of the stainless steel layer is chromium ions (Cr 3+ Step of chromatizing with an aqueous solution containing ).

[0108] At least one of the first surface and the second surface of the stainless steel layer, preferably the first surface and the second surface, chromium ions (Cr 3+ It can be treated with an aqueous solution containing ) said chromium ions. Treating with the aqueous solution containing chromium ions may involve immersing the stainless steel layer in the aqueous solution containing chromium ions.

[0109] The above aqueous solution may be an aqueous anhydrous chromate solution or an aqueous potassium dichromate solution, but is not limited thereto. Additionally, the above aqueous solution may additionally contain zinc ions.

[0111] c) a step of corona treating at least one of the chromate-treated first surface and the second surface.

[0112] The present invention does not specifically limit the corona treatment conditions, but rather involves a step of corona treating one or more of the above-mentioned chromate-treated first surface and second surface.

[0114] d) A step of forming an external resin layer on the first surface of the stainless steel layer.

[0115] In the step of forming an external resin layer on the first surface of the stainless steel layer of the stainless steel pouch film for a secondary battery according to the present invention, the external resin layer is formed by laminating the polyethylene terephthalate using a dry lamination method or an extrusion lamination method. When laminating the external resin layer, the thickness of the laminated external resin layer is preferably 10 to 30 μm, and particularly preferably 12 to 25 μm. If the above range is not satisfied, that is, if it is less than 10 μm, the physical properties deteriorate and it tears easily, and if it exceeds 30 μm, there is a problem that the moldability deteriorates.

[0116] In addition, in the step of bonding an outer resin layer to the first surface of the stainless steel layer, a urethane-based adhesive or the like can be used as the first adhesive layer bonding the stainless steel layer and the outer resin layer.

[0118] e) A step of forming an internal resin layer on the second surface of the stainless steel layer.

[0119] In the step of adhering an internal resin layer to a second surface of a stainless steel layer of a stainless steel pouch film for a secondary battery according to the present invention, the second adhesive layer adhering the stainless steel layer and the internal resin layer may be polyurethane, acid-modified polyolefin resin, or epoxy, and specific examples may include maleic anhydride polypropylene (MAHPP).

[0120] Considering the adhesion with the inner resin layer and the thickness after molding, the second adhesive layer is preferably 2 to 30 μm, and more preferably 3 to 15 μm. If the above range is not satisfied, the adhesion is reduced if it is less than 2 μm, and problems such as cracking may occur if it exceeds 30 μm.

[0121] When laminating the above internal resin layer onto the stainless steel layer, there are no specific limitations, but preferably, the internal resin layer can be laminated by using a dry lamination method or an extrusion lamination method.

[0123] Although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims are also not included within the scope of the present invention.

[0125] Example 1.

[0126] A 40㎛ thick thin film of SUS 304 series alloy (POSCO product) was used as the stainless steel layer.

[0127] The stainless steel layer was immersed in an aqueous solution of anhydrous chromic acid (product of Pungwon Chemical Co., Ltd.) to chromate-treat the first and second surfaces of the stainless steel layer.

[0128] The above-mentioned chromate-treated first and second surfaces were corona-treated, and the corona treatment was discharged under the same conditions of AC 220V (input voltage) / 10kW using a system having an aluminum metal bar (width 2.5mm, bar spacing 10mm) as an electrode.

[0129] In order to laminate an external resin layer on the first surface of a stainless steel layer, the first surface and the second surface were chromate and corona treated, a 4㎛ thick polyurethane adhesive resin (product of SK Chemicals) was applied using a gravure roll method, and then a 25㎛ thick polyethylene terephthalate (product of Hyosung) was dry laminated to laminate a polyethylene terephthalate film on the stainless steel layer.

[0130] Subsequently, to laminate an internal resin layer on the second surface of the stainless steel layer, a maleic anhydride modified polyolefin adhesive (product of Jokwang Paint Co.) was applied to a thickness of 4 μm, and then 40 μm thick cast polypropylene (product of Yusang Co.) was laminated onto the stainless steel layer using a dry lamination method to produce a stainless steel pouch film for a secondary battery.

[0132] Example 2.

[0133] A stainless steel pouch film for a secondary battery was manufactured in the same manner as in Example 1, except that a mixture containing polyethylene terephthalate, 100 ppm of spherical silicon beads, and 100 ppm of amide slip agent was dry laminated to laminate an outer resin layer onto the first surface of a stainless steel layer.

[0135] Comparative Example 1.

[0136] An aluminum pouch film for a secondary battery was manufactured in the same manner as Example 1 above, except that an aluminum layer (Dongil Aluminum Co. A8021) was used instead of a stainless steel layer.

[0138] Comparative Example 2.

[0139] A stainless steel pouch film for a secondary battery was manufactured in the same manner as Example 1 above, except that nylon (product of Kolon Corporation) was used as the outer resin layer.

[0141] Comparative Example 3.

[0142] A stainless steel pouch film for a secondary battery was manufactured in the same manner as in Example 1, except that the first surface and the second surface of the stainless steel layer were not treated with chromate and corona.

[0144] Comparative Example 4.

[0145] A stainless steel pouch film for a secondary battery was manufactured in the same manner as in Example 2, except that the first and second surfaces of the stainless steel layer were not treated with chromate and corona.

[0147] Comparative Example 5.

[0148] A stainless steel pouch film for a secondary battery was manufactured in the same manner as in Example 1, except that the first and second surfaces of the stainless steel layer were chromate-treated and corona-treated was not performed.

[0150] Comparative Example 6.

[0151] A stainless steel pouch film for a secondary battery was manufactured in the same manner as in Example 2, except that the first and second surfaces of the stainless steel layer were chromate-treated and corona-treated was not performed.

[0153] Comparative Example 7.

[0154] A stainless steel pouch film for a secondary battery was manufactured in the same manner as in Example 1, except that the first and second surfaces of the stainless steel layer were corona treated and chromate treatment was not performed.

[0156] Comparative Example 8.

[0157] A stainless steel pouch film for a secondary battery was manufactured in the same manner as in Example 2, except that the first and second surfaces of the stainless steel layer were corona treated and chromate treatment was not performed.

[0159] Experimental Example 1. Evaluation of Penetration Strength

[0160] The puncture strength of the stainless steel pouch film for secondary batteries of Examples 1 and 2 and Comparative Examples 2 to 8 and the aluminum pouch film for secondary batteries of Comparative Example 1 was evaluated.

[0161] Each pouch film was measured at 5 points at regular intervals. The puncture strength of the outermost layer was measured in the TD direction, and during measurement, the width of the pouch film was 30 mm, the speed was 200 mm / min, and the punch diameter was Φ mm. It was determined that higher puncture strength indicated superior durability, and the results are shown in Table 1 below.

[0163] Experimental Example 2. Insulation Evaluation

[0164] The insulation properties of the stainless steel pouch films for secondary batteries of Examples 1 and 2 and Comparative Examples 2 to 8, and the aluminum pouch film for secondary batteries of Comparative Example 1 were evaluated.

[0165] After filling each of the above pouch films with an electrode assembly consisting of an anode, a separator, and a cathode and LiPF6 electrolyte (a product of Richem), sealing them, and storing them at 85°C for 24 hours, the stainless steel layer on the upper surface of the electrode was artificially exposed to measure whether it was electrically insulated, and the results are shown in Table 1 below.

[0167] Experimental Example 3. Weathering Resistance Evaluation

[0168] The weather resistance of the stainless steel pouch films for secondary batteries of Examples 1 and 2 and Comparative Examples 2 to 8, and the aluminum pouch film for secondary batteries of Comparative Example 1 was evaluated.

[0169] Each of the above pouch films was cut into 5x5cm pieces and immersed in seawater at 85°C with a salt concentration of 3.5% for 24 hours. The adhesive strength between the outer resin layer and the metal layer was measured and maintained without degradation, and the results are shown in Table 1 below.

[0171] Experimental Example 4. Evaluation of High Temperature Adhesion

[0172] The adhesion strength of the stainless steel pouch films for secondary batteries of Examples 1 and 2 and Comparative Examples 2 to 8 and the aluminum pouch film for secondary batteries of Comparative Example 1 was evaluated. The experiment was conducted under a constant temperature and humidity environment of 85°C for long-term reliability evaluation, and the results are shown in Table 1 below.

[0174] Experimental Example 5. Scratch Resistance Evaluation

[0175] The scratch resistance of the stainless steel pouch films for secondary batteries of Examples 1 and 2 and Comparative Examples 2 to 8 and the aluminum pouch film for secondary batteries of Comparative Example 1 was evaluated.

[0176] To measure the hardness of the surface, an HB pencil was moved 50 mm across the surface of each pouch film under loads of 100, 300, and 500 g to determine the presence of marks on the surface, and the results are shown in Table 1 below.

[0178] Experimental Example 6. Evaluation of Electrolyte Resistance

[0179] The electrolyte resistance of the stainless steel pouch films for secondary batteries of Examples 1 and 2 and Comparative Examples 2 to 8 and the aluminum pouch film for secondary batteries of Comparative Example 1 was evaluated.

[0180] Each of the above pouch films was cut to 2.5 x 10 cm, placed in a test container with LiPF6 standard electrolyte and 1000 ppm distilled water, sealed, and heated to 85°C. The pouch films were collected every 30 days until 24 hours had passed, and delamination between the films was observed visually. The results are shown in Table 1 below.

[0182] Experimental Example 7. Evaluation of Moldability

[0183] For the pouch films prepared in the examples and comparative examples, the depth was changed by 0.1 mm increments using the cold drawing method (Mold size: 5 X 6 cm), and the occurrence of cracks in the corners and tips was measured.

[0184] The occurrence of cracks was determined by shining light on the molded product in a dark room and observing the leaking light under a microscope to check for the presence of microscopic cracks. Based on this, the molding depth at which no cracks occurred was set as the limiting molding depth to evaluate formability.

[0186] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 Penetration strength (N) 60.0 60.0 21.0 58.0 60.0 60.0 52.0 52.0 52.0 52.0 Insulation (G ohm) 64.0 64.0 44.0 44.0 40.0 40.0 64.0 64.0 64.0 64.0 Weather resistance (N / 15mm) 6.5 6.5 4.0 3.0 5.0 5.0 6.5 6.5 6.5 6.5 High temperature adhesion (N / 15mm) 5.0 5.0 3.0 3.0 3.5 3.5 4.0 4.0 4.0 4.0 Scratch resistance (g / 50mm) 150.0 150.0 100.0 100.0 150.0 150.0 150.0 150.0 150.0 150.0 Electrolyte resistance (N / 15mm) 12.0 12.0 10.0 12.0 12.0 12.0 12.0 12.0 12.0 12.0 Formability (mm) 10.0 11.0 10.5 10.8 8.0 10.5 9.5 10.5 9.5 10.5

[0187] Through the results of Table 1 above, it can be seen that the stainless steel pouch film for secondary batteries of the present invention, by using stainless steel as the metal layer, not only has excellent puncture strength, insulation, weather resistance, high temperature adhesion, scratch resistance, electrolyte resistance, and moldability, but also has improved insulation, weather resistance, and high adhesion by applying chromate treatment and corona treatment to the stainless steel layer.

[0188] In addition, it can be seen that using polyethylene terephthalate as the outer resin layer provides excellent insulation, weather resistance, high-temperature adhesion, and scratch resistance.

[0189] In particular, it was found that in Example 2, moldability was further increased by additionally using inorganic particles and an amide slip agent.

[0190] On the other hand, in the case of Comparative Example 1, there was a problem with reduced penetration strength due to the use of an aluminum barrier layer, and in the case of Comparative Example 2, there was a problem with reduced weather resistance, high-temperature adhesion, and scratch resistance due to the use of nylon for the outer resin layer.

[0191] In addition, in the case of Comparative Examples 3 and 4, there was a problem with reduced insulation and high adhesion because chromate treatment was not performed.

[0192] In addition, in the case of Comparative Examples 5 to 8, there was a problem with reduced insulation, weather resistance, and high-temperature adhesion as only one of the chromate treatment or corona treatment was performed.

Claims

Claim 1 A stainless steel pouch film for a secondary battery comprising: a stainless steel layer in which at least one of a first surface and a second surface is chromate- and corona-treated; an outer resin layer formed on the first surface of the stainless steel layer; and an inner resin layer formed on the second surface of the stainless steel layer; wherein the corona treatment is performed after chromate-treating at least one of the first surface and the second surface of the stainless steel layer, and the outer resin layer comprises polyethylene terephthalate, inorganic particles, and an amide slip agent, wherein the inorganic particles are included in an amount of 50 to 400 ppm and the amide slip agent is included in an amount of 50 to 400 ppm. Claim 2 A stainless steel pouch film for a secondary battery according to claim 1, wherein the thickness of the stainless steel layer is 20 to 150 μm. Claim 3 A stainless steel pouch film for a secondary battery, wherein, in claim 1, the stainless steel is an austenitic steel. Claim 4 A stainless steel pouch film for a secondary battery according to claim 1, wherein the stainless steel layer has a first surface and a second surface that are chromate and corona treated. Claim 5 In claim 1, the chromate treatment comprises at least one of the first surface and the second surface of the stainless steel layer, chromium ions (Cr 3+ A stainless steel pouch film for a secondary battery, formed by treatment with an aqueous solution containing ). Claim 6 delete Claim 7 delete Claim 8 delete Claim 9 A stainless steel pouch film for a secondary battery according to claim 1, wherein the inorganic particles are one or more selected from the group consisting of spherical silicon beads, silica gel, and spherical alumina silica. Claim 10 A stainless steel pouch film for a secondary battery, wherein the amide slip agent comprises erucamide in the first paragraph. Claim 11 A stainless steel pouch film for a secondary battery according to claim 1, wherein the thickness of the inner resin layer is 20 to 100 μm. Claim 12 A stainless steel pouch film for a secondary battery according to claim 1, wherein a first adhesive layer is laminated between the stainless steel layer and the outer resin layer, and a second adhesive layer is laminated between the stainless steel layer and the inner resin layer.

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