Nickel-plated heat-treated steel sheet material for battery case having excellent surface corrosion resistance and electrical conductivity

Abstract

The present invention relates to a nickel-plated heat-treated steel sheet for a battery case having excellent surface corrosion resistance and electrical conductivity. In an embodiment, the nickel-plated heat-treated steel sheet for a battery case comprises: a base steel sheet; a nickel layer having a thickness of 0.5 [mu] m to 6 [mu] m and formed on one or more surfaces of the base steel sheet; and a Ni-Fe diffusion layer formed between the base steel sheet and the nickel layer, in which the Ni-Fe diffusion layer contains 0.3% by weight to 25% by weight of Ni, and the nickel layer has a surface contact resistance of 0.8 m [Omega] or less.

Description

[0001] Cross - reference to related applications

[0002] This application claims priority to Korean Patent Application No. 10 - 2024 - 0000383, filed with the Korean Intellectual Property Office on January 2, 2024, the entire disclosure of which is incorporated herein by reference. Technical field

[0003] The present invention relates to a nickel - plated heat - treated steel sheet having excellent surface corrosion resistance and electrical conductivity for a battery case. Background art

[0004] Nickel - plated heat - treated steel sheets are generally used as the cases of lithium (Li) - ion cylindrical batteries.

[0005] This is because the plating element nickel (Ni) of the nickel - plated heat - treated steel sheet is a more noble metal than iron (Fe), which is beneficial for protecting the surface, and has excellent spot weldability, formability, and corrosion resistance. Since Fe has high resistance to alkali metal ions such as lithium ions, the inner surface of the battery case contains less Ni plating amount than the outer surface.

[0006] In the manufacturing process of nickel - plated heat - treated steel sheets, a basic substrate steel sheet is manufactured through hot rolling, cold rolling, and annealing heat treatment, which determines the main quality factors - shape and mechanical properties of the final product. Next, the nickel - plated heat - treated steel sheet is manufactured through nickel - plating layer formation, diffusion heat treatment, and skin pass rolling processes, thereby determining the characteristics of plating layers such as the Fe - Ni diffusion layer and the soft nickel layer, and important quality factors of the battery case, such as surface corrosion resistance and electrical conductivity during the process.

[0007] The nickel - plated heat - treated steel sheet is processed into the case for a lithium - ion cylindrical battery through a deep - drawing process, and the nickel - plated heat - treated steel sheet is electrically connected to a stack composed of a positive electrode, a negative electrode, and a separator through resistance welding. If the surface resistance of the nickel - plated heat - treated steel sheet is highSS, self - discharge occurs in the no - load state when used as a cylindrical battery, and the life is reduced. However, if the surface resistance is low, self - discharge in the no - load state is reduced, which is beneficial for maintaining the life.

[0008] When manufacturing the nickel - plated heat - treated steel sheet, the Fe - Ni diffusion layer and the soft nickel layer are formed through diffusion heat treatment, which is necessary to ensure the firmness of the nickel - plating layer when processing the nickel - plated heat - treated steel sheet.

[0009] When the Fe-Ni diffusion layer of the nickel-plated heat-treated steel sheet is too thick, due to the microcracks in the nickel plating layer caused by the processing of the battery case, iron may be exposed, and thus corrosion may occur. On the contrary, when the Fe-Ni diffusion layer is too thin, when processing the battery case, the microcracks in the plating layer may cause delamination, resulting in corrosion. Therefore, when processing the battery case, it is necessary to optimize the thickness and composition of the Fe-Ni diffusion layer of the nickel-plated heat-treated steel sheet.

[0010] Therefore, it can be said that the surface corrosion resistance and conductivity of the nickel-plated heat-treated steel sheet used as the cylindrical battery case have a significant impact on the product quality.

[0011] The background art related to the present invention is disclosed in Japanese Patent Laid-Open No. 4698205 (published on June 8, 2011, invention title: "Steel plate for battery case, surface treated steel plate for battery case, battery case, and battery"). Summary of the Invention

[0012] The present invention aims to provide a nickel-plated heat-treated steel sheet for a battery case having excellent surface conductivity and corrosion resistance, thereby maximizing the life of the battery in the external environment.

[0013] The present invention also aims to provide a nickel-plated heat-treated steel sheet for a battery case that effectively prevents the reduction in life caused by the short circuit and standby power of the battery.

[0014] The present invention also aims to provide a method for manufacturing a nickel-plated heat-treated steel sheet for a battery case.

[0015] According to one aspect of the present invention, there is provided a nickel-plated heat-treated steel sheet for a battery case. In an embodiment, the nickel-plated heat-treated steel sheet for a battery case includes: a base steel sheet; a nickel layer having a thickness of 0.5 μm to 6 μm, formed on one or more surfaces of the base steel sheet; and a Ni-Fe diffusion layer formed between the base steel sheet and the nickel layer, wherein the Ni-Fe diffusion layer contains 0.3% by weight to 25% by weight of Ni, and the nickel layer has a surface contact resistance of 0.8 mΩ or less.

[0016] In an embodiment, the base steel sheet may have an average roughness (Ra) of 0.5 μm to 1.3 μm and a maximum height (Ry) of 5 μm to 8 μm.

[0017] In an embodiment, the nickel-plated heat-treated steel sheet may have a crystal structure - a face-centered cubic (FCC) structure containing nickel and γ-(Fe,Ni), and a body-centered cubic (BCC) structure of an alloy containing α-Fe and Fe-Ni (kamacite).

[0018] In an embodiment, the face-centered cubic structure of the nickel-plated heat-treated steel sheet may include a fourth crystal plane (220) accounting for 4% or more of the sum of the volumes of the second crystal plane (111), the third crystal plane (200), the fourth crystal plane (220), the seventh crystal plane (311), and the sixth crystal plane (222), and the body-centered cubic structure may include a third crystal plane (200) accounting for 1.5% or more of the sum of the volumes of the first crystal plane (110), the third crystal plane (200), the fifth crystal plane (221), and the fourth crystal plane (220).

[0019] According to another aspect of the present invention, a method for manufacturing a nickel-plated heat-treated steel sheet for a battery case is provided. In an embodiment, the method for manufacturing the nickel-plated heat-treated steel sheet includes: forming a nickel layer by plating Ni on one or more surfaces of a base steel sheet; and heat-treating the base steel sheet and the nickel layer to form a Ni-Fe diffusion layer between the base steel sheet and the nickel layer, wherein the nickel-plated heat-treated steel sheet includes a base steel sheet, a nickel layer with a thickness of 0.5 μm to 6 μm formed on one or more surfaces of the base steel sheet, and a Ni-Fe diffusion layer formed between the base steel sheet and the nickel layer, and the Ni-Fe diffusion layer contains 0.3% to 25% by weight of Ni, and the nickel layer has a surface contact resistance of 0.8 mΩ or less.

[0020] The nickel-plated heat-treated steel sheet for a battery case according to the present invention has excellent surface conductivity and corrosion resistance, and these characteristics can maximize the life of the battery in an external environment and can effectively prevent the reduction in life caused by short-circuit and standby power of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] By referring to the accompanying drawings and describing the exemplary embodiments of the present invention in detail, the above and other objects, features, and advantages of the present invention will become more apparent to those of ordinary skill in the art, wherein:

[0022] Figure 1 a nickel-plated heat-treated steel sheet according to an embodiment of the present invention is shown; and

[0023] Figure 2 is a graph showing the X-ray diffraction spectrum analysis results of Example 4, Comparative Example 2, and Comparative Example 10. DETAILED DESCRIPTION

[0024] In describing the present invention, when it is determined that a detailed description of related known technologies or configurations may unnecessarily obscure the gist of the present invention, such detailed description will be omitted.

[0025] The terms described below are those defined in consideration of their functions in the present invention and may vary according to the intentions or habits of users and operators. Therefore, these definitions should be based on the content of the entire specification describing the present invention.

[0026] Nickel-plated heat-treated steel sheet for battery case

[0027] One aspect of the present invention relates to a nickel-plated heat-treated steel sheet (or heat-treated steel sheet) for a battery case.

[0028] Figure 1 A nickel-plated heat-treated steel sheet according to an embodiment of the present invention is shown. Refer to Figure 1 , the nickel-plated heat-treated steel sheet 100 for a battery case includes: a base steel sheet 10; a nickel layer 20 formed on one or more surfaces of the base steel sheet 10; and a Ni-Fe diffusion layer 30 formed between the base steel sheet 10 and the nickel layer 20.

[0029] In an embodiment, the thickness of the nickel layer 20 is 0.5 μm to 6 μm. In an embodiment, the Ni-Fe diffusion layer contains 0.3 wt% to 25 wt% of Ni, and the nickel layer has a surface contact resistance of 0.8 mΩ or less. Herein, the expression "0.3 wt% to 25 wt% of Ni" means that the weight percentage of Ni is 0.3% to 25%, and similar expressions hereinafter have the same or similar meanings.

[0030] Base steel sheet

[0031] The base steel sheet 10 can be a steel sheet commonly used for metal plating. In an embodiment, the base steel sheet may contain carbon (C), silicon (Si), manganese (Mn), phosphorus (P), and iron (Fe).

[0032] For example, based on the total weight, the base steel sheet may contain 0.005 wt% to 0.1 wt% of carbon (C), greater than 0 to 0.05 wt% or less of silicon (Si), 0.1 wt% to 0.6 wt% of manganese (Mn), greater than 0 to 0.01 wt% or less of phosphorus (P), the balance of iron (Fe), and other inevitable impurities. When the components are included within the above content ranges, the base steel sheet can have excellent rigidity and mechanical properties.

[0033] Based on the total weight of the base steel plate, the content of carbon (C) can be 0.005% by weight to 0.1% by weight. Within this range, mechanical properties such as strength can be excellent. For example, the content of carbon can be 0.01% by weight to 0.06% by weight. For example, based on the total weight of the base steel plate, the content of carbon can be 0.005% by weight, 0.01% by weight, 0.02% by weight, 0.03% by weight, 0.04% by weight, 0.05% by weight, 0.06% by weight, 0.07% by weight, 0.08% by weight, 0.09% by weight or 0.1% by weight.

[0034] Based on the total weight of the base steel plate, the content of silicon (Si) can be greater than 0 to 0.05% by weight or less. Within this range, the ductility and workability of the base steel plate can be excellent. For example, the content of silicon can be greater than 0 to 0.02% by weight or less. For example, based on the total weight of the base steel plate, the content of carbon can be 0.001% by weight, 0.005% by weight, 0.01% by weight, 0.02% by weight, 0.03% by weight, 0.04% by weight, 0.05% by weight.

[0035] Based on the total weight of the base steel plate, the content of manganese (Mn) can be 0.1% by weight to 0.6% by weight. Within this range, the base steel plate can have excellent mechanical properties such as strength. For example, the content of manganese can be 0.2% by weight to 0.5% by weight. For example, based on the total weight of the base steel plate, the content of manganese can be 0.1% by weight, 0.2% by weight, 0.3% by weight, 0.4% by weight, 0.5% by weight, 0.6% by weight.

[0036] Based on the total weight of the base steel plate, the content of phosphorus (P) can be greater than 0 to 0.01% by weight or less. Within this range, the base steel plate can have excellent mechanical properties while preventing defects such as segregation of the base steel plate. For example, based on the total weight of the base steel plate, the content of phosphorus can be 0.001% by weight, 0002% by weight, 0.003% by weight, 0.004% by weight, 0.005% by weight, 0.006% by weight, 0.007% by weight, 0.008% by weight, 0.009% by weight or 0.01% by weight.

[0037] Also, the base steel plate can be a tin-plated material (BP: black steel plate), a cold-rolled steel sheet (CR: cold-rolled steel), or a full-hard material that has not undergone an annealing process after cold rolling during the manufacture of the cold-rolled steel sheet.

[0038] When using cold-rolled steel sheets such as BP or CR as the base steel sheet, the main purpose is the alloying heat treatment of the nickel layer and iron of the base steel sheet during the alloying heat treatment after plating Ni on the base steel sheet. And when using a fully hard material that does not undergo an annealing process after cold rolling as the base steel sheet, during the alloying heat treatment after plating Ni on the base steel sheet, the annealing of the base steel sheet and the alloying of the nickel plating layer and iron of the base steel sheet are carried out simultaneously.

[0039] In an embodiment, the base steel sheet 10 may have an average surface roughness (Ra) of 0.5 μm to 1.3 μm. Under such conditions, the adhesion between the base steel sheet and the Ni-Fe diffusion layer is excellent, the heat-treated steel sheet has excellent workability and formability, and it is easy to form aggregates that include a face-centered cubic (FCC) structure containing Ni and γ-(Fe,Ni) and a body-centered cubic (BCC) structure of an alloy containing α-Fe and Fe-Ni (kamacite), and the electrical conductivity can be made excellent by minimizing the surface contact resistance of the heat-treated steel sheet. For example, the average roughness (Ra) of the base steel sheet may be 0.6 μm to 1.3 μm or 0.7 μm to 1.3 μm. For example, the average roughness (Ra) of the base steel sheet may be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, or 1.3 μm.

[0040] In an embodiment, the base steel sheet 10 may have a maximum surface height (Ry) of 5 μm to 8 μm. Under such conditions, the adhesion between the base steel sheet and the Ni-Fe diffusion layer is excellent, the heat-treated steel sheet has excellent workability and formability, and it is easy to form aggregates that include a face-centered cubic (FCC) structure containing Ni and γ-(Fe,Ni) and a body-centered cubic (BCC) structure of an alloy containing α-Fe and Fe-Ni (kamacite), and the electrical conductivity can be made excellent by minimizing the surface contact resistance of the heat-treated steel sheet. For example, the maximum height (Ry) of the base steel sheet may be 5 μm to 7.5 μm. For example, the maximum height (Ry) of the base steel sheet may be 5.0 μm, 5.1 μm, 5.2 μm, 5.3 μm, 5.4 μm, 5.5 μm, 5.6 μm, 5.7 μm, 5.8 μm, 5.9 μm, 6.0 μm, 6.1 μm, 6.2 μm, 6.3 μm, 6.4 μm, 6.5 μm, 6.6 μm, 6.7 μm, 6.8 μm, 6.9 μm, 7.0 μm, 7.1 μm, 7.2 μm, 7.3 μm, 7.4 μm, 7.5 μm, 7.6 μm, 7.7 μm, 7.8 μm, 7.9 μm, or 8.0 μm.

[0041] The average roughness (Ra) and maximum height (Ry) of the base steel plate are specified in JIS B0601-1994, and can be measured using a stylus-type measuring device.

[0042] For example, the average roughness (Ra) and maximum height (Ry) of the base steel plate can be measured according to JIS B0601-1994 using a contact-type measuring device (SV-2100M4 from Mitutoyo Corporation, Japan).

[0043] Nickel layer

[0044] The nickel layer 20 can be included to ensure the corrosion resistance and conductivity of the present invention. Refer to Figure 1 , the Ni-Fe diffusion layer 30 is formed on at least one surface of the base steel plate 10, and the nickel layer 20 is formed on top of the Ni-Fe diffusion layer 30.

[0045] For example, the nickel layer may contain only Ni.

[0046] In an embodiment, the nickel layer has a thickness of 0.5 μm to 6 μm. When the thickness of the nickel layer is less than 0.5 μm, the surface contact resistance increases and the conductivity and corrosion resistance decrease. When the thickness of the nickel layer exceeds 6 μm, the formability and economic efficiency may decrease. For example, the nickel layer may have a thickness of 1 μm to 6 μm. For example, the nickel layer may have a thickness of 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or 6 μm.

[0047] Ni-Fe diffusion layer

[0048] The Ni-Fe diffusion layer 30 is formed between the base steel plate 10 of the heat-treated steel sheet and the nickel layer 20. The Ni-Fe diffusion layer 30 can be formed during the diffusion heat treatment of the nickel layer 20, which will be described later.

[0049] In an embodiment, the Ni-Fe diffusion layer 30 may contain 0.3% by weight to 25% by weight of Ni. In an embodiment, the Ni content in the Ni-Fe diffusion layer 30 can be measured using an energy dispersive spectrometer (EDS) or electron probe X-ray microanalysis (EPMA) after removing the nickel layer 20 of the heat-treated steel sheet.

[0050] When the Ni-Fe diffusion layer contains less than 0.3% by weight of Ni, the corrosion resistance and formability of the heat-treated steel sheet are reduced, and when the Ni-Fe diffusion layer contains more than 25% by weight of Ni, the corrosion resistance of the heat-treated steel sheet is reduced and the surface contact resistance increases, so the conductivity may be reduced. For example, the Ni-Fe diffusion layer may contain 0.5% to 25% by weight or 1% to 24% by weight of Ni. For example, the Ni-Fe diffusion layer may contain 0.3% by weight, 0.4% by weight, 0.5% by weight, 0.6% by weight, 0.7% by weight, 0.8% by weight, 0.9% by weight, 1% by weight, 2% by weight, 3% by weight, 4% by weight, 5% by weight, 6% by weight, 7% by weight, 8% by weight, 9% by weight, 10% by weight, 11% by weight, 12% by weight, 13% by weight, 14% by weight, 15% by weight, 16% by weight, 17% by weight, 18% by weight, 19% by weight, 20% by weight, 21% by weight, 22% by weight, 23% by weight, 24% by weight or 25% by weight of Ni.

[0051] In the diffusion heat treatment process, Ni diffuses and dissolves in iron, and a kamacite phase can be formed in the third crystal plane (200) and the fifth crystal plane (221), respectively. Specifically, under conditions higher than the α-Fe + γ-(Fe,Ni) region, a γ-(Fe,Ni) phase is formed during the diffusion heat treatment, and when cooled, this phase can be divided into an Fe-rich phase and a Ni-rich phase, which can be confirmed in the fourth crystal plane (220) and the seventh crystal plane (311) of the face-centered cubic structure, respectively.

[0052] In an embodiment, the heat-treated steel sheet may have a crystal structure - a face-centered cubic (FCC) structure containing Ni and γ-(Fe,Ni) and a body-centered cubic (BCC) structure of an alloy containing α-Fe and Fe-Ni (kamacite).

[0053] The crystal structure of the heat-treated steel sheet can be measured by X-ray diffraction (XRD) spectroscopy using to CuKα rays. For example, within the diffraction angle (2θ) ranges of 42° to 48°, 50° to 54°, 72° to 78°, 90° to 96°, and 93° to 99°, the face-centered cubic structure of the heat-treated steel sheet has effective peaks, and these diffraction angle ranges can represent the second crystal plane (111), the third crystal plane (200), the fourth crystal plane (220), the seventh crystal plane (311), and the sixth crystal plane (222), respectively.

[0054] In an embodiment, the face-centered cubic structure of the heat-treated steel sheet may include a fourth crystal plane (220) that accounts for 4% or more of the sum of the volumes of the second crystal plane (111), the third crystal plane (200), the fourth crystal plane (220), the seventh crystal plane (311), and the sixth crystal plane (222). Under such conditions, the nickel-plated heat-treated steel sheet may have excellent corrosion resistance and electrical conductivity by minimizing the surface contact resistance. For example, it may include 4% to 10%, 4% to 8%, or 4% to 6% of the (220) crystal plane. For example, it may include 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, or 10% of the fourth crystal plane (220).

[0055] For example, within the diffraction angle (2θ) ranges of 42° to 48°, 63° to 67°, 81° to 84°, and 93° to 99°, the body-centered cubic structure of the heat-treated steel sheet has effective peaks, and these diffraction angle ranges may respectively represent the first crystal plane (110), the third crystal plane (200), the fifth crystal plane (221), and the fourth crystal plane (220).

[0056] In an embodiment, the body-centered cubic structure of the heat-treated steel sheet may include a third crystal plane (200) that accounts for 1.5% or more of the sum of the volumes of the first crystal plane (110), the third crystal plane (200), the fifth crystal plane (221), and the fourth crystal plane (220). Under such conditions, the nickel-plated heat-treated steel sheet may have excellent corrosion resistance and electrical conductivity by minimizing the surface contact resistance. For example, it may include 1.5% to 20%, 1.5% to 18%, 3% to 17%, or 3% to 15% of the third crystal plane (200). For example, it may include 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20% of the third crystal plane (200).

[0057] In an embodiment, the fourth crystal plane (220) and the seventh crystal plane (311) in the face-centered cubic structure of the heat-treated steel sheet may be composed of Ni and γ-(Fe,Ni), and the third crystal plane (200) and the fifth crystal plane (221) in the body-centered cubic structure of the heat-treated steel sheet may be composed of α-Fe and an alloy of Fe-Ni.

[0058] In an embodiment, the heat-treated nickel-plated steel sheet has a surface contact resistance of 0.8 mΩ or less. Under this surface contact resistance condition, self-discharge is reduced in the no-load state, which can be advantageous for maintaining the lifespan. When the surface contact resistance of the heat-treated steel sheet exceeds 0.8 mΩ, the conductivity decreases, and when used as a cylindrical battery, self-discharge may occur in the no-load state, and the lifespan may be reduced. For example, the heat-treated steel sheet may have a surface contact resistance of 0.2 mΩ to 0.8 mΩ or 0.5 mΩ to 0.8 mΩ. For example, the heat-treated steel sheet may have a surface contact resistance of 0.2 mΩ, 0.25 mΩ, 0.3 mΩ, 0.35 mΩ, 0.4 mΩ, 0.45 mΩ, 0.5 mΩ, 0.55 mΩ, 0.6 mΩ, 0.65 mΩ, 0.7 mΩ, 0.75 mΩ, or 0.8 mΩ.

[0059] For example, the surface contact resistance of the heat-treated nickel-plated steel sheet can be measured using a surface contact resistance tester (CMT-SR2000N from AIT Co., Ltd.) under the AC 4-terminal method and a measurement current of 10 mA.

[0060] Method for manufacturing nickel-plated heat-treated steel sheet

[0061] Another aspect of the present invention relates to a method for manufacturing a heat-treated nickel-plated steel sheet. In an embodiment, the method for manufacturing a heat-treated nickel-plated steel sheet includes: plating Ni on one or more surfaces of a base steel sheet to form a nickel layer; and heat-treating the base steel sheet and the nickel layer to form a Ni-Fe diffusion layer between the base steel sheet and the nickel layer.

[0062] Form nickel layer

[0063] This step is used to form a nickel layer by plating Ni on one or more surfaces of the base steel sheet. In an embodiment, before forming the nickel layer by an electroplating nickel bath, the base steel sheet can be subjected to a pretreatment process. For example, a pretreatment process including conventional degreasing, water washing, and pickling processes can be carried out, but it is not particularly limited thereto.

[0064] The base steel sheet can be the same as that described above.

[0065] In an embodiment, the base steel sheet 10 may have an average surface roughness (Ra) of 0.5 μm to 1.3 μm. Under such conditions, the adhesion between the base steel sheet and the Ni-Fe diffusion layer is excellent, the heat-treated steel sheet has excellent workability and formability, the crystal structure of the heat-treated steel sheet includes a face-centered cubic (FCC) structure containing Ni and γ-(Fe,Ni) and a body-centered cubic (BCC) structure containing α-Fe and an alloy of Fe-Ni, and the electrical conductivity is excellent by minimizing the surface contact resistance of the heat-treated steel sheet. For example, the average roughness (Ra) of the base steel sheet may be 0.6 μm to 1.3 μm or 0.7 μm to 1.3 μm. For example, the average roughness (Ra) of the base steel sheet may be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, or 1.3 μm.

[0066] In an embodiment, the base steel sheet 10 may have a maximum surface height (Ry) of 5 μm to 8 μm. Under such conditions, the adhesion between the base steel sheet and the Ni-Fe diffusion layer is excellent, the heat-treated steel sheet has excellent workability and formability, the crystal structure of the heat-treated steel sheet includes a face-centered cubic (FCC) structure containing Ni and γ-(Fe,Ni) and a body-centered cubic (BCC) structure containing α-Fe and an alloy of Fe-Ni, and the electrical conductivity is excellent by minimizing the surface contact resistance of the heat-treated steel sheet. For example, the maximum height (Ry) of the base steel sheet may be 5 μm to 7.5 μm. For example, the maximum height (Ry) of the base steel sheet may be 5.0 μm, 5.1 μm, 5.2 μm, 5.3 μm, 5.4 μm, 5.5 μm, 5.6 μm, 5.7 μm, 5.8 μm, 5.9 μm, 6.0 μm, 6.1 μm, 6.2 μm, 6.3 μm, 6.4 μm, 6.5 μm, 6.6 μm, 6.7 μm, 6.8 μm, 6.9 μm, 7.0 μm, 7.1 μm, 7.2 μm, 7.3 μm, 7.4 μm, 7.5 μm, 7.6 μm, 7.7 μm, 7.8 μm, 7.9 μm, or 8.0 μm.

[0067] In an embodiment, electroplating may be used for Ni plating. For example, Ni plating may be performed by a conventional electroplating method using a Ni plating solution (or Ni plating bath). For example, a Watts bath and a sulfamate bath may be used as the plating solution.

[0068] In an embodiment, based on 1 L of the plating bath, a Watts bath may contain 150 g / L to 400 g / L of nickel sulfate (NiSO4), 20 g / L to 60 g / L of nickel chloride (NiCl2), 10 g / L to 50 g / L of boric acid (H3BO3), and the balance of water. When electroplating is carried out by applying the plating bath, the corrosion resistance and electrical conductivity of the heat-treated steel sheet can be excellent, but the plating bath conditions are not limited thereto.

[0069] In an embodiment, electroplating using the plating bath may be carried out at a pH of 3.0 to 4.8, a plating bath temperature of 45 °C to 70 °C, and a current density of 2 A / dm 2 to 40 A / dm 2 , but not limited thereto. When electroplating is carried out under the plating bath conditions described above, the corrosion resistance and electrical conductivity of the heat-treated steel sheet can be excellent.

[0070] Additives may be used to provide luster to the Ni plating layer. For example, additives without sulfur components may be used.

[0071] In an embodiment, during Ni electroplating, based on one side of the base steel sheet, the plating amount of Ni may be 2.7 g / m 2 to 53.4 g / m 2 . Under this plating amount condition, the heat-treated steel sheet can have excellent workability, corrosion resistance, and electrical conductivity. For example, based on one side of the base steel sheet, the plating amount of Ni may be 2.7 g / m 2 , 3.0 g / m 2 , 3.5 g / m 2 , 4.0 g / m 2 , 4.5 g / m 2 , 5.0 g / m 2 , 5.5 g / m 2 , 6.0 g / m 2 , 6.5 g / m 2 , 7.0 g / m 2 , 7.5 g / m 2 , 8.0 g / m 2 , 8.5 g / m 2 , 9.0 g / m 2 , 9.5 g / m 2 , 10 g / m 2 , 11 g / m 2 , 12 g / m 2 , 13 g / m 2 , 14 g / m 2 , 15 g / m 2 , 16 g / m 2 , 17 g / m 2 , 18 g / m 2 , 19 g / m2 , 20 g / m 2 , 21 g / m 2 , 22 g / m 2 , 23 g / m 2 , 24 g / m 2 , 25 g / m 2 , 26 g / m 2 , 27 g / m 2 , 28 g / m 2 , 29 g / m 2 , 30 g / m 2 , 31 g / m 2 , 32 g / m 2 , 33 g / m 2 , 34 g / m 2 , 35 g / m 2 , 36 g / m 2 , 37 g / m 2 , 38 g / m 2 , 39 g / m 2 , 40 g / m 2 , 41 g / m 2 , 42 g / m 2 , 43 g / m 2 , 44 g / m 2 , 45 g / m 2 , 46 g / m 2 , 47 g / m 2 , 48 g / m 2 , 49 g / m 2 , 50 g / m 2 , 51 g / m 2 , 52 g / m 2 , 53 g / m 2 or 53.4 g / m 2 .

[0072] Heat treatment

[0073] This step is used to perform heat treatment (diffusion heat treatment) on the base steel plate and the nickel layer to form a Ni-Fe diffusion layer between the base steel plate and the nickel layer.

[0074] Through heat treatment, a diffusion layer containing Ni-Fe is formed between the nickel layer and the base steel plate. The Ni layer and the Ni-Fe diffusion layer are softened to have excellent workability, and the heat-treated steel sheet can have excellent corrosion resistance and electrical conductivity.

[0075] In an embodiment, the heat treatment may be carried out at a temperature of 400°C to 800°C. When the heat treatment is carried out under this condition, the heat-treated steel sheet may have excellent corrosion resistance and electrical conductivity. In addition, after the Ni-Fe heat treatment under the above conditions, the wear and tear on the equipment during the skin rolling, cutting, and forming processes of the battery housing can be minimized, thereby reducing equipment replacement, ultimately leading to increased productivity, reduced production costs, and improved quality. For example, the heat treatment may be carried out at a temperature of 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C, 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C, or 800°C.

[0076] In an embodiment, the heat treatment may be carried out for 10 minutes to 48 hours. When the heat treatment is carried out under this condition, the heat-treated steel sheet may have excellent corrosion resistance and electrical conductivity.

[0077] The atmospheric gas used during the heat treatment is not particularly limited. For example, the atmospheric gas may contain one or more of nitrogen (N2) and hydrogen (H2). When used, based on the total volume of N2 and H2, the mixed gas may contain 70% to 98% by volume of N2 and 2% to 30% by volume of H2. For example, the mixed gas may contain 80% to 97% by volume of N2 and 3% to 20% by volume of H2.

[0078] In an embodiment, during the heat treatment, the oxygen concentration may be 1.0 ppm to 500 ppm, for example 5.0 ppm to 400 ppm, relative to the total volume of the atmospheric gas.

[0079] In an embodiment, the method for manufacturing a heat-treated steel sheet may further include: after forming a Ni-Fe diffusion layer, manufacturing a rolled material by skin rolling the base steel sheet on which the Ni-Fe diffusion layer is formed.

[0080] Skin rolling

[0081] This step is used to manufacture a skin-rolled material (or nickel-plated heat-treated steel sheet) by skin rolling the base steel sheet on which the Ni-Fe diffusion layer is formed. Skin rolling can be carried out to adjust the thickness, shape, and surface roughness of the steel sheet, minimize the residual stress in the heat-treated steel sheet, and ensure uniform material properties.

[0082] Rolling can be carried out by placing a base steel plate formed with a Ni-Fe diffusion layer thereon into a rolling mill and performing skin pass rolling using the upper work roll and the lower work roll of the rolling mill.

[0083] In an embodiment, the skin pass rolling can be carried out under the condition that the reduction per pass is 0.3% to 2.0%. During the skin pass rolling under the above conditions, the residual stress of the steel sheet can be minimized, and the crystal structure of the skin-rolled material can include a face-centered cubic (FCC) structure containing Ni and γ-(Fe,Ni) and a body-centered cubic (BCC) structure containing an alloy of α-Fe and Fe-Ni. For example, the skin pass rolling can be carried out under the condition that the reduction per pass is 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9% or 2.0%.

[0084] The skin-rolled material (or nickel-plated heat-treated steel sheet) has a nickel layer with a thickness of 0.5 μm to 6 μm formed on one or more surfaces of the base steel plate, an Fe-Ni diffusion layer is formed between the base steel plate and the nickel layer, the nickel layer has a surface contact resistance of 0.8 mΩ or less, and the Fe-Ni diffusion layer contains 0.3% to 25% by weight of Ni. The base steel plate, nickel layer and Fe-Ni diffusion layer of the skin-rolled material can be the same as those of the nickel-plated heat-treated steel sheet described above.

[0085] In an embodiment, the skin-rolled material (or nickel-plated heat-treated steel sheet) includes a crystal structure - a face-centered cubic (FCC) structure containing nickel and γ-(Fe,Ni) and a body-centered cubic (BCC) structure containing an alloy of α-Fe and Fe-Ni, and the face-centered cubic structure can include a fourth crystal plane (220) accounting for 4% or more of the sum of the volumes of the second crystal plane (111), third crystal plane (200), fourth crystal plane (220), seventh crystal plane (311) and sixth crystal plane (222), and the body-centered cubic structure can include a third crystal plane (200) accounting for 1.5% or more of the sum of the volumes of the first crystal plane (110), third crystal plane (200), fifth crystal plane (221) and fourth crystal plane (220).

[0086] In an embodiment, the skin-rolled material (or nickel-plated heat-treated steel sheet) can contain Ni and γ-(Fe,Ni) in the fourth crystal plane (220) and seventh crystal plane (311) of the face-centered cubic structure, and the skin-rolled material (nickel-plated heat-treated steel sheet) can contain an alloy of α-Fe and Fe-Ni in the third crystal plane (200) and fifth crystal plane (221) of the body-centered cubic structure.

[0087] In an embodiment, the skin-rolled material (or nickel-plated heat-treated steel sheet) has a surface contact resistance of 0.8 mΩ or less. Under this surface contact resistance condition, self-discharge is reduced in the no-load state, which can be advantageous for maintaining the lifespan. When the surface contact resistance of the heat-treated steel sheet exceeds 0.8 mΩ, the conductivity decreases, and when used as a cylindrical battery, self-discharge may occur in the no-load state, and the lifespan may be reduced. For example, the heat-treated steel sheet may have a surface contact resistance of 0.2 mΩ to 0.8 mΩ or 0.5 mΩ to 0.8 mΩ. For example, the heat-treated steel sheet may have a surface contact resistance of 0.2 mΩ, 0.25 mΩ, 0.3 mΩ, 0.35 mΩ, 0.4 mΩ, 0.45 mΩ, 0.5 mΩ, 0.55 mΩ, 0.6 mΩ, 0.65 mΩ, 0.7 mΩ, 0.75 mΩ, or 0.8 mΩ.

[0088] In an embodiment, the method of manufacturing a heat-treated steel sheet may further include: after the skin bright rolling step, manufacturing a strip of steel sheet by cutting the skin-rolled material.

[0089] Cutting

[0090] This step is used to manufacture a strip of steel sheet by cutting the skin-rolled material. After the skin bright rolling process, according to the requirements of the customer, a cutting blade can be used to cut in different widths in the rolling direction of the product.

[0091] In an embodiment, after cutting, it may further include the step of forming the processed strip into the shape of a housing. For example, the strip can be formed into the shape of a housing by press forming.

[0092] The nickel-plated heat-treated steel sheet manufactured by the method of manufacturing a nickel-plated heat-treated steel sheet has excellent surface corrosion resistance and conductivity, and can effectively prevent a reduction in lifespan caused by short circuits and standby power of secondary batteries during the resistance welding of a stack composed of a positive electrode, a negative electrode, and a separator.

[0093] Hereinafter, the configuration and operation of the present invention will be described in more detail by preferred examples of the present invention. However, these are provided as preferred examples of the present invention and should not be construed as limiting the present invention in any way. Since any information not described herein can be technically inferred by any person skilled in the art, its description will be omitted.

[0094] Examples and comparative examples

[0095] Example 1

[0096] (1) Preparation of the base steel plate: A slab containing 0.03% by weight (300 ppm) of carbon (C), more than 0 and less than or equal to 0.001% by weight (10 ppm) of silicon (Si), 0.31% by weight (3100 ppm) of manganese (Mn), more than 0 and less than or equal to 0.001% by weight (10 ppm) of phosphorus (P), the balance of iron (Fe) and other inevitable impurities is reheated, hot-rolled and cold-rolled to prepare a base steel plate (cold-rolled carbon steel sheet) with a thickness of 0.30 mm. The base steel plate measured using a contact measuring device (SV-2100M4 from Mitutoyo Corporation, Japan) according to JIS B0601-1994 has an average roughness (Ra) of 1.04 μm and a maximum height (Ry) of 7.16 μm.

[0097] (2) Formation of the nickel layer: The base steel plate is pretreated by alkaline degreasing, alkaline electrolytic degreasing and pickling (sulfuric acid aqueous solution), and then nickel electroplating is carried out. Specifically, a plating bath containing 250 g / L of NiSO4, 40 g / L of NiCl2, 40 g / L of H3BO3 and the balance of water is prepared at a temperature of 60 °C and a pH of 3.2 to 4.5, and electroplating is carried out under the condition of a current density of 10 ASD to form a nickel layer. At this time, the Ni adhesion amount is measured using an X-ray fluorescence measuring device (X-ray fluorescence spectrometer, XRF). The Ni adhesion amount on the upper surface of the base steel plate is 10 g / m 2 , and the Ni adhesion amount on the lower surface is 30 g / m 2 .

[0098] (3) Heat treatment: The base steel plate on which the nickel layer is formed is heat-treated. The base steel plate on which the nickel layer is formed is put into a heat treatment furnace, and the base steel plate is heat-treated in an atmospheric gas containing N2 with a volume fraction of 95.5% based on the sum of the volumes of N2 and H2 and H2 with a volume fraction of 4.5% and containing 5 ppm of O2 relative to the total volume of the atmospheric gas at a heat treatment temperature higher than 600 °C and 700 °C or lower, and the heat treatment time is more than 0 and less than 1 hour.

[0099] (4) Skin pass rolling and cutting: The base steel plate on which the Ni-Fe alloy layer is formed is put into a skin pass rolling mill, and skin pass rolling is carried out at a reduction rate of 1.2% per pass to manufacture a skin pass rolled material (or nickel-plated heat-treated steel sheet).

[0100] Examples 2 to 10 and Comparative examples 1 to 12

[0101] The nickel-plated heat-treated steel sheet is manufactured in the same manner as in Example 1, except that the base steel plate and heat treatment conditions shown in Table 1 below are used.

[0102] Experimental example

[0103] For the nickel-plated heat-treated steel sheets of the examples and comparative examples, the physical properties were evaluated according to the following experimental examples, and the results are shown in Tables 1 and 2 below.

[0104] (1) Ni content (weight percentage) in the Ni-Fe diffusion layer: For the above examples and comparative examples, a Ni removal solution including an acidic solution and an alkaline solution was optionally used to remove the nickel layer (pure Ni) on the surface, and then the content of Ni contained in the Ni-Fe alloy layer ((Ni / (Ni+Fe))*100) was measured using a scanning electron microscope (SEM) and an energy dispersive spectrometer (EDS) under the following conditions: magnification of 200x, acceleration voltage of 20 kV, and the number of secondary electrons incident on the EDS instrument was set to 2 kCPS or more, and the results are shown in Table 1 below.

[0105] (2) Surface contact resistance (mΩ): The surface contact resistances of the examples and comparative examples were measured and evaluated. Specifically, the surface contact resistance was measured using a surface contact resistance tester (CMT-SR2000N from AIT Co., Ltd.) by the AC 4-terminal method and a measurement current of 10 mA, and the results are shown in Table 2 below.

[0106] (3) Ratio (%) of the fourth crystal plane (220): For the examples and comparative examples, the crystal structure was analyzed by X-ray diffraction (XRD) spectroscopy using to CuKα rays. Specifically, for the examples and comparative examples, the ratio of the volume of the fourth crystal plane (220) to the sum of the volumes of the second crystal plane (111), the third crystal plane (200), the fourth crystal plane (220), the seventh crystal plane (311), and the sixth crystal plane (222) in the face-centered cubic structure of the nickel-plated heat-treated steel sheet was obtained, and the results are shown in Table 2 below.

[0107] (4) Ratio (%) of the third crystal plane (200): For the examples and comparative examples, the crystal structure was analyzed by X-ray diffraction (XRD) spectroscopy using to CuKα rays. Specifically, for the examples and comparative examples, the ratio of the volume of the third crystal plane (200) to the sum of the volumes of the first crystal plane (110), the third crystal plane (200), the fifth crystal plane (221), and the fourth crystal plane (220) in the body-centered cubic structure of the nickel-plated heat-treated steel sheet was obtained, and the results are shown in Table 2 below.

[0108] (5) Corrosion resistance: For the examples and comparative examples, the rust test was carried out according to JIS-H-8617. Specifically, samples of the examples and comparative examples with dimensions of 80 mm × 80 mm (length × width) were prepared. Filter paper for analysis was impregnated with a rust aqueous solution containing 1% by weight of potassium ferrocyanide, 1% by weight of potassium ferricyanide (potassium hexacyanoferrate(III)), and 6% by weight of NaCl, and then this filter paper was attached to the surface of the sample and left standing for 30 minutes. Then, the filter paper was peeled off, and the surface of the sample in contact with the filter paper was visually evaluated for the presence or absence of blue spots, and the results are shown in Table 2 below (A: no rust reaction; B: less than 3 spots; C: 3 or more and less than 10 spots; D: 10 or more spots).

[0109] [Table 1]

[0110]

[0111]

[0112] (1) Heat treatment temperature = (A: higher than or equal to 400 °C and lower than or equal to 500 °C, B: greater than 500 °C and lower than or equal to 600 °C, C: greater than 600 °C and lower than or equal to 700 °C, D: greater than 700 °C and lower than or equal to 800 °C)

[0113] (2) Heat treatment time = (1: greater than 0 and less than 1 hour, 2: greater than or equal to 1 hour and less than 10 hours, 3: greater than or equal to 10 hours and less than 20 hours, 4: greater than or equal to 20 hours)

[0114] [Table 2]

[0115] Category (220) Ratio (%) (200) Ratio (%) Corrosion resistance Surface contact resistance (mΩ) Example 1 5.58 16.75 A 0.73 Example 2 4.52 3.33 A 0.73 Example 3 5.29 5.58 A 0.75 Example 4 4.46 3.99 A 0.69 Example 5 4.11 4.21 A 0.75 Example 6 4.90 3.52 A 0.77 Example 7 4.29 3.92 A 0.73 Example 8 4.50 1.70 A 0.79 Example 9 4.31 4.14 A 0.71 Example 10 4.58 3.88 A 0.74 Comparative example 1 0.88 11.93 D 0.60 Comparative example 2 1.36 10.28 D 0.62 Comparative example 3 1.88 9.56 C 0.62 Comparative example 4 4.39 3.41 B 0.83 Comparative example 5 4.77 3.21 C 0.81 Comparative example 6 4.41 4.27 B 0.65 Comparative example 7 5.22 15.77 C 0.81 Comparative example 8 4.96 3.67 D 0.84 Comparative example 9 4.77 2.15 D 0.83 Comparative example 10 0.92 5.77 C 0.88 Comparative example 11 0.91 1.67 C 1.02 Comparative example 12 1.10 2.53 D 0.81

[0116] Referring to the results in Table 1 and Table 2, it can be seen that Examples 1 to 10 have lower surface contact resistance and excellent corrosion resistance compared with Comparative Examples 1 to 12.

[0117] Figure 2 is a graph showing the X-ray diffraction spectrum analysis results of Example 4, Comparative Example 2, and Comparative Example 10 as representative examples and representative comparative examples. Referring to Figure 2 the results, it can be seen that in Example 4, intensities of 55,000 cps or greater were detected in the diffraction angle (2θ) ranges of 42° to 48° and 50° to 54°, indicating that peaks with greater intensities were detected compared with Comparative Example 2 and Comparative Example 10.

[0118] In Example 4, it can be seen that peak intensities of 4500 cps or greater are detected in the diffraction angle (2θ) range of 72° to 78°, and peak intensities of 6000 cps or greater are detected in the diffraction angle range of 90° to 96°.

[0119] Reference Figure 2 , it can be seen that in the diffraction angle (2θ) ranges of 42° to 48°, 50° to 54°, 72° to 78°, 90° to 96°, and 93° to 99°, the face-centered cubic structure of Example 4 has effective peaks, and these diffraction angle ranges can respectively represent the second crystal plane (111), the third crystal plane (200), the fourth crystal plane (220), the seventh crystal plane (311), and the sixth crystal plane (222).

[0120] In addition, it can be seen that in the diffraction angle (2θ) ranges of 42° to 48°, 63° to 67°, 81° to 84°, and 93° to 99°, the body-centered cubic structure of Example 4 has effective peaks, and these diffraction angle ranges can respectively represent the first crystal plane (110), the third crystal plane (200), the fifth crystal plane (221), and the fourth crystal plane (220).

[0121] So far, the present invention has been examined by focusing on the implementation examples. Those skilled in the art to which the present invention pertains will understand that the present invention can be implemented in modified forms without departing from the basic characteristics thereof. Therefore, the disclosed implementation examples should be considered from an illustrative rather than a restrictive perspective. The scope of the present invention is indicated in the claims, rather than in the above description, and all differences within the equivalent scope should be understood to be included in the present invention.

Claims

1. A nickel-plated heat-treated steel sheet, comprising: A base steel sheet; A nickel layer having a thickness of 0.5 μm to 6 μm, formed on one or more surfaces of the base steel sheet; And A Ni-Fe diffusion layer formed between the base steel sheet and the nickel layer, Wherein the Ni-Fe diffusion layer contains 0.3% to 25% by weight of Ni, and the nickel layer has a surface contact resistance of 0.8 mΩ or less.

2. The nickel-plated heat-treated steel sheet according to claim 1, wherein the base steel sheet has an average roughness (Ra) of 0.5 μm to 1.3 μm and a maximum height (Ry) of 5 μm to 8 μm.

3. The nickel-plated heat-treated steel sheet according to claim 1, wherein the crystal structure of the nickel-plated heat-treated steel sheet includes a face-centered cubic (FCC) structure containing nickel and γ-(Fe,Ni) and a body-centered cubic (BCC) structure of an alloy containing α-Fe and Fe-Ni (kamacite).

4. The nickel-plated heat-treated steel sheet according to claim 3, wherein the face-centered cubic structure of the nickel-plated heat-treated steel sheet includes the fourth crystal plane (220) accounting for 4% or more of the sum of the volumes of the second crystal plane (111), the third crystal plane (200), the fourth crystal plane (220), the seventh crystal plane (311), and the sixth crystal plane (222), and the body-centered cubic structure of the nickel-plated heat-treated steel sheet includes the third crystal plane (200) accounting for 1.5% or more of the sum of the volumes of the first crystal plane (110), the third crystal plane (200), the fifth crystal plane (221), and the fourth crystal plane (220).

5. A method for manufacturing a nickel-plated heat-treated steel sheet, comprising: Forming a nickel layer by plating Ni on one or more surfaces of a base steel sheet; And Heat-treating the base steel sheet and the nickel layer to form a Ni-Fe diffusion layer between the base steel sheet and the nickel layer, Wherein the nickel-plated heat-treated steel sheet includes a base steel sheet, a nickel layer having a thickness of 0.5 μm to 6 μm formed on one or more surfaces of the base steel sheet, and a Ni-Fe diffusion layer formed between the base steel sheet and the nickel layer, The Ni-Fe diffusion layer contains 0.3% to 25% by weight of Ni, and the nickel layer has a surface contact resistance of 0.8 mΩ or less.

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