Nickel plated heat treated steel sheet for battery case having excellent surface corrosion resistance with conductivity

Abstract

The present invention relates to a nickel-plated heat-treated steel sheet for a battery case having excellent surface corrosion resistance and conductivity. In one embodiment, the nickel-plated heat-treated steel sheet for a battery case comprises: a base steel sheet; a nickel layer formed on one or more surfaces of the base steel sheet and having a thickness of 0.5 to 6 μm; and a nickel-iron (Ni-Fe) diffusion layer formed between the base steel sheet and the nickel layer; wherein the iron-nickel diffusion layer contains 3 to 25 weight percent nickel (Ni), and the nickel layer has a surface contact resistance of 0.8 mΩ or less.

Description

Technology Field

[0001] The present invention relates to a nickel-plated heat-treated steel sheet for battery cases having excellent surface corrosion resistance and conductivity. Background Technology

[0003] Nickel-plated heat-treated steel sheets are used as cases for conventional lithium (Li) cylindrical batteries.

[0004] This is because nickel (Ni), the plating element of nickel-plated heat-treated steel sheets, is a more precious metal than iron (Fe), making it advantageous for surface protection, and it offers excellent spot weldability, formability, and corrosion resistance. Additionally, since iron (Fe) has high resistance to alkalis such as lithium ions, the inner surface of the battery case is manufactured with a lower nickel plating amount compared to the outer surface.

[0005] In the manufacturing process of nickel-plated heat-treated steel sheets, the base steel sheet is produced through hot rolling, cold rolling, and annealing processes via heat treatment, which determines the key quality factors of the shape and mechanical properties of the final product. Subsequently, nickel-plated heat-treated steel sheets are manufactured through nickel plating layer formation, diffusion heat treatment, and temper rolling processes. At this time, plating layer characteristics such as the Fe-Ni diffusion layer and the softened nickel layer are determined, and through this, important quality factors for the battery case, such as surface corrosion resistance and conductivity, are determined.

[0006] Nickel-plated heat-treated steel sheets are processed into cases for lithium-ion cylindrical batteries through deep machining and electrically connected to a stack consisting of an anode, a cathode, and a separator via electric resistance welding. In this case, if the surface resistance of the nickel-plated heat-treated steel sheets is high, self-discharge occurs under no-load conditions when used as a cylindrical battery, reducing its lifespan; however, if the surface resistance is low, self-discharge under no-load conditions is reduced, which is advantageous for maintaining the battery's lifespan.

[0007] Furthermore, when manufacturing nickel-plated heat-treated steel sheets, an iron-nickel diffusion layer and a softened nickel layer are formed through diffusion heat treatment; these are necessary to ensure the integrity of the nickel plating layer during the processing of the nickel-plated heat-treated steel sheets.

[0008] In addition, if the iron-nickel diffusion layer of the above-mentioned nickel-plated heat-treated steel sheet is excessively thick, corrosion may occur as iron is exposed due to microcracks in the nickel plating layer that occur during battery case processing. Conversely, if the iron-nickel diffusion layer is excessively thin, corrosion may occur as microcracks in the plating layer expand into delamination during battery case processing. Therefore, it is necessary to optimize the thickness and composition of the iron-nickel diffusion layer of the above-mentioned nickel-plated heat-treated steel sheet when processing the battery case.

[0009] Therefore, it can be said that the surface corrosion resistance and conductivity of nickel-plated heat-treated steel sheets used as cylindrical battery cases have a significant impact on the quality of product characteristics.

[0010] The background technology related to the present invention is disclosed in Japanese Registered Patent Publication No. 4698205 (published June 8, 2011; Title of Invention: Steel plate for battery case, surface-treated steel plate for battery case, battery case and battery). The problem to be solved

[0012] One objective of the present invention is to provide a nickel-plated heat-treated steel sheet for a battery case that has excellent surface conductivity and corrosion resistance, thereby maximizing battery life from external environments.

[0013] Another objective of the present invention is to provide a nickel-plated heat-treated steel sheet for a battery case that is highly effective in preventing a reduction in lifespan caused by short circuits and standby power of the battery.

[0014] Another objective of the present invention is to provide a method for manufacturing the nickel-plated heat-treated steel sheet for the battery case. means of solving the problem

[0016] One aspect of the present invention relates to a nickel-plated heat-treated steel sheet for a battery case. In one embodiment, the nickel-plated heat-treated steel sheet for a battery case comprises: a base steel sheet; a nickel layer formed on one or more surfaces of the base steel sheet and having a thickness of 0.5 to 6 μm; and a nickel-iron (Ni-Fe) diffusion layer formed between the base steel sheet and the nickel layer; wherein the iron-nickel diffusion layer contains 3 to 25 weight percent nickel (Ni), and the nickel layer has a surface contact resistance of 0.8 mΩ or less.

[0017] In one embodiment, the base steel plate may have an average roughness (Ra) of 0.5 to 1.3 μm and a maximum height (Ry) of 5 to 8 μm.

[0018] In one embodiment, the nickel-plated heat-treated steel sheet may include a face-centered cubic structure (FCC) in which the crystal structure includes nickel and γ-(Fe, Ni) and a body-centered cubic structure (BCC) in which the crystal structure includes an alloy of α-Fe and Fe-Ni (kamacite).

[0019] In one embodiment, the face-centered cubic structure of the nickel-plated heat-treated steel sheet may contain at least 4% of the sum of the volumes of the (111), (200), (220), (311) and (222) planes, and the body-centered cubic structure may contain at least 1.5% of the sum of the volumes of the (110), (200), (221) and (220) planes, including the (200) plane.

[0020] Another aspect of the present invention relates to a method for manufacturing a nickel-plated heat-treated steel sheet for a battery case. In one embodiment, the method for manufacturing a nickel-plated heat-treated steel sheet for a battery case comprises the steps of: forming a nickel layer by plating nickel (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 nickel-iron (Ni-Fe) diffusion layer between the base steel sheet and the nickel layer; wherein the nickel-plated heat-treated steel sheet comprises a base steel sheet, a nickel layer formed on one or more surfaces of the base steel sheet having a thickness of 0.5 to 6 μm, and a nickel-iron (Ni-Fe) diffusion layer formed between the base steel sheet and the nickel layer, wherein the nickel-iron diffusion layer contains 3 to 25 weight percent of nickel (Ni), and the nickel layer has a surface contact resistance of 0.8 mΩ or less. Effects of the invention

[0022] The nickel-plated heat-treated steel sheet for a battery case according to the present invention has excellent surface conductivity and corrosion resistance, thereby maximizing battery life from external environments and effectively preventing reduction in lifespan caused by short circuits and standby power. Brief explanation of the drawing

[0024] FIG. 1 shows a nickel-plated heat-treated steel sheet according to one embodiment of the present invention. Figure 2 is a graph of the X-ray diffraction spectrum analysis results of Example 4, Comparative Example 2, and Comparative Example 8. Specific details for implementing the invention

[0025] In describing the present invention, if it is determined that a detailed description of related known technologies or configurations could unnecessarily obscure the essence of the invention, such detailed description will be omitted.

[0026] Furthermore, the terms described below are defined in consideration of their functions in the present invention; since these may vary depending on the intentions or practices of the user or operator, their definitions should be based on the content throughout this specification describing the present invention.

[0028] Nickel-plated heat-treated steel sheets for battery cases

[0029] One aspect of the present invention relates to a nickel-plated heat-treated steel sheet (or heat-treated steel sheet) for a battery case.

[0030] FIG. 1 shows a nickel-plated heat-treated steel sheet according to one embodiment of the present invention. Referring to FIG. 1, a nickel-plated heat-treated steel sheet (100) for a battery case comprises: a base steel sheet (10); a nickel layer (20) formed on one or more surfaces of the base steel sheet (10); and a nickel-iron (Ni-Fe) diffusion layer (30) formed between the base steel sheet (10) and the nickel layer (20).

[0031] In one embodiment, the nickel layer (20) has a thickness of 0.5 to 6 μm. In one embodiment, the iron-nickel diffusion layer contains 3 to 25 weight percent of nickel (Ni), and the nickel layer has a surface contact resistance of 0.8 mΩ or less.

[0033] Base steel plate

[0034] The base steel plate (10) may be a steel plate used for conventional metal plating. In one embodiment, the base steel plate may include carbon (C), silicon (Si), manganese (Mn), phosphorus (P), and iron (Fe).

[0035] For example, the base steel plate may contain, based on the total weight, 0.005 wt% to 0.1 wt% of carbon (C), more than 0 wt% to 0.05 wt% of silicon (Si), 0.1 wt% to 0.6 wt% of manganese (Mn), more than 0 wt% to 0.01 wt% of phosphorus (P), and the remainder being iron (Fe) and other unavoidable impurities. When the above components and content are included, the stiffness and mechanical properties of the base steel plate may be excellent.

[0036] The carbon (C) may be included in an amount of 0.005% to 0.1% by weight relative to the total weight of the base steel plate. When included within this range, mechanical properties such as strength may be excellent. For example, the carbon may be included in an amount of 0.01% to 0.06% by weight.

[0037] The above silicon (Si) may be included in an amount greater than 0 weight% and less than or equal to 0.05 weight% with respect to the total weight of the base steel plate. When included within the above range, the ductility and workability of the base steel plate may be excellent. For example, the above silicon may be included in an amount greater than 0 weight% and less than or equal to 0.02 weight%.

[0038] The above manganese (Mn) may be included in an amount of 0.1% to 0.6% by weight relative to the total weight of the base steel plate. When included within this range, the mechanical properties of the base steel plate, such as strength, may be excellent. For example, the above manganese may be included in an amount of 0.2% to 0.5% by weight.

[0039] The above phosphorus (P) may be included in an amount greater than 0 weight% and less than or equal to 0.01 weight% with respect to the total weight of the base steel plate. When included within this range, the mechanical strength can be excellent while preventing defects such as segregation of the base steel plate.

[0040] As another example, the above base steel plate may be a black plate (BP), cold-rolled steel (CR), or a full-hard material that has not undergone an annealing process after cold rolling during the cold-rolled steel manufacturing process.

[0041] When a cold-rolled steel sheet such as BP or CR is used as the base steel sheet, the main purpose of the alloying heat treatment process after nickel plating the base steel sheet is to alloy the nickel layer and the base steel sheet iron. However, if a full hard material that does not undergo an annealing process after cold rolling is used as the base steel sheet, the annealing of the base steel sheet and the alloying process of the nickel plating layer and the base steel sheet iron can be carried out simultaneously during the alloying heat treatment after nickel plating the base steel sheet.

[0042] In one embodiment, the base steel plate (10) may have an average surface roughness (Ra) of 0.5 to 1.3 μm. Under the above conditions, the adhesion between the base steel plate and the nickel-iron diffusion layer is excellent, the processability and formability of the heat-treated steel plate are excellent, a texture including a face-centered cubic structure (FCC) containing nickel and γ-(Fe, Ni) and a body-centered cubic structure (BCC) containing an alloy of α-Fe and Fe-Ni (kamacite) is easily formed, and the surface contact resistance of the heat-treated steel plate is minimized so that the conductivity properties may be excellent. For example, the average roughness (Ra) of the base steel plate may be 0.6 to 1.3 μm or 0.7 to 1.3 μm.

[0043] In one embodiment, the base steel plate (10) may have a maximum surface height (Ry) of 5 to 8 μm. Under the above conditions, the adhesion between the base steel plate and the nickel-iron diffusion layer is excellent, the processability and formability of the heat-treated steel plate are excellent, a texture including a face-centered cubic structure (FCC) containing nickel and γ-(Fe, Ni) and a body-centered cubic structure (BCC) containing an alloy of α-Fe and Fe-Ni (kamacite) is easily formed, and the surface contact resistance of the heat-treated steel plate is minimized so that the conductivity properties may be excellent. For example, the maximum height (Ry) of the base steel plate may be 5 to 7.5 μm.

[0044] The average roughness (Ra) and maximum height (Ry) of the above base steel plate are specified in the JIS B0601-1994 standard and can each be measured using a stylus-type measuring instrument.

[0045] For example, the average roughness (Ra) and maximum height (Ry) of the above base steel plate can be measured using a contact measuring instrument (Mitutoyo, product name: SV-2100M4) in accordance with the JIS B0601-1994 standard.

[0047] nickel layer

[0048] A nickel layer (20) may be included to ensure corrosion resistance and conductivity of the present invention. Referring to FIG. 1, a nickel-iron diffusion layer (30) is formed on at least one surface of the base steel plate (10), and a nickel layer (20) is formed on the upper surface of the nickel-iron diffusion layer (30).

[0049] For example, the nickel layer above may contain only nickel (Ni).

[0050] In one embodiment, the nickel layer has a thickness of 0.5 to 6 μm. If the thickness of the nickel layer is less than 0.5 μm, the surface contact resistance increases and the conductivity and corrosion resistance decrease, and if 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 to 6 μm.

[0052] Nickel-iron diffusion layer

[0053] The nickel-iron diffusion layer (30) is formed between the base steel plate (10) and the nickel layer (20) of the heat-treated steel plate. The nickel-iron diffusion layer (30) can be formed during the diffusion heat treatment of the nickel layer (20) described later.

[0054] In one embodiment, the nickel-iron diffusion layer (30) may contain 3 to 25 weight percent of nickel (Ni). In one embodiment, the nickel content in the nickel-iron diffusion layer (30) can be measured using an energy dispersive spectrometer (EDS) or an electron probe X-ray microanalysis (EPMA) after removing the nickel layer (20) of the heat-treated steel plate.

[0055] When the nickel in the nickel-iron diffusion layer is less than 3 weight%, the corrosion resistance and formability of the heat-treated steel sheet are reduced, and when the nickel in the nickel-iron diffusion layer is more than 25 weight%, the corrosion resistance of the heat-treated steel sheet is reduced, and the surface contact resistance increases, which may reduce conductivity. For example, the nickel-iron diffusion layer may contain a nickel content of 0.5 to 25 weight% or 1 to 24 weight%.

[0056] Meanwhile, in the above diffusion heat treatment process, the nickel is diffused and dissolved in iron, and a kamacite phase can be formed on the (200) and (221) planes, respectively. In particular, when diffusion heat treatment is performed under conditions greater than the α-Fe + γ-(Fe, Ni) region, a γ-(Fe, Ni) phase is formed, and upon cooling, these can be separated into an iron-rich (Fe-rich) phase and a nickel-rich (Ni-rich) phase, which can be confirmed on the (220) and (311) planes of the face-centered cubic structure, respectively.

[0057] In one embodiment, the heat-treated steel sheet may include a face-centered cubic structure (FCC) in which the crystal structure includes nickel and γ-(Fe, Ni) and a body-centered cubic structure (BCC) in which the crystal structure includes an alloy of α-Fe and Fe-Ni (kamacite).

[0058] The crystal structure of the heat-treated steel sheet can be measured through an X-ray diffraction (XRD) spectrum using CuKα rays of 1.54 to 2.0 Å. For example, the face-centered cubic structure of the heat-treated steel sheet has effective peaks in regions where the diffraction angle (2θ) values ​​are 42 to 48˚, 50 to 54˚, 72 to 78˚, 90 to 96˚, and 93 to 99˚, respectively, which may represent planes (111), (200), (220), (311), and (222), respectively.

[0059] In one sphere, the face-centered cubic structure of the heat-treated steel sheet may include at least 4% of the (220) plane among the sum of the volumes of the (111), (200), (220), (311), and (222) planes. Under the above conditions, the nickel-plated heat-treated steel sheet may have excellent corrosion resistance and excellent conductivity by minimizing surface contact resistance. For example, the (220) plane may include 4 to 10%, 4 to 8%, or 4 to 6%.

[0060] For example, the body-centered cubic structure of the heat-treated steel plate has effective peaks in regions where the diffraction angle (2θ) value is 42 to 48˚, 63 to 67˚, 81 to 84˚, and 93 to 99˚, respectively, which may represent planes (110), (200), (221), and (220), respectively.

[0061] In one embodiment, the body-centered cubic structure of the heat-treated steel sheet may include at least 1.5% of the (200) plane among the sum of the volumes of the (110), (200), (221), and (220) planes. Under these conditions, the nickel-plated heat-treated steel sheet may have excellent corrosion resistance and excellent conductivity by minimizing surface contact resistance. For example, the (200) plane may include 1.5 to 20%, 1.5 to 18%, 3 to 17%, or 3 to 15%.

[0062] In one embodiment, the nickel-plated heat-treated steel sheet may have (220) and (311) planes of the face-centered cubic structure of the heat-treated steel sheet composed of nickel and γ-(Fe, Ni), and (200) and (221) planes of the body-centered cubic structure of the heat-treated steel sheet may be composed of an alloy of α-Fe and Fe-Ni.

[0063] In one embodiment, the nickel-plated heat-treated steel sheet has a surface contact resistance of 0.8 mΩ or less. Under the above surface resistance condition, self-discharge in a no-load state is reduced, which may be advantageous for maintaining lifespan. If the surface contact resistance of the heat-treated steel sheet exceeds 0.8 mΩ, conductivity is reduced, and when used as a cylindrical battery, self-discharge occurs in a no-load state, which may reduce lifespan. For example, the surface resistance of the heat-treated steel sheet may be 0.2 to 0.8 mΩ or 0.5 to 0.8 mΩ.

[0064] For example, the surface contact resistance of the above nickel-plated heat-treated steel sheet can be measured using a surface contact resistance measuring tester (AIT Inc., product name: CMT-SR2000N) under the AC 4-terminal method and a measurement current of 10mA.

[0066] Method for manufacturing nickel-plated heat-treated steel sheets

[0067] Another aspect of the present invention relates to a method for manufacturing the nickel-plated heat-treated steel sheet. In one embodiment, the method for manufacturing the nickel-plated heat-treated steel sheet comprises: (S10) a step of forming a nickel layer by plating nickel (Ni) on one or more surfaces of a base steel sheet; and (S20) a step of heat-treating the base steel sheet and the nickel layer to form a nickel-iron (Ni-Fe) diffusion layer between the base steel sheet and the nickel layer.

[0069] (S10) Nickel layer formation step

[0070] The above step is to form a nickel layer by plating nickel (Ni) on one or more surfaces of a base steel plate. In one embodiment, the base steel plate may undergo a pretreatment process before forming a nickel layer by electroplating a nickel bath. For example, a pretreatment process including conventional degreasing, rinsing, and pickling processes may be performed, but is not particularly limited thereto.

[0071] The above base steel plate may be the same as that described above.

[0072] In one embodiment, the base steel plate (10) may have an average surface roughness (Ra) of 0.5 to 1.3 μm. The adhesion between the base steel plate and the nickel-iron diffusion layer is excellent, and the processability and formability are excellent. The crystal structure of the heat-treated steel plate is formed to include a face-centered cubic structure (FCC) containing nickel and γ-(Fe, Ni) and a body-centered cubic structure (BCC) containing an alloy of α-Fe and Fe-Ni, and the surface contact resistance of the heat-treated steel plate is minimized to provide excellent conductivity. For example, the average surface roughness (Ra) of the base steel plate may be 0.6 to 1.3 μm or 0.7 to 1.3 μm.

[0073] In one embodiment, the base steel plate (10) may have a maximum surface height (Ry) of 5 to 8 μm. Under the above conditions, the adhesion between the base steel plate and the nickel-iron diffusion layer is excellent, and the processability and formability are excellent. The crystal structure of the heat-treated steel plate is formed to include a face-centered cubic structure (FCC) containing nickel and γ-(Fe, Ni) and a body-centered cubic structure (BCC) containing an alloy of α-Fe and Fe-Ni, and the surface contact resistance of the heat-treated steel plate is minimized to ensure excellent conductivity. For example, the maximum height (Ry) of the base steel plate may be 5 to 7.5 μm.

[0074] In one embodiment, the nickel (Ni) plating may be performed using electroplating (or electrolytic plating). For example, the nickel plating may be performed using a nickel plating solution (or nickel plating bath) by a conventional electroplating method. For example, the plating solution may use a watt bath and a sulfamate bath, etc.

[0075] In one embodiment, the above Watt bath may contain 150 to 400 g / L of nickel sulfate (NiSO4), 20 to 60 g / L of nickel chloride (NiCl2), 10 to 50 g / L of boric acid (H3BO3), and the remainder being water, based on 1 L of plating bath. When electroplating using the above plating bath, the corrosion resistance and conductivity of the heat-treated steel sheet may be excellent, but are not limited to the above plating bath conditions.

[0076] In one embodiment, electroplating using the plating bath is performed at a pH of 3.0 to 4.8, a plating bath temperature of 45 to 70°C, and a current density of 2 to 40 A / dm² 2 It may be carried out under the above conditions, but is not limited thereto. When electroplating under the above plating bath conditions, the corrosion resistance and conductivity of the heat-treated steel sheet may be excellent.

[0077] Additives may be used to provide gloss to the nickel plating layer. For example, additives that do not contain sulfur components may be used.

[0078] In one embodiment, the plating amount of nickel (Ni) during the nickel electroplating is 2.7 to 53.4 g / m² based on one side of the base steel sheet. 2 It is possible. Under the above plating amount conditions, the heat-treated steel sheet may have excellent processability, corrosion resistance, and conductivity.

[0080] (S20) Heat treatment step

[0081] The above step is to heat-treat (diffusion heat treatment) the base steel plate and the nickel layer to form a nickel-iron (Ni-Fe) diffusion layer between the base steel plate and the nickel layer.

[0082] Through the above heat treatment process, a diffusion layer containing nickel-iron (Fe) is formed between the nickel layer and the base steel plate, and the nickel (Ni) layer and the nickel-iron (Ni-Fe) diffusion layer are softened to have excellent processability, and the heat-treated steel plate may have excellent corrosion resistance and conductivity.

[0083] In one embodiment, the heat treatment may be performed at 400 to 800°C. When the heat treatment is performed under these conditions, the corrosion resistance and conductivity of the heat-treated steel sheet may be excellent. In addition, after the nickel-iron heat treatment under these conditions, equipment wear can be minimized during processes such as temper rolling, slitting, and battery case forming, thereby reducing the number of equipment replacements and ultimately realizing improved productivity, reduced production costs, and improved quality.

[0084] In one embodiment, the heat treatment may be performed for 10 minutes to 48 hours. When the heat treatment is performed under these conditions, the corrosion resistance and conductivity of the heat-treated steel plate may be excellent.

[0085] The atmosphere gas used during the above heat treatment is not particularly limited. For example, the atmosphere gas may include one or more of nitrogen (N2) and hydrogen (H2). If the above mixed gas is used, it may contain 70 to 98 volume% of nitrogen and 2 to 30 volume% of hydrogen based on the sum of the volumes of nitrogen and hydrogen. For example, it may contain 80 to 97 volume% of nitrogen and 3 to 20 volume% of hydrogen.

[0086] In one embodiment, the oxygen concentration may be 1.0 to 500 ppm, for example, 5.0 to 400 ppm, relative to the total volume of the atmosphere gas during the heat treatment.

[0087] In one embodiment, the method for manufacturing the heat-treated steel plate may further include the step of manufacturing a rolled material by temper rolling the base steel plate having the nickel-iron diffusion layer (S30) formed thereon after the step of forming the nickel-iron diffusion layer (S20).

[0089] (S30) Tempering rolling stage

[0090] The above step is to manufacture a skin-pass rolled material (or nickel-plated heat-treated steel sheet) by skin-pass rolling the base steel sheet on which the nickel-iron diffusion layer is formed. The skin-pass rolling may be performed to control the thickness, shape, and surface roughness of the steel sheet, to minimize residual stress in the heat-treated steel sheet, and to ensure uniform material properties.

[0091] The above rolling can be performed by feeding the base steel plate formed with the nickel-iron diffusion layer into a rolling mill and using the upper rolling roll (Work roll) and lower rolling roll of the rolling mill for temper rolling.

[0092] In one embodiment, the temper rolling can be performed under conditions of a reduction rate of 0.3 to 2.0% per pass. When temper rolling under these conditions, the residual stress of the steel sheet is minimized, and the crystal structure of the temper rolled material can be formed to include a face-centered cubic structure (FCC) containing nickel and γ-(Fe, Ni) and a body-centered cubic structure (BCC) containing an alloy of α-Fe and Fe-Ni.

[0093] The above-described tempered rolled material (or nickel-plated heat-treated steel sheet) comprises a nickel layer with a thickness of 0.5 to 6 μm formed on one or more surfaces of a base steel sheet and an iron-nickel (Fe-Ni) diffusion layer formed between the base steel sheet and the nickel layer, wherein the nickel layer has a surface contact resistance of 0.8 mΩ or less and the iron-nickel diffusion layer contains 3 to 25 weight percent nickel (Ni). The base steel sheet, nickel layer, and iron-nickel diffusion layer of the above-described tempered rolled material may be identical to the nickel-plated heat-treated steel sheet described above.

[0094] In one embodiment, the tempered rolled material (or nickel-plated heat-treated steel sheet) comprises a face-centered cubic structure (FCC) containing nickel and γ-(Fe, Ni) and a body-centered cubic structure (BCC) containing an alloy of α-Fe and Fe-Ni, wherein the face-centered cubic structure comprises at least 4% of the sum of the volumes of the (111), (200), (220), (311), and (222) planes, and the body-centered cubic structure may comprise at least 1.5% of the sum of the volumes of the (110), (200), (221), and (220) planes.

[0095] In one embodiment, the (220) and (311) planes of the face-centered cubic structure of the tempered rolled material (or nickel-plated heat-treated steel sheet) contain nickel and γ-(Fe, Ni), and the (200) and (221) planes of the body-centered cubic structure of the tempered rolled material (nickel-plated heat-treated steel sheet) may contain an alloy of α-Fe and Fe-Ni.

[0096] In one embodiment, the tempered rolled material (or nickel-plated heat-treated steel sheet) has a surface contact resistance of 0.8 mΩ or less. Under the above surface resistance condition, self-discharge in the no-load state is reduced, which may be advantageous for maintaining lifespan. If the surface contact resistance of the heat-treated steel sheet exceeds 0.8 mΩ, conductivity is reduced, and when used as a cylindrical battery, self-discharge occurs in the no-load state, which may reduce lifespan. For example, the surface contact resistance of the heat-treated steel sheet may be 0.2 to 0.8 mΩ or 0.5 to 0.8 mΩ.

[0097] In one embodiment, the method for manufacturing the heat-treated steel plate may further include, after the temper rolling step (S30), a step (S40) of slitting the temper rolled material to manufacture a steel plate strip.

[0099] (S40) Slit processing step

[0100] The above step is a step of manufacturing a steel plate strip by slitting the above temper-rolled material. The slitting can be performed by using a slitting blade in the rolling direction of the product after the temper-rolling process, according to the requirements of the customer, to slit from wide to narrow.

[0101] In one embodiment, after the slit processing step, the process may further include a step of forming the processed strip into a case shape. For example, it may be formed into a case shape by press forming.

[0102] The nickel-plated heat-treated steel sheet produced by the above method for manufacturing nickel-plated heat-treated steel sheets has excellent surface corrosion resistance and conductivity, and can be highly effective in preventing short circuits and reduced lifespan due to standby power of the secondary battery when electric resistance welding with a stack consisting of an anode, a cathode, and a separator.

[0104] Hereinafter, the structure and operation of the present invention will be explained in more detail through preferred embodiments. However, these are presented as preferred examples of the present invention and should not be interpreted in any way as limiting the present invention. Details not described herein can be sufficiently technically inferred by those skilled in the art, so such descriptions will be omitted.

[0106] Examples and Comparative Examples

[0107] Example 1

[0108] (1) Preparation of base steel plate: A slab containing 0.03 wt% (300 ppm) carbon (C), greater than 0 and less than 0.001 wt% (10 ppm) silicon (Si), 0.31 wt% (3100 ppm) manganese (Mn), greater than 0 and less than 0.001 wt% (10 ppm) phosphorus (P), and the remainder being iron (Fe) and other unavoidable impurities was reheated and subjected to hot rolling and cold rolling to prepare a base steel plate (carbon steel cold-rolled steel plate) with a thickness of 0.30 mm. In accordance with JIS B0601-1994, the base steel plate measured using a contact measuring instrument (Mitutoyo, product name: SV-2100M4) had an average roughness (Ra) of 1.04 μm and a maximum height (Ry) of 7.16 μm.

[0109] (2) Formation of Nickel Layer: The base steel plate was pretreated by alkaline degreasing, alkaline electrolytic degreasing, and pickling (aqueous sulfuric acid solution), and then nickel electroplating was performed. Specifically, a plating bath was prepared containing 250 g / L of nickel sulfate (NiSO4), 40 g / L of nickel chloride (NiCl2), 40 g / L of boric acid (H3BO3), and the remainder being water, at a temperature of 60°C and a pH of 3.2 to 4.5, and a nickel layer was formed by performing electroplating under conditions of a current density of 10 ASD. At this time, the amount of nickel deposited was measured using a fluorescence X-ray measuring device (X-ray fluorescence analyzer, XRF), and the amount of nickel deposited on the upper surface of the base steel plate was 10 g / m²2 and the nickel coating amount on the lower surface is 30 g / m² 2 It was.

[0110] (3) Heat treatment: The base steel plate having the nickel layer formed thereon was heat treated. The base steel plate having the nickel layer formed thereon was loaded into a heat treatment furnace and heat treatment was performed in an atmosphere gas containing 95.5 volume% nitrogen and 4.5 volume% hydrogen relative to the sum of the volumes of nitrogen (N2) and hydrogen (H2), and containing 5 ppm oxygen (O2) relative to the total volume of the atmosphere gas, under the conditions of: heat treatment temperature: greater than 600°C and less than 700°C and heat treatment time: greater than 0 and less than 1 hour.

[0111] (4) Temper rolling and slit processing: The base steel plate with the nickel-iron alloy layer formed above was fed into a temper rolling mill and temper rolled for one pass at a reduction rate of 1.2% to produce a temper rolled material (or nickel-plated heat-treated steel plate).

[0113] Examples 2–10 and Comparative Examples 1–12

[0114] A nickel-plated heat-treated steel plate was manufactured using the same method as Example 1 above, except that the base steel plate under the conditions of Table 1 below and the heat treatment conditions were applied.

[0116] Test example

[0117] For the nickel-plated heat-treated steel sheets of the above examples and comparative examples, physical properties were evaluated according to the following test examples, and the results are shown in Tables 1 and 2 below.

[0118] (1) Nickel (Ni) content (weight%) in the nickel-iron (Ni-Fe) diffusion layer: For the above examples and comparative examples, the nickel layer (pure Ni) on the surface was selectively removed using a Ni removal solution containing an acidic solution and an alkaline solution, and then the nickel (Ni) content ((Ni / (Ni+Fe))*100) contained in the nickel-iron alloy layer was measured using a scanning electron microscope (SEM) and an energy dispersive spectrometer (EDS) with a magnification of 200x, an acceleration voltage of 20kV, and an EDS equipment with a secondary energy of 2kCPS or more. The results are shown in Table 1 below.

[0119] (2) Surface contact resistance (mΩ): The surface contact resistance was measured and evaluated for the examples and comparative examples. Specifically, the surface contact resistance was measured using a surface contact resistance tester (AIT Inc., product name: CMT-SR2000N) under AC 4-terminal method and a measurement current of 10 mA, and the results are shown in Table 2 below.

[0120] (3) (220) Ratio (%) = The crystal structure of the examples and comparative examples was analyzed through X-ray diffraction (XRD) spectra using CuKα rays of 1.54 to 2.0 Å. Specifically, the ratio of the (220) plane to the sum of the volumes of the (111), (200), (220), (311) and (222) planes in the face-centered cubic structure of the nickel-plated heat-treated steel sheets of the examples and comparative examples was derived, and the results are shown in Table 2 below.

[0121] (4) (200) Ratio (%) = The crystal structure of the examples and comparative examples was analyzed through X-ray diffraction (XRD) spectra using CuKα rays of 1.54 to 2.0 Å. Specifically, the ratio of the (200) plane to the sum of the volumes of the (110), (200), (221), and (220) planes in the body-centered cubic structure of the nickel-plated heat-treated steel sheets of the examples and comparative examples was derived, and the results are shown in Table 2 below.

[0122] (5) Corrosion resistance: A peroxyl test was performed on the examples and comparative examples based on the JIS-H-8617 standard. Specifically, specimens of the examples and comparative examples were prepared with dimensions of 80 mm x 80 mm (width x height). An aqueous peroxyl solution containing 1 wt% potassium ferrocyanide, 1 wt% potassium ferrocyanide (potassium hexacyanoferrate(III)), and 6 wt% NaCl was impregnated onto an analytical filter paper. The filter paper was then attached to the surface of the specimen and left for 30 minutes. Afterward, the filter paper was peeled off, and the presence or absence of blue spots on the surface of the specimen in contact with the filter paper was visually evaluated. The results are shown in Table 2 below (A: no peroxyl reaction, B: fewer than 3 reactions, C: 3 or more but less than 10 reactions, D: 10 or more reactions).

[0123]

[0124] (1) Heat treatment temperature = (A: 400℃ or higher and 500℃ or lower, B: 500℃ or higher and 600℃ or lower, C: 600℃ or higher and 700℃ or lower, D: 700℃ or higher and 800℃ or lower).

[0125] (2) Heat treatment time = (1: greater than 0 and less than 1 hour, 2: 1 hour or more and less than 10 hours, 3: 10 hours or more and less than 20 hours, 4: 20 hours or more).

[0126]

[0127] Referring to the results of Tables 1 and 2 above, it was found that Examples 1 to 10 of the present invention had lower surface contact resistance and superior corrosion resistance compared to Comparative Examples 1 to 10.

[0128] Figure 2 below is a graph of the X-ray diffraction spectrum analysis results of Example 4, Comparative Example 2, and Comparative Example 8 among the examples and comparative examples. Referring to the results in Figure 2, it was found that in Example 4, an intensity of 55,000 cps or higher was detected in the diffraction angle (2θ) regions of 42~48˚ and 50~54˚, respectively, during X-ray diffraction analysis, and that a peak of higher intensity was detected compared to Comparative Example 2 and Comparative Example 8.

[0129] And in the above Example 4, it was found that an intensity peak of 4,500 cps or more was detected in the diffraction angle (2θ) region of 72 to 78˚, and an intensity peak of 6,000 cps or more was detected in the region of 90 to 96˚.

[0130] Referring to FIG. 2 above, it was found that the face-centered cubic structure of Example 4 has effective peaks in regions where the diffraction angle (2θ) values ​​are 42–48˚, 50–54˚, 72–78˚, 90–96˚, and 93–99˚, respectively, and these represent planes (111), (200), (220), (311), and (222), respectively.

[0131] In addition, it was found that the body-centered cubic structure of Example 4 has effective peaks in regions where the diffraction angle (2θ) values ​​are 42–48˚, 63–67˚, 81–84˚, and 93–99˚, respectively, and these represent planes (110), (200), (221), and (220), respectively.

[0133] The present invention has been described above with reference to embodiments. Those skilled in the art will understand that the present invention may be embodied in modified forms without departing from the essential characteristics of the invention. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the invention is defined by the claims, not by the foregoing description, and all variations within the scope of equivalents should be interpreted as being included in the invention. Explanation of the symbols

[0135] 10: Base steel plate 20: Nickel layer 30: Nickel-iron diffusion layer 100: Nickel-plated heat-treated steel sheet

Claims

Claim 1 A nickel-plated heat-treated steel plate comprising: a base steel plate; a nickel layer formed on one or more surfaces of the base steel plate and having a thickness of 0.5 to 6 μm; and a nickel-iron (Ni-Fe) diffusion layer formed between the base steel plate and the nickel layer; wherein the nickel-iron diffusion layer contains 3 to 25 weight% of nickel (Ni), the nickel layer has a surface contact resistance of 0.8 mΩ or less, the base steel plate has an average roughness (Ra) of 0.7 to 1.3 μm and a maximum height (Ry) of 5 to 7.5 μm, and is heat-treated at 600 to 700°C for more than 0 hours and less than 1 hour. Claim 2 delete Claim 3 A nickel-plated heat-treated steel sheet according to claim 1, characterized in that the nickel-plated heat-treated steel sheet comprises a face-centered cubic structure (FCC) containing nickel and γ-(Fe, Ni) and a body-centered cubic structure (BCC) containing an alloy of α-Fe and Fe-Ni (kamacite). Claim 4 In paragraph 3, the face-centered cubic structure of the nickel-plated heat-treated steel sheet comprises at least 4% of the sum of the volumes of the (111), (200), (220), (311) and (222) faces, and the body-centered cubic structure comprises at least 1.5% of the sum of the volumes of the (110), (200), (221) and (220) faces, wherein the nickel-plated heat-treated steel sheet. Claim 5 A method for manufacturing a nickel-plated heat-treated steel plate comprising: a step of forming a nickel layer by plating nickel (Ni) on one or more surfaces of a base steel plate; and a step of heat-treating the base steel plate and the nickel layer at 600 to 700°C for more than 0 and less than 1 hour to form a nickel-iron (Ni-Fe) diffusion layer between the base steel plate and the nickel layer; wherein the nickel-plated heat-treated steel plate comprises a base steel plate, a nickel layer formed on one or more surfaces of the base steel plate having a thickness of 0.5 to 6 μm, and a nickel-iron (Ni-Fe) diffusion layer formed between the base steel plate and the nickel layer, wherein the nickel-iron diffusion layer contains 3 to 25 weight% of nickel (Ni), wherein the nickel layer has a surface contact resistance of 0.8 mΩ or less, and the base steel plate has an average roughness (Ra) of 0.7 to 1.3 μm and a maximum height (Ry) of 5 to 7.5 μm.

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