Surface-treated steel plate

Abstract

A surface-treated steel sheet according to one embodiment of the present invention comprises a base steel sheet and a plating layer containing Ni and W provided on the surface of the base steel sheet, wherein the ratio of the average value of W concentration to the sum of the average value of Ni concentration, the average value of W concentration, and the average value of Fe concentration in a unit atomic % within a region from the outermost surface of the plating layer to a depth of 150 nm is 2.0 to 20.0 atomic %, and the ratio of the average value of W concentration to the sum of the average value of Ni concentration, the average value of W concentration, and the average value of Fe concentration in a unit atomic % within a region from a depth of 150 nm to a depth of 300 nm within the plating layer is 0.7 times or less of the ratio in the region from the outermost surface of the plating layer to a depth of 150 nm.

Description

Technology Field

[0001] The present invention relates to a surface-treated steel plate.

[0002] The present application claims priority based on patent application No. 2021-065675 filed in Japan on April 8, 2021, and incorporates the contents thereof herein by reference. Background Technology

[0003] Lithium-ion rechargeable batteries (LIBs) are widely used as power sources for electric vehicles. Lithium-ion rechargeable battery cans are classified into cylindrical and prismatic types. Cylindrical battery cans are used with the can connected to the negative electrode. Therefore, nickel-plated steel sheets and stainless steel (SUS) are used as materials for cylindrical lithium-ion rechargeable battery cans. When the can is connected to the negative electrode, aluminum cannot be used as a can material because it absorbs lithium. On the other hand, since prismatic can types are used in neutral environments, aluminum and stainless steel are currently used as materials.

[0004] However, there is a demand to replace aluminum in battery cans with other materials to further enhance safety, such as heat resistance. While SUS is superior to aluminum in terms of heat resistance, it lags behind aluminum in terms of resistance to LIB electrolytes (LIB electrolyte resistance).

[0005] Surface-treated steel sheets are considered as candidates for battery can materials to replace aluminum and SUS. The advantages of steel battery cans include high heat resistance, high strength which allows for weight reduction through thinning, improved volumetric energy density, and low cost.

[0006] However, conventional surface-treated steel sheets, such as Ni-plated steel sheets, have a problem in that their resistance to LIB electrolytes lags behind that of aluminum and SUS. In order to use steel sheets as materials for automotive battery cans, it is desirable to increase the resistance to LIB electrolytes of the steel sheets to a level equivalent to or close to that of aluminum.

[0007] As a technology regarding steel sheets for battery cans, Patent Document 1 discloses a technology in which nickel plating is performed on the side of the steel sheet that becomes the inner surface of the battery container, or after nickel plating, heat treatment is performed in a non-oxidizing atmosphere, and then nickel-tungsten alloy plating is performed, or after nickel plating, nickel-tungsten alloy plating is performed, and then heat treatment is performed in a non-oxidizing atmosphere to form a plated steel sheet for a battery container, and then the steel sheet is formed and processed into a battery container and applied to a battery.

[0008] Patent Document 2 discloses a Ni-containing surface-treated steel plate for a container formed by press forming, comprising a steel plate having a first surface that becomes the outer side of the container after press forming, a Ni-containing layer disposed on the first surface of the steel plate, and a Ni-W alloy plating layer disposed on the Ni-containing layer; wherein the Ni-containing layer has an Fe-Ni diffusion alloy layer and the amount of Ni contained in the Ni-containing layer is 5 g / m² or more and 89 g / m² or less; the thickness of the Ni-W alloy plating layer is 0.02 μm or more and 2 μm or less; and the concentration of W in the Ni-W alloy plating layer is 10% or more and 65% or less in mass%.

[0009] Patent document 3 discloses a steel plate for a non-aqueous electrolyte secondary battery case, characterized by comprising: a steel plate; and a Ni-W-Fe alloy plating layer formed on the surface of the steel plate, containing a Ni-W-Fe alloy, and forming the inner surface of the non-aqueous electrolyte secondary battery case. Prior art literature

[0010] Japanese Patent Publication No. 2007-51325, International Publication No. 2012 / 137823, International Publication No. 2017 / 006834 The problem to be solved

[0011] However, in Patent Documents 1 and 2, no special examination was conducted regarding the resistance to LIB electrolytes, nor was a configuration for it disclosed.

[0012] In Patent Document 3, the deterioration of battery performance and corrosion of the case associated with metal leaching have been investigated. However, the applications of the surface-treated steel sheet disclosed in Patent Document 3 are mainly for small consumer mobile devices. For example, in battery cans constituting large batteries such as automotive batteries, even better resistance to LIB electrolyte than that of the surface-treated steel sheet disclosed in Patent Document 3 is required.

[0013] Taking into account the circumstances described above, the present invention aims to provide a surface-treated steel sheet with significantly better resistance to LIB electrolyte than conventional SUS sheets and Ni-plated steel sheets. means of solving the problem

[0014] The gist of the present invention is as follows.

[0015] (1) A surface-treated steel sheet according to one embodiment of the present invention comprises a base steel sheet and a plating layer containing Ni and W provided on the surface of the base steel sheet, wherein the ratio of the average value of W concentration to the sum of the average value of Ni concentration, the average value of W concentration, and the average value of Fe concentration in a unit atomic % within a region from the outermost surface of the plating layer to a depth of 150 nm is 2.0 to 20.0 atomic %, and the ratio of the average value of W concentration to the sum of the average value of Ni concentration, the average value of W concentration, and the average value of Fe concentration in a region from the depth of 150 nm to a depth of 300 nm within the plating layer is 0.7 times or less of the ratio in the region from the outermost surface of the plating layer to a depth of 150 nm.

[0016] (2) In the surface-treated steel plate described in (1) above, the amount of Ni included in the plating layer may be 2.6 to 35.6 g / m².

[0017] (3) In the surface-treated steel plate described in (1) or (2) above, the base steel plate may be low-carbon aluminum killed steel or IF steel. Effects of the invention

[0018] According to the present invention, a surface-treated steel sheet with even better resistance to LIB electrolyte than conventional SUS sheets and Ni-plated steel sheets can be provided. Brief explanation of the drawing

[0019] FIG. 1 is a schematic cross-sectional view of a surface-treated steel plate according to one embodiment of the present invention. Figure 2 is a conceptual diagram of the average value of W concentration in the W high concentration layer and the W low concentration layer. FIG. 3 is a flowchart of a method for manufacturing a surface-treated steel sheet according to another embodiment of the present invention. Figure 4 is a diagram illustrating the draw bead test of an example. Figure 5a shows the surface analysis results of a level 1 surface-treated steel plate after a draw bead test. Figure 5b shows the surface analysis results of a level 3 surface-treated steel plate after a draw bead test. Specific details for implementing the invention

[0020] The inventors have repeatedly examined means to improve the LIB electrolyte resistance of surface-treated steel sheets. As a result, it was determined that making the plating layer of the surface-treated steel sheet an alloy containing Ni-W is electrochemically effective for improving LIB electrolyte resistance.

[0021] However, the inventors also discovered that merely increasing the electrochemical properties of the Ni plating layer by adding W to the Ni plating bath is not sufficient to sufficiently improve the LIB electrolyte resistance of the surface-treated steel sheet. It was presumed that this reason is that the Ni-W-based plating is hard and prone to cracking. Fine cracks are prone to occur in hard plating. The inventors believed that these cracks may be impairing the LIB electrolyte resistance of the surface-treated steel sheet.

[0022] Based on the findings described above, the inventors conducted further investigations. As a result, the inventors discovered that forming a plating layer containing Ni and W on the surface of a base steel sheet, and providing a high-concentration W layer near the surface of the plating layer and a low-concentration W layer located beneath it, is highly effective for improving resistance to LIB electrolytes. This is presumed to be because the low-concentration W layer suppresses the propagation of cracks from the surface of the surface-treated steel sheet toward the interior.

[0023] A surface-treated steel plate (1) according to one embodiment of the present invention obtained based on the above findings, as shown in FIG. 1, comprises a base steel plate (11) and a plating layer (12) containing Ni and W provided on the surface of the base steel plate (11), wherein the ratio of the average value of W concentration to the sum of the average value of Ni concentration, the average value of W concentration, and the average value of Fe concentration in a unit atomic % within a region (W high concentration layer (121)) from the outermost surface of the plating layer (12) to a depth of 150 nm is 2.0 to 20.0 atomic %, and the ratio of the average value of W concentration to the sum of the average value of Ni concentration, the average value of W concentration, and the average value of Fe concentration in a unit atomic % within a region (W low concentration layer (122)) from a depth of 150 nm to a depth of 300 nm is 0.7 times or less of the ratio in the region from the outermost surface of the plating layer to a depth of 150 nm. Hereinafter, the surface-treated steel plate (1) according to the present embodiment will be described in detail.

[0024] (base steel plate (11))

[0025] The surface-treated steel plate (1) has a base steel plate (11). The base steel plate (11) is a steel plate that serves as the base for the surface-treated steel plate (1). The composition, plate thickness, and metal structure of the base steel plate (11) are not particularly limited. When the surface-treated steel plate (1) is used as a material for a battery container, for example, the base steel plate (11) is preferably made of low-carbon aluminum killed steel and IF steel (Interstitial Free Steel / ultra-low carbon steel). Specific examples of the chemical composition (unit: mass%) of the base steel plate (11) are as follows.

[0026] (Example 1) Low-carbon aluminum killed steel

[0027] C: 0.057, Si: 0.004, Mn: 0.29, P: 0.014, S: 0.007, Al: 0.050, Cu: 0.034, Ni: 0.021, remainder: contains iron and impurities.

[0028] (Example 2) IF steel

[0029] C: 0.004, Si: 0.01, Mn: 0.16, P: 0.013, S: 0.006, Al: 0.029, Cu: 0.027, Ni: 0.022, Ti: 0.013, remainder: contains iron and impurities.

[0030] (Example 3) IF steel

[0031] C: 0.0012, Si: <0.01, Mn: 0.16, P: 0.013, S: 0.006, Al: 0.029, Cu: 0.027, Ni: 0.022, Ti: 0.020, remainder: contains iron and impurities.

[0032] The thickness of the base steel plate (11) is not particularly limited. When the surface-treated steel plate (1) is used, for example, as a material for a battery container, it is preferable to make the thickness of the base steel plate (11) 0.15 to 2.0 mm.

[0033] (Plating layer (12))

[0034] The surface-treated steel plate (1) according to the present embodiment has a plating layer (12) containing Ni and W provided on the surface of the base steel plate (11).

[0035] The plating layer (12) may be an alloy plating layer formed by the diffusion of Fe from the base steel plate (11) into a plating layer composed of Ni and W. That is, the plating layer (12) may include Ni, Fe, and W. The alloy plating layer may be a fully diffused plating layer in which Fe is diffused to its surface, or a partially diffused plating layer in which Fe is not diffused to its surface. When the plating layer (12) is a partially diffused plating layer, the Fe concentration is considered to be 0 atomic% in the measurement of the “ratio of average value of W concentration” described later.

[0036] The plating layer (12) may include elements other than Ni, Fe, and W (e.g., impurity elements). Additionally, the plating layer (12) may be provided on only one surface of the base steel plate (11) or on both surfaces. When the plating layer (12) is provided on both surfaces of the base steel plate (11), the Ni attachment amount described below refers to the Ni attachment amount per one side of the surface-treated steel plate (1).

[0037] In addition, among the plating layer (12), the regions other than the W high concentration layer (121) and W low concentration layer (122) described later may be configured in the same way as a conventional surface-treated steel plate (e.g., Ni-plated steel plate for battery cans and alloyed Ni-plated steel plate, etc.). This is because the LIB electrolyte resistance of the surface-treated steel plate (1) according to this embodiment is achieved by the W high concentration layer (121) and the W low concentration layer (122).

[0038] (W high concentration layer (121) of the plating layer (12))

[0039] In the region from the outermost surface of the plating layer (12) to a depth of 150 nm, the ratio of the average value of W concentration to the sum of the average value of Ni concentration in unit atomic %, the average value of W concentration, and the average value of Fe concentration (including 0 atomic %) is 2.0 to 20.0 atomic %. Hereinafter, the region from the outermost surface of the plating layer (12) to a depth of 150 nm is referred to as the “W high concentration layer (121).” In addition, the ratio of the average value of W concentration to the sum of the average value of Ni concentration in unit atomic %, the average value of W concentration, and the average value of Fe concentration is referred to as the “W ratio.” As described above, when Fe is not diffused to the surface of the plating layer (12) and the W high concentration layer (121) and / or the W low concentration layer (122) described later does not contain Fe, the Fe concentration is considered to be 0 atomic% when calculating the W ratio of the W high concentration layer (121) and / or the W low concentration layer (122).

[0040] The average values ​​of Ni concentration, W concentration, and Fe concentration in the W high concentration layer (121) are obtained by continuously measuring the atomic concentrations of Ni, W, and Fe from the surface of the plating layer (12) toward the interior using XPS (X-ray Photoelectron Spectroscopy). Fig. 2 shows a conceptual diagram of the average value of W concentration. The specific method for the W ratio will be explained in detail later.

[0041] The W high concentration layer (121) is composed of a Ni-W alloy or a Ni-Fe-W alloy, which has excellent LIB electrolyte resistance. Therefore, the W high concentration layer (121) has the effect of improving the LIB electrolyte resistance of the surface-treated steel plate (1). However, if the W ratio in the W high concentration layer (121) is less than 2.0 atomic%, the LIB electrolyte resistance of the surface-treated steel plate (1) is insufficient. Therefore, the W ratio in the W high concentration layer (121) is set to 2.0 atomic% or more. The W ratio in the W high concentration layer (121) may be 5.0 atomic% or more, 6.0 atomic% or more, 7.0 atomic% or more, or 8.0 atomic% or more.

[0042] Meanwhile, if the W ratio in the W high concentration layer (121) exceeds 20.0 atomic%, the resistance to LIB electrolyte is insufficient. This is presumed to be because the W high concentration layer (121) becomes embrittled, making it easy for fine cracks to occur in the W high concentration layer (121), and these cracks impair the resistance to LIB electrolyte. Therefore, the W ratio in the W high concentration layer (121) is set to 20.0 atomic% or less. The W ratio in the W high concentration layer (121) may be set to 18.0 atomic% or less, 16.0 atomic% or less, or 15.0 atomic% or less.

[0043] (W low concentration layer (122) of the plating layer (12))

[0044] In the plating layer (12) of the surface-treated steel plate (1) according to the present embodiment, the ratio of the average value of W concentration to the sum of the average value of Ni concentration in unit atomic %, the average value of W concentration, and the average value of Fe concentration (including 0 atomic %) in the region from the outermost surface of the plating layer (12) to a depth of 300 nm is 0.7 times or less of the ratio in the region from the outermost surface of the plating layer to a depth of 150 nm. Hereinafter, the region from a depth of 150 nm to a depth of 300 nm of the plating layer (12) is referred to as the "low W concentration layer (122)." That is, in the plating layer (12) of the surface-treated steel plate (1) according to the present embodiment, the W ratio in the low W concentration layer (122) is 0.7 times or less of the W ratio in the high W concentration layer (121).

[0045] According to the experimental results of the inventors, the W low concentration layer (122) further improves the LIB electrolyte resistance of the surface-treated steel plate (1). Although the reason for this is not clear, the inventors presume that the W low concentration layer (122) has the effect of hindering fine cracks that occur in the hard W high concentration layer (121) from advancing into the interior of the plating layer (12). It is presumed that the LIB electrolyte resistance of the surface-treated steel plate (1) is further improved as the advancing of cracks is hindered. Accordingly, the W ratio in the W low concentration layer (122) is 0.7 times or less of the W ratio in the W high concentration layer (121). The W ratio in the W low concentration layer (122) may be 0.6 times or less, 0.5 times or less, or 0.4 times or less of the W ratio in the W high concentration layer (121).

[0046] (Method for measuring the ratio of W in the W high concentration layer (121) and W low concentration layer (122))

[0047] The measurement of the W ratio in the W high concentration layer (121) and the W ratio in the W low concentration layer (122) is performed using XPS as described above.

[0048] First, the surface of the surface-treated steel plate (1) is sputtered using noble gas ions such as argon and xenon. Next, the composition of the plating layer (12) is measured from the surface of the surface-treated steel plate (1) toward the interior. After the measurement is completed, the sputtering is performed again, and the measurement cycle is repeated.

[0049] Next, the analysis results of W concentration along the depth direction are plotted on a graph shown in FIG. 2, where the horizontal axis is depth and the vertical axis is W concentration. Then, the value obtained by integrating the graph of W concentration in the range of 0 nm to 150 nm corresponding to the high W concentration layer (121), divided by the width of the range of 0 nm to 150 nm (i.e., 150 nm), is considered as the average value C1 of W concentration within the region from the outermost surface of the plating layer to a depth of 150 nm. Similarly, the value obtained by integrating the graph of W concentration in the range of 150 nm to 300 nm corresponding to the low W concentration layer (122), divided by the width of the range of 150 nm to 300 nm (i.e., 150 nm), is considered as the average value C2 of W concentration within the region from a depth of 150 nm to a depth of 300 nm of the plating layer.

[0050] By applying the above-described calculation performed on the W concentration to the Ni and Fe analysis results, the average value of the Ni concentration and the average value of the Fe concentration in unit atomic % can be obtained within the region from the outermost surface of the plating layer to a depth of 150 nm and within the region from a depth of 150 nm to a depth of 300 nm of the plating layer. Based on these values, the average W concentration in the W high concentration layer (121) and the average W concentration in the W low concentration layer (122) can be calculated.

[0051] Additionally, the composition of the plating layer (12) using XPS is measured using a Mg source. In the analysis using the Mg source, there are no Auger peaks that overlap with the photoelectron peaks of Ni, W, and Fe. Peaks of the 2p orbital for Fe, the 2p orbital for Ni, and the 4f orbital for W were observed.

[0052] In the surface-treated steel plate (1) according to the present embodiment, other configurations may be appropriately selected as long as the above-described conditions regarding the W high-concentration layer (121) and the W low-concentration layer (122) are satisfied. Below, a more preferred configuration of the surface-treated steel plate (1) according to the present embodiment is exemplified.

[0053] (Ni attachment amount)

[0054] The amount of Ni deposited in the plating layer (12) is not particularly limited, but, for example, it may be 2.6 to 35.6 g / m². By making the amount of Ni deposited 2.6 g / m² or more, the resistance to LIB electrolyte of the surface-treated steel plate (1) is further enhanced. On the other hand, by making the amount of Ni deposited 35.6 g / m² or less, the manufacturing cost of the plating layer (12) can be reduced. The amount of Ni deposited may be 4.5 g / m² or more, 6.2 g / m² or more, or 8.9 g / m² or more. The amount of Ni deposited may be 26.7 g / m² or less, 17.8 g / m² or less, or 13.4 g / m² or less. In addition, the thickness of the plating layer (12) is not particularly limited. Since the W high concentration layer (121) and the W low concentration layer (122) are included in the plating layer (12), the thickness of the plating layer (12) is inevitably 300 nm or more, which is the total thickness of these layers, but within this range, a preferred thickness of the plating layer (12) can be appropriately selected. For example, the thickness of the plating layer (12) may be within the range of 0.3 μm to 3.0 μm. In addition, the thickness of the plating layer (12) is approximately determined by the amount of Ni deposited.

[0055] The amount of Ni deposited in the plating layer (12) is measured by ICP-OES (Inductively Coupled Optical Emission Spectroscopic Analysis). First, a plating layer (12) of a predetermined area is dissolved in acid. Then, the amount of Total-Ni contained in the solution is quantitatively analyzed by ICP-OES. By dividing the amount of Total-Ni quantified by ICP-OES by the aforementioned predetermined area, the amount of Ni deposited per unit area can be obtained.

[0056] (use)

[0057] The use of the surface-treated steel plate (1) according to the present embodiment is not particularly limited. For example, the surface-treated steel plate (1) according to the present embodiment can be applied to a large lithium-ion battery can. Since the base material of the surface-treated steel plate (1) according to the present embodiment is a steel plate, it has high strength and heat resistance. Therefore, the surface-treated steel plate (1) according to the present embodiment can increase the heat resistance and strength of the lithium-ion battery and also reduce its weight. In addition, according to the surface-treated steel plate (1) according to the present embodiment, the volumetric energy density can be improved along with thinning the battery can. Furthermore, the surface-treated steel plate (1) according to the present embodiment has higher resistance to LIB electrolyte than conventional surface-treated steel plates. Therefore, the surface-treated steel plate (1) according to the present embodiment contributes to extending the lifespan of the lithium-ion battery.

[0058] (Method for manufacturing surface-treated steel plate (1))

[0059] The method of manufacturing the surface-treated steel plate (1) according to the present embodiment is not particularly limited, but, for example, the surface-treated steel plate (1) according to the present embodiment can be obtained by the manufacturing method described below.

[0060] A method for manufacturing a surface-treated steel sheet according to another embodiment of the present invention is, as shown in FIG. 3,

[0061] Process S1 for plating Ni onto base steel plates, and

[0062] A process S2 for plating a Ni-W alloy onto a base steel plate having a Ni plating layer, and

[0063] Process S3 for annealing a base steel sheet having a Ni plating layer and a Ni-W alloy plating layer disposed thereon.

[0064] It is equipped with. Here,

[0065] The thickness of the Ni plating layer is set within the range of 0.3 to 3.5 μm, and

[0066] The thickness of the Ni-W alloy plating layer is set within the range of 0.010 to 0.30 μm, and

[0067] The average W concentration of the Ni-W alloy plating layer is set to 20 to 45 mass%, and also,

[0068] The heating rate in annealing S3 is set to 5 to 10°C / second within a temperature range of 600 to 700°C.

[0069] (Ni plating process S1)

[0070] First, Ni is plated onto the base steel sheet using an electroplating bath. The type of base steel sheet is not particularly limited, and, for example, the aforementioned low-carbon aluminum killed steel and IF steel may be appropriately adopted. The conditions for the electroplating of Ni are also not particularly limited. For example, the Ni plating conditions used for conventional Ni-plated steel sheets for batteries may be appropriately adopted. If necessary, pretreatments such as degreasing or pickling may be performed on the base steel sheet prior to Ni plating.

[0071] The thickness of the Ni plating layer plated in Ni plating process S1 is measured using XRF (X-ray Fluorescence). First, a calibration curve is constructed following the steps below.

[0072] (1) Various Ni platings with different coating amounts are produced on the surface of the base steel plate. When producing various Ni platings, the bath composition and current density were kept under the same conditions.

[0073] (2) The above-described plated steel sheet is analyzed using XRF to obtain the quantitative analysis result of Ni.

[0074] (3) Using ICP-MS (Inductively Coupled Plasma Mass Spectrometry), the amount of Ni in the above-described plated steel sheet is quantitatively analyzed and measured.

[0075] (4) A calibration curve for XRF is prepared by comparing the amount of Ni deposited using ICP-MS with the quantitative analysis value of Ni obtained using XRF.

[0076] Next, the thickness of the Ni plating layer plated in the Ni plating process S1 can be measured by analyzing the Ni plating layer to be measured using XRF with the calibration curve obtained in the above-described procedure.

[0077] (Ni-W alloy plating process S2)

[0078] (Annealing process S3)

[0079] Next, a Ni-W alloy is plated on a base steel plate having a Ni plating layer using an electroplating bath. Additionally, the base steel plate having a Ni plating layer and a Ni-W alloy plating layer placed thereon is annealed. By annealing this two-layer plating structure, alloy components are diffused to form a high-concentration W layer and a low-concentration W layer.

[0080] Here, it is necessary to set the thickness of the Ni-W alloy plating layer plated in the Ni-W alloy plating process S2 to be within the range of 0.010 to 0.30 μm, and also to set the average W concentration of the Ni-W alloy plating layer plated in the Ni-W alloy plating process S2 to 20 to 45 mass%. More preferably, the thickness of the Ni-W alloy plating layer plated in the Ni-W alloy plating process S2 is 0.20 μm or less. By annealing a base steel sheet having such a Ni-W alloy plating layer, a plating layer can be obtained in which the W ratio in the high-concentration W layer is 2.0 to 20.0 atomic%, and the W ratio in the low-concentration W layer is 0.7 times or less of the W ratio in the high-concentration W layer. If the thickness of the Ni-W alloy plating layer plated in the Ni-W alloy plating process S2 is insufficient, or if the concentration of the Ni-W alloy plating layer plated in the Ni-W alloy plating process S2 is insufficient, the W ratio in the high-concentration W layer is insufficient. Meanwhile, if the thickness of the Ni-W alloy plating layer is excessive, or if the concentration of the Ni-W alloy plating layer is excessive, the ratio of W in the high-concentration W layer and / or the ratio of W in the low-concentration W layer becomes excessive.

[0081] The thickness and composition of the Ni-W alloy plating layer plated in the Ni-W alloy plating process S2 can be arbitrarily controlled through the composition of the plating bath and the current application conditions. In other words, as long as the thickness and composition of the Ni-W alloy plating layer plated in the Ni-W alloy plating process S2 are within the range described above, the composition of the plating bath and the current application conditions for the Ni-W alloy plating in the Ni-W alloy plating process S2 are not particularly limited.

[0082] The thickness and composition of the Ni-W alloy plating layer plated in Ni-W alloy plating process S2 can be measured using XRF (X-ray Fluorescence). First, a calibration curve is prepared in the following steps.

[0083] (1) Various Ni-W alloy platings with different coating amounts are produced on the surface of a Ni-plated steel sheet with a Ni weight per unit area. When producing various Ni-W alloy platings, the bath composition and current density are kept under the same conditions.

[0084] (2) The above-described plated steel sheet is analyzed using XRF to obtain quantitative analysis results of Ni and W.

[0085] (3) Using ICP-MS (Inductively Coupled Plasma Mass Spectrometry), the Ni and W of the above-described plated steel sheet are quantitatively analyzed, and the amount of deposition (the total amount of deposition of the lower layer Ni plating and the upper layer Ni-W alloy plating) is measured.

[0086] (4) A calibration curve for XRF is prepared by comparing the amount of Ni and W deposited using ICP-MS with the quantitative analysis values ​​of Ni and W obtained using XRF.

[0087] Next, the thickness and composition of the Ni-W alloy plating layer being measured can be measured by analyzing the Ni-W alloy plating layer using XRF with the calibration curve obtained in the above-described procedure S2.

[0088] In the annealing process S3 following the Ni-W alloy plating process S2, it is necessary to set the heating rate within a temperature range of 600 to 700°C to 5 to 10°C / second. By doing so, the concentration of Ni and W can be preferably formed in the outermost layer of the plating layer. If the heating rate is less than 5°C / second, the diffusion of Ni and W proceeds too much, causing the W concentration in the high-concentration W layer to decrease and the W concentration in the low-concentration W layer to increase, resulting in an increase in the W ratio (W ratio of low-concentration W layer ÷ high-concentration W layer). If the heating rate exceeds 10°C / second, the diffusion of Ni and W proceeds insufficiently, causing the W concentration in the high-concentration W layer to increase. Furthermore, the "heating rate within a temperature range of 600 to 700°C" refers to the "average heating rate" within the said temperature range. The average heating rate is the value obtained by dividing 100℃ (=700℃-600℃) by the time required for the temperature to rise from 600℃ to 700℃.

[0089] As long as the heating rate is within the range described above, other annealing conditions are not particularly limited, and the annealing conditions of a conventional Ni-plated steel sheet can be appropriately adopted while considering the amount of Ni deposited. For example, as described above, the plating layer (12) of the surface-treated steel sheet (1) according to the present embodiment may be a partially diffusion alloyed plating layer or a fully diffusion alloyed plating layer. Therefore, known annealing conditions for obtaining these alloyed plating layers can be appropriately adopted.

[0090] Although the amount of Ni deposited is not specifically limited, for example, the total amount of Ni deposited in the Ni plating layer and the Ni-W alloy plating layer may be 2.6 to 35.6 g / m². By making the total amount of Ni deposited 2.6 g / m² or more, the resistance to LIB electrolyte of the surface-treated steel plate (1) is further enhanced. On the other hand, by making the total amount of Ni deposited 35.6 g / m² or less, the manufacturing cost of the plating layer (12) can be reduced. The total amount of Ni deposited may be 4.5 g / m² or more, 6.2 g / m² or more, or 8.9 g / m² or more. The total amount of Ni deposited may be 26.7 g / m² or less, 17.8 g / m² or less, or 13.4 g / m² or less.

[0091] Examples

[0092] Under the conditions shown below, various surface-treated steel sheets of levels 1 to 11, 14, and 15 were produced.

[0093] · Base steel sheet: 0.40 mm thick, meannealed Al-K steel

[0094] · Plating bath components: As listed in Tables 1-1 and 1-2

[0095] · Plating bath temperature: 60℃

[0096] · Ni plating conditions and Ni-W alloy plating conditions: Plating was performed on the base steel plate in the order of Ni plating followed by Ni-W alloy plating to achieve the deposition amounts listed in Table 2-1. At this time, the current density was 1.0 to 50.0 A / dm² 2 The current application time was appropriately adjusted for each level between 0.1 and 50.0 seconds to achieve the target weight per unit area (however, Ni plating was not performed at Level 1. Also, Ni-W alloy plating was not performed at Level 12). The thickness of the Ni plating was as described in Table 2-1.

[0097] · Annealing: Performed under temperature conditions of heating to 800°C and maintaining the temperature for 20 seconds. The heating rate within the temperature range of 600 to 700°C was as described in Table 2-1.

[0098] In addition, as level 13, a SUS304 (hereinafter SUS plate) with a thickness of 0.40 mm was prepared.

[0099] The ratio of W in the high-concentration W layer of various surface-treated steel sheets obtained by the above-described procedure (i.e., the ratio of the average W concentration to the sum of the average Ni concentration, the average W concentration, and the average Fe concentration in the region from the outermost surface of the plating layer to a depth of 150 nm) was measured and shown in the column “Ratio of W in the High-Concentration W Layer” of Table 2-2. In addition, the ratio of W in the low-concentration W layer (i.e., the ratio of the average W concentration to the sum of the average Ni concentration, the average W concentration, and the average Fe concentration in the region from a depth of 150 nm to a depth of 300 nm) was measured and shown in the column “Ratio of W in the Low-Concentration W Layer” of Table 2-2. From the measured ratio of W in the high-concentration W layer and the ratio of W in the low-concentration W layer, the ratio of W in the low-concentration W layer to the ratio of W in the high-concentration W layer was calculated and shown in the column “Ratio of W in the low-concentration W layer ÷ Ratio of W in the high-concentration W layer” of Table 2-2. In addition, the resistance to LIB electrolyte of various surface-treated steel sheets and SUS sheets obtained by the above-described procedure was evaluated.

[0100] The analysis method for the thickness of the Ni plating prior to Ni-W alloy plating, the analysis method for the W concentration and thickness of the Ni-W alloy plating layer of the plated steel sheet prior to annealing, and the measurement method for the W ratio in the high-W concentration layer and the W ratio in the low-W concentration layer of the surface-treated steel sheet after annealing were as described above. The results are shown in Table 2-2. The XPS apparatus used was an Al-Bac P&I, model number PHI 5600. XRF measurements were performed using a Rigaku, model number ZSX Primus II. In addition, the measurement method for the amount of Ni deposited in the plating layer was as described above. The results are shown in the "Alloy Plating Layer" column of Table 2-2. Furthermore, the LIB electrolyte resistance of the surface-treated steel sheet and SUS sheet was evaluated by using a combination of a processing simulation test (draw bead test) and an anode current test. The results are shown in the "Evaluation Results" column of Table 2-2.

[0101] The draw bead test was performed by placing a surface-treated steel plate and a SUS plate between the molds shown in Fig. 4, then press-forming the molds by pressing them in, and then drawing the surface-treated steel plate and the SUS plate out of the molds while the molds were still pressed in. The draw bead test is a test that simulates the press-forming of surface-treated steel plates and SUS plates for the manufacture of battery cans. By evaluating the electrochemical properties of the surface-treated steel plate and the SUS plate after performing the draw bead test, the electrochemical performance of the battery can manufactured using the surface-treated steel plate and the SUS plate can be predicted.

[0102] The anode current test was performed by taking microelectrochemical measurements on the surface of the surface-treated steel plate and SUS plate after the draw bead test. The anode current test was performed using a Solartron Analytical Model 1287A potentiometer. The evaluation conditions were as follows.

[0103] · Shape of the evaluation area: A circle with a diameter of 500㎛

[0104] · Measurement locations: 5 (The average of the measurement results from the 5 locations was used as the final evaluation result)

[0105] · Potential control: After establishing the measuring system, the Open Circuit Voltage (OCV) was maintained for 5 minutes and then raised to 4.5V. The sweep rate of the vs. Li Linear Sweep Voltammetry (LSV) during the rise was set to 20 mV / s.

[0106] · Measurement environment: Temperature 23℃, dew point -80℃ or lower, oxygen concentration 0.7ppm or lower

[0107] · Electrolyte: 1 mol / L LiPF6EC (ethylene carbonate): EMC (ethylmethyl carbonate) (1:3 v / v%) + VC (vinylene carbonate) 2 wt%

[0108] · Pass / Fail Criteria: Passes when the anode current value at 3.8V is 0.025µA or less.

[0109] [Table 1-1]

[0110]

[0111] [Table 1-2]

[0112]

[0113] [Table 2-1]

[0114]

[0115] [Table 2-2]

[0116]

[0117] Level 1 is a surface-treated steel sheet obtained by forming only a Ni-W alloy plating layer on the surface of a base steel sheet and then annealing. Levels 2 to 11, 14, and 15 are surface-treated steel sheets obtained by forming a Ni plating layer on the surface of a base steel sheet, and then forming a thin Ni-W alloy plating layer thereon and then annealing. Level 12 is a surface-treated steel sheet obtained by forming only a Ni plating layer on the surface of a base steel sheet and then annealing. Level 13 is a SUS sheet without a plating layer.

[0118] Levels 3 to 6 and levels 8 to 11 are examples of the invention having a high-concentration W layer with a W ratio of 2.0 to 20.0 atomic% and a low-concentration W layer with a W ratio of 0.7 times or less of the high-concentration W layer. The LIB electrolyte resistance of these was superior to that of a conventional Ni-W alloy plated steel sheet (Level 1), a conventional Ni-plated steel sheet (Level 12), and a conventional SUS sheet (Level 13). That is, according to the present invention, it was possible to provide a surface-treated steel sheet with even better LIB electrolyte resistance than conventional SUS sheets and Ni-plated steel sheets, and a method for manufacturing the same.

[0119] In addition, Levels 2 and 7 were obtained by annealing after forming a Ni plating layer and a Ni-W alloy plating layer, just like Levels 3 to 6 and Levels 8 to 10. However, in Level 2, the W ratio in the high-W concentration layer was excessive, and a large amount of W was also contained in the low-W concentration layer, so the LIB electrolyte resistance was unsatisfactory. This is thought to be because the Ni-W alloy plating layer in Level 2 was too thick. In Level 7, the LIB electrolyte resistance was unsatisfactory because the W ratio in the high-W concentration layer was too low. This is thought to be because the Ni-W alloy plating layer in Level 7 was too thin.

[0120] At level 14, the heating rate in the temperature range of 600°C to 700°C was too low, so the LIB electrolyte resistance was unsatisfactory. This is thought to be because the diffusion of Ni and W proceeded too much, causing the W concentration in the high-concentration W layer to decrease and the W concentration in the low-concentration W layer to increase, so the W ratio in the low-concentration W layer exceeded 0.7 times that of the high-concentration W layer.

[0121] At level 15, the heating rate in the temperature range of 600°C to 700°C was too high, so the LIB electrolyte resistance was unsatisfactory. This is thought to be because the diffusion of Ni and W was insufficient, and the ratio of W in the high-concentration W layer increased.

[0122] Figure 5a shows the surface analysis results of a Level 1 surface-treated steel sheet after a draw bead test, and Figure 5b shows the surface analysis results of a Level 3 surface-treated steel sheet after a draw bead test. In Figures 5a and 5b, the upper left image is an SEM photograph of the surface-treated steel sheet, the upper right image is the surface analysis result of Fe concentration at the location where the SEM photograph was taken, the lower left image is the surface analysis result of Ni concentration at the location where the SEM photograph was taken, and the lower right image is the surface analysis result of W concentration at the location where the SEM photograph was taken.

[0123] On the surface of the Level 1 surface-treated steel sheet, there were numerous deficient areas of Ni and W. The Fe concentration was high in these deficient areas. In the Level 1 surface-treated steel sheet, it is thought that numerous cracks occurred in the hard Ni-W alloy plating layer, exposing the base steel sheet. On the other hand, no deficient areas of Ni and W were observed on the surface of the Level 4 surface-treated steel sheet. As the exposure of the base steel sheet was suppressed, it is estimated that the LIB electrolyte resistance of the Level 4 surface-treated steel sheet was significantly improved compared to Level 1. Explanation of the symbols

[0124] 1: Surface-treated steel plate 11: Base steel plate 12: Plating layer 121: W high concentration layer 122: W low concentration layer C1: Average value of W concentration in the high-concentration W layer C2: Average value of W concentration in the low-concentration layer S1: Ni plating process S2: Ni-W alloy plating process S3: Annealing process

Claims

Claim 1 A surface-treated steel plate used as a material for a battery container, comprising a base steel plate and a plating layer containing Ni and W provided on one surface of the base steel plate that becomes the inner surface of the battery container, wherein the ratio of the average value of the W concentration to the sum of the average value of the Ni concentration, the average value of the W concentration, and the average value of the Fe concentration in a unit atomic % within a region from the outermost surface of the plating layer to a depth of 150 nm is 2.0 to 20.0 atomic %, and the ratio of the average value of the W concentration to the sum of the average value of the Ni concentration, the average value of the W concentration, and the average value of the Fe concentration in a region from a depth of 150 nm to a depth of 300 nm within the plating layer is 0.7 times or less of the ratio within the region from the outermost surface of the plating layer to a depth of 150 nm. Claim 2 A surface-treated steel sheet according to claim 1, characterized in that the amount of Ni attached to the plating layer is 2.6 to 35.6 g / m². Claim 3 A surface-treated steel plate according to claim 1 or 2, characterized in that the base steel plate is low-carbon aluminum killed steel or IF steel.

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