Ferritic stainless steel foil, electrode, and battery

Abstract

To provide ferritic stainless steel foil that offers excellent corrosion resistance.SOLUTION: The ferritic stainless steel foil disclosed in this invention comprises a foil main body made of ferritic stainless steel. In a region from a 0.38 μm depth position, starting from the surface of the foil body, to a 2.82 μm depth position, a maximum value IMAX of IR, as defined by formula (1), is 15.0 or more. IR=II110 / II211 (1) The integral intensity of the {110} plane obtained by the grazing incidence X-ray diffraction method is substituted into II110 in formula (1), and the integral intensity of the {211} plane obtained by the grazing incidence X-ray diffraction method is substituted into II211.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a ferritic stainless steel foil, an electrode using the ferritic stainless steel foil as a current collector, and a battery using the electrode. [Background technology]

[0002] Batteries such as primary batteries and secondary batteries have been used as power sources for various electronic devices. In recent years, secondary batteries, typified by lithium-ion batteries, have become increasingly popular due to the widespread use of small electronic devices such as home video cameras, laptops, and smartphones.

[0003] A secondary battery includes electrodes having a positive electrode and a negative electrode, and an electrolyte. Both the positive electrode and the negative electrode have an electrode mixture layer formed on a current collector. The electrode mixture layer is a layer containing an active material. The current collector has the function of supplying current to the active material and the function of serving as a substrate for supporting the electrode mixture layer.

[0004] Traditionally, electrolyte solutions have been used as electrolytes in secondary batteries. However, because electrolyte solutions contain flammable organic solvents, the temperature range in which they can be used is narrow. For this reason, in recent years, development of all-solid-state batteries that use solid electrolytes instead of electrolyte solutions has been progressing. Because all-solid-state batteries do not contain organic solvents, stable battery performance can be achieved over a wide temperature range. Among the solid electrolytes used in all-solid-state batteries, sulfide-based solid electrolytes, including LPS (Lithium Phosphorus Sulfide), have particularly high ionic conductivity. Therefore, the use of sulfide-based solid electrolytes can achieve high output in all-solid-state batteries.

[0005] On the other hand, when a sulfide-based solid electrolyte is used, the current collector may be corroded by sulfides. Corrosion of the current collector results in a decrease in battery performance. In other words, the current collector must have high corrosion resistance. For this reason, the use of highly corrosion-resistant stainless steel as the current collector material is being considered. Among stainless steels, ferritic stainless steel in particular has lower electrical resistance and higher conductivity than austenitic stainless steel. For this reason, ferritic stainless steel is suitable as a current collector material.

[0006] However, even when ferritic stainless steel is used as a current collector, corrosion reactions due to sulfide-based solid electrolytes still occur in all-solid-state batteries, so there is a need for technology to further improve the corrosion resistance of ferritic stainless steel.

[0007] A technology for improving the corrosion resistance of ferritic stainless steel for current collector applications is proposed in International Publication No. 2021 / 006089 (Patent Document 1).

[0008] Patent Document 1 discloses a ferritic stainless steel sheet for use as a current collector in a sulfide-based solid battery, which contains 0.001 to 0.050% C, 0.01 to 2.00% Si, 0.01 to 1.00% Mn, 0.050% or less P, 0.010% or less S, 18.00 to 32.00% Cr, 0.01 to 4.00% Ni, 0.001 to 0.150% Al, and 0.050% or less N, with the balance being Fe and unavoidable impurities. Patent Document 1 also describes that this ferritic stainless steel sheet exhibits excellent sulfidation resistance when the Cr content is increased to 18.00% or more. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2021 / 006089 Summary of the Invention [Problem to be solved by the invention]

[0010] However, the corrosion resistance of ferritic stainless steel may be improved by a means different from that of the ferritic stainless steel sheet disclosed in Patent Document 1.

[0011] An object of the present disclosure is to provide a ferritic stainless steel foil that can provide excellent corrosion resistance, an electrode that uses the ferritic stainless steel foil as a current collector, and a battery that uses the electrode. [Means for solving the problem]

[0012] The ferritic stainless steel foil of the present disclosure is A foil body made of ferritic stainless steel, I defined by formula (1) in the region from a depth of 0.38 μm to a depth of 2.82 μm starting from the surface of the foil body R The maximum value of I MAX is 15.0 or greater. I R =II 110 / II 211 (1) Here, II in formula (1) 110 is substituted with the integrated intensity of the {110} plane obtained by grazing incidence X-ray diffraction, and II 211 is substituted with the integrated intensity of the {211} plane obtained by grazing incidence X-ray diffraction.

[0013] The electrode of the present disclosure comprises: The ferritic stainless steel foil; and an electrode mixture layer formed on the surface of the ferritic stainless steel foil.

[0014] The battery of the present disclosure comprises: The electrode; and an electrolyte. [Effects of the Invention]

[0015] The ferritic stainless steel foil of the present disclosure provides excellent corrosion resistance. The electrode of the present disclosure comprises the ferritic stainless steel foil of the present disclosure. The battery of the present disclosure comprises the electrode of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present inventors have investigated means for improving the corrosion resistance of ferritic stainless steel foil, and as a result, have made the following findings.

[0017] In Patent Document 1, the Cr content of ferritic stainless steel is increased to improve its corrosion resistance. Thus, adding alloying elements that improve corrosion resistance is effective for improving the corrosion resistance of ferritic stainless steel foil. However, increasing the content of alloying elements can reduce the workability of the ferritic stainless steel foil and increase manufacturing costs. Therefore, the present inventors focused on the crystal orientation of the surface layer of a ferritic stainless steel foil having a foil body made of ferritic stainless steel, rather than the chemical composition of the foil body.

[0018] In the body-centered cubic lattice of the ferritic stainless steel foil, the {110} plane is the lattice plane with the most densely packed atoms (closest-packed atomic plane). Because the interatomic distance is short on the {110} plane, the bonding force between atoms within the plane is strong.

[0019] Corrosion of ferritic stainless steel foil progresses from the surface of the foil body in the depth direction. Here, the more perpendicularly the {110} plane, which is the close-packed atomic plane, is oriented to the depth direction at a certain depth, the slower the rate of corrosion progression in the depth direction at that depth. Therefore, by increasing the orientation of the {110} plane in the depth direction in the surface layer of the foil body, the progression of corrosion starting from the surface can be suppressed. As a result, the corrosion resistance of ferritic stainless steel foil can be improved.

[0020] The crystal orientation in the surface layer of the foil body can be evaluated by grazing incidence X-ray diffraction (GIXD). Grazing incidence X-ray diffraction can measure the crystal orientation at any depth starting from the surface. Furthermore, grazing incidence X-ray diffraction measurements of the surface layer of the foil body mainly detect peaks of the {110} plane and the {211} plane. At a certain depth, the greater the ratio of the integrated intensity of the {110} plane to the integrated intensity of the {211} plane, the more the {110} plane oriented perpendicular to the depth direction is present at that depth. In other words, to improve the corrosion resistance of ferritic stainless steel foil, it is preferable that the ratio of the integrated intensity of the {110} plane to the integrated intensity of the {211} plane be large in the surface layer of the foil body.

[0021] Based on the above findings, the inventors investigated the relationship between the ratio of the integrated intensity of the {110} plane to the integrated intensity of the {211} plane in the surface layer of the foil body, which is obtained by grazing incidence X-ray diffraction, and corrosion resistance. As a result, the I defined by formula (1) in the region from the surface of the foil body to the depth position of 0.38 μm to the depth position of 2.82 μm was R The maximum value of I MAX The present inventors have found that if the {110} plane is 15.0 or more, the orientation of the {110} plane in the depth direction can be sufficiently increased in the surface layer of the foil body, and as a result, excellent corrosion resistance can be obtained in the ferritic stainless steel foil. I R =II 110 / II 211 (1) Here, II in formula (1) 110 is substituted with the integrated intensity of the {110} plane obtained by grazing incidence X-ray diffraction, and II 211 is substituted with the integrated intensity of the {211} plane obtained by grazing incidence X-ray diffraction.

[0022] The ferritic stainless steel foil of this embodiment, the electrode of this embodiment, and the battery of this embodiment have been completed based on the above technical concept, and have the following configurations.

[0023] The ferritic stainless steel foil of the first configuration is A foil body made of ferritic stainless steel, I defined by formula (1) in the region from a depth of 0.38 μm to a depth of 2.82 μm starting from the surface of the foil body R The maximum value of I MAX is 15.0 or greater. I R =II 110 / II 211 (1) Here, II in formula (1) 110 is substituted with the integrated intensity of the {110} plane obtained by grazing incidence X-ray diffraction, and II 211 is substituted with the integrated intensity of the {211} plane obtained by grazing incidence X-ray diffraction.

[0024] The ferritic stainless steel foil of the second configuration is A ferritic stainless steel foil of a first configuration, The chemical composition of the foil body is, in mass%, C: 0.001 to 0.030%, Si: 0.01 to 1.00%, Mn: 0.01 to 1.00%, P: 0.050% or less, S: 0.030% or less, Ni: 0.01 to 0.50% Cr: 12.00~20.00%, Mo: 0.01 to 2.50% N: 0~0.100%, Ti: 0 to 0.80% Nb: 0 to 0.80%, and Zr: 0 to 0.80%; The balance is Fe and impurities.

[0025] The electrodes of the first configuration are: A ferritic stainless steel foil having a first or second configuration; and an electrode mixture layer formed on the surface of the ferritic stainless steel foil.

[0026] The battery of the first configuration comprises: Electrodes in a first configuration; and an electrolyte.

[0027] The battery in the second configuration is 1. A battery of a first configuration, comprising: The electrolyte is a sulfide-based solid electrolyte.

[0028] The ferritic stainless steel foil of this embodiment, the electrode of this embodiment, and the battery of this embodiment will be described in detail below. Note that "%" for elements means mass % unless otherwise specified.

[0029] [Composition of ferritic stainless steel foil] The ferritic stainless steel foil of this embodiment has a foil body made of ferritic stainless steel. That is, the ferritic stainless steel foil of this embodiment may be composed only of a foil body made of ferritic stainless steel. Here, ferritic stainless steel refers to a steel having a Cr content of 10.5% or more and a microstructure mainly composed of ferrite. In this specification, a microstructure mainly composed of ferrite means that the volume fraction of ferrite in the microstructure is 95% or more.

[0030] [I R The maximum value of I MAX About In the ferritic stainless steel foil of this embodiment, the I defined by formula (1) in the region from the surface of the foil body to the depth position of 0.38 μm to the depth position of 2.82 μm is R The maximum value of I MAX is 15.0 or greater. I R =II 110 / II 211 (1) Here, II in formula (1) 110 is substituted with the integrated intensity of the {110} plane obtained by grazing incidence X-ray diffraction, and II 211 is substituted with the integrated intensity of the {211} plane obtained by grazing incidence X-ray diffraction.

[0031] I R is an index that represents the ratio of the amount of {110} planes to the amount of {211} planes that constitute the crystal orientation in the depth direction at an arbitrary depth position starting from the surface of the foil body. Here, the region from the surface of the foil body to a depth position of 2.82 μm is defined as the surface layer. In other words, the I in the region from a depth position of 0.38 μm to a depth position of 2.82 μm starting from the surface of the foil body R The maximum value of I MAX is the surface I R It is an index that represents the maximum value of

[0032] As mentioned above, I R The larger the value of I is, the higher the orientation of the {110} plane, which is the closest-packed atomic plane, in the depth direction at that depth, and therefore the rate of corrosion progression in the depth direction slows. R The maximum value of I MAX If the {110} plane is 15.0 or more, the orientation of the {110} plane in the depth direction in the surface layer is sufficiently high. In this case, the progression of corrosion originating from the surface layer can be sufficiently suppressed. As a result, the ferritic stainless steel foil can achieve excellent corrosion resistance.

[0033] I MAX The preferred lower limit is 20.0, and more preferably 30.0. I MAX There is no particular upper limit for I. Considering normal industrial production, MAX The upper limit is, for example, 120.0.

[0034] [Method for measuring the integrated intensity of each lattice plane] Integrated intensity of {110} plane II 110 , and the integrated intensity of the {211} plane II 211 is calculated in the following way:

[0035] A test piece is taken from the surface of the ferritic stainless steel foil body as the observation surface. The size of the test piece is not particularly limited. The location from which the test piece is taken is also not particularly limited, but for example, it can be taken from the center of the foil body width. The observation surface of the test piece is measured using grazing incidence X-ray diffraction. For the measurement, for example, a SmartLab (trade name) manufactured by Rigaku Corporation can be used. The measurement uses CoKα radiation as the radiation source, a tube voltage of 40 kV, and a tube current of 135 mA. The X-ray beam is collimated using a mirror. A 5.0° Soller slit is installed on the entrance side, a 5.0° Soller slit is installed on the receiving side, a parallel slit analyzer (PSA) is installed at 0.5°, receiving slit 1 (RS1) = 1.0 mm, and receiving slit 2 (RS2) = open. The incident direction of the X-rays is parallel to a plane containing the rolling direction and the direction perpendicular to the surface of the foil body.

[0036] The measurement depth from the observation surface at each incidence angle in the grazing incidence X-ray diffraction method can be calculated from the X-ray penetration depth t that satisfies μt = 1, where μ is the linear absorption coefficient. The linear absorption coefficient μ is calculated using the mass absorption coefficient of 19.11Cr-1.77Mo-78.38Fe (mass%), which is equivalent to SUS444, and the density is 7.75g / cm. 3 Based on this conversion method, when the incident angle is 2.0° to 15.0°, the measurement depth corresponds to a depth of 0.38 μm to a depth of 2.82 μm. Therefore, measurements are performed under nine conditions, with incident angles of 2.0°, 3.0°, 4.0°, 5.0°, 6.0°, 8.0°, 10.0°, 12.0°, and 15.0°. From the diffraction profiles obtained under each condition, the peaks of the {110} plane and the {211} plane are identified. From the peaks of each lattice plane, the integrated intensity II of the {110} plane is calculated. 110 and {211} plane integrated intensity II 211 Calculate.

[0037] Obtained II 110 and II 211 Based on equation (1), I R Calculate I R is the value obtained by rounding off the second decimal place to the first decimal place. I obtained under nine conditions corresponding to measurement depths of 0.38 to 2.82 μm RThe maximum value of I MAX Let's say.

[0038] [Chemical composition] In the ferritic stainless steel foil of this embodiment, the chemical composition of the foil body may be that of a known ferritic stainless steel.

[0039] The chemical composition of the foil body of the ferritic stainless steel foil of this embodiment may satisfy, for example, any one selected from the group consisting of SUS405, SUS410L, SUS429, SUS430, SUS430LX, SUS430J1L, SUS434, SUS436L, SUS436J1L, SUS443J1, SUS444, SUS445J1, SUS445J2, SUS447J1, and SUSXM27 as specified in JIS G 4305 (2015).

[0040] The chemical composition of the foil body of the ferritic stainless steel foil of this embodiment may further satisfy, for example, any one selected from the group consisting of 403, 405, 409L, 410, 410L, 410S, 415, 420J1, 420J2, 420, 429, 429J1, 430, 430J1L, 430LX, 430Ti, 434, 436, 436J1L, 439, 441, 444, 445, 445J1, 445J2, 446, 447, and 448 as specified in ASTM A 240 (2006).

[0041] The chemical composition of the foil body of the ferritic stainless steel foil of this embodiment may contain, for example, the following elements.

[0042] C: 0.001 to 0.030% Carbon (C) increases the strength of the ferritic stainless steel foil. If the C content is 0.001% or more, this effect can be sufficiently obtained. On the other hand, if the C content is 0.030% or less, the formation of a Cr-deficient layer due to the generation of Cr carbides can be suppressed, which in turn suppresses the embrittlement of the oxide film and improves the corrosion resistance of the ferritic stainless steel foil. Therefore, the preferred C content is 0.001 to 0.030%. A more preferable lower limit of the C content is 0.003%, and even more preferably 0.005%. The upper limit of the C content is more preferably 0.025%, and even more preferably 0.020%.

[0043] Si: 0.01 to 1.00% Silicon (Si) deoxidizes steel during the steelmaking process, and if the Si content is 0.01% or more, this effect can be sufficiently obtained. On the other hand, if the Si content is 1.00% or less, the workability of the ferritic stainless steel foil is improved. Therefore, the preferred Si content is 0.01 to 1.00%. The lower limit of the Si content is more preferably 0.03%, and even more preferably 0.05%. The upper limit of the Si content is more preferably 0.90%, and even more preferably 0.80%.

[0044] Mn: 0.01 to 1.00% Manganese (Mn) increases the strength of the ferritic stainless steel foil, and if the Mn content is 0.01% or more, this effect can be sufficiently obtained. On the other hand, if the Mn content is 1.00% or less, the corrosion resistance of the ferritic stainless steel foil is improved. Therefore, the preferred Mn content is 0.01 to 1.00%. A more preferable lower limit of the Mn content is 0.03%, and even more preferably 0.05%. A more preferable upper limit of the Mn content is 0.90%, and even more preferably 0.80%.

[0045] P:0.050% or less Phosphorus (P) is an impurity. If the P content is 0.050% or less, the workability and corrosion resistance of the ferritic stainless steel foil are improved. Therefore, the preferred P content is 0.050% or less. The lower the P content, the better. However, excessively reducing the P content increases the production cost. Therefore, in consideration of normal industrial production, the lower limit of the P content is preferably more than 0%, more preferably 0.001%, and even more preferably 0.010%. A more preferable upper limit of the P content is 0.045%, and even more preferably 0.040%.

[0046] S: 0.030% or less Sulfur (S) is an impurity. If the S content is 0.030% or less, the workability and corrosion resistance of the ferritic stainless steel foil are improved. Therefore, the preferred S content is 0.030% or less. The S content is preferably as low as possible. However, excessively reducing the S content increases the production cost. Therefore, in consideration of normal industrial production, the lower limit of the S content is preferably more than 0%, more preferably 0.001%, and even more preferably 0.010%. The upper limit of the S content is more preferably 0.025%, and even more preferably 0.020%.

[0047] Ni: 0.01 to 0.50% Nickel (Ni) improves the corrosion resistance of the ferritic stainless steel foil, and if the Ni content is 0.01% or more, this effect can be sufficiently obtained. On the other hand, if the Ni content is 0.50% or less, the workability of the ferritic stainless steel foil is improved. Therefore, the Ni content is preferably 0.01 to 0.50%. A more preferable lower limit of the Ni content is 0.03%, and even more preferably 0.05%. A more preferable upper limit of the Ni content is 0.40%, and even more preferably 0.30%.

[0048] Cr: 12.00~20.00% Chromium (Cr) forms an oxide film and improves the corrosion resistance of the ferritic stainless steel foil. If the Cr content is 12.00% or more, this effect can be sufficiently obtained. On the other hand, if the Cr content is 20.00% or less, the workability of the ferritic stainless steel foil is improved. Therefore, the preferred Cr content is 12.00 to 20.00%. The lower limit of the Cr content is more preferably 12.50%, and even more preferably 13.00%. The upper limit of the Cr content is more preferably 19.00%, and even more preferably 18.00%.

[0049] Mo: 0.01 to 2.50% Molybdenum (Mo) enhances the strength and corrosion resistance of ferritic stainless steel foil, and if the Mo content is 0.01% or more, these effects can be sufficiently obtained. On the other hand, if the Mo content is 2.50% or less, the workability of the ferritic stainless steel foil is improved. Therefore, the preferred Mo content is 0.01 to 2.50%. A more preferable lower limit of the Mo content is 0.03%, and even more preferably 0.05%. A more preferable upper limit of the Mo content is 2.40%, and even more preferably 2.30%.

[0050] N: 0 to 0.100% Nitrogen (N) may not be contained. On the other hand, if the N content is 0.100% or less, the strength of the ferritic stainless steel foil increases. Therefore, the preferred N content is 0 to 0.100%. A more preferable lower limit of the N content is more than 0%, even more preferably 0.001%, and even more preferably 0.003%. The upper limit of the N content is more preferably 0.090%, and even more preferably 0.080%.

[0051] Ti: 0 to 0.80% Titanium (Ti) may not be contained. On the other hand, if the Ti content is 0.80% or less, it fixes C and suppresses the formation of Cr carbides, thereby suppressing the formation of a Cr-depleted layer. As a result, embrittlement of the oxide film is suppressed, and the corrosion resistance of the ferritic stainless steel foil is improved. Therefore, the preferred Ti content is 0 to 0.80%. A more preferable lower limit of the Ti content is more than 0%, even more preferably 0.01%, and even more preferably 0.03%. A more preferable upper limit of the Ti content is 0.70%, and even more preferably 0.60%.

[0052] Nb: 0 to 0.80% Niobium (Nb) may not be contained. On the other hand, if the Nb content is 0.80% or less, the corrosion resistance of the ferritic stainless steel foil is improved. Therefore, the Nb content is preferably 0 to 0.80%. A more preferable lower limit of the Nb content is more than 0%, even more preferably 0.01%, and even more preferably 0.03%. The upper limit of the Nb content is more preferably 0.70%, and even more preferably 0.60%.

[0053] Zr: 0 to 0.80% Zirconium (Zr) may not be contained. On the other hand, if the Zr content is 0.80% or less, the corrosion resistance of the ferritic stainless steel foil is improved. Therefore, the preferred Zr content is 0 to 0.80%. A more preferable lower limit of the Zr content is more than 0%, even more preferably 0.01%, and even more preferably 0.03%. A more preferable upper limit of the Zr content is 0.70%, and even more preferably 0.60%.

[0054] The balance of the preferred chemical composition of the foil body of the ferritic stainless steel foil of this embodiment consists of Fe and impurities. Here, the impurities in the chemical composition refer to substances that are mixed in from raw materials or the manufacturing environment during industrial production of the ferritic stainless steel foil, and are acceptable within a range that does not adversely affect the ferritic stainless steel foil of this embodiment.

[0055] Plate Thickness The thickness of the foil body of the ferritic stainless steel foil of this embodiment is not particularly limited, and is, for example, 6 to 20 μm.

[0056] [Uses of the ferritic stainless steel foil of this embodiment] The ferritic stainless steel foil of this embodiment has excellent corrosion resistance. Therefore, it is suitable for use as a current collector in an all-solid-state battery using a highly corrosive sulfide-based solid electrolyte. The ferritic stainless steel foil of this embodiment can also be used for applications other than as a current collector in a secondary battery.

[0057] [Method for producing ferritic stainless steel foil according to the present embodiment] An example of a method for producing the ferritic stainless steel foil of this embodiment will be described. The method for producing the ferritic stainless steel foil described below is one example for producing the ferritic stainless steel foil of this embodiment. Therefore, the ferritic stainless steel foil having the above-mentioned configuration may be produced by a production method other than the production method described below. However, the production method described below is a preferred example of a method for producing the ferritic stainless steel foil of this embodiment.

[0058] An example of a method for producing the ferritic stainless steel foil of this embodiment includes the following steps. (Process 1) Material preparation process (Process 2) Intermediate cold rolling process (Process 3) Intermediate annealing process (Process 4) Final cold rolling process Each step will be described below.

[0059] [(Process 1) Material preparation process] In the material preparation step, a ferritic stainless steel sheet having a thickness of several hundred μm to several mm is prepared as a material for producing the ferritic stainless steel foil of this embodiment. The material is, for example, a cold-rolled coil obtained by cold-rolling a hot-rolled coil. The material may be prepared by manufacturing or by purchasing from a third party. In other words, the process for preparing the material is not particularly limited.

[0060] When manufacturing a raw material, for example, it is manufactured by the following method. Molten steel having a desired chemical composition is manufactured. A slab is manufactured using the molten steel by continuous casting. The manufactured slab is hot worked and cold rolled to manufacture a steel plate having a thickness of several hundred μm to several mm. Through the above steps, the raw material for the ferritic stainless steel foil of this embodiment is prepared.

[0061] [(Process 2) Intermediate cold rolling process] In the intermediate cold rolling process, cold rolling is performed on the prepared material to produce an intermediate steel plate having a thickness of several tens of μm to several hundreds of μm. In the intermediate cold rolling process, for example, cold rolling may be performed using a continuous rolling mill equipped with multiple rolling stands, or cold rolling may be performed using a reversing rolling mill. There is no particular limitation on the cumulative reduction ratio in the intermediate cold rolling process.

[0062] [(Process 3) Intermediate annealing process] In the intermediate annealing step, bright annealing is performed on the intermediate steel sheet after the intermediate cold rolling step. Bright annealing is an annealing treatment performed in an extremely low oxygen atmosphere. The surface of the intermediate steel sheet that has been subjected to bright annealing is hardly oxidized, and the surface gloss can be maintained. The extremely low oxygen atmosphere in bright annealing is preferably a mixed gas atmosphere of H2 gas and N2 gas. The N2 fraction in the atmospheric gas is, for example, 35 to 65% by volume.

[0063] In the bright annealing performed in the intermediate annealing process, the intermediate steel sheet is passed through a heat treatment furnace in an extremely low-oxygen atmosphere at a predetermined speed. The heat treatment furnace is divided into a heating chamber, an annealing chamber, and a rapid cooling chamber in the order in which the intermediate steel sheet passes through. In the heating chamber, the intermediate steel sheet is heated and maintained at a predetermined temperature. Here, the temperature in the heating chamber is the heating temperature T (°C), and the time it takes for the intermediate steel sheet to pass through the heating chamber is the holding time t (seconds). In the annealing chamber, the intermediate steel sheet is cooled from the heating temperature T (°C) to 400°C at a predetermined cooling rate. In the rapid cooling chamber, the intermediate steel sheet cooled to 400°C is rapidly cooled to room temperature. The rapid cooling method is not particularly limited, but may be air cooling, for example.

[0064] The intermediate cold rolling step and the intermediate annealing step may be alternately repeated multiple times. For example, when the intermediate cold rolling step and the intermediate annealing step are alternately repeated twice, a first intermediate cold rolling step and a first intermediate annealing step are performed, followed by a second intermediate cold rolling step and a second intermediate annealing step.

[0065] The intermediate annealing step satisfies the following conditions: When the intermediate annealing step is performed multiple times, it is sufficient that the following conditions are satisfied in the intermediate annealing step that is performed last. (Condition 1) The heat treatment parameter FA defined by the formula (A) is 8418 or less. FA = (T-780) × (log 10 t+30) (A) Here, the heating temperature T (°C) is substituted for T in the formula (A), and the holding time t (seconds) is substituted for t. Condition 1 will be explained below.

[0066] [About the heat treatment parameter FA] In the intermediate annealing step, the higher the heating temperature T or the longer the holding time t, the lower the orientation of the {110} plane in the depth direction. If the FA is 8418 or less, excessive deterioration of the orientation of the {110} plane in the surface layer of the foil body can be suppressed. In this case, assuming that the final cold rolling step satisfies condition 2 described below, the I in the manufactured ferritic stainless steel foil can be MAXis 15.0 or more. Therefore, FA is 8418 or less. The lower limit of FA is not particularly limited. In consideration of normal industrial production, the lower limit of FA is, for example, 2000.

[0067] [(Process 4) Final cold rolling process] In the final cold rolling step, the intermediate steel sheet after the intermediate annealing step is cold rolled again to obtain a ferritic stainless steel foil having a foil body of a predetermined thickness. A well-known cold rolling mill may be used in the final cold rolling step. For example, cold rolling may be performed using a continuous rolling mill equipped with multiple rolling stands arranged in a row, or cold rolling may be performed using a reverse rolling mill. The cumulative reduction ratio in the final cold rolling step is not particularly limited.

[0068] The final cold rolling process satisfies the following conditions: (Condition 2) Maximum rolling reduction rate R in one pass MAX is less than 26%. Condition 2 will be explained below.

[0069] [Maximum rolling reduction in one pass R MAX About Here, "pass" means the operation of the material passing through one rolling stand once. In the final cold rolling process, cold rolling consisting of multiple passes is carried out. "The maximum reduction ratio R MAX " refers to the reduction rate in the pass with the largest reduction rate in the final cold rolling process. If there is even one pass with an excessively large reduction rate, intense processing heat will occur. As a result, the temperature of the intermediate steel sheet will rise excessively, and the orientation of the {110} plane in the depth direction will decrease. The maximum reduction rate in one pass, R MAX When the rolling reduction is 26% or less, it means that there are no passes with rolling reductions exceeding 26%. In this case, the heat generated by processing is sufficiently suppressed, and the decrease in the orientation of the {110} plane in the depth direction is also suppressed. As a result, assuming that the intermediate annealing process satisfies condition 1, the I MAX is 15.0 or more. Therefore, the maximum rolling reduction in one pass R MAXshall be 26% or less. Maximum reduction rate in one pass R MAX There is no particular lower limit for the maximum rolling reduction R in one pass, considering normal industrial production. MAX The lower limit is, for example, 5%.

[0070] The ferritic stainless steel foil of this embodiment is manufactured by the above-described manufacturing method.

[0071] [electrode] The electrode of this embodiment comprises the ferritic stainless steel foil of this embodiment and an electrode mixture layer formed on the surface of the ferritic stainless steel foil. That is, in the electrode of this embodiment, the ferritic stainless steel foil of this embodiment is used as a current collector. The electrode of this embodiment may be a positive electrode or a negative electrode. That is, the configuration of the electrode of this embodiment is not particularly limited as long as it comprises the ferritic stainless steel foil of this embodiment and an electrode mixture layer.

[0072] [Electrode mixture layer] In the electrode of this embodiment, the electrode mixture layer is not particularly limited as long as it has a known configuration. The electrode mixture layer contains an active material. The electrode mixture layer may contain materials other than the active material. The electrode mixture layer may contain, for example, a binder and a conductive additive. Furthermore, the electrode mixture layer used in an all-solid-state battery may contain, for example, a solid electrolyte.

[0073] [Active material] In the electrode of this embodiment, the active material contained in the electrode mixture layer is not particularly limited, and well-known active materials can be used. When the electrode is a positive electrode, the positive electrode active material may be, for example, LiCoO2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3The negative electrode active material may be, for example, a carbon-based material such as graphite, an alloy material such as CuSn alloy and NiTiSi alloy, a Si-based material such as Si and SiO, or Li4Ti5O 12 It may also be an oxide-based material represented by the following.

[0074] [binder] In the electrode of this embodiment, the binder contained in the electrode mixture layer is not particularly limited, and well-known binders can be used. The binder may be, for example, a rubbery polymer such as styrene-butadiene rubber or isoprene rubber, a synthetic resin such as polyethylene, polyimide, polyacrylic acid, or polyamide, a styrene-butadiene-styrene block copolymer or its hydrogenated product, a thermoplastic elastomer such as styrene-ethylene-butadiene, styrene copolymer, styrene-isoprene, or styrene block copolymer or their hydrogenated products, a soft resinous polymer such as syndiotactic 1,2-polybutadiene, ethylene-vinyl acetate copolymer, or copolymer of ethylene with an α-olefin having 3 to 12 carbon atoms, or a fluorinated polymer such as polytetrafluoroethylene, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride, polypentafluoropropylene, or polyhexafluoropropylene.

[0075] [Conductive additive] In the electrode of this embodiment, the conductive additive contained in the electrode mixture layer is not particularly limited, and any known conductive additive can be used. The conductive additive may be, for example, acetylene black, carbon black, or ketjen black.

[0076] [Electrode manufacturing method] The method for producing the electrode of this embodiment is not particularly limited. The electrode of this embodiment is produced by a well-known method using the ferritic stainless steel foil of this embodiment as a current collector. The method for producing the electrode of this embodiment includes, for example, an electrode slurry preparation step and an electrode mixture layer formation step.

[0077] [Electrode slurry preparation process] In the electrode slurry preparation step, a composition (electrode slurry) for forming an electrode mixture layer is prepared. The electrode slurry may be prepared according to the electrode mixture layer to be obtained. For example, the electrode slurry may be prepared by kneading an active material, a binder, and a solvent. For example, the electrode slurry may be prepared by further kneading an active material, a conductive additive, a binder, and a solvent. Furthermore, when preparing an electrode slurry to be used in an all-solid-state battery, the electrode slurry may be prepared by kneading an active material, a solvent, a solid electrolyte, and a binder. The kneading method is adjusted appropriately depending on the active material, the conductive additive, the binder, the solid electrolyte, and the solvent. In other words, the electrode slurry preparation step may be performed by a known method.

[0078] [Electrode mixture layer formation process] In the electrode mixture layer forming step, an electrode mixture layer is formed on the surface of the ferritic stainless steel foil of this embodiment. Specifically, the kneaded electrode slurry is applied to the ferritic stainless steel foil of this embodiment. The application method is not particularly limited and may be a well-known method. For example, application may be performed using an applicator with a gap. Furthermore, application may be performed by spraying using a sprayer.

[0079] The electrode of this embodiment can be manufactured by the above steps.

[0080] [battery] The battery of this embodiment includes the electrode of this embodiment and an electrolyte. The battery of this embodiment may have any known configuration other than the electrode of this embodiment, and is not particularly limited. The battery of this embodiment may further include, for example, a separator. The shape of the battery of this embodiment is not particularly limited, and may be cylindrical, prismatic, coin-shaped, or sheet-shaped. Furthermore, the battery of this embodiment may be a secondary battery or a primary battery. When the battery according to this embodiment is a secondary battery, it may be, for example, a non-aqueous electrolyte secondary battery, an aqueous electrolyte secondary battery, or an all-solid-state secondary battery.

[0081] [Electrolyte] The electrolyte conducts ions between the positive electrode and the negative electrode. In the battery of this embodiment, the electrolyte is not particularly limited, and a well-known electrolyte can be used. The electrolyte may be a liquid electrolytic solution or a solid electrolyte.

[0082] The electrodes of the battery of this embodiment use the ferritic stainless steel foil of this embodiment as a current collector. Therefore, the current collector has excellent corrosion resistance. Therefore, the electrolyte of the battery of this embodiment can be a sulfide-based solid electrolyte, which is highly corrosive to the current collector. Examples of sulfide-based solid electrolytes include Li3PS4 and Li7P3S 11 It may be an LPS system represented by Li6PS5Cl x Br (1-x) (0≦x≦1) may be an argyrodite type, 10 GeP2S 12 and Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 The thiolicon represented by the following may also be used.

[0083] [Battery manufacturing method] The method for manufacturing the battery of the present embodiment is not particularly limited. For example, the battery of the present embodiment is manufactured by a well-known method by placing a laminate of the electrode of the present embodiment, an electrolyte, and a counter electrode in a battery case. [Example]

[0084] The effects of the ferritic stainless steel foil of this embodiment will be explained more specifically using examples. The conditions in the following examples are one example of conditions adopted to confirm the feasibility and effects of the ferritic stainless steel foil of this embodiment. Therefore, the ferritic stainless steel foil of this embodiment is not limited to this one example of conditions.

[0085] As a material for producing ferritic stainless steel foil, a steel plate having the chemical composition shown in Table 1 was prepared. The thickness of the steel plate was 300 μm.

[0086] [Table 1]

[0087] The material of each test number was subjected to an intermediate cold rolling process once to produce an intermediate steel plate. Specifically, the material of each test number was cold rolled using a reverse rolling mill.

[0088] The intermediate steel sheets after the intermediate cold rolling process were subjected to a single intermediate annealing process. Specifically, the intermediate steel sheets of each test number were bright annealed in a mixed gas atmosphere of 35 to 65 volume % N2 gas and the remainder H2 gas. The heating temperature T (°C), holding time t (seconds), and calculated heat treatment parameter FA for each test number are shown in Table 2.

[0089] [Table 2]

[0090] The intermediate steel sheets after the intermediate annealing process were subjected to a final cold rolling process. In the final cold rolling process, the intermediate steel sheets of each test number were subjected to cold rolling using a reverse rolling mill to produce ferritic stainless steel foils having a foil body with a thickness of 10 μm. The maximum rolling reduction R in one pass for each test number was MAX (%) are shown in Table 2.

[0091] By the above manufacturing process, ferritic stainless steel foils with each test number were manufactured.

[0092] [About the evaluation test] The following evaluation tests were carried out on the produced ferritic stainless steel foils with each test number. (Test 1) Integrated intensity measurement test (Test 2) Corrosion resistance evaluation test Each test will be explained below.

[0093] [(Test 1) Integrated intensity measurement test] Based on the method described in the above [Method for measuring the integrated intensity of each lattice plane], the integrated intensity II of the {110} plane from the depth position of 0.38 μm to the depth position of 2.82 μm in the foil body of the ferritic stainless steel foil of each test number 110 , and the integrated intensity of the {211} plane II 211 The obtained II 110 and II 211 Based on equation (1), I R Calculate I in the region from the 0.38 μm depth position to the 2.82 μm depth position. R The maximum value of I MAX The I of each test number was calculated. MAX is shown in Table 3.

[0094] [Table 3]

[0095] [(Test 2) Corrosion resistance evaluation test] The corrosion resistance of the ferritic stainless steel foil of each test number was evaluated by the following method. First, a circular test piece with a diameter of 11 mm was taken from the ferritic stainless steel foil. One surface of the test piece was used as the evaluation surface. The developed area ratio Sdr, as specified in ISO25178-2:2012, was measured on the evaluation surface of the test piece. The developed area ratio Sdr is an index that represents the rate of increase in the surface area of ​​the measured surface compared to a flat surface. Since the corrosion reaction begins on the surface of the foil itself, the greater the developed area ratio Sdr of the test piece, the faster the corrosion progresses.

[0096] The developed area ratio Sdr of the evaluation surface of the test specimen was measured using a laser microscope. The laser microscope used was a Keyence VK-X100. A measurement area of ​​280 μm × 200 μm was measured at a magnification of 2000x. Specifically, four locations within the measurement area were measured with a 145 μm × 109 μm observation field to measure the entire area, and a surface image was obtained. The four surface images were linked using the accompanying image linking software to obtain a surface image of the 280 μm × 200 μm measurement area. A reference plane was set by cutting 0.3% of the area from the low-brightness side from the surface shape profile obtained by analyzing the surface image of the measurement area, and a three-dimensional image was generated. Filtering was performed using a high-pass filter with a cutoff wavelength of 50 μm. A Gaussian filter was used for filtering. The developed area ratio Sdr, as defined in ISO25178-2:2012, was calculated in a 200 μm × 150 μm region of the obtained three-dimensional image.

[0097] Using the test specimens with the measured developed area ratio (Sdr), evaluation cells simulating sulfide-based all-solid-state batteries were fabricated. Specifically, 0.12 g of sulfide-based solid electrolyte was placed in a mold with an inner diameter of 11 mm and then pressurized at 300 MPa to form a cylindrical sulfide-based solid electrolyte pellet with a thickness of 700 μm and a bottom diameter of 11 mm. β-Li3PS4 was used as the sulfide-based solid electrolyte. The resulting pellet was placed on the evaluation surface of each test specimen. Furthermore, a cylindrical Li foil with a thickness of 1.2 mm and a bottom diameter of 11 mm was placed on top of the sulfide-based solid electrolyte pellet. These were placed in a measurement cell with an inner diameter of 11 mm, which was sealed from the outside air, and then bolted to a pressure of 5 MPa. The process from preparing the sulfide-based solid electrolyte pellet to sealing the evaluation cell was carried out in a glove box with an Ar atmosphere. The evaluation cells for each test specimen were fabricated using the above process.

[0098] Cyclic voltammetry (CV) measurements were carried out using the evaluation cells of each test number. In the cyclic voltammetry measurements, the test piece was used as the working electrode, and metal Li foil was used as the counter electrode and reference electrode. Specifically, the voltage was measured for the evaluation cell held at 60°C for 24 hours, and the open-circuit voltage V OC (V) to 3.0V, then to 0.005V, and again to the open circuit voltage V OC (V), and the current density (μA / cm 2 The open-circuit voltage V was measured at a sweep rate of 5 mV / sec. A series of voltage sweeps constituted one cycle, which was repeated five times. OC was 2.0 to 2.5 V for the evaluation cells of all test numbers.

[0099] Based on the measurement results, the open-circuit voltage V at the nth cycle (n is an integer between 1 and 5) OC The current density (μA / cm) flowing during the sweep from (V) to 3.0 V 2 ) was integrated by the time (seconds) it took to sweep. Furthermore, the integrated value was divided by the developed area ratio Sdr to eliminate the influence of minute irregularities on the evaluation surface of the test piece, and the result was calculated as C n (μC / cm2 ) is defined as C n (μC / cm 2 ) is the open circuit voltage V OC The time elapsed from the start of the sweep from (V) to 3.0V is defined as the test time t (seconds), and the time it takes to reach 3.0V is defined as t 3.0 (seconds), and the current density flowing through the evaluation cell at test time t (seconds) is I(t) (μA / cm 2 ) and the developed area ratio of the test piece is Sdr, it can be calculated using the following formula.

number

[0100] The sum of C1 to C5 is the integrated current value C (μC / cm 2 ) and was used as an index to represent the progress of the corrosion reaction on the test piece. 2 ) can be calculated using the following formula: C=C1+C2+C3+C4+C5 Accumulated current value C (μC / cm 2 ) are shown in Table 3. When the integrated current value C is 8500 μC / cm 2 When the integrated current value C was 8500 μC / cm or less, it was judged that excellent corrosion resistance was obtained. 2 When the value exceeded this, it was determined that excellent corrosion resistance was not obtained.

[0101] [Evaluation results] Referring to Tables 1 to 3, for the ferritic stainless steel foils of test numbers 1 to 6, I MAX was 15.0 or more, and therefore, excellent corrosion resistance was obtained.

[0102] On the other hand, in test No. 7, the FA in the intermediate annealing process was too high. MAX As a result, excellent corrosion resistance was not obtained.

[0103] In test number 8, the maximum reduction rate R in one pass in the final cold rolling process MAX (%) was too large. Therefore, IMAX As a result, excellent corrosion resistance was not obtained.

[0104] The embodiments of the present disclosure have been described above. However, the above-described embodiments are merely examples for implementing the present disclosure. Therefore, the present disclosure is not limited to the above-described embodiments, and can be implemented by appropriately modifying the above-described embodiments within the scope of the present disclosure.

Claims

1. A foil body made of ferritic stainless steel, I defined by formula (1) in the region from a depth of 0.38 μm to a depth of 2.82 μm starting from the surface of the foil body Ｒ The maximum value of I ＭＡＸ is 15.0 or more, Ferritic stainless steel foil. I Ｒ =-- １１０ / -- ２１１ (1) Here, II in formula (1) １１０ is substituted with the integrated intensity of the {110} plane obtained by grazing incidence X-ray diffraction, and II ２１１ is substituted with the integrated intensity of the {211} plane obtained by grazing incidence X-ray diffraction.

2. The ferritic stainless steel foil according to claim 1, The chemical composition of the foil body is, in mass%, C: 0.001-0.030%, Si: 0.01-1.00%, Mn: 0.01-1.00%, P: 0.050% or less, S: 0.030% or less, Ni: 0.01-0.50%, Cr: 12.00-20.00%, Mo: 0.01-2.50%, N: 0-0.100%, Ti: 0 to 0.80%, Nb: 0 to 0.80%, and Zr: 0 to 0.80%; The balance consists of Fe and impurities. Ferritic stainless steel foil.

3. The ferritic stainless steel foil according to claim 1 or claim 2; an electrode mixture layer formed on the surface of the ferritic stainless steel foil, electrode.

4. The electrode according to claim 3; an electrolyte; battery.

5. 5. The battery of claim 4, The electrolyte is a sulfide-based solid electrolyte. battery.

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