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. The S parameter obtained from the positron annihilation coincidence Doppler broadening method measurement of the foil main body is 0.592 or more, and the W parameter is 2.80×10-3 or less.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. Therefore, 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, The foil body is measured by a positron annihilation coincidence Doppler broadening method, and the S parameter is 0.592 or more and the W parameter is 2.80 × 10 -3 The following is the result.

[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 lattice defects contained in a ferritic stainless steel foil having a foil body made of ferritic stainless steel, rather than the chemical composition of the foil body.

[0018] Many dislocations are introduced into the foil body of ferritic stainless steel foil to ensure sufficient strength. Furthermore, when ferritic stainless steel foil is used as a current collector, the electrode manufacturing process often involves pressing, which can introduce additional dislocations into the foil body. The dislocations introduced into the foil body move within the crystal grains, forming cellular tangles (dislocation cells). Eventually, the dislocations within the cells annihilate each other, and the dislocations tangled at the cell walls rearrange to form subgrain boundaries.

[0019] Corrosion of ferritic stainless steel foils occurs preferentially at subgrain boundaries. At subgrain boundaries, the atomic arrangement is significantly more disordered than within the grains, resulting in a high-energy state. Therefore, the corrosion reaction proceeds more quickly. In other words, it is preferable to suppress the formation of subgrain boundaries in order to suppress the progression of corrosion.

[0020] Ferritic stainless steel foil is generally manufactured through rolling. During rolling, plastic strain is introduced into the foil body. As a result, lattice defects are generated within the foil body. Because the amount of plastic strain introduced during rolling differs between the surface and the interior of the foil body, the amount of lattice defects introduced differs. Here, by introducing an appropriate amount of lattice defects into the interior, the formation of subgrain boundaries within the foil can be suppressed. In this case, even if corrosion progresses from the surface, the progress of corrosion within the foil can be delayed. As a result, the corrosion resistance of ferritic stainless steel foil is improved.

[0021] The amount of lattice defects introduced into the foil body can be evaluated using the S parameter and W parameter obtained by the positron annihilation coincidence Doppler broadening (CDB) method. The positron annihilation Doppler broadening method detects the energy of two gamma rays emitted when a positron incident on a sample annihilates with an electron. Although the energy of each gamma ray is 511 keV, it is actually detected as a certain broadened energy distribution (CDB spectrum) due to the Doppler effect depending on the motion state of the annihilated electron. In the obtained energy distribution, the S parameter represents the proportion of gamma rays detected in the energy range with a small deviation from 511 keV. The W parameter represents the proportion of gamma rays detected in the energy range with a large deviation from 511 keV. Here, if the amount of lattice defects introduced into the foil body is large, the number of positrons that annihilate with conduction electrons and the number of positrons that annihilate with core electrons will increase. Compared to core electrons, conduction electrons have a smaller momentum, so the gamma rays generated by their annihilation with conduction electrons are less susceptible to the Doppler effect. Therefore, the greater the amount of lattice defects introduced into the foil itself, the narrower the distribution of detected energies. As a result, the S parameter becomes larger and the W parameter becomes smaller. In other words, the larger the S parameter and the smaller the W parameter obtained by the positron annihilation coincidence Doppler broadening method, the more the formation of subgrain boundaries is suppressed, and the higher the corrosion resistance of ferritic stainless steel foil.

[0022] Based on the above findings, the inventors investigated the relationship between the S parameter and W parameter of the foil body obtained by the positron annihilation coincidence Doppler broadening method and the corrosion resistance. As a result, it was found that the S parameter was 0.592 or more and the W parameter was 2.80 × 10 -3 The present inventors have found that excellent corrosion resistance can be obtained in a ferritic stainless steel foil if the thickness is less than or equal to the range.

[0023] 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.

[0024] The ferritic stainless steel foil of the first configuration is A foil body made of ferritic stainless steel, The foil body is measured by a positron annihilation coincidence Doppler broadening method, and the S parameter is 0.592 or more and the W parameter is 2.80 × 10 -3 The following is the result.

[0025] 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.

[0026] 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.

[0027] The battery of the first configuration comprises: Electrodes in a first configuration; and an electrolyte.

[0028] The battery in the second configuration is 1. A battery of a first configuration, comprising: The electrolyte is a sulfide-based solid electrolyte.

[0029] 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.

[0030] [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 with 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.

[0031] [About S parameters and W parameters] In the ferritic stainless steel foil of this embodiment, the foil body is measured by the positron annihilation coincidence Doppler broadening method, and the S parameter is 0.592 or more and the W parameter is 2.80 × 10 -3 The following is the result.

[0032] As mentioned above, the larger the S parameter obtained by positron annihilation coincidence Doppler broadening and the smaller the W parameter, the greater the amount of lattice defects introduced into the foil body. -3 If the thickness is less than 100 μm, the amount of lattice defects introduced into the foil body is sufficiently large. In this case, the formation of subgrain boundaries that promote the progression of corrosion is sufficiently suppressed. As a result, excellent corrosion resistance is obtained.

[0033] A preferred lower limit for the S parameter is 0.594, and more preferably 0.596. There is no particular limit to the upper limit of the S parameter. Taking into account normal industrial production, the upper limit of the S parameter is, for example, 0.610. The lower limit of the W parameter is not particularly limited. Considering normal industrial production, the lower limit of the W parameter is, for example, 2.60 × 10 -3 is. The preferred upper limit of the W parameter is 2.75 × 10 -3 and more preferably 2.70 × 10 -3 is.

[0034] [Method for measuring S-parameters and W-parameters] The S and W parameters of the foil body are determined by the following method.

[0035] A test piece is taken from the ferritic stainless steel foil itself, and measurements are carried out using the positron annihilation coincidence Doppler broadening method. Specifically, three of the test pieces are stacked together to create two laminates. A positron source is sandwiched between the two laminates to carry out measurements. The positron source is: 22 Na is used. The positron source is, for example, NA351 manufactured by the Japan Radioisotope Association. For gamma-ray detection, for example, a DSP module for gamma-ray spectrometer APV8002 manufactured by Techno AP Co., Ltd. is used. The count number is set to 10 million counts or more. From the energy distribution of gamma rays obtained by measurement, the half-width is calculated in the range of 509 to 513 keV. The common resolution is set to 1.04 keV, and the measurement resolution is set to the calculated half-width, and the S parameter and W parameter are calculated. Specifically, the average count number at each energy in the range of 540 to 545 keV is set to the count number corresponding to the background. The sum of the values ​​obtained by subtracting the count number corresponding to the background from the count number at each energy in the entire measured energy range is set to C. totalSimilarly, the energy range used to calculate the S parameters is set to 511 to 512 keV, and the sum of the counts at each energy in this energy range minus the counts corresponding to the background is defined as C S The energy range corresponding to the W parameter is set to 516 to 518 keV, and the sum of the counts at each energy in this energy range minus the counts corresponding to the background is defined as C W The S and W parameters were calculated using the following formulas. S-parameter = C S / C total W parameter = C W / C total The S parameter is a value rounded off to three decimal places, and the W parameter is a value rounded off to five decimal places.

[0036] [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.

[0037] 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).

[0038] 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).

[0039] The chemical composition of the foil body of the ferritic stainless steel foil of this embodiment may contain, for example, the following elements.

[0040] 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%.

[0041] 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%.

[0042] 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%.

[0043] 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%.

[0044] 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%.

[0045] 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%.

[0046] 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%.

[0047] 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%.

[0048] 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%.

[0049] 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%.

[0050] 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%.

[0051] 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%.

[0052] 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.

[0053] 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.

[0054] [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.

[0055] [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.

[0056] 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.

[0057] [(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.

[0058] 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.

[0059] [(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.

[0060] [(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.

[0061] In the bright annealing performed in the intermediate annealing step, the intermediate steel sheet is passed through a heat treatment furnace in an extremely low-oxygen atmosphere at a predetermined speed. At this time, a predetermined amount of tension is applied to the intermediate steel sheet. 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 is passed through. In the heating chamber, the intermediate steel sheet is heated and maintained at a heating temperature T (°C). The heating temperature T is, for example, 800 to 1200°C. 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 is, for example, air cooling.

[0062] 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.

[0063] 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 tension Ts applied to the intermediate steel plate during the cooling process from the heating temperature T (℃) to 400℃ is 1.0 N / mm 2 That's all. Condition 1 will be explained below.

[0064] [About tension Ts] During the cooling process from the heating temperature T (°C) to 400°C in the intermediate annealing step, the greater the tension Ts applied to the intermediate steel sheet, the more likely it is that a structure containing many lattice defects will be formed. 2 If this is the case, the crystal lattice of the intermediate steel sheet after the intermediate annealing process will contain a sufficient amount of lattice defects. In this case, assuming that the final cold rolling process satisfies condition 2 described below, the S parameter of the foil body in the manufactured ferritic stainless steel foil will be 0.592 or more, and the W parameter will be 2.80 × 10 -3 Therefore, the tension Ts is 1.0 N / mm 2 That's all. The upper limit of the tension Ts is not particularly limited. Considering normal industrial production, the upper limit of the tension Ts is, for example, 8.0 N / mm 2 is.

[0065] [(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.

[0066] The final cold rolling process satisfies the following conditions: (Condition 2) Maximum rolling reduction rate R in one pass MAX is less than 28%. Condition 2 will be explained below.

[0067] [Maximum reduction rate 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, reducing the lattice defects contained in the crystal lattice of the intermediate steel sheet. The maximum reduction rate in one pass, R MAX If the rolling reduction is 28% or less, this means that there are no passes with rolling reductions exceeding 28%. In this case, the heat generated by processing is sufficiently suppressed, and the reduction in lattice defects in the intermediate steel sheet is also suppressed. As a result, assuming that the intermediate annealing process satisfies condition 1, the S parameter of the foil body in the manufactured ferritic stainless steel foil will be 0.592 or more, and the W parameter will be 2.80 × 10 -3 Therefore, the maximum reduction rate in one pass R MAX shall be 28% 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%.

[0068] The ferritic stainless steel foil of this embodiment is manufactured by the above-described manufacturing method.

[0069] [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.

[0070] [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.

[0071] [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 / 3 The 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.

[0072] [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. Examples of the binder include rubbery polymers such as styrene-butadiene rubber and isoprene rubber, synthetic resins such as polyethylene, polyimide, polyacrylic acid, and polyamide, styrene-butadiene-styrene block copolymers or their hydrogenated derivatives, thermoplastic elastomers such as styrene-ethylene-butadiene, styrene copolymers, styrene-isoprene, or styrene block copolymers or their hydrogenated derivatives, soft resinous polymers such as syndiotactic 1,2-polybutadiene, ethylene-vinyl acetate copolymers, and copolymers of ethylene with α-olefins having 3 to 12 carbon atoms, and fluorinated polymers such as polytetrafluoroethylene, tetrafluoroethylene-ethylene copolymers, polyvinylidene fluoride, polypentafluoropropylene, and polyhexafluoropropylene.

[0073] [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.

[0074] [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.

[0075] [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.

[0076] [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.

[0077] The electrode of this embodiment can be manufactured by the above steps.

[0078] [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.

[0079] [Electrolytes] 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.

[0080] 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.

[0081] [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]

[0082] 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.

[0083] 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.

[0084] [Table 1]

[0085] 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.

[0086] The intermediate steel sheets after the intermediate cold rolling process were subjected to one 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. In the bright annealing, the heating temperature T was 800 to 1200°C. The tension Ts (N / mm 2 ) are shown in Table 2.

[0087] [Table 2]

[0088] The intermediate steel sheet after the intermediate annealing process was subjected to a final cold rolling process. In the final cold rolling process, the intermediate steel material of each test number was subjected to cold rolling using a reverse rolling mill to produce a ferritic stainless steel foil 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.

[0089] By the above manufacturing process, ferritic stainless steel foils with each test number were manufactured.

[0090] [About the evaluation test] The following evaluation tests were carried out on the produced ferritic stainless steel foils with each test number. (Test 1) S-parameter and W-parameter measurement test (Test 2) Corrosion resistance evaluation test Each test will be explained below.

[0091] [(Test 1) S-parameter and W-parameter measurement test] Based on the method described above in [Method for measuring S parameters and W parameters], the S parameters and W parameters of the foil body of the ferritic stainless steel foil of each test number were measured. The obtained S parameters and W parameters are shown in Table 3.

[0092] [Table 3]

[0093] [(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.

[0094] 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 field of view 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.

[0095] 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.

[0096] 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 OC was 2.0 to 2.5 V for the evaluation cells of all test numbers.

[0097] From the measurement results, the open circuit voltage V OC The maximum current density (μA / cm) flowed during the sweep from 0.0V to 3.0V. 2 ) was divided by the developed area ratio Sdr to eliminate the influence of minute irregularities on the evaluation surface of the test piece. The obtained value was used as the maximum current value I MAX (μA / cm 2 ) and was used as an index to represent the progress of the corrosion reaction in the test piece.

[0098] Maximum current value I for each test number MAX (μA / cm 2 ) are shown in Table 3. Maximum current value I MAX is 25.0 μA / cm 2 If the maximum current value I was less than 100%, it was judged that excellent corrosion resistance was obtained. MAX is 25.0 μA / cm 2 When the value exceeded this, it was determined that excellent corrosion resistance was not obtained.

[0099] [Evaluation results] Referring to Tables 1 to 3, the ferritic stainless steel foils of test numbers 1 to 6 had an S parameter of 0.592 or more and a W parameter of 2.80 × 10 -3 Therefore, excellent corrosion resistance was obtained.

[0100] On the other hand, in test number 7, the tension Ts in the intermediate annealing process was too small, so the S parameter was less than 0.592 and the W parameter was 2.80 × 10 -3 As a result, excellent corrosion resistance was not obtained.

[0101] In test number 8, the maximum reduction rate R in one pass in the final cold rolling process MAX (%) was too large. As a result, the S parameter was less than 0.592 and the W parameter was 2.80×10 -3 As a result, excellent corrosion resistance was not obtained.

[0102] 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, The foil body is measured by a positron annihilation coincidence Doppler broadening method, and the S parameter is 0.592 or more and the W parameter is 2.80 × 10 －３ Below is the Ferritic stainless steel foil.

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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