Ferritic stainless steel foil, electrode, and battery

Abstract

Provided is a ferritic stainless steel foil exhibiting excellent corrosion resistance. A ferritic stainless steel foil according to the present disclosure is provided with a foil main body made of ferritic stainless steel, wherein, in an inverse pole figure in the ND direction obtained by measuring the rolled surface of the foil main body by an electron backscattered diffraction method, the maximum pole density M001 in the 001 orientation and the maximum pole density M111 in the 111 orientation satisfy formula (1).　M001 / M111 ≤ 0.16 (1)

Description

Ferritic stainless steel foil, electrode, and battery

[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.

[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] Conventionally, electrolyte solutions have been used as electrolytes in secondary batteries. However, because electrolyte solutions contain flammable organic solvents, their usable temperature range is narrow. For this reason, in recent years, development of all-solid-state batteries using solid electrolytes instead of electrolyte solutions has been progressing. Because all-solid-state batteries do not contain organic solvents, stable battery performance can be obtained 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] The ferritic stainless steel sheet for use as a current collector in a sulfide-based solid battery disclosed in Patent Document 1 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 consisting of Fe and unavoidable impurities. Patent Document 1 states that this ferritic stainless steel sheet exhibits excellent sulfidation resistance by increasing the Cr content to 18.00% or more.

[0009] International Publication No. 2021 / 006089

[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.

[0012] The ferritic stainless steel foil of the present disclosure comprises a foil body made of ferritic stainless steel, and in an ND inverse pole figure obtained by measuring the rolled surface of the foil body by electron backscatter diffraction, the maximum pole density M in the <001> orientation is ００１ and the maximum pole density M of the <111> orientation １１１ and satisfy the formula (1). ００１ / M １１１ ≦0.16 (1)

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

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

[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.

[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, the inclusion of 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 reduces the workability of the ferritic stainless steel foil and increases the manufacturing cost. Therefore, the inventors focused on the texture on the surface 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] The ND crystal planes of a ferritic stainless steel foil body are primarily composed of the {001}<110> orientation of the rolling texture and the {111}<112> orientation of the recrystallization texture. Here, the ND direction refers to the normal direction of the rolled surface of the ferritic stainless steel foil body. The rolled surface of the foil body refers to the surface perpendicular to the thickness direction of the foil body. In this specification, the rolled surface is also simply referred to as the "surface." The RD direction is also referred to as the rolling direction. The rolling texture is a texture formed by rolling. Compared to a recrystallized texture, the rolling texture contains many unrecrystallized grains. Unrecrystallized grains also contain many subgrain boundaries formed by dislocation multiplication. The atomic arrangement around subgrain boundaries is significantly more disordered than within the grains, resulting in a high-energy state. Therefore, the corrosion rate is faster. In other words, corrosion progresses preferentially in a rolling texture containing many subgrain boundaries compared to a recrystallized texture.

[0019] Corrosion of ferritic stainless steel foil begins at the surface of the foil itself. The greater the amount of rolling texture containing many subgrains compared to the recrystallization texture on the surface of the foil itself, the more corrosion of the foil itself progresses. In other words, by reducing the ratio of rolling texture to recrystallization texture on the surface of the foil itself, the progression of corrosion originating from the surface can be suppressed. As a result, the corrosion resistance of the ferritic stainless steel foil can be improved.

[0020] The amount of rolling texture and recrystallization texture on the surface of the foil body can be evaluated using an ND inverse pole figure obtained by measurement using the electron backscatter diffraction (EBSD) method. The ND inverse pole figure shows the tendency of the crystal orientation that constitutes the crystal plane in the ND direction. Here, the amount of rolling texture on the measurement surface is expressed as the maximum pole density M ００１ The amount of recrystallization texture is expressed as the maximum pole density M １１１ The maximum pole density means the intensity ratio with respect to the random orientation. In other words, the maximum pole density M １１１ Maximum pole density M ００１The smaller the value, the lower the ratio of rolling texture to recrystallization texture at the surface of the foil body.

[0021] Based on the above findings, the present inventors have determined that the maximum pole density M of the <001> orientation in the ND inverse pole figure obtained by measuring the rolled surface of the foil body by electron backscatter diffraction is ００１ and the maximum pole density M of the <111> orientation １１１ As a result, the present inventors have found that excellent corrosion resistance can be obtained in a ferritic stainless steel foil if the following formula (1) is satisfied: M ００１ / M １１１ ≦0.16 (1)

[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 comprises a foil body made of ferritic stainless steel, and in an ND inverse pole figure obtained by measuring the rolled surface of the foil body by electron backscatter diffraction, the maximum pole density M in the <001> orientation is ００１ and the maximum pole density M of the <111> orientation １１１ and satisfy the formula (1). ００１ / M １１１ ≦0.16 (1)

[0024] The ferritic stainless steel foil of the second configuration is the ferritic stainless steel foil of the first configuration, further characterized in that the foil body has an S parameter of 0.592 or more and a W parameter of 2.80×10 or more, which are obtained by measuring the foil body by a positron annihilation coincidence Doppler broadening method. －３ The following is the result.

[0025] A ferritic stainless steel foil of a third configuration is the ferritic stainless steel foil of the first or second configuration, wherein the chemical composition of the foil body contains, 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 to 20.00%, Mo: 0.01 to 2.50%, N: 0 to 0.100%, Ti: 0 to 0.80%, Nb: 0 to 0.80%, and Zr: 0 to 0.80%, with the balance consisting of Fe and impurities.

[0026] The electrode of the first configuration comprises a ferritic stainless steel foil of any one of the first to third configurations, and an electrode mixture layer formed on the surface of the ferritic stainless steel foil.

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

[0028] The battery of the second configuration is the battery of the first configuration, wherein 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 "%" regarding elements means mass % unless otherwise specified.

[0030] [Configuration 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 means 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.

[0031] [Regarding Formula (1)] In the ferritic stainless steel foil of this embodiment, the maximum pole density M ００１ and the maximum pole density M of the <111> orientation １１１ and satisfy the formula (1). ００１ / M １１１ ≦0.16 (1)

[0032] F1 is defined as follows: F1 = M ００１ / M １１１ F1 is an index representing the ratio of the rolling texture to the recrystallization texture on the surface of the foil body. As described above, the lower the ratio of the rolling texture containing more dislocations compared to the recrystallization texture on the surface of the foil body, the more effectively corrosion initiated from the surface can be suppressed. When F1 is 0.16 or less, the ratio of the rolling texture to the recrystallization texture is sufficiently low. In this case, corrosion initiated from the surface can be sufficiently suppressed. As a result, excellent corrosion resistance can be obtained.

[0033] The lower limit of F1 is not particularly limited. In consideration of normal industrial production, the lower limit of F1 is, for example, 0.01. The upper limit of F1 is preferably 0.15, and more preferably 0.13.

[0034] [Method for measuring maximum pole density] The maximum pole density M of the <001> orientation in the inverse pole figure in the ND direction ００１ and the maximum pole density M of the <111> orientation １１１ is calculated in the following way:

[0035] A test piece is taken from the rolled surface of the foil body of the ferritic stainless steel foil 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 may be, for example, the center of the width of the foil body. The observation surface of the test piece is electropolished. The applied voltage for electropolishing is 35 V, and the polishing time is 10 seconds. The electrolyte is a mixed solution of 78 mL of perchloric acid, 90 mL of distilled water, 730 mL of ethanol, and 100 mL of butyl cellosolve. Three measurement areas of 200 μm x 200 μm are set on the observation surface after electropolishing, with no overlapping. EBSD measurement is performed for each measurement area. The EBSD measurement is performed with an acceleration voltage of 20 kV, a probe current of 28 nA, and a working distance (WD) of 15.0 mm. The observation magnification is 400x, and the step size is 0.3 μm. The measurement results in the three measurement regions are analyzed using OIM-Analysis Ver. 7, a product name of TSL Solutions Co., Ltd., to obtain an inverse pole figure in the ND direction. Note that in the sample coordinate system in which the A1 axis corresponds to the Y axis, the A2 axis corresponds to the X axis, and the A3 axis corresponds to the Z axis, the analysis is performed by rotating the sample so that the A2 axis coincides with the RD direction of the observation surface and the A3 axis coincides with the ND direction of the observation surface. Furthermore, measurement points for which the confidence index (CI value), which indicates the certainty of the obtained crystal orientation, is 0.1 or less are not used in the analysis. From the obtained inverse pole figure, the maximum pole density M of the <001> orientation is determined. ００１ and the maximum pole density M of the <111> orientation １１１ and get.

[0036] The maximum pole density obtained, M ００１ and maximum pole density M １１１ F1 is calculated based on the above formula. Note that F1 is a value rounded off to two decimal places.

[0037] [Regarding S-parameter and W-parameter] Preferably, the ferritic stainless steel foil of the present embodiment has an S-parameter of 0.592 or more and a W-parameter of 2.80×10 or more, which are obtained by measuring the foil body by a positron annihilation coincidence Doppler broadening method. －３ The following is the result.

[0038] To ensure sufficient strength, dislocations are introduced into the foil body of ferritic stainless steel foil, not only on the surface but also within the foil itself. 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.

[0039] During rolling in the manufacturing process of ferritic stainless steel foil, 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, in a ferritic stainless steel foil that can suppress the progression of corrosion originating from the surface by satisfying formula (1), the progression of corrosion within the foil can also be delayed. As a result, the corrosion resistance of the ferritic stainless steel foil is further improved.

[0040] 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 measurement sample annihilates with an electron. The energy of one gamma ray is 511 keV, but in reality, it is affected by the Doppler effect depending on the motion state of the annihilated electron and is detected as an energy distribution (CDB spectrum) with a certain degree of broadening. In the obtained energy distribution, the S parameter represents the proportion of gamma rays detected in an energy range with a small deviation from 511 keV. The W parameter represents the proportion of gamma rays detected in an 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 increases, and the number of positrons that annihilate with core electrons decreases. Compared to core electrons, conduction electrons have a smaller momentum, so the gamma rays generated by the annihilation of conduction electrons are less susceptible to the Doppler effect. Therefore, the greater the amount of lattice defects introduced into the foil body, the narrower the detected energy distribution. 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 greater the corrosion resistance of ferritic stainless steel foil.

[0041] In the foil body, the S parameter is 0.592 or more, and the W parameter is 2.80 × 10 －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, resulting in even better corrosion resistance.

[0042] A more preferable lower limit of the S parameter is 0.594, and even more preferably 0.596. The upper limit of the S parameter is not particularly limited. In consideration of 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. In consideration of normal industrial production, the lower limit of the W parameter is, for example, 2.60×10 －３ A more preferable upper limit of the W parameter is 2.75×10 －３ and more preferably 2.70 × 10 －３ is.

[0043] [Method for Measuring S Parameters and W Parameters] The S parameters and W parameters of the foil body are determined by the following method.

[0044] A test piece is taken from the foil body of the ferritic stainless steel foil, and measurements are performed using the positron annihilation coincidence Doppler broadening method. Specifically, three of the test pieces are stacked to create two laminates. A positron source is sandwiched between the two laminates to perform measurements. The positron source is: ２２ Na is used. For example, the positron source is NA351 manufactured by the Japan Radioisotope Association. For example, a DSP module for gamma ray spectrometer APV8002 manufactured by Techno AP Co., Ltd. is used to detect gamma rays. 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 value of the 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. ｔｏｔａｌ Similarly, the energy range used to calculate the S parameters is set to 511 to 512 keV, and the sum of the values ​​obtained by subtracting the count number corresponding to the background from the count number at each energy in this energy range is set to C ＳThe energy range corresponding to the W parameter is set to 516 to 518 keV, and the sum of the values ​​obtained by subtracting the count number corresponding to the background from the count number at each energy in this energy range is C Ｗ The S parameter and W parameter were calculated using the following formula: S parameter = C Ｓ / C ｔｏｔａｌ W parameter = C Ｗ / C ｔｏｔａｌ The S parameter is a value obtained by rounding off to three decimal places, and the W parameter is a value obtained by rounding off to five decimal places.

[0045] [Chemical Composition] In the ferritic stainless steel foil of this embodiment, the chemical composition of the foil body may be the chemical composition of a known ferritic stainless steel.

[0046] 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).

[0047] 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).

[0048] The chemical composition of the foil body of the ferritic stainless steel foil of this embodiment may contain, for example, the following elements.

[0049] C: 0.001 to 0.030% Carbon (C) increases the strength of ferritic stainless steel foil. When the C content is 0.001% or more, the above effect is sufficiently achieved. On the other hand, when 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. 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 C content is 0.001 to 0.030%. A more preferred lower limit of the C content is 0.003%, and even more preferred is 0.005%. A more preferred upper limit of the C content is 0.025%, and even more preferred is 0.020%.

[0050] Si: 0.01 to 1.00% Silicon (Si) deoxidizes steel during the steelmaking process. If the Si content is 0.01% or more, the above effect is 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%. A more preferred lower limit of the Si content is 0.03%, and even more preferred is 0.05%. A more preferred upper limit of the Si content is 0.90%, and even more preferred is 0.80%.

[0051] Mn: 0.01 to 1.00% Manganese (Mn) increases the strength of ferritic stainless steel foil. If the Mn content is 0.01% or more, the above effect is 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 preferred lower limit of the Mn content is 0.03%, and even more preferred is 0.05%. A more preferred upper limit of the Mn content is 0.90%, and even more preferred is 0.80%.

[0052] 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 more preferable it is. However, if the P content is reduced too much, the manufacturing cost increases. Therefore, considering normal industrial production, the preferred lower limit of the P content is more than 0%, more preferably 0.001%, and even more preferably 0.010%. The more preferred upper limit of the P content is 0.045%, and even more preferably 0.040%.

[0053] 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 lower the S content, the more preferable it is. However, if the S content is reduced too much, the manufacturing cost increases. Therefore, considering normal industrial production, the preferred lower limit of the S content is more than 0%, more preferably 0.001%, and even more preferably 0.010%. The more preferred upper limit of the S content is 0.025%, and even more preferably 0.020%.

[0054] Ni: 0.01 to 0.50% Nickel (Ni) improves the corrosion resistance of ferritic stainless steel foil. If the Ni content is 0.01% or more, the above effect is 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%.

[0055] Cr: 12.00 to 20.00% Chromium (Cr) forms an oxide film and improves the corrosion resistance of ferritic stainless steel foil. When the Cr content is 12.00% or more, the above effect is sufficiently obtained. On the other hand, when 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%. A more preferred lower limit of the Cr content is 12.50%, and even more preferred is 13.00%. A more preferred upper limit of the Cr content is 19.00%, and even more preferred is 18.00%.

[0056] Mo: 0.01 to 2.50% Molybdenum (Mo) enhances the strength and corrosion resistance of ferritic stainless steel foil. When the Mo content is 0.01% or more, the above effects are sufficiently obtained. On the other hand, when 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 preferred lower limit of the Mo content is 0.03%, and even more preferred is 0.05%. A more preferred upper limit of the Mo content is 2.40%, and even more preferred is 2.30%.

[0057] N: 0 to 0.100% Nitrogen (N) does not necessarily need to be contained. On the other hand, if the N content is 0.100% or less, the strength of the ferritic stainless steel foil is increased. Therefore, the N content is preferably 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%. A more preferable upper limit of the N content is 0.090%, and even more preferably 0.080%.

[0058] Ti: 0 to 0.80% Titanium (Ti) does not necessarily need to be contained. On the other hand, if Ti is contained in an amount of 0.80% or less, it fixes C and suppresses the formation of Cr carbides. Therefore, the formation of a Cr-deficient layer is suppressed. 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 preferred lower limit of the Ti content is more than 0%, more preferably 0.01%, and even more preferably 0.03%. A more preferred upper limit of the Ti content is 0.70%, and even more preferably 0.60%.

[0059] Nb: 0 to 0.80% Niobium (Nb) does not necessarily have to 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 preferred Nb content is 0 to 0.80%. A more preferred lower limit of the Nb content is over 0%, more preferably 0.01%, and even more preferably 0.03%. A more preferred upper limit of the Nb content is 0.70%, and even more preferably 0.60%.

[0060] Zr: 0 to 0.80% Zirconium (Zr) does not necessarily have to 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 Zr content is preferably 0 to 0.80%. A more preferable lower limit of the Zr content is more than 0%, 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%.

[0061] 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.

[0062] [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.

[0063] [Uses of the Ferritic Stainless Steel Foil of the Present Embodiment] The ferritic stainless steel foil of the present 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 the present embodiment can also be used for purposes other than as a current collector in a secondary battery.

[0064] [Method for manufacturing ferritic stainless steel foil of this embodiment] An example of a method for manufacturing the ferritic stainless steel foil of this embodiment will be described. The method for manufacturing the ferritic stainless steel foil described below is one example for manufacturing the ferritic stainless steel foil of this embodiment. Therefore, the ferritic stainless steel foil having the above-mentioned configuration may be manufactured by a manufacturing method other than the manufacturing method described below. However, the manufacturing method described below is a preferred example of a method for manufacturing the ferritic stainless steel foil of this embodiment.

[0065] An example of the method for producing the ferritic stainless steel foil of this embodiment includes the following steps: (Step 1) Material preparation step (Step 2) Intermediate cold rolling step (Step 3) Intermediate annealing step (Step 4) Final cold rolling step Each step will be described below.

[0066] [(Step 1) Material Preparation Step] In the material preparation step, a ferritic stainless steel sheet having a thickness of several hundred μm to several mm is prepared as the 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 material preparation step is not particularly limited.

[0067] When manufacturing a raw material, for example, it is manufactured by the following method: Produce molten steel having a desired chemical composition. Produce a slab using the molten steel by continuous casting. Produce the slab by hot working and cold rolling to produce a steel plate with 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.

[0068] [(Step 2) Intermediate Cold Rolling Step] In the intermediate cold rolling step, 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 step, cold rolling may be performed using a continuous rolling mill equipped with a plurality of rolling stands arranged in a row, or cold rolling may be performed using a reverse rolling mill. The cumulative reduction rate in the intermediate cold rolling step is not particularly limited.

[0069] The intermediate cold rolling step satisfies the following conditions. As will be described later, the intermediate cold rolling step and the intermediate annealing step may be alternately repeated multiple times. In this case, it is sufficient that the following conditions are satisfied in the final intermediate cold rolling step: (Condition 1) Reduction ratio R in the final pass Ｌ The condition 1 is 15.0% or more. Condition 1 will be described below.

[0070] [Reduction rate in the final pass R Ｌ Regarding the rolling reduction ratio R in the final pass] Here, "pass" means the operation of the material to be rolled passing through one rolling stand once. In the intermediate cold rolling process, cold rolling consisting of multiple passes is carried out. Ｌ " means the reduction rate in the final pass (final pass) among the multiple passes performed in the intermediate cold rolling process. Ｌ The larger the reduction ratio R in the final pass, the larger the strain that can be accumulated in the intermediate steel sheet after the intermediate cold rolling process. Here, the larger the amount of strain accumulated in the intermediate steel sheet after the intermediate cold rolling process, the more the formation of recrystallization texture is promoted in the subsequent intermediate annealing process. As a result, the proportion of recrystallization texture on the surface of the foil body increases. ＬIf the reduction ratio R in the final pass is 15.0% or more, a sufficient amount of strain is accumulated in the intermediate steel sheet after the intermediate cold rolling process. In this case, assuming that the intermediate annealing process satisfies the condition 2 described below, the F1 in the ferritic stainless steel foil produced will be 0.16 or less. Therefore, Ｌ The reduction rate R in the final pass is 15.0% or more. Ｌ Considering normal industrial production, the upper limit of the rolling reduction R Ｌ The upper limit is, for example, 50.0%.

[0071] [(Step 3) Intermediate Annealing Step] In the intermediate annealing step, the intermediate steel sheet after the intermediate cold rolling step is subjected to bright annealing. Bright annealing is an annealing treatment carried out in an extremely low oxygen atmosphere. The intermediate steel sheet that has been subjected to bright annealing has its surface hardly oxidized and can maintain its surface gloss. The extremely low oxygen atmosphere in bright annealing is preferably an H ２ Gas and N ２ The atmosphere is a mixed gas of N and N gas. ２ The volume fraction is, for example, 35 to 65%.

[0072] In the bright annealing performed in the intermediate annealing step, an 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.

[0073] 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, and then a second intermediate cold rolling step and a second intermediate annealing step are performed.

[0074] The intermediate annealing step satisfies the following conditions: When the intermediate annealing step is performed multiple times, the following condition should be satisfied in the last intermediate annealing step: (Condition 2) The average cooling rate CR from the heating temperature T (°C) to 400°C is 200°C / sec or less. Condition 2 will be explained below.

[0075] [Regarding the average cooling rate CR] As described above, the formation of recrystallization texture progresses during the intermediate annealing step. However, if the average cooling rate CR from the heating temperature T (°C) to 400°C is too fast, the formation of recrystallization texture on the surface of the foil body may be insufficient. If the average cooling rate CR is 200°C / s or less, the formation of recrystallization texture also progresses sufficiently on the surface of the foil body. In this case, assuming that the intermediate annealing step satisfies condition 1, the F1 of the manufactured ferritic stainless steel foil will be 0.16 or less. Therefore, the average cooling rate CR from the heating temperature T (°C) to 400°C is set to 200°C / s or less. The lower limit of the average cooling rate CR is not particularly limited. Considering normal industrial production, the lower limit of the average cooling rate CR is, for example, 20°C / s.

[0076] In the intermediate annealing step, the following conditions are preferably satisfied. When the intermediate annealing step is performed multiple times, the following conditions should be satisfied in the final intermediate annealing step: (Preferred condition 1) The tension Ts applied to the intermediate steel sheet during the cooling process from the heating temperature T (°C) to 400°C is 1.0 N / mm ２ The above is the end of the description. Preferred condition 1 will now be described.

[0077] [Regarding tension Ts] In 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 the S parameter of the foil body of the ferritic stainless steel foil is 0.592 or more and the W parameter is 2.80×10 or more, the crystal lattice of the intermediate steel sheet after the intermediate annealing step will contain a sufficient amount of lattice defects. In this case, provided that the final cold rolling step satisfies the preferred condition 2 described below, the S parameter of the foil body of the ferritic stainless steel foil produced will be 0.592 or more and the W parameter will be 2.80×10 or more.－３ Therefore, the tension Ts is 1.0 N / mm ２ 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.

[0078] [(Step 4) Final Cold Rolling Step] 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. In the final cold rolling step, a well-known cold rolling mill may be used. 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.

[0079] In the final cold rolling step, the following condition is preferably satisfied: (Preferred condition 2) The maximum rolling reduction R in one pass is ＭＡＸ The preferable condition 2 will be explained below.

[0080] [Maximum rolling reduction in one pass R ＭＡＸ In the final cold rolling process, cold rolling consisting of multiple passes is carried out. ＭＡＸ " means 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 lattice defects contained in the crystal lattice of the intermediate steel sheet will decrease. The maximum reduction rate R in one pass ＭＡＸ When the rolling reduction ratio is 28% or less, it means that there is no pass with a rolling reduction ratio exceeding 28%. In this case, the heat generated by processing is sufficiently suppressed, and the reduction in lattice defects contained in the crystal lattice of the intermediate steel sheet is also suppressed. As a result, assuming that the intermediate annealing process satisfies the preferred condition 1, the S parameter of the foil body in the manufactured ferritic stainless steel foil is 0.592 or more, and the W parameter is 2.80 × 10 －３ Therefore, the maximum rolling reduction rate in one pass R ＭＡＸ The maximum rolling reduction R in one pass is preferably 28% or less.ＭＡＸ Considering normal industrial production, the maximum rolling reduction R ＭＡＸ The lower limit is, for example, 5%.

[0081] The ferritic stainless steel foil of this embodiment is manufactured by the above-described manufacturing method.

[0082] [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.

[0083] [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. Note that 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.

[0084] [Active Material] In the electrode of this embodiment, the active material contained in the electrode mixture layer is not particularly limited, and a well-known active material can be used. When the electrode is a positive electrode, the positive electrode active material is, for example, LiCoO ２ And LiNi １／３ Co １／３ Mn １／３ O ２ and ternary systems such as LiFePO ４ Olivine system represented by S, Fe ２ S, Mo ３ S ４ When the electrode is a negative electrode, the negative electrode active material may be, for example, a carbon-based material represented by graphite, an alloy material represented by CuSn alloy and NiTiSi alloy, an Si-based material represented by Si and SiO, or Li ４ Ti５ O １２ and oxide-based materials represented by the following.

[0085] [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 any one or more selected from the group consisting of rubbery polymers represented by styrene-butadiene rubber and isoprene rubber, synthetic resins represented by polyethylene, polyimide, polyacrylic acid, and polyamide, styrene-butadiene-styrene block copolymers or hydrogenated products thereof, thermoplastic elastomers such as styrene-ethylene-butadiene, styrene copolymers, styrene-isoprene, or styrene block copolymers or hydrogenated products thereof, soft resinous polymers represented by syndiotactic-1,2-polybutadiene, ethylene-vinyl acetate copolymers, and copolymers of ethylene and an α-olefin having 3 to 12 carbon atoms, and fluorinated polymers represented by polytetrafluoroethylene, tetrafluoroethylene-ethylene copolymers, polyvinylidene fluoride, polypentafluoropropylene, and polyhexafluoropropylene.

[0086] [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 may be used. The conductive additive may be, for example, one or more selected from the group consisting of graphite material, acetylene black, carbon black, ketjen black, carbon fiber, carbon nanotube, and graphene.

[0087] [Electrode Manufacturing Method] The electrode manufacturing method of this embodiment is not particularly limited. The electrode of this embodiment is manufactured by a well-known method using the ferritic stainless steel foil of this embodiment as a current collector. The electrode manufacturing method of this embodiment includes, for example, an electrode slurry preparation step and an electrode mixture layer formation step.

[0088] [Electrode Slurry Preparation Step] 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. That is, the electrode slurry preparation step may be performed by a known method.

[0089] [Electrode Mixture Layer Forming Step] 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.

[0090] The electrode of this embodiment can be manufactured by the above steps.

[0091] [Battery] The battery of this embodiment includes the electrode of this embodiment and an electrolyte. As long as the battery of this embodiment includes the electrode of this embodiment, other configurations may be well-known and are 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.

[0092] [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.

[0093] 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. The sulfide-based solid electrolyte can be, for example, Li ３ P.S. ４ and Li ７ P ３ S １１ LPS systems, such as Li ６ P.S. ５ Cl ｘ Br （１－ｘ） Argyrodite type represented by (0≦x≦1) and Li １０ GeP ２ S １２ and Li ９．５４ Si １．７４ P １．４４ S １１．７ Cl ０．３ and thiolisicones represented by the following:

[0094] [Method for Manufacturing Battery] The method for manufacturing the battery of the present embodiment is not particularly limited. The battery of the present embodiment is manufactured, for example, 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.

[0095] 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.

[0096] 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.

[0097]

[0098] 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. The reduction ratio R Ｌ (%) is shown in Table 2.

[0099]

[0100] 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 subjected to 35 to 65 volume % N ２ gas and the remainder is H ２ Bright annealing was carried out in a mixed gas atmosphere with gas. In bright annealing, the intermediate steel sheets were heated and held at a heating temperature T of 800 to 1200°C, and then cooled to 400°C at an average cooling rate CR (°C / sec). Thereafter, they were rapidly cooled to room temperature by air cooling. The tension Ts (N / mm ２ ), and the average cooling rate CR (°C / sec) from the heating temperature T (°C) to 400°C are shown in Table 2.

[0101] The intermediate steel sheet after the intermediate annealing step was subjected to a final cold rolling step. In the final cold rolling step, 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 sheet thickness of 10 μm. The maximum rolling reduction R ＭＡＸ (%) is shown in Table 2.

[0102] By the above manufacturing process, ferritic stainless steel foils with each test number were manufactured.

[0103] [Regarding Evaluation Tests] The following evaluation tests were carried out on the produced ferritic stainless steel foils with each test number: (Test 1) Maximum pole density measurement test (Test 2) S-parameter and W-parameter measurement test (Test 3) Corrosion resistance evaluation test Each test will be described below.

[0104] [(Test 1) Maximum pole density measurement test] Based on the method described in the above [Method for measuring maximum pole density], the maximum pole density M of the <001> orientation on the rolled surface of the foil body of the ferritic stainless steel foil of each test number was measured. ００１ and the maximum pole density M of the <111> orientation １１１ The maximum pole density M ００１ and maximum pole density M １１１ The F1 was calculated based on the above. The obtained F1 is shown in Table 3.

[0105]

[0106] [(Test 2) S-parameter and W-parameter measurement test] Based on the method described in the above [Method for measuring S-parameter and W-parameter], the S-parameter and W-parameter 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.

[0107] [(Test 3) 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 foil body of the ferritic stainless steel foil. One surface of the test piece was used as the evaluation surface. The developed area ratio Sdr defined in ISO 25178-2:2012 was measured for the evaluation surface of the test piece. The developed area ratio Sdr is an index representing the rate of increase in the surface area of ​​the measured surface compared to a flat surface. Since the corrosion reaction proceeds from the surface of the foil body as the starting point, the greater the developed area ratio Sdr of the test piece, the faster the corrosion progresses.

[0108] The developed area ratio Sdr of the evaluation surface of the test piece was measured using a laser microscope. The laser microscope used was a Keyence Corporation product name: VK-X100. The observation magnification was set to 2000 times, and a measurement area of ​​280 μm × 200 μm was measured. Specifically, four points within the measurement area were measured with an observation field of 145 μm × 109 μm so that the entire range within the measurement area could be measured, and a surface image was obtained. The four obtained surface images were linked using the attached image linking software to obtain a surface image of a measurement area of ​​280 μm × 200 μm. From the surface shape profile obtained by analyzing the surface image of the measurement area, a reference plane was set by cutting 0.3% of the area from the low brightness side, and a three-dimensional image was generated. At this time, filtering was performed using a high-pass filter with a cutoff wavelength of 50 μm. A Gaussian filter was used as the filtering method. The developed area ratio Sdr defined in ISO25178-2:2012 was determined in a 200 μm × 150 μm region of the obtained three-dimensional image.

[0109] Using the test pieces with the respective test numbers for which the developed area ratio Sdr was measured, evaluation cells simulating sulfide-based all-solid-state batteries were fabricated. Specifically, 0.12 g of the 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. The sulfide-based solid electrolyte contained β-Li ３ P.S. ４ The prepared pellet was placed on the evaluation surface of the test piece of each test number. Furthermore, a cylindrical metal Li foil having 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 that could block the outside air, and a pressure of 5 MPa was applied by tightening bolts. The measurement cell was then sealed. Note that the process from preparing the sulfide-based solid electrolyte pellet to sealing the evaluation cell was carried out in a glove box in an Ar atmosphere. Through the above process, an evaluation cell of each test number was prepared.

[0110] Cyclic voltammetry (CV) measurements were performed 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 After sweeping from (V) to 3.0 V, it was swept to 0.005 V, and then 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 all evaluation cells of all test numbers.

[0111] From the measurement results, the open circuit voltage V ＯＣ The maximum current density (μA / cm) that flowed during the sweep from 0.0 V to 3.0 V 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 showing the progress of the corrosion reaction in the test piece.

[0112] Maximum current value I for each test number ＭＡＸ (μA / cm ２ ) are shown in Table 3. Maximum current value I ＭＡＸ is 18.0 μA / cm ２ Super ~25.0μA / cm ２ When the maximum current value I ＭＡＸ is 18.0 μA / cm ２ If the maximum current value I was less than or equal to the maximum current value I, it was determined that even better 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.

[0113] [Evaluation Results] Referring to Tables 1 to 3, the ferritic stainless steel foils of test numbers 1 to 9 had F1 of 0.16 or less, and therefore had excellent corrosion resistance.

[0114] Furthermore, in the ferritic stainless steel foils of test numbers 1 to 6, the S parameter was 0.592 or more, and the W parameter was 2.80 × 10 －３ Therefore, even better corrosion resistance was obtained.

[0115] On the other hand, in test number 10, the reduction rate R Ｌ was too small, so F1 exceeded 0.16, and as a result, excellent corrosion resistance was not obtained.

[0116] In test number 11, the average cooling rate CR in the intermediate annealing step was too fast, so F1 exceeded 0.16, and as a result, excellent corrosion resistance was not obtained.

[0117] 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, wherein the maximum pole density M in the <001> orientation is found in the ND inverse pole figure obtained by measuring the rolled surface of the foil body by electron backscatter diffraction. ００１ and the maximum pole density M of the <111> orientation １１１ and a ferritic stainless steel foil, which satisfies formula (1). ００１ / M １１１ ≦0.16 (1) 2. The ferritic stainless steel foil according to claim 1, further comprising: an S parameter of 0.592 or more and a W parameter of 2.80 x 10, as measured by a positron annihilation coincidence Doppler broadening method for the foil body. －３ The following is a ferritic stainless steel foil.

3. A ferritic stainless steel foil according to claim 1, wherein the chemical composition of the foil body contains, 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: 0-0.80%, Nb: 0-0.80%, and Zr: 0-0.80%, with the balance being Fe and impurities.

4. A ferritic stainless steel foil according to claim 2, wherein the chemical composition of the foil body contains, 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: 0-0.80%, Nb: 0-0.80%, and Zr: 0-0.80%, with the balance being Fe and impurities.

5. An electrode comprising the ferritic stainless steel foil according to any one of claims 1 to 4 and an electrode mixture layer formed on the surface of the ferritic stainless steel foil.

6. A battery comprising the electrode according to claim 5 and an electrolyte.

7. The battery according to claim 6, wherein the electrolyte is a sulfide-based solid electrolyte.

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