Ferritic stainless steel foil, electrode and battery

Abstract

Provided is a ferrite system stainless steel foil that exhibits excellent corrosion resistance. The ferrite system stainless steel foil of the present disclosure has a foil main body composed of a ferrite system stainless steel, and in a pole figure in the ND direction obtained by measuring a rolling surface of the foil main body by electron backscatter diffraction, the maximum pole density M 001 of <001> orientation 111 and the maximum pole density M 001 of <111> orientation satisfy formula (1), M 111 / M 111 ≦0.16 (1).

Description

Technical Field

[0001] This disclosure relates to ferritic stainless steel foil, electrodes using the ferritic stainless steel foil as current collectors, and batteries using the electrodes. Background Technology

[0002] To date, primary and secondary batteries have been used as power sources for various electronic devices. In recent years, with the widespread adoption of small electronic devices such as home video cameras, laptops, and smartphones, secondary batteries, represented by lithium-ion batteries, are rapidly gaining popularity.

[0003] A secondary battery has electrodes with positive and negative electrodes, as well as an electrolyte. In both the positive and negative electrodes, an electrode flux layer is formed on a current collector. The electrode flux layer is a layer containing active material. The current collector functions to supply current to the active material and also serves as a substrate for maintaining the electrode flux layer.

[0004] Traditionally, electrolytes have been used as electrolytes in secondary batteries. However, because electrolytes contain flammable organic solvents, their usable temperature range is relatively narrow. Therefore, in recent years, all-solid-state batteries using solid electrolytes to replace electrolytes have been developed. All-solid-state batteries do not contain organic solvents, thus achieving stable battery performance over a wide temperature range. Among solid electrolytes used in all-solid-state batteries, sulfide-based solid electrolytes, particularly those represented by LPS (Lithium Phosphorus Sulfide), exhibit high ionic conductivity. Therefore, by using sulfide-based solid electrolytes, high output power in all-solid-state batteries can be achieved.

[0005] On the other hand, when using sulfide-based solid electrolytes, the current collector is sometimes corroded by sulfides. If the current collector is corroded, the battery performance deteriorates. In other words, the current collector needs to have high corrosion resistance. Therefore, the application of highly corrosion-resistant stainless steel as a raw material for the current collector is being researched. Among stainless steels, ferritic stainless steels, in particular, have lower electrical resistance and higher electrical conductivity compared to austenitic stainless steels. Therefore, ferritic stainless steels are suitable as raw materials for current collectors.

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

[0007] International Publication No. 2021 / 006089 (Patent Document 1) discloses a technique for improving the corrosion resistance of ferritic stainless steel for current collector applications.

[0008] The ferritic stainless steel sheet for the current collector of a sulfide-based solid-state battery disclosed in Patent Document 1 has the following composition: C: 0.001~0.050%, Si: 0.01~2.00%, Mn: 0.01~1.00%, P: less than 0.050%, S: less than 0.010%, Cr: 18.00~32.00%, Ni: 0.01~4.00%, Al: 0.001~0.150%, and N: less than 0.050%, with the remainder consisting of Fe and unavoidable impurities. Patent Document 1 describes that by increasing the Cr content to 18.00% or more in this ferritic stainless steel sheet, excellent sulfidation resistance can be obtained.

[0009] Prior art literature

[0010] Patent documents

[0011] Patent Document 1: International Publication No. 2021 / 006089 Summary of the Invention

[0012] The technical problem that the invention aims to solve

[0013] However, the corrosion resistance of ferritic stainless steel can also be improved by means different from those disclosed in Patent Document 1.

[0014] The purpose of this disclosure is to provide a ferritic stainless steel foil with excellent corrosion resistance, an electrode using the ferritic stainless steel foil as a current collector, and a battery using the electrode.

[0015] Technical means for solving technical problems

[0016] The ferritic stainless steel foil disclosed herein

[0017] It has a foil body made of ferritic stainless steel.

[0018] In the inverse pole figure of the ND direction obtained by measuring the rolled surface of the foil body using electron backscatter diffraction, <001> Maximum polar density M of orientation 001 and <111> Maximum polar density M of orientation 111 Satisfy equation (1)

[0019] M 001 / M 111 ≦0.16 (1)。

[0020] The electrodes disclosed herein possess:

[0021] The ferritic stainless steel foil disclosed herein; and

[0022] An electrode mixture layer is formed on the surface of the ferrite-based stainless steel foil.

[0023] The battery disclosed herein has the following features:

[0024] The electrodes of this disclosure; and

[0025] Electrolytes.

[0026] Invention Effects

[0027] Excellent corrosion resistance is achieved in the ferritic stainless steel foil of this disclosure. The electrodes of this disclosure utilize the ferritic stainless steel foil of this disclosure. The batteries of this disclosure utilize the electrodes of this disclosure. Detailed Implementation

[0028] The inventors have investigated methods to improve the corrosion resistance of ferritic stainless steel foil. As a result, the inventors have obtained the following insights.

[0029] In Patent Document 1, increasing the Cr content in ferritic stainless steel improves its corrosion resistance. Thus, including alloying elements that enhance corrosion resistance is effective in improving the corrosion resistance of ferritic stainless steel foil. However, increasing the content of these alloying elements reduces the processability of the ferritic stainless steel foil or increases manufacturing costs. Therefore, the inventors, in their ferritic stainless steel foil having a foil body composed of ferritic stainless steel, focus on the surface texture of the foil body rather than its chemical composition.

[0030] The ND direction crystal plane of the foil matrix, composed of ferritic stainless steel, is mainly composed of {001} with a rolled texture. <110> Orientation and recrystallization texture {111} <112> Orientation configuration. Here, the ND direction refers to the normal direction of the rolled surface of the foil body of the ferritic stainless steel foil. Furthermore, 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". Additionally, the RD direction is defined as the rolling direction. Rolled texture is a texture formed through rolling. Compared to recrystallization texture, rolled texture contains a large number of non-recrystallized grains. Non-recrystallized grains also contain a large number of subgrain boundaries generated by dislocation proliferation. The atomic arrangement around the subgrain boundaries is significantly disordered compared to within the grains, resulting in a high-energy state. Therefore, corrosion occurs rapidly. In other words, in rolled textures containing a large number of subgrain boundaries, corrosion occurs more preferentially than in recrystallization textures.

[0031] Corrosion of ferritic stainless steel foil begins at the surface of the foil substrate. On the surface of the foil substrate, the greater the presence of rolling texture containing numerous subgrain boundaries compared to recrystallization texture, the more it promotes corrosion. In other words, reducing the ratio of rolling texture to recrystallization texture on the surface of the foil substrate can suppress surface-initiated corrosion. As a result, the corrosion resistance of ferritic stainless steel foil can be improved.

[0032] The amount of rolling texture and recrystallization texture on the surface of the foil substrate can be evaluated using an inverse pole figure in the ND direction obtained by electron backscatter diffraction (EBSD). The inverse pole figure in the ND direction represents the tendency of crystal orientation of the crystal planes constituting the ND direction. Here, the amount of rolling texture in the surface is measured using... <001> Maximum polar density M of orientation 001 The amount of recrystallization texture is indicated by... <111> Maximum polar density M of orientation 111 This is indicated by... Furthermore, the maximum polar density refers to the intensity ratio relative to random orientation. That is, the maximum polar density M... 001 Relative to the maximum polar density M 111 The smaller the value, the lower the ratio of the rolling texture to the recrystallization texture on the surface of the foil body.

[0033] Based on the above insights, the inventors have made improvements to the inverse pole figure in the ND direction. <001> Maximum polar density M of orientation 001 and <111> Maximum polar density M of orientation 111 The relationship with corrosion resistance was studied, and the inverse pole figure in the ND direction was obtained by measuring the rolled surface of the foil body using electron backscatter diffraction. As a result, the inventors found that excellent corrosion resistance can be obtained in ferritic stainless steel foil if the following equation (1) is satisfied.

[0034] M 001 / M 111 ≦0.16 (1)

[0035] The ferritic stainless steel foil, the electrode, and the battery of this embodiment are completed based on the above technical concept and have the following structure.

[0036] The first type of ferritic stainless steel foil.

[0037] It has a foil body made of ferritic stainless steel.

[0038] In the inverse pole figure of the ND direction obtained by measuring the rolled surface of the foil body using electron backscatter diffraction, <001> Maximum polar density M of orientation 001 and <111> Maximum polar density M of orientation 111 Satisfy equation (1)

[0039] M 001 / M 111 ≦0.16 (1)。

[0040] The second type of ferritic stainless steel foil,

[0041] It is the first type of ferritic stainless steel foil.

[0042] Furthermore, the S-parameter obtained by measuring the foil body using the positron annihilation coincidence Doppler broadening method is greater than 0.592, and the W-parameter is 2.80 × 10⁻⁶. -3 the following.

[0043] The third type of ferritic stainless steel foil,

[0044] It is a ferritic stainless steel foil of the first or second composition.

[0045] The chemical composition of the foil body is as follows: by mass%, it contains...

[0046] C: 0.001~0.030%

[0047] Si: 0.01~1.00%

[0048] Mn: 0.01~1.00%,

[0049] P: below 0.050%

[0050] S: Below 0.030%

[0051] Ni: 0.01~0.50%

[0052] Cr: 12.00~20.00%

[0053] Mo: 0.01~2.50%,

[0054] N: 0~0.100%

[0055] Ti: 0~0.80%,

[0056] Nb: 0~0.80%, and

[0057] Zr: 0~0.80%,

[0058] The remainder consists of Fe and impurities.

[0059] The first electrode configuration includes:

[0060] Ferritic stainless steel foil of any one of the first to third compositions; and

[0061] An electrode mixture layer is formed on the surface of the ferrite-based stainless steel foil.

[0062] The first type of battery has the following features:

[0063] The first type of electrode; and

[0064] Electrolytes.

[0065] The second component of the battery,

[0066] It is the first component of the battery.

[0067] The electrolyte is a sulfide-based solid electrolyte.

[0068] The following provides a detailed description of the ferritic stainless steel foil, the electrode, and the battery of this embodiment. Furthermore, unless otherwise specified, the percentage of elements (%) refers to mass.

[0069] [Structure of ferritic stainless steel foil]

[0070] The ferritic stainless steel foil of this embodiment comprises a foil body made of ferritic stainless steel. That is, the ferritic stainless steel foil of this embodiment may also consist solely of a foil body made of ferritic stainless steel. Here, ferritic stainless steel refers to steel with a Cr content of 10.5% or more and a microstructure primarily composed of ferrite. In this specification, a microstructure primarily composed of ferrite means that the volume fraction of ferrite in the microstructure is 95% or more.

[0071] [Regarding equation (1)]

[0072] In the ferritic stainless steel foil of this embodiment, the inverse polarimetric diagram in the ND direction, obtained by measuring the rolling surface of the foil body using electron backscatter diffraction, is shown. <001> Maximum polar density M of orientation 001 and <111> Maximum polar density M of orientation 111 Satisfy equation (1)

[0073] M 001 / M 111 ≦0.16 (1)。

[0074] F1 is defined as follows.

[0075] F1= M 001 / M 111

[0076] Fl is an indicator representing the ratio of the rolled texture to the recrystallized texture on the surface of the foil substrate. As mentioned above, the lower the ratio of the rolled texture, which contains a large number of dislocations, to the recrystallized texture on the surface of the foil substrate, the better the surface-initiated corrosion can be suppressed. If Fl is below 0.16, the ratio of the rolled texture to the recrystallized texture is sufficiently low. In this case, the surface-initiated corrosion can be sufficiently suppressed. As a result, excellent corrosion resistance can be obtained.

[0077] There is no specific lower limit for F1. If we consider typical industrial production, the lower limit for F1 would be, for example, 0.01.

[0078] The preferred upper limit for F1 is 0.15, and further, 0.13.

[0079] [Method for determining maximum extreme density]

[0080] In the inverse pole figure in the ND direction <001> Maximum polar density M of orientation 001 and <111> Maximum polar density M of orientation 111 It can be obtained using the following method.

[0081] Test pieces were collected using the rolled surface of the ferritic stainless steel foil as the observation surface. The size of the test pieces was not particularly limited, nor was the location of the test pieces; for example, the center of the foil's width could be used. The observation surface of the test pieces was electropolished. The applied voltage during electropolishing was 35V, and the polishing time was 10 seconds. The electrolyte used was a mixture of 78 mL perchloric acid, 90 mL distilled water, 730 mL ethanol, and 100 mL butyl cellosolve. Three 200 μm × 200 μm measurement areas were set on the electropolished observation surface in a non-overlapping manner. EBSD measurements were performed on each measurement area. In the EBSD measurements, the accelerating voltage was set to 20 kV, the irradiation current to 28 nA, and the working distance (WD) to 15.0 mm. Additionally, the magnification was set to 400x, and the step size to 0.3 μm. The measurement results in the three measurement regions were analyzed using OIM-Analysis Ver.7, manufactured by TSL Solutions, Inc., to obtain the inverse pole figure in the ND direction. Furthermore, in the sample coordinate system where A1 corresponds to the Y-axis, A2 to the X-axis, and A3 to the Z-axis, the analysis was performed by rotating the sample with A2 aligned with the RD direction of the observation plane and A3 aligned with the ND direction of the observation plane. Additionally, measurement points with a confidence index (CI value) of 0.1 or less, indicating the confidence level of the obtained crystal orientation, were not used for analysis. Based on the obtained inverse pole figure, the following was obtained: <001> Maximum polar density M of orientation 001 and <111> Maximum polar density M of orientation 111 .

[0082] Based on the obtained maximum polar density M 001 and maximum extreme density M 111 Calculate F1. Furthermore, F1 is the value obtained by rounding the third decimal place to the second decimal place.

[0083] [Regarding S-parameters and W-parameters]

[0084] Preferably, in the ferritic stainless steel foil of this embodiment, the S-parameter obtained by measuring the foil body using the positron annihilation coincidence Doppler broadening method is 0.592 or higher, and the W-parameter is 2.80 × 10⁻⁶. -3 the following.

[0085] In the foil body of ferritic stainless steel foil, dislocations are introduced not only on the surface but also within it to ensure sufficient strength. Furthermore, when ferritic stainless steel foil is used as a current collector, stamping and other processes are frequently performed during electrode manufacturing, sometimes introducing further dislocations into the foil body. These dislocations introduced into the foil body move within the grains, forming unitary entanglements (dislocation cells). Soon after, the dislocation pairs within the cells annihilate, and the dislocations entangled at the cell walls rearrange to form subgrain boundaries.

[0086] During the rolling process in the manufacturing of ferritic stainless steel foil, plastic strain is introduced into the foil body. As a result, lattice defects are generated within the foil body. The amount of plastic strain introduced during rolling differs between the surface and interior of the foil body, thus the amount of lattice defects introduced differs. Here, by introducing an appropriate amount of lattice defects into the interior, the formation of subgrain boundaries can be suppressed. In this case, in ferritic stainless steel foil where surface-based corrosion can be suppressed by satisfying equation (1), the corrosion process in the interior can also be delayed. As a result, the corrosion resistance of the ferritic stainless steel foil is further improved.

[0087] The amount of lattice defects introduced into the interior of the foil substrate can be evaluated using the S-parameters and W-parameters obtained by the Coincidence Doppler Broadening (CDB) method. In CDB, the energies of the two gamma rays emitted when an incident positron annihilates another electron in the sample are detected. While the energy of a single gamma ray is 511 keV, it is actually detected with a somewhat extended energy distribution (CDB spectrum) due to the Doppler effect corresponding to 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, and 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 interior of the foil substrate is large, the number of positrons annihilating with conduction electrons increases, while the number of positrons annihilating with inner-shell electrons decreases. Compared to inner-shell electrons, conduction electrons have less mobility, therefore the gamma rays generated through their annihilation are less affected by the Doppler effect. Consequently, the greater the number of lattice defects introduced into the interior of the foil, the narrower the detected energy distribution. As a result, the S-parameter increases and the W-parameter decreases. In other words, the larger the S-parameter and the smaller the W-parameter obtained by the positron annihilation coincident Doppler broadening method, the more effectively the formation of subgrain boundaries is suppressed, further improving the corrosion resistance of the ferritic stainless steel foil.

[0088] In the foil body, if the S-parameter is above 0.592, the W-parameter is 2.80 × 10⁻⁶. -3 In this case, the amount of lattice defects introduced into the interior of the foil substrate is sufficiently large. This effectively suppresses the formation of subgrain boundaries that promote corrosion. As a result, superior corrosion resistance is achieved.

[0089] The lower limit for the S-parameter is 0.594, and the further preferred value is 0.596.

[0090] There is no specific upper limit for the S-parameter. If we consider typical industrial production, the upper limit for the S-parameter is, for example, 0.610.

[0091] There is no specific lower limit for the W parameter. If we consider typical industrial production, the lower limit for the W parameter could be, for example, 2.60 × 10⁻⁶. -3 .

[0092] The upper limit for further optimization of the W parameter is 2.75 × 10⁻⁶. -3 A further preferred value is 2.70 × 10⁻⁶. -3 .

[0093] [Methods for determining S-parameters and W-parameters]

[0094] The S-parameters and W-parameters of the foil body are obtained by the following method.

[0095] Test pieces were collected from the bulk of ferritic stainless steel foil and measured using the positron annihilation coincidence Doppler broadening method. Specifically, two stacks were fabricated, each consisting of three collected test pieces. The two stacks were then sandwiched within a positron beam source for measurement. The positron beam source used was... 22 Na. The positron beam source is, for example, NA351 manufactured by the Japan Isotope Society. Gamma-ray detection is performed, for example, using the APV8002 DSP module for gamma-ray spectrometer manufactured by Techno AP Co., Ltd. The count is set to 10 million counts or higher. Based on the measured gamma-ray energy distribution, the half-value width is calculated in the range of 509–513 keV. The common resolution is set to 1.04 keV, and the measurement resolution is set to the calculated half-value width. The S-parameters and W-parameters are then calculated. Specifically, the average count value of each energy in the 540–545 keV range is taken as the count equivalent to the background. The sum of the values ​​obtained by subtracting the background count value from the count value of each energy in the entire measured energy range is set as C. total Similarly, the energy range used in the S-parameter calculations will be set to 511~512 keV, and the sum of the values ​​obtained by subtracting the corresponding background counts from the counts of each energy within this range will be set as C. S Additionally, the energy range corresponding to the W parameter is set to 516~518 keV, and the sum of the values ​​obtained by subtracting the corresponding background count value from the count value of each energy in this energy range is set as C. W Calculate the S-parameters and W-parameters using the following formulas.

[0096] S-parameters = C S / C total ,

[0097] W parameter = C W / C total .

[0098] Additionally, the S parameter rounds the fourth decimal place to the third decimal place. The W parameter rounds the sixth decimal place to the fifth decimal place.

[0099] [Chemical Composition]

[0100] In the ferritic stainless steel foil of this embodiment, the chemical composition of the foil body can also be composed of the chemical composition of known ferritic stainless steel.

[0101] The chemical composition of the ferritic stainless steel foil of this embodiment can, for example, satisfy any one of the groups consisting of SUS405, SUS410L, SUS429, SUS430, SUS430LX, SUS430J1L, SUS434, SUS436L, SUS436J1L, SUS443J1, SUS444, SUS445J1, SUS445J2, SUS447J1 and SUSXM27 as specified in JIS G4305 (2015).

[0102] The chemical composition of the ferritic stainless steel foil of this embodiment may, for example, satisfy any one of the following groups as specified in ASTM A 240 (2006): 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.

[0103] The chemical composition of the ferritic stainless steel foil in this embodiment may also contain, for example, the following elements.

[0104] C: 0.001~0.030%

[0105] Carbon (C) increases the strength of ferritic stainless steel foil. This effect is fully achieved when the C content is 0.001% or higher.

[0106] On the other hand, if the C content is below 0.030%, the formation of a Cr-deficient layer caused by the formation of Cr carbides can be suppressed. As a result, the embrittlement of the oxide film is suppressed, and the corrosion resistance of the ferritic stainless steel foil is improved.

[0107] Therefore, the preferred C content is 0.001~0.030%.

[0108] The lower limit for the C content is 0.003%, and the lower limit is 0.005%.

[0109] The upper limit for the C content is further preferably 0.025%, and even more preferably 0.020%.

[0110] Si: 0.01~1.00%

[0111] Silicon (Si) is used to deoxidize steel during the steelmaking process. The desired effect can be achieved when the Si content is 0.01% or higher.

[0112] On the other hand, if the Si content is below 1.00%, the processability of ferritic stainless steel foil is improved.

[0113] Therefore, the preferred Si content is 0.01~1.00%.

[0114] The lower limit for the Si content is 0.03%, and the lower limit is 0.05%.

[0115] The upper limit for the Si content is further preferably 0.90%, and more preferably 0.80%.

[0116] Mn: 0.01~1.00%

[0117] Manganese (Mn) improves the strength of ferritic stainless steel foil. The above effect can be fully achieved if the Mn content is 0.01% or higher.

[0118] On the other hand, if the Mn content is below 1.00%, the corrosion resistance of ferritic stainless steel foil is improved.

[0119] Therefore, the preferred Mn content is 0.01~1.00%.

[0120] The lower limit for the Mn content is 0.03%, and the lower limit is 0.05%.

[0121] The upper limit for the Mn content is further preferred to be 0.90%, and even more preferred to be 0.80%.

[0122] P: below 0.050%

[0123] Phosphorus (P) is an impurity. If the P content is below 0.050%, the processability and corrosion resistance of ferritic stainless steel foil are improved.

[0124] Therefore, the preferred P content is below 0.050%.

[0125] The phosphorus (P) content is preferably as low as possible. However, excessively reducing the P content increases manufacturing costs. Therefore, considering typical industrial production, the preferred lower limit for the P content is more than 0%, more preferably 0.001%, and even more preferably 0.010%.

[0126] The upper limit for the P content is further preferred to be 0.045%, and further preferred to be 0.040%.

[0127] S: below 0.030%

[0128] Sulfur (S) is an impurity. If the S content is below 0.030%, the workability and corrosion resistance of ferritic stainless steel foil are improved.

[0129] Therefore, the preferred S content is below 0.030%.

[0130] The sulfur content is preferably as low as possible. However, excessively reducing the sulfur content increases manufacturing costs. Therefore, considering typical industrial production, the preferred lower limit for the sulfur content is more than 0%, more preferably 0.001%, and even more preferably 0.010%.

[0131] The upper limit for the S content is further preferably 0.025%, and even more preferably 0.020%.

[0132] Ni: 0.01~0.50%

[0133] Nickel (Ni) improves the corrosion resistance of ferritic stainless steel foil. This effect is fully achieved when the Ni content is 0.01% or higher.

[0134] On the other hand, if the Ni content is below 0.50%, the processability of ferritic stainless steel foil is improved.

[0135] Therefore, the preferred Ni content is 0.01~0.50%.

[0136] The lower limit for the Ni content is 0.03%, and the lower limit is 0.05%.

[0137] The upper limit for the Ni content is further preferably 0.40%, and more preferably 0.30%.

[0138] Cr: 12.00~20.00%

[0139] Chromium (Cr) forms an oxide film, improving the corrosion resistance of ferritic stainless steel foil. This effect is fully achieved when the Cr content is 12.00% or higher.

[0140] On the other hand, if the Cr content is below 20.00%, the processability of ferritic stainless steel foil is improved.

[0141] Therefore, the preferred Cr content is 12.00~20.00%.

[0142] The lower limit for the Cr content is 12.50%, and the higher limit is 13.00%.

[0143] The upper limit for the Cr content is further preferred to be 19.00%, and further preferred to be 18.00%.

[0144] Mo: 0.01~2.50%

[0145] Molybdenum (Mo) improves the strength and corrosion resistance of ferritic stainless steel foil. These effects are fully achieved when the Mo content is 0.01% or higher.

[0146] On the other hand, if the Mo content is below 2.50%, the processability of ferritic stainless steel foil is improved.

[0147] Therefore, the preferred Mo content is 0.01~2.50%.

[0148] The lower limit for the Mo content is 0.03%, and the lower limit is 0.05%.

[0149] The upper limit for the Mo content is further preferred to be 2.40%, and even more preferred to be 2.30%.

[0150] N: 0~0.100%

[0151] It may also be free of nitrogen (N).

[0152] On the other hand, if the content of N is less than 0.100%, the strength of the ferritic stainless steel foil is improved.

[0153] Therefore, the preferred N content is 0~0.100%.

[0154] The lower limit for the N content is more than 0%, more preferably 0.001%, and more preferably 0.003%.

[0155] The upper limit for the N content is further preferred to be 0.090%, and further preferred to be 0.080%.

[0156] Ti: 0~0.80%

[0157] It may also be free of titanium (Ti).

[0158] On the other hand, if the Ti content is below 0.80%, C is fixed, inhibiting the formation of Cr carbides. Therefore, the formation of the Cr-deficient layer is suppressed. As a result, oxide film embrittlement is inhibited, and the corrosion resistance of the ferritic stainless steel foil is improved.

[0159] Therefore, the preferred Ti content is 0~0.80%.

[0160] The lower limit for the Ti content is more than 0%, more preferably 0.01%, and more preferably 0.03%.

[0161] The upper limit for the Ti content is further preferred to be 0.70%, and further preferred to be 0.60%.

[0162] Nb: 0~0.80%

[0163] It may also be free of niobium (Nb).

[0164] On the other hand, if the Nb content is less than 0.80%, the corrosion resistance of the ferritic stainless steel foil is improved.

[0165] Therefore, the preferred Nb content is 0~0.80%.

[0166] The further preferred lower limit for Nb content is more than 0%, more preferably 0.01%, and more preferably 0.03%.

[0167] The upper limit for Nb content is further preferred to be 0.70%, and even more preferred to be 0.60%.

[0168] Zr: 0~0.80%

[0169] It may also be free of zirconium (Zr).

[0170] On the other hand, if the Zr content is less than 0.80%, the corrosion resistance of the ferritic stainless steel foil is improved.

[0171] Therefore, the preferred Zr content is 0~0.80%.

[0172] The further preferred lower limit for Zr content is more than 0%, more preferably 0.01%, and more preferably 0.03%.

[0173] The upper limit for Zr content is further preferred to be 0.70%, and further preferred to be 0.60%.

[0174] The remaining portion of the preferred chemical composition of the ferritic stainless steel foil of this embodiment consists of Fe and impurities. Here, impurities in the chemical composition refer to substances that may be introduced from raw materials or the manufacturing environment during the industrial manufacture of ferritic stainless steel foil, and are substances that are permissible within a range that do not adversely affect the ferritic stainless steel foil of this embodiment.

[0175] [Plate thickness]

[0176] The thickness of the foil body of the ferritic stainless steel foil in this embodiment is not particularly limited. For example, the thickness of the foil body of the ferritic stainless steel foil in this embodiment is 6~20μm.

[0177] [Applications of the ferritic stainless steel foil in this embodiment]

[0178] The ferritic stainless steel foil of this embodiment exhibits excellent corrosion resistance. Therefore, it is suitable for use as a current collector in all-solid-state batteries using highly corrosive sulfide-based solid electrolytes. Furthermore, the ferritic stainless steel foil of this embodiment can also be used for applications other than current collectors in secondary batteries.

[0179] [Method for manufacturing ferritic stainless steel foil according to this embodiment]

[0180] This section describes an example of a method for manufacturing the ferritic stainless steel foil according to this embodiment. The method described below is an example for manufacturing the ferritic stainless steel foil of this embodiment. Therefore, the ferritic stainless steel foil having the above configuration can also be manufactured by other manufacturing methods besides the method described below. However, the manufacturing method described below is a preferred example of the method for manufacturing the ferritic stainless steel foil of this embodiment.

[0181] An example of the method for manufacturing ferritic stainless steel foil according to this embodiment includes the following steps.

[0182] (Process 1) Raw material preparation process

[0183] (Process 2) Intermediate cold rolling process

[0184] (Process 3) Intermediate annealing process

[0185] (Process 4) Final cold rolling process

[0186] The following is a description of each process.

[0187] [(Process 1) Raw Material Preparation Process]

[0188] In the raw material preparation process, ferritic stainless steel sheets with a thickness of several hundred µm to several mm are prepared as raw materials for manufacturing the ferritic stainless steel foil of this embodiment. For example, the raw material is a cold-rolled coil after cold rolling a hot-rolled coil. The raw material can be prepared through manufacturing or by purchasing it from a third party. That is, the process for preparing the raw material is not particularly limited.

[0189] In the case of manufacturing raw materials, for example, the following method is used: Molten steel with the desired chemical composition is produced. A slab is manufactured using the molten steel via continuous casting. The manufactured slab is then subjected to hot working and cold rolling to produce a steel plate with a thickness of several hundred µm to several mm. The above steps are used to prepare the raw materials for the ferritic stainless steel foil of this embodiment.

[0190] [(Process 2) Intermediate cold rolling process]

[0191] In the intermediate cold rolling process, the prepared raw materials are cold rolled to produce intermediate steel plates with a thickness of tens to hundreds of μm. The intermediate cold rolling process can be carried out using either a continuous rolling mill with multiple rolling stands arranged in a row or a reversible rolling mill. There is no particular limitation on the cumulative reduction rate in the intermediate cold rolling process.

[0192] In the intermediate cold rolling process, the following conditions must be met. Furthermore, as explained later, the intermediate cold rolling process and the intermediate annealing process can be performed alternately multiple times. In this case, the following conditions need to be met in the final intermediate cold rolling process.

[0193] (Condition 1) The reduction rate R of the final pass L It is above 15.0%.

[0194] Condition 1 is explained below.

[0195] Regarding the final track drawdown rate R L ]

[0196] Here, "pass" refers to the action of the rolled material passing through one rolling mill stand in one cycle. In the intermediate cold rolling process, cold rolling is carried out in multiple passes, and the reduction rate R of the final pass is... L "Reduction" refers to the reduction rate in the final pass (final pass) among multiple passes in the intermediate cold rolling process. The reduction rate R of the final pass... L The larger the value, the greater the strain that can accumulate in the intermediate steel sheet after the intermediate cold rolling process. Therefore, the greater the amount of strain accumulated in the intermediate steel sheet after the intermediate cold rolling process, the more it promotes the formation of recrystallization texture in the subsequent intermediate annealing process. As a result, the proportion of recrystallization texture on the surface of the foil substrate increases. If the reduction rate R of the final pass... L If the strain is 15.0% or higher, sufficient strain accumulates in the intermediate steel sheet after the intermediate cold rolling process. In this case, assuming that the intermediate annealing process meets condition 2 (described later), F1 in the manufactured ferritic stainless steel foil is 0.16 or lower. Therefore, the reduction rate R in the final pass... L Set it to 15.0% or higher.

[0197] Final pass reduction rate R L There is no specific upper limit. If we consider typical industrial production, the final pass reduction R... L The upper limit is, for example, 50.0%.

[0198] (Process 3) Intermediate annealing process

[0199] In the intermediate annealing process, the intermediate steel sheet following the intermediate cold rolling process undergoes bright annealing. Bright annealing is an annealing treatment performed under an extremely low oxygen atmosphere. The surface of the intermediate steel sheet after bright annealing is almost unoxidized, maintaining its surface gloss. The extremely low oxygen atmosphere used in bright annealing is preferably a mixture of H2 and N2 gases. The N2 fraction in the atmosphere is, for example, 35-65% by volume.

[0200] In the bright annealing process of the intermediate annealing step, an intermediate steel plate is passed through a heat treatment furnace in an extremely low oxygen atmosphere at a specified speed. A specified tension is applied to the intermediate steel plate during this process. The heat treatment furnace is divided into a heating chamber, a slow cooling chamber, and a quenching chamber according to the order in which the intermediate steel plate passes through. In the heating chamber, the intermediate steel plate is heated and held at a heating temperature T (°C). The heating temperature T is, for example, 800~1200°C. In the slow cooling chamber, the intermediate steel plate is cooled from the heating temperature T (°C) to 400°C at a specified cooling rate. In the quenching chamber, the intermediate steel plate, after being cooled to 400°C, is rapidly cooled to room temperature. The quenching method is not particularly limited; for example, air cooling.

[0201] Furthermore, intermediate cold rolling and intermediate annealing processes can be performed alternately multiple times. For example, in the case of alternating intermediate cold rolling and intermediate annealing processes, a second intermediate cold rolling and second intermediate annealing process is performed after the first intermediate cold rolling and first intermediate annealing process.

[0202] In the intermediate annealing process, the following conditions must be met. Furthermore, in cases where multiple intermediate annealing processes are performed, the following conditions must be met in the final intermediate annealing process.

[0203] (Condition 2) The average cooling rate CR from heating temperature T (°C) to 400°C is less than 200°C / second.

[0204] Condition 2 will be explained below.

[0205] [Regarding Average Cooling Rate (CR)]

[0206] As described above, recrystallization texture formation occurs during the intermediate annealing process. However, if the average cooling rate CR from the heating temperature T (°C) to 400°C is too fast, the recrystallization texture formation on the surface of the foil body may be insufficient. If the average cooling rate CR is 200°C / second or less, the recrystallization texture formation on the surface of the foil body is also sufficient. In this case, assuming that condition 1 is met in the intermediate annealing process, F1 becomes 0.16 or less in the manufactured ferritic stainless steel foil. Therefore, the average cooling rate CR from the heating temperature T (°C) to 400°C is set to 200°C / second or less.

[0207] There is no specific lower limit for the average cooling rate CR. However, if typical industrial production is considered, the lower limit for the average cooling rate CR is, for example, 20°C / second.

[0208] In the intermediate annealing process, the following conditions are preferably met. Furthermore, in cases where multiple intermediate annealing processes are performed, the following conditions should be met in the final intermediate annealing process.

[0209] (Preferred Condition 1) The tension Ts applied to the intermediate steel plate during the cooling process from heating temperature T (°C) to 400°C is 1.0 N / mm. 2 above.

[0210] The following explains the preferred condition 1.

[0211] [Regarding Tension Ts]

[0212] During the intermediate annealing process, from a heating temperature T (°C) to 400°C and then cooling, a higher tension Ts applied to the intermediate steel sheet makes it easier to form a microstructure containing numerous lattice defects. If the tension Ts applied to the intermediate steel sheet is 1.0 N / mm... 2 The above results in a sufficient amount of lattice defects in the intermediate steel sheet after the intermediate annealing process. In this case, assuming the final cold rolling process meets the preferred condition 2 described later, the manufactured ferritic stainless steel foil has a foil body with an S-parameter of 0.592 or higher and a W-parameter of 2.80 x 10⁻⁶. -3 Therefore, the tension Ts is preferably set to 1.0 N / mm. 2 above.

[0213] There is no specific upper limit to the tension Ts. However, considering typical industrial production, the upper limit of tension Ts could be, for example, 8.0 N / mm. 2 .

[0214] (Process 4) Final cold rolling process

[0215] In the final cold rolling process, the intermediate steel sheet after the intermediate annealing process is cold rolled again to obtain a ferritic stainless steel foil with a foil body of a specified thickness. A known cold rolling mill can be used in the final cold rolling process. For example, a continuous rolling mill with multiple rolling stands arranged in a row or a reversible rolling mill can be used. There is no particular limitation on the cumulative reduction rate in the final cold rolling process.

[0216] In the final cold rolling process, the following conditions are preferably met.

[0217] (Preferred Condition 2) Maximum reduction rate R in one pass MAX It is below 28%.

[0218] The following explains the preferred condition 2.

[0219] [Regarding the maximum reduction rate R of a single test] MAX ]

[0220] In the final cold rolling process, cold rolling is carried out in multiple passes, with "the maximum reduction R of a single pass" being... MAX"" refers to the reduction rate of the pass with the highest reduction rate in the final cold rolling process. If even one pass has an excessively high reduction rate, it will generate intense processing heat. As a result, the temperature of the intermediate steel sheet rises excessively, and the number of lattice defects in the intermediate steel sheet's crystal lattice decreases. The maximum reduction rate R in a single pass... MAX When the reduction rate is below 28%, it means there are no passes with a reduction rate exceeding 28%. In this case, processing heat is sufficiently suppressed, and the reduction of lattice defects in the intermediate steel sheet is also suppressed. As a result, assuming the intermediate annealing process meets preferred condition 1, the manufactured ferritic stainless steel foil has an S-parameter of 0.592 or higher and a W-parameter of 2.80 x 10⁻⁶. -3 Therefore, the maximum reduction rate R in a single pass is as follows. MAX The preferred setting is below 28%.

[0221] Maximum reduction rate R in a single pass MAX There is no specific lower limit. If we consider typical industrial production, the maximum reduction rate R per pass is... MAX The lower limit is, for example, 5%.

[0222] The ferritic stainless steel foil of this embodiment is manufactured using the above manufacturing method.

[0223] [electrode]

[0224] The electrode of this embodiment includes a ferritic stainless steel foil of this embodiment and an electrode flux layer formed on the surface of the ferritic stainless steel foil. In other words, the ferritic stainless steel foil of this embodiment is used as the current collector in the electrode of this embodiment. The electrode of this embodiment can be either a positive or negative electrode. That is, the structure of the electrode of this embodiment is not particularly limited as long as it includes the ferritic stainless steel foil of this embodiment and the electrode flux layer.

[0225] [Electrode Mixture Layer]

[0226] In the electrode of this embodiment, the electrode binder layer is not particularly limited and can have a known structure. The electrode binder layer contains an active material. Furthermore, the electrode binder layer may also contain substances other than the active material. For example, the electrode binder layer may also contain a binder and a conductive additive. Additionally, the electrode binder layer for all-solid-state batteries may, for example, contain a solid electrolyte.

[0227] [Active Substances]

[0228] In the electrode of this embodiment, the active material contained in the electrode mixture layer is not particularly limited, and known active materials can be used. When the electrode is a positive electrode, the positive electrode active material can, for example, be derived from LiCoO2, LiNi... 1 / 3Co 1 / 3 Mn 1 / 3 The active material can be any one or more of the following groups: ternary materials represented by O2, olivine materials represented by LiFePO4, and sulfur-based materials represented by S, Fe2S, Mo3S4, and sulfur-modified polyacrylonitrile. When the electrode is a negative electrode, the active material can also be, for example, carbon-based materials represented by graphite, alloy materials represented by CuSn alloys and NiTiSi alloys, Si-based materials represented by Si and SiO, and materials such as Li4Ti5O4. 12 Choose one or more from the group consisting of oxide-based materials, represented by [the group name is missing].

[0229] [Adhesive]

[0230] In the electrode of this embodiment, the adhesive contained in the electrode adhesive layer is not particularly limited, and known adhesives can be used. The adhesive may, for example, be any one or more selected from the group consisting of: rubber-like 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 their hydrogenates; thermoplastic elastomers such as styrene-ethylene-butadiene, styrene copolymers, styrene-isoprene, or styrene block copolymers or their hydrogenates; soft resin-like polymers represented by isotactic-1,2-polybutadiene, ethylene-vinyl acetate copolymers, and copolymers of ethylene with α-olefins having 3 to 12 carbon atoms; and fluorinated polymers represented by polytetrafluoroethylene, tetrafluoroethylene-ethylene copolymers, polyvinylidene fluoride, polypentafluoropropylene, and polyhexafluoropropylene.

[0231] [Conductive additives]

[0232] In the electrode of this embodiment, the conductive additive contained in the electrode mixture layer is not particularly limited, and known conductive additives can be used. For example, the conductive additive can be any one or more from the group consisting of graphite materials, acetylene black, carbon black, Ketjen black, carbon fibers, carbon nanotubes, and graphene.

[0233] [Electrode manufacturing method]

[0234] The manufacturing method of the electrode in this embodiment is not particularly limited. The electrode in this embodiment uses the ferritic stainless steel foil of this embodiment as the current collector and is manufactured using a known method. The manufacturing method of the electrode in this embodiment includes, for example, an electrode slurry preparation step and an electrode binder layer formation step.

[0235] [Electrode paste preparation process]

[0236] In the electrode slurry preparation process, a composition (electrode slurry) for forming the electrode binder layer is prepared. The electrode slurry can be prepared according to the desired electrode binder layer. For example, it can be prepared by mixing active material, binder, and solvent. For example, it can also be prepared by mixing active material, conductive additive, binder, and solvent. In addition, when preparing an electrode slurry for all-solid-state batteries, for example, it can be prepared by mixing active material, solvent, solid electrolyte, and binder. The mixing method is appropriately adjusted according to the active material, conductive additive, binder, solid electrolyte, and solvent. That is, the electrode slurry preparation process can be carried out by known methods.

[0237] [Electrode Mixture Layer Formation Process]

[0238] In the electrode paste layer formation process, an electrode paste layer is formed on the surface of the ferritic stainless steel foil of this embodiment. Specifically, a mixed electrode slurry is coated onto the ferritic stainless steel foil of this embodiment. The coating method is not particularly limited and can be a known method. For example, a coater with gaps can be used for coating. For example, a sprayer can be used for spraying coating.

[0239] The electrodes of this embodiment can be manufactured through the above processes.

[0240] [Battery]

[0241] The battery of this embodiment includes the electrodes and electrolyte of this embodiment. As long as the battery of this embodiment includes the electrodes of this embodiment, other structures can be known structures and are not particularly limited. The battery of this embodiment may also include a separator, for example. The shape of the battery of this embodiment is not particularly limited; it can be cylindrical, square, coin-shaped, or sheet-shaped. Furthermore, the battery of this embodiment can be either a secondary battery or a primary battery. When the battery of this embodiment is a secondary battery, it can be, for example, a non-aqueous electrolyte secondary battery, an aqueous electrolyte secondary battery, or an all-solid-state secondary battery.

[0242] [Electrolytes]

[0243] The electrolyte conducts ions between the positive and negative electrodes. In the battery of this embodiment, the electrolyte is not particularly limited and any known electrolyte can be used. The electrolyte can be either a liquid electrolyte or a solid electrolyte.

[0244] In the battery of this embodiment, ferritic stainless steel foil of this embodiment is used as the current collector in the electrodes. Therefore, this current collector has excellent corrosion resistance. Therefore, the electrolyte of the battery of this embodiment can be a sulfide-based solid electrolyte that is highly corrosive to the current collector. For example, the sulfide-based solid electrolyte can also be made from materials such as Li3PS4 and Li7P3S4. 11 LPS-based systems, represented by Li6PS5Cl x Br (1-x) Argyrodite type, represented by (0≦x≦1), and Li 10 GeP2S 12 Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 Choose one or more from the group consisting of thio-LISICON, represented by thio-LISICON.

[0245] [Battery manufacturing method]

[0246] The manufacturing method of the battery in this embodiment is not particularly limited. For example, the battery in this embodiment is manufactured by a known method, in which a laminate is formed by stacking the electrode, electrolyte and counter electrode of this embodiment.

[0247] Example

[0248] The effects of the ferritic stainless steel foil of this embodiment will be further explained in detail through examples. The conditions in the following examples are one example used to confirm the feasibility and effects of implementing the ferritic stainless steel foil of this embodiment. Therefore, the ferritic stainless steel foil of this embodiment is not limited to this one example.

[0249] As a raw material for manufacturing ferritic stainless steel foil, a steel sheet with the chemical composition shown in Table 1 is prepared. The thickness of the steel sheet is 300 μm.

[0250] [Table 1]

[0251]

[0252] An intermediate cold rolling process was performed on the raw materials for each test number to produce intermediate steel plates. Specifically, a reversible rolling mill was used to cold roll the raw materials for each test number. The reduction rate RL (%) of the final pass for each test number is shown in Table 2.

[0253] [Table 2]

[0254]

[0255] An intermediate annealing process was performed on the intermediate steel sheets after the intermediate cold rolling process. Specifically, for each test number of intermediate steel sheets, bright annealing was performed in a mixed gas atmosphere of 35-65% by volume N2 gas and the remainder being H2 gas. During bright annealing, the intermediate steel sheets were heated and held at a heating temperature T of 800-1200°C, and then cooled to 400°C at an average cooling rate CR (°C / sec). Subsequently, they were quenched to room temperature by air cooling. The tension Ts (N / mm) applied to each test number of intermediate steel sheets during the cooling process from heating temperature T (°C) to 400°C was recorded. 2 The average cooling rate CR (°C / sec) from heating temperature T (°C) to 400°C is shown in Table 2.

[0256] The intermediate steel sheet after the intermediate annealing process undergoes a final cold rolling process. In this final cold rolling process, the intermediate steel sheets from each test number are cold rolled using a reversible mill to produce ferritic stainless steel foil with a foil body of 10 μm thickness. The maximum reduction R of one pass for each test number is... MAX (%) is shown in Table 2.

[0257] Through the above manufacturing processes, ferritic stainless steel foils of various test numbers are manufactured.

[0258] [Regarding the evaluation test]

[0259] The following evaluation tests were performed on the ferritic stainless steel foils of each test number.

[0260] (Experiment 1) Maximum Extreme Density Determination Test

[0261] (Experiment 2) Determination of S-parameters and W-parameters

[0262] (Experiment 3) Corrosion resistance evaluation test

[0263] The following is a description of each experiment.

[0264] [(Experiment 1) Maximum Extreme Density Determination Test]

[0265] Based on the method described above in [Method for Determining Maximum Extreme Density], the maximum extreme density of the rolled surface of the foil body of ferritic stainless steel foil for each test number was determined. <001> Maximum polar density M of orientation 001 and <111> Maximum polar density M of orientation 111 Based on the obtained maximum polar density M 001 and maximum extreme density M 111 The F1 value is calculated and shown in Table 3.

[0266] [Table 3]

[0267]

[0268] [Experiment 2: Determination of S-parameters and W-parameters]

[0269] Based on the methods described above in [Determination Methods of S-parameters and W-parameters], the S-parameters and W-parameters of the foil body of the ferritic stainless steel foil for each test number were determined. The obtained S-parameters and W-parameters are shown in Table 3.

[0270] [(Experiment 3) Corrosion Resistance Evaluation Test]

[0271] The corrosion resistance of ferritic stainless steel foils for each test number was evaluated using the following method.

[0272] First, circular test pieces with a diameter of 11 mm were collected from the main body of ferritic stainless steel foil. One surface of the test piece was used as the evaluation surface. The unfolded area ratio Sdr, as specified in ISO 25178-2:2012, was measured on the evaluation surface of the test piece. The unfolded area ratio Sdr is an indicator of the rate of increase in surface area of ​​the test surface compared to a flat surface. The corrosion reaction begins at the surface of the main foil body; therefore, the larger the unfolded area ratio Sdr of the test piece, the faster the corrosion proceeds.

[0273] The unfolded area ratio (Sdr) of the evaluation surface of the test specimen was determined using a laser microscope. The laser microscope used was a Keyence VK-X100. The magnification was set to 2000x, and measurements were taken over a 280µm × 200µm measurement area. Specifically, to measure the entire measurement area, four locations within the area were measured with a 145µm × 109µm field of view, resulting in surface images. The four surface images were then stitched together using the accompanying image stitching software to obtain a surface image of the 280µm × 200µm measurement area. From the surface shape profile obtained by analyzing the surface image of the measurement area, a reference plane was established by removing 0.3% of the area from the side with lower brightness, generating a three-dimensional image. A high-pass filter with a cutoff wavelength of 50µm was then applied for filtering. A Gaussian filter was used for the filtering. The unfolded area ratio (Sdr) as specified in ISO 25178-2:2012 was calculated within a 200µm × 150µm region of the obtained three-dimensional image.

[0274] Evaluation units simulating sulfide-based all-solid-state batteries were fabricated using test pieces with measured unfolded area ratios (Sdr) for each test number. Specifically, 0.12 g of sulfide-based solid electrolyte was added to a mold with an inner diameter of 11 mm, and pressure was applied at 300 MPa to form a cylindrical sulfide-based solid electrolyte sheet with a thickness of 700 μm and a bottom diameter of 11 mm. β-Li3PS4 was used as the sulfide-based solid electrolyte. The fabricated sheet was placed on the evaluation surface of the test piece with each test number. Then, a cylindrical Li metal foil with a thickness of 1.2 mm and a bottom diameter of 11 mm was placed on the sulfide-based solid electrolyte sheet. These were placed in a measurement unit with an inner diameter of 11 mm that could isolate them from external air, and a pressure of 5 MPa was applied by tightening with bolts. The measurement unit was then sealed. Furthermore, the process from fabricating the sulfide-based solid electrolyte sheet to sealing the evaluation unit was performed in a glove box under an Ar atmosphere. Evaluation units for each test number were fabricated through these processes.

[0275] Cyclic voltammetry (CV) measurements were performed using evaluation units with various test numbers. In the CV measurements, the test piece was used as the working electrode, and metallic Li foil was used as both the counter and reference electrodes. Specifically, for the evaluation units held at 60°C for 24 hours, the voltage was changed from the open-circuit voltage V... OC (V) After scanning to 3.0V, scan to 0.005V, and then scan again to the open circuit voltage V. OC (V), the current density flowing through it (μA / cm) is measured. 2 The scan rate is set to 5 mV / second. Additionally, the open-circuit voltage V... OC The voltage is 2.0~2.5V in any test unit.

[0276] Based on the measurement results, in order to eliminate the influence of the minute irregularities on the evaluation surface of the test piece, the value of the voltage V from the open circuit is determined. OC The maximum current density (μA / cm) flowing through the device during the scan from (V) to 3.0V. 2 The value obtained by dividing the unfolded area ratio Sdr is defined as the maximum current value I. MAX (μA / cm) 2 (), used as an indicator of the degree of corrosion reaction in the test piece.

[0277] The maximum current value I for each test number MAX (μA / cm) 2 The results are shown in Table 3. At the maximum current value I... MAX For more than 18.0 μA / cm 2 ~25.0μA / cm 2Under these conditions, excellent corrosion resistance can be obtained. At the maximum current value I... MAX 18.0 μA / cm 2 The following conditions indicate that superior corrosion resistance can be achieved: At the maximum current value I... MAX More than 25.0 μA / cm 2 In such cases, it is determined that excellent corrosion resistance cannot be obtained.

[0278] [Evaluation Results]

[0279] Referring to Tables 1-3, in the ferritic stainless steel foils of test numbers 1-9, F1 is below 0.16. Therefore, excellent corrosion resistance can be obtained.

[0280] In the ferritic stainless steel foils tested (numbers 1-6), the S-parameter was greater than 0.592, and the W-parameter was 2.80 × 10⁻⁶. -3 Therefore, further superior corrosion resistance can be obtained.

[0281] On the other hand, in test number 10, the reduction rate R of the final pass in the intermediate cold rolling process... L Too small. Therefore, F1 exceeds 0.16. As a result, excellent corrosion resistance is not obtained.

[0282] In test number 11, the average cooling rate CR during the intermediate annealing process was too fast. Therefore, F1 exceeded 0.16. As a result, excellent corrosion resistance was not achieved.

[0283] The embodiments of this disclosure have been described above. However, the above embodiments are merely illustrative examples for implementing this disclosure. Therefore, this disclosure is not limited to the above embodiments, and appropriate modifications can be made to the embodiments without departing from its spirit.

Claims

1. A ferritic stainless steel foil, It has a foil body made of ferritic stainless steel. In the inverse pole figure of the ND direction obtained by measuring the rolled surface of the foil body using electron backscatter diffraction, <001> Maximum polar density M of orientation 001 and <111> Maximum polar density M of orientation 111 Satisfy equation (1) M 001 / M 111 ≦0.16 (1)。 2. The ferritic stainless steel foil as described in claim 1, Furthermore, the S-parameter obtained by measuring the foil body using the positron annihilation coincidence Doppler broadening method is greater than 0.592, and the W-parameter is 2.80 × 10⁻⁶. -3 the following.

3. The ferritic stainless steel foil as described in claim 1, The chemical composition of the foil body is as follows: by mass%, it contains... C：0.001~0.030%、 Si: 0.01~1.00% Mn: 0.01~1.00%, P: below 0.050% S: Below 0.030% 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%， The remainder consists of Fe and impurities.

4. The ferritic stainless steel foil as described in claim 2, The chemical composition of the foil body is as follows: by mass%, it contains... C：0.001~0.030%、 Si: 0.01~1.00% Mn: 0.01~1.00%, P: below 0.050% S: Below 0.030% 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%， The remainder consists of Fe and impurities.

5. An electrode comprising: Ferritic stainless steel foil as described in any one of claims 1 to 4; and An electrode mixture layer is formed on the surface of the ferrite-based stainless steel foil.

6. A battery comprising: The electrode as described in claim 5; and Electrolytes.

7. The battery as described in claim 6, The electrolyte is a sulfide-based solid electrolyte.

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