JP2017047466A - Ni-PLATED STEEL FOIL, BATTERY CONDUCTIVE MEMBER, AND MANUFACTURING METHOD OF Ni-PLATED STEEL FOIL - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Ni-plated steel foil excellent in corrosion resistance and weldability as a more inexpensive alternate material than Ni.SOLUTION: In a Ni-plated steel foil including, in the order from the surface, a Ni layer having a thickness of 0.5-3 μm and containing Ni over 90%, and a Ni-Fe layer having a thickness of 0.1-2 μm and containing 50-90% Ni, a total thickness of the Ni layer and the Ni-Fe layer is 1 μm or more, and the maximum height roughness Rz measured vertically in the rolling direction is 0.9 μm or less.SELECTED DRAWING: None

Description

  The present invention relates to a Ni-plated steel foil and a battery conductive member using the same.

  Lithium ion secondary batteries (hereinafter referred to as “LiB”) are small and capable of high output, so they are widely used from small electronic devices such as smartphones and laptop computers to large devices such as hybrid cars and auxiliary power supplies in times of disaster. Yes. Since further miniaturization and higher output are progressing now, the application field is expected to further expand in the future.

  Since the negative electrode lead material which is one of the parts for LiB is required to have conductivity, corrosion resistance, and weldability with an outer can, pure Ni is often used. However, pure Ni is more expensive than Fe and Cu, and an inexpensive alternative material is required.

  In many cases, SUS or Ni-plated steel is used for the outer can of LiB. Fe or Cu, which is cheaper than pure Ni, is not suitable as a negative electrode lead material because it is inferior in weldability and corrosion resistance to an outer can compared to pure Ni. On the other hand, SUS, which is excellent in corrosion resistance and weldability with an outer can, is not suitable as a negative electrode lead material because it is significantly inferior in conductivity as compared with pure Ni.

  As an alternative to pure Ni used in the current negative electrode lead material, Fe is a base material made of Fe, which is cheaper and has better conductivity than SUS, and Ni and its corrosion resistance and weldability with external cans are complemented by Ni. Fe laminates are promising.

  Patent Document 1 discloses a method of manufacturing a Ni / Fe / Ni laminated material by joining and rolling Ni and Fe. However, this method is disadvantageous in cost because the Ni layer is thicker than the Ni plating method. Furthermore, since it is a joining rolling method, there is a possibility that foreign matter is always mixed into the joining interface.

  Patent Document 2 discloses a manufacturing method in which Ni plating is applied to a steel plate. An Ni-Fe alloy layer is formed between the Ni plating and the steel plate by annealing after Ni plating, and Ni is formed by annealing. It is disclosed that the rolling property of plating is improved. However, pinholes that are inevitably generated during plating (locations where plating has not been performed) are not disclosed. Moreover, since the rolling after plating is not disclosed, the influence of plating pinholes inevitably generated during rolling and countermeasures are not disclosed.

  Patent Document 3 discloses a manufacturing method in which a steel plate excellent in rollability is rolled to a foil and then Ni plating is performed. However, it is more efficient and lower cost to manufacture a Ni-plated foil if Ni is plated on a steel sheet of a certain thickness (about 0.5 mm thick) and then rolled to a foil, more efficiently than this method.

International Publication No. 2011/099160 JP-A-6-2104 JP 2013-222696 A

  As described above, as a method for producing Ni-plated steel foil at a low cost, after plating Ni to a steel plate of a certain thickness, the pinholes are eradicated by annealing and then rolled to foil Is effective.

  However, a 0.5 mm thick Ni-plated steel sheet annealed by the present inventors was rolled to a 0.1 mm thick foil, and then SEM observation was performed to confirm the soundness of the plating. It was. When the cracked portion was analyzed by EDX, the Fe content exceeded 80% by mass, and it was revealed that it was a pinhole. Since the pinhole has disappeared due to the heat treatment after Ni plating, it can be seen that this pinhole was formed during the rolling up to the foil.

  However, few Ni-plated steels that have been annealed are rerolled and applied as lead materials, and no countermeasures have been established for pinholes that are re-formed when the steel sheet is rolled to foil.

  In addition, since the LIB negative electrode lead material is used after resistance welding or ultrasonic welding, the surface roughness affecting the weldability is an important factor. However, there is no literature on Ni-plated steel foil that mentions surface roughness.

  An object of this invention is to provide Ni plating steel foil excellent in corrosion resistance and weldability as an alternative material cheaper than Ni in view of said situation.

  The inventors diligently studied a method for obtaining a Ni-plated steel foil excellent in corrosion resistance and weldability.

  The present inventors paid attention to the relationship between the structure of the Ni-plated layer and the rollability because the pinhole was re-formed when the Ni-plated steel sheet was rolled into a foil. Moreover, the structure of the Ni plating layer which can obtain high corrosion resistance was investigated. In addition, the surface roughness with which excellent weldability was obtained was investigated.

  As a result, before rolling the Ni-plated steel sheet to form a foil, the Ni-plated steel sheet is annealed under appropriate conditions, and the Ni plating layer is appropriately configured so that it is unavoidably re-formed when rolling to foil. It has been found that excellent pinholes can be suppressed and excellent corrosion resistance can be obtained. Furthermore, it has been found that excellent resistance weldability and appearance can be ensured by a unique rolling method in which the surface has a low roughness.

  The present invention has been made based on the above findings, and the gist thereof is as follows.

  (1) In order from the surface, the Ni layer has a thickness of 0.5 to 3 μm and contains more than 90% of Ni, and the Ni— has a thickness of 0.1 to 2 μm and contains 50 to 90% of Ni. Ni plating comprising an Fe layer, wherein the total thickness of the Ni layer and the Ni—Fe layer is 1 μm or more, and the maximum height roughness Rz measured perpendicular to the rolling direction is 0.9 μm or less Steel foil.

  (2) The Ni-plated steel foil of (1) above, wherein the thickness is 0.04 to 0.20 mm

  (3) A battery conductive member comprising the Ni-plated steel foil of (1) or (2).

  (4) A step of subjecting the steel slab to hot rolling and cold rolling to obtain a cold-rolled steel plate, a step of applying Ni plating to the cold-rolled steel plate to obtain a Ni-plated steel plate, and the Ni-plated steel plate at 750 to 900 ° C. at 10 to 10 ° C. A step of performing annealing for 30 seconds and a step of rolling the Ni-plated steel sheet after annealing to form a Ni-plated steel foil. In the step of rolling the Ni-plated steel sheet, the rolling of the final two passes or more is performed. A method for producing a Ni-plated steel foil, which is performed using a roll having no deposited Ni.

  (5) The method for producing a Ni-plated steel foil according to (4) above, wherein the roll in which the adhered Ni is not present is an unused or repolished roll.

  According to the present invention, Ni-plated steel foil can be provided as an inexpensive alternative material compared to Ni. The Ni-plated steel foil according to the present invention can be manufactured at a lower cost than the conventional Ni-plated steel foil, and is excellent in corrosion resistance and weldability, and is particularly suitable as a steel foil for battery conductive members.

  Hereinafter, the present invention will be described in detail. First, the configuration of the Ni plating layer will be described. The foil for a battery conductive member of the present invention includes, in order from the surface, a Ni layer containing more than 90% Ni and a Ni-Fe layer containing 50 to 90% Ni.

  In order to suppress the re-formation of pinholes that deteriorate the corrosion resistance, the Ni-Fe layer (50 ≦ Ni (mass%) ≦ 90) and the steel layer are significantly harder than the above-described Ni layer, Ni—Fe layer. It is necessary to reduce the influence of the layer (5 ≦ Ni (mass%) <50). The Vickers hardness of the Ni layer, Ni-Fe layer (50 ≦ mass% Ni ≦ 90) and steel sheet layer is around 100, but the Ni—Fe layer (5 ≦ mass% Ni <50) is about 200 at the maximum. . Therefore, it is considered that the Ni—Fe layer (5 ≦ Ni (mass%) <50) has a large difference in rolling followability from other layers, and promotes the re-formation of pinholes during rolling up to the foil. In order to suppress re-formation of pinholes and maintain corrosion resistance, it is necessary to have the above-described plating layer configuration.

  The Ni-Fe layer is necessary to eradicate pinholes that are inevitably generated when Ni plating is applied to the steel sheet and to improve the adhesion with the steel sheet, and by annealing the steel sheet after Ni plating Let it form.

  Annealing is performed in order to recrystallize the steel plate and the Ni plating and improve the rollability. In the present invention, the annealing condition is very important for controlling the configuration of the Ni layer.

  In order to suppress pinholes re-formed when rolling the steel sheet into a foil and maintain corrosion resistance, the Ni layer in the foil is 0.5 μm or more, Ni—Fe layer (50% ≦ Ni ≦ 90%) is 0.1 or more, and the total of the Ni layer and the Ni—Fe layer is 1 μm or more. From an economical viewpoint, the Ni layer is 3 μm or less, and the Ni—Fe layer is 2 μm or less.

  By annealing, a Ni—Fe layer (5 ≦ Ni (mass%) <50), which is a diffusion layer, is inevitably formed below the Ni—Fe layer (50% ≦ Ni ≦ 90%). As described above, the Ni—Fe layer (5 ≦ Ni (mass%) <50) is hard and promotes the re-formation of pinholes during rolling to foil, but the Ni—Fe layer (5 ≦ Ni (mass%)) When <50) is sufficiently thin, specifically, it is 75% or less and 1.5 μm or less of the total thickness of the Ni layer + Ni—Fe layer (50 ≦ Ni (mass%) ≦ 90) when the foil is formed. Will not have any adverse effects.

  In order to make the Ni—Fe layer (5 ≦ Ni (mass%) <50) sufficiently thin, the balance of the thicknesses of the Ni layer and the Ni—Fe layer (50% ≦ Ni ≦ 90%) must be adjusted as described above. It is necessary to set the annealing conditions so as to be in the range. For that purpose, the annealing temperature needs to be 750 to 900 ° C., and the holding time needs to be 10 to 30 seconds.

  The Ni plating is formed by electroplating the steel plate. According to electroplating, the plating thickness can be set to a required thickness by controlling the current density and time. What is necessary is just to adjust the plating thickness of a steel plate so that said required plating thickness can be obtained in steel foil.

  Next, the surface roughness will be described.

  When the surface roughness, particularly the maximum height roughness Rz, is high, non-uniform contact is caused on the weld surface, and defects are likely to occur in resistance welding. In the rolling method of the present invention, the measurement was performed perpendicular to the rolling direction by using a roll in which Ni adhered during rolling does not exist, more specifically, a roll that has not been used or has been repolished, in the final two passes or more. It has excellent resistance weldability with a maximum height roughness Rz of 0.9 μm or less, and can have a beautiful appearance. Rolling with a clean roll having no adhered Ni is also effective for pinhole suppression.

  The Ni-plated steel foil of the present invention preferably has a thickness of 0.04 to 0.20 mm. If the thickness is less than 0.04 mm, the production process may be broken or cracks may occur on the surface. Even if the thickness exceeds 0.20 mm, there is no problem in characteristics as a negative electrode lead material for a lithium ion secondary battery, but this leads to an increase in the size and weight of the battery to be incorporated.

  Using extremely low carbon steel, a cold rolled steel sheet having a thickness of 0.5 mm was obtained through hot rolling and cold rolling (hereinafter referred to as cold rolling). The obtained cold-rolled steel sheet was subjected to Ni plating with various thicknesses by electroplating. Thereafter, except for Comparative Example 10, annealing was performed at 750 ° C. to 900 ° C. × 10 to 30 seconds, and Ni—Fe alloy layers having various thicknesses were formed between the Ni plating layer and the steel plate. Since the Ni—Fe alloy is formed in the Ni plated pinhole portion by annealing, there is no pinhole at the time before rolling to the foil.

  Subsequently, in the rolling process up to the foil, the rolling reduction in the first rolling pass was 30% or less, and the cumulative rolling reduction in the fourth rolling pass was 70% or less. Thereafter, the roll of the rolling mill is changed to an unused or polished roll without Ni adhesion, and the difference between the cumulative reduction rate in the rolling pass two steps before the final pass and the cumulative reduction rate in the final pass is 5% or less. As a result, a 0.1 mm thick Ni-plated steel foil was produced.

  The negative electrode lead material is exposed to a metal ion elution (corrosion) environment by an electrolytic solution in a state where voltage is applied. In view of this situation, the present inventors devised the following test method and investigated the corrosion resistance as a negative electrode lead material.

A laminate cell in which the electrolytic solution was 1 mol / L LiPF ₆ and the solvent was ethylene carbonate: ethyl methyl carbonate = 1: 3 was produced. When voltage is applied, the metal ion elution (corrosion) environment of the negative electrode foil in the cell is the same as the metal ion elution environment of the negative electrode lead material. Therefore, it can be judged that a sample in which elution of metal ions does not occur in this test can be used as a negative electrode lead material.

  The applied voltage was controlled by a metal Li foil electrode. Further, if metal ions are eluted in the cell, the current value in the cell increases. In this test, a current of 1 mA was passed, and it was determined that “metal ions were eluted”.

  When the above test was performed on pure Ni currently used as a negative electrode lead material at 25 ° C., it was not eluted for 12 hours at 3.4 V or less. However, it eluted at about 8 h at 3.5 V. Therefore, it was judged that it had the same performance as the currently used pure Ni if it did not elute for 12 h under an applied voltage of 3.4 V at 25 ° C. Moreover, when the same test was implemented with respect to Fe for comparison, it eluted within 12 hours. From the fact that the difference in corrosion resistance between pure Ni and Fe can be clearly confirmed, this test method can be judged to be appropriate as a corrosion resistance investigation test for lead materials.

  The structure of the Ni plating layer was investigated by glow discharge mass spectrometry (hereinafter referred to as GDS). In addition, the Vickers hardness of each layer was measured. As a result, the Vickers hardness of the annealed Ni layer and the steel sheet layer was almost equal to a little less than 100, and the Vickers hardness of the Ni—Fe layer (50 ≦% by mass Ni ≦ 90) was 120. However, the Vickers hardness of the Ni—Fe layer (5 ≦ mass% Ni <50) is 120 to 200, which is remarkably hard as compared with other layers, and it is considered that pinhole re-formation is promoted due to the difference in rolling followability.

  Table 1 shows the test results of the inventive examples and the comparative examples. In Inventive Examples 1 to 8, elution of metal ions did not occur. It can be judged that this is because, with an appropriate plating configuration, even if the rolling cannot be followed and the surface layer of the Ni layer is partially torn off, the Ni plating layer is sufficiently thick so that it does not become a pinhole but maintains corrosion resistance.

  In Comparative Example 9, since the Ni layer was too thin, it is considered that pinholes re-formed during rolling reached the Fe base material and elution occurred.

  Since Comparative Example 10 was not annealed after Ni plating, the rollability was poor, and furthermore, pinholes before rolling were not eradicated by the Ni—Fe alloy layer. In addition, it is thought that many pinholes were formed during rolling up to the foil, and the corrosion resistance was lowered.

  In Comparative Example 11, since the Ni layer was entirely made of the Ni—Fe alloy phase, the hard Ni—Fe layer (5 ≦ mass% Ni <50) also increased, and the pinhole re-formation was promoted during rolling, resulting in a decrease in corrosion resistance. It is thought that.

  In Comparative Examples 12 and 13, since the total thickness of the plating layer is less than 1 μm, it is considered that the pinholes re-formed during rolling reached the Fe base material and elution occurred.

  Continuously, the resistance weldability of Nos. 14 to 16 in which the timing of roll change was changed in the above-described Example 1 of the present invention and rolling to foil was investigated. Each number of samples was resistance-welded to 0.3 mm thick SUS under the same conditions, and then the weldability was examined by a T-shaped peel test. The number of samples is 10 each, and all samples are placed with “Ni-plated steel foil ruptured” with good weldability, and even with one “Ni-plated steel foil and SUS plate peeled” as poor weldability It was judged. Moreover, the maximum height roughness Rz perpendicular to the rolling direction was an average value of 10 samples.

  The results are shown in Table 2. In Comparative Examples 15 and 16 having a high maximum height roughness Rz, many samples were peeled off, and sparks were often scattered during resistance welding. This is thought to be because the roughness was high and non-uniform contact occurred and the welding current was not stable.

Claims (5)

From the surface,
A Ni layer having a thickness of 0.5-3 μm and containing more than 90% of Ni;
It has a thickness of 0.1 to 2 μm and a Ni—Fe layer containing 50 to 90% of Ni,
The total thickness of the Ni layer and the Ni—Fe layer is 1 μm or more,
A Ni-plated steel foil, wherein the maximum height roughness Rz measured perpendicularly to the rolling direction is 0.9 μm or less.   The Ni-plated steel foil according to claim 1, wherein the thickness is 0.04 to 0.20 mm.   A battery conductive member comprising the Ni-plated steel foil according to claim 1. A step of subjecting the steel slab to hot rolling and cold rolling to form a cold rolled steel sheet,
Applying Ni plating to the cold-rolled steel sheet to form a Ni-plated steel sheet,
A step of annealing the Ni-plated steel sheet at 750 to 900 ° C. for 10 to 30 seconds, and a step of rolling the Ni-plated steel sheet after annealing to form a Ni-plated steel foil,
In the step of rolling the Ni-plated steel sheet, a method for producing a Ni-plated steel foil is characterized in that the rolling of the final two passes or more is performed using a roll having no adhered Ni.   The method for producing a Ni-plated steel foil according to claim 4, wherein the roll in which the adhered Ni is not present is an unused or re-polished roll.