Metal foil for current collectors, electrodes, and batteries

Abstract

The present invention provides a metal foil for current collectors, the metal foil being able to achieve enhanced adhesion to an electrode mixture layer, while maintaining the discharge capacity of a battery. A metal foil for current collectors according to the present disclosure is provided with a base material and a plurality of composite bodies that are held on the surface of the base material. The plurality of composite bodies each contain: Ni particles having an average particle diameter of 20 μm or less; a sintered body formed by sintering a plurality of Ni particles; and 14.0-40.0% by volume of a resin. On the surface of the metal foil for current collectors, the number of mountains, the height of which from the surface of the base material exceeds 10 μm, is 20.0-50.0 per mm as determined by line roughness analysis.

Description

Technical Field

[0001] The present disclosure relates to a current collector metal foil used for an electrode of a battery, an electrode using the current collector metal foil, and a battery using the electrode.

Background Art

[0002] Hitherto, batteries such as primary batteries and secondary batteries have been used as power sources for various electronic devices. Specifically, in recent years, with the spread of small electronic devices such as home video cameras, notebook personal computers, and smartphones, secondary batteries typified by lithium-ion batteries have been rapidly spreading. Along with the further miniaturization and high performance of such small electronic devices, further miniaturization and performance improvement have been demanded for batteries. In this specification, the "secondary battery" is a general term including, for example, non-aqueous electrolyte secondary batteries, aqueous electrolyte secondary batteries, and all-solid-state secondary batteries.

[0003] A battery includes an electrode and an electrolyte. The electrode has a positive electrode and a negative electrode. In both the positive electrode and the negative electrode, an electrode active material layer is formed on a current collector. The current collector is a base material of the electrode. The electrode active material layer is a layer containing an active material. The electrode active material layer may contain a binder. The current collector has a function of supplying current to the active material and a function of holding the active material. Hitherto, metal foil has been used as the current collector. Specifically, for example, in a lithium-ion battery at present, copper foil is used as the negative electrode current collector and aluminum foil is used as the positive electrode current collector.

[0004] The active material means a material capable of occluding and releasing ions contained in the electrolyte. Specifically, for example, in a lithium-ion battery at present, a graphite-based carbon material is used as the negative electrode active material and an oxide typified by LiCoO2 is used as the positive electrode active material. The binder has a function of binding the active materials to each other and binding the active material and the current collector. The binder is, for example, a resin.

[0005] When the electrolyte is dissolved in a liquid, the battery includes electrodes, the electrolyte, and a separator. The separator is positioned as an insulator between the positive and negative electrodes, preventing electrical short circuits. Specifically, for example, in liquid-based lithium-ion batteries, porous organic membranes are currently used as separators. The electrolyte exchanges ions with the positive and negative electrodes. In recent years, solid electrolytes have been developed in addition to liquid electrolytes.

[0006] Incidentally, it is preferable that the metal foil used as the base material for the current collector has high adhesion to the electrode mixture layer. If the adhesion to the electrode mixture layer is low, the electrode mixture layer is likely to peel off from the metal foil for the current collector. As a result, the electrode comprising the metal foil for the current collector and the electrode mixture layer will not be able to fully perform its function. Therefore, excellent adhesion to the electrode mixture layer is required for the metal foil for the current collector. Japanese Patent Publication No. 2011-009207 (Patent Document 1) and Japanese Patent Publication No. 2009-026491 (Patent Document 2) propose a metal foil for a current collector with improved adhesion to the electrode mixture layer.

[0007] The metal foil for current collectors disclosed in Patent Document 1 is a rolled copper foil for lithium battery current collectors, wherein the surface roughness in the direction parallel to the rolling of the upper and lower surfaces satisfies 0.01 μm ≤ Ra ≤ 0.10 μm and RSm ≤ 20 μm. Patent Document 1 discloses that this metal foil for current collectors has high adhesion to the negative electrode active material by appropriately controlling the rolling conditions rather than roughening the surface to form finer irregularities.

[0008] The metal foil for current collectors disclosed in Patent Document 2 has a metal film formed by applying a dispersion of metal fine particles in a non-aggregated state onto a base foil to form a coating film, and then heating the coating film in an inert atmosphere to aggregate and precipitate the metal fine particles. This metal film has a roughly mountain-like shape with a series of protruding fine particles having pointed tips, and the maximum particle diameter of the protruding fine particles is 100 μm or less, and the ten-point average roughness Rz according to JIS B 0601-1994 is 0.4 to 10 μm. When an electrode mixture layer such as Si constituting an alloy-based negative electrode is formed on this metal foil for current collectors, even if the electrode mixture layer expands and contracts, the electrode mixture layer does not peel off, and excellent adhesion is exhibited, as disclosed in Patent Document 2. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2011-009207 [Patent Document 2] Japanese Patent Publication No. 2009-026491 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] As described above, metal foil for current collectors is required to have excellent adhesion to the electrode mixture layer. Patent documents 1 and 2 propose metal foil for current collectors that has excellent adhesion to the electrode mixture layer. However, metal foil for current collectors that has excellent adhesion to the electrode mixture layer may be obtained by technologies other than those disclosed in patent documents 1 and 2.

[0011] Generally speaking, increasing the volume of components involved in power storage within a battery (for example, active material and electrolyte) increases the battery's discharge capacity. Also, as mentioned above, there has been a growing demand for further miniaturization of batteries in recent years. In other words, strict constraints on the battery's volume may be imposed during battery development. On the other hand, the current collector does not participate in power storage. Therefore, if the volume occupied by the current collector increases, the volume of components involved in power storage will decrease due to the constraints on the battery's volume. In this case, there is a concern that the battery's discharge capacity will decrease.

[0012] In the above-mentioned Patent Documents 1 and 2, an uneven surface is formed on the metal foil for the current collector to improve adhesion with the electrode mixture layer. When an uneven surface is formed on the metal foil for the current collector to improve adhesion with the electrode mixture layer, the volume of the current collector increases by the amount of that uneven surface. In this case, there is a concern that the discharge capacity of the battery will decrease due to the constraints of the battery's volume. In other words, metal foil for current collectors is required to have both excellent adhesion to the electrode mixture layer and the maintenance of the battery's discharge capacity.

[0013] The purpose of this disclosure is to provide a metal foil for current collectors that can improve adhesion to the electrode mixture layer while maintaining the discharge capacity of the battery, an electrode using the metal foil for current collectors, and a battery using the electrode. [Means for solving the problem]

[0014] The metal foil for current collectors according to this disclosure is Substrate and The substrate comprises a plurality of composites held on the surface of the substrate, The aforementioned multiple complexes are Ni particles with an average particle size of 20 μm or less, A sintered body formed by sintering multiple Ni particles, It contains 14.0 to 40.0 volume percent of resin, On the surface of the metal foil for the current collector, The number of peaks with a height of more than 10 μm from the surface of the substrate, as identified by line roughness analysis, is 20.0 to 50.0 peaks / mm.

[0015] The electrode according to the present disclosure is the metal foil for a current collector, and an electrode mixture layer formed on the surface of the metal foil for a current collector, and includes these.

[0016] The battery according to the present disclosure is the electrode and an electrolyte, and includes these.

Advantages of the Invention

[0017] The metal foil for a current collector according to the present disclosure can enhance the adhesion to the electrode mixture layer while maintaining the discharge capacity of the battery. The electrode according to the present disclosure has high adhesion between the metal foil for a current collector and the electrode mixture layer. The battery according to the present disclosure can maintain the discharge capacity of the battery to some extent.

Brief Description of the Drawings

[0018] [Figure 1] FIG. 1 is a diagram showing an example of a microscopic observation image of a metal foil for a current collector in which a composite of Ni particles and resin is formed on the surface of a base material. [Figure 2] FIG. 2 is a diagram showing another example of a microscopic observation image of a metal foil for a current collector in which a composite of Ni particles and resin is formed on the surface of a base material. [Figure 3] FIG. 3 is a diagram showing another example of a microscopic observation image of a metal foil for a current collector in which a composite of Ni particles and resin is formed on the surface of a base material.

Modes for Carrying Out the Invention

[0019] The inventors of the present invention studied means for obtaining a metal foil for a current collector that can enhance the adhesion to the electrode mixture layer while maintaining the discharge capacity of the battery. As a result, the following findings were obtained.

[0020] The inventors initially focused on the surface of metal foil for current collectors. There is a concern that if metal foil with a smooth surface is used, adhesion to the electrode mixture layer may not be achieved. In particular, metal foil manufactured by cold rolling tends to have a very smooth surface. Even in such cases, the inventors considered that roughening the surface of the metal foil could potentially improve adhesion to the electrode mixture layer.

[0021] On the other hand, as mentioned above, the current collector itself does not participate in power storage. In other words, while roughening the surface of the metal foil used for the current collector to form large irregularities on the surface of the metal foil may improve adhesion to the electrode mixture layer, there is a concern that the proportion of the battery volume occupied by the current collector will increase, reducing the battery's discharge capacity. Therefore, the inventors considered forming fine irregularities on the substrate surface of the metal foil using fine metal particles.

[0022] Specifically, the inventors focused on nickel (Ni) particles as fine metal particles. Ni particles have a larger particle size compared to fine carbon particles such as carbon black. Therefore, if Ni particles can be bound together and dispersed and retained on the surface of a metal foil, it may be possible to form large irregularities. Furthermore, when Ni particles are dispersed and retained on the surface of a metal foil, their high corrosion resistance can maintain high electrical conductivity on the surface of the metal foil. Therefore, by using Ni particles, it may be possible to maintain low contact resistance of electrodes.

[0023] Therefore, the inventors investigated the possibility of binding Ni particles with a resin and holding them on the surface of a metal foil substrate. The inventors' investigations revealed that if a composite formed by binding Ni particles with a resin is held on a portion of the surface of the metal foil substrate, large irregularities can be formed on the surface of the metal foil. Hereinafter, in this specification, the composite formed by binding Ni particles with a resin will also be simply referred to as the "composite." The composite held on the surface of the metal foil substrate will be specifically described with reference to the drawings.

[0024] Figures 1 and 2 show examples of microscopic images of a metal foil for current collectors in which a composite of Ni particles and resin is formed on the substrate surface. Figures 1 and 2 were obtained by observing the metal foil for current collectors in which the composite of Ni particles and resin is held on the substrate surface using a scanning electron microscope (SEM) to obtain secondary electron images. In Figures 1 and 2, composites were formed using Ni particles with different average particle sizes.

[0025] Referring to Figures 1 and 2, the white area 10 in the figures represents the area occupied by Ni particles and resin. Referring further to Figures 1 and 2, the black area 20 in the figures represents the area where Ni particles and resin are absent, and the substrate surface is exposed. In other words, when a composite of Ni particles and resin is formed on the substrate surface, it can be confirmed that large irregularities can be formed on the surface of the metal foil for the current collector while leaving a portion of the substrate surface exposed. In this case, it may be possible to form large irregularities on the surface while keeping the volume of the metal foil for the current collector to a certain extent.

[0026] Detailed investigations based on the above findings revealed that in metal foil for current collectors, where composites are formed on the surface of the substrate, the density of composites with a certain height or higher affects the adhesion of the metal foil to the electrode mixture layer. Therefore, in this embodiment, the density of composites formed on the substrate surface of the metal foil for current collectors is defined by line roughness analysis. Specifically, in this embodiment, the number of peaks with a height of 10 μm or more from the substrate surface, as identified by line roughness analysis of the surface of the metal foil for current collectors, is also called the high spot count (HSC). In the metal foil for current collectors according to this embodiment, the "peaks" identified by line roughness analysis substantially correspond to composites. Therefore, in this embodiment, HSC substantially corresponds to the number of composites with a certain height or higher formed on a line segment of 1 mm, assuming such a line segment on the surface of the metal foil for current collectors.

[0027] Here, if the HSCs on the surface of the current collector metal foil are too small, there will be too few irregularities with a certain height formed on the surface of the current collector metal foil. As a result, sufficient adhesion of the current collector metal foil to the electrode mixture layer cannot be obtained. On the other hand, if the HSCs on the surface of the current collector metal foil are too large, the gaps between the composites become narrow, making it difficult for the active material and binder of the electrode mixture layer to penetrate into the gaps between the composites. As a result, sufficient adhesion of the current collector metal foil to the electrode mixture layer cannot be obtained. In this case, there is also a concern that the volume of the composite will become too large, reducing the discharge capacity of the battery. Therefore, in this embodiment, the HSCs on the surface of the current collector metal foil are set to 20.0 to 50.0 pieces / mm.

[0028] Therefore, in this embodiment, the number of HSCs on the surface of the metal foil for the current collector is set to 20.0 to 50.0 particles / mm. Based on the above, further detailed studies by the inventors revealed that the adhesion of the metal foil for the current collector to the electrode mixture layer and the discharge capacity of the battery are influenced not only by HSCs, but also by the size of the Ni particles, the proportion of resin in the composite, and the morphology of the Ni particles.

[0029] First, in this embodiment, the Ni particles have an average particle size of 20 μm or less per single particle (primary particle). If the average particle size of the primary particles is too large, it may be difficult to form a composite between the Ni particles and the resin. Furthermore, if the average particle size of the primary particles is too large, there is a concern that the volume of the composite will become too large, reducing the discharge capacity of the battery. Therefore, in this embodiment, the average particle size of the Ni particles (primary particles) is set to 20 μm or less.

[0030] Furthermore, the resin volume ratio in the composite of Ni particles and resin is 14.0 to 40.0%. If the resin volume ratio is too high, the resin may fill the gaps between multiple Ni particles, causing the surface of the composite to become smooth. In this case, the adhesion of the metal foil for the current collector to the electrode mixture layer decreases. On the other hand, if the resin volume ratio is too low, the composite of Ni particles and resin becomes difficult to retain on the substrate surface. In this case, the adhesion of the metal foil for the current collector to the electrode mixture layer decreases. Therefore, in this embodiment, the resin volume ratio in the composite is set to 14.0 to 40.0%.

[0031] Furthermore, at least a portion of the Ni particles in the composite are sintered. Here, particles formed by the sintering of Ni particles are also called "sintered bodies." Sintered bodies have void regions formed inside them. Therefore, if a composite contains a sintered body, the active material and binder of the electrode mixture layer can enter the void regions inside the sintered body, dramatically increasing the adhesion of the metal foil for the current collector to the electrode mixture layer. The presence of a sintered body in the composite also makes it easier to form a higher composite. As a result, the adhesion of the metal foil for the current collector to the electrode mixture layer is further increased. Therefore, in this embodiment, the composite includes a sintered body formed by the sintering of Ni particles.

[0032] Based on the above findings, the gist of the metal foil for the current collector, electrodes, and battery according to this embodiment is as follows.

[0033] [1] A metal foil for current collectors, Substrate and The substrate comprises a plurality of composites held on the surface of the substrate, Multiple of the aforementioned composites are Ni particles with an average particle size of 20 μm or less, A sintered body formed by sintering multiple Ni particles, It contains 14.0 to 40.0 volume percent of resin, On the surface of the metal foil for the current collector, The number of peaks with a height of more than 10 μm from the surface of the substrate, as identified by line roughness analysis, is 20.0 to 50.0 peaks / mm. Metal foil for current collectors.

[0034] [2] [1] A metal foil for current collector as described above, The average thickness of the substrate is 5 to 30 μm. Metal foil for current collectors.

[0035] [3] [1] or [2] describes a metal foil for current collectors, The current collector comprises an electrode mixture layer formed on the surface of the metal foil for the current collector, electrode.

[0036] [4] [3] The electrode described above, Electrolytes, battery.

[0037] The following describes the metal foil for the current collector, the electrodes, and the battery according to this embodiment.

[0038] [Metal foil for current collectors] The metal foil for current collector according to this embodiment comprises a base material and a plurality of composites held on the surface of the base material.

[0039] [Base material] In this embodiment, the substrate is a metal foil. In this specification, "metal foil" means a metal plate with a thickness of 50 μm or less. In short, the thickness of the substrate for the metal foil current collector according to this embodiment is 50 μm or less. The thinner the substrate, the lower the volume of the metal foil current collector including the substrate. As a result, the volume of the current collector relative to the battery volume can be suppressed, and the discharge capacity of the battery can be increased. However, if the substrate is too thin, it becomes difficult to manufacture the substrate and the metal foil current collector using that substrate. In this specification, the thickness of the substrate means the average thickness of the substrate.

[0040] The base material is not particularly limited as long as it is a metal foil, and any well-known metal foil can be used. The metal foil may be, for example, a metal foil made of a single metal, a metal foil made of an alloy, or a metal foil having a plating layer on its surface. If the base material is a metal foil made of a single metal, the single metal may be, for example, copper, aluminum, iron, nickel, zinc, silver, gold, manganese, and platinum. If the base material is a metal foil made of an alloy, the alloy may be, for example, an iron-based alloy (steel), a nickel-based alloy (Ni-based alloy), or a copper-based alloy.

[0041] More specifically, when the base material is an iron-based alloy foil (steel foil), the base material may be carbon steel foil or stainless steel foil. When the base material is stainless steel foil, the type of stainless steel is not particularly limited; for example, it may be ferritic stainless steel foil, martensitic stainless steel foil, austenitic stainless steel foil, ferritic-martensitic duplex stainless steel foil, or ferritic-austenitic duplex stainless steel foil.

[0042] In the case of a metal foil having a plating layer on its surface, a well-known plating layer can be used. In this case, the plating layer may be made of a single metal or an alloy. If it is made of a single metal, the plating layer may be, for example, a nickel plating layer, a copper plating layer, or a zinc plating layer. The plating layer may further be a single-layer plating or a multi-layer plating.

[0043] More preferably, the substrate is a steel foil having a nickel plating layer (Ni-plated steel foil) or stainless steel foil. When the substrate is Ni-plated steel foil or stainless steel foil, the substrate has excellent strength, heat resistance, and corrosion resistance. In this case, the Ni particles contained in the composite described later have excellent corrosion resistance, making it difficult for an oxide film to form. Therefore, in electrodes made using metal foil for current collectors in which the composite is formed, the Ni particles become electrical contact points, and the electrical resistance of the electrodes can be reduced. In other words, when the substrate is Ni-plated steel foil or stainless steel foil, the performance as a battery is further enhanced by the synergistic effect with the Ni particles.

[0044] In this embodiment, the preferred upper limit of the substrate thickness is 45 μm, more preferably 40 μm, more preferably 35 μm, and still more preferably 30 μm. In this embodiment, the preferred lower limit of the substrate thickness is 1 μm, more preferably 3 μm, and still more preferably 5 μm. In short, in this embodiment, the substrate thickness is preferably 5 to 30 μm. In this case, the substrate can be manufactured stably, and the discharge capacity of a battery using electrodes manufactured using the substrate is further increased.

[0045] [complex] In this embodiment, the metal foil for current collectors has multiple composites held on the surface of the substrate. Each composite includes Ni particles (primary particles) with an average particle size of 20 μm or less, a sintered body formed by sintering the Ni particles, and a resin. In other words, in this embodiment, it is sufficient that the multiple composites formed on the surface of the substrate as a whole contain Ni particles, a sintered body, and a resin; it is not necessary for all composites to contain Ni particles, a sintered body, and a resin.

[0046] Specifically, in this embodiment, the composites are classified into the following three types. (Composite A) A composite comprising Ni particles, a sintered body, and a resin; (Composite B) A composite comprising a sintered body and a resin, but without Ni particles; (Composite C) A composite containing Ni particles and resin, but without a sintered body.

[0047] Here, composites A and B form large irregularities on the surface of the substrate, greatly improving the adhesion of the metal foil for the current collector to the electrode mixture layer. Therefore, in this embodiment, the density of composites A and B is simulated using a high spot count (HSC), which will be described later. On the other hand, composite C forms small irregularities on the surface of the substrate, and therefore does not contribute much to the adhesion of the metal foil for the current collector to the electrode mixture layer. However, the multiple composites held on the surface of the substrate of the metal foil for the current collector according to this embodiment may also include composites that do not contain a sintered body (composite C).

[0048] Furthermore, the composite according to this embodiment includes a resin. Therefore, Ni particles and / or sintered bodies can be bound to it. The resin further binds the composite to the surface of the substrate, and holds the composite on the surface of the substrate. As a result, even if a certain amount of stress is applied when manufacturing the electrode, the shape of the composite is maintained and the adhesion to the electrode mixture layer is maintained.

[0049] [Ni particles] In this embodiment, Ni particles refer to primary particles among particles whose main component is Ni. That is, the chemical composition constituting the Ni particles may be a chemical composition consisting of Ni and impurities, or a chemical composition consisting of a Ni-based alloy. In this specification, "primary particle" refers to a single, unsintered particle. In this specification, the average particle size of the Ni particles is 20 μm or less. In addition, commercially available, well-known Ni particles can be used.

[0050] Ni particles have a larger particle size compared to carbon particles, such as those coated on substrates like carbon black. Therefore, the composite according to this embodiment can form large irregularities on the surface of the substrate, improving the adhesion of the metal foil for the current collector to the electrode mixture layer. On the other hand, if the average particle size of the Ni particles is too large, it may be difficult to form a composite between the Ni particles and the resin. Furthermore, if the average particle size of the Ni particles is too large, there is a concern that the volume of the composite will become too large, reducing the discharge capacity of the battery. Therefore, in this embodiment, the average particle size of the Ni particles (primary particles) is set to 20 μm or less.

[0051] The lower limit of the average particle size of Ni particles is not particularly limited. For example, the lower limit of the average particle size of Ni particles may be 0.1 μm, 0.5 μm, or 1 μm. A preferred lower limit for the average particle size of Ni particles is 2 μm. If the average particle size of Ni particles is 2 μm or more, the void region in the composite containing Ni particles increases, further increasing the discharge capacity. Therefore, the average particle size of Ni particles is preferably 2 to 20 μm. A more preferred lower limit for the average particle size of Ni particles is 3 μm, and even more preferably 5 μm. A preferred upper limit for the average particle size of Ni particles is 15 μm, and even more preferably 10 μm. The method for determining the average particle size of Ni particles will be described later.

[0052] [Sintered body] In this embodiment, the term "sintered body" refers to a mass formed by the sintering of Ni particles (primary particles). The Ni particles in the sintered body are bonded together more strongly than by aggregation. As a result, void regions are formed within the sintered body of the composite. Consequently, the active material of the electrode mixture layer and part of the binder enter these void regions, dramatically increasing the adhesion of the metal foil for the current collector to the electrode mixture layer. If the composite includes a sintered body, the composite becomes even more easily formed. As a result, the adhesion of the metal foil for the current collector to the electrode mixture layer is further increased.

[0053] The more sintered body is included in the composite, the higher the proportion of void regions in the composite. In this case, the surface irregularities of the metal foil for the current collector formed by the composite become larger, and the volume occupied by the metal foil for the current collector becomes smaller. As a result, the adhesion of the metal foil for the current collector to the electrode mixture layer is high, and the discharge capacity of the battery is less likely to decrease. Therefore, it is preferable for the composite to contain a large amount of sintered body. However, in this embodiment, it is not necessary for all of the multiple composites to contain sintered body. In the metal foil for the current collector according to this embodiment, the effects shown in this embodiment can be obtained if at least some of the multiple composites formed on the substrate surface contain sintered body. A method for identifying whether a composite contains sintered body will be described later.

[0054] In this embodiment, the measurement of the average particle size of Ni particles and the confirmation of whether or not a sintered body is present can be carried out by the following method. Specifically, a test specimen for SEM observation is prepared from the metal foil for current collector according to this embodiment. The test specimen is prepared by CP (Cross-Section Polisher: trademark) processing using an Ar ion beam. Specifically, first, the metal foil for current collector according to this embodiment is fixed to a Si wafer using an adhesive. CP processing is performed on the Si wafer with the metal foil for current collector fixed to it using a CP cross-section sample preparation device. Through the above steps, a test specimen is prepared with the cross-section of the metal foil for current collector as the observation surface.

[0055] The observation surface of the prepared test specimen is observed using a scanning electron microscope (SEM) to obtain 10 fields of view as secondary electron images. The field of view area is, for example, 0.02 mm². 2 (Magnification 1000x). In each field of view, Ni particles can be identified from the contrast. In this case, if multiple Ni particles are not only arranged adjacent to each other, but also if a void region is formed by multiple Ni particles, it can be determined that the multiple Ni particles have been sintered.

[0056] This point will be explained in more detail using drawings. Figure 3 shows another example of a microscopic image of a metal foil for a current collector in which a composite of Ni particles and resin is formed on the substrate surface. Figure 3 is a backscattered electron image obtained by observing the cross-section of the metal foil for a current collector according to this embodiment, which was cut in the thickness direction by CP processing. Note that Figure 3 is an image obtained by observation at a magnification of 3000x. Referring to Figure 3, the lower region 50 in the figure is the substrate (metal foil) of the metal foil for the current collector. Referring further to Figure 3, the white region 30 in the figure corresponds to the cross-section of the Ni particles.

[0057] Referring to Figure 3, it can be seen that the cross-sections 30 of the Ni particles in the figure have both circular and complex contours. Specifically, the cross-section 30 of the Ni particles near the center of Figure 3 can be seen to be formed by the integration of at least three or more Ni particles. In this way, when the cross-section confirms that the Ni particles are integrated rather than simply having their outer surfaces in contact, it can be determined that the multiple Ni particles have been sintered.

[0058] Furthermore, the primary particle size of Ni particles can be determined as follows: As described above, identify 100 or more arbitrary Ni particles in 10 fields of view. Determine the particle size of the identified Ni particles from image analysis. Define the arithmetic mean of the determined Ni particle sizes as the average particle size (μm) of the Ni particles. Note that the average particle size of the Ni particles is used after rounding the obtained value to the first decimal place.

[0059] Furthermore, the measurement of the average particle size of Ni particles and the confirmation of the presence or absence of sintered bodies can also be carried out by the following method. Specifically, measuring the average particle size of Ni particles and confirming the presence of sintered bodies in the composition used when manufacturing metal foil for current collectors can be carried out more simply than the method described above. Specifically, the particle size distribution of Ni particles in the composition is measured using a laser diffraction particle size analyzer (Microtrac FRA, manufactured by Microtrac-Bell Co., Ltd.).

[0060] If the Ni particles include not only primary particles but also sintered bodies, the histogram of particle size and frequency will show two peaks. In other words, in this case, the particle size distribution is bimodal. Assuming that each of the two peaks follows a normal distribution, the histogram is separated into a peak for small particle size and a peak for large particle size. The particle size (μm) that shows the mode of the small particle size peak identified in this way is defined as the average particle size (μm) of Ni particles (primary particles). Even in this case, the average particle size of Ni particles is used after rounding the obtained value to the first decimal place.

[0061] Furthermore, as mentioned above, if the Ni particles include not only primary particles but also sintered bodies, the particle size distribution will be bimodal. Therefore, in this embodiment, if the particle size distribution is bimodal and the frequency of peaks with larger particle sizes is greater than 1 / 5 of the frequency of peaks with smaller particle sizes, it can be determined that the particles also contain sintered bodies.

[0062] In the metal foil for current collectors according to this embodiment, the average particle size of Ni particles may be determined using any of the methods described above. Regardless of the method used, the average particle size of Ni particles will be approximately the same. Similarly, in the metal foil for current collectors according to this embodiment, the presence or absence of a sintered body may be confirmed using any of the methods described above. Regardless of the method used, the presence or absence of a sintered body can be confirmed in the same manner.

[0063] [resin] In this embodiment, the resin binds Ni particles and a sintered body to form a composite. In this embodiment, the resin is not particularly limited, and any well-known resin can be used. The resin may be, for example, an aqueous resin or an organic solvent resin. Examples of aqueous resins include polyvinyl alcohol (PVA), carboxymethylcellulose (CMC), polyacrylic acid (PAA), and styrene-butadiene rubber (SBR). Examples of organic solvent resins include polymethyl methacrylate (PMMA), polytetrafluoroethylene (PTFE), polyimide (PI), polyamide (PA), and polyvinylidene fluoride (PVdF).

[0064] Preferably, the resin used in the composite of metal foil for current collectors according to this embodiment is an aqueous resin. Aqueous resins have a low environmental impact during manufacturing. For this reason, aqueous resins have been widely used as a binder for the electrode composite layer of the electrode described later. Even more preferably, the resin used in the composite of metal foil for current collectors according to this embodiment is styrene-butadiene rubber (SBR).

[0065] In this embodiment, the volume percentage of resin is 14.0 to 40.0%. If the volume percentage of resin is too high, the resin may fill the gaps between multiple Ni particles, causing the surface of the composite to become smooth. In this case, the adhesion of the metal foil for the current collector to the electrode mixture layer decreases. On the other hand, if the volume percentage of resin is too low, the composite of Ni particles and resin becomes difficult to retain on the substrate surface. In this case, the adhesion of the metal foil for the current collector to the electrode mixture layer decreases. Therefore, in this embodiment, the volume percentage of resin in the composite is 14.0 to 40.0%.

[0066] The preferred lower limit of the resin volume percentage is 16.0%, more preferably 18.0%, and even more preferably 20.0%. The preferred upper limit of the resin volume percentage is 38.0%, more preferably 36.0%, and even more preferably 35.0%.

[0067] In this embodiment, the volume ratio of the resin can be determined by the following method. Specifically, elemental analysis is performed on a test piece used for SEM observation to measure the average particle size of the Ni particles as described above, using an electron probe microanalyzer (EPMA). Preferably, a field emission electron probe microanalyzer (FE-EPMA) is used as the EPMA. In elemental analysis using EPMA, a wavelength dispersive X-ray spectrometer (WDX) is used as the characteristic X-ray source.

[0068] More specifically, similar to the measurement of the average particle size of Ni particles described above, 10 fields of view are observed using a scanning electron microscope (SEM) to obtain secondary electron images. The field of view area is, for example, 0.02 mm². 2 (Magnification 1000x). Elemental analysis is performed using EPMA in each measurement field of view to generate an elemental map. In the EPMA elemental analysis using WDX, the target elements are Ni, Fe, C, and O. The region where C is detected as a result of the elemental analysis is defined as the region occupied by resin. The area fraction of the region occupied by resin is determined in the observation field of view. In this embodiment, since Ni particles and resin are present randomly, the difference between the area fraction and the volume fraction is small. Therefore, in this embodiment, the area fraction occupied by resin is defined as the volume fraction (%) of resin. The volume fraction of resin is rounded to the second decimal place of the obtained value.

[0069] Furthermore, the volume percentage of resin can also be determined by the following method. Specifically, the volume percentage of resin can be determined from the mixed weight ratio of the composition used when manufacturing metal foil for current collectors. For example, the specific gravities are 0.97 for styrene-butadiene rubber (SBR), 1.6 for carboxymethylcellulose (CMC), and 1.78 for polyvinylidene fluoride (PVdF). In addition, the volume percentage of resin can be determined using the specific gravity of Ni particles. For example, the specific gravity of Ni particles is 8.9. This method yields almost the same value as the method using SEM to determine the volume percentage of resin described above.

[0070] [High Spot Count (HSC)] The metal foil for current collectors according to this embodiment has a high spot count (HSC) of 20.0 to 50.0 spots / mm, which is the number of peaks (HSCs) with a height exceeding 10 μm from the substrate surface, as determined by line roughness analysis of its surface. As described above, the "peaks" determined by line roughness analysis are substantially equivalent to composites. Therefore, in this embodiment, the HSC is substantially equivalent to the number of composites with a certain height or greater formed on a line segment of 1 mm, assuming such a segment on the surface of the metal foil for current collectors.

[0071] If the HSCs on the surface of the current collector metal foil are too small, there will be too few irregularities of a certain height formed on the surface of the current collector metal foil. As a result, sufficient adhesion of the current collector metal foil to the electrode mixture layer cannot be obtained. On the other hand, if the HSCs on the surface of the current collector metal foil are too large, the gaps between the composites become narrow, making it difficult for the active material and binder of the electrode mixture layer to penetrate into the gaps between the composites. As a result, sufficient adhesion of the current collector metal foil to the electrode mixture layer cannot be obtained. In this case, there is also a concern that the volume of the composite will become too large, reducing the discharge capacity of the battery. Therefore, in this embodiment, the HSCs on the surface of the current collector metal foil are set to 20.0 to 50.0 pieces / mm.

[0072] In this embodiment, the preferred lower limit of HSC on the surface of the metal foil for the current collector is 21.0 particles / mm, more preferably 25.0 particles / mm, and even more preferably 30.0 particles / mm. The preferred upper limit of HSC on the surface of the metal foil for the current collector is 48.0 particles / mm, more preferably 46.0 particles / mm, and even more preferably 42.0 particles / mm.

[0073] In this embodiment, the HSC of the metal foil surface for the current collector can be determined by the following method. Specifically, a line roughness analysis is performed on the surface of the metal foil for the current collector according to this embodiment to obtain a roughness curve. The cross-sectional curve for obtaining the roughness curve is determined using a method compliant with JIS B 0601 (2013). More specifically, a line roughness measurement is performed on the surface of the metal foil for the current collector according to this embodiment using a shape measuring laser microscope. The shape measuring laser microscope is not particularly limited, but for example, the VK-X100 shape measuring laser microscope manufactured by Keyence Corporation can be used. The magnification for line roughness measurement is set to 2000x. The evaluation length is not particularly limited, but for example, it is set to 100 to 150 μm.

[0074] From the results of the line roughness measurement, a cross-sectional curve is obtained in accordance with JIS B 0601 (2013). A low-pass filter with a reference length of 2.5 μm is applied to the obtained cross-sectional curve to obtain a roughness curve. Depending on the average particle size of the Ni particles, it may not be possible to determine the height position of the substrate surface in the roughness curve. In this case, a portion of the surface of the metal foil for the current collector may be peeled off and defined as the height position of the substrate surface. In this case, it is preferable to perform line roughness analysis in multiple regions so that the total evaluation length in the unpeeled region is 100 μm or more.

[0075] When the base material (metal foil) is manufactured by rolling, preferably, the direction in which the wire roughness measurement is performed is perpendicular to the rolling direction of the base material. That is, if the length direction of the base material and the rolling direction are parallel, it is preferable to perform the wire roughness measurement along the width direction of the base material. The rolling direction of the base material is determined by microscopic observation of the surface of the metal foil for the current collector. However, even a person skilled in the art may not be able to determine the rolling direction of the base material by microscopic observation of the surface of the metal foil for the current collector. In this case, the direction in which the wire roughness measurement is performed does not have to be perpendicular to the rolling direction.

[0076] For the obtained roughness curve, a line is drawn 10 μm above the substrate surface (in the direction from the current collector metal foil towards the space, and in the height direction from the substrate surface) to serve as the reference line. The portion above the reference line is defined as a "peak," and the number of peaks is counted. The number of peaks is divided by the evaluation length and defined as the High Spot Count (HSC) (points / mm). The High Spot Count (HSC) is used after rounding the obtained value to two decimal places.

[0077] [electrode] The electrode according to this embodiment comprises the current collector metal foil described above and an electrode mixture layer formed on the surface of the current collector metal foil. The electrode according to this embodiment may be a positive electrode or a negative electrode. In other words, it is not particularly limited as long as it comprises the current collector metal foil described above and an electrode mixture layer.

[0078] [Electrode mixture layer] In this embodiment, the electrode mixture layer is not particularly limited and may have a well-known configuration. The electrode mixture layer contains an active material. The electrode mixture layer may further contain a binder and may contain compositions other than the active material and binder. In this case, for example, the electrode mixture layer contains a conductive additive. The conductive additive helps to improve the conductivity of electrons. In this embodiment, the binder is not particularly limited and any well-known binder can be used. The binder used in the electrode mixture layer is preferably of the same type as the resin used in the composite described above.

[0079] [Active material] In this embodiment, the active material is not particularly limited, and any well-known active material can be used. The active material is a powder particle that does not dissolve in the electrolyte, which will be described later. When the electrode is the negative electrode, the negative electrode active material may be a carbon-based material such as graphite, an alloy material such as CuSn alloy or NiTiSi alloy, or a Si-based material such as SiO. When the electrode is the positive electrode, the positive electrode active material may be lithium cobalt oxide, a ternary material, lithium manganese oxide, or lithium iron phosphate. In other words, both the positive electrode active material and the negative electrode active material may have well-known configurations and are not particularly limited.

[0080] The electrode according to this embodiment comprises the current collector metal foil described above and a well-known electrode mixture layer formed on the surface of the current collector metal foil. As a result, the electrode according to this embodiment can maintain the discharge capacity of the battery and has high adhesion between the current collector metal foil and the electrode mixture layer.

[0081] [battery] The battery according to this embodiment comprises the electrodes and electrolyte described above. If the battery according to this embodiment is a liquid-type secondary battery, it comprises a separator in addition to the electrodes and electrolyte. As long as the battery according to this embodiment includes electrodes containing the metal foil for current collector described above, the other components may be well-known configurations and are not particularly limited. The shape of the battery according to this embodiment is not particularly limited and may be cylindrical, rectangular, coin-shaped, or sheet-shaped. Furthermore, the battery according to this embodiment may be a secondary battery or a primary battery. If the battery according to this embodiment is a secondary battery, for example, it may be a non-aqueous electrolyte secondary battery, an aqueous electrolyte secondary battery, or an all-solid-state secondary battery.

[0082] [Electrolyte] In liquid-based batteries, the electrolyte exchanges ions with the positive and negative electrodes through the electrolyte solution. In solid-state batteries, the electrolyte directly exchanges ions with the positive and negative electrodes. In this embodiment, the electrolyte is not particularly limited, and well-known electrolytes can be used.

[0083] The battery according to this embodiment comprises the electrodes described above and a well-known electrolyte. As a result, the battery according to this embodiment can maintain its discharge capacity and has high adhesion between the metal foil for the current collector and the electrode mixture layer.

[0084] [Adhesion] The metal foil for the current collector according to this embodiment exhibits high adhesion to the electrode mixture layer. In this embodiment, the adhesion of the metal foil for the current collector to the electrode mixture layer is evaluated by the following method.

[0085] A test specimen is prepared from the metal foil for current collector according to this embodiment. Specifically, the electrode mixture layer composition is applied to the metal foil for current collector, dried, and then the test specimen is cut out. The size of the metal foil for current collector is, for example, 210 mm in length and 150 mm in width. The electrode mixture layer composition is not particularly limited, but for example, NiTiSi alloy powder, styrene-butadiene rubber (SBR), and carboxymethylcellulose (CMC) are mixed and kneaded in a ratio of 95:4:1. In this case, water is used as the solvent. The electrode mixture layer composition is applied to the test specimen using an applicator with a coating width of 80 mm and a gap of 150 μm.

[0086] The coated composition is heated at 75°C for 20 minutes to dry. A test specimen is cut from the electrode after drying. The size of the test specimen shall be 15 mm in width and 50 mm or longer. At this time, it is preferable to cut the test specimen so that the length of the test specimen (50 mm or longer) includes 30 mm or more of the coated portion and 5 mm or more of the uncoated portion. Furthermore, it is preferable that the length direction of the test specimen is parallel to the rolling direction of the substrate. A test specimen with an electrode mixture layer formed thereon is prepared by the above method. A 90° peel test described in JIS Z 0237 (2009) is performed on the test specimen. If excellent peel strength is obtained as a result of the 90° peel test, it is judged that the adhesion of the metal foil for the current collector to the electrode mixture layer is excellent.

[0087] [Discharge capacity] The metal foil for the current collector according to this embodiment can maintain its discharge capacity even when its adhesion to the electrode mixture layer is increased. In this embodiment, the discharge capacity is evaluated by the following method.

[0088] Specifically, when a composite is formed on a metal foil of the same thickness (for example, 50 μm), the higher the volume fraction occupied by the composite, the lower the discharge capacity when a battery is formed. Therefore, the volume fraction occupied by the composite is calculated, and it is determined that the discharge capacity has decreased by that volume. The volume fraction occupied by the composite can be determined from the coating weight of the composition, the specific gravity of the composition's components (Ni particles, sintered body, and resin), and their mixing ratio. If the volume fraction occupied by the composite is small, it is determined that the discharge capacity can be maintained when the metal foil used as a current collector is used as a battery.

[0089] [Manufacturing method for metal foil for current collectors] An example of a method for manufacturing metal foil for current collectors according to this embodiment will be described. The manufacturing method described below is an example for manufacturing metal foil for current collectors according to this embodiment, and the manufacturing method for metal foil for current collectors according to this embodiment may be a method other than the one described below. However, the manufacturing method described below is a preferred example of a method for manufacturing metal foil for current collectors according to this embodiment. The manufacturing method for metal foil for current collectors according to this embodiment comprises a substrate preparation step, a composition preparation step, and a composite formation step.

[0090] [Base material preparation process] In the base material preparation process, the base material for the metal foil used in the current collector is prepared. The method for preparing the base material is not particularly limited and any well-known method may be used. For example, the base material may be prepared by preparing an intermediate steel material having a desired chemical composition and then cold-working the intermediate steel material to prepare the base material. This case will be explained in detail below.

[0091] The intermediate steel material having the desired chemical composition can be appropriately determined according to the mechanical properties of the base material to be obtained. Here, intermediate steel material refers to a steel sheet with a thickness of several hundred micrometers to several millimeters. The intermediate steel material may be a stainless steel sheet or a plated steel sheet.

[0092] When preparing a base material by cold working an intermediate steel material, the preferred cold working method is cold rolling. Cold rolling can be carried out using well-known equipment. For example, multiple reversible cold rolling mills may be used. In this case, the degree of processing in cold rolling is not particularly limited. The degree of processing can be set appropriately according to the thickness of the base material to be obtained. Furthermore, the base material may be subjected to appropriate heat treatment after cold rolling.

[0093] As described above, the substrate preparation step involves preparing the substrate. The substrate may be manufactured by the preferred process described above, or it may be a substrate manufactured by a third party, or a substrate manufactured at a factory or business other than the factory where the composition preparation step described later is carried out. In short, the substrate preparation step in this embodiment is not particularly limited and can be carried out by any well-known method.

[0094] As mentioned above, the substrate may have a plating layer on its surface. When forming a plating layer on the surface of the substrate, it is preferable to form the plating layer on the surface of the intermediate steel material and then perform cold rolling. In this case, a thin plating layer can be formed on the surface of the substrate. Preferably, a Ni plating layer is formed on the surface of the intermediate steel material. In this case, for example, an intermediate steel material (thickness several hundred μm) having a Ni plating layer is cold-rolled to obtain a substrate with a thickness of 50 μm or less. The method for forming the Ni plating layer is not particularly limited and any well-known method may be used.

[0095] [Composition preparation process] In the composition preparation step, a composition for forming and retaining a composite on the surface of the substrate is prepared. The Ni particles, sintered body, and resin that make up the composition can be purchased commercially as appropriate.

[0096] Furthermore, Ni particles may be heated at high temperatures during the manufacturing process. Therefore, commercially available Ni particles may contain a portion that has been sintered. In other words, when purchasing known Ni particles, it is possible that the Ni particles (primary particles) and sintered bodies are mixed together. In this case, the composite formed by the method described later may also include sintered bodies. On the other hand, if a certain level of stress is applied to a mixture of sintered bodies and Ni particles, the sintered bodies will disintegrate. Therefore, in the composition preparation step according to this embodiment, it is preferable to purchase Ni particles containing sintered bodies from a third party. In this case, it is also preferable to consider the stress applied to the composition when mixing the compositions so as not to disintegrate the sintered bodies.

[0097] The prepared Ni particles, sintered body, and resin are mixed with a solvent as needed. Specifically, it is preferable to mix them using a planetary rotation / revolution mixer. In this case, a solvent is also used to appropriately control the viscosity. The solvent may be water, or an organic solvent such as N-methyl-2-pyrrolidone (NMP).

[0098] [Complex formation process] In the composite formation step, the prepared composition is used to form and retain the composite on the surface of the substrate. Specifically, the mixed composition is applied to the surface of the substrate. The application method is not particularly limited, but for example, a doctor blade method with gaps, a spray application method, or a gravure coating method may be used.

[0099] The substrate coated with the composition is dried to form a composite on the surface of the substrate. The drying method is not particularly limited and any well-known method may be used. For example, it may be dried by heating at 75°C for 20 minutes. For example, it may also be dried without further heating. The composite composition according to this embodiment contains a solvent. Therefore, even if the resin containing the solvent enters the void regions inside the sintered body, these void regions will reappear after drying. It is presumed that such void regions are obtained because the bonding force of sintering is stronger than that of aggregation, etc.

[0100] By following the steps described above, a metal foil for current collectors according to this embodiment can be manufactured. As stated above, the manufacturing process described above is a preferred example for manufacturing a metal foil for current collectors according to this embodiment, and the method for manufacturing a metal foil for current collectors according to this embodiment is not limited to the method described above.

[0101] [Method for manufacturing electrodes] An example of an electrode manufacturing method using metal foil for current collectors according to this embodiment is as follows. The electrode manufacturing method according to this embodiment comprises an electrode mixture preparation step and an electrode mixture layer formation step.

[0102] [Electrode mixture preparation process] In the electrode mixture preparation step, a composition for forming the electrode mixture layer is prepared. The composition for forming the electrode mixture layer should be prepared according to the electrode mixture layer to be obtained. For example, it may be prepared by kneading an active material and a binder. For example, it may be prepared by further kneading an active material, a binder, and a conductive additive. For example, it may be prepared by further kneading an active material, a binder, and a solvent. For example, it may be prepared by further kneading an active material, a binder, a conductive additive, and a solvent. The kneading method should be adjusted as appropriate depending on the active material, binder, conductive additive, and solvent. In other words, the electrode mixture preparation step can be carried out by a well-known method.

[0103] [Electrode mixture layer formation process] In the electrode mixture layer formation step, an electrode mixture layer is formed on the surface of the metal foil for the current collector described above. Specifically, a composition for forming a kneaded electrode mixture layer is applied to the metal foil for the current collector described above. The application method is not particularly limited and any well-known method may be used. For example, it may be applied to the metal foil for the current collector using an applicator with a gap. For example, it may also be applied to the metal foil for the current collector by spraying it using a sprayer.

[0104] Furthermore, the composition coated on the metal foil for the current collector is dried to form an electrode mixture layer. The drying method is not particularly limited and any well-known method may be used. For example, it may be dried by heating at 75°C for 20 minutes. For example, it may also be dried without further heating.

[0105] By following the steps described above, an electrode according to this embodiment can be manufactured. As stated above, the manufacturing process described above is a preferred example for manufacturing an electrode according to this embodiment, and the method for manufacturing an electrode according to this embodiment is not limited to the method described above.

[0106] [Battery manufacturing method] The method for manufacturing the battery according to this embodiment is not particularly limited. The battery according to this embodiment is manufactured by a known method, in which a laminate is formed by stacking the above-mentioned electrodes and a counter electrode. The laminate is then placed in a case to manufacture the battery. [Examples]

[0107] The base materials for each test number shown in Table 1 were prepared. The size of the base material for each test number was a rectangle with a length of 210 mm and a width of 150 mm, so that the longitudinal direction was parallel to the rolling direction. "Ni-plated steel foil" in the "Base Material" column of Table 1 refers to Ni-plated steel foil with a thickness of 10 μm. The Ni-plated steel foil was prepared by cold rolling a Ni-plated steel sheet with a thickness of 200 μm. The base material of the Ni-plated steel foil was extremely low carbon steel. "Stainless steel foil 1" in the "Base Material" column of Table 1 refers to ferritic stainless steel foil with a thickness of 10 μm, equivalent to SUS430 as specified in JIS G 4305 (2012). "Stainless steel foil 2" in the "Base Material" column of Table 1 refers to ferritic stainless steel foil with a thickness of 10 μm, equivalent to SUS444 as specified in JIS G 4305 (2012).

[0108] [Table 1]

[0109] For each test number, a composition was prepared to form a composite on the surface of the substrate. Specifically, the composition was prepared using the particles and resin listed in Table 1. Note that no composite was formed in test number 1. In the "Particles" column of Table 1, "Ni-A" refers to Ni particles having a chemical composition consisting of Ni and impurities, with an average primary particle size of 8 μm. These Ni particles were manufactured by Niraco Co., Ltd., product number: NI-314010. In the "Particles" column of Table 1, "Ni-B" refers to Ni particles having a chemical composition consisting of Ni and impurities, with an average primary particle size of 5 μm. These Ni particles were manufactured by VALE INCO, product number: C-255.

[0110] In Table 1, "Ni-C" in the "Particles" column refers to the same Ni particles as "Ni-B," but these particles were obtained by crushing a sintered body through rigorous prior mixing. Specifically, 10g of "Ni-B" particles and 8.5g of water were mixed and processed for 2 minutes at a rotational speed of 30m / sec using a rotational-orbital mixing machine (model number ARE250, manufactured by Thinky Co., Ltd.) to crush the particles.

[0111] In Table 1, "Ni-D" in the "Particles" column refers to Ni particles having a chemical composition consisting of Ni and impurities, with an average primary particle size of 53 μm or less. These Ni particles were manufactured by Kojun Chemical Laboratory Co., Ltd., product code: NIE18PB. In Table 1, "C" in the "Particles" column refers to the use of carbon particles instead of Ni particles. These carbon particles had an average particle size of 1 μm. In Table 1, "Ni-E" in the "Particles" column refers to Ni particles having a chemical composition consisting of Ni and impurities, with an average primary particle size of 0.4 μm. These Ni particles were ultrafine nickel powder (particle size 400 nm) manufactured by Toho Titanium Co., Ltd.

[0112] In Table 1, "SBR" in the "Resin" column refers to styrene-butadiene rubber. SBR used was JSR Corporation, product code: TRD2001. "CMC" in the "Resin" column refers to carboxymethylcellulose. CMC used was Daicel Corporation, product code: 2110. "PVdF" in the "Resin" column refers to polyvinylidene fluoride. PVdF used was Kureha Corporation, product code: KFP9100.

[0113] For test numbers 2 to 18, compositions mixed in the weight ratios listed in Table 1 were mixed using a rotary-orbiting kneader. Since SBR and CMC are aqueous resins, water was used as the solvent. Since PVdF is an organic solvent-based resin, N-methyl-2-pyrrolidone (NMP) was used as the solvent.

[0114] For test numbers 2 to 18, the prepared compositions were applied to the surface of the substrates. The application was carried out using an automatic coating machine (manufactured by Imoto Seisakusho Co., Ltd., model number: IMC-70F0). The substrates were fixed to the stage of the automatic coating machine by vacuum suction, and the compositions were applied using an applicator. At this time, the application amount was controlled by adjusting the gap between the applicators to 25 to 50 μm, and the application speed was set to 20 mm / second. The amount of composition applied to the surface of the substrate was adjusted by changing the gap between the applicators.

[0115] Tests 2 through 18 were dried by holding them in a dryer set to 75°C for 20 minutes. The metal foil for current collectors was manufactured using the above method.

[0116] For each metal foil current collector manufactured as described above, the following tests were performed: calculation of the amount of composition applied, confirmation of the presence or absence of a sintered composite, calculation of the volume ratio of resin in the composite, HSC measurement, adhesion test, and discharge capacity evaluation. Note that for test number 1, no composite was formed, so only the adhesion test and discharge capacity evaluation were performed. For test number 16, the Ni particles were too large, and during composition application, the Ni particles were dragged by the applicator, preventing the formation of a composite. Therefore, the above tests were not performed.

[0117] [Calculation of the amount of composition to be applied] For each test number except test numbers 1 and 16, the amount of composition applied was calculated. Specifically, a portion of the metal foil for the current collector of each test number except test numbers 1 and 16 was punched out with a 13 mm diameter punch. For each test number except test numbers 1 and 16, the amount of application (mg / cm²) was calculated from the weight difference compared to test number 1 and the punched area. 2The amount of coating obtained was calculated. The obtained coating amounts are shown in Table 1.

[0118] [Confirmation of the presence or absence of a sintered composite body] For the metal foil current collectors of each test number except for test numbers 1 and 16, it was confirmed whether or not a sintered body was included in the composite. In this example, as a simple method, the presence or absence of a sintered body in the composition was confirmed using a laser diffraction particle size analyzer. If the particle size distribution obtained by the laser diffraction particle size analyzer was bimodal, and the frequency of peaks with large particle sizes was greater than 1 / 5 of the frequency of peaks with small particle sizes, it was determined that the particles also contained a sintered body (indicated as "A (Acceptable)" in Table 2). Otherwise, it was determined that the particles did not contain a sintered body (indicated as "NA (Not Acceptable)" in Table 2). The results of the determination are shown in Table 2.

[0119] [Table 2]

[0120] [Calculation of the volume percentage of resin in the composite] For the metal foil current collectors of each test number, excluding test numbers 1 and 16, the volume percentage of the resin in the composite was calculated. In this example, as a simple method, the volume percentage of the resin was calculated using the weight ratio of the resins in the composition and their specific gravity. The specific gravities used were 0.97 for SBR, 1.6 for CMC, 1.78 for PVdF, 8.9 for Ni particles, and 1.8 for carbon particles. The obtained volume percentages of the resins are shown in Table 2.

[0121] [HSC measurement] For the metal foil current collectors of each test number except test numbers 1 and 16, the HSC (pieces / mm) was measured using the method described above. Line roughness measurement was performed using a shape measuring laser microscope VK-X100 manufactured by Keyence Corporation. Line roughness measurement was performed at three arbitrary locations perpendicular to the longitudinal direction (rolling direction) of the metal foil current collector. The HSC was calculated and its arithmetic mean was used. The obtained HSC is shown in Table 2.

[0122] [Adhesion Test] Adhesion tests were conducted on the metal foil current collectors for each test number except test number 16 using the method described above. The test specimens were 15 mm wide and 74 mm long (40 mm coated portion). The peel strength (N / m) was determined for each test specimen. The peel strength of test number 1 was used as the baseline value, and the peel strengths of the other test numbers were determined as relative values. The obtained peel strengths (relative values) are shown in the "Adhesion" column of Table 2.

[0123] [Discharge capacity evaluation] The discharge capacity of the metal foil current collectors for each test number, excluding test number 16, was evaluated using the method described above. Specifically, the composition was applied to the substrate surface of each test number, excluding test number 16, to a thickness of 50 μm. The composition was dried at 75°C for 20 minutes, and the volume occupied by the composite was determined. The volume occupied by the composite was determined from the weight of the applied composition, the components of the composition, and the mixing ratio. Furthermore, an electrode mixture layer was formed on the substrate surface that did not have the composition applied, to a thickness of 50 μm. When the volume of the 50 μm thick electrode mixture layer was set to 100.0, the volume occupied by the composite was subtracted, and this was defined as the discharge capacity. The obtained discharge capacities are shown in the "Discharge Capacity" column of Table 2.

[0124] [Evaluation Results] Referring to Tables 1 and 2, the current collector metal foils for test numbers 2 to 10 contained composites consisting of Ni particles with an average particle size of 20 μm or less, a sintered body, and 14.0 to 40.0 volume percent of resin. These current collector metal foils also had an HSC (High-Screw Capacitance) of 20.0 to 50.0 particles / mm². As a result, they exhibited excellent adhesion, with a peel strength (relative value) of 1.50 or higher. Furthermore, these current collector metal foils had a discharge capacity (relative value) of 85.0 or higher, demonstrating that they maintained discharge capacity despite their high adhesion.

[0125] The metal foils used for current collectors in test numbers 2-9 also met the requirement of having an average Ni particle size of 2-20 μm. As a result, these metal foils for current collectors achieved a discharge capacity (relative value) of 89.0 or higher, demonstrating their ability to maintain discharge capacity.

[0126] On the other hand, the metal foil for the current collector in test number 11 did not contain a sintered body in the composite. As a result, this metal foil for the current collector had a peel strength (relative value) of less than 1.50 and did not have good adhesion.

[0127] The metal foil for the current collector in test number 12 had too high a volume ratio of resin in the composite. As a result, this metal foil for the current collector had a peel strength (relative value) of less than 1.50, indicating poor adhesion.

[0128] The metal foil for the current collector in test number 13 had too high a volume ratio of resin in the composite, resulting in an excessive amount of HSC. As a result, this metal foil for the current collector had a peel strength (relative value) of less than 1.50, indicating poor adhesion.

[0129] The metal foil for the current collector in test number 14 had too little HSC. As a result, this metal foil for the current collector had a peel strength (relative value) of less than 1.50 and did not have good adhesion.

[0130] The metal foil used for the current collector in test number 15 had too much HSC. As a result, this metal foil for the current collector had a peel strength (relative value) of less than 1.50 and did not have good adhesion.

[0131] The metal foil for the current collector in test number 16 failed to form a composite and was unable to retain its shape.

[0132] The metal foil for the current collector in test number 17 had too low a volume ratio of resin in the composite. As a result, this metal foil for the current collector had a peel strength (relative value) of less than 1.50 and did not have good adhesion.

[0133] Test number 18, a metal foil for current collectors, did not contain Ni particles or sintered material in its composite. Furthermore, this metal foil for current collectors had too low a volume percentage of resin in its composite, resulting in a low HSC (High-Stress Concentration) value. As a result, this metal foil for current collectors had a peel strength (relative value) of less than 1.50 and did not exhibit good adhesion.

[0134] The embodiments of this disclosure have been described above. However, the embodiments described above are merely examples for implementing this disclosure. Therefore, this disclosure is not limited to the embodiments described above, and the embodiments described above can be modified as appropriate without departing from the spirit of this disclosure.

Claims

1. A metal foil for current collectors, Substrate and The substrate comprises a plurality of composites held on the surface of the substrate, Multiple of the aforementioned composites are Ni particles with an average particle size of 20 μm or less, A sintered body formed by sintering a plurality of Ni particles, It contains 14.0 to 40.0 volume percent of resin, On the surface of the metal foil for the current collector, The number of peaks with a height of more than 10 μm from the surface of the substrate, as identified by line roughness analysis, is 20.0 to 50.0 peaks / mm. Metal foil for current collectors.

2. A metal foil for a current collector according to claim 1, The average thickness of the substrate is 5 to 30 μm. Metal foil for current collectors.

3. A metal foil for a current collector according to claim 1 or claim 2, The current collector comprises an electrode mixture layer formed on the surface of the metal foil for the current collector, electrode.

4. The electrode according to claim 3, Electrolytes, battery.

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