WO2013061890A1 - Electrode material, electrode, secondary cell, and method for producing electrode material - Google Patents

Abstract

Provided is an electrode material of excellent tab weldability, and capable of forming thin films of the electrode material, and with which low internal resistance of the cell may be achieved. The electrode material (1) is equipped with a base material (1a) including metal foil, and a conductive substance (1b). The surface of the base material (1a) is constituted by an exposed flat portion and a plurality of depressions (average depth: 0.3 µm-3.0 µm inclusive). The conductive substance (1b), which is disposed in the depressions, is disposed in a staggered pattern on the surface of the base material (1a), and the coverage of the base material (1a) surface by the conductive substance (1b) is 1-80%.

Description

Electrode material, electrode, secondary battery, and method for producing electrode material

The present invention relates to an electrode material used for an electrode of a secondary battery, an electrode using the electrode material, a secondary battery using the electrode, and a method for manufacturing the electrode material.

Research on current collectors in which a carbon-based conductive material is coated on a metal foil such as an aluminum foil or a copper foil used as a base material for secondary battery electrodes has been conducted in various research institutions. Many patent applications have been filed, and examples thereof include Patent Documents 1 to 4.

Patent Document 1 and Patent Document 2 describe a current collector in which a film made of carbon fine particles as a conductive material and a film-forming compound is formed on the surface of a base material such as an aluminum foil or a copper foil. Patent Document 3 describes a current collector in which a conductive layer made of carbon powder (conductive material) and a binder is provided between an active material. Patent Document 4 describes a current collector in which a conductive coating layer using carbon as a conductive agent (conductive substance) is provided on the surface. By reducing the contact resistance between the current collector and the active material layer formed thereon, the internal resistance of the battery using these current collectors is reduced, and the high-speed charge / discharge characteristics of the battery This is intended to improve the cycle characteristics.

Japanese Unexamined Patent Publication No. 2007-226969 Japanese Unexamined Patent Publication No. 2010-135338 Japanese Unexamined Patent Publication No. 9-97625 Japanese Unexamined Patent Publication No. 2001-351612

Here, with reference to FIG. 5, the configuration of the current collector in the prior art described in Patent Documents 1 to 4 will be described together. FIG. 5 is a schematic cross-sectional view for explaining the configuration of the current collector in the prior art. As shown in FIG. 5, in the current collector 3 in the prior art, a conductive material layer 3b is uniformly formed on the surface of a base material 3a made of a metal foil. That is, the entire surface of the base material 3a is covered with the conductive material layer 3b.

As shown in FIG. 5, when the conductive material layer 3b is uniformly formed on the surface of the substrate 3a, the current collector 3 and the battery terminals are electrically connected to produce a battery using the current collector 3. When a metal tab (not shown) or the like for connecting to the current collector 3 is welded to the surface of the current collector 3, there is a problem that the conductive material layer 3b becomes an obstacle to welding and weldability deteriorates.

Furthermore, since the conductive material layer 3b uniformly formed on the surface of the substrate 3a has a certain thickness, the current collector 3 on which such a conductive material layer 3b is formed becomes thick as a whole. For this reason, when an electrode formed by laminating an active material layer (not shown) on the current collector 3 is used for a battery, the active material layer (not shown) formed on the current collector 3 accommodated in a battery of the same volume is used. There is a problem that the thickness of the figure is limited.

The present invention was devised in view of the above-described problems, has excellent tab weldability, enables the electrode material (current collector) to be thinned, and lowers the contact resistance with the active material layer. It is an object of the present invention to provide an electrode material that can reduce the internal resistance of a battery, an electrode that uses the electrode material, a secondary battery that uses the electrode, and a method for manufacturing the electrode material.

In order to solve the above-described problems, an electrode material according to the present invention is an electrode material comprising a base material including a metal foil, and a conductive substance disposed on at least one surface of the base material, The surface of the substrate is composed of a flat portion and a plurality of depressions, and the average depth of the depressions is 0.3 μm or more and 3.0 μm or less, the conductive material is disposed in the depressions, and the flat portions are When exposed in a 300 μm square field of view, the conductive material is arranged in an island shape on the surface of the substrate, and the coverage of the surface of the substrate by the conductive material is 1 to 80%. It is characterized by being.

According to such a configuration, since the coverage of the surface of the base material including the metal foil with the conductive material is 80% or less, a portion exceeding 20% of the surface of the base material is not covered with the conductive material and is a flat metal. The base of the will be exposed. For this reason, when this electrode material is used as, for example, a current collector of an electrode of a lithium ion secondary battery, and when welding a metal tab for connecting the current collector and the battery terminal, The metal tab is well welded to the exposed metal substrate. Moreover, when the coverage of the surface of the base material with the conductive material is 1% or more, when this electrode material is used as, for example, a current collector of an electrode of a lithium ion secondary battery, a current collector and a current collector Contact resistance with the active material layer laminated on the body is reduced.
In addition, the contact area between the base material and the conductive material is increased by placing the conductive material in a recess with a predetermined average depth formed on the surface of the base material, thus improving the adhesion of the conductive material to the base material. And the contact resistance can be further reduced.
Furthermore, by arranging the conductive material in the depression formed on the substrate surface, the electrode material can be made thinner than in the case where the conductive material is formed in layers on the substrate surface.

In the electrode material according to the present invention, the metal foil is preferably made of aluminum, an aluminum alloy, copper, or a copper alloy. Furthermore, in the electrode material according to the present invention, the conductive material preferably contains a carbon-based material.

According to such a configuration, since the metal foil and conductive material of the electrode material are made of a predetermined material, the electrode material can be suitably applied as an electrode of a lithium ion secondary battery.

The electrode according to the present invention is an electrode including the electrode material, and an active material layer is provided on a surface of the electrode material.

According to such a configuration, the contact resistance between the electrode material that is the current collector and the active material layer is reduced by the conductive material disposed in the plurality of depressions on the surface of the base material. In addition, the tab weldability can be improved and the film thickness can be reduced.

The secondary battery according to the present invention is a secondary battery including a positive electrode and a negative electrode, and at least one of the positive electrode and the negative electrode is the electrode.

According to such a configuration, since the contact resistance between the electrode material that is the current collector and the active material layer is reduced, the secondary battery has an internal resistance that is low as the secondary battery. It becomes. In addition, the tab weldability can be improved and the film thickness can be reduced.

The method for producing an electrode material according to the present invention is a method for producing the electrode material, the step of forming a plurality of depressions on the surface of the base material, and the conductive material in the formed depressions. And a conductive material disposing step of disposing a conductive material.

According to this manufacturing method, a plurality of depressions can be formed on the surface of the substrate by the depression formation step, and the conductive substance can be arranged in the depression formed on the surface of the substrate by the conductive substance arrangement step. it can. As a result, the electrode material as described above can be manufactured.

Further, in the method for producing an electrode material according to the present invention, the depression forming step forms a plurality of depressions on the surface of the substrate by pressing a transfer body having a plurality of convex portions against the substrate. It is preferable that it is a process.

According to this manufacturing method, by pressing a transfer body having a plurality of convex portions against the substrate, the plurality of depressions are appropriately formed on the surface of the substrate, and a conductive material is disposed in the depressions. Thus, the electrode material as described above can be manufactured.

Further, the electrode material manufacturing method according to the present invention is a pressure bonding method in which the conductive material is pressed into the depression by pressing the base material on which the conductive substance is arranged in the depression after the conductive substance arranging step. It is preferable to further include a step.

According to such a manufacturing method, the adhesion of the conductive material to the substrate can be further improved and the contact resistance can be further reduced by performing a crimping step of crimping the conductive material to the recess after the conductive material arranging step. it can.

Further, in the method for producing an electrode material according to the present invention, the depression forming step is a step of forming a plurality of depressions on a surface of the base material by roughening a surface of the base material, It is preferable that the method further includes a rolling step of forming the flat portion by rolling the base material on which the conductive material is placed in the depression after the conductive material placement step.

According to this manufacturing method, by roughening the surface of the base material, a plurality of depressions are formed on the surface of the base material, and the conductive material is disposed in the depressions. Then, by performing a rolling process, it is possible to improve the tab weldability by forming a flat portion to which the conductive material is not attached on the surface of the base material, and improve the adhesion of the conductive material to the base material. And contact resistance can be reduced.

According to the electrode material according to the present invention, the conductive material is arranged in an island shape on the surface of the metal foil as a base material, and the coverage of the conductive material is limited to partially expose the metal foil substrate on the surface of the electrode material. By doing so, it is possible to ensure tab weldability and reduce the contact resistance of the electrode material.
In addition, by arranging the conductive material in the depression formed on the surface of the base material, the contact area between the base material and the conductive material can be increased, and as a result, the adhesion of the conductive material to the base material can be improved. In addition to the improvement, the contact resistance of the electrode material can be further reduced.

Furthermore, by arranging the conductive material in the recess formed on the surface of the substrate, the electrode material can be made thinner compared to the case where the conductive material is formed in layers on the surface of the substrate, and as a result, The amount of the active material layer per unit volume is not greatly limited, and a reduction in battery capacity can be avoided.

According to the electrode and the secondary battery of the present invention, by providing the predetermined electrode material, the contact resistance between the electrode material and the active material layer can be reduced, the internal resistance of the battery can be reduced, and the tab It is possible to improve the weldability and reduce the thickness.

According to the method for manufacturing an electrode material according to the present invention, by forming a plurality of depressions on the surface of the base material and arranging the conductive material in the depressions, the conductive material can be arranged in an island shape on the surface of the base material. In addition to reducing contact resistance, an electrode material having excellent tab weldability can be produced.

According to the method for producing an electrode material according to the present invention, the contact resistance is further increased because the adhesion between the base material and the conductive material is improved by arranging the conductive material in the plurality of depressions formed on the surface of the base material. An electrode material that can be reduced and made thinner can be manufactured.

According to the method for producing an electrode material according to the present invention, the tab weldability can be improved by rolling the base material after the conductive material arranging step to form a flat portion to which no conductive material is adhered. In addition, the adhesion of the conductive material to the substrate can be improved, and the contact resistance can be reduced.

1A and 1B are schematic cross-sectional views for explaining the structure of a current collector according to the present invention, and FIG. FIG. 1B is a schematic cross-sectional view of a current collector manufactured without application, and FIG. 1B is a current collector manufactured by applying a crimping process in the current collector manufacturing process A, or a current collector manufactured in current collector manufacturing process B It is a typical sectional view of an electric body. FIG. 2 is a schematic cross-sectional view for explaining the structure of an electrode using the current collector according to the present invention. FIG. 3 is a schematic cross-sectional view for explaining the structure of a secondary battery using the electrode according to the present invention. 4 (a) and 4 (b) are flowcharts showing a method for manufacturing a current collector according to the present invention, FIG. 4 (a) is a flowchart showing a method A for manufacturing a current collector, and FIG. 4 (b). These are the flowcharts which show the manufacturing method B of an electrical power collector. FIG. 5 is a schematic cross-sectional view for explaining the structure of a current collector according to the prior art.

Hereinafter, embodiments of an electrode material according to the present invention (hereinafter, appropriately referred to as a current collector) will be described in detail.
[Current collector structure]
The structure of the current collector according to this embodiment will be described with reference to FIG.
The current collector 1 according to this embodiment includes a base material 1a made of a metal foil and a conductive material 1b arranged in an island shape on the surface of the base material 1a. Moreover, the conductive material 1b may be arrange | positioned only on one side, as shown in FIG. 1, and may be arrange | positioned on both surfaces of the base material 1a.
Note that the current collector 1 according to the present embodiment can be suitably used as, for example, a current collector of an electrode of a lithium ion secondary battery. The electrode and the secondary battery using the current collector 1 will be described later.

When the current collector 1 is used as an electrode of a battery, the current collector 1 has a structure in which the conductive material 1b is arranged in an island shape on the surface of the base 1a when observed in a 300 μm square field of view. The tab weldability when welding a metal tab (not shown) that electrically connects the current collector 1 and the battery terminal can be improved. Further, the contact resistance between the current collector 1 and the active material layer (see FIG. 2) laminated on the surface of the current collector 1 is reduced by the conductive material 1b arranged in an island shape on the surface of the substrate 1a. Can be reduced.
In the present specification, “island shape” refers to a state in which the conductive material 1b is arranged such that at least a part of the surface of the substrate 1a is exposed without being covered with the conductive material 1b. For example, as shown in FIGS. 1 (a) and 1 (b), conductive materials 1b filled in a plurality of depressions may be arranged isolated from each other, and aggregates are joined and arranged in a mesh shape. It may be.

(Base material)
As shown in FIG. 1, the substrate 1 a has a flat surface and a plurality of depressions.
The average depth of the depression is 0.3 to 3.0 μm (preferably 0.4 to 2.7 μm, more preferably 0.5 to 2.3 μm). By setting the average depth of the recesses to 0.3 μm or more, the adhesion of the conductive material 1b to the base material 1a can be ensured even when the later-described press-bonding step A4 is not performed. On the other hand, by setting the average depth of the depressions to 3.0 μm or less, it is possible to prevent the strength of the base material 1a (metal foil) from being lowered and to avoid breakage of the base material 1a at the stage of manufacturing the electrode. Because it can.
Further, a plurality of depressions are provided when observed in a 300 μm square field of view so that the conductive material 1b disposed in the depression has the above-described island shape.

The base material 1a can use metals, such as aluminum (Al) and copper (Cu), which are generally used as electrode materials for secondary batteries.
When the substrate 1a is used as a secondary battery electrode material, the substrate 1a is generally used in the form of a foil having a thickness of about 5 to 50 μm. In addition, in the manufacturing method of the electrical power collector which concerns on this embodiment, what is necessary is just to use the base material 1a of the thickness which considered the rolling reduction ratio of the said rolling process B4 when implementing the rolling process B4 mentioned later.
The substrate 1a is not limited to Al or Cu having a specific composition, and when used for an electrode, various pure metals and alloys thereof suitable for the use environment of the electrode can be used. Preferable examples include aluminum, aluminum alloy, copper, and copper alloy.

(Conductive material)
The conductive material 1b reduces the contact resistance between the current collector 1 and the active material layer 2 (see FIG. 2). As shown in FIGS. 1 (a) and 1 (b), the conductive material 1b It arrange | positions at the hollow formed in the surface, and is arrange | positioned at the surface of the base material 1a at island shape.
Here, the state in which the conductive material 1b is disposed in the depression of the base material 1a is a state in which the depression is filled with the conductive substance 1b as shown in FIGS. 1 (a) and 1 (b). The substance 1b may protrude from the depression (see FIG. 1A), and the conductive substance 1b may be flush with the flat surface of the substrate 1a by performing rolling or pressure bonding (FIG. 1). (See (b)).
Note that the conductive material 1b is basically not disposed on the flat portion of the surface of the substrate 1a, and the flat portion of the substrate 1a is exposed. However, it is not necessary that the entire area of the flat portion is completely exposed, and the conductive material 1b may be disposed in a part of the flat portion as long as the coverage described later is satisfied.

Since the conductive material 1b can increase the contact area of the conductive material 1b with respect to the base material 1a by being disposed in the depression of the base material 1a, it improves the adhesion of the conductive material 1b to the base material 1a and is in contact with the base material 1a. Resistance can be reduced. Further, since the conductive material 1b is positively filled in the recess of the base material 1a, the amount of the conductive material 1b protruding from the surface of the base material 1a can be suppressed, and the current collector 1 is prevented from becoming thick. can do.

The coverage of the surface of the substrate 1a with the conductive material 1b is 1 to 80% (covered area / observed visual field area × 100) when observed in a substantially square field of view of 300 μm square, that is, 300 μm on a side.
When the coverage by the conductive material 1b is 1% or more, when used as an electrode of a secondary battery, the current collector 1 and the current collector 1 are compared with those of only an Al foil in which the conductive material 1b is not disposed. The contact resistance with the active material layer 2 (see FIG. 2) laminated on the surface of the substrate can be reduced. Moreover, favorable tab weldability is securable by making the coverage with the electroconductive substance 1b on the surface of the base material 1a 80% or less. The coverage is preferably 7 to 70%, more preferably 15 to 60%.

It is preferable that the conductive material 1b is evenly arranged on the surface of the substrate 1a at least in the unit of the observation area described above. Since the conductive material 1b is arranged in an island shape within a sufficiently small area, practically uniform contact resistance and tab weldability can be obtained.

Here, the coverage of the surface of the base material 1a with the conductive material 1b is obtained by, for example, photographing the surface of the prepared sample using an SEM (scanning electron microscope) and conducting the carbon or the like contained in the photographed field of view. The area of the substrate surface covered with the substance 1b can be calculated and obtained by image processing.

As the conductive material 1b, a material including a carbon-based material can be used. As the carbon-based conductive material (carbon-based material), natural or artificial crystalline graphite, expanded graphite, artificial graphite, pyrolytic graphite, various carbon blacks, or a mixture thereof can be used. Examples of carbon black include acetylene black, ketjen black, and carbon nanotube. The average particle size of the conductive material 1b is 0.01 to 20 μm, preferably 0.01 to 1 μm.
The conductive material 1b is preferably composed of a carbon-based material, but may be configured to include 10% by mass or more of the carbon-based material. In the conductive material arranging steps A2 and B2 described later, The binder used may be included.

[electrode]
Next, with reference to FIG. 2, the structure of the electrode of the lithium ion secondary battery using the current collector 1 according to this embodiment will be described.

An electrode 10 shown in FIG. 2 includes a current collector 1 according to this embodiment and an active material layer 2 laminated on the surface of the current collector 1. In FIG. 2, the active material layer 2 is laminated only on one side of the current collector 1, but the active material layer 2 is laminated on both sides of the current collector 1 in which the conductive material 1b is arranged on both sides of the base material 1a. You may let them.
When the positive electrode of the lithium ion secondary battery is configured, a metal such as Al or an Al alloy can be used as the base material 1a of the current collector 1. As the positive electrode active material, a known material, for _example, it can be used LiCoO _2, LiNiO 2, lithium-containing oxides such as LiMn ₂ O _4. The method for producing the positive electrode active material layer 2 is not particularly limited, and a known method, for example, a powdery lithium-containing oxide is added with a conductive material, a solvent, etc., if necessary, in addition to a binder. Then, after sufficiently kneaded, it can be applied to the current collector 1, dried and pressed.

Further, when constituting the negative electrode of the lithium ion secondary battery, the base material 1a of the current collector 1 can be a metal such as Cu, Cu alloy, nickel (Ni), Ni alloy, and stainless steel. Moreover, as a negative electrode active material, a graphite-type carbon material can be used, for example, and it can manufacture like the manufacturing method of the active material layer 2 of a positive electrode.

[Secondary battery]
Next, the configuration of the lithium ion secondary battery 20 using the electrode 10 provided with the current collector 1 according to this embodiment will be described with reference to FIG.

A lithium ion secondary battery (secondary battery) 20 shown in FIG. 3 includes a positive electrode 11 and a negative electrode 12, which are electrodes 10 using the current collector 1 according to the present embodiment, a separator 13, and an electrolytic solution 14. It is comprised including. The positive electrode 11 and the negative electrode 12 are separated by a separator 13, and the electrolyte solution 14 is filled between the positive electrode 11 and the negative electrode 12 and the separator 13. Further, the entire lithium ion secondary battery 20 is housed in a container (not shown), and the positive electrode 11 and the negative electrode 12 are each welded with a metal tab (not shown) to be electrically connected to an electrode terminal (not shown). Connected.

As for the positive electrode 11 and the negative electrode 12, the active material layer 2 containing the above-mentioned positive electrode active material and negative electrode active material is formed on the surface of the current collector 1 according to this embodiment, respectively.
Moreover, the separator 13 and the electrolyte solution 14 can each be comprised using a well-known material. As the separator 13, for example, a polyethylene microporous film having a thickness of 20 to 30 μm can be used. In addition, as the electrolytic solution 14, for example, a non-aqueous electrolytic solution in which an electrolyte such as LiPF ₆ or LiBF ₄ is dissolved in an organic solvent such as propylene carbonate or ethylene carbonate can be used.

Next, a method for manufacturing a current collector according to this embodiment will be described.
[Production method]
In order to produce a current collector having a structure in which conductive materials are arranged in an island shape on the surface of a base material made of metal foil, several production methods can be mentioned. These manufacturing methods will be described in order with reference to FIGS. 4 (a) to 4 (b).

<Current collector manufacturing method A>
In the current collector manufacturing method A, a plurality of indentations are provided on the surface of a base material made of metal foil (indentation forming step A1), and a conductive material is disposed by applying a solution containing an electrically conductive material in the indentations (conductivity). This is a method of manufacturing a current collector by drying the solution (substance placement step A2) (drying step A3) (see FIG. 4A).
Moreover, by further crimping the current collector as necessary (crimping step A4), it is possible to further improve the adhesion and reduce the contact resistance.

(Dent formation process)
The dent forming step A1 is a step of forming a dent on the surface of the substrate. In the case of the current collector manufacturing method A, a transfer body having a plurality of projections prepared in advance is pressed against the surface of the substrate ( This is a step of forming a plurality of depressions on the surface of the base material.
In addition, a flat part other than the convex part exists on the surface of the transfer body, so that a flat part can be left (formed) on the surface of the base material, and tab weldability is ensured by the presence of the flat part. Can do.

The detailed dent formation method in dent formation process A1 is a method of forming a plurality of dents on the substrate surface by, for example, pressing a plate-like or sheet-like transfer body on which a convex portion is formed together with the substrate. . About the press here, a known press machine may be used.
Moreover, the method of pressing a base material with a roll press machine provided with the roll (roll-shaped transfer body) which formed the convex part on the roll surface, and a rolling mill may be used.

The structure of the transfer body used in the dent forming step A1 is not particularly limited as long as it has a plurality of convex portions, but the particle size as the convex portions on the above-described plate-shaped, sheet-shaped, cylindrical (roll) -shaped objects. Any structure may be used as long as the powder is controlled. The material of the transfer body is not particularly limited, but metal, plastic, paper, and ceramic may be used.

The size of each convex portion of the transfer body, the density (number / unit area) of the convex portions, the arrangement pattern of the convex portions, and the like can be appropriately designed and determined.
Note that the size (height) of the protrusions corresponds to the average depth of the depressions described above, so that the average depth of the depressions is a predetermined value (0.3 to 3.0 μm). What is necessary is just to determine a size (height). Further, the size of the protrusions (the area of the protrusions) and the density of the protrusions (number / unit area) correspond to the coverage of the surface of the base material with the above-described conductive material, so the coverage is a predetermined value. The size of the protrusions (the area of the protrusions) and the density of the protrusions (number / unit area) may be determined so as to be (1 to 80%).

As the dent forming step A1 in the manufacturing method A of the current collector, in addition to the above method, after forming the dent by roughening by a physical method such as sandpaper or a chemical method such as etching. There is also a method in which both a depression and a flat part are formed by providing a flat part on the surface of the substrate by performing a slight rolling (light rolling).

(Conductive substance placement process)
Conductive substance arrangement | positioning process A2 is a process of arrange | positioning a conductive substance in the hollow of the surface of the base material formed in hollow formation process A1.

The detailed conductive material arrangement method in the conductive material arrangement step A2 is, for example, a method in which a conductive material is filled in a depression on the surface of the substrate by applying a solution containing the conductive material to the surface of the substrate.
Here, in order to apply the solution containing the conductive material to the surface of the substrate, generally used coating methods such as a bar coater, a roll coater, a gravure coater, a dip coater, and a spray coater can be used. Then, the solution applied other than the depression provided in the substrate immediately after the application is removed. For example, when the solution is applied with a bar coater, a mirror-finished metal rod (SUS or the like) is used immediately after the application, and the excess solution is removed in the manner of performing the bar coater again. When applying the solution using a roll-to-roll facility such as a gravure coater, the coating thickness should be as thin as possible, and a sheet-like material made of a material softer than the metal foil immediately after application (preferably polypropylene) (Plastic such as polyethylene, PET, Teflon (registered trademark)) is pressed against the substrate (attached to the apparatus) to remove excess solution.

In the solution used in the conductive material arranging step A2, it is preferable that the conductive material contained therein has an average particle diameter of 0.01 to 1 μm and a conductive material concentration of 0.1 to 10% by mass.
The reason why the average particle diameter of the conductive material is set to 1 μm or less is that the conductive material can be appropriately introduced into the depression formed on the surface of the base material. In addition, the average particle size of the conductive material is set to 0.01 μm or more because if the particle size is too small, the bulk density becomes large, and it becomes difficult to mix the conductive material with the solvent, and it takes too much time to formulate. This is for sex. The average particle size of the conductive material is more preferably 0.05 to 0.6 μm, and further preferably 0.1 to 0.3 μm.
And, the concentration of the conductive material is set to 10% by mass or less because it is necessary to remove the excess coating solution adhering to the flat portion of the base material after coating the solution. This is because the area covered with the conductive material can be minimized even if the solution remains in a flat portion other than the depression. The reason why the concentration of the conductive material is 0.1% by mass or more is to ensure the effect of reducing the contact resistance. The concentration of the conductive material is more preferably 0.5 to 8% by mass, and further preferably 1 to 6% by mass.

As the conductive substance used in the conductive substance arranging step A2, a carbon-based material can be used. Specifically, natural or artificial crystalline graphite, expanded graphite, artificial graphite, pyrolytic graphite and various carbon blacks can be used. More preferred are various carbon blacks such as acetylene black, ketjen black, and carbon nanotube.

As the solvent used in the conductive substance arranging step A2, various water-based and organic solvent-based solvents such as water, alcohols such as toluene, N-methylpyrrolidone, MEK, and IPA can be used. Moreover, you may add various resins, such as a thickener and a fluorine resin generally used as a binder, for example, carboxymethylcellulose, a polyvinylidene fluoride, a styrene butadiene rubber, a polypropylene, polyethylene.

(Drying process)
The drying step A3 is a step for evaporating the solvent after the coating step. In the drying step, drying may be performed at room temperature, or heat drying using a heat treatment furnace or the like may be performed as necessary. In the case of performing heat drying, the heating temperature is preferably 100 to 170 ° C., which is a temperature at which the solvent easily evaporates (lower limit reason) and does not decrease the strength of the metal foil (upper limit reason).
Note that the drying step A3 may not be provided if the current collector is allowed to stand for a certain period of time after the conductive material disposing step A2 so that the solvent spontaneously evaporates.

(Crimping process)
If necessary, after the drying step A3 (or conductive material placement step A2), the current collector is pressed (crimping step A4) to improve the adhesion between the conductive material and the substrate, and to improve the contact resistance. Can be reduced. Furthermore, the conductive material remaining in a portion (flat portion) other than the depression on the surface of the base material can be pressure-bonded to the base material. Here, various rolling mills and roll press machines can be used as the crimping method.
In the present embodiment, “crimping” refers to applying a reduction in which the reduction ratio of the base material is substantially 0%, unlike “rolling” in the current collector manufacturing method B described later.

<Manufacturing process B of current collector>
Next, the current collector manufacturing method B will be described with a focus on the differences from the current collector manufacturing method A.
The manufacturing method B of the current collector is provided with a recess for introducing a solution containing a conductive material by roughening the surface of a substrate made of a metal foil (depression forming step B1), and the solution containing the conductive material in the recess This is a method of manufacturing a current collector by applying conductive material (conductive material arranging step B2), drying the solution (drying step B3), and rolling (rolling step B4) (FIG. 4). (See (b)).

(Dent formation process)
In the manufacturing method B of a current collector, the dent forming step B1 is a step of roughening a base material made of metal foil and forming a dent for introducing a coating solution containing a conductive material.
Thus, by roughening the base material and forming a plurality of depressions, the contact area between the base material and the conductive material can be increased, and the contact resistance can be further reduced.

As a roughening method in the depression forming step B1, there are a mechanical method and a chemical method.
As a mechanical method, a surface of a base material is roughened using sandpaper, a grindstone, an abrasive, and the like, and a roughened plate or a roughened cylinder (roll) is pressed against a metal foil. Thus, there is a method of transferring the rough surface to a metal foil. The former can be performed manually, and the latter method can be performed by a press, a crimping machine, a rolling mill, or the like.
As a chemical method, the surface of the substrate can be roughened by etching with a chemical such as NaOH, KOH, or ammonium fluoride.

(Conductive material placement process)
In the recess formation step B1 described above, a recess is formed on the surface of the base material, but the flat portion is not formed or only partially formed. Therefore, the conductive material arrangement method in the conductive material arrangement step B2 may be performed by applying the solution to the entire surface of the substrate with various coaters such as a bar coater, a roll coater, a gravure coater, a dip coater, and a spray coater. It is not essential to remove excess solution adhering to the surface.

The solution used in the conductive material arranging step B2 does not need to be controlled as strictly as the solution used in the conductive material arranging step A2 of the manufacturing method A. The average particle size of the conductive material contained in the solution may be 0.01 to 20 μm. That's fine.

As the conductive substance used in the conductive substance arranging step B2, a carbon-based material can be used. Specifically, natural or artificial crystalline graphite, expanded graphite, artificial graphite, pyrolytic graphite and various carbon blacks can be used. In addition, various carbon blacks such as acetylene black, ketjen black, and carbon nanotubes may be mixed with graphite made of natural or artificial crystalline graphite, expanded graphite, artificial graphite, or pyrolytic graphite.

As the solvent used in the conductive material arrangement step B2, the same solvent as that used in the conductive material arrangement step A2 may be used.

(Drying process)
What is necessary is just to perform drying process B3 by the same method as drying process A3 of the manufacturing method A of an electrical power collector.

(Rolling process)
After the drying step B3 (or conductive material arranging step B2), the current collector is rolled (rolling step B4), so that no conductive material is arranged (or hardly arranged) on the surface of the substrate. A flat surface will be formed. As a result, a current collector is obtained in which the conductive material is coated in an island shape on the substrate surface.

By forming a flat portion on which the conductive material is not attached to the surface of the base material by this rolling step B4, the tab weldability can be improved, the adhesion between the conductive material and the base material is improved, and the contact resistance Can be reduced.
A known rolling mill may be used for rolling.
“Rolling” refers to plastic working in which the base material is deformed by, for example, crushing the convex portions of the base material having irregularities by pressing the base material with a pair of rolls.

When the current collector manufactured by the above manufacturing method is used, for example, as the current collector 1 of the electrode 10 of the lithium ion secondary battery as shown in FIG. 2, the conductive material 1b is not layered on the surface of the base material. By forming an island shape in the depression, the entire current collector 1 can be thinned. As a result, the thickness of the active material layer 2 laminated on the surface of the current collector 1 is not restricted, and the battery The capacity is not reduced.

Next, the current collector of this embodiment will be described by comparing an example that satisfies the requirements of the present invention with a comparative example that does not satisfy the requirements of the present invention.

A sample was prepared by the following method.
(Base material)
When an Al foil was used as the substrate, a 1000 series Al alloy was used. Moreover, when using Cu foil as a base material, 99.9% or more pure Cu foil was used.
Note that a 15 μm thick Al foil or Cu foil was used for a sample that was not rolled and a sample that was lightly pressed (pressed). In addition, as the sample subjected to rolling, Al foil or Cu foil having different thicknesses was appropriately used so that the thickness after rolling was 15 μm.

(Conductive material)
Carbon black having an average particle size of 0.03 μm (Tokai Carbon Talker Black # 5500) and expanded graphite having an average particle size of 6 μm (SEC carbon SNE-6G expanded graphite) were used as the conductive material. The concentration of the conductive material in the entire slurry is as shown in Table 1.

(Dent formation process)
Sample No. In No. 1, a # 800 sandpaper was affixed to a roller (φ75 mm), and the roller was pressed against an Al foil to form recesses having an average depth shown in Table 1.
Sample No. In No. 2, a # 2400 sandpaper was affixed to a roller (φ75 mm), and the roller was pressed against an Al foil to form a recess having an average depth shown in Table 1.
Sample No. In No. 3, the surface of the Al foil was roughened by sanding with # 400 sandpaper.
Sample No. No. 4 did not perform the dent formation process in Al foil.
Sample No. In No. 5, the surface of the Al foil was roughened by sanding with # 400 sandpaper.
Sample No. In No. 6, the Al foil was sanded with # 800 sandpaper to roughen the surface.
Sample No. In No. 7, a # 800 sandpaper was affixed to a roller (φ75 mm), and the roller was pressed against Cu foil, thereby forming recesses having an average depth shown in Table 1.
Sample No. In No. 8, the surface of the Cu foil was roughened by sanding with a # 800 sandpaper.
Sample No. In No. 9, the surface of the Cu foil was roughened by sanding with # 800 sandpaper.

(Conducting substance placement process: coating process)
In the coating step, water was used as a solvent for the solution (slurry) containing the conductive material, and CMC sodium salt (carboxymethylcellulose sodium salt) was added at a concentration of 1% by mass. Moreover, the application | coating of the solution was apply | coated to the surface of Al foil or Cu foil using the bar coater (counter No. 5). In addition, the solution was applied to both surfaces of an Al foil or Cu foil for a sample for weldability evaluation, and the solution was applied to one surface of an Al foil or Cu foil for samples for other item evaluations. .
And sample no. For 1, 2 and 7, the excess slurry on the Al foil or Cu foil was removed immediately after application with a 7 mm diameter mirror-finished bar.

(Drying process)
A solution containing a conductive material was applied to the surface of the Al foil or Cu foil, and then dried by holding the Al foil or Cu foil in an oven at 110 ° C. for 2 minutes.

(Crimping process, rolling process)
Sample No. About 3, 5, 6, 8, and 9, it rolled. Rolling was performed using a skin pass roll having a roll diameter of φ100 mm.
Sample No. 2 and 7 were subjected to pressure bonding. The crimping was performed using the same apparatus as the rolling described above. In the case of pressure bonding, the rolling reduction was set to 0% (the thickness of the base material did not change).
The rolling reduction was calculated by the equation (1) by measuring the thickness of the sample (foil + conductive material) before and after rolling using a micrometer.

(Calculation of rolling reduction)
The rolling reduction is as follows: the thickness of the sample before rolling is t0, and the thickness of the sample after rolling is t1.
(Rolling ratio) = (t0−t1) / t0 × 100 (%) (1)
Calculated by

<Evaluation method>
(Evaluation of dent depth)
The depth of the depression formed on the surface of the Al foil or Cu foil is determined by the electric field emission made by Hitachi after processing the sample cross section using a cross section processing apparatus (Cross Section Polisher (CP) SM-09010 made by JEOL). Using a scanning electron microscope (FE-SEM) SU-70, observe five fields of view at a magnification of 2000 times from the sample cross-section direction, and all the depressions included in the photographed field of view (the reference surface is a flat part of the metal foil) The depth of the depression was determined.
When the dent was unclear, the portion was enlarged up to 30,000 times to obtain the dent depth. The minimum depth resolution at that time was about 0.1 μm. Moreover, the maximum depth of each hollow was made into the depth of the hollow, and the average of the obtained depth was made into the average depth of a hollow.

(Evaluation of coverage)
The coverage of the conductive material (carbon) was determined by photographing the surface of a sample produced using a field emission scanning electron microscope (FE-SEM) SU-70 manufactured by Hitachi, Ltd. at a magnification of 300 times ( The area of the substrate surface covered with the conductive material contained in the 300 μm square area) was calculated by image processing.

(Foil strength)
The Al foil or Cu foil was cut into a size of 15 mm × 250 mm, and the tensile strength was determined by performing a test at a speed of 5 mm / min with a tensile tester according to JIS B 7721. Since the untreated Al foil had a tensile strength of 200 N / mm ² , 175 N / mm ² or more, which is 87.5% or more of the tensile strength, was judged as good (◯), and a case where it was smaller than that was judged as poor (x). The tensile strength of the untreated Cu foil because it was through 411N / mm ^2, the tensile 87.5% or more of strength 360N / mm ² or more good (○), the smaller than bad (×) did. The tensile strength was calculated from the maximum tensile force and the cross-sectional area of the foil.

(Adhesion evaluation)
On Al foil or Cu foil prepared by applying a roller (diameter: 90 mm, length: 50 mm, mass: 700 g) with an adhesive strength of 1 N / 20 mm (40 mm width x 120 mm length x 0.08 mm thickness) Was rolled 10 cm, and then the peeled area was estimated (estimated). When there was no peeling at all, it was judged as very good (◯), when 20% or less peeling was observed (Δ), and when more peeling was observed, it was judged as bad (x).

(Internal resistance required from battery evaluation)
When an Al foil was used as the substrate, a battery cell using the Al foil as a current collector was prepared, and evaluation was performed by measuring its internal resistance.
A slurry in which lithium cobaltate, acetylene black, and PVdF (polyvinylidene fluoride) were mixed was applied to a surface (one side) of a sample on which a conductive material (carbon) was disposed to a thickness of 25 μm to produce a positive electrode material. Moreover, as a negative electrode material, what coated graphite with the thickness of 35 micrometers on the single side | surface of Al foil was used.

Using these positive electrode and negative electrode, a battery cell was manufactured using an HS flat cell manufactured by Hosen. This battery cell was subjected to a conditioning charge / discharge treatment for 3 cycles at a current of charge / discharge rate of 0.2C, and then a discharge test was performed at a plurality of current values of 0.2C to 10C. In the discharge curve of each current value obtained by the discharge test, the relationship between the current value and the voltage value when discharging a capacity of 1 mAh was plotted, and the internal resistance was calculated based on the slope of the straight line obtained by plotting. .

In addition, using only a 15 μm-thick Al foil base material having no conductive material as a current collector, a positive electrode is produced in the same manner as other samples, and a battery cell is produced in the same manner using this positive electrode. did. About this battery cell, the discharge curve was measured similarly to the battery cell using another sample, and internal resistance was computed. And what reduced internal resistance compared with the internal resistance of the battery cell produced using the collector only of this base material was determined to have the effect of reducing internal resistance. In addition, the internal resistance of the battery cell produced using only the Al foil as the base material as a current collector was 45Ω.

(Evaluation of contact resistance)
About the resistance reduction effect at the time of using Cu foil as a base material, it measured as follows.
Both sides of the sample are sandwiched between two carbon cloths, and the outside is sandwiched between two copper electrodes with a contact area of 1 cm ^2. A pressure of 1 kgf (9.8 N) is applied to the copper electrodes, and a direct current power supply is applied. A current of 7.4 mA was applied using a voltmeter, and the voltage applied between the carbon cloths was measured with a voltmeter. The contact resistance was calculated from the above-described current value, contact area, and measured voltage. The same measurement was performed using only the base material, and it was determined that there was an effect of reducing the contact resistance when the contact resistance was reduced compared to the case of only the base material. In addition, the contact resistance in the case of only Cu foil which did not perform any surface treatment was 98 mΩ · cm ² .

(Evaluation of weldability 1)
Evaluation of weldability to Al foil was made by stacking 10 samples each having a conductive material (carbon) on both sides of a 15 μm thick Al foil, and 30 μm thick Al foil and 250 μm Al on the upper and lower sides (both ends). A plate was placed and welding was performed with a constant pressure applied, and it was determined that 8 or more pieces were welded as good (◯), and 7 or less pieces were welded as bad (x).
For the welding, an ultrasonic welding machine MH2026 / CLF2500 manufactured by Sonobond Co., Ltd. was used, and welding was performed with a current supply time of 70 μsec under the conditions of a pressure of 0.28 MPa, a power of 400 W, and an energy of 20 J.

(Evaluation of weldability 2)
Evaluation of weldability to Cu foil is made by stacking 10 samples with conductive material (carbon) on both sides of a 15 μm thick Cu foil, welding under a constant pressure, and welding 8 or more sheets. The test piece was judged as good (◯), and the case where only 7 or less pieces were welded was judged as bad (x).
For welding, Yokodai. Using a spot welder HSW-02A manufactured by jp, welding was performed at a voltage of 25 V and an energization time of 500 μsec.

Table 1 shows a list of production conditions and characteristic evaluation results of the produced samples. In Table 1, numerical values outside the range defined by the present invention and numerical values whose characteristic evaluation does not satisfy the acceptance criteria are underlined.
In each of the obtained samples, the conductive material was arranged in an island shape on the surface of the Al foil or Cu foil when observed in a 300 μm square field of view.

Sample No. Since 1-3, 7, and 8 satisfy the requirements defined by the present invention, the foil strength, adhesion, internal resistance, and weldability were all good or better.

Sample No. In No. 4, no depression was formed, so that adhesion could not be obtained. Sample No. No. 4 was a result of good weldability. Compared with 1-3, the results were slightly inferior.

Sample No. 5 is roughened with a relatively rough sandpaper, but the rolling reduction after the roughening was not sufficient, the average depth of the dent becomes deeper than the average depth defined by the present invention, sufficient The foil strength could not be obtained.

Sample No. Nos. 6 and 9 were not sufficient in rolling reduction after roughening, so that the flat portion of the metal foil was not sufficiently formed, and the coverage of the conductive material was higher than the coverage defined in the present invention, which was good Tab weldability could not be obtained.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made as long as they are described in the claims. .
This application is based on a Japanese patent application filed on October 26, 2011 (Japanese Patent Application No. 2011-234528) and a Japanese patent application filed on September 18, 2012 (Japanese Patent Application No. 2012-204167). Incorporated herein by reference.

According to the electrode material according to the present invention, the conductive material is arranged in an island shape on the surface of the metal foil as a base material, and the coverage of the conductive material is limited to partially expose the metal foil substrate on the surface of the electrode material. By doing so, it is possible to ensure tab weldability and reduce the contact resistance of the electrode material.
In addition, by arranging the conductive material in the depression formed on the surface of the base material, the contact area between the base material and the conductive material can be increased, and as a result, the adhesion of the conductive material to the base material can be improved. In addition to the improvement, the contact resistance of the electrode material can be further reduced.
Furthermore, by arranging the conductive material in the depression formed on the substrate surface, the electrode material can be made thinner compared to the case where the conductive material is formed in layers on the substrate surface. The amount of the active material layer per unit volume is not greatly limited, and a reduction in battery capacity can be avoided.
According to the electrode and the secondary battery of the present invention, by providing the predetermined electrode material, the contact resistance between the electrode material and the active material layer can be reduced, the internal resistance of the battery can be reduced, and the tab It is possible to improve the weldability and reduce the thickness.
According to the method for manufacturing an electrode material according to the present invention, by forming a plurality of depressions on the surface of the base material and arranging the conductive material in the depressions, the conductive material can be arranged in an island shape on the surface of the base material. In addition to reducing contact resistance, an electrode material having excellent tab weldability can be produced.
According to the method for producing an electrode material according to the present invention, the contact resistance is further increased because the adhesion between the base material and the conductive material is improved by arranging the conductive material in the plurality of depressions formed on the surface of the base material. An electrode material that can be reduced and made thinner can be manufactured.
According to the method for producing an electrode material according to the present invention, the tab weldability can be improved by rolling the base material after the conductive material arranging step to form a flat portion to which no conductive material is adhered. In addition, the adhesion of the conductive material to the substrate can be improved, and the contact resistance can be reduced.

1 Current collector (electrode material)
DESCRIPTION OF SYMBOLS 1a Base material 1b Conductive material 2 Active material layer 10 Electrode 11 Positive electrode (electrode)
12 Negative electrode (electrode)
13 Separator 14 Electrolyte 20 Lithium ion secondary battery (secondary battery)

Claims (10)

1. An electrode material comprising a base material including a metal foil and a conductive substance disposed on at least one surface of the base material,
   The surface of the substrate is composed of a flat portion and a plurality of depressions,
   The average depth of the depression is 0.3 μm or more and 3.0 μm or less,
   The conductive material is disposed in the depression, the flat portion is exposed,
   When observed in a 300 μm square field of view, the conductive material is arranged in an island shape on the surface of the substrate, and the coverage of the surface of the substrate with the conductive material is 1 to 80%. An electrode material characterized by.
2. The electrode material according to claim 1, wherein the metal foil is made of aluminum, an aluminum alloy, copper, or a copper alloy.
3. 2. The electrode material according to claim 1, wherein the conductive material includes a carbon-based material.
4. 3. The electrode material according to claim 2, wherein the conductive substance includes a carbon-based material.
5. A secondary battery electrode,
   An electrode material according to claim 1;
   An electrode of a secondary battery, comprising: an active material layer formed on a surface of the inducer of the electrode material.
6. A secondary battery comprising a positive electrode and a negative electrode,
   The secondary battery according to claim 5, wherein at least one of the positive electrode and the negative electrode is the electrode according to claim 5.
7. It is a manufacturing method of the electrode material according to claim 1,
   Forming a plurality of depressions on the surface of the substrate; and
   And a conductive substance arranging step of arranging the conductive substance in the formed recess.
8. The said dent formation process is a process of forming the said some dent on the surface of the said base material by pressing the transfer body which has a some convex part on the said base material, The said recessed part is a process characterized by the above-mentioned. Manufacturing method of electrode material.
9. 9. The method according to claim 8, further comprising a crimping step of pressing the conductive material in the depression by pressing the base material on which the conductive substance is arranged in the depression after the conductive substance arranging step. The manufacturing method of the electrode material as described in any one of.
10. The indentation forming step is a step of forming a plurality of indentations on the surface of the base material by roughening the surface of the base material.
    The electrode according to claim 7, further comprising a rolling step of forming the flat portion by rolling the base material on which the conductive material is disposed in the depression after the conductive material disposing step. Material manufacturing method.

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