JP2014107194A - Current collector material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current collector material in which the surface of aluminum as a current collector material is modified to improve adhesion with an active material and electrical resistance caused between the current collector and a coat containing the active material can be reduced.SOLUTION: Electrical resistance caused between a current collector and a coat containing an active material can be reduced by using a current collector material including a zinc coat formed on the surface of aluminum used in the current collector and a chromium coat on the zinc coat. Further, in the current collector material, the surface of aluminum is modified after removing an oxide film on the surface of aluminum, the oxide film being a factor of internal resistance.

Description

  The present invention relates to a current collector material for an electricity storage device, and examples of the electricity storage device include a secondary battery and a capacitor, and more specifically, a lithium ion secondary battery and a lithium ion capacitor.

  Aluminum, which is mainly used as a positive electrode current collector in lithium ion secondary batteries and lithium ion capacitors, has a strong oxide film on the surface under normal handling, and therefore has good adhesion regardless of organic or inorganic materials. It is a low metal, and the active material layer deposited on the aluminum foil may peel off due to repeated expansion and contraction due to handling in the manufacturing process and charge / discharge during use. Furthermore, the oxide film on the aluminum surface causes an increase in internal resistance of the electricity storage device, which is a problem. Recently, lithium ion secondary batteries using lithium iron phosphate as a positive electrode active material have been developed. In some cases, a paste containing an active material is used as an aqueous paste. There is a current situation where it is more difficult to maintain the adhesion as compared.

  As a means for improving the adhesion between the active material layer and the current collector, a method of providing an adhesive layer between the current collector and the active material layer is known (Patent Documents 1 to 3). Patent Document 1 proposes a method using an adhesive layer composed of carbon fine particles and an ion-permeable compound that is not swellable with respect to an organic solvent. Patent Document 2 discloses a carbon-containing adhesive layer on the surface of an aluminum foil. There has been proposed a method of forming an aluminum carbide between the adhesive layer and the surface of the aluminum foil by heat treatment in a low oxygen state. Patent Document 3 proposes a method in which boehmite treatment is performed on the surface of an aluminum foil to form an adhesive layer having an anchor effect on the positive electrode material.

JP 2010-135338 A JP 2008-283152 A Patent 4250809

  However, the method of providing an adhesive layer between the current collector and the active material layer is considered to improve the adhesion between the current collector and the adhesive layer and between the adhesive layer and the active material layer. The adhesion between the body and the adhesive layer cannot be said to be sufficient, and the adhesive layer itself is a factor that increases the internal resistance.

  Therefore, the present invention can modify the surface of the aluminum, which is a current collector material, to improve the adhesion to the active material, and reduce the electrical resistance generated between the current collector and the coating containing the active material. A current collector material is provided. Furthermore, the present invention provides a current collector material obtained by modifying the aluminum surface after removing the oxide film on the aluminum surface, which is one of the main causes of internal resistance.

The present invention comprises the following items.
Item 1.
A current collector material for an electricity storage device, wherein zinc or a zinc composition coating is formed on an aluminum or aluminum alloy surface, and further chromium or a chromium composition coating is formed thereon.
Item 2.
Item 2. The current collector material for an electricity storage device according to Item 1, wherein the aluminum or aluminum alloy to be used is an oxide film removal-treated product in advance.
Item 3.
Item 3. The current collector material for an electricity storage device according to Item 1 or 2, wherein the zinc or zinc composition film is formed using a zincate treatment method.
Item 4.
Item 4. The current collector material for an electricity storage device according to any one of Items 1 to 3, wherein the chromium or chromium composition film is formed using a chromate treatment method.
Item 5.
Item 5. The current collector material for an electricity storage device according to any one of Items 1 to 4, wherein the thickness of the zinc or zinc composition coating is 0.01 μm or more and 5 μm or less.
Item 6.
Item 6. The current collector material for an electricity storage device according to any one of Items 1 to 5, wherein the chromium or chromium composition film has a thickness of 0.01 µm to 5 µm.

By using aluminum whose surface has been modified according to the present invention as a current collector, adhesion to the active material is improved, and electric resistance generated between the current collector and the film containing the active material is reduced. . Furthermore, in the current collector material in which the aluminum surface is modified after removing the oxide film on the aluminum surface, even better results can be obtained particularly in terms of reducing electric resistance. This gives good output characteristics.
The material provided in the present invention is not limited to the positive electrode material of a lithium ion secondary battery, and can be used as a material for a positive electrode and a negative electrode of an electricity storage device including a primary battery, a secondary battery, a capacitor, and the like.

  Hereinafter, preferred embodiments of the present invention will be described.

  The aluminum foil used in the present invention is not particularly limited, and pure aluminum or an aluminum alloy can be used. Aluminum used in the present invention is composed of lead (Pb), silicon (Si), iron (Fe), copper (Cu), manganese (Mn), magnesium (Mg), chromium (Cr), zinc (Zn). ), Titanium (Ti), vanadium (V), gallium (Ga), nickel (Ni) and boron (B) at least one alloy element added within the necessary range, or the above inevitable impurities Also includes aluminum with limited elemental content. In addition, when using pure aluminum as an aluminum foil, it is preferable that the purity is 99.3% or more.

  The thickness of the aluminum foil is not particularly limited, but is preferably in the range of 5 μm or more and 100 μm or less from the balance between the mechanical strength of the foil and the storage capacity. Further, the foil may have a hole and is not particularly limited.

  What was manufactured by a well-known method can be used for said aluminum foil. For example, a molten aluminum or aluminum alloy having the above predetermined composition is prepared, and an ingot obtained by casting this is appropriately homogenized. Thereafter, an aluminum foil can be obtained by subjecting the ingot to hot rolling and cold rolling. In addition, you may perform an intermediate annealing process in the range of 150 degreeC or more and 400 degrees C or less in the middle of said cold rolling process.

  Zinc or a zinc composition can be used for the zinc coating covering the surface of the aluminum foil. Examples of the zinc composition include 90% by weight or more of zinc, and a composition containing one or more elements such as copper, nickel, and iron in addition to zinc.

  The method for forming the zinc or zinc composition coating is not particularly limited as long as it is a plating method that is usually used, and specific examples include dry plating or wet plating.

  As dry plating, zinc or a zinc composition film having good adhesion to aluminum can be obtained by sputtering. Moreover, you may use combining the method of using reverse sputtering as pre-processing in a vacuum. In either case, the oxide film removal, which is a wet pretreatment described below, is performed as the pretreatment. Further, in combination with the removal of the oxide film, a pretreatment such as degreasing and roughening treatment may be used in combination.

  As the wet plating, a zincate treatment using a zinc bath containing an alkaline aqueous solution can be used. In addition to performing oxide film removal as a pretreatment for zincate treatment, zinc plating is displacement plating, and zinc in the zinc bath is replaced with zinc to form a zinc or zinc composition coating, so that the final plating A zinc or zinc composition coating can be formed while removing the thin oxide coating remaining in stages. The zincate treatment is optimal as a method for forming a zinc or zinc composition coating after removing the oxide coating, and is most suitable as a method for producing a current collector material provided in the present invention. Further, a roughening treatment of the aluminum surface can be added as a pretreatment for the zincate treatment.

  The zincate treatment includes at least a step of immersing aluminum in a zinc bath to replace zinc, and it is preferable that a degreasing step, an oxide film removal (etching) step, and a smut removal step are appropriately performed as pretreatment steps. The zinc bath refers to a zinc replacement treatment bath containing at least zinc oxide and appropriately containing sodium hydroxide, Rochelle salt and sodium sulfate as components.

  The degreasing step is a step of removing oil adhering to the surface of aluminum or aluminum alloy, and is generally performed with an alkaline solution using a sodium salt and a surfactant. Examples of the sodium salt include sodium phosphate, sodium metaphosphate, sodium metasilicate, sodium orthophosphate, sodium carbonate, sodium bicarbonate and the like, preferably sodium phosphate and sodium metasilicate. As the surfactant, nonionic surfactants such as fatty acid diethanolamide, isopropanolamide and polyoxyethylene fatty acid ester, and anionic surfactants such as alkylbenzenesulfonic acid and alkylallylsulfonic acid can be used. The treatment is preferably performed at 50 ° C. to 70 ° C. for 1 minute to 5 minutes.

  The oxide film removal (etching) step is a step of removing the oxide film by etching aluminum or an aluminum alloy with an alkaline solution or acid, and can be performed using sodium hydroxide, hydrochloric acid, or the like. The oxide film removal (etching) step is preferably performed after the degreasing step (preferably through a washing process). When using sodium hydroxide, the treatment is preferably carried out at 50 to 60 ° C. for 0.5 to 1 minute, and when using hydrochloric acid, it is preferably carried out at 30 to 40 ° C. for 1 to 3 minutes.

  The smut removal step is a step of removing impurities (silicon dioxide, magnesium oxide) contained in the smut (aluminum oxide, aluminum), aluminum or aluminum alloy generated during the removal of the oxide film, and the oxide film removal (etching) step. (Preferably through a washing process). In general, nitric acid and fluoride can be used, and the treatment is preferably performed at 20 to 30 ° C. for 10 to 60 seconds.

  The zinc replacement step is a step in which the thin remaining oxide film is removed and zinc is replaced and deposited on the newly exposed active surface, and is preferably performed after the smut removal step (preferably through a water washing step). The treatment is preferably performed at 20 to 40 ° C. for 10 to 60 seconds.

  In the zincate treatment, it is preferable to perform the zinc substitution step twice or more (in this application, a double zincate treatment). Double zincate treatment is preferable in that zinc is densely coated on the aluminum or aluminum alloy surface. When the zinc replacement step is performed twice, after the above zinc replacement step (preferably through the water washing treatment step), an acid immersion step is performed (preferably through the water washing treatment step), and the zinc replacement step is performed again. Preferably it is done.

  The thickness of the zinc or zinc composition coating on the surface of the aluminum foil is not particularly limited as long as the object of the present invention can be achieved, but is in the range of 0.01 μm or more and 5 μm or less from the relationship between the moldability of the coating and the internal electrical resistance. And most preferably 0.1 μm or more and 1 μm or less.

  As the chromium film covering the surface of the aluminum foil covered with zinc or the zinc composition film, chromium or a chromium composition can be used. Examples of the chromium composition include 90% by weight or more of chromium, and a composition containing one or more elements such as cobalt, zinc, and silicon in addition to chromium.

  The chromium or chromium composition film can be formed by a chromate treatment, and any of an etching method, an electrolytic method, and a coating method can be selected, but an etching method is preferable from the viewpoint of solubility and corrosion resistance. Examples of the etching chromate treatment include a chromate chromate treatment and a phosphoric acid chromate treatment.

  In the etching chromate treatment, it is preferable to perform an alkali or acid dipping step (preferably through a water washing treatment step) and a chromium replacement step. The treatment is preferably carried out at 15 to 70 ° C. for 3 to 60 seconds by immersion in a chromium bath or spraying with a liquid.

  The thickness of the chromium or chromium composition film on the surface of the aluminum foil is not particularly limited as long as the object of the present invention can be achieved, but is in the range of 0.01 μm or more and 5 μm or less from the relationship between the formability of the film and the internal electrical resistance. Is preferable, and 0.05 to 1 μm is most preferable.

  Evaluation of the current collector material for an electricity storage device of the present invention was performed by forming a known active material layer on the current collector material of the present invention and using a known separator, electrolytic solution, electrolyte, etc. Can be done using.

EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated concretely, this invention is not limited to the following Example.
Example 1

An aluminum foil (JIS H-4000 A1085-H18) having a thickness of 30 μm was prepared, and the following zincate treatment and chromate treatment were performed. The zincate treatment was a double zincate treatment in which zinc substitution was performed twice. The conditions for the zincate treatment and the chromate treatment are shown in Table 1. The thickness of the coating is measured by scanning electron microscope (SEM) observation, the zinc coating after the double zincate treatment is in the range of 0.5 to 0.8 μm, and the chromium coating after the chromate treatment is in the range of 0.4 to 0.6 μm. Met.
Alkaline degreasing → Washing → Etching → Smut removal → Washing → Zinc replacement → Washing → Acid soaking → Washing → Zinc replacement → Washing → Acid soaking → Washing → Chrome replacement → Washing In the following examples and comparative examples, 30 μm thick aluminum A foil (JIS H-4000 A1085-H18) was used.

Next, a positive electrode active material layer having a thickness of 50 μm was formed using a positive electrode paste made of a positive electrode active material, a conductive additive, a binder, and a solvent, to obtain a positive electrode. At this time, lithium iron phosphate was used as the positive electrode active material, acetylene black was used as the conductive assistant, styrene-butadiene rubber / carboxymethylcellulose sodium salt (weight ratio 2/1) was used as the binder, and water was used as the solvent. The composition ratio of each component was positive electrode active material: conducting aid: binder: solvent = 48: 3: 1: 48 (weight ratio). The negative electrode active material is made of natural graphite, a negative electrode paste made of conductive auxiliary agent: binder: solvent = 48: 3: 1: 48 (weight ratio) is formed on the copper foil of the negative electrode current collector, did. Furthermore, a separator was incorporated between the positive electrode and the negative electrode, and these were impregnated with an organic electrolyte solution to obtain a 2032 type coin cell lithium ion secondary battery.
(Example 2)

The aluminum foil was subjected to zincate treatment and chromate treatment in the following steps. The conditions for the zincate treatment and the chromate treatment are shown in Table 1. The thickness of the coating was in the range of 0.5 to 0.8 μm for the zinc coating after the double zincate treatment, and in the range of 0.4 to 0.6 μm for the chromium coating after the chromate treatment.
Alkaline degreasing → Washing → Etching → Smut removal → Washing → Zinc replacement → Washing → Acid soaking → Washing → Zinc replacement → Washing → Acid soaking → Washing → Chrome replacement → Washing The difference between Example 1 and Example 2 is the zincate treatment In this etching, sodium hydroxide was used in Example 1, and hydrochloric acid was used in Example 2. The surface roughness of the aluminum foil surface could be increased by changing the etching agent. In this way, an aluminum foil subjected to the zincate treatment was prepared, and a lithium ion secondary battery was produced by the method shown in Example 1.
(Comparative Example 1)

The zinc foil was only subjected to zincate treatment in the following steps. The conditions for the zincate treatment are shown in Table 1.
Alkaline degreasing → Washing → Etching → Smut removal → Washing → Zinc replacement → Washing → Acid soaking → Washing → Zinc replacement → Washing In this way, an aluminum foil only subjected to zincate treatment was prepared and subjected to the method shown in Example 1. A lithium ion secondary battery was produced.
(Comparative Example 2)

Only the chromate treatment was performed on the aluminum foil in the following steps. The conditions for the zincate treatment are shown in Table 1.
Alkaline degreasing → Washing → Etching → Smut removal → Washing → Chromium replacement → Washing In this way, an aluminum foil subjected only to chromate treatment was prepared, and a lithium ion secondary battery was produced by the method shown in Example 1.
(Comparative Example 3)

  A lithium ion secondary battery was obtained by the method shown in Example 1 without coating the surface of the aluminum foil with zinc or chromium coating.

  For each sample of Examples 1 and 2 and Comparative Examples 1 to 3 produced as described above, the adhesion between the active material layer and the current collector material, the internal resistance of the secondary battery, and the charge / discharge cycle characteristics evaluated. The evaluation results are shown in Table 2.

  The adhesion between the active material layer and the current collector material is prepared by preparing a positive electrode plate in which a positive electrode active material layer is formed on the current collector material prepared by the methods of Examples 1 and 2 and Comparative Examples 1 to 3. Then, according to JIS K-5600-5-6, a 25 square lattice pattern (cut interval 2 mm) was subjected to a cross-cut method test, and the peeled state was evaluated in 6 stages of 0-5. The smaller the number, the better the adhesion.

  The charge / discharge cycle characteristics were evaluated for lithium ion secondary batteries prepared by the methods of Examples 1 and 2 and Comparative Examples 1 to 3, respectively. The voltage range was 2.5 to 3.8V. In the measurement, the capacity reduction rate was shown as a percentage by comparing the initial 3rd cycle and the 500th cycle at 25 ° C. and 1C. The lower the capacity reduction rate, the better the lithium ion secondary battery.

  The internal resistance was measured for lithium ion secondary batteries prepared by the methods of Examples 1 and 2 and Comparative Examples 1 to 3. The measurement method was an alternating current four-terminal method, and was measured at a frequency of 1 kHz and 10 mA. The smaller the resistance value, the better the lithium ion secondary battery.

  From the results of Table 2, in the case where lithium iron phosphate was used as the positive electrode active material, the adhesion of the positive electrode active material layer to the aluminum foil was improved in Examples 1 and 2 as compared with Comparative Examples 1 and 3. It was shown that the resistance was kept low. From the results of the capacity reduction rate, it was shown that the cycle characteristics of the lithium ion secondary battery were improved by applying the aluminum foil current collector having both coatings, rather than only the zinc coating and the chromium coating alone. By further providing a chromium coating on the zinc coating, the adhesion to the positive electrode active material is improved compared to the zinc coating, and the internal resistance is suppressed to a low level, which is considered to be effective in the cycle life of the battery.

The present invention provides a current collector capable of reducing the internal resistance of a power storage device and improving the cycle life. In recent electricity storage devices, reduction of internal resistance is an important issue in the field of automobiles and the like that require faster charging and discharging. The current collector of the present invention is suitable for application to an electricity storage device mounted on an automobile.

Claims (6)

  A current collector material for an electricity storage device, wherein zinc or a zinc composition coating is formed on an aluminum or aluminum alloy surface, and further chromium or a chromium composition coating is formed thereon.   2. The current collector material for an electricity storage device according to claim 1, wherein the aluminum or aluminum alloy to be used is an oxide film removal-treated product in advance.   The current collector material for an electricity storage device according to claim 1 or 2, wherein the zinc or zinc composition film is formed using a zincate treatment method.   The current collector material for an electricity storage device according to any one of claims 1 to 3, wherein the chromium or chromium composition film is formed using a chromate treatment method.   The current-collector material for an electricity storage device according to any one of claims 1 to 4, wherein the thickness of the zinc or zinc composition coating is 0.01 µm or more and 5 µm or less.   The current collector material for an electricity storage device according to any one of claims 1 to 5, wherein the chromium or chromium composition film has a thickness of 0.01 µm or more and 5 µm or less.