JP2022190788A - Manufacturing method for bipolar current collector - Google Patents

Abstract

To provide a bipolar current collector capable of suppressing reduction in the stability of operation of a power storage device in the reaction potential of a negative electrode active material.SOLUTION: A manufacturing method for a bipolar current collector includes an oxide film forming step for forming an oxide film 13 on the surface of a negative electrode current collector 12 in a composite material including a positive electrode current collector 11 having an aluminum layer 11a and a negative electrode current collector 12 having a copper layer 12a. The oxide film 13 includes an oxide of at least one specific metal M selected from Sc, Y, Ca, Er, Tm, Ho, Lu, Dy, Be, Sm, Yb, Nd, Mg, Ce, and La.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for manufacturing a bipolar current collector.

In recent years, research has been conducted on power storage devices using bipolar electrodes. The bipolar electrode includes a bipolar current collector having a positive electrode current collector and a negative electrode current collector, a positive electrode active material layer provided on the surface of the positive electrode current collector, and a negative electrode active material provided on the surface of the negative electrode current collector. a layer; Power storage devices using bipolar electrodes are expected to be superior to other power storage devices in terms of improvement in volumetric energy density and output.

Patent Literature 1 discloses a bipolar electrode in which a clad material obtained by rolling an aluminum foil with a thickness of 20 μm and a copper foil with a thickness of 10 μm is used as a bipolar current collector. In the case of the bipolar current collector of Patent Document 1, an aluminum layer formed by rolling an aluminum foil serves as a positive electrode collector, and a copper layer formed by rolling a copper foil serves as a negative electrode collector.

Japanese Patent Application Laid-Open No. 08-007926

From the viewpoint of reducing the weight of a power storage device using bipolar electrodes and improving the volume energy density, it is preferable to form a thin bipolar current collector. As a method for thinning the bipolar current collector, for example, in the case of the bipolar current collector of Patent Document 1, the copper layer formed by rolling a copper foil having a thickness of 10 μm is changed to a copper plating layer. Therefore, it is conceivable to thin the negative electrode current collector composed of the copper layer. However, as the thickness of the copper layer is reduced, pinholes are more likely to occur in the copper layer, and new problems caused by pinholes arise.

For example, consider applying the bipolar current collector of Patent Document 1 to a power storage device using lithium ions as charge carriers. In this case, if there are pinholes in the copper layer of the bipolar current collector, the lithium ions passing through the pinholes in the copper layer react with the aluminum layer, corroding the aluminum layer. When the aluminum layer corrodes excessively, the voltage does not drop to the reaction potential of the negative electrode active material, and the operation of the power storage device becomes unstable at the reaction potential of the negative electrode active material.

A method for producing a bipolar current collector of the present invention is a method for producing a bipolar current collector used for a bipolar electrode provided with a negative electrode active material layer containing a negative electrode active material capable of intercalating and deintercalating lithium ions, wherein aluminum an oxide film forming step of forming an oxide film containing a metal oxide on the surface of the negative electrode current collector in a composite material comprising a positive electrode current collector having a layer and a negative electrode current collector having a copper layer; The coating contains at least one metal oxide selected from Sc, Y, Ca, Er, Tm, Ho, Lu, Dy, Be, Sm, Yb, Nd, Mg, Csze and La.

In the method for manufacturing a bipolar current collector, the oxide film forming step includes heating a mixed solution obtained by mixing a metal salt of the metal and a solvent capable of dissolving the metal salt, and applying a chemical conversion treatment solution to the negative electrode. It is preferable that the step be a step of heating in a state of adhering to the surface of the current collector.

In the method for producing a bipolar current collector, the chemical conversion treatment liquid preferably further contains one or both of a basic compound and a Lewis acid.
In the method for manufacturing a bipolar current collector, the copper layer is preferably a plated layer.

ADVANTAGE OF THE INVENTION According to this invention, the bipolar collector which can suppress the deterioration of the stability of the operation|movement of an electrical storage apparatus in the reaction potential of a negative electrode active material is manufactured.

Sectional drawing of a bipolar electrode.

An embodiment embodying the present invention will be described below with reference to the drawings.
<Bipolar current collector>
First, referring to FIG. 1, a bipolar current collector 10 manufactured by the manufacturing method of the present embodiment will be described.

The bipolar current collector 10 is a laminate in which a sheet-like positive electrode current collector 11 and a sheet-like negative electrode current collector 12 are integrally joined together in the thickness direction. The bipolar current collector 10 has a positive electrode active material layer 20 formed on a first main surface 10 a formed by a positive electrode current collector 11 , and a negative electrode active material layer 20 on a second main surface 10 b formed by a negative electrode current collector 12 . By forming the material layer 30, it can be used as a bipolar electrode of a power storage device. Bipolar current collector 10 is a chemically inert electrical conductor for continuing current flow through positive electrode active material layer 20 and negative electrode active material layer 30 during discharge or charge of the power storage device.

The positive electrode current collector 11 has, as an essential component, an aluminum layer 11a containing aluminum as a main component. The aluminum layer 11a may be a layer made of aluminum alone or a layer made of an aluminum alloy. Examples of aluminum alloys include Al--Mn alloys, Al--Mg alloys and Al--Mg--Si alloys. The content of aluminum in the aluminum layer 11a is, for example, 50% by mass or more, preferably 70% by mass or more. The form of the aluminum layer 11a is, for example, foil, sheet, or film. The thickness of the aluminum layer 11a is, for example, 10 μm or more and 100 μm or less.

Moreover, the positive electrode current collector 11 may be a single body composed only of the aluminum layer 11a, or may be a composite body including portions other than the aluminum layer 11a. FIG. 1 shows, as an example, a positive electrode current collector 11 composed only of an aluminum layer 11a.

Examples of the composite include a multilayer structure having an aluminum layer 11a on the first main surface 10a, and a substrate coated with an aluminum film corresponding to the aluminum layer 11a. Examples of materials that form portions other than the aluminum layer 11a include metal materials, conductive resin materials, and conductive inorganic materials. Examples of the metal material include titanium and stainless steel (eg, SUS304, SUS316, SUS301, SUS304, etc. defined in JIS G 4305:2015). Examples of the conductive resin material include a resin obtained by adding a conductive filler to a conductive polymer material or a non-conductive polymer material as necessary.

The negative electrode current collector 12 includes, as an essential component, a copper layer 12a containing copper as a main component. The copper layer 12a may be a layer made of copper alone or a layer made of a copper alloy. Examples of copper alloys include nickel silver, cupronickel, and beryllium copper. The content of copper in the copper layer 12a is, for example, 50% by mass or more, preferably 70% by mass or more.

The form of the copper layer 12a is, for example, a plated layer or foil. From the viewpoint of reducing the weight of the power storage device and improving the volumetric energy density, it is preferable to form the copper layer 12a thin. The thickness of the copper layer 12a is, for example, 8 μm or more and 20 μm or less. The thickness of the copper layer 12a in the case of being a plated layer is, for example, 1 μm or more and 10 μm or less, preferably 3 μm or more and 8 μm or less.

Further, the negative electrode current collector 12 may be a single body composed only of the copper layer 12a, or may be a multilayer structure including layers other than the copper layer 12a. Examples of the other layer include a nickel layer containing nickel as a main component. The other layers may be provided closer to the positive electrode current collector 11 than the copper layer 12a, or may be provided closer to the second main surface 10b than the copper layer 12a. FIG. 1 shows, as an example, a negative electrode current collector 12 having a two-layer structure including a copper layer 12a and a nickel layer 12b laminated on the surface of the copper layer 12a and forming the second main surface 10b. .

The nickel layer 12b may be a layer made of nickel alone or a layer made of a nickel alloy. Nickel alloys include, for example, Hastelloy, Nichrome, Monel, Sunplatinum, and Permalloy. The content of nickel in the nickel layer 12b is, for example, 50% by mass or more. The form of the nickel layer 12b is, for example, a plated layer or foil. The thickness of the nickel layer 12b is, for example, 8 μm or more and 20 μm or less. In addition, the thickness of the nickel layer 12b in the case of being a plated layer is, for example, 1 μm or more and 10 μm or less, preferably 3 μm or more and 8 μm or less.

As the bipolar current collector 10, for example, a clad metal or a plated aluminum foil subjected to a predetermined plating treatment can be used. Examples of the clad metal include clad metal obtained by rolling aluminum foil and copper foil, and clad metal obtained by rolling aluminum foil, copper foil and nickel foil. Examples of the plated aluminum foil include a copper-plated aluminum foil obtained by plating one side of an aluminum foil with copper, and a copper-nickel-plated aluminum foil obtained by sequentially plating one side of an aluminum foil with copper and nickel.

An oxide film 13 is provided on the surface of the negative electrode current collector 12 that is the second main surface 10 b of the bipolar current collector 10 . Oxide film 13 is provided on at least part of second main surface 10b, preferably on the entire second main surface 10b. FIG. 1 illustrates, as an example, the case where the oxide film 13 is provided over the entire second main surface 10b.

The thickness of the oxide film 13 is, for example, 10 μm or more, preferably 30 μm or more. Also, the thickness of the oxide film 13 is, for example, 500 μm or less, preferably 200 μm or less.

The oxide film 13 is a film containing a specific metal oxide. The metal oxide contained in the oxide film 13 is an oxide of a specific metal M selected from Sc, Y, Ca, Er, Tm, Ho, Lu, Dy, Be, Sm, Yb, Nd, Mg, Ce and La. is. The oxide of the specific metal M is a metal oxide whose activation energy is lower than the formation energy of lithium aluminum, which is a corrosion product. Here, Table 1 shows the differential value of the activation energy of the oxide of the specific metal M with respect to the formation energy of lithium aluminum. The numerical values shown in Table 1 were calculated using known literature and first-principles calculations. Moreover, the oxide film 13 may contain one kind of the above metal oxides alone, or may contain two or more kinds thereof.

酸化被膜１３における特定の金属酸化物の含有割合は、第２主面１０ｂにおける酸化被膜１３が設けられている部分を対象とする蛍光Ｘ線分析で測定される各成分の検出値に基づく特定金属Ｍの質量割合として規定される。例えば、酸化被膜１３に含有される金属酸化物が酸化マグネシウムである場合、蛍光Ｘ線分析で測定される各成分の検出値に基づくマグネシウムの質量割合として規定される。

The content ratio of the specific metal oxide in the oxide film 13 is the specific metal based on the detected value of each component measured by fluorescent X-ray analysis of the portion of the second main surface 10b where the oxide film 13 is provided. Defined as the mass fraction of M. For example, when the metal oxide contained in the oxide film 13 is magnesium oxide, it is defined as the mass ratio of magnesium based on the detection value of each component measured by fluorescent X-ray analysis.

The content of the specific metal M in the oxide film 13 is 1% by mass or more, preferably 1.5% by mass or more. The content of magnesium in the oxide film 13 is, for example, 30% by mass or less.

Assume that the second main surface 10b of the bipolar current collector 10 is formed of the copper layer 12a. In this case, the content ratio of the specific metal M in the oxide film 13 is, for example, 1 part by mass or more, preferably 1.5 parts by mass or more, as a relative value with the mass of copper based on the detected value being 100 parts by mass. Yes, more preferably 2 parts by mass or more. Moreover, the content ratio of the specific metal M in the oxide film 13 in this case is, for example, 30 parts by mass or less as the relative value.

Further, as shown in FIG. 1, the negative electrode current collector 12 of the bipolar current collector 10 has a two-layer structure of a copper layer 12a and a nickel layer 12b, and the second main surface 10b is formed of the nickel layer 12b. do. In this case, the content ratio of the specific metal M in the oxide film 13 is, for example, 1 part by mass or more, preferably 1.5 parts by mass, as a relative value with the total mass of copper and nickel based on the detected value being 100 parts by mass. parts or more, more preferably 2 parts by mass or more. Moreover, the content ratio of the specific metal M in the oxide film 13 in this case is, for example, 30 parts by mass or less as the relative value.

<Positive electrode active material layer and negative electrode active material layer>
Next, the positive electrode active material layer 20 and the negative electrode active material layer 30 formed on the bipolar current collector 10 will be described.

The positive electrode active material layer 20 includes a positive electrode active material capable of intercalating and deintercalating lithium ions as charge carriers. Examples of positive electrode active materials include polyanionic compounds such as olivine-type lithium iron phosphate (LiFePO ₄ ), lithium composite metal oxides having a layered rock salt structure, and metal oxides having a spinel structure. A positive electrode active material that can be used as a positive electrode active material for a power storage device such as a lithium ion secondary battery is employed.

The negative electrode active material layer 30 includes a negative electrode active material capable of intercalating and deintercalating charge carriers such as lithium ions. The negative electrode active material is not particularly limited as long as it is a simple substance, alloy, or compound that can occlude and release charge carriers such as lithium ions. Examples of negative electrode active materials include Li, carbon, metal compounds, elements that can be alloyed with lithium, and compounds thereof. Examples of carbon include natural graphite, artificial graphite, hard carbon (non-graphitizable carbon), and soft carbon (easily graphitizable carbon). Examples of artificial graphite include highly oriented graphite and mesocarbon microbeads. Elements that can be alloyed with lithium include, for example, silicon (silicon) and tin.

The positive electrode active material layer 20 and the negative electrode active material layer 30 may contain a conductive aid, a binder, an electrolyte (a polymer matrix, an ion-conductive polymer, a liquid electrolyte, etc.) for increasing electrical conductivity, an ion-conductive material, if necessary. It may contain other ingredients such as electrolyte-supporting salts (lithium salts) to increase the . The types of other components contained in the positive electrode active material layer 20 and the negative electrode active material layer 30 and their compounding ratios are not particularly limited.

Conductive aids include, for example, acetylene black, carbon black, and graphite.
Examples of binders include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins, Examples include acrylic resins such as poly(meth)acrylic acid, styrene-butadiene rubber, carboxymethylcellulose, alginates such as sodium alginate and ammonium alginate, water-soluble cellulose ester crosslinked products, and starch-acrylic acid graft polymers. These binders may be used singly or in combination. Water, N-methyl-2-pyrrolidone, and the like are used as the solvent or dispersion medium, for example.

The thickness of the positive electrode active material layer 20 and the negative electrode active material layer 30 is, for example, 2 to 150 μm.
Examples of a method for forming the positive electrode active material layer 20 and the negative electrode active material layer 30 on the first main surface 10a and the second main surface 10b of the bipolar current collector 10 include known methods such as roll coating.

<Manufacturing method of bipolar current collector>
Next, a method for manufacturing the bipolar current collector 10 will be described.
The manufacturing method of the bipolar current collector 10 includes an oxide film forming step of forming the oxide film 13 . In the oxide film forming step, a composite material including a positive electrode current collector 11 having an aluminum layer 11a and a negative electrode current collector 12 having a copper layer 12a is prepared. Then, an oxide film containing a specific metal oxide is formed on the surface of the composite material formed by the negative electrode current collector 12 .

The composite material used in the oxide film forming step is a laminate having a structure in which the oxide film 13 is removed from the bipolar current collector 10 described above. As the composite material, for example, a clad metal or a plated aluminum foil subjected to a predetermined plating treatment can be used. Examples of the clad metal include clad metal obtained by rolling aluminum foil and copper foil, and clad metal obtained by rolling aluminum foil, copper foil and nickel foil. Examples of the plated aluminum foil include a copper-plated aluminum foil obtained by plating one side of an aluminum foil with copper, and a copper-nickel-plated aluminum foil obtained by sequentially plating one side of an aluminum foil with copper and nickel.

In the oxide film forming step, first, a chemical conversion treatment solution to be used for chemical conversion treatment is prepared. The chemical conversion treatment solution is a mixture of a metal salt of a specific metal M selected from Sc, Y, Ca, Er, Tm, Ho, Lu, Dy, Be, Sm, Yb, Nd, Mg, Ce, and La, and a solvent. is obtained by filtering the precipitate after heat treatment. It is preferable to further mix one or both of a basic compound and a Lewis acid into the mixed solution. In this case, oxide film 13 can be formed more efficiently.

Examples of metal salts of the specific metal M include acetates, formates, carbonates, and metal ethoxides. The metal salt contained in the mixed solution may be one of the above specific examples, or may be a combination of two or more. The concentration of the metal salt in the mixed solution is, for example, 0.1 g/ml or more and 5 g/ml or less, preferably 0.5 g/ml or more and 3 g/ml or less.

As the solvent, a solvent capable of dissolving the metal salt to be mixed is appropriately selected and used. Examples of the solvent include water, ethanol, and acetic acid.
Examples of the basic compound include sodium hydroxide, lithium hydroxide, potassium hydroxide and sodium acetate. The basic compound contained in the liquid mixture may be one of the above specific examples, or may be a combination of two or more. The concentration of the basic compound in the mixture is, for example, 0.01 g/ml or more and 0.5 g/ml or less, preferably 0.05 g/ml or more and 0.1 g/ml or less.

Examples of the Lewis acid include boric acid, acetic acid, and calcium chloride. The Lewis acid contained in the mixed solution may be one of the above specific examples, or may be a combination of two or more. The concentration of the Lewis acid in the mixed solution is, for example, 0.1 g/ml or more and 5 g/ml or less, preferably 0.5 g/ml or more and 3 g/ml or less.

The heating temperature in the heat treatment is, for example, 20° C. or higher and 60° C. or lower, preferably 30° C. or higher and 50° C. or lower. The heating time in the heat treatment is, for example, 0.5 minutes or more and 10 minutes or less, preferably 1 minute or more and 5 minutes or less.

Next, using the obtained chemical conversion treatment solution, a chemical conversion treatment is performed to form an oxide film 13 on the surface formed by the negative electrode current collector in the composite material. The surface of the composite material on which the oxide film 13 is formed may be a metal surface, a surface on which an oxide film such as an anodized film is formed, or an alkali-treated surface. good too.

In the chemical conversion treatment, first, a first heat treatment is performed in a state in which the chemical conversion treatment liquid is adhered to the surface of the composite material. Examples of methods for applying the chemical conversion treatment solution include spray treatment and immersion treatment. The heating temperature in the first heat treatment is, for example, 20° C. or higher and 60° C. or lower, preferably 30° C. or higher and 50° C. or lower. The heating time in the first heat treatment is, for example, 0.5 minutes or more and 10 minutes or less, preferably 1 minute or more and 5 minutes or less.

After that, the chemical conversion treatment liquid remaining on the second main surface 10b of the composite material is removed by washing with water or the like, and a second heat treatment is performed to form the oxide film 13 and manufacture the bipolar current collector 10. be. The heating temperature in the second heat treatment is, for example, 20° C. or higher and 60° C. or lower, preferably 30° C. or higher and 50° C. or lower. The heating time in the second heat treatment is, for example, 0.5 minutes or more and 10 minutes or less, preferably 1 minute or more and 5 minutes or less.

(1) A method for manufacturing a bipolar current collector 10 is a composite material comprising a positive electrode current collector 11 having an aluminum layer 11a and a negative electrode current collector 12 having a copper layer 12a. An oxide film forming step for forming 13 is provided. The oxide film 13 contains at least one specific metal M oxide selected from Sc, Y, Ca, Er, Tm, Ho, Lu, Dy, Be, Sm, Yb, Nd, Mg, Ce and La.

According to the above configuration, when a pinhole exists in the copper layer 12a, the oxide film 13 is also formed inside the pinhole. The oxide of the specific metal M contained in the oxide film 13 has activation energy smaller than the formation energy of lithium aluminum, which is a corrosion product, and is stable against the reduction reaction by lithium. Corrosion of aluminum layer 11a is suppressed by oxide film 13 located in the pinhole acting as a lithium corrosion-resistant film. As a result, deterioration in stability of operation of the power storage device at the reaction potential of the negative electrode active material is suppressed. In addition, by suppressing deterioration in the stability of the operation of the power storage device, it becomes easier to form the copper layer 12a thinner, and the degree of freedom in designing the bipolar electrode is improved.

(2) In the oxide film forming step, a chemical conversion treatment liquid obtained by heating a mixed liquid obtained by mixing a metal salt of the specific metal M and a solvent capable of dissolving the metal salt is attached to the surface of the negative electrode current collector 12. It is a step of heating in a state of

According to the above configuration, the oxide film 13 can be easily formed.
(3) The chemical conversion treatment liquid further contains one or both of a basic compound and a Lewis acid.
According to the above configuration, it is easy to increase the content of the oxide of the specific metal M in the oxide film 13 .

(4) A composite material having a copper layer 12a composed of a plated layer is used.
As the copper layer 12a is formed thinner, pinholes are more likely to occur in the copper layer 12a. Therefore, when the copper layer 12a is a plated layer, the effect based on the oxide film 13 can be obtained more remarkably.

Examples that further embody the above embodiment will be described below.
(Production of composite material A)
A test piece for plating treatment was obtained by attaching an aluminum foil having a thickness of 15 μm to a SUS plate using a masking tape so that an aluminum surface of 70 mm×70 mm was exposed.

The exposed aluminum surface of the test piece was degreased by treating it with an aqueous solution of Top Alclean 101 from Okuno Pharmaceutical Co., Ltd. at 60° C. for 5 minutes. After degreasing, the test piece was washed with water and etched by treating it with an aqueous solution of Top Alsoft 108 manufactured by Okuno Pharmaceutical Co., Ltd. at 55° C. for 1 minute. After the etching, the test piece was washed with water and treated with Top Desmut N-20 from Okuno Pharmaceutical Co., Ltd. for 1 minute at room temperature to remove the smut.

Next, the test piece was washed with water and treated with an aqueous solution of Substar ZN-291 from Okuno Pharmaceutical Co., Ltd. for 1 minute at room temperature to replace the surface with zinc. The test piece after substitution was washed with water, and the zinc was stripped off once with an aqueous nitric acid solution, and then treated with an aqueous solution of Substar Zn-291 at room temperature for 1 minute to perform zinc substitution again.

A copper plating bath was prepared by making copper sulfate 150 g/L, sulfuric acid 150 g/L, and hydrochloric acid 80 ppm, and adding Top Lucina SF Base WR, Top Lucina SF-B, and Top Lucina SF Leveler manufactured by Okuno Seiyaku Co., Ltd. as additives. A test piece was immersed in the prepared plating bath, and copper plating was formed on the surface of the test piece using phosphorous copper as an anode at room temperature at a current density of 2 A/dm ² for 2 minutes. A composite material A was obtained by washing the plated test piece with water and applying an antirust treatment using Okuno Seiyaku Co., Ltd. Top Rinse.

(Test example 1)
After adding 2 g of magnesium ethoxide and 1.05 g of acetic acid to 9 ml of water and performing heat treatment at 60° C. for 2 hours, a chemical conversion treatment liquid A was obtained by filtering the precipitate. A first heat treatment was performed at 60° C. for 5 minutes while the composite material A was immersed in the chemical conversion treatment solution A. The composite material A after the first heat treatment was washed with water and subjected to a second heat treatment at 120° C. for 1 hour to obtain a bipolar current collector of Test Example 1.

(Test example 2)
After adding 2 g of magnesium acetate, 50 mg of sodium hydroxide and 77 mg of boric acid to 8 ml of water and performing heat treatment at 60° C. for 2 hours, a chemical conversion treatment liquid B was obtained by filtering the precipitate. A first heat treatment was performed at 60° C. for 5 minutes while the composite material A was immersed in the chemical conversion treatment solution B. The composite material A after the first heat treatment was washed with water and subjected to a second heat treatment at 120° C. for 1 hour to obtain a bipolar current collector of Test Example 2.

(Test example 3)
After adding 2 g of magnesium acetate and 50 mg of calcium chloride to 8 ml of water and performing heat treatment at 60° C. for 2 hours, a chemical conversion treatment liquid C was obtained by filtering the precipitate. A first heat treatment was performed at 60° C. for 5 minutes while the composite material A was immersed in the chemical conversion treatment solution C. The composite material A after the first heat treatment was washed with water and subjected to a second heat treatment at 120° C. for 1 hour to obtain a bipolar current collector of Test Example 3.

(Test example 4)
After adding 2 g of magnesium acetate to 8 ml of water and performing heat treatment at 60° C. for 2 hours, a chemical conversion treatment liquid D was obtained by filtering the precipitate. Further, an alkaline treatment liquid was obtained by adding 100 mg of sodium hypophosphite to 10 ml of a 3% by mass sodium hydroxide aqueous solution.

Composite material A was impregnated with an alkali treatment solution and heat-treated at 50° C. for 2 minutes to obtain alkali-treated composite material A. The composite material A was immersed in the chemical conversion treatment solution D and subjected to heat treatment at 60° C. for 2 minutes to obtain a bipolar current collector of Test Example 4.

(Test Example 5)
Composite material A that was not subjected to chemical conversion treatment was used as Test Example 5.
(Fluorescent X-ray analysis and measurement of resistance)
Each mass of magnesium (Mg) and copper (Cu) was measured by performing fluorescent X-ray analysis on the chemically treated portions of the bipolar current collectors of Test Examples 1 to 5. Then, the content ratio of magnesium to 100 parts by mass of copper was calculated. In addition, the resistance of the chemically treated surfaces of the bipolar current collectors of Test Examples 1 to 5 was measured using a four-probe method. Those results are shown in Table 2. In addition, "n.d." in the component ratio column of Table 2 indicates non-detection.

蛍光Ｘ線分析の結果から、化成処理を行った試験例１～４には、酸化マグネシウムを含有する酸化被膜が形成されていることが確認できる。そして、化成処理液の組成を異ならせることにより、酸化被膜における酸化マグネシウムの含有割合を調整することができた。また、酸化被膜が形成されている試験例１～４の抵抗は、酸化被膜が形成されていない試験例５と同程度であった。この結果から、酸化被膜を設けることによる導電性の低下はない又は非常に小さいと考えられる。

From the results of the fluorescent X-ray analysis, it can be confirmed that an oxide film containing magnesium oxide was formed in Test Examples 1 to 4 in which chemical conversion treatment was performed. By varying the composition of the chemical conversion treatment solution, the content of magnesium oxide in the oxide film could be adjusted. Moreover, the resistances of Test Examples 1 to 4 in which an oxide film was formed were comparable to Test Example 5 in which an oxide film was not formed. Based on these results, it is considered that there is no or very little decrease in electrical conductivity due to the provision of the oxide film.

(Preparation of composite material B)
A test piece for plating treatment was obtained by attaching an aluminum foil having a thickness of 15 μm to a SUS plate using a masking tape so that an aluminum surface of 70 mm×70 mm was exposed.

The exposed aluminum surface of the test piece was degreased by treating it with an aqueous solution of Top Alclean 101 from Okuno Pharmaceutical Co., Ltd. at 60° C. for 5 minutes. After degreasing, the test piece was washed with water and etched by treating it with an aqueous solution of Top Alsoft 108 manufactured by Okuno Pharmaceutical Co., Ltd. at 55° C. for 1 minute. After the etching, the test piece was washed with water and treated with Top Desmut N-20 from Okuno Pharmaceutical Co., Ltd. for 1 minute at room temperature to remove the smut.

Next, the test piece was washed with water and treated with an aqueous solution of Substar ZN-291 from Okuno Pharmaceutical Co., Ltd. for 1 minute at room temperature to replace the surface with zinc. The test piece after substitution was washed with water, and the zinc was stripped off once with an aqueous nitric acid solution, and then treated with an aqueous solution of Substar Zn-291 at room temperature for 1 minute to perform zinc substitution again.

A copper plating bath was prepared by preparing a bath containing 150 g/l of copper sulfate, 150 g/l of sulfuric acid, and 80 ppm of hydrochloric acid, and adding Top Lucina SF Base WR, Top Lucina SF-B, and Top Lucina SF Leveler manufactured by Okuno Seiyaku Co., Ltd. as additives. A test piece was immersed in the prepared plating bath, and copper plating was formed on the surface of the test piece using phosphorous copper as an anode at room temperature at a current density of 2 A/dm ² for 5 minutes. A composite material B was obtained by washing the plated test piece with water and applying an antirust treatment using Okuno Seiyaku Co., Ltd. Top Rinse.

(Production of composite material C)
After performing the steps up to the step of forming the copper plating in the same manner as in the preparation of the composite material B, the test piece was washed with water. The test piece was immersed in a plating bath prepared to have 250 g/l nickel sulfate, 50 g/l nickel chloride, and 50 g/l boric acid, and the test piece was immersed in a current density of 1 A/dm ² at room temperature for 2 minutes. Nickel plating was formed on the surface. A composite material C was obtained by washing the plated test piece with water.

(Test Example 6 and Test Example 7)
A first heat treatment was performed at 60° C. for 5 minutes while the composite material B was immersed in the chemical conversion treatment solution B. Composite material B after the first heat treatment was washed with water and subjected to a second heat treatment at 120° C. for 1 hour to obtain a bipolar current collector of Test Example 6. In addition, a composite material B that was not subjected to chemical conversion treatment was used as Test Example 7.

(Test Example 8 and Test Example 9)
A first heat treatment was performed at 60° C. for 5 minutes while the composite material C was immersed in the chemical conversion treatment solution B. Composite material C after the first heat treatment was washed with water and subjected to a second heat treatment at 120° C. for 1 hour to obtain a bipolar current collector of Test Example 8. Composite material C that was not subjected to chemical conversion treatment was used as Test Example 9.

(Fluorescent X-ray analysis)
By performing fluorescent X-ray analysis on the chemically treated portions of the bipolar current collectors of Test Examples 6 to 9, each mass of magnesium (Mg), copper (Cu), and nickel (Ni) was determined. It was measured. Then, the content ratio of magnesium to 100 parts by mass of the total mass of copper and nickel was calculated. Those results are shown in Table 3.

蛍光Ｘ線分析の結果から、化成処理を行った試験例６及び試験例８には、酸化マグネシウムを含有する酸化被膜が形成されていること、及び化成処理を行った試験例７及び試験例９には、酸化被膜が形成されていないことが確認できる。

From the results of the fluorescent X-ray analysis, it was found that an oxide film containing magnesium oxide was formed in Test Examples 6 and 8 in which chemical conversion treatment was performed, and Test Examples 7 and 9 in which chemical conversion treatment was performed. It can be confirmed that no oxide film is formed on the .

(Test Example 10 and Test Example 11)
A focused ion beam apparatus was used to gradually etch a 10 μm square range of the copper-plated portion of the composite material B. As shown in FIG. By stopping the etching when the underlying aluminum foil was observed, a composite material with pinholes in which artificial pinholes were formed in the copper-plated portion was obtained.

A first heat treatment was performed at 60° C. for 5 minutes while the composite material with pinholes was immersed in the chemical conversion treatment solution B. After the first heat treatment, the composite material was washed with water and subjected to a second heat treatment at 120° C. for 1 hour to obtain a bipolar current collector of Test Example 10. A composite material with pinholes that was not subjected to chemical conversion treatment was used as Test Example 11 as it was.

(Fluorescent X-ray analysis)
Each mass of magnesium (Mg) and copper (Cu) was measured by performing fluorescent X-ray analysis on the chemically treated portions of the bipolar current collectors of Test Examples 10 and 11. Then, the content ratio of magnesium to 100 parts by mass of copper was calculated. Those results are shown in Table 3.

(Electrochemical test)
A negative electrode (evaluation electrode) formed by cutting the bipolar current collectors of Test Examples 10 and 11 into a circle with a diameter of 11 mm, and a positive electrode formed by cutting a metal lithium foil with a thickness of 500 μm into a circle with a diameter of 13 mm. A separator was sandwiched between them to form an electrode battery. A half cell for an electrochemical test was obtained by housing the electrode body battery in a battery case, injecting a non-aqueous electrolyte, and sealing the battery case. As a separator, a glass filter manufactured by Hoechst Celanese was used. As the nonaqueous electrolyte, a nonaqueous electrolyte obtained by dissolving lithium hexafluorophosphate to a concentration of 1M in a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 1:1 was used.

The obtained half-cell for electrochemical test was swept to 0 V as the counter electrode lithium potential at a current of 0.1 mA. After the voltage reached 0 V, a current of 0.1 mA and a voltage of 0 V were applied by CC-CV for 3 hours. Table 4 shows the voltage reached during the sweep, the holding time during which the voltage of 0 V was held, and the CC-CV voltage after 3 hours.

蛍光Ｘ線分析の結果から、試験例１０については、酸化マグネシウムを含有する酸化被膜が形成されていること、及び試験例１１については、酸化被膜が形成されていないことが確認できた。

From the results of the fluorescent X-ray analysis, it was confirmed that an oxide film containing magnesium oxide was formed in Test Example 10, and that an oxide film was not formed in Test Example 11.

In Test Example 11 in which no oxide film was formed, although the final voltage reached 0 V during sweeping, the voltage could not be maintained at 0 V after 90 minutes, and the CC-CV voltage after 3 hours was 0.0 V. It was 11V. From this result, in the case of Test Example 11, after reaching 0 V, lithium ions reached the aluminum foil through pinholes in the copper plating after a while, and the lithium ions corroded the aluminum foil. On the other hand, in Test Example 10 in which an oxide film was formed, the state of 0 V was maintained during the measurement time of 3 hours. From this result, it can be seen that the provision of an oxide film containing magnesium oxide has the effect of suppressing corrosion of the aluminum foil caused by pinholes in the copper plating.

Next, the corrosion inhibition effect of the oxide film was verified in a simple test system using the evaluation electrodes of Test Examples 12 to 24 in which the oxide film was formed directly on the surface of the aluminum foil.
(Test Example 12)
After adding 2 g of magnesium ethoxide to 10 ml of ethanol and performing heat treatment at 60° C. for 5 minutes, a chemical conversion treatment liquid E was obtained by filtering the precipitate. A 15 μm-thick aluminum foil whose surface had been degreased was immersed in a 15 mass % sulfuric acid aqueous solution, and the surface was oxidized at a current density of 2 A/dm ² to obtain an anodized aluminum foil. A first heat treatment was performed at 60° C. for 5 minutes while immersing an anodized aluminum foil into a circle having a diameter of 9 mm and immersing it in the chemical conversion treatment solution E. After the first heat treatment, the aluminum foil was washed with water and subjected to a second heat treatment at 120° C. for 1 hour to obtain an evaluation electrode of Test Example 12.

(Test Example 13)
After adding 2 g of magnesium ethoxide and 1.05 mg of acetic acid to 9 ml of water and performing heat treatment at 60° C. for 5 minutes, a chemical conversion treatment liquid F was obtained by filtering the precipitate. An electrode for evaluation of Test Example 13 was obtained by performing the same treatment as in Test Example 12 except that the chemical conversion treatment solution E was changed to the chemical conversion treatment solution F.

(Test Example 14)
After adding 2 g of magnesium ethoxide to 10 ml of water and performing heat treatment at 60° C. for 5 minutes, a chemical conversion treatment liquid G was obtained by filtering the precipitate. An electrode for evaluation of Test Example 13 was obtained by performing the same treatment as in Test Example 12 except that the chemical conversion treatment solution E was changed to the chemical conversion treatment solution G.

(Test Example 15)
After adding 1.5 g of calcium ethoxide to 10 ml of water and performing heat treatment at 60° C. for 5 minutes, chemical conversion treatment solution H was obtained by filtering the precipitate. An electrode for evaluation of Test Example 15 was obtained by performing the same treatment as in Test Example 12 except that the chemical conversion treatment solution E was changed to the chemical conversion treatment solution H.

(Test Example 16)
After adding 1.5 g of calcium ethoxide and 0.5 g of sodium acetate to 10 ml of water and performing heat treatment at 60° C. for 5 minutes, a chemical conversion treatment liquid I was obtained by filtering the precipitate. An electrode for evaluation of Test Example 16 was obtained by performing the same treatment as in Test Example 15 except that the chemical conversion treatment solution H was changed to the chemical conversion treatment solution I.

(Test Example 17)
A 15 μm-thick aluminum foil was immersed in a 10 mass % LiPF ₆ aqueous solution and heat-treated at 60° C. for 5 minutes to obtain a fluorinated aluminum foil. A fluorinated aluminum foil cut into a circle with a diameter of 9 mm was immersed in the chemical conversion treatment solution H, and then subjected to a first heat treatment at 60° C. for 5 minutes. After the first heat treatment, the aluminum foil was washed with water and subjected to a second heat treatment at 120° C. for 1 hour to obtain an evaluation electrode of Test Example 17.

(Test Example 18)
After adding 1.5 g of calcium chloride to 8 ml of water and performing heat treatment at 60° C. for 5 minutes, a chemical conversion treatment liquid J was obtained by filtering the precipitate. An electrode for evaluation of Test Example 18 was obtained by performing the same treatment as in Test Example 17 except that the chemical conversion treatment solution H was changed to the chemical conversion treatment solution J.

(Test Example 19)
An alkaline treatment liquid was obtained by adding 100 mg of sodium hypophosphite to 10 ml of a 3% by mass sodium hydroxide aqueous solution. An aluminum foil having a thickness of 15 μm was impregnated with an alkali treatment solution and heat-treated at 50° C. for 2 minutes to obtain an alkali-treated aluminum foil. A first heat treatment was performed at 60° C. for 5 minutes while immersing an alkali-treated aluminum foil into a circle having a diameter of 9 mm and immersing it in the chemical conversion treatment solution H. After the first heat treatment, the aluminum foil was washed with water and subjected to a second heat treatment at 120° C. for 1 hour to obtain an evaluation electrode of Test Example 19.

(Test Example 20)
An electrode for evaluation of Test Example 20 was obtained by performing the same treatment as in Test Example 19 except that the chemical conversion treatment solution H was changed to the chemical conversion treatment solution I.

(Test Examples 21 to 24)
An evaluation electrode of Test Example 21 was obtained by cutting a 15 μm thick aluminum foil whose surface was degreased into a circle with a diameter of 9 mm. An electrode for evaluation in Test Example 22 was obtained by cutting the anodized aluminum foil prepared in Test Example 12 into a circle with a diameter of 9 mm. An electrode for evaluation in Test Example 23 was obtained by cutting the fluorinated aluminum foil prepared in Test Example 17 into a circle with a diameter of 9 mm. An electrode for evaluation in Test Example 23 was obtained by cutting the alkali-treated aluminum foil prepared in Test Example 19 into a circle with a diameter of 9 mm.

(Fluorescent X-ray analysis)
Each mass of magnesium (Mg), calcium (Ca), and aluminum (Al) was measured by performing fluorescent X-ray analysis on the chemically treated portions of the evaluation electrodes of Test Examples 12 to 24. . Those results are shown in Table 5.

(Electrochemical test)
A separator was sandwiched between the evaluation electrodes of Test Examples 12, 13, 15 to 24 and a positive electrode formed by cutting a metallic lithium foil of 500 μm in thickness into a circle with a diameter of 13 mm to prepare an electrode battery. A half cell for an electrochemical test was obtained by housing the electrode body battery in a battery case, injecting a non-aqueous electrolyte, and sealing the battery case. As a separator, a glass filter manufactured by Hoechst Celanese was used. As the nonaqueous electrolyte, a nonaqueous electrolyte obtained by dissolving lithium hexafluorophosphate to a concentration of 1M in a mixed solvent of ethylene carbonate and diethyl carbonate at a volume ratio of 1:1 was used.

The obtained half-cell for electrochemical test was swept to 0 V as the counter electrode lithium potential at a current of 0.1 mA. After the voltage reached 0 V, a current of 0.1 mA and a voltage of 0 V were applied by CC-CV for 3 hours. Table 5 shows the voltage reached during the sweep, the holding time during which the voltage of 0 V was held, and the CC-CV voltage after 3 hours.

蛍光Ｘ線分析の結果から、試験例１４を除いて、化成処理を行った試験例１２～２０には、酸化マグネシウム又は酸化カルシウムを含有する酸化被膜が形成されていることが確認できる。特に、ルイス酸である酢酸を含む化成処理液を用いた試験例１３は、酢酸を含まない化成処理液を用いた試験例１２と比較して、酸化被膜における酸化マグネシウムの含有割合が高い。また、塩基性化合物である酢酸ナトリウムを含む化成処理液を用いた試験例１６は、酢酸ナトリウムを含まない化成処理液を用いた試験例１５と比較して、酸化被膜における酸化カルシウムの含有割合が高い。なお、試験例１４は、マグネシウムエトキシドが化成処理液中に十分に溶解できていなかったために、酸化被膜が形成されなかったと考えられる。

From the results of the fluorescent X-ray analysis, it can be confirmed that, except for Test Example 14, an oxide film containing magnesium oxide or calcium oxide was formed in Test Examples 12 to 20 in which chemical conversion treatment was performed. In particular, Test Example 13 using the chemical conversion solution containing acetic acid, which is a Lewis acid, has a higher magnesium oxide content in the oxide film than Test Example 12 using the chemical conversion solution containing no acetic acid. Further, in Test Example 16 using a chemical conversion treatment solution containing sodium acetate, which is a basic compound, compared to Test Example 15 using a chemical conversion treatment solution containing no sodium acetate, the content of calcium oxide in the oxide film was expensive. In Test Example 14, it is considered that the oxide film was not formed because magnesium ethoxide was not sufficiently dissolved in the chemical conversion treatment solution.

Also, in Test Examples 21 to 24 in which no oxide film was formed, the final voltage during sweep did not reach 0V, or could not be maintained at 0V several minutes after reaching 0V. On the other hand, in Test Examples 12, 13, and 15-20 in which an oxide film was formed, the ultimate voltage reached 0 V during sweeping, and the retention time was longer than Test Examples 21-24. In particular, Test Examples 13 and 16, in which an oxide film with a high content of magnesium oxide or calcium oxide was formed, were maintained at 0 V even after 3 hours. This result suggests that the corrosion inhibition effect is obtained based on magnesium oxide or calcium oxide contained in the oxide film.

Further, as shown in Table 1, the oxide of the specific metal M has a differential value of the activation energy of the oxide of the specific metal M with respect to the formation energy of lithium aluminum equal to or greater than that of magnesium oxide. Therefore, similar to magnesium oxide, it is considered that the corrosion inhibitory effect can be obtained by including it in the oxide film.

Next, technical ideas that can be grasped from the above embodiment will be described below.
(b) A bipolar current collector used for a bipolar electrode provided with a negative electrode active material layer containing a negative electrode active material capable of intercalating and deintercalating lithium ions, the bipolar current collector having a positive electrode current collector having an aluminum layer and a copper layer. A negative electrode current collector is provided, and at least one selected from Sc, Y, Ca, Er, Tm, Ho, Lu, Dy, Be, Sm, Yb, Nd, Mg, Ce, and La is formed on the surface of the negative electrode current collector. A bipolar current collector provided with an oxide film containing a kind of metal oxide.

DESCRIPTION OF SYMBOLS 10... Bipolar collector 11... Positive electrode collector 11a... Aluminum layer 12... Negative electrode collector 12a... Copper layer 13... Oxide film 20... Positive electrode active material layer 30... Negative electrode active material layer

Claims (4)

A method for producing a bipolar current collector used in a bipolar electrode provided with a negative electrode active material layer containing a negative electrode active material capable of intercalating and deintercalating lithium ions, comprising:
An oxide film forming step of forming an oxide film containing a metal oxide on the surface of the negative electrode current collector in a composite material comprising a positive electrode current collector having an aluminum layer and a negative electrode current collector having a copper layer,
The oxide film contains at least one metal oxide selected from Sc, Y, Ca, Er, Tm, Ho, Lu, Dy, Be, Sm, Yb, Nd, Mg, Ce, and La. A method for manufacturing a bipolar current collector. In the oxide film forming step, a chemical conversion treatment solution obtained by heating a mixture obtained by mixing a metal salt of the metal and a solvent capable of dissolving the metal salt is attached to the surface of the negative electrode current collector. 2. The method for manufacturing a bipolar current collector according to claim 1, wherein the step of heating is as follows. 3. The method for manufacturing a bipolar current collector according to claim 2, wherein the chemical conversion treatment liquid further contains one or both of a basic compound and a Lewis acid. The method for manufacturing a bipolar current collector according to any one of claims 1 to 3, wherein the copper layer has a thickness of a plated layer.

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