Current collector, electrode, and lithium-ion secondary battery

Abstract

A secondary-battery current collector according to one aspect of the present disclosure has a laminated structure including, in this order, a resin layer, a base layer containing at least one of a metal and a metal oxide, and a conductive layer containing a metal and a metal oxide.

Description

Current collector, electrode and lithium ion secondary battery

[0001] The present disclosure relates to a current collector, an electrode, and a lithium-ion secondary battery.

[0002] As a lightweight current collector, a composite film in which the surface of an insulating layer such as a polymer is metallized has been proposed. For example, Patent Documents 1 and 2 disclose current collectors that include a predetermined insulating layer, a conductive layer, and a protective layer.

[0003] Patent No. 6715896 Patent No. 6724083

[0004] However, the current collector may be damaged by the electrolyte, resulting in corrosion or peeling of the metal film, and the above-mentioned conventional current collectors have room for improvement in terms of electrolyte resistance.

[0005] The present disclosure provides a current collector having excellent resistance to an electrolyte solution, an electrode including such a current collector, and a lithium-ion secondary battery including such an electrode.

[0006] In order to solve the above problems, the present disclosure provides the following current collector, electrode, and lithium-ion secondary battery. [1] A current collector for a secondary battery having a laminated structure including, in this order: a resin layer; an underlayer containing at least one of a metal and a metal oxide; and a conductive layer containing a metal and a metal oxide. [2] The current collector for a secondary battery according to [1], in which at least a portion of a region containing a metal oxide in the conductive layer is separated from the underlayer. [3] The current collector for a secondary battery according to [2], in which the distance between the region and the underlayer is 10 nm to 100 nm. [4] The current collector for a secondary battery according to any one of [1] to [3], in which the thickness of the region containing a metal oxide in the conductive layer is 1 nm to 20 nm. [5] The current collector for a secondary battery according to any one of [1] to [4], wherein the metal contained in the conductive layer includes one of Cu and Al, the metal oxide contained in the conductive layer includes at least one oxide selected from the group consisting of Ni, Cr, Mo, W, Nb, and Ta, and the underlayer includes at least one oxide selected from the group consisting of Ni, Cr, Mo, W, Nb, Cu, and Ta. [6] The current collector for a secondary battery according to any one of [1] to [5], wherein the thickness of the conductive layer is 400 nm to 2500 nm. [7] The current collector for a secondary battery according to any one of [1] to [6], wherein the thickness of the underlayer is 1 nm to 20 nm. [8] The current collector for a secondary battery according to any one of [1] to [7], wherein the content of the metal oxide in the conductive layer is 500 ppm by volume to 5000 ppm by volume based on the entire conductive layer. [9] An electrode for a secondary battery, comprising the current collector according to any one of [1] to [8].

[10] A lithium ion secondary battery comprising the electrode according to [9].

[0007] The present disclosure provides a current collector having excellent resistance to an electrolyte solution, an electrode including such a current collector, and a lithium-ion secondary battery including such an electrode.

[0008] FIG. 1 is a schematic cross-sectional view of a current collector according to one embodiment. FIG. 2 is a schematic cross-sectional view of a current collector according to another embodiment. FIG. 3 is a schematic cross-sectional view of a current collector according to another embodiment. FIG. 4 is a schematic cross-sectional view of a current collector according to another embodiment. FIG. 5 is a diagram schematically showing the configuration of a secondary battery according to one embodiment. FIG. 6 is a diagram schematically showing the configuration of a secondary battery according to another embodiment.

[0009] Various exemplary embodiments will be described in detail below with reference to the drawings. In each drawing, the same or equivalent parts will be denoted by the same reference numerals, and duplicate explanations will be omitted. In this specification, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. Individually stated upper and lower limit values ​​can be arbitrarily combined.

[0010] [Current Collector] <First Embodiment> Fig. 1 is a schematic cross-sectional view of a current collector according to this embodiment. The current collector 10 shown in Fig. 1 is a current collector for a secondary battery. The current collector 10 has a laminated structure including, in this order, a resin layer 1, an underlayer 2 containing at least one of a metal and a metal oxide, and a conductive layer 3 containing a metal and a metal oxide. The conductive layer 3 has a region 3a containing a metal but not a metal oxide, and a region 3b containing a metal oxide. The region 3b containing the metal oxide is layered. The region 3b containing the metal oxide is separated from the underlayer 2.

[0011] When the current collector 10 is immersed in an electrolyte, the hydrofluoric acid contained in the electrolyte penetrates through the copper grain boundaries. In the current collector 10, the conductive layer 3 has a region 3b containing a metal oxide. This prevents the hydrofluoric acid from penetrating into the underlayer and resin layer. The current collector 10 also has an underlayer. The underlayer improves the adhesive strength between the conductive layer and the resin layer. As a result, the current collector has improved electrolyte resistance.

[0012] (Resin Layer) Examples of materials for the resin layer 1 include polyamide resin, polyethylene terephthalate resin, polyimide resin, polyethylene resin, polypropylene resin, polystyrene resin, polyvinyl chloride resin, acrylonitrile-butadiene-styrene copolymer, polybutylene terephthalate resin, poly-p-phenylene terephthalamide resin, epoxy resin, polyformaldehyde resin, phenolic resin, polypropylene ethylene resin, polytetrafluoroethylene resin, silicone rubber, polyvinylidene fluoride resin, polycarbonate resin, polyphenylene sulfide resin, and cyclic olefin polymer. From the viewpoints of low water absorption, high adhesion to the conductive layer, and high tensile strength, polyethylene naphthalate resin, polypropylene resin, polyphenylene sulfide resin, and cycloolefin resin are preferred. These materials may be used alone or in combination of two or more.

[0013] The content of these resins may be 80% by mass or more, 90% by mass or more, 95% by mass or more, or 100% by mass.

[0014] The thickness of the resin layer 1 may be, for example, 20 μm or less, 15 μm or less, 12 μm or less, 10 μm or less, or 8 μm or less, or 1 μm or more, 1.5 μm or more, 2 μm or more, 3 μm or more, 4 μm or more, or 5 μm or more.

[0015] The resin layer may or may not be stretched. The stretching may be uniaxial or biaxial.

[0016] The resin layer may be subjected to a surface treatment such as a plasma treatment or a corona treatment. The surface treatment tends to improve the adhesion strength between the resin layer and the underlayer. Furthermore, the surface treatment removes fine contaminants adhering to the surface of the resin layer and low-molecular-weight components that may precipitate on the surface of the resin layer. This tends to reduce erosion of the interface between the resin layer and the underlayer by the electrolyte.

[0017] The atmosphere in which the above-mentioned surface treatment is carried out may be, for example, air, argon, nitrogen, or oxygen.

[0018] (Underlayer) The underlayer contains at least one of a metal and a metal oxide. Examples of such metals include Ni, Cr, Mo, W, Nb, Cu, Ta, Ni—Cr alloys, Zr, and Mg. Ni, Cr, Mo, W, Nb, Cu, Ta, and Ni—Cr alloys are preferred because they improve the adhesive strength between the resin layer and the underlayer. The metal oxide may be, for example, an oxide of these metals.

[0019] When the metal is a Ni-Cr alloy, the mass ratio of Ni to Cr (Ni:Cr) is preferably 98:2 to 10:90, and more preferably 80:20 to 30:70. When the mass ratio of Ni to Cr is within this range, electrolyte resistance tends to be further improved. When the proportion of Cr in the Ni and Cr is 20% by mass or more, the conductive layer becomes nonmagnetic, which tends to suppress the occurrence of defects during film formation. When the proportion of Cr in the Ni and Cr is 30% by mass or less, the conductive layer becomes a single-phase film, which tends to make it easier to obtain a film with a uniform composition.

[0020] The thickness of the underlayer is, for example, preferably 0.5 nm or more, 1 nm or more, 2 nm or more, 3 nm or more, 4 nm or more, or 5 nm or more, and is preferably 25 nm or less, and more preferably 20 nm or less, 15 nm or less, or 10 nm or less. When the thickness of the underlayer is in such a range, the electrolyte resistance tends to be further improved. The thickness may be an average value.

[0021] Methods for forming the underlayer include, for example, vapor deposition, in-situ formation, and coating. Vapor deposition includes physical vapor deposition (PVD). Physical vapor deposition includes evaporation and sputtering. Vapor deposition includes vacuum evaporation, thermal evaporation, and electron beam evaporation (EBEM). Sputtering includes magnetron sputtering. In-situ formation includes in-situ passivation, which forms a metal oxide passivation layer on a metal surface in-situ. As the coating method, for example, roll press coating, pressure coating, blade coating, and gravure coating are preferred.

[0022] (Conductive Layer) When the current collector is used as a positive electrode, the metal contained in the conductive layer 3 may be, for example, aluminum (Al). When the current collector is used as a negative electrode, the metal contained in the conductive layer 3 may be, for example, copper (Cu). The material of the conductive layer 3 may be any material that does not easily form an alloy with metal ions contained in the electrolyte.

[0023] The thickness of the conductive layer 3 may be, for example, 100 nm to 5000 nm, and is preferably 400 to 2500 nm because this tends to further improve the electrolyte resistance. The thickness may be an average value.

[0024] Examples of metal oxides contained in the conductive layer include oxides of Ni, Cr, Mo, W, Nb, Ta, Ni—Cr alloy, Zr, and Mg. The metal oxide is preferably an oxide of Ni, Cr, Mo, W, Nb, Ta, or Ni—Cr alloy, and more preferably an oxide of Ni—Cr alloy, because these tend to further improve electrolyte resistance. The metal oxides can be used alone or in combination of two or more.

[0025] When the metal oxide is a Ni—Cr alloy, the mass ratio of Ni to Cr (Ni:Cr) is preferably 98:2 to 10:90, and more preferably 20:80 to 25:75. When the mass ratio of Ni to Cr is within this range, the electrolyte resistance is further improved, and a film with a uniform composition tends to be easily obtained.

[0026] The content of the metal oxide in the conductive layer may be, for example, 50 to 8000 ppm by volume based on the entire conductive layer, and is more preferably 500 to 5000 ppm by volume because this tends to further improve electrolyte resistance.

[0027] The surface of the conductive layer 3 that is not in contact with the resin layer may contain a metal oxide. An oxide film can be formed on the surface of the conductive layer 3 that is not in contact with the resin layer by reacting with oxygen in the air.

[0028] The metal content in the region 3 a containing metal but not metal oxide may be 90 vol% or more, 95 vol% or more, 98 vol% or more, 99 vol% or more, 99.9 vol% or more, or 100 vol% based on the entire region 3 a.

[0029] The content of the metal oxide in the region 3b containing the metal oxide may be 90 vol% or more, 95 vol% or more, 98 vol% or more, 99 vol% or more, 99.9 vol% or more, or 100 vol% based on the entire region 3b.

[0030] The thickness of the region 3b containing metal oxide may be, for example, 0.5 to 50 nm, and is more preferably 1 to 20 nm because this tends to further improve electrolyte resistance. The thickness may be an average value.

[0031] The distance between the metal oxide-containing region 3b and the underlayer 2 may be, for example, 1 to 200 nm, and is preferably 10 to 100 nm because this tends to further improve electrolyte resistance. The distance between the metal oxide-containing region 3b and the underlayer 2 is the shortest distance between the region 3b and the underlayer 2.

[0032] Examples of methods for forming a conductive layer include vapor deposition, in-situ formation, coating, electrolytic plating, and electroless plating, followed by oxidation of a metal film. Examples of vapor deposition include physical vapor deposition (PVD). Examples of physical vapor deposition include evaporation and sputtering. Examples of evaporation include vacuum evaporation, thermal evaporation, and electron beam evaporation (EBEM). Examples of sputtering include magnetron sputtering. Examples of in-situ formation methods include an in-situ passivation method in which a passivation layer of metal oxide is formed in-situ on the surface of a metal. Preferred coating methods include roll press coating, pressure coating, blade coating, and gravure coating. The methods for forming the conductive layer can be used alone or in combination of two or more.

[0033] Although the current collector according to one embodiment has been described above, the current collector of the present disclosure is not limited to the above embodiment. For example, the region containing a metal oxide in the conductive layer 3 may be in the form of a discontinuous layer. Fig. 2 is a schematic cross-sectional view of a current collector according to another embodiment. In the current collector 11 shown in Fig. 2, the region 3b containing a metal oxide in the conductive layer 3 is in the form of a discontinuous layer. The area ratio of the region 3b containing a metal oxide may be 60 area% or more, 75 area% or more, or 90 area% or more, based on the area of ​​the main surface of the conductive layer, in a plan view.

[0034] In the current collector, the conductive layer 3 may have two or more regions containing a metal oxide. Fig. 3 is a schematic cross-sectional view of a current collector according to another embodiment. The current collector 12 shown in Fig. 3 has two regions 3b containing a metal oxide in the conductive layer 3. The regions 3b containing a metal oxide may be in the form of discontinuous layers (Fig. 4).

[0035] The current collector may also include an underlayer on each of the main surfaces of the resin layer, and a conductive layer on the surface of the underlayer opposite to the resin layer. The region 3b containing the metal oxide of the conductive layer 3 does not need to be separated from the underlayer.

[0036] [Secondary Battery] <First Embodiment> FIG. 5 is a diagram schematically illustrating the configuration of a secondary battery according to this embodiment. The secondary battery 100 illustrated in FIG. 5 includes a positive electrode p, a separator 30, and a negative electrode n inside a container 60. The positive electrode p includes a current collector 10 and a positive electrode active material 20. The negative electrode n includes a negative electrode active material 40 and a current collector 10. The container 60 is filled with an electrolyte 50. The positive electrode active material 20 is provided on the upper surface of the current collector 10 and faces the negative electrode active material 40 via the separator 30. The negative electrode active material 40 is provided on the lower surface of the current collector 10. The current collector 10 is electrically connected to a positive electrode T1. The current collector 10 is electrically connected to a negative electrode T2. Secondary batteries are available in various shapes, and the layer structure inside the container can be rolled up to increase the surface area.

[0037] The secondary battery may be a metal ion battery in which metal ions are involved in charging and discharging. The metal ions may be lithium ions. That is, the secondary battery may be a lithium ion secondary battery. The active material is a substance that undergoes an oxidation-reduction reaction in the secondary battery to convert chemical energy and electrical energy.

[0038] Examples of the positive electrode active material 20 include lithium cobalt oxide, lithium manganese oxide, and lithium iron phosphate.

[0039] Examples of the negative electrode active material 40 include graphite and silicon-based materials.

[0040] The separator 30 is made of a material containing an electrolyte solution. For the separator 30, for example, a resin film made of a polyolefin resin such as polypropylene or polyethylene and having a plurality of pores formed therein can be used.

[0041] The electrolyte solution 50 is a conductive solution containing metal ions. In this example, the electrolyte solution 50 is a solution containing lithium ions, and is a 1 molar (1M) solution of lithium hexafluorophosphate (LiPF ６ ) in a solvent containing ethylene carbonate. Other solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0042] The material of the container 60 is not particularly limited as long as it is resistant to the electrolyte, but an aluminum alloy or the like can be used.

[0043] The positive electrode T1 and the negative electrode T2 may be made of a common electrode material, such as aluminum (Al), copper (Cu), or gold (Au).

[0044] Second Embodiment Fig. 6 is a diagram schematically illustrating the configuration of a secondary battery according to this embodiment. The secondary battery 101 shown in Fig. 6 is composed of two secondary batteries connected in series. The current collector 10 between adjacent secondary batteries is a bipolar current collector, thereby reducing the number of components. The other configurations are the same as those of the secondary battery according to the first embodiment.

[0045] The present disclosure will be described below based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0046] [Manufacturing of Current Collector] (Example 1) A PP substrate was prepared as the resin layer. After plasma treatment was performed on both sides of the substrate in an argon atmosphere, an underlayer (thickness: 2 nm) was formed on both sides of the substrate by sputtering. An alloy of 80% by mass of Ni and 20% by mass of Cr was used as the material. The average thickness of the underlayer was used as the thickness of the underlayer. A Cu film (thickness: 5 nm) was formed on the surface of the underlayer by sputtering as the non-oxide region of the conductive layer. An alloy film of 80% by mass of Ni and 20% by mass of Cr was formed on the Cu film by sputtering. The alloy film was oxidized. This resulted in an oxide region (thickness: 3 nm) of the conductive layer. A Cu film (thickness: 995 nm) was formed on the surface of the oxide region of the conductive layer by electroplating as the non-oxide region of the conductive layer. This resulted in a current collector having a laminated structure including a resin layer, an underlayer, and a conductive layer (Cu film / Ni and Cr alloy oxide film / Cu film) in this order.

[0047] Examples 2 to 43 Current collectors were obtained in the same manner as in Example 1, except that the materials and thicknesses of the resin layer, underlayer, and conductive layer, the distance between the underlayer and the metal oxide region of the conductive layer, and the content of the metal oxide region were changed as shown in Tables 1 to 3. In Tables 1 to 3, the numerical values ​​listed next to the materials indicate the content (mass ratio) of each material. For example, Ni(80) and Cr(20) indicate that the underlayer is an alloy containing 80% by mass of Ni and 20% by mass of Cr. The content of the metal oxide region is a value based on the entire conductive layer. Details of the abbreviations in Tables 1 to 3 are as follows. The thickness of the non-metal oxide region is the sum of the thickness of the non-metal oxide region formed on the underlayer side of the metal oxide region and the thickness of the non-metal oxide region formed on the opposite side of the metal oxide region from the underlayer.

[0048] PP: Polypropylene resin PPS: Polyphenylene sulfide resin COP: Cyclic olefin polymer

[0049] Comparative Example 1 A current collector was obtained in the same manner as in Example 1, except that the metal oxide region was not formed.

[0050] Comparative Example 2 A current collector was obtained in the same manner as in Example 30, except that no underlayer was formed.

[0051] [Appearance Observation] LiPF was used as an electrolyte in an electrolytic solution consisting of diethyl carbonate (DEC) and ethylene carbonate (EC) (DEC:EC = 7:3 (mass ratio)). ６ A test solution was obtained by mixing 1 mol of resin and 1000 ppm of water. Test pieces (30 mm square) were cut out from the current collectors of each Example and Comparative Example. A container was filled with 50 ml of the test solution, and the test pieces were immersed in the test solution. The container was sealed and heated at 85°C for 72 hours. The appearance of the test pieces after heating was observed and evaluated according to the following criteria. The results are shown in Tables 1 to 3. (Criteria) A: No peeling was observed between the resin layer of the test piece and the base layer or conductive layer. B: Peeling was observed between the resin layer of the test piece and the base layer or conductive layer.

[0052] [Adhesion Strength Test 1] A test piece after heating was obtained in the same manner as in the appearance observation. Cellophane tape (manufactured by Nitto Denko Corporation, product name "N29") was attached to one surface of the test piece. The cellophane tape was peeled off, and the surface of the test piece was observed for peeling and evaluated according to the following criteria. The results are shown in Tables 1 to 3. (Criteria) A: No peeling was observed on the surface of the test piece. B: Peeling was observed on part of the surface of the test piece. C: Peeling was observed on the entire surface of the test piece.

[0053] [Adhesion Strength Test 2] Test pieces after heating were obtained in the same manner as in the appearance observation. The adhesion strength between the resin layer and the (underlayer) of the test piece was measured using a tensile strength tester. The conditions were 180° peel and a tensile speed of 50 mm / min. The results are shown in Tables 1 to 3.

[0054] [Measurement of Electrical Resistivity] Test pieces after heating were obtained in the same manner as in the appearance observation. The surface resistance of the test pieces was measured using an electrical resistance measuring device (Nitto Seiko Analytech: Loresta-GXII), and the resistivity was calculated from the film thickness of the conductive layer. The results are shown in Tables 1 to 3.

[0055] [Measurement of Metal Oxide Content] The metal oxide content in the conductive layer of the current collector obtained in each example and comparative example was measured. Specifically, the conductive layer was analyzed by X-ray fluorescence analysis (XRF). A wavelength dispersive X-ray fluorescence analyzer manufactured by Shimadzu Corporation was used for the XRF analysis. The results are shown in Tables 1 to 3.

[0056]

[0057]

[0058]

[0059] 1…resin layer, 2…underground layer, 3…conductive layer, 3a, 3b…field, 10, 11, 12, 13…current collector.

Claims

1. A current collector for a secondary battery having a laminated structure including, in this order: a resin layer; an underlayer containing at least one of a metal and a metal oxide; and a conductive layer containing a metal and a metal oxide.

2. The current collector for a secondary battery according to claim 1, wherein at least a portion of the region containing the metal oxide in the conductive layer is separated from the underlayer.

3. The current collector for a secondary battery according to claim 2, wherein the distance between said region and said underlayer is 10 nm to 100 nm.

4. The current collector for a secondary battery according to any one of claims 1 to 3, wherein the thickness of the region containing the metal oxide in the conductive layer is 1 nm to 20 nm.

5. The current collector for a secondary battery according to claim 4, wherein the metal contained in the conductive layer includes one of Cu and Al, the metal oxide contained in the conductive layer includes at least one oxide selected from the group consisting of Ni, Cr, Mo, W, Nb, and Ta, and the underlayer includes at least one oxide selected from the group consisting of Ni, Cr, Mo, W, Nb, Cu, and Ta.

6. The current collector for a secondary battery according to claim 1, wherein the conductive layer has a thickness of 400 nm to 2500 nm.

7. The current collector for a secondary battery according to claim 1, wherein the thickness of the underlayer is 1 nm to 20 nm.

8. The current collector for a secondary battery according to claim 1, wherein the content of said metal oxide in said conductive layer is 500 ppm by volume to 5000 ppm by volume based on the entire conductive layer.

9. An electrode for a secondary battery, comprising the current collector according to claim 1.

10. A lithium ion secondary battery comprising the electrode according to claim 9.

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