WO2012147761A1 - 二次電池 - Google Patents
二次電池 Download PDFInfo
- Publication number
- WO2012147761A1 WO2012147761A1 PCT/JP2012/061028 JP2012061028W WO2012147761A1 WO 2012147761 A1 WO2012147761 A1 WO 2012147761A1 JP 2012061028 W JP2012061028 W JP 2012061028W WO 2012147761 A1 WO2012147761 A1 WO 2012147761A1
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- WO
- WIPO (PCT)
- Prior art keywords
- secondary battery
- negative electrode
- resin film
- acid
- aluminum foil
- Prior art date
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/64—Carriers or collectors
- H01M4/66—Selection of materials
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0566—Liquid materials
- H01M10/0568—Liquid materials characterised by the solutes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0566—Liquid materials
- H01M10/0569—Liquid materials characterised by the solvents
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/64—Carriers or collectors
- H01M4/66—Selection of materials
- H01M4/661—Metal or alloys, e.g. alloy coatings
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/64—Carriers or collectors
- H01M4/66—Selection of materials
- H01M4/665—Composites
- H01M4/667—Composites in the form of layers, e.g. coatings
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/64—Carriers or collectors
- H01M4/66—Selection of materials
- H01M4/668—Composites of electroconductive material and synthetic resins
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/64—Carriers or collectors
- H01M4/66—Selection of materials
- H01M4/663—Selection of materials containing carbon or carbonaceous materials as conductive part, e.g. graphite, carbon fibres
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/64—Carriers or collectors
- H01M4/66—Selection of materials
- H01M4/665—Composites
- H01M4/666—Composites in the form of mixed materials
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Definitions
- the present invention relates to a secondary battery. More specifically, the present invention relates to a secondary battery using an aluminum foil as a negative electrode current collector.
- This application claims priority based on Japanese Patent Application No. 2011-098316 filed in Japan on April 26, 2011, the contents of which are incorporated herein by reference.
- a lithium ion secondary battery generally includes a positive electrode current collector and a negative electrode current collector, a positive electrode active material layer and a negative electrode active material layer, an electrolyte solution, a separator, and an exterior material.
- the current collector is generally a metal foil, and is selected in consideration of conductivity, cost, weight, versatility, suppression of alloying, and corrosivity due to components in the electrolyte.
- a lithium-containing oxide as the positive electrode active material and graphite as the negative electrode active material
- it does not corrode against the potentials of the positive electrode and the negative electrode, or is alloyed with lithium.
- an aluminum foil is used for the positive electrode and a copper foil is used for the negative electrode.
- Copper foil is one of the materials that can withstand the negative electrode potential, and since it is a versatile metal, it is widely used as a negative electrode current collector.
- copper foil is expensive and easily oxidized due to environmental conditions, so that an oxide film is formed unevenly, reducing the electrical conductivity inside the battery and affecting the variation of battery products. Further, as a countermeasure, oxidation can be prevented by chromate treatment of the copper surface.
- chromium may be eluted in the electrolytic solution, which is not preferable in terms of characteristics. Thus, in addition to being inexpensive, studies are underway to replace the negative electrode current collector with aluminum having a thin and stable oxide film.
- Patent Document 1 discloses a lithium ion secondary battery, and for the prevention of alloying with lithium and the prevention of corrosion due to halogen elements in the electrolyte, an electrolyte containing no halogen element is used for the negative electrode. It is also described that aluminum foil can be used.
- the negative electrode active material is limited to what contains the element alloyed with lithium.
- graphite graphite
- aluminum and lithium are alloyed around 0V. Is described.
- the electrolytic solution does not contain a halogen element, a halogenated film is not formed on the surface of the aluminum foil used for the positive electrode current collector, and long-term durability is poor. Therefore, the present invention makes it possible to use an aluminum foil for the negative electrode current collector even when general graphite (graphite) is used as the negative electrode active material, and the cycle characteristics of the secondary battery are good and low cost.
- An object is to provide a secondary battery.
- the present invention relates to secondary batteries shown in the following [1] to [10].
- the first aspect of the present invention is the following secondary battery.
- the secondary battery of [1] is also preferably the following secondary battery.
- the carbonaceous material is one or more selected from the group consisting of carbon black, vapor grown carbon fiber, carbon nanofiber, and carbon nanotube. battery.
- non-aqueous electrolyte contains one or more selected from the group consisting of a cyclic carbonate, a chain carbonate, and a fatty acid ester as a solvent, and contains a fluorine-containing lithium salt as an electrolyte.
- the second aspect of the present invention is the following power supply system. [10] A power supply system including the secondary battery according to any one of [1] to [9].
- the secondary battery according to the present invention uses a current collector in which a resin film that does not transmit an electrolyte solution is formed on an aluminum foil as a negative electrode current collector. This suppresses the alloying of lithium and aluminum that occurred in the steel. Thereby, deterioration of a current collector can be prevented and cycle characteristics of the secondary battery can be improved.
- a lightweight and inexpensive aluminum foil can be used for the negative electrode current collector. Material processing and manufacturing costs can be greatly reduced by continuous processing such as a manufacturing method in which the material is fed out by a roll and wound by a roll.
- a conductive film containing a conductive material is used as the resin film, the electron conductivity between the negative electrode active material and the aluminum foil is good, and the internal resistance and impedance as a secondary battery can be reduced. .
- the secondary battery according to the present invention includes a positive electrode and a negative electrode, and the negative electrode includes a current collector in which a resin film that does not transmit electrolyte is formed on an aluminum foil, and a negative electrode active material layer.
- the thickness is usually preferably 5 ⁇ m to 200 ⁇ m, more preferably 15 ⁇ m to 70 ⁇ m.
- a roll having a thickness of 5 ⁇ m to 200 ⁇ m is preferably used.
- the material of the aluminum foil is not particularly limited, and a known material can be used as a current collector for the secondary battery.
- a pure aluminum foil or an aluminum alloy foil having a purity of 95% by mass or more can be used.
- foils such as A1085 material (pure aluminum type) and A3003 material (Mn addition type), can be mentioned, for example.
- the shape of the aluminum foil may be a foil having no holes, or a foil having holes such as a net-like foil or a punching metal foil.
- the aperture ratio can be arbitrarily selected. For example, 10 to 70% is preferable in that the secondary battery can be reduced in weight and size while maintaining the strength of the foil.
- the surface of the aluminum foil may be subjected to a known surface treatment.
- the surface treatment include alkali cleaning, solvent cleaning, mechanical surface processing, etching, chemical conversion treatment, anodization, wash primer, corona discharge, glow discharge, and the like.
- surface treatments when surface treatment is performed to form an insulating film other than the natural oxide film on the surface of the aluminum foil, it is necessary to control the thickness of the aluminum foil so as not to reduce the function as a current collector. .
- the thickness of the resin film used in the present invention is from 0.01 ⁇ m to 5 ⁇ m, preferably from 0.05 ⁇ m to 3 ⁇ m, more preferably from 0.1 ⁇ m to 3 ⁇ m. By setting it as such thickness, the thin collector which is advantageous to size reduction of a secondary battery can be formed, and permeation
- the thickness of the resin film is outside the range of the present invention, for example, if it is too thin, it is easy to form cracks and pinholes due to stress or impact during the battery manufacturing process, and conversely it is too thick Is not preferable because the resistance depending on the film thickness increases and the internal resistance and impedance of the secondary battery increase.
- the thickness of the resin film is measured by the following procedure using a TEM (transmission electron microscope).
- a TEM transmission electron microscope
- the sample is processed with FIB (focused ion beam) to cut out a cross section.
- the negative electrode current collector can be embedded in an epoxy resin (for example, product name: G2 manufactured by Gatan) and then processed.
- an epoxy resin for example, product name: G2 manufactured by Gatan
- platinum is preferably selected because the difference becomes clear.
- the cut section is first subjected to elemental analysis by EDX (energy dispersive X-ray spectroscopy) or the like, and a portion where aluminum is mainly detected is made of aluminum foil.
- the thin film area to be detected is confirmed as an aluminum oxide film, and the boundary of aluminum foil / aluminum oxide film / resin film is determined. Since both have different contrasts, the boundary can be easily identified.
- it is preferable to specify the element by appropriately changing the magnification within the range of 10,000 to 200,000 times.
- the thickness of the resin film is measured.
- the number of photographs taken is preferably 3 fields or more, more preferably 5 fields or more.
- the measurement of the thickness of the resin film is preferably 3 or more, more preferably 5 or more per field of view. A plurality of points selected at random are measured, and the average of the thicknesses at all measurement points is taken as the thickness of the resin film. At this time, if the resin film is significantly uneven, the minimum thickness portion and the maximum thickness portion must be included in the measurement points.
- the resin film is formed at least in a portion where the non-aqueous electrolyte solution contacts.
- the resin film may be formed on a part of the aluminum foil, or may be formed on the entire surface.
- the resin film is preferably applied to both surfaces of the aluminum foil, but may be applied to only one surface as necessary.
- the aluminum foil which formed the resin film is cut, it is possible to form a resin film further on the end surface.
- the resin film used here does not permeate the non-aqueous electrolyte described later.
- “not permeating non-aqueous electrolyte” means not permeating non-aqueous electrolyte in the following permeation test.
- the transmission test will be described.
- a perforated aluminum foil of A1085 material having a thickness of 20 ⁇ m, a hole diameter of 0.5 mm, and an aperture ratio of 40% is used as a supporting base, and a resin film to be tested is formed on one side of the supporting base with a predetermined thickness for testing.
- This is a perforated aluminum foil with a resin film. That is, the predetermined thickness is the thickness of the resin film actually formed on the current collector, and is 0.01 ⁇ m or more and 5 ⁇ m or less.
- the perforated aluminum foil with a resin film is cut into a size of 30 cm ⁇ 30 cm, and the edge portion of the cut aluminum foil is left outside the beaker and set in a bag shape inside the 200 ml glass beaker. At this time, the resin film is set on the outside.
- 100 ml of the non-aqueous electrolyte actually used for the secondary battery is put inside the perforated aluminum foil with a resin film in a bag shape, left at a temperature of 25 ° C. for 100 hours, and then the electrolyte is discharged using a dropper. .
- the perforated aluminum foil with resin film is taken out from the beaker while maintaining the bag shape.
- this aluminum foil was immersed in 150 ml of isopropyl alcohol so that the back side of the portion of the aluminum foil with a resin film that was in contact with the electrolyte was immersed, and the resin film portion was washed while rocking for 5 minutes. The aluminum foil is taken out after washing.
- the isopropyl alcohol cleaning solution is subjected to ICP-AES (Induction Plasma Emission Spectroscopy), ion chromatography, and GC-FID (gas chromatography-hydrogen ion). Analyze with a detector. ICP-AES analyzes lithium and phosphorus, ion chromatography analyzes fluorine, and GC-FID analyzes carbonate, which is a solvent, under the following conditions. If no analysis object is detected by any analysis, it is assumed that the electrolyte does not permeate.
- ICP-AES Induction Plasma Emission Spectroscopy
- ion chromatography analyzes fluorine
- GC-FID analyzes carbonate, which is a solvent, under the following conditions. If no analysis object is detected by any analysis, it is assumed that the electrolyte does not permeate.
- ICP-AES Analysis of lithium and phosphorus
- a standard sample (0 to 10 ppm) is prepared using a commercially available standard solution, thereby creating a calibration curve and performing quantitative analysis.
- 50 ppm was used as the lower limit of quantification for both lithium and phosphorus.
- the detection limit of ICP measurement the same measurement is performed with isopropyl alcohol (measured three times) instead of the isopropyl alcohol cleaning solution, and a value obtained by multiplying the standard deviation of the quantitative result by three is employed. If the measurement result of the sample solution is less than the detection limit, it is determined that the measurement target element is not detected.
- the measurement wavelengths are Li: 670.785 nm and P: 178.287 nm.
- ⁇ Ion chromatograph fluorine analysis
- the isopropyl alcohol washing solution after washing the aluminum foil is diluted 500 times, and this solution is subjected to ion chromatography measurement.
- a standard sample 0.5 ⁇ g / ml, 1.0 ⁇ g / ml, 2.0 ⁇ g / ml
- a calibration curve is created thereby to perform quantitative analysis.
- the detection limit of the ion chromatograph measurement is based on JIS K0124: 2002 general rules for high performance liquid chromatography, and a value obtained by multiplying S / N (signal / noise) by 3 is adopted.
- the measurement result of the sample solution is less than the detection limit, it is determined that the measurement target element is not detected.
- 50 ppm of fluorine was set as the lower limit of quantification. Measurement conditions are eluent: 1.8 mM-NaCO 3 aqueous solution + 1.7 mM-NaHCO 3 aqueous solution, flow rate: 1 ml / min.
- ⁇ GC-FID analysis of carbonate ester
- the isopropyl alcohol washing solution after washing the aluminum foil is diluted 100 times with dehydrated acetonitrile and then quantitatively analyzed by GC-FID under the following conditions.
- the column is a nonpolar capillary column.
- a standard sample is prepared by diluting a commercially available reagent (ethylene carbonate, propylene carbonate, dimethyl carbonate) with dehydrated acetonitrile, and a quantitative value is obtained from an area percentage with respect to the standard sample.
- the detection limit is based on JIS K0114: 2000, and a value obtained by triple the signal / noise ratio is adopted. If the measurement result of the sample solution is less than the detection limit, it is determined that the measurement target element is not detected.
- the resin film that does not transmit the non-aqueous electrolyte can be arbitrarily selected as necessary.
- the resin that can be included in the resin film having an impermeability to such a non-aqueous electrolyte include, for example, acrylic acid, methacrylic acid, itaconic acid, (meth) acryloylmorpholine, N, N-dimethyl (meth) acrylamide. Obtained by polymerizing one or more acrylic monomers such as N, N-dimethylaminoethyl (meth) acrylate, N, N-dimethylaminopropyl (meth) acrylamide, and glycerin (meth) acrylate.
- vinyl polymers such as polyvinyl acetal, ethylene-vinyl alcohol copolymer, polyvinyl alcohol, poly (N-vinylformamide), poly (N-vinyl-2-pyrrolidone); and resins such as polysaccharides I can give you.
- the above resins may be used alone or as a film containing two or more.
- two or more kinds of resins may be simply mixed with each other, different resins may form a crosslinked structure, or an interpenetrating polymer network (Interpenetratingpolymer network) structure) or semi-interpenetrating polymer structures.
- Interpenetratingpolymer network Interpenetratingpolymer network
- a cross-linked structure, an interpenetrating polymer structure or a semi-interpenetrating polymer structure is formed.
- the total amount of the resin is preferably 20 to 100% by mass, more preferably 20 to 70% by mass, and still more preferably 20 to 60% by mass in the resin film.
- a polysaccharide is a compound in which monosaccharides are polycondensed.
- the polysaccharide used in the present invention preferably has a weight average molecular weight of 1.0 ⁇ 10 4 to 2.0 ⁇ 10 5 , more preferably 5.0 ⁇ 10 4 to 2.0 ⁇ 10 5 . . When the molecular weight is within this range, the workability of resin film formation and the strength of the resin film are excellent.
- the molecular weight can be determined as a value converted to a standard sample such as pullulan using gel permeation chromatography.
- the polysaccharide may be either a homopolysaccharide or a heteropolysaccharide.
- the polysaccharide used in the present invention may be derivatized.
- derivatives include hydroxyalkylated, carboxyalkylated, sulfate esterified and the like.
- hydroxyalkylation is preferable because the solubility in a solvent can be increased and the resin film can be easily formed.
- the hydroxyalkyl group include a hydroxyethyl group, a hydroxypropyl group, a glyceryl group, and the like, preferably a glyceryl group.
- the hydroxyalkylated polysaccharide can be produced by a known method.
- polysaccharides include agarose, amylose, amylopectin, alginic acid, inulin, carrageenan, chitin, glycogen, glucomannan, keratan sulfate, colominic acid, chondroitin sulfate, cellulose, dextran, starch, hyaluronic acid, pectin, pectic acid, Examples include heparan sulfate, levan, lentinan, chitosan, pullulan, curdlan, and derivatives thereof. Of these polysaccharides, chitin, chitosan, and cellulose are preferable, and chitosan is more preferable.
- the polysaccharide is preferably contained in the resin film in an amount of 20 to 100% by mass, more preferably 20 to 70% by mass, and further preferably 20 to 50% by mass.
- the resin film preferably has conductivity. Therefore, the resin film preferably contains a conductive material.
- a conductive material can be selected as needed, it is more preferable that a carbonaceous material is included as a conductive material.
- Carbonaceous materials can be selected as needed, but examples include carbon blacks such as acetylene black, ketjen black, and furnace black, carbon fibers, vapor-grown carbon fibers, carbon nanotubes, and carbon nanofibers. It is. These conductive carbon materials can be used singly or in combination of two or more. Examples of conductive materials other than carbonaceous materials include powders of metals such as gold, silver, copper, nickel, iron, and zinc. Of these, gold, silver, and / or copper are preferably used because they are difficult to alloy with lithium.
- the shape of the conductive material can be arbitrarily selected.
- the conductive material may be spherical or irregularly shaped particles, or may have an anisotropic shape such as a needle shape or a rod shape.
- the particulate conductive material can be used without any particular limitation depending on the particle size.
- the number average primary particle size is preferably 10 nm to 5 ⁇ m, more preferably 10 nm to 100 nm.
- the number average primary particle size of the conductive material can be obtained by measuring the primary particle size of 100 to 1000 conductive material particles using an electron microscope and averaging them. In the case of a spherical shape, the equivalent diameter of the sphere is used.
- An anisotropic conductive material has a large surface area per mass and a large contact area with a current collector or an electrode active material, so that even when added in a small amount, it is between the current collector and the electrode active material or the electrode active material.
- the conductivity between them can be increased.
- Particularly effective anisotropic conductivity imparting materials include carbon nanotubes and carbon nanofibers.
- the carbon nanotube or carbon nanofiber has an average fiber diameter of usually 0.001 to 0.5 ⁇ m, preferably 0.003 to 0.2 ⁇ m, and an average fiber length of usually 1 to 100 ⁇ m, preferably 1 to 30 ⁇ m. Those are suitable for improving conductivity.
- the average fiber diameter and average fiber length of the conductive material can be obtained by observing the fiber diameter and fiber length of 100 to 1000 conductive material fibers using an electron microscope and determining the average value based on the number.
- the conductive material may be completely buried in the resin film or may be fixed in a state where it is partially exposed from the resin film. As long as the conductivity of the resin film is obtained, the dispersion state in the resin film is not limited. At that time, it is preferable that the conductive material does not fall off from the resin film, and the thickness of the resin film and the particle size of the conductive material can be selected so that the binding property is good.
- the conductive material is preferably contained in the resin film in an amount of 30 to 80% by mass, more preferably 30 to 70% by mass, and further preferably 40 to 70% by mass. By including the conductive material at this ratio, the conductivity of the resin film is improved, and the electrical conductivity between the aluminum foil and the negative electrode active material layer is improved.
- the conductive material is preferably 80 to 200 parts by weight, more preferably 90 to 180 parts by weight, and even more preferably 100 parts by weight with respect to 100 parts by weight of the polysaccharide. It is preferably contained in an amount of ⁇ 160 parts by mass.
- resin film in addition to the above resins and conductive materials, dispersion stabilizers, thickeners, anti-settling agents, anti-skinning agents, antifoaming agents, antistatic agents, anti-sagging agents, leveling agents, and crosslinking catalysts , And additives such as repellency inhibitors may be included.
- Organic acid When the resin film contains a polysaccharide, it is preferable to contain an organic acid as an additive.
- the organic acid has a function of improving the dispersibility of the polysaccharide in the solvent in the coating solution described later.
- the organic acid is a divalent or higher organic acid, it can be bonded to the polysaccharide when the coating solution is heated and dried to crosslink the polysaccharide, improve the membrane density, and suppress the electrolyte solution permeability of the resin film.
- a trivalent or higher valent organic acid is more preferable from the viewpoint of crosslink density.
- the amount of the organic acid is preferably 50 to 150 parts by mass, more preferably 70 to 100 parts by mass.
- the organic acid may be present as a free component in the resin film, but as described above, it is preferably present in a form bound to the polysaccharide.
- the organic acid can be selected as necessary, and preferred examples include carboxylic acid, sulfonic acid, phosphonic acid, and the like, and a particularly preferred example is carboxylic acid.
- carboxylic acid is used as the organic acid, it can be confirmed by the following method that the organic acid is bonded to the polysaccharide in the resin film.
- the formed resin film is cut out and subjected to FT-IR (infrared spectroscopic analysis) measurement by a microscopic ATR method (single reflection diamond ATR) under the following conditions.
- Microscopic ATR method FT-IR measurement conditions: Reference: Air Scan speed: 5 kHz Resolution: 4cm -1 Integration count: 100 times Measurement range: 4000-400 cm -1 Measurement area: 0.8mm ⁇ The measurement conditions are a resolution of 4 cm ⁇ 1 , an integration count (100 times), a measurement range (4000-400 cm ⁇ 1 ), and a measurement area (0.8 mm ⁇ ).
- the type of carboxylic acid can be selected as necessary, and examples thereof include aromatic carboxylic acid, aliphatic carboxylic acid, and alicyclic carboxylic acid. From the viewpoint of the heat resistance of the resin film, an aromatic carboxylic acid is preferable, and from the viewpoint of the effect as a dispersant, an aliphatic carboxylic acid is preferable.
- aromatic carboxylic acids include divalent carboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, tetrachlorophthalic acid, naphthalene dicarboxylic acid, diphenylsulfone dicarboxylic acid, and diphenylmethane dicarboxylic acid.
- the carboxylic acid include trimellitic acid, pyromellitic acid, and 1,4,5,8-naphthalenetetracarboxylic acid. Of these aromatic carboxylic acids, pyromellitic acid is preferred.
- the type of the aliphatic carboxylic acid can be selected according to need.
- Examples of the divalent carboxylic acid include oxalic acid, malonic acid, succinic acid, methyl succinic acid, glutaric acid, methyl glutaric acid, adipic acid, and pimelic acid.
- Examples of the trivalent or higher carboxylic acids include citric acid, 1,2,3-propanetricarboxylic acid, 1,2 , 4-butanetricarboxylic acid, 2-phosphono-1,2,4-butanetricarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, ethylenediaminetetraacetic acid, 1,2,3,4-butanetetracarboxylic acid, Examples include 2,4,5-cyclohexanetetracarboxylic acid and 1,2,3,4,5,6-cyclohexanehexacarboxylic acid. Of these aliphatic carboxylic acids, 1,2,3,4-butanetetracarboxylic acid is preferred.
- organic acids can be used singly or in combination of two or more.
- the organic acid is preferably contained in an amount of 40 to 120 parts by weight, more preferably 40 to 100 parts by weight, and still more preferably 40 to 90 parts by weight with respect to 100 parts by weight of the polysaccharide.
- the negative electrode current collector of the present invention can be produced by applying a coating liquid obtained by mixing each component contained in the resin film and a solvent onto the aluminum foil base material.
- the solvent used in the coating liquid can be arbitrarily selected, and examples thereof include aprotic polar solvents such as N-methylpyrrolidone and ⁇ -butyrolactone, protic polar solvents such as ethanol, isopropyl alcohol and n-propyl alcohol, And water.
- the amount of the solvent in the coating liquid is preferably 20 to 99% by mass, more preferably 50 to 98% by mass, and 80 to 95% by mass with respect to 100% by mass of the coating liquid. Is most preferred. By setting the amount of the solvent to such an amount, workability such as coating is excellent, and the coating amount of the resin film obtained by applying and drying the coating liquid can be made suitable.
- a free organic acid may be added to the coating liquid, or an acid derivative such as an acid anhydride or an ester is added, and the free organic acid or polyisocyanate is added by heating. You may make it become the organic acid couple
- an organic acid is bonded to the polysaccharide by heating and drying of the coating solution, it is preferably added as a free organic acid or acid anhydride because no by-product is produced.
- the polymer when an acrylic polymer or vinyl polymer is contained in the resin film, the polymer itself may be added to the coating solution, or a monomer constituting the polymer is added, followed by heating and light irradiation.
- the polymer may be formed by a method such as The method of mixing each component contained in the resin film and the solvent can be arbitrarily selected.
- examples of the mixer include a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, and a Hobart mixer.
- the method for applying the coating solution to the aluminum foil is not particularly limited and can be selected as necessary.
- a known coating method used in the production of an undercoat layer or an active material layer used for a lithium ion battery can be employed as it is.
- Specific examples include a casting method, a bar coater method, a dip method, and a printing method.
- a method such as slide die coating or dip coating is preferred.
- the application operation may be performed on each side, or the application operation may be performed on both sides simultaneously.
- the coating amount of the coating liquid on the aluminum foil can be arbitrarily selected.
- the weight after drying is preferably 0.01 to 5 g / m 2 , more preferably 0.1 to 3 g / m 2 , and most preferably 1 to 2 g / m 2 .
- the resin film can fully coat
- the measurement of the coating amount can be performed as follows.
- the coated part including the aluminum foil and the resin film is cut out, and the accurate area of the resin film and the mass of the aluminum foil with the resin film are measured. Thereafter, the resin film is peeled off using a release agent.
- the mass of the aluminum foil after peeling is measured, the mass of the resin film is obtained as the difference between the mass of the aluminum foil before peeling and the mass of the aluminum foil after peeling, and the coating amount is calculated by dividing by the area. .
- a general paint or resin release agent can be used.
- the drying method of the coating liquid is not particularly limited, but it is preferably heated within a temperature range of 100 to 300 ° C., more preferably 120 to 250 ° C., for 10 seconds to 10 minutes.
- the solvent remains in the resin film obtained by drying the coating liquid while maintaining the productivity, or the reaction for forming the polymer or the crosslinking reaction proceeds sufficiently.
- the organic component in the coating solution may be decomposed to reduce the fear, and the roughness of the resin film surface can be reduced.
- the negative electrode of the secondary battery is obtained by forming a negative electrode active material layer on the resin film.
- a negative electrode active material layer There is no restriction
- a graphite-based material such as natural graphite or artificial graphite, or an alloy-based material containing silicon or tin elements can be used.
- a slurry obtained by mixing 100 parts by mass of the negative electrode active material, 3 to 15 parts by mass of a conductive additive, 1 to 25 parts by mass of a binder, and a dispersion solvent is used.
- coating to and drying is mentioned.
- the amount of the dispersion solvent is not limited and can be appropriately selected so that the operation such as coating can be easily performed.
- the amount of the dispersion solvent is 70 to 70 parts per 100 parts by mass in total of the negative electrode active material, the conductive auxiliary agent, and the binder. 400 parts by mass.
- the secondary battery has the above-described negative electrode, and further usually has a positive electrode, a separator, and an electrolytic solution.
- a positive electrode and a separator will not be restrict
- Electrode non-aqueous electrolyte
- a known material used in a secondary battery can be used.
- cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), etc.
- a fluorine-containing lithium salt such as lithium hexafluorophosphate (LiPF 6 ) or lithium tetrafluoroborate (LiBF 4 ) in a solvent such as a chain carbonate ester or a fatty acid ester
- a solvent such as a chain carbonate ester or a fatty acid ester
- a fluoride film is formed on the surface of the electric body.
- solvents can be used alone or in admixture of two or more at any ratio.
- a gel electrolyte, a polymer electrolyte, an inorganic solid electrolyte, or a molten salt electrolyte can also be used.
- Secondary batteries can be applied to power supply systems.
- this power supply system includes automobiles; transport equipment such as railways, ships and airplanes; portable equipment such as mobile phones, personal digital assistants and portable electronic computers; office equipment; solar power generation systems, wind power generation systems, fuel cell systems, etc. It can be applied to the power generation system.
- Comparative production example A comparative current collector 1 and a comparative current collector 2 were produced in the same manner as in the above production example except that the raw materials shown in Table 1 were used.
- the current collectors 1 to 6 and the comparative current collectors 1 and 2 were processed by FIB (focused ion beam) to cut out a cross section and deposit platinum. Subsequently, the resin film was observed by a TEM (manufactured by Hitachi, Ltd., model: H-9500) by the method described above. The number of photographs was 5 fields, the thickness of the resin film was measured at 5 locations per field, and the thickness of the resin film was determined by arithmetic average. Table 1 shows the thickness of the resin film.
- a portion 10 cm ⁇ 10 cm of the current collectors 1 to 6 and the comparative current collectors 1 and 2 where the resin film was formed was cut out, and the product name Neo River # 346 manufactured by Sansai Processing Co., Ltd. was used as a release agent. The coating amount of the coating film was measured by this method.
- Non-aqueous electrolyte 1M LiPF 6 -EC: DMC: DEC (1: 1: 1 v / v) solution (manufactured by Kishida Chemical Co., 1 wt% vinyl chloride added)
- ICP-AES manufactured by Shimadzu Corporation, product name ICPS-8000
- Ion chromatograph Product name DX-500, manufactured by Dionex Column for ion chromatography: Showa Denko, product name SI-90 GC-FID: Product name HP6890, manufactured by Agilent Technologies Column for gas chromatography: Product name DB-1 manufactured by J & W Scientific (inner diameter 0.32 mm, length 20 m, film thickness 1 ⁇ m)
- Examples 1 to 6 Manufacture of secondary batteries
- Each of the current collectors 1 to 6 described above was cut into a size of 10 cm ⁇ 10 cm.
- Artificial graphite made by Showa Denko KK, trade name SCMG-AR
- acetylene black trade name Denka Black (powdered product) made by Denki Kagaku Kogyo Co., Ltd.
- a slurry obtained by mixing 5 parts by mass of polyvinylidene fluoride (trade name KF polymer # 9130, manufactured by Kureha Co., Ltd.) as a binder and 94 parts by mass of N-methyl-2-pyrrolidone (industrial grade) as a dispersion solvent,
- a negative electrode was formed by coating the current collectors 1 to 6 on both surfaces, drying, and pressing to form a negative electrode active material layer having a thickness of 55 ⁇ m on one side.
- a separator (made by POLYPORE International, Inc., trade name Celgard 2500) is incorporated between the positive electrode and the negative electrode, and the positive electrode and the negative electrode are alternately stacked so that the outermost layer is the negative electrode with three positive electrodes and four negative electrodes (design)
- the capacity was 1 Ah
- the positive electrode was attached with an aluminum tab electrode
- the negative electrode was attached with a nickel tab electrode by an ultrasonic welding machine.
- These are put into a bag-like aluminum laminate packaging material, and after removing moisture with a vacuum dryer at 60 ° C., the LiPF 6 solution used for the permeation test is injected as a non-aqueous electrolyte and impregnated in a vacuum atmosphere for 24 hours.
- the secondary battery was fabricated by sealing the opening of the aluminum laminate packaging material with a vacuum sealer.
- the secondary battery was evaluated as follows.
- the internal resistance was measured by an AC impedance method using an impedance meter (manufactured by Hioki Electric Co., Ltd., model 3532-80) at a measurement frequency of 1 kHz.
- cycle characteristics were measured. Measurement was performed using a charge / discharge device (manufactured by Toyo System Co., Ltd.), changing the current rate to 0.2C, 2C, and 20C, the initial capacity maintenance ratio after 200 cycles, and the capacity maintenance ratio for 0.2C to 100%. As displayed. Note that the cut voltage was 2.7 to 4.2 V and the SOC was 100%.
- Comparative Example 4 A secondary battery was fabricated and evaluated in the same manner as in Example except that the aluminum foil of Comparative Example 1 was heat-treated in an oxidizing atmosphere at 150 ° C. for 3 hours and the oxide film was thickened to 25 nm. Table 2 shows the evaluation results of the secondary batteries produced in the examples and comparative examples.
- An object of the present invention is to provide a low-cost secondary battery that can use an aluminum foil as a negative electrode current collector and that has good cycle characteristics of the secondary battery.
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Abstract
Description
本願は、2011年4月26日に、日本に出願された特願2011-098316号に基づき優先権を主張し、その内容をここに援用する。
そこで本発明は、一般的な黒鉛(グラファイト)を負極活物質として用いた場合にも、負極集電体にアルミニウム箔を用いることを可能とし、かつ二次電池のサイクル特性が良好で低コストな二次電池を提供することを目的とする。
本発明の第1の態様は以下の二次電池である。
[1]正極と負極とを備えた二次電池であって、前記負極は負極集電体と負極活物質層とを有し、前記負極集電体が、アルミニウム箔製の基材と、非水電解液を透過しない0.01~5μm厚の樹脂皮膜とを有する二次電池。
上記[1]の二次電池は、以下の二次電池であることも好ましい。
[2] 前記樹脂皮膜が多糖類を含む、[1]に記載の二次電池。
[3] 前記樹脂皮膜が導電材を含む[1]または[2]に記載の二次電池。
[4] 前記導電材が炭素質材料である[1]から[3]のいずれかに記載の二次電池。
[5] 前記炭素質材料が、カーボンブラック、気相法炭素繊維、カーボンナノファイバー、カーボンナノチューブよりなる群から選ばれる1種以上である[1]から[4]のいずれかに記載の二次電池。
[7] 前記多糖類に有機酸がエステル結合している[1]から[6]のいずれかに記載の二次電池。
[8] 前記負極活物質層が黒鉛を含む[1]から[7]のいずれかに記載の二次電池。
[9] 前記非水電解液が溶媒として環状炭酸エステル、鎖状炭酸エステル、脂肪酸エステルからなる群より選ばれる1種類以上を含み、電解質として含フッ素リチウム塩を含む[1]から[8]のいずれかに記載の二次電池。
本発明の第二の態様は以下の電源システムである。
[10] [1]から[9]のいずれかの二次電池を有する電源システム。
本発明に係る二次電池は、正極と負極とを有し、前記負極は、アルミニウム箔上に電解液を透過しない樹脂皮膜を形成した集電体と、負極活物質層とを有する。
本発明で使用されるアルミニウム箔の厚さによって特に制限されず、任意に選択できる。二次電池の小型化や、アルミニウム箔およびそれを用いて得られる集電体や電極等のハンドリング性などの観点からは、通常5μm厚~200μm厚が好ましく、15μm厚~70μmがより好ましい。ロールトゥロール製法を行う場合、好ましくは5μm厚~200μm厚のものを用いる。
本発明で使用される樹脂皮膜の厚さは、0.01μm以上5μm以下、好ましくは0.05μm以上3μm以下、より好ましくは0.1μm以上3μm以下である。このような厚さとすることにより、二次電池の小型化に有利な薄型の集電体を形成でき、かつ、非水電解液の透過を抑制できる。また導電性の観点では、樹脂皮膜の厚さが5μm以下であると、膜厚に依存する抵抗が小さく、二次電池の内部抵抗やインピーダンスを低減することができる。本発明の範囲外の樹脂皮膜の厚さであると、例えば薄すぎる場合は電池の製造工程時に応力を受けたり、衝撃を受けたりすることでクラックやピンホールが出来やすく、逆に厚すぎる場合は膜厚に依存する抵抗が大きくなり、二次電池の内部抵抗やインピーダンスが増大するので好ましくない。
ただし、後述される導電材として炭素質材料を用いている場合は、差異が明確になる為に、白金の方が好ましく選ばれる。続いて、切り出された断面に対して、TEMを用いて、まず、EDX(エネルギー分散X線分光法)などで元素分析し、主にアルミニウムが検出される部分はアルミニウム箔とし、アルミニウムと酸素が検出される薄膜領域はアルミニウム酸化膜として確認し、アルミニウム箔/アルミニウム酸化膜/樹脂皮膜の境界を決定する。いずれもコントラストが異なるので境界は容易に判別できる。
この際、10,000~200,000倍の範囲で適宜倍率を変えることで元素を特定することが好ましい。次に樹脂皮膜の厚さを測定する。写真撮影点数は、好ましくは3視野以上、より好ましくは5視野以上である。さらに樹脂皮膜の厚さの測定は1視野あたり、好ましくは3箇所以上、さらに好ましくは5箇所以上である。ランダムに選んだ複数点を測定し、全ての測定箇所での厚みを算術平均したものを樹脂皮膜の厚さとする。この際、樹脂皮膜に著しく凹凸がある場合は、最小厚部分と最大厚部分を必ず測定点に含める。
ここで用いる樹脂皮膜は、後述する非水電解液を透過しない。ここで、非水電解液を透過しないとは、以下の透過試験において、非水電解液を透過しないことを言う。
透過試験に使用するサンプルを形成する。まず厚み20μm、孔径0.5mm、開口率40%のA1085材の孔開きアルミニウム箔を支持基材とし、試験対象となる樹脂皮膜を支持基材の片面に、所定の厚みで形成し、試験用の樹脂皮膜付き孔開きアルミニウム箔とする。所定の厚みとはすなわち、実際に集電体に形成される樹脂皮膜の厚みであり、0.01μm以上5μm以下である。
次に、樹脂皮膜付き孔開きアルミニウム箔を30cm×30cmの大きさに切り出し、切り出したアルミニウム箔の縁端部はビーカーの外に出したままで、200mlガラスビーカーの内側に袋状にセットする。なおこの際、樹脂皮膜が外側になるようにセットする。袋状にした樹脂皮膜付き孔開きアルミニウム箔の内側に、実際に二次電池に用いる非水電解液を100ml投入し、温度25℃で100時間放置した後、電解液をスポイトを用いて排出する。
樹脂皮膜付き孔開きアルミニウム箔を、袋状を維持したままビーカーから取り出す。続いてこのアルミニウム箔を、樹脂皮膜付き孔開きアルミニウム箔の、電解液が接していた部分の裏側がほぼ浸るよう、150mlのイソプロピルアルコールに浸漬させ、5分間揺動させながら樹脂皮膜部分を洗浄し、洗浄後アルミニウム箔を取り出す。
上記アルミニウム箔を洗浄した後のイソプロピルアルコール洗浄液を、別に用意した100mlのビーカーに1ml採取した後、洗浄液を加熱してイソプロピルアルコールを除去する。その後、このビーカーを10mlの純水で洗浄して、その洗浄水をポリプロピレン製容器に回収する。この操作を4回繰り返した後、回収した洗浄水に硝酸1mlを添加し、純水で50mlに定容する。この定容後の溶液をICP-AES測定に供する。
上記アルミニウム箔を洗浄した後のイソプロピルアルコール洗浄液を、500倍に希釈し、この溶液を、イオンクロマトグラフの測定に供する。測定は、市販の標準溶液を用いて濃度既知の標準試料(0.5μg/ml、1.0μg/ml、2.0μg/ml)を調製し、これにより検量線を作成して定量分析を行う。イオンクロマトグラフ測定の検出限界は、JIS K0124:2002 高速液体クロマトグラフィー通則に準拠し、S/N(シグナル/ノイズ)を3倍した値を採用する。試料溶液の測定結果が検出限界未満であれば、測定対象元素は検出されないと判定する。本分析方法にてフッ素50ppmを定量下限とした。測定条件は、溶離液:1.8mM―NaCO3水溶液+1.7mM-NaHCO3水溶液、流量:1ml/分である。
前記アルミニウム箔を洗浄した後のイソプロピルアルコール洗浄液を、脱水アセトニトリルで100倍に希釈した後、GC-FIDにより、下記の条件で定量分析を行う。カラムは無極性のキャピラリーカラムを用いる。標準試料は市販の試薬(エチレンカーボネート、プロピレンカーボネート、ジメチルカーボネート)を脱水アセトニトリルにより希釈することにより調製し、標準試料に対する面積百分率により定量値を求める。なお、検出限界は、JIS K0114:2000に準拠し、シグナル/ノイズ比を3倍した値を採用する。試料溶液の測定結果が検出限界未満であれば、測定対象元素は検出されないと判定する。
キャリアガス:He
カラム流量:1.5ml/min(コンスタントフロー)
注入モード:スプリット(スプリット比1:20)
注入口温度:280℃
注入量:1μl
試料濃度:1%(v/w。脱水アセトニトリルで希釈)
FID温度:350℃
上記の樹脂は、樹脂皮膜中に合計で好ましくは20~100質量%、より好ましくは20~70質量%、さらに好ましくは20~60質量%含まれる。
多糖類は単糖類が重縮合した化合物である。本発明で使用される多糖類は、好ましくは重量平均分子量が1.0×104~2.0×105であり、より好ましくは5.0×104~2.0×105である。分子量がこの範囲内であると、樹脂皮膜形成の作業性や、樹脂皮膜の強度に優れる。分子量は、ゲルパーミエーションクロマトグラフィーを用いて、プルランなどの標準サンプルに換算した値として求めることができる。多糖類はホモ多糖、ヘテロ多糖のいずれでもよい。
多糖類は、樹脂皮膜中に好ましくは20~100質量%、より好ましくは20~70質量%、さらに好ましくは20~50質量%含まれる。
アルミニウム箔と負極活物質層との電子のやりとりを円滑にする観点から、上記樹脂皮膜は、導電性を有することが好ましい。そのため、樹脂皮膜は導電材を含むことが好ましい。導電材は必要に応じて選択できるが、導電材として炭素質材を含むことがより好ましい。
炭素質材は必要に応じて選択できるが、例を挙げれば、アセチレンブラック、ケッチェンブラック、ファーネスブラックなどのカーボンブラックや、炭素繊維、気相成長炭素繊維、カーボンナノチューブ、カーボンナノファイバーなどが好適である。これらの導電性炭素材は1種単独でまたは2種以上を組み合わせて用いることができる。
炭素質材料以外の導電材としては、金、銀、銅、ニッケル、鉄、亜鉛などの金属の粉末があげられる。リチウムと合金化しにくいことから、これらのうちで金、銀、及び/または銅が使用されることが好ましい。
粒子状の導電材は、その粒子サイズによって特に制限されず使用できる。しかしながら、数平均一次粒径が10nm~5μmのものが好ましく、10nm~100nmのものがより好ましい。導電材の数平均一次粒径は、電子顕微鏡を用いて100~1000個の導電材粒子の一次粒径を計測し、これを平均することによって得られる。球状の場合は球換算径、不定形状の場合は、最大長径を粒子径とする。
本発明において、導電材は樹脂皮膜中に好ましくは30~80質量%、より好ましくは30~70質量%、さらに好ましくは40~70質量%含まれる。この割合で導電材を含むことによって、樹脂皮膜の導電性が向上し、アルミニウム箔と負極活物質層の間の電気伝導性が向上する。
なお多糖類と導電材の両方が樹脂皮膜中に含まれる場合、多糖類100質量部に対して、導電材は好ましくは80~200質量部、より好ましくは90~180質量部、さらに好ましくは100~160質量部含まれることが好ましい。
樹脂皮膜には上記の樹脂および導電材の他、分散安定剤、増粘剤、沈降防止剤、皮張り防止剤、消泡剤、静電塗装性改良剤、タレ防止剤、レベリング剤、架橋触媒、及びハジキ防止剤などの添加剤を含んでもよい。
樹脂皮膜が多糖類を含む場合は、添加剤として有機酸を含むことが好ましい。有機酸は後述する塗工液中で、多糖類の溶媒への分散性を向上させる働きをもつ。有機酸は2価以上の有機酸であると、塗工液の加熱乾燥時に多糖類に結合して多糖類を架橋し、膜密度を向上させ、樹脂皮膜の電解液透過性を抑制させられることから好ましい。さらには架橋密度の観点から3価以上の有機酸であることがより好ましい。有機酸の量は好ましくは50~150質量部、より好ましくは70~100質量部である。
顕微ATR法FT-IR測定条件:
リファレンス:Air
スキャン速度:5kHz
分解能:4cm-1
積算回数:100回
測定範囲:4000~400cm-1
測定面積:0.8mmφ
測定条件は、分解能4cm-1、積算回数(100回)、測定範囲(4000-400cm-1)、測定面積(0.8mmφ)である。
有機酸は多糖類100質量部に対し、好ましくは40~120質量部、より好ましくは40~100質量部、さらに好ましくは40~90質量部含まれる。
本発明の負極集電体は、上述の樹脂皮膜に含まれる各成分と、溶媒と、を混合した塗工液を、上記アルミニウム箔製の基材上に塗布して製造することができる。
塗工液に用いる溶媒は任意に選択でき、その例としては、N-メチルピロリドン及びγ-ブチロラクトンなどの非プロトン性極性溶媒や、エタノール、イソプロピルアルコール及びn-プロピルアルコールなどのプロトン性極性溶媒、及び水などが挙げられる。塗工液中の溶媒の量は、塗工液100質量%に対し、20~99質量%であることが好ましく、50~98質量%であることがより好ましく、80~95質量%であることが最も好ましい。溶媒の量をこのような量にすることにより、塗布などの作業性に優れ、塗工液を塗布、乾燥して得られる樹脂皮膜の塗布量を好適なものとすることができる。
樹脂皮膜に含まれる各成分と、溶媒とを混合する方法は任意で選択できる。混合機を用いる場合、混合機の例としては、ボールミル、サンドミル、顔料分散機、擂潰機、超音波分散機、ホモジナイザー、プラネタリーミキサー、及びホバートミキサーなどが挙げられる。
塗工液をアルミニウム箔に塗布する方法は特に制限されず必要に応じて選択できる。例えば、リチウムイオン電池に使用されるアンダーコート層や活物質層の製造において用いられる、公知の塗布方法がそのまま採用できる。
具体的には、キャスト法、バーコーター法、ディップ法、印刷法などが例として挙げられる。これらのうち、塗布膜の厚さを制御しやすい点から、バーコート、グラビアコート、グラビアリバースコート、ロールコート、マイヤーバーコート、ブレードコート、ナイフコート、エアーナイフコート、コンマコート、スロットダイヤコート、スライドダイコート、ディップコート等の方法が好ましい。両面に塗布する場合は、片面ずつ塗布操作を行ってもよいし、両面に同時に塗布操作を行ってもよい。
二次電池の負極は、上記の樹脂皮膜上に、負極活物質層を形成して得られる。負極活物質層に用いられる材料や負極活物質層の形成方法に特に制限はなく、二次電池の製造に用いられている公知の材料、及び方法を採用することができる。負極活物質層には、例えば、天然黒鉛や人造黒鉛などのグラファイト系、及びケイ素や錫の元素を含む合金系などの材料が使用可能である。負極活物質層の製法の具体例を挙げれば、負極活物質100質量部、導電助剤3~15質量部、バインダー1~25質量部と、分散溶剤とを混合したスラリーを集電体の表面に塗布し、乾燥する方法が挙げられる。分散溶剤の量には制限が無く、塗布等の作業が行いやすいように適宜選択することができ、例えば、負極活物質と、導電助剤と、バインダーとの合計100質量部に対し、70~400質量部である。
二次電池は、上述の負極を有し、さらに正極、セパレーターおよび電解液を、通常有するものである。正極およびセパレーターは、リチウムイオン二次電池などの二次電池に使用されるものであれば特に制限されない。
電解質は二次電池に使用されている公知の材料を用いることが可能である。例えば正極集電体としてアルミニウム箔を用いる場合、プロピレンカーボネート(PC)、エチレンカーボネート(EC)などの環状炭酸エステル類、ジメチルカーボネート(DMC)、エチルメチルカーボネート(EMC)、ジエチルカーボネート(DEC)などの鎖状炭酸エステル類、脂肪酸エステル類などの溶媒に、六フッ化リン酸リチウム(LiPF6)、四フッ化ホウ酸リチウム(LiBF4)などの含フッ素リチウム塩を溶解したものを用いると、集電体表面にフッ化膜が形成されるため好ましい。前記溶媒は、単独でまたは2種以上を任意の割合で混合して用いることができる。
その他、ゲル電解質、ポリマー電解質、無機固体電解質、あるいは溶融塩電解質を用いることもできる。
表1に示す原料をディゾルバータイプの撹拌機を用いて回転数300rpmで10分間分散し、さらにホモジナイザー(家田貿易(株)製、製品名PRO200)で20000rpmで30秒間処理し、十分に分散した塗工液を作製した。
次にアルカリ洗浄したA1085材からなる厚さ30μm(酸化皮膜の膜厚3nm)のアルミニウム箔を用意した。形成する皮膜の厚みに応じ、マイヤーバー♯0番、♯1番、又は♯2番を用いて、バーコーター法でアルミニウム箔の片面に塗工液を塗工した。その後、大気中180℃にて3分間加熱乾燥した。同様にもう一方の片面にも同様に塗工後、加熱乾燥することで、樹脂皮膜を備えた集電体1~6を得た。
表1に示す原料を用いた他は、上記製造例と同様にして、比較集電体1および比較集電体2を作製した。
集電体1~6および比較集電体1、2を、FIB(集束イオンビーム)で加工することで断面を切り出し、白金を蒸着した。続いて、TEM(日立製作所製、型式:H-9500)にて、上述の方法で樹脂皮膜の観察を行った。写真撮影点数は5視野とし、1視野あたり5箇所で樹脂皮膜の厚さを測定し、算術平均により樹脂皮膜の厚さを求めた。樹脂皮膜の厚さを表1に示す。
集電体1~6および比較集電体1、2の、樹脂皮膜が形成された部分10cm×10cmを切り出し、剥離剤として三彩加工(株)製、製品名ネオリバー♯346を用いて、上述の方法で塗膜の塗布量を測定した。
孔径0.5mm、開口度40%、厚み20μmの孔開きアルミニウム箔の片面に、集電体1~6および比較集電体1、2と同様の樹脂皮膜を形成し、それぞれ上述の非水電解液の透過性試験を行った。試験条件は以下の通りである。結果を表1に示す。
非水電解液:1M LiPF6-EC:DMC:DEC(1:1:1v/v)溶液(キシダ化学製、1wt%ビニルクロライド添加)
ICP-AES:島津製作所製、製品名ICPS―8000
イオンクロマトグラフ装置:ダイオネックス社製、製品名DX―500
イオンクロマトグラフィー用カラム:昭和電工製、製品名SI―90
GC-FID:アジレント・テクノロジー社製、製品名HP6890
ガスクロマトグラフィー用カラム:J&W Scientific社製 製品名DB―1(内径0.32mm、長さ20m、膜厚1μm)
(二次電池の製造)
上述の集電体1~6をそれぞれ10cm×10cmの大きさに切り出した。負極活物質として人造黒鉛(昭和電工(株)製、商品名SCMG-AR)94質量部、導電助剤としてアセチレンブラック(電気化学工業(株)製、商品名デンカブラック(粉状品))1質量部、バインダーとしてポリフッ化ビニリデン((株)クレハ製、商品名KFポリマー#9130)5質量部、分散溶剤としてN-メチル-2-ピロリドン(工業用グレード)94質量部を混合したスラリーを、集電体1~6それぞれの両面に塗布し、乾燥、及びプレスして、片面55μm厚の負極活物質層を形成したものを負極とした。
二次電池を以下のようにして評価した。
内部抵抗はインピーダンスメーター(日置電機(株)製、型式3532-80)を用い、ACインピーダンス法で、測定周波数1kHzにて測定した。
さらにサイクル特性を測定した。測定は充放電装置(東洋システム(株)製)を用い、電流レートを0.2C、2C 、及び20C と変えて200サイクル後の初期容量維持率を、0.2Cに対する容量維持率を100%として表示した。なお、カット電圧は2.7~4.2VでSOCは100%として測定した。
上述の比較集電体1および2を負極集電体とした他は、実施例と同様にして二次電池の作製、評価を行った。
アルカリ洗浄したA1085材からなる厚さ30μmアルミニウム箔(酸化膜3nm)を負極集電体とした他は、実施例と同様にして二次電池の作製、評価を行った。
比較例1のアルミニウム箔を、酸化雰囲気で150℃、3時間加熱処理し、酸化膜を25nmと厚くした他は、実施例と同様にして二次電池の作製、評価を行った。
実施例および比較例で作製した二次電池の評価結果を表2に示す。
二次電池のサイクル試験終了後、実施例1、比較例1ならびに比較例3の二次電池を分解し、負極集電体を取り出した。イソプロピルアルコールで十分洗浄、乾燥した後に解析を行った。
目視の観察として、実施例1の負極集電体に変化は見られなかったが、比較例1および比較例3の負極集電体では所々に変質した部分が観察された。実施例1の負極集電体の一部および比較例1および比較例3の変質した部分を回折X線にて分析したところ、比較例1および比較例3の負極集電体ではリチウムとアルミニウムの合金が検知された。一方、実施例1の負極集電体ではリチウムは検知されなかった。
Claims (10)
- 正極と負極とを備えた二次電池であって、
前記負極は負極集電体と負極活物質層とを有し、
前記負極集電体が、アルミニウム箔製の基材と、非水電解液を透過しない0.01~5μm厚の樹脂皮膜とを有する二次電池。 - 前記樹脂皮膜が多糖類を含む請求項1に記載の二次電池。
- 前記樹脂皮膜が導電材を含む請求項1に記載の二次電池。
- 前記導電材が炭素質材料である請求項1に記載の二次電池。
- 前記炭素質材料が、カーボンブラック、気相法炭素繊維、カーボンナノファイバー、カーボンナノチューブよりなる群から選ばれる1種以上である請求項1に記載の二次電池。
- 前記多糖類がキトサン、キチン、セルロースおよびそれらの誘導体からなる群より選ばれる1種類以上を含む請求項1に記載の二次電池。
- 前記多糖類に有機酸がエステル結合している請求項1に記載の二次電池。
- 前記負極活物質層が黒鉛を含む請求項1に記載の二次電池。
- 前記非水電解液が溶媒として環状炭酸エステル、鎖状炭酸エステル、脂肪酸エステルからなる群より選ばれる1種類以上を含み、電解質として含フッ素リチウム塩を含む、請求項1に記載の二次電池。
- 請求項1の二次電池を有する電源システム。
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JP2016521914A (ja) * | 2013-06-21 | 2016-07-25 | ハイドロ−ケベック | 高エネルギー電池用アノード |
WO2021033469A1 (ja) * | 2019-08-19 | 2021-02-25 | 株式会社村田製作所 | 二次電池 |
US11621417B2 (en) | 2017-11-22 | 2023-04-04 | Gs Yuasa International Ltd. | Lithium ion secondary battery |
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JPWO2013172256A1 (ja) * | 2012-05-15 | 2016-01-12 | 株式会社Uacj | 集電体、電極構造体、非水電解質電池及び蓄電部品、集電体の製造方法 |
CN105375034B (zh) * | 2015-10-30 | 2017-12-19 | 上海璞泰来新能源科技股份有限公司 | 一种锂离子电池集流体及其制备方法和一种锂离子电池 |
CN106784987A (zh) * | 2015-11-23 | 2017-05-31 | 深圳市比克动力电池有限公司 | 锂离子电池负极材料、负极和锂离子电池 |
CN105977524A (zh) * | 2016-07-07 | 2016-09-28 | 无锡市宝来电池有限公司 | 一种环保型的电池导电密封涂层 |
KR20190114151A (ko) | 2018-03-29 | 2019-10-10 | 현대자동차주식회사 | 리튬 이차전지 및 그 제조방법 |
DE102019104721A1 (de) | 2019-02-25 | 2020-08-27 | Hydro Aluminium Rolled Products Gmbh | Aluminiumfolie für Batterieelektroden und Verfahren zur Herstellung |
CN110429240B (zh) | 2019-08-08 | 2020-12-04 | 宁德时代新能源科技股份有限公司 | 正极极片及包括该正极极片的电化学装置 |
CN110400933B (zh) | 2019-08-08 | 2020-12-04 | 宁德时代新能源科技股份有限公司 | 正极极片及包括该正极极片的电化学装置 |
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