WO2011121950A1 - 非水電解質二次電池用負極、およびその製造方法、ならびに非水電解質二次電池 - Google Patents
非水電解質二次電池用負極、およびその製造方法、ならびに非水電解質二次電池 Download PDFInfo
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- WO2011121950A1 WO2011121950A1 PCT/JP2011/001741 JP2011001741W WO2011121950A1 WO 2011121950 A1 WO2011121950 A1 WO 2011121950A1 JP 2011001741 W JP2011001741 W JP 2011001741W WO 2011121950 A1 WO2011121950 A1 WO 2011121950A1
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- H01M4/64—Carriers or collectors
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- H01M4/80—Porous plates, e.g. sintered carriers
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- 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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- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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- 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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- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/139—Processes of manufacture
- H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/139—Processes of manufacture
- H01M4/1393—Processes of manufacture of electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
- H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/621—Binders
- H01M4/622—Binders being polymers
- H01M4/623—Binders being polymers fluorinated polymers
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/64—Carriers or collectors
- H01M4/70—Carriers or collectors characterised by shape or form
- H01M4/72—Grids
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- H—ELECTRICITY
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- 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
- H01M4/70—Carriers or collectors characterised by shape or form
- H01M4/72—Grids
- H01M4/74—Meshes or woven material; Expanded metal
- H01M4/742—Meshes or woven material; Expanded metal perforated material
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- 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
- H01M2004/021—Physical characteristics, e.g. porosity, surface area
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- H—ELECTRICITY
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- 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
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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- 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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- 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 non-aqueous electrolyte secondary battery, and in particular, to an improvement of a negative electrode used therefor.
- non-aqueous electrolyte secondary batteries having high electromotive force and energy density have been widely used as power sources for portable electronic devices.
- non-aqueous electrolyte secondary batteries are used as in-vehicle batteries, and studies have been conducted for the purpose of improving performance suitable for in-vehicle use such as output characteristics.
- the electrode of a nonaqueous electrolyte secondary battery generally has a current collector made of metal and a mixture layer containing an active material formed on the surface of the current collector.
- the current collector is a porous substrate (Patent Documents 1 and 2) or a metal foil having a plurality of through holes (Patent Documents 3 and 4). ) Is under consideration.
- JP-A-9-45334 JP 2008-41971 A Japanese Patent Laid-Open No. 11-67218 JP 2008-59765 A
- an object of the present invention is to provide a nonaqueous electrolyte secondary battery having excellent charge / discharge cycle characteristics.
- One aspect of the present invention is: A sheet-like current collector having a plurality of through holes; A carbon layer formed in the surface of the current collector and in the through hole; A mixture layer formed on the surface of the carbon layer; With The mixture layer includes an active material and a conductive agent, The active material includes a lithium-titanium-containing composite oxide having a spinel crystal structure, The current collector has a porosity of 20 to 60%; The carbon layer has an average density of 0.05 to 0.4 g / cm 3 ; The present invention relates to a non-aqueous electrolyte secondary battery.
- Another aspect of the present invention relates to a nonaqueous electrolyte secondary battery including a positive electrode, the negative electrode, a separator disposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte.
- Still another aspect of the present invention provides: (A) applying a first paste containing a carbon material to the surface of a sheet-like current collector having a plurality of through-holes and a porosity of 20 to 60%, and drying the current collector; Forming a carbon layer on the surface and in the through hole; (B) On the surface of the carbon layer, a second paste containing a lithium-titanium-containing composite oxide having a spinel crystal structure and a conductive agent as an active material is applied and dried to form a mixture layer.
- the charge / discharge cycle characteristics of the nonaqueous electrolyte secondary battery can be improved.
- the negative electrode for a non-aqueous electrolyte secondary battery of the present invention has the following features i) to iv).
- the negative electrode has a plurality of through holes, a sheet-like current collector, a surface of the current collector and a carbon layer formed in the through holes, and a mixture formed on the surface of the carbon layer A layer.
- the mixture layer includes a lithium-titanium-containing composite oxide (hereinafter, titanium-based active material) having a spinel crystal structure as an active material, and a conductive agent.
- the current collector has a porosity of 20 to 60%.
- the average density of the carbon layer is 0.05 to 0.4 g / cm 3 .
- the carbon layer formed on the surface of the current collector of i) refers to a carbon layer covering the main surface of the current collector.
- the carbon layer formed in the through hole of i) refers to a part where a part of the carbon layer covering the main surface of the current collector enters the through hole. This part occupies a part of the space in the through hole.
- a titanium-based active material that hardly expands or contracts during charge / discharge is used as the negative electrode active material. Accordingly, it is possible to prevent the active material from dropping from the current collector during charging / discharging, or the electron conductivity between the active material particles from being deteriorated due to the poor contact state between the active material particles.
- the titanium-based active material since the titanium-based active material has poor thermal conductivity, there is a problem that heat unevenness is likely to occur inside the battery during the charge / discharge cycle.
- the current collector is provided with a plurality of through-holes penetrating in the thickness direction, the electrolyte is held in the through-holes, and the thermal conductivity in the thickness direction of the current collector is improved. It is considered effective to do this.
- a mixture paste containing an active material is directly applied to the surface of a current collector having a plurality of through holes and dried to form a mixture layer, The active material enters the through hole, and it is difficult to secure the through hole as a part for holding the electrolyte.
- the surface of the current collector is coated with a carbon layer so that the mixture does not enter the through-holes of the current collector, and the mixture layer is disposed via the carbon layer. Furthermore, the area
- the carbon layer has both the role of improving the electron conductivity between the current collector and the mixture layer and the role of improving the retention of the electrolyte. Since the carbon layer includes a low density region, the average density of the carbon layer as a whole is 0.05 to 0.4 g / cm 3 , which is a density compared to the case where no through hole exists (about 0.5 g / cm 3 ). Becomes lower. When the average density of the carbon layer is in the above range, an electrode excellent in electron conductivity and electrolyte retention can be obtained.
- the porosity of the current collector is the ratio of the total volume of the through holes to the total occupied volume of the current collector and the through holes.
- the through hole of the current collector is a hole provided to hold the electrolyte. At least the hole penetrating in the thickness direction of the current collector, that is, from one surface of the sheet-like current collector to the other It is a hole that penetrates the surface.
- the shape of the cross section of the through hole perpendicular to the thickness direction of the current collector is, for example, a substantially polygonal shape such as a substantially circular shape, an elliptical shape, or a substantially rectangular shape.
- the average diameter of the through-holes (the average maximum diameter if not substantially circular) is preferably 100 to 700 ⁇ m, more preferably 200 to It is 600 ⁇ m, more preferably 250 to 500 ⁇ m.
- a punching metal, an expanded metal, or a mesh metal plate is used for the current collector.
- the mixture layer and the carbon layer may be formed on one side or both sides of the current collector.
- the content of the active material in the mixture layer is preferably 1.5 to 2.3 g per 1 cm 3 of the mixture layer.
- the content of the active material in the mixture layer is preferably 1.5 to 2.3 g per 1 cm 3 of the mixture layer.
- the present invention relates to a nonaqueous electrolyte secondary battery including a positive electrode, the above negative electrode, a separator disposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte.
- a nonaqueous electrolyte secondary battery including a positive electrode, the above negative electrode, a separator disposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte.
- 30 to 90% by volume of the inner space of the through hole (the current collector gap) is preferably filled with a non-aqueous electrolyte. That is, the carbon material and the binder preferably occupy 10 to 70% by volume of the inner space in the through hole. If at least 30% by volume of the inner space of the through hole is filled with the nonaqueous electrolyte, the charge / discharge cycle characteristics are improved.
- the ratio P (volume%) that the nonaqueous electrolyte occupies in the through-hole is obtained by, for example, the following method.
- a cross section in the thickness direction of the negative electrode is observed using a scanning electron microscope (SEM).
- SEM scanning electron microscope
- the image processing SEM, to volume Q v occupied by the through holes, the ratio of the volume R v occupied by the space in which the electrolyte is retained in the through hole: Request R v / Q v. R v / Q v ⁇ 100 is set as the value of P.
- Volume R v the space occupied by the electrolyte is retained in the through hole, for example, as can be clearly discriminated space formed by the through holes, obtained by performing a binarization process on the SEM image.
- the magnification of the image (projected image) is, for example, 200 to 1000 times.
- the area of the image (projected image) is, for example, 50 to 100 ⁇ m ⁇ 50 to 100 ⁇ m.
- the number of pixels (pixels) that divide the image (projected image) is, for example, 480 to 1024 ⁇ 480 to 1024. Each pixel is binarized. This treatment is performed on the cross section in the thickness direction of the negative electrode in one through hole.
- the positive electrode has a current collector and a mixture layer formed on the surface of the current collector.
- the mixture layer of the positive electrode includes, for example, an active material, a conductive agent, and a binder.
- the positive electrode is obtained, for example, by the following method. A paste in which a dispersion medium is added to a mixture of an active material, a conductive agent, and a binder is obtained. This paste is applied to the surface of the current collector to form a coating film. After the coating film is dried to form a mixture layer, it is compressed.
- the positive electrode mixture layer may be formed on one side or both sides of the positive electrode current collector.
- a lithium-containing composite oxide capable of reversibly occluding and releasing lithium is used.
- the lithium-containing composite oxide LiCoO 2 , LiNiO 2 , LiMn 2 O 4 , LiMnO 2 , LiNi 1-y Co y O 2 (0 ⁇ y ⁇ 1), LiNi 1-yz Co y Mn and z O 2 (0 ⁇ y + z ⁇ 1).
- the positive electrode binder for example, a fluororesin such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF) is used.
- PTFE polytetrafluoroethylene
- PVDF polyvinylidene fluoride
- the same material as the negative electrode conductive agent is used for the positive electrode conductive agent.
- a metal foil such as an aluminum foil or an aluminum alloy foil is used.
- the thickness of the positive electrode current collector is, for example, 10 to 30 ⁇ m.
- an insulating microporous thin film having a large ion permeability and a predetermined mechanical strength is used.
- an olefin polymer or a glass fiber sheet or non-woven fabric obtained by combining polypropylene or polyethylene alone or in combination thereof is used.
- the pore diameter of the separator is preferably in a range in which the active material, the binder, the conductive agent and the like detached from the electrode sheet do not permeate, and is preferably 0.1 to 1 ⁇ m, for example.
- the thickness of the separator is preferably 10 to 100 ⁇ m.
- the porosity is determined according to the permeability of electrons and ions, the material, and the film thickness, but is generally preferably 30 to 80%.
- the non-aqueous electrolyte is composed of a non-aqueous solvent and a lithium salt dissolved in the solvent.
- a non-aqueous solvent for example, a cyclic carbonate, a cyclic carboxylic acid ester, an acyclic carbonate, or an aliphatic carboxylic acid ester is used.
- the non-aqueous solvent is preferably a mixed solvent containing a cyclic carbonate and an acyclic carbonate, or a mixed solvent containing a cyclic carboxylic acid ester and a cyclic carbonate.
- non-aqueous solvent examples include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinylene carbonate (VC), dimethyl carbonate (DMC), and diethyl carbonate (DEC). ), Ethyl methyl carbonate (EMC), and acyclic carbonates such as dipropyl carbonate (DPC), methyl formate (MF), methyl acetate (MA), methyl propionate (MP), and ethyl propionate (MA).
- cyclic carboxylic acid esters such as aliphatic carboxylic acid esters and ⁇ -butyrolactone (GBL).
- cyclic carbonate EC, PC, and VC are preferable.
- GBL is preferred as the cyclic carboxylic acid ester.
- acyclic carbonate DMC, DEC, and EMC are preferable.
- aliphatic carboxylic acid ester is included as needed.
- lithium salt examples include LiClO 4 , LiBF 4 , LiPF 6 , LiAlCl 4 , LiSbF 6 , LiSCN, LiCF 3 SO 3 , LiCF 3 CO 2 , Li (CF 3 SO 2 ) 2 , LiAsF 6 , LiN (CF 3 SO 2 ) 2 , lithium chloroborane such as LiB 10 Cl 10 , lower aliphatic lithium carboxylate, lithium tetraphenylborate, LiN (CF 3 SO 2 ) (C 2 F 5 SO 2 ) and LiN (CF 3 SO 2 ) 2 and imides such as LiN (C 2 F 5 SO 2 ) 2 and LiN (CF 3 SO 2 ) (C 4 F 9 SO 2 ).
- LiPF 6 is preferable.
- the concentration of the lithium salt in the nonaqueous electrolyte is not particularly limited, but is preferably 0.2 to 2 mol / L, more preferably 0.5 to 1.5 mol / L.
- any of a coin type, a button type, a sheet type, a cylindrical type, a flat type and a square type may be adopted.
- the negative electrode 11 has a sheet-like current collector 12 and a multilayer 14 formed on both surfaces of the current collector 12.
- the multilayer 14 includes a carbon layer 15 containing a carbon material and a mixture layer 16 containing an active material.
- the current collector 12 is made of a punching metal having a plurality of through holes 13.
- the mixture layer 16 is formed on the current collector 12 via the carbon layer 15.
- the carbon layer 15 includes a surface covering portion 17 that is a portion covering one surface S 1 and the other surface S 2 of the current collector 12, and a hole filling portion 18 that fills the hole 13.
- a portion (hereinafter referred to as a sparse portion) that combines the hole filling portion 18 and the extension portion 17a corresponding to the portion extending in the thickness direction of the current collector 12 from the hole filling portion 18 is sparsely filled with a carbon material and has a density. Lower. Thereby, in this sparse part, the space
- the low density carbon layer is mainly formed in the hole filling portion 18. That is, most of the voids are formed in the through holes 13.
- a large number of small voids may be formed, or a large void may be locally formed.
- the sparse filling of the carbon material in the sparse part can be confirmed, for example, by observing the cross section of the negative electrode with a scanning electron microscope (SEM) or the like.
- the average density of the carbon layer 15 is preferably 0.05 to 0.3 g / cm 3 .
- the average density of the carbon layer 15 is more preferably 0.1 to 0.3 g / cm 3 .
- the lower limit of the average density of the carbon layer is 0.05 g / cm 3, preferably 0.1 g / cm 3, more preferably 0.15 g / cm 3 It is.
- the upper limit of the average density of the carbon layer is 0.4 g / cm 3 , preferably 0.3 g / cm 3 , more preferably 0.25 g / cm 3 .
- the range of the average density of a carbon layer you may combine said upper limit and a lower limit arbitrarily.
- the weight of the carbon material contained per 1 cm 3 of the through holes is preferably 0.05 to 0.35 g, more preferably 0.05 to 0.15 g.
- the through-hole 13 reaches from the one surface S 1 in the thickness direction X of the current collector 12 to the other surface S 2 .
- the cross-sectional shape along the surface direction Y of the current collector 12 of the through hole 13 is substantially circular.
- the average diameter of the through holes 13 is preferably 100 to 700 ⁇ m, more preferably 200 to 600 ⁇ m, and even more preferably 250 to 500 ⁇ m.
- the upper limit of the average diameter of the through holes 13 is preferably 700 ⁇ m, more preferably 600 ⁇ m, and even more preferably 500 ⁇ m.
- the lower limit of the average diameter of the through holes 13 is preferably 100 ⁇ m, more preferably 200 ⁇ m, and even more preferably 250 ⁇ m.
- the distance L between the through holes 13 in FIG. 1 is preferably 100 to 1000 ⁇ m.
- the interval L between the through holes 13 is set to 100 ⁇ m or more, the surface of the current collector 12 can be stably covered with the carbon layer.
- the interval L between the through holes 13 is set to 1000 ⁇ m or less, it is possible to sufficiently ensure the thermal conductivity in the thickness direction of the current collector.
- the through holes 13 are preferably provided with a constant size and a constant interval.
- the porosity of the current collector 12 is 20 to 60%.
- the porosity means the ratio of the total volume of the through holes 13 to the total occupied volume of the current collector 12 and the through holes 13.
- the lower limit of the porosity of the current collector is 20%, preferably 30%, more preferably 35%.
- the upper limit of the porosity of the current collector is 60%, preferably 50%, More preferably, it is 45%.
- the range of the porosity of the current collector the above upper limit and lower limit may be arbitrarily combined.
- the porosity of the current collector can be adjusted by changing the size of the through holes, the interval L, and the like.
- the porosity of the current collector can be obtained by calculation from the average diameter of the through holes and the thickness of the current collector.
- the thickness T of the current collector 12 is preferably 5 to 40 ⁇ m, more preferably 5 to 25 ⁇ m. By setting the thickness T of the current collector 12 to 5 ⁇ m or more, a sufficient amount of electrolyte can be retained in the current collector, and charge / discharge cycle characteristics can be significantly improved. By setting the thickness T of the current collector 12 to 40 ⁇ m or less, the thickness of the negative electrode can be sufficiently reduced, and a battery having a high energy density can be obtained.
- the ratio of the average diameter R of the through holes 13 to the thickness T of the current collector 12: R / T is preferably 2.5-60. More preferably, it is 15-50.
- the material constituting the current collector 12 is preferably aluminum or an aluminum alloy. From the viewpoint of electrolyte resistance and strength, the aluminum alloy preferably contains at least one selected from the group consisting of copper, manganese, silicon, magnesium, zinc, and nickel in addition to aluminum. In the aluminum alloy, the content of elements other than aluminum is preferably 0.05 to 0.3% by weight.
- the carbon layer 15 includes a carbon material and a first binder.
- the carbon material for example, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, carbon fiber, and graphite are used. Among these, acetylene black is preferable as the carbon material.
- the carbon material may be particulate or fibrous.
- the particulate carbon material preferably has a volume-based average particle diameter (D50) of 10 to 50 nm.
- the fibrous carbon material preferably has an average fiber length of 0.1 to 20 ⁇ m and an average fiber diameter of 5 to 150 nm.
- Examples of the first binder include styrene butadiene rubber (SBR), polyethylene (PE), polypropylene (PP), and fluororesin.
- Examples of the fluororesin include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA).
- PTFE and PVDF are preferable from the viewpoint of the strength of the carbon layer.
- the content of the first binder in the carbon layer 15 is preferably 150 to 300 parts by weight per 100 parts by weight of the carbon material, more preferably 175 to 275 parts by weight per 100 parts by weight of the carbon material, and even more preferably the carbon material 100 200 to 250 parts by weight per part by weight.
- the content of the first binder in the carbon layer 15 is preferably 150 to 300 parts by weight per 100 parts by weight of the carbon material, more preferably 175 to 275 parts by weight per 100 parts by weight of the carbon material, and even more preferably the carbon material 100 200 to 250 parts by weight per part by weight.
- the lower limit of the content of the first binder in the carbon layer is preferably 150 parts by weight per 100 parts by weight of the carbon material. More preferably, it is 175 parts by weight per 100 parts by weight of the carbon material, and more preferably 200 parts by weight per 100 parts by weight of the carbon material.
- the upper limit of the content of the first binder in the carbon layer is preferably 300 parts by weight per 100 parts by weight of the carbon material, more preferably 275 parts by weight per 100 parts by weight of the carbon material. More preferably, it is 250 parts by weight per 100 parts by weight of the carbon material.
- the range of content of the 1st binder in a carbon layer what is necessary is just to combine said upper limit and a lower limit arbitrarily.
- the thickness T c (thickness per layer) of the surface covering portion 17 of the carbon layer 15 is preferably 5 to 30 ⁇ m, more preferably. Is 5 to 20 ⁇ m.
- the thickness Tc of the surface covering portion 17 of the carbon layer 15 is preferably 5 to 30 ⁇ m, more preferably. Is 5 to 20 ⁇ m.
- the mixture layer 16 includes an active material and a conductive agent, and further includes a second binder as necessary.
- a titanium-based active material is used as the active material. Since the titanium-based active material has almost no volume change due to expansion / contraction associated with charge / discharge, a decrease in the binding property of the mixture layer associated with the charge / discharge cycle is suppressed.
- the titanium-based active material preferably has a structure represented by the general formula: Li 4 + x Ti 5-y M y O 12 + z .
- M is at least one selected from the group consisting of Mg, Al, Ca, Ba, Bi, Ga, V, Nb, W, Mo, Ta, Cr, Fe, Ni, Co, and Mn.
- x is a value immediately after synthesis or in a completely discharged state.
- the conductive agent is acetylene black, which is the same carbon black as the carbon material of the carbon layer.
- metal fibers, carbon fluoride, metal (for example, aluminum) powders, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, or Organic conductive materials such as phenylene derivatives are listed.
- nickel powder is particularly preferable.
- the content of the conductive agent in the mixture layer 16 is preferably 2 to 15 parts by weight per 100 parts by weight of the active material, and more preferably 3 to 12 parts by weight per 100 parts by weight of the active material.
- the content of the conductive agent in the mixture layer 16 is preferably 2 to 15 parts by weight per 100 parts by weight of the active material, and more preferably 3 to 12 parts by weight per 100 parts by weight of the active material.
- the content of the second binder in the mixture layer 16 is preferably 2 to 6 parts by weight per 100 parts by weight of the active material, and more preferably 3 to 5 per 100 parts by weight of the active material.
- the content of the second binder in the mixture layer 16 is preferably 2 to 6 parts by weight per 100 parts by weight of the active material, and more preferably 3 to 5 per 100 parts by weight of the active material.
- the thickness T m (thickness per layer) of the mixture layer 16 is preferably 20 to 150 ⁇ m, more preferably 20 to 50 ⁇ m. It is.
- the ratio of the thickness T c of the surface covering portion 17 of the carbon layer 15 to the thickness T m of a mixture layer 16: T c / T m is preferably from 0.03 to 1.5, more preferably 0.1 to 1. 5.
- the content of the active material in the mixture layer 16 is preferably 1.5 to 2.3 g per 1 cm 3 of the mixture layer.
- the content of the active material in the mixture layer 16 is preferably 1.5 to 2.3 g per 1 cm 3 of the mixture layer.
- the method is (A) A first paste containing a carbon material is applied to the surface of a sheet-like current collector having a plurality of through holes and a porosity of 20 to 60%, and then dried to obtain a surface of the current collector And forming the carbon layer in the through hole; (B) applying a second paste containing a titanium-based active material and a conductive agent to the surface of the carbon layer and drying to form a mixture layer to obtain a negative electrode precursor; (C) compressing the negative electrode precursor to obtain a negative electrode having an average density of the carbon layer of 0.05 to 0.4 g / cm 3 ; including.
- a first binder is added to a powdery carbon material, and an appropriate amount of a first dispersion medium is further added to obtain a first paste.
- a first dispersion medium water, N-methyl-2-pyrrolidone, or the like is used.
- a 1st paste is apply
- the ratio of the dispersion medium in the first paste is preferably 800 parts by weight or less per 100 parts by weight of the carbon material.
- the proportion of the dispersion medium in the first paste is more preferably 300 parts by weight or more per 100 parts by weight of the carbon material.
- a general method can be used as a method for applying the first paste.
- a general method can be used as a method for applying the first paste.
- examples thereof include a reverse roll method, a direct roll method, a blade method, a knife method, an extrusion method, a curtain method, a gravure method, a bar method, a casting method, a dip method, and a squeeze method.
- blade method, knife method and extrusion method are preferred.
- the coating method may be continuous, intermittent, or striped. In order to make it difficult for the first coating film to enter the through hole, the blade method is particularly preferable.
- the first paste it is preferable to apply the first paste at a speed of 0.5 to 12 m / min in order to prevent the first paste from excessively entering the through hole and to form a good coating film.
- coating method according to the drying property of a 1st coating film Thereby, a favorable surface state of the carbon layer can be obtained.
- the first coating film is dried to form a carbon layer.
- drying conditions a drying temperature of 80 to 120 ° C. and a drying time of 10 to 30 minutes are preferable.
- the second paste is obtained, for example, by adding a conductive agent and a second binder to the active material, and further adding an appropriate amount of the second dispersion medium.
- the second dispersion medium water, N-methyl-2-pyrrolidone, or the like is used.
- the second dispersion medium may be the same as or different from the first dispersion medium.
- the second binder may be the same as or different from the first binder.
- the proportion of the dispersion medium in the second paste is preferably 80 to 150 parts by weight per 100 parts by weight of the active material.
- a second paste is applied on the carbon layer to form a second coating film.
- the same method as that for the first paste is used.
- the second paste is preferably applied at a speed of 0.5 to 5 m / min.
- the second coating film is blown and dried to form a mixture layer.
- drying conditions a drying temperature of 80 to 120 ° C. and a drying time of 10 to 30 minutes are preferable.
- a negative electrode precursor in which a carbon layer and a mixture layer are formed on both sides of the current collector is used as a pair of rollers. Is compressed at a predetermined linear pressure to obtain a negative electrode.
- the linear pressure applied to the negative electrode precursor by the pair of rollers is preferably 1000 to 3000 kgf / cm, more preferably 1500 to 2500 kgf / cm.
- the linear pressure By setting the linear pressure to 3000 kgf / cm or less, the carbon layer can be reliably prevented from entering the through hole.
- the linear pressure By setting the linear pressure to 1000 kgf / cm or more, the active material density of the mixture layer can be increased, and the energy density of the battery can be increased. Further, the strength of the negative electrode (binding property of the mixture layer and the carbon layer) can be sufficiently obtained.
- the carbon layer present in the through hole and in the region extending from the through hole in the thickness direction of the current collector is not sufficiently compressed in the step (c) due to the presence of the through hole. Therefore, even after the step (c), the carbon material is not densely filled in the through hole and in the region extending from the through hole in the thickness direction of the current collector, and a sparse carbon layer is formed. This sparse carbon layer has a low density particularly in the through holes.
- the carbon layer existing on the surface of the current collector is pressed against the current collector and sufficiently compressed in step (c), so that it becomes a dense layer, and the current collector, the mixture layer and the current collector Good adhesion to the body is obtained.
- a negative electrode having a structure as shown in FIG. 1 was produced by the following procedure. a) Formation of carbon layer 100 parts by weight of acetylene black powder (manufactured by Denki Kagaku Kogyo Co., Ltd., average particle size 35 nm) as a carbon material, and 230 weight of polyvinylidene fluoride resin (manufactured by Kureha Co., Ltd.) as a binder 700 parts by weight of N-methyl-2-pyrrolidone as a dispersion medium was added to the mixture with the parts to obtain a first paste.
- acetylene black powder manufactured by Denki Kagaku Kogyo Co., Ltd., average particle size 35 nm
- polyvinylidene fluoride resin manufactured by Kureha Co., Ltd.
- the first paste was applied to both surfaces of the negative electrode current collector by a comma coater at a speed of 1 m / min to form a first coating film.
- a sheet-like aluminum punching metal obtained by punching (porosity 40%, thickness T 20 ⁇ m, average pore diameter 500 ⁇ m, interval L 500 ⁇ m) was used.
- the first coating film was not interrupted and did not enter the through-hole, and both surfaces of the negative electrode current collector were covered in a planar shape.
- the first coating film was blown and dried to form a carbon layer (first layer).
- the drying temperature was 80 ° C. and the drying time was 20 minutes.
- the second paste was applied to the surface of the carbon layer with a comma coater at a speed of 1 m / min to form a second coating film.
- the coating amount of the second coating film was 7.5 mg / cm 2 .
- the second coating film was blown and dried to form a mixture layer (second layer).
- the drying temperature was 80 ° C. and the drying time was 20 minutes. In this way, a negative electrode precursor was obtained.
- the negative electrode precursor was compressed with a pair of rollers and cut into a predetermined band-like size (longitudinal dimension 240 mm, width direction dimension 55 mm) to obtain a negative electrode.
- the collector exposed part for welding the negative electrode lead mentioned later was provided in the one end part of the negative electrode.
- the average density of the carbon layer was changed to the values shown in Table 1, and negative electrodes A1 to A4 of Examples 1 to 4 and negative electrodes B1 to B2 of Comparative Examples 1 to 2 were produced.
- the linear pressure applied by the pair of rollers during compression of the negative electrode precursor was changed in the range of 500 to 3500 kgf / cm.
- the amount of the first paste applied was changed in the range of 0.05 to 0.8 mg / cm 2 so that the thickness T c of the surface coating after compression was about 15 ⁇ m.
- the thickness T m of the negative electrode mixture layer is 37 to 44 ⁇ m
- the thickness T c of the surface covering portion of the carbon layer is 14 to 17 ⁇ m
- the amount of active material per 1 cm 3 of the negative electrode mixture layer is 2.0 to 2 0.5 g.
- Average density of carbon layer (Filling amount of carbon material) / (volume of surface coating portion + total volume of through holes)
- the volume of the surface covering portion was obtained by multiplying the area of the surface covering portion facing the current collector (including the through hole) by the thickness dimension of the surface covering portion.
- the total volume of the through holes was obtained by multiplying the volume of the through holes obtained using the average diameter of the through holes and the thickness of the current collector by the number of through holes.
- the ratio P (volume%) which a nonaqueous electrolyte accounts in the through-hole of a collector was calculated
- a cross section in the thickness direction of the negative electrode (a cross section including the axis of the cylindrical through hole) was observed using a scanning electron microscope (SEM).
- SEM scanning electron microscope
- the SEM image is image processing, with respect to the volume Q v occupied by the through holes, the ratio of the volume R v occupied by the space in which the electrolyte is retained in the through-hole: sought R v / Q v.
- R v / Q v ⁇ 100 was taken as the value of P.
- the magnification of the image (projected image) was 600 times.
- the area of the image (projected image) was 100 ⁇ m ⁇ 100 ⁇ m.
- the number of pixels (pixels) for dividing the image (projected image) was 1024 ⁇ 1024. Each pixel was binarized. This treatment was performed on the cross section in the thickness direction of the negative electrode in one through hole. This operation was repeated for five through holes in the current collector. And the average value was calculated
- the positive electrode precursor was compressed at a linear pressure of 2000 kgf / cm and cut into a predetermined band-like size (longitudinal dimension 200 mm, width direction dimension 50 mm) to obtain a positive electrode. At this time, the thickness of the mixture layer was 30 ⁇ m.
- the collector exposed part for welding the positive electrode lead mentioned later was provided in the one end part of the positive electrode.
- the positive electrode and the negative electrode were spirally wound between the positive electrode and the negative electrode with a separator interposed therebetween, whereby an electrode group 4 was obtained.
- a separator a polyethylene microporous film (thickness 20 ⁇ m) was used.
- the electrode group 4 was housed in a battery case 1 made of stainless steel.
- One end of the positive electrode lead 5 made of aluminum was connected to the positive electrode.
- the other end of the positive electrode lead 5 was connected to the sealing plate 2.
- One end of an aluminum negative electrode lead 6 was connected to the negative electrode.
- the other end of the negative electrode lead 6 was connected to the bottom of the battery case 1.
- Resin insulating rings 7 were respectively disposed on the upper and lower portions of the electrode group 4.
- a nonaqueous electrolyte was injected into the battery case 1.
- a non-aqueous solvent in which LiPF 6 was dissolved was used.
- a mixed solvent (volume ratio 3: 7) of ethylene carbonate (EC) and diethyl carbonate (DEC) was used.
- the concentration of LiPF 6 in the nonaqueous electrolyte was 1.0 mol / L.
- the opening end portion of the battery case 1 was caulked to the peripheral edge portion of the sealing plate 2 through the resin sealing body 3 to seal the battery case 1. In this way, the cylindrical battery (diameter 18 mm, height 65 mm) of FIG. 2 was obtained.
- batteries A1 to A4 were produced using the negative electrodes A1 to A4 of Examples 1 to 4.
- batteries B1 and B2 were fabricated using the negative electrodes B1 and B2 of Comparative Examples 1 and 2.
- the negative electrode paste was directly applied to the surface of the negative electrode current collector by the blade method at a speed of 1 m / min to form a coating film.
- the second paste of Example 1 was used as the negative electrode current collector.
- the negative electrode current collector of Example 1 was used as the negative electrode current collector.
- the drying temperature was 80 ° C. and the drying time was 20 minutes. A part of the mixture layer was formed in the through hole. In this way, a negative electrode precursor was obtained.
- a negative electrode C was obtained in the same manner as in Example 1. At this time, the thickness of the mixture layer was 41 ⁇ m.
- a cylindrical battery C was produced in the same manner as in Example 1 except that the negative electrode C was used instead of the negative electrode A1.
- a negative electrode D was produced in the same manner as in Example 1 except that an aluminum foil (thickness: 15 ⁇ m) having no through hole was used instead of the punching metal for the negative electrode current collector.
- a cylindrical battery D was produced in the same manner as in Example 1 except that the negative electrode D was used instead of the negative electrode A1.
- Comparative Example 5 Without forming the carbon layer, the negative electrode paste was directly applied to the negative electrode current collector at a speed of 1 m / min with a comma coater to form a coating film.
- the negative electrode paste the second paste of Example 1 was used.
- the aluminum foil (thickness 15 ⁇ m) of Comparative Example 4 was used.
- the coating film was dried to form a mixture layer. The drying temperature was 80 ° C. and the drying time was 20 minutes. In this way, a negative electrode precursor was obtained.
- a negative electrode E was obtained in the same manner as in Example 1 using the negative electrode precursor. At this time, the thickness of the mixture layer was 39 ⁇ m.
- a cylindrical battery E was produced in the same manner as in Example 1 except that the negative electrode E was used instead of the negative electrode A1. The production conditions for the negative electrode are summarized in Table 1.
- the discharge voltage 10 seconds after the start of discharge in steps 1, 3, 5, 7, and 9 was measured and plotted against the current value.
- the plot was subjected to linear approximation by the least square method, and the value of the slope was defined as a direct current internal resistance (DCIR; Direct Current Current Internal Resistance).
- DCIR Direct Current Current Internal Resistance
- a smaller DCIR value indicates higher output characteristics and better rate characteristics.
- non-aqueous electrolyte secondary battery of the present invention is excellent in output characteristics, it is suitably used as a vehicle battery.
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Abstract
Description
電極における集電効率の向上および合剤層の保持性の改善を目的として、集電体に多孔質基材(特許文献1および2)または複数の貫通孔を有する金属箔(特許文献3および4)を用いることが検討されている。
これに対しては、充放電時に膨張および収縮をほとんど生じないスピネル構造の結晶構造を有するリチウムチタン含有複合酸化物(以下、チタン系活物質)を活物質に用いることが考えられる。
しかし、チタン系活物質は熱伝導性に乏しいため、充放電サイクル時に電池内部に熱ムラを生じ易く、依然として、充放電サイクル特性の改善は不十分である。
複数の貫通孔を有する、シート状の集電体と、
前記集電体の表面および前記貫通孔内に形成されたカーボン層と、
前記カーボン層の表面に形成された合剤層と、
を備え、
前記合剤層が、活物質および導電剤を含み、
前記活物質が、スピネル型の結晶構造を有するリチウムチタン含有複合酸化物を含み、
前記集電体の空隙率が、20~60%であり、
前記カーボン層の平均密度が、0.05~0.4g/cm3である、
非水電解質二次電池に関する。
(a)複数の貫通孔を有し、空隙率が20~60%である、シート状の集電体の表面に、炭素材料を含む第1ペーストを塗布し、乾燥させて、前記集電体の表面および前記貫通孔内にカーボン層を形成する工程と、
(b)前記カーボン層の表面に、活物質としてスピネル型の結晶構造を有するリチウムチタン含有複合酸化物および導電剤を含む第2ペーストを塗布し、乾燥させて、合剤層を形成し、負極前駆体を得る工程と、
(c)前記負極前駆体を圧縮し、前記カーボン層の平均密度が0.05~0.4g/cm3である負極を得る工程と、を含む非水電解質二次電池用負極の製造方法に関する。
i)負極は、複数の貫通孔を有する、シート状の集電体と、前記集電体の表面および前記貫通孔内に形成されたカーボン層と、前記カーボン層の表面に形成された合剤層と、を備える。
ii)合剤層が、活物質としてスピネル型の結晶構造を有するリチウムチタン含有複合酸化物(以下、チタン系活物質)、および導電剤を含む。
iii)集電体の空隙率が20~60%である。
iV)カーボン層の平均密度が0.05~0.4g/cm3である。
上記i)の集電体の表面に形成されたカーボン層とは、集電体の主面を覆うカーボン層を指す。上記i)の貫通孔内に形成されたカーボン層とは、集電体の主面を覆うカーボン層の一部が貫通孔内に入り込んだ部分を指す。この部分は貫通孔内の空間の一部を占める。
さらに、集電体の空隙率を20~60%とすることにより、集電体の強度が十分に確保されるとともに、集電体の電解質保持部に十分量の電解質が確保され、負極内部へのリチウムイオンの移動がスムーズに行われるため、非水電解質二次電池のレート特性が向上する。なお、空隙率とは、集電体および貫通孔の合計占有体積に対する貫通孔の総容積の割合をいう。
上記i)~iv)の条件を満たすことにより、充放電サイクル特性およびレート特性に優れた非水電解質二次電池を提供することができる。
集電体の強度および厚み方向の熱伝導性をバランス良く得るためには、貫通孔の平均径(略円形状でない場合、平均の最大径)は、好ましくは100~700μm、より好ましくは200~600μm、さらに好ましくは250~500μmである。
集電体には、例えば、パンチングメタル、エキスパンドメタル、またはメッシュ状の金属板が用いられる。合剤層およびカーボン層の形成は、集電体の片面でもよく、両面でもよい。
電池内において、貫通孔の内空間(集電体の空隙)の30~90体積%は、非水電解質で満たされているのが好ましい。すなわち、貫通孔内の内空間の10~70体積%は、炭素材料および結着剤が占めるのが好ましい。少なくとも貫通孔の内空間の30体積%が非水電解質で満たされていれば、充放電サイクル特性が向上する。
貫通孔内にて電解質が保持された空間が占める容積Rvは、例えば、貫通孔内にて形成される空間を明確に判別できるように、SEM像に二値化処理を施して求められる。画像(投影像)の倍率は、例えば、200~1000倍である。画像(投影像)の面積は、例えば、50~100μm×50~100μmである。画像(投影像)を分割するピクセル(画素)数は、例えば、480~1024×480~1024である。各ピクセルを二値化処理する。この処理を、1つの貫通孔における負極の厚み方向の断面に対して行う。
正極の集電体には、例えば、アルミニウム箔またはアルミニウム合金箔等の金属箔が用いられる。正極の集電体の厚みは、例えば、10~30μmである。
非水溶媒には、例えば、環状カーボネート、環状カルボン酸エステル、非環状カーボネート、脂肪族カルボン酸エステルが用いられる。非水溶媒は、環状カーボネートと非環状カーボネートとを含む混合溶媒、または環状カルボン酸エステルと環状カーボネートとを含む混合溶媒が好ましい。
環状カーボネートとしては、EC、PC、およびVCが好ましい。環状カルボン酸エステルとしてはGBLが好ましい。非環状カーボネートとしては、DMC、DEC、およびEMCが好ましい。また、必要に応じ、脂肪族カルボン酸エステルを含むのが好ましい。
非水電解質中のリチウム塩の濃度は、特に限定されないが、好ましくは0.2~2mol/L、より好ましくは0.5~1.5mol/Lである。
図1に示すように、負極11は、シート状の集電体12、および集電体12の両面に形成された複層14を有する。複層14は、炭素材料を含むカーボン層15、および活物質を含む合剤層16からなる。集電体12は、複数の貫通孔13を有するパンチングメタルからなる。合剤層16は、カーボン層15を介して集電体12上に形成されている。
疎部にて炭素材料が疎に充填されていることは、例えば、走査型電子顕微鏡(SEM)等による負極の断面観察により確認することができる。
活物質の貫通孔内への入り込みを抑制するためには、カーボン層の平均密度の下限は、0.05g/cm3、好ましくは0.1g/cm3、より好ましくは0.15g/cm3である。負極の電解液保持性の観点から、カーボン層の平均密度の上限は、0.4g/cm3、好ましくは0.3g/cm3、より好ましくは0.25g/cm3である。カーボン層の平均密度の範囲については、上記の上限と下限とを任意に組み合わせてもよい。
カーボン層15の平均密度=
(炭素材料の充填量)/(表面被覆部17の体積+貫通孔13の総容積)
表面被覆部17の体積は、表面被覆部17の集電体(貫通孔13を含む)との対向面積に、表面被覆部17の厚みを乗じることにより求められる。
集電体の強度および厚み方向の熱伝導性をバランス良く得るためには、貫通孔13の平均径は、好ましくは100~700μm、より好ましくは200~600μm、さらに好ましくは250~500μmである。
集電体の空隙率を20%以上とすることで、集電体が電解液を十分に保持することができ、レート特性が向上する。また、集電体の厚み方向の熱伝導性が十分に改善される。集電体の空隙率が60%以下とすることで、集電体の強度が十分に確保され、また、貫通孔内に炭素材料が過度に充填されない。集電体12の空隙率は、30~50%が好ましく、35~45%がより好ましい。
集電体の電解液保持性の観点から、集電体の空隙率の下限は、20%、好ましくは30%、より好ましくは35%である。集電体の強度を十分に確保し、かつ貫通孔内に炭素材料が過度に充填されるのを抑制するためには、集電体の空隙率の上限は、60%、好ましくは50%、より好ましくは45%である。集電体の空隙率の範囲については、上記の上限と下限とを任意に組み合わせてもよい。
集電体の空隙率は、貫通孔の大きさおよび間隔L等を変えることにより調整することができる。集電体の空隙率は、貫通孔の平均径および集電体の厚みから計算で求めることができる。
集電体12を構成する材料は、アルミニウムまたはアルミニウム合金が好ましい。耐電解質性および強度の観点から、アルミニウム合金は、アルミニウム以外に、銅、マンガン、珪素、マグネシウム、亜鉛、およびニッケルからなる群より選択される少なくとも1種を含むのが好ましい。アルミニウム合金中にて、アルミニウム以外の元素の含有量は、0.05~0.3重量%が好ましい。
炭素材料には、例えば、アセチレンブラック、ケッチェンブラック、チャンネルブラック、ファーネスブラック、ランプブラック、サーマルブラックなどのカーボンブラック類、炭素繊維、グラファイトが用いられる。これらの中でも、炭素材料は、アセチレンブラックが好ましい。
炭素材料は、粒子状でも繊維状でもよい。粒子状の炭素材料は、体積基準の平均粒径(D50)10~50nmが好ましい。繊維状の炭素材料は、平均繊維長0.1~20μmおよび平均繊維径5~150nmが好ましい。
カーボン層15中の第1結着剤の含有量を、炭素材料100重量部あたり150重量部以上とすることで、炭素材料間の結着性およびカーボン層と集電体との結着性を十分に確保することができる。カーボン層15中の第1結着剤の含有量を、炭素材料100重量部あたり300重量部以下とすることで、十分量の炭素材料を含むカーボン層を得ることができ、合剤層と集電体との間の電子伝導性を十分に確保することができる。
炭素材料間の結着性およびカーボン層と集電体との結着性の観点から、カーボン層中の第1結着剤の含有量の下限は、好ましくは炭素材料100重量部あたり150重量部、より好ましくは炭素材料100重量部あたり175重量部、さらに好ましくは炭素材料100重量部あたり200重量部である。カーボン層の電子伝導性の観点から、カーボン層中の第1結着剤の含有量の上限は、好ましくは炭素材料100重量部あたり300重量部、より好ましくは炭素材料100重量部あたり275重量部、さらに好ましくは炭素材料100重量部あたり250重量部である。カーボン層中の第1結着剤の含有量の範囲については、上記の上限と下限とを任意に組み合わせればよい。
カーボン層15の表面被覆部17の厚みTcを5μm以上とすることで、カーボン層により集電体(貫通孔)が十分に保護され、活物質の貫通孔への侵入が抑制される。カーボン層15の表面被覆部17の厚みTcを30μm以下とすることで、負極の厚みを十分に小さくすることができ、高エネルギー密度の電池を得ることができる。
チタン系活物質は、一般式:Li4+xTi5-yMyO12+zで表される構造を有するのが好ましい。ここで、Mは、Mg、Al、Ca、Ba、Bi、Ga、V、Nb、W、Mo、Ta、Cr、Fe、Ni、Co、およびMnからなる群より選択された少なくとも1種であり、-1≦x≦1、0≦y≦1、および-1≦z≦1である。なお、xは合成直後または完全放電状態における値である。Tiの一部を、Mg、Al、Ca、Ba、Gaで置換することにより、熱安定性が向上する。これらのなかでも、MgおよびAlがより好ましい。Tiの一部を、Bi、V、Nb、W、Mo、Ta、Cr、Fe、Ni、Co、Mnで置換することにより、サイクル特性が向上する。これらのなかでも、BiおよびVがより好ましい。充放電に伴う膨張収縮による体積変化が特に小さいことから、チタン系活物質は、Li4Ti5O12が特に好ましい。チタン系活物質の体積基準の平均粒径(D50)は、0.2~30μmが好ましい。
また、炭素材料以外に、金属繊維類、フッ化カーボン、金属(例えば、アルミニウム)粉末類、酸化亜鉛やチタン酸カリウムのような導電性ウィスカー類、酸化チタンのような導電性金属酸化物、またはフェニレン誘導体のような有機導電性材料が挙げられる。これらのなかでも、ニッケル粉末が特に好ましい。
合剤層16中の第2結着剤の含有量は、活物質100重量部あたり2~6重量部が好ましく、活物質100重量部あたり3~5がより好ましい。合剤層16中の第2結着剤の含有量を、活物質100重量部あたり2重量部以上とすることで、活物質粒子間の結着性および合剤層とカーボン層との結着性が十分に得られる。合剤層16中の第2結着剤の含有量を、活物質100重量部あたり6重量部以下とすることで、十分量の活物質を含む合剤層が得られ、負極容量が十分に得られる。
合剤層16の厚みTmに対するカーボン層15の表面被覆部17の厚みTcの比:Tc/Tmは、0.03~1.5が好ましく、より好ましくは0.1~1.5である。
(a)複数の貫通孔を有し、空隙率が20~60%である、シート状の集電体の表面に炭素材料を含む第1ペーストを塗布し、乾燥させて、集電体の表面および貫通孔内に前記カーボン層を形成する工程と、
(b)前記カーボン層の表面に、チタン系活物質および導電剤を含む第2ペーストを塗布し、乾燥させて、合剤層を形成し、負極前駆体を得る工程と、
(c)前記負極前駆体を圧縮し、前記カーボン層の平均密度が0.05~0.4g/cm3である負極を得る工程と、
を含む。
例えば、粉末状の炭素材料に、第1結着剤を加え、さらに適量の第1分散媒を加え、第1ペーストを得る。第1分散媒には、水またはN-メチル-2-ピロリドン等が用いられる。
第1塗膜を貫通孔内に入り難くさせるためには、第1ペースト内に占める分散媒の割合を、炭素材料100重量部あたり800重量部以下とするのが好ましい。
集電体の両面への安定した塗布性を確保するためには、第1ペースト内に占める分散媒の割合を、炭素材料100重量部あたり300重量部以上とするのがより好ましい。
貫通孔内に第1塗膜を入り込み難くさせるためには、塗布方法は、特に、ブレード法が好ましい。
第1塗膜が貫通孔内に入り込み過ぎることなく、カーボン層を安定して形成するためには、第1塗膜を送風乾燥機により乾燥させるのが好ましい。乾燥条件としては、乾燥温度80~120℃、乾燥時間10~30分が好ましい。上記条件を採用することにより、工程(a)において、貫通孔の開口部上に塗布された第1ペーストの大部分は、開口部付近で貫通孔の開口を覆うように塗布され、第1塗膜は貫通孔内に密には入り込まない。よって、貫通孔内および貫通孔から集電体の厚み方向に延びる領域(孔充填部および延長部)では、炭素材料は密には充填されず、疎なカーボン層が形成される。
第2ペーストは、例えば、活物質に、導電剤および第2結着剤を加え、さらに適量の第2分散媒を加えることにより得られる。第2分散媒には、水またはN-メチル-2-ピロリドン等が用いられる。第2分散媒は、第1分散媒と同じでもよく、異なっていてもよい。第2結着剤は、第1結着剤と同じでもよく、異なっていてもよい。
カーボン層の表面に安定して塗膜を形成するためには、第2ペースト中に占める分散媒の割合を、活物質100重量部あたり80~150重量部とするのが好ましい。
第2塗膜を送風乾燥させて合剤層を形成する。乾燥条件としては、乾燥温度80~120℃、乾燥時間10~30分間が好ましい。
工程(b)の後、集電体の両面にカーボン層および合剤層が形成された負極前駆体を、一対のローラを用いて所定の線圧で圧縮し、負極を得る。
一対のローラにより負極前駆体に加えられる線圧は、好ましくは1000~3000kgf/cm、より好ましくは1500~2500kgf/cmである。線圧を3000kgf/cm以下とすることで、カーボン層が貫通孔内に密に入り込むのを確実に抑制することができる。線圧を1000kgf/cm以上とすることで、合剤層の活物質密度を大きくすることができ、電池のエネルギー密度を高めることができる。また、負極の強度(合剤層およびカーボン層の結着性)が十分に得られる。
一方、集電体の表面に存在するカーボン層は、工程(c)にて、集電体に押さえつけられ十分に圧縮されるため、密な層となり、集電体と、合剤層および集電体との間の良好な密着性が得られる。
(1)負極の作製
以下の手順で、図1に示すような構造の負極を作製した。
a)カーボン層の形成
炭素材料としてのアセチレンブラック粉末(電気化学工業(株)製、平均粒径35nm)100重量部と、結着剤としてのポリフッ化ビニリデン樹脂((株)クレハ製)230重量部との混合物に、分散媒としてのN-メチル-2-ピロリドンを700重量部加え、第1ペーストを得た。第1ペーストを、コンマコーターにより、負極集電体の両面に1m/分の速度で塗布し、第1塗膜を形成した。負極集電体には、パンチング加工にて得られたシート状のアルミニウム製のパンチングメタル(空隙率40%、厚みT20μm、平均孔径500μm、間隔L500μm)を用いた。このとき、第1塗膜は途切れることなく、かつ貫通孔内に入り込み過ぎず、負極集電体の両面を平面状に覆った。第1塗膜を送風乾燥させ、カーボン層(第1層)を形成した。乾燥温度は80℃とし、乾燥時間は20分間とした。
活物質としてのLi4Ti5O12(Li[Li1/3Ti5/3]O4)粉末(平均粒径1μm)85重量部と、導電剤としてのアセチレンブラック粉末(電気化学工業(株)製、平均粒径35nm)10重量部と、結着剤としてのポリフッ化ビニリデン樹脂((株)クレハ製)5重量部との混合物に、分散媒としてのN-メチル-2-ピロリドンを100重量部加え、第2ペーストを得た。第2ペーストを、コンマコーターにて、カーボン層の表面に1m/分の速度で塗布し、第2塗膜を形成した。第2塗膜の塗布量は、7.5mg/cm2とした。第2塗膜を送風乾燥させ、合剤層(第2層)を形成した。乾燥温度は80℃とし、乾燥時間は20分間とした。このようにして、負極前駆体を得た。
カーボン層の平均密度=
(炭素材料の充填量)/(表面被覆部の体積+貫通孔の総容積)
表面被覆部の体積は、表面被覆部の集電体(貫通孔を含む)との対向面積に、表面被覆部の厚み寸法を乗じて求めた。貫通孔の総容積は、貫通孔の平均径および集電体の厚みを用いて求めた貫通孔の体積に貫通孔の数を乗じて求めた。
負極の厚み方向の断面(円柱状の貫通孔の軸心を含む断面)を、走査型電子顕微鏡(SEM)を用いて観察した。その結果、孔貫通部、特に孔充填部では炭素材料が密に充填されず、電解質を保持する空間が形成されていることがわかった。
SEM像を画像処理し、貫通孔が占める容積Qvに対して、貫通孔内にて電解質が保持された空間が占める容積Rvの比:Rv/Qvを求めた。Rv/Qv×100をPの値とした。
貫通孔内にて電解質が保持された空間が占める容積Rvは、貫通孔内にて形成される空間を明確に判別できるように、SEM像に二値化処理を施して求めた。画像(投影像)の倍率は、600倍とした。画像(投影像)の面積は、100μm×100μmとした。画像(投影像)を分割するピクセル(画素)数は、1024×1024とした。各ピクセルを二値化処理した。この処理を、1つの貫通孔における負極の厚み方向の断面に対して行った。
集電体における5個の貫通孔に対してこの作業を繰り返し実施した。そして、その平均値を求めた。
活物質としてのコバルト酸リチウム(LiCoO2)粉末85重量部と、導電剤としてのアセチレンブラック粉末10重量部と、結着剤としてのポリフッ化ビニリデン樹脂5重量部との混合物に、分散媒としてのN-メチル-2-ピロリドンを50重量部加え、正極ペーストを得た。正極ペーストを、コンマコーターにて、アルミニウム箔(厚み15μm)からなる正極集電体の両面に1m/分の速度で塗布し、塗膜を形成した。この塗膜を送風乾燥させ、合剤層を形成し、正極前駆体を得た。乾燥温度は80℃とし、乾燥時間は20分間とした。
正極と、負極とを、正極と負極との間にセパレータを介して、渦巻状に巻回し、電極群4を得た。セパレータには、ポリエチレン製の微多孔フィルム(厚み20μm)を用いた。電極群4を、ステンレス鋼製の電池ケース1内に収納した。アルミニウム製の正極リード5の一端を正極に接続した。正極リード5の他端を封口板2に接続した。アルミニウム製の負極リード6の一端を負極に接続した。負極リード6の他端を電池ケース1の底部に接続した。電極群4の上下部に、それぞれ樹脂製の絶縁リング7を配した。電池ケース1内に非水電解質を注入した。非水電解質には、LiPF6が溶解した非水溶媒を用いた。非水溶媒には、エチレンカーボネート(EC)およびジエチルカーボネート(DEC)の混合溶媒(体積比3:7)を用いた。非水電解質中のLiPF6の濃度は1.0mol/Lとした。電池ケース1の開口端部を、樹脂製の封口体3を介して、封口板2の周縁部にかしめつけ、電池ケース1を密封した。このようにして、図2の円筒型電池(直径18mm、高さ65mm)を得た。具体的には、実施例1~4の負極A1~A4を用いて、電池A1~A4を作製した。また、比較例1~2の負極B1~B2を用いて、電池B1~B2を作製した。
カーボン層を形成せずに、負極ペーストを、ブレード法にて、直接負極集電体の表面に1m/分の速度で塗布し、塗膜を形成した。負極ペーストには、実施例1の第2ペーストを用いた。負極集電体には、実施例1の負極集電体を用いた。このとき、塗膜の一部が、貫通孔内に入り込んだ。塗膜を送風乾燥させ、合剤層を形成した。乾燥温度は80℃とし、乾燥時間は20分間とした。合剤層の一部は、貫通孔内に形成された。このようにして、負極前駆体を得た。
負極集電体に、パンチングメタルの代わりに、貫通孔を有さないアルミニウム箔(厚み15μm)を用いた以外、実施例1と同様の方法により、負極Dを作製した。負極A1の代わりに、負極Dを用いた以外、実施例1と同様の方法により、円筒型電池Dを作製した。
カーボン層を形成せず、負極ペーストを、コンマコーターにて、直接負極集電体に1m/分の速度で塗布し、塗膜を形成した。負極ペーストには、実施例1の第2ペーストを用いた。負極集電体には、比較例4のアルミニウム箔(厚み15μm)を用いた。塗膜を乾燥させ、合剤層を形成した。乾燥温度は80℃とし、乾燥時間は20分間とした。このようにして、負極前駆体を得た。
上記負極の作製条件を表1にまとめる。
(1)直流内部抵抗の測定
レート特性を評価するため、以下の測定を実施した。
25℃の環境下において、充電容量が満充電の60%に達するまで、電池を1Aの定電流で充電した。SOC60%の電池を用い、下記の表2に示す条件で、100~2000mAの範囲内で電流値を変えながら間欠的に充電および放電した。
25℃の環境下において、下記に示す条件で充放電サイクル試験を実施した。
充電条件:電池電圧が4.2Vに達するまで1Aの定電流で充電した後、電流値が0.1Aに減衰するまで4.2Vの定電圧で充電
放電条件:電池電圧が1.5Vに達するまで1Aの定電流で放電
そして、充放電サイクルは500サイクルとし、1サイクル目および500サイクル目の放電容量を用いて、下記式より容量維持率を求めた。
容量維持率(%)=500サイクル目の放電容量/1サイクル目の放電容量×100
その試験結果を表3に示す。
比較例3の電池Cでは、実施例1の電池A1と同じ集電体を用いたが、電池Cを解体し、負極の断面を観察した結果、貫通孔内に合剤層が密に充填され、電解質を保持する空間が形成されていないことが確かめられた。
なお、上記実施例では、空隙率が40%の集電体を用いたが、集電体の空隙率が40%以外の場合でも、集電体の空隙率が20~60%であれば、上記実施例と同様の本発明の効果が得られる。
Claims (8)
- 複数の貫通孔を有する、シート状の集電体と、
前記集電体の表面および前記貫通孔内に形成されたカーボン層と、
前記カーボン層の表面に形成された合剤層と、
を備え、
前記合剤層が、活物質および導電剤を含み、
前記活物質が、スピネル型の結晶構造を有するリチウムチタン含有複合酸化物を含み、
前記集電体の空隙率が、20~60%であり、
前記カーボン層の平均密度が、0.05~0.4g/cm3である、ことを特徴とする非水電解質二次電池用負極。 - 前記貫通孔の平均径が、100~700μmである、請求項1記載の非水電解質二次電池用負極。
- 前記合剤層中の前記活物質の含有量は、合剤層1cm3あたり1.5~2.3gである、請求項1または2記載の非水電解質二次電池用負極。
- 前記リチウムチタン含有複合酸化物が、一般式:
Li4+xTi5-yMyO12+z
(式中、Mは、Mg、Al、Ca、Ba、Bi、Ga、V、Nb、W、Mo、Ta、Cr、Fe、Ni、Co、およびMnからなる群より選択された少なくとも1種であり、-1≦x≦1、0≦y≦1、および-1≦z≦1)で表される、請求項1~3のいずれか1項に記載の非水電解質二次電池用負極。 - 正極、負極、前記正極と前記負極との間に配されたセパレータ、および非水電解質を備え、
前記負極が、請求項1~4のいずれか1項に記載の負極である非水電解質二次電池。 - 前記集電体の貫通孔の内空間の30~90体積%が、前記非水電解質で満たされている、請求項5記載の非水電解質二次電池。
- (a)複数の貫通孔を有し、空隙率が20~60%である、シート状の集電体の表面に、炭素材料を含む第1ペーストを塗布し、乾燥させて、前記集電体の表面および前記貫通孔内にカーボン層を形成する工程と、
(b)前記カーボン層の表面に、活物質としてスピネル型の結晶構造を有するリチウムチタン含有複合酸化物および導電剤を含む第2ペーストを塗布し、乾燥させて、合剤層を形成し、負極前駆体を得る工程と、
(c)前記負極前駆体を圧縮し、前記カーボン層の平均密度が0.05~0.4g/cm3である負極を得る工程と、
を含む、非水電解質二次電池用負極の製造方法。 - 前記リチウムチタン含有複合酸化物が、一般式:
Li4+xTi5-yMyO12+z
(式中、Mは、Mg、Al、Ca、Ba、Bi、Ga、V、Nb、W、Mo、Ta、Cr、Fe、Ni、Co、およびMnからなる群より選択された少なくとも1種であり、-1≦x≦1、0≦y≦1、および-1≦z≦1)で表される、請求項7記載の非水電解質二次電池用負極の製造方法。
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US13/388,642 US20120135306A1 (en) | 2010-03-29 | 2011-03-24 | Negative electrode for non-aqueous electrolyte secondary battery, method for producing the same, and non-aqueous electrolyte secondary battery |
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JP4920803B2 (ja) | 2012-04-18 |
CN102473901A (zh) | 2012-05-23 |
JPWO2011121950A1 (ja) | 2013-07-04 |
US20120135306A1 (en) | 2012-05-31 |
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