WO2010016217A1 - リチウム二次電池の製造方法およびリチウム二次電池 - Google Patents
リチウム二次電池の製造方法およびリチウム二次電池 Download PDFInfo
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- WO2010016217A1 WO2010016217A1 PCT/JP2009/003662 JP2009003662W WO2010016217A1 WO 2010016217 A1 WO2010016217 A1 WO 2010016217A1 JP 2009003662 W JP2009003662 W JP 2009003662W WO 2010016217 A1 WO2010016217 A1 WO 2010016217A1
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- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/134—Electrodes based on metals, Si or alloys
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- H01M4/04—Processes of manufacture in general
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- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
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- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
- H01M4/381—Alkaline or alkaline earth metals elements
- H01M4/382—Lithium
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- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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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
- H01M4/139—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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- H01M4/02—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
- H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
- H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
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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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- 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
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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
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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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
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49002—Electrical device making
- Y10T29/49108—Electric battery cell making
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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
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49002—Electrical device making
- Y10T29/49108—Electric battery cell making
- Y10T29/49115—Electric battery cell making including coating or impregnating
Definitions
- the present invention relates to a method for manufacturing a lithium secondary battery and a lithium secondary battery.
- the theoretical capacity of carbon which is a negative electrode active material mainly used in lithium secondary batteries at present, is 372 mAh / g.
- As an active material capable of having a higher capacity than carbon development of a negative electrode using an element alloying with lithium such as silicon, germanium, and tin has been performed. In particular, silicon having a theoretical capacity of 4200 mAh / g is considered promising.
- the negative electrode active material When a material containing an element that is alloyed with lithium, such as silicon, is used as the negative electrode active material, the negative electrode active material is greatly expanded and contracted by inserting and extracting lithium by charge and discharge. In contrast, the current collector hardly expands or contracts. Therefore, when charging / discharging is repeated, the negative electrode active material is separated from the current collector and does not contribute to charging / discharging. Further, when the negative electrode active material expands, the current collector extends beyond the elastic deformation region, and as a result, the negative electrode is deformed (buckled). The deformation of the negative electrode is also not preferable because it directly leads to a decrease in battery capacity.
- a material containing an element that is alloyed with lithium such as silicon
- JP 2005-196970 A discloses that a columnar body made of a negative electrode active material is formed on a current collector by oblique vapor deposition.
- the oblique vapor deposition is a vapor deposition technique in which the arrangement of the vapor deposition source, the vapor deposition surface, and the mask is improved so that particles from the vapor deposition source are incident on the vapor deposition surface obliquely.
- a gap is formed between adjacent columnar bodies, so that deformation of the negative electrode due to expansion and contraction of the negative electrode active material can be suppressed to some extent.
- the deformation of the negative electrode cannot always be reduced to a satisfactory level.
- Japanese Patent Application Laid-Open No. 2006-260928 discloses that the negative electrode is mechanically stretched before the battery is assembled as a technique for suppressing deformation of the negative electrode during charging.
- lithium is occluded in advance in the negative electrode active material layer, lithium is present in both the positive electrode and the negative electrode when the battery is assembled. This means that the amount of lithium that can move between the positive electrode and the negative electrode decreases, that is, the charge / discharge capacity decreases. Depending on the amount of lithium previously stored in the negative electrode, the charge / discharge capacity may be significantly reduced. Further, excessive lithium may be deposited on the surface of the positive electrode or the negative electrode during charging and discharging.
- the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a high-capacity lithium secondary battery in which deformation of the negative electrode is suppressed to be small. Another object of the present invention is to provide a method for producing the lithium secondary battery.
- the present invention Forming a negative electrode active material layer containing at least one element selected from the group consisting of silicon, germanium and tin on the negative electrode current collector; Preparing a negative electrode by forming a lithium metal layer on the negative electrode active material layer; A positive electrode including a composite oxide represented by the general formula Li 1-x MO 2 (0.2 ⁇ x ⁇ 0.6, M includes at least one transition metal selected from the group consisting of cobalt, nickel, and manganese) Preparing a positive electrode having a configuration in which an active material layer is formed on a positive electrode current collector; Assembling a lithium secondary battery using the negative electrode, the positive electrode and the separator; A method for producing a lithium secondary battery is provided.
- the present invention provides: A negative electrode current collector, and a negative electrode active material layer that is provided on the negative electrode current collector and includes at least one element selected from the group consisting of silicon, germanium, and tin, and A positive electrode current collector, and a positive electrode active material layer that is provided on the positive electrode current collector and includes a lithium composite oxide; A separator disposed between the negative electrode and the positive electrode, Regarding the thickness direction of the separator, a first region where the negative electrode active material layer faces the positive electrode active material layer and a second region where the negative electrode active material layer does not face the positive electrode active material layer Exists, The amount of lithium contained in the negative electrode per unit area in the second region is M 1 , the amount of lithium that compensates the irreversible capacity of the negative electrode per unit area is M 2 , and the amount of lithium per unit area in the first region is The amount of lithium contained in the negative electrode is m 1 , the amount of lithium contained in the positive electrode per unit area in the first region is m 2 , and the lithium composite oxide has
- a lithium secondary battery in which the following relationship is established when the amount of lithium to be included in the positive electrode per unit area in the first region is m 3 .
- M 1 > M 2 and (m 1 + m 2 ) ⁇ (M 1 + m 3 )
- the lithium metal layer is formed on the negative electrode active material layer before the battery is assembled.
- the negative electrode current collector can be stretched in advance. Therefore, deformation of the negative electrode during charge / discharge can be reduced or suppressed.
- a lithium composite oxide deficient in lithium is used as the positive electrode active material. That is, a space for storing lithium is previously provided in the positive electrode. In this way, it is possible to avoid a decrease in charge / discharge capacity due to the formation of the lithium metal layer on the negative electrode active material layer. Moreover, it can prevent that an excessive lithium metal precipitates on the surface of a positive electrode or a negative electrode at the time of charging / discharging. Therefore, according to the present invention, it is possible to provide a high capacity lithium secondary battery with small deformation of the negative electrode.
- FIG. 1 is a schematic cross-sectional view of a lithium secondary battery according to an embodiment of the present invention.
- Schematic diagram of vapor deposition equipment for oblique vapor deposition Schematic cross-sectional view of the negative electrode when the negative electrode active material layer is formed on the negative electrode current collector
- Schematic cross-sectional view of a charged lithium secondary battery Schematic cross-sectional view of a lithium secondary battery in a discharged state
- Schematic showing the state of charge and discharge of a lithium secondary battery compensated for the amount of lithium corresponding to the irreversible capacity Schematic diagram showing the charge and discharge states of a lithium secondary battery fabricated with a negative electrode compensated for lithium exceeding the amount corresponding to the irreversible capacity and a positive electrode using a composite oxide having a stoichiometric composition.
- Schematic showing the charge state and discharge state of a lithium secondary battery produced by the method of the present invention Schematic showing a method for specifying the amount of lithium contained in a lithium secondary battery produced by the method of the present invention
- Schematic showing the distribution of lithium contained in a lithium secondary battery compensated for an amount of lithium corresponding to the irreversible capacity Schematic showing the distribution of lithium contained in a lithium secondary battery fabricated with a negative electrode compensated for an amount of lithium exceeding the amount corresponding to the irreversible capacity and a positive electrode using a composite oxide having a stoichiometric composition
- Figure Schematic showing the distribution of lithium contained in the lithium secondary battery produced by the method of the present invention
- FIGS. 1-10 A typical structure of a lithium secondary battery that can be manufactured by the method of this embodiment is shown in FIGS.
- FIG. 1 shows a stacked lithium secondary battery.
- the lithium secondary battery 100 includes an electrode group that includes a positive electrode 13, a negative electrode 11, and a separator 4 disposed therebetween. An electrode group and an electrolyte having lithium ion conductivity are accommodated in the outer case 14.
- the positive electrode 13 includes a positive electrode current collector 5 and a positive electrode active material layer 6 in contact with the positive electrode current collector 5.
- the negative electrode 11 includes a negative electrode current collector 1 and a negative electrode active material layer 3 in contact with the negative electrode current collector 1.
- One end of a positive electrode lead 15 and a negative electrode lead 16 is connected to the positive electrode current collector 5 and the negative electrode current collector 1, respectively.
- the other ends of the leads 15 and 16 extend outside the outer case 14.
- the opening of the outer case 14 is sealed with a resin material 17.
- the positive electrode active material layer 6 releases lithium ions during charging and occludes lithium ions released from the negative electrode active material layer 3 during discharge.
- the negative electrode active material layer 3 occludes lithium ions released from the positive electrode active material layer 6 during charging, and releases lithium ions during discharge.
- FIG. 2 shows a wound lithium secondary battery.
- the lithium secondary battery 200 includes a wound electrode group 24 and a battery case 28 that houses the electrode group 24.
- the electrode group 24 is produced by winding a belt-like positive electrode 21 and a belt-like negative electrode 22 together with a wide separator 23 disposed therebetween.
- the electrode group 24 is impregnated with an electrolytic solution.
- the opening of the battery case 28 is closed with a sealing plate 29 having a positive electrode terminal 25.
- One end of a positive electrode lead 21 a is connected to the positive electrode 21.
- the other end of the positive electrode lead 21 a is connected to the back surface of the sealing plate 29.
- An insulating packing 26 is disposed on the periphery of the sealing plate 29.
- One end of a negative electrode lead (not shown) is connected to the negative electrode 22.
- the other end of the negative electrode lead is connected to the battery case 28.
- An upper insulating ring (not shown) and a lower insulating ring 27 are disposed above and below the electrode group 24, respectively.
- the structure of the lithium secondary battery is not particularly limited, and other structures such as a coin type other than the structures shown in FIGS.
- a metal foil such as a copper foil or a copper alloy foil is prepared as a material for the negative electrode current collector 1.
- the metal foil has, for example, a width of 50 to 1000 mm and a thickness of 3 to 150 ⁇ m.
- the metal foil is preferably a rolled foil having heat resistance.
- the metal foil is processed so that a plurality of convex portions having a predetermined shape in plan view are formed on the surface at predetermined intervals. Thereby, the negative electrode collector 1 is obtained.
- the shape of the convex portion is, for example, a circle or a polygon in plan view.
- the processing for forming the convex portion may be mechanical processing such as press processing or chemical processing such as etching.
- FIG. 3 shows a schematic diagram of a vacuum deposition apparatus.
- the vacuum deposition apparatus 50 includes a vacuum chamber 51, a substrate transport mechanism 56, a shielding plate 57, and a deposition source 58.
- the substrate transport mechanism 56, the shielding plate 57, and the vapor deposition source 58 are disposed in the vacuum chamber 51.
- a vacuum pump 59 is connected to the vacuum chamber 51.
- the inside of the vacuum chamber 51 is kept at a pressure (for example, 1.0 ⁇ 10 ⁇ 2 to 1.0 ⁇ 10 ⁇ 4 Pa) suitable for forming the negative electrode active material layer 3 by the vacuum pump 59.
- the substrate transport mechanism 56 includes an unwinding roll 52, a guide roller 54, a winding roll 53, and a can 55.
- a long negative electrode current collector 1 as a substrate is prepared on an unwinding roll 52.
- the guide roller 54 is disposed on each of the upstream side and the downstream side in the conveying direction of the negative electrode current collector 1.
- the upstream guide roller 54 guides the negative electrode current collector 1 fed from the unwinding roll 52 to the can 55.
- the downstream guide roller 54 takes over the deposited negative electrode current collector 1 from the can 55 and guides it to the take-up roll 53.
- the vapor deposition source 58 is configured to heat and evaporate the negative electrode active material 58b accommodated in the crucible 58a by an electron beam or electromagnetic induction.
- the negative electrode active material 58b at least one element selected from the group consisting of silicon, germanium, and tin can be used.
- the negative electrode active material layer 3 formed on the negative electrode current collector 1 may contain oxides of the above elements, nitrides of the above elements, alloys of the above elements with other metals, and the like.
- the shielding plate 57 is disposed between the vapor deposition source 58 and the can 55.
- the vapor deposition region on the surface of the negative electrode current collector 1 is defined by the opening of the shielding plate 57.
- Particles (for example, silicon particles) from the deposition source 58 are incident on the negative electrode current collector 1 mainly from an oblique direction. That is, the negative electrode active material layer 3 can be formed on the negative electrode current collector 1 by an oblique vapor deposition technique in which a material to be vapor deposited is incident on the negative electrode current collector 1 having a convex portion from an oblique direction. By oblique deposition, the negative electrode active material layer 3 having a gap can be formed by a self-shading effect.
- the thickness of the negative electrode active material layer 3 is, for example, 1 to 50 ⁇ m.
- FIG. 4 is a schematic cross-sectional view of the negative electrode when the negative electrode active material layer is formed. Protrusions are regularly formed on the surface of the negative electrode current collector 1.
- the negative electrode active material layer 3 having the column 3 a is formed on the negative electrode current collector 1 by the synergistic effect of the convex portion and the oblique deposition.
- the longitudinal direction of each column 3 a is inclined with respect to the normal direction of the negative electrode current collector 1.
- Each column 3a contains a negative electrode active material. A gap is formed between adjacent columns 3a.
- the formation method of the negative electrode active material layer 3 is not limited to a vapor deposition method, Various thin film formation methods, such as sputtering method and CVD method, are employable.
- the negative electrode active material layer 3 may be formed by a coating method.
- a material having random irregularities such as an electrolytic copper foil can be used as the negative electrode current collector 1. This is because a negative electrode active material layer having a gap can be formed regardless of whether the irregularities are regular. It is known that when a material having random irregularities is used, a negative electrode active material layer separated into a columnar shape by a cut can be formed (for example, International Publication No. 2001/031720).
- the lithium metal layer is formed by vacuum depositing lithium metal on the negative electrode active material layer 3.
- Lithium is deposited on the negative electrode active material layer 3. In this way, lithium can quickly diffuse into the negative electrode active material layer 3. If the temperature is not raised too much, the strength of the negative electrode current collector 1 will not decrease. By maintaining the negative electrode current collector 1 with high strength, deformation of the negative electrode 11 due to stress during charging and discharging can be suppressed.
- FIG. 5 is a schematic cross-sectional view of the negative electrode when a lithium metal layer is formed on the negative electrode active material layer.
- the deposited lithium is occluded in the negative electrode active material layer 3.
- the column 3a constituting the negative electrode active material layer 3 expands and becomes slightly longer, and there is no gap between the adjacent columns 3a.
- the negative electrode 11 extends in the in-plane direction of the negative electrode current collector 1 due to the stress generated when the adjacent columns 3 a come into contact with each other.
- the column 3a extends in the normal direction of the negative electrode current collector 1, and the inclination of the column 3a is also reduced.
- the “in-plane direction of the negative electrode current collector 1” means an in-plane direction when it is assumed that no convex portion exists on the surface of the negative electrode current collector 1.
- the formation method of the lithium metal layer is not limited to the vapor deposition method, and various thin film formation methods such as a sputtering method and a CVD method can be employed.
- lithium can be preliminarily occluded in the negative electrode active material layer 3 by attaching a lithium foil to the negative electrode active material layer 3 and then performing a heat treatment.
- a metal foil such as an aluminum foil or an aluminum alloy foil is prepared as a material for the positive electrode current collector 5.
- the width and thickness of the positive electrode current collector 5 are about the same as those of the negative electrode current collector 1.
- the positive electrode active material layer 6 is formed on the positive electrode current collector 5 by applying a positive electrode mixture in a thickness of, for example, 10 to 100 ⁇ m by a known method such as a doctor blade method.
- the positive electrode mixture is obtained by mixing a positive electrode active material, a conductive material, a binder, and a solvent.
- conductive material conductive carbon such as acetylene black can be used.
- fluorine resins such as polyvinylidene fluoride (PVdF), hexafluoropropylene (HFP), and polytetrafluoroethylene (PTEF) can be used.
- organic solvent such as N-methyl-2-pyrrolidone (NMP) can be used.
- a composite oxide lacking lithium can be used as the positive electrode active material.
- “Composite oxide deficient in lithium” means a general formula Li 1-x MO 2 (0.2 ⁇ x ⁇ 0.6, where M is at least one transition metal selected from the group consisting of cobalt, nickel and manganese. It is a substance represented by However, even when the positive electrode 13 is manufactured using a composite oxide deficient in lithium, the positive electrode active material can be changed to a stoichiometric composition (LiMO 2 ) by charging and discharging after the battery is assembled. . This is because in this embodiment, lithium is occluded in advance in the negative electrode active material layer 3 before the battery is assembled.
- a composite oxide deficient in lithium can be produced by firing a mixture of a lithium compound (for example, lithium carbonate) and a transition metal compound (for example, cobalt oxide). Specifically, the ratio of lithium to the transition metal (“x” in the above general formula) can be adjusted by adjusting the mixing ratio of the lithium compound and the transition metal compound.
- a positive electrode including a composite oxide deficient in lithium is prepared by intentionally reducing the amount of lithium in the positive electrode before the battery is assembled using a composite oxide having a stoichiometric composition. An active material layer can be formed. The amount of lithium in the positive electrode can be reduced by charging a half battery using the positive electrode.
- M in the composite oxide represented by the general formula Li 1-x MO 2 is typically a transition metal such as cobalt, but a part of the transition metal is partially added to other additive metals, for example, It is also possible to replace with aluminum or zirconium.
- the negative electrode lead 16 and the positive electrode lead 15 are welded to the negative electrode 11 and the positive electrode 13, respectively.
- the positive electrode lead 15 is made of, for example, aluminum or an aluminum alloy.
- the negative electrode lead 16 is made of, for example, copper, a copper alloy, nickel, or a nickel alloy.
- the negative electrode 11 and the positive electrode 13 are arranged on the left and right of the separator 4.
- the separator 4 is typically a microporous film made of polyethylene or polypropylene.
- An electrode group composed of the negative electrode 11, the separator 4, and the positive electrode 13 is housed in an outer case 14, and the electrode group is impregnated with an electrolytic solution having lithium ion conductivity.
- an electrolytic solution having lithium ion conductivity typically, a nonaqueous electrolytic solution in which a lithium salt such as LiPF 6 is dissolved in an organic solvent such as ethylene carbonate or propylene carbonate can be used.
- the composition of the nonaqueous electrolytic solution is not particularly limited.
- a solid electrolyte may be used instead of the electrolytic solution.
- the exterior case 14 can be configured by a flexible sheet in which resin layers are provided on both surfaces of a metal foil such as an aluminum foil. By sealing the opening of the outer case 14 with the resin material 17, the lithium secondary battery 100 (see FIG. 1) is obtained.
- FIG. 8A is a schematic diagram showing a charged state and a discharged state of a conventional lithium secondary battery (Comparative Example 1 described later) in which an amount of lithium corresponding to the irreversible capacity is compensated.
- the hatched portion represents the actual battery capacity.
- the positive electrode also has irreversible capacity, but when the irreversible capacity of the negative electrode is large as shown in FIG. 8A (when the negative electrode active material is silicon, germanium, tin, or an oxide thereof), the irreversible capacity of the positive electrode is Because it is far less, the irreversible capacity of the positive electrode is ignored.
- the charge / discharge capacity is improved by preliminarily occluding an amount of lithium corresponding to the irreversible capacity in the negative electrode.
- the elongation of the negative electrode is not necessarily large.
- the negative electrode occludes lithium.
- the column (see FIGS. 4 to 7) forming the negative electrode active material layer expands greatly, and the negative electrode expands.
- the negative electrode shrinks. Based on the dimensions at the time of battery assembly, the degree of expansion and contraction of the negative electrode during charging and discharging is large. Therefore, the effect of suppressing the deformation of the negative electrode during charge / discharge is insufficient.
- FIG. 8B shows a lithium secondary battery manufactured with a negative electrode compensated for lithium exceeding the amount corresponding to the irreversible capacity and a positive electrode using a composite oxide having a stoichiometric composition (Comparative Example 4 described later). It is the schematic which shows the charge condition and discharge state of. By compensating lithium excessively, the elongation of the negative electrode before assembly can be made relatively large. When the battery is assembled and charged with the negative electrode stretched to some extent, the negative electrode is still stretched, but the magnitude of the stretch is not as high as that of the conventional lithium secondary battery shown in FIG. 8A.
- the positive electrode is made of an active material having a stoichiometric composition
- the amount of lithium that can move between the negative electrode and the positive electrode is limited, that is, the charge / discharge capacity is small.
- the precipitation of lithium dendrite due to the excessive presence of lithium in the battery.
- the negative electrode shrinks when discharged, the negative electrode can exhibit a negative dimension based on the dimensions at the time of battery assembly. That is, the degree of expansion / contraction of the negative electrode during charging / discharging is within a certain range based on the dimensions at the time of battery assembly. As a result, an effect of suppressing deformation of the negative electrode during charging / discharging is produced.
- the problem of the lithium secondary battery shown in FIG. 8A and the problem of the lithium secondary battery shown in FIG. 8B can be overcome.
- the amount of lithium to be compensated can be calculated by the following method. Specifically, the charge capacity and discharge capacity of the negative electrode active material layer on which the lithium metal layer is to be formed are measured, and the irreversible capacity of the negative electrode active material layer is determined based on the capacity obtained by subtracting the discharge capacity from the measured charge capacity. Calculate in advance. Specifically, a half battery using a laminate of a negative electrode active material layer and a negative electrode current collector (hereinafter referred to as a “basic negative electrode” in this specification) and a counter electrode (for example, a lithium metal counter electrode) before vapor deposition of lithium. Is made. The value obtained by subtracting the discharge capacity from the charge capacity of the half battery is the irreversible capacity.
- the lithium metal layer is formed on the negative electrode active material layer so that the lithium metal layer contains an amount of lithium that exceeds the amount of lithium that can compensate for the irreversible capacity calculated in advance.
- the elongation of the negative electrode before assembly can be increased as described above.
- the degree of expansion / contraction of the negative electrode during charging / discharging is within a certain range based on the dimensions at the time of battery assembly.
- the length in a predetermined direction in the plane of the negative electrode current collector before forming the lithium metal layer is S 0
- the length in the predetermined direction of the negative electrode current collector when the lithium metal layer is formed is S 1
- S C is the length of the negative electrode current collector in the discharged state of the assembled lithium secondary battery.
- the length in the predetermined direction is represented by SD .
- the elongation rate in the charged state and the discharged state is adjusted so that the deformation of the negative electrode during charging and discharging can be suppressed.
- the lithium metal layer has a value obtained by subtracting the initial elongation from the elongation in the charged state to 1% or less and a value obtained by subtracting the initial elongation from the discharged in the discharged state from ⁇ 1% or more. Adjust the amount of lithium. If it does in this way, precipitation of lithium in a battery can also be prevented, obtaining the effect which controls modification of a negative electrode enough.
- the elongation rate in the vertical direction and the elongation rate in the horizontal direction may be calculated separately, and an average value thereof may be adopted as each elongation rate. Note that the value obtained by subtracting the initial elongation from the elongation in the charged state is greater than 0%, and the value obtained by subtracting the initial elongation from the elongation in the discharged state is less than 0%.
- the lithium secondary battery manufactured by the method of the present invention is indistinguishable from the conventional lithium secondary battery (FIG. 8A) when it is repeatedly charged and discharged.
- the lithium secondary battery manufactured by the method of the present invention can be distinguished from the conventional lithium secondary battery by the following method.
- region 32 where the negative electrode active material layer 3 does not oppose the positive electrode active material layer 6 (it protrudes) exists.
- the lithium secondary battery manufactured by the method of the present invention the following relationship is established.
- M 1 the amount of lithium contained in the negative electrode 11 per unit area in the second region 32
- M 2 > the relationship of M 2 is established. That is, in the second region 32, the negative electrode 11 maintains the state shown in the left diagram of FIG. 8C. This is based on the fact that the negative electrode 11 in the second region 32 hardly contributes to charge / discharge.
- the amount of lithium contained in the negative electrode 11 per unit area in the first region 31 is m 1
- the amount of lithium contained in the positive electrode 13 per unit area in the first region 31 is m 2
- the positive electrode 13 is the composite oxide contained in the cathode has a stoichiometric composition
- m 3 is the amount of lithium to be included in the positive electrode 13 per unit area in the first region 31, (m 1 + m 2 ) ⁇ (M 1 + m 3 ).
- the above relationship can be easily derived by calculating the amount of lithium for the negative electrode and positive electrode before assembly. That is, as shown in FIG. 10C, before assembly, the amount of lithium occluded in the negative electrode 11 matches the values M 1 and m 1 , and the amount of lithium contained in the positive electrode 13 becomes the value m 2 . Match. The value M 2 matches the amount of lithium remaining in the negative electrode 11 after full discharge. The value m 3 can be calculated from the amount (weight or molar amount) of other metals contained in the positive electrode 13. These values satisfy the above relationship. “Full discharge” means a state in which the voltage of the battery reaches a discharge end voltage (for example, 2 V).
- M 1 0.
- a copper alloy foil having a thickness of 26 ⁇ m was prepared as a material for the negative electrode current collector.
- the front and back surfaces of the copper alloy foil were pressed so that the rhombic protrusions were formed at intervals of 30 ⁇ m in plan view having a diagonal length of 10 ⁇ 20 ⁇ m.
- the height of the convex part was set to 6 ⁇ m.
- a copper roughening plating layer having a thickness of about 2 ⁇ m was formed on the surface of the copper alloy foil by electrolytic copper plating. Thereby, a negative electrode current collector was obtained.
- the arithmetic average roughness Ra (JIS B 0601 (1994)) of the copper roughening plating layer was about 0.5 ⁇ m.
- a negative electrode active material layer containing silicon and silicon oxide was formed on the negative electrode current collector by oblique vapor deposition described with reference to FIG. By performing the same vapor deposition on the back surface of the negative electrode current collector, a negative electrode active material layer was formed on both surfaces of the negative electrode current collector.
- the thickness of the negative electrode active material layer (the height of the column 3a shown in FIG. 4) was 14 ⁇ m.
- a half cell was prepared using a laminate (basic negative electrode) of a negative electrode active material layer and a negative electrode current collector before forming a lithium metal layer, and a lithium metal counter electrode. By charging / discharging this half-cell, the charge / discharge capacity and the irreversible capacity were measured. Specifically, a part of the basic negative electrode was cut out to a size of 15 ⁇ 15 mm, and a nickel lead was joined to the end portion by spot welding. A lithium metal counter electrode was prepared by fixing a nickel lead to the end of a lithium metal plate having the same dimensions as the basic negative electrode.
- the half cell was charged with a current of 1 mA / cm 2 until the voltage between the two electrodes became 0V. Then, it discharged until the voltage between both electrodes became 2V with the electric current of 1 mA / cm ⁇ 2 >, and the charge / discharge capacity was measured. The capacity obtained by subtracting the discharge capacity from the charge capacity at this time was calculated as the irreversible capacity of the negative electrode to be produced. Since basic negative electrode had a discharge capacity of the charge capacity and 5.0mAh / cm 2 of 6.5mAh / cm 2, the irreversible capacity was 1.5 mAh / cm 2.
- the positive electrode mixture was applied to one surface of a positive electrode current collector (thickness 15 ⁇ m) made of aluminum foil at a thickness of 85 ⁇ m, dried and rolled. In this way, a positive electrode having lithium cobalt oxide having a stoichiometric composition as a positive electrode active material was obtained.
- this positive electrode is referred to as a “basic positive electrode”.
- a nickel compound, a cobalt compound, an aluminum compound, and lithium hydroxide were mixed at a predetermined ratio and fired to obtain a lithium nickelate positive electrode active material (LiNi 0.8 Co 0.15 Al 0.05 O 2 ).
- a positive electrode mixture was prepared in the same manner as in the case of lithium cobaltate. The positive electrode mixture was applied to one side of the positive electrode current collector to a thickness of 70 ⁇ m, dried and rolled. In this way, a positive electrode (basic positive electrode) containing a lithium nickelate positive electrode active material having a stoichiometric composition was obtained.
- Li 1-x MO 2 Li 1-x MO 2
- the true density of the lithium nickelate-based positive electrode active material (LiNi 0.8 Co 0.15 Al 0.05 O 2 ) is 4.8 g / cm 3 .
- the density of the lithium nickelate-based positive electrode active material in the positive electrode active material layer was about 3.2 g / cm 3 .
- the lithium nickelate-based positive electrode active material has a theoretical charge / discharge capacity of 279 mAh / g and the thickness of the positive electrode active material layer was about 70 ⁇ m, the lithium nickelate-based positive electrode active material was used.
- the theoretical charge / discharge capacity of the basic positive electrode is about 6.1 mAh / cm 2 . In other words, the amount of deficiency x of lithium increases or decreases by 0.1 by charge / discharge of about 0.61 mAh / cm 2 .
- a lithium secondary battery was produced using the negative electrode and the positive electrode.
- a nickel lead was joined to the end of the negative electrode by spot welding.
- the positive electrode lacking lithium was cut out to a size of 15 ⁇ 15 mm, and an aluminum lead was joined to the end by ultrasonic welding.
- the negative electrode was sandwiched between two positive electrodes through a separator (polyethylene microporous film, thickness 16 ⁇ m).
- An electrode group composed of a positive electrode, a separator, and a negative electrode was housed in an outer case, and 1 cm 3 of an electrolyte was placed in the outer case.
- the outer case was sealed by heat sealing. Thereby, a lithium secondary battery was obtained.
- a plurality of lithium secondary batteries were manufactured using the negative electrode and the positive electrode manufactured under the same conditions.
- ⁇ Calculation of elongation rate of negative electrode in charged and discharged state The manufactured lithium secondary battery was charged with a current of 1 mA / cm 2 until the voltage between both electrodes reached 4.2V. The lithium secondary battery was disassembled in the charged state, and the elongation percentage of the negative electrode in the charged state was calculated. Further, it was visually observed whether lithium was deposited on the surface of the negative electrode. Further, the charged lithium secondary battery was discharged at a current of 1 mA / cm 2 until the voltage between both electrodes reached 2V. The lithium secondary battery was disassembled in the discharged state, and the elongation percentage of the negative electrode in the discharged state was calculated. Further, it was visually observed whether lithium on the surface of the positive electrode was deposited. The elongation rate in the charged state and the discharged state was calculated based on the equations (2) and (3) described above.
- Table 1 shows the calculation results of various elongation rates and the observation results of the presence or absence of lithium precipitation.
- Examples 1, 2 and Comparative Examples 1 to 4 show the results when lithium cobaltate was used as the positive electrode active material.
- Example 3 and Comparative Example 5 show the results when using a lithium nickelate-based positive electrode active material.
- Examples 1 to 3 had substantially the same reversible charge / discharge capacity as Comparative Example 1 in which an amount of lithium corresponding to the irreversible capacity was compensated. On the other hand, the capacities of Comparative Examples 2 to 5 were small.
- the elongation rate in the charged state and the discharged state was less than ⁇ 1% when the initial elongation rate was 0%. That is, by adjusting the deposition amount of lithium and the lithium deficiency amount x of the positive electrode, it was possible to balance the elongation in the charged state and the elongation in the discharged state.
- “Change amount of elongation” in Table 1 represents a value obtained by subtracting the initial elongation from the elongation in the charged state, and a value obtained by subtracting the initial elongation from the elongation in the discharged state.
- the elongation (1.3%) in the charged state increased by 0.9% from the initial elongation (0.4%). Further, the elongation (0.1%) in the discharged state was reduced by 0.3% from the initial elongation (0.4%). That is, the dimension of the negative electrode in the discharged state was smaller than the dimension of the negative electrode when lithium was deposited.
- Example 2 the elongation rate in the charged state increased by 0.4% from the initial elongation rate, and the elongation rate in the discharged state decreased by 0.7% from the initial elongation rate.
- Example 3 the elongation in the charged state increased by 0.8% from the initial elongation, and the elongation in the discharged state decreased by 0.2% from the initial elongation.
- Comparative Example 1 the elongation in the charged state increased by 1.2% from the initial elongation, and the elongation in the discharged state decreased by 0.1% from the initial elongation.
- Comparative Example 2 the elongation in the charged state increased by 0.9% from the initial elongation, and the elongation in the discharged state decreased by 0.1% from the initial elongation.
- Comparative Example 3 the elongation in the charged state increased by 0.4% from the initial elongation, and the elongation in the discharged state decreased by 1.0% from the initial elongation.
- Comparative Example 4 the elongation in the charged state increased by 0.4% from the initial elongation, and the elongation in the discharged state decreased by 0.4% from the initial elongation.
- Comparative Example 5 the elongation in the charged state increased by 0.9% from the initial elongation, and the elongation in the discharged state decreased by 0.1% from the initial elongation.
- the lithium deficiency x in the lithium-deficient composite oxide is preferably in the range of 0.2 to 0.6. More preferably, 0.3 ⁇ x ⁇ 0.5.
- the amount of the positive electrode active material it is possible to increase or decrease the amount of the positive electrode active material while maintaining the precharge amount of the positive electrode at a constant value.
- the amount of the positive electrode active material is reduced, the positive electrode is used in a region where x is large. Therefore, the lithium secondary battery is likely to deteriorate due to the charge / discharge cycle.
- the amount of the positive electrode active material is increased, the positive electrode is used in a region where x is small. Therefore, although charge / discharge characteristics are maintained well, an extra positive electrode active material is used, which is disadvantageous in terms of charge / discharge energy density of the lithium secondary battery.
Abstract
Description
シリコン、ゲルマニウムおよびスズからなる群より選ばれる少なくとも1つの元素を含む負極活物質層を負極集電体の上に形成する工程と、
前記負極活物質層の上にリチウム金属層を形成することによって負極を準備する工程と、
一般式Li1-xMO2(0.2≦x≦0.6、Mはコバルト、ニッケルおよびマンガンからなる群より選ばれる少なくとも1つの遷移金属を含む)で表される複合酸化物を含む正極活物質層が正極集電体の上に形成された構成を有する正極を準備する工程と、
前記負極、前記正極およびセパレータを用いてリチウム二次電池を組み立てる工程と、
を含む、リチウム二次電池の製造方法を提供する。
負極集電体と、前記負極集電体の上に設けられているとともに、シリコン、ゲルマニウムおよびスズからなる群より選ばれる少なくとも1つの元素を含む負極活物質層と、を有する負極と、
正極集電体と、前記正極集電体の上に設けられているとともに、リチウム複合酸化物を含む正極活物質層と、を有する正極と、
前記負極と前記正極との間に配置されたセパレータと、を備え、
前記セパレータの厚さ方向に関して、前記負極活物質層が前記正極活物質層に対向している第1領域と、前記負極活物質層が前記正極活物質層に対向していない第2領域とが存在し、
前記第2領域において単位面積あたりの前記負極に含まれているリチウムの量をM1、単位面積あたりの前記負極の不可逆容量を補償するリチウムの量をM2、前記第1領域において単位面積あたりの前記負極に含まれているリチウムの量をm1、前記第1領域において単位面積あたりの前記正極に含まれているリチウムの量をm2、前記リチウム複合酸化物が化学量論的組成を有すると仮定した場合に前記第1領域において単位面積あたりの前記正極が含むべきリチウムの量をm3としたとき、下記の関係が成立している、リチウム二次電池を提供する。
M1>M2、かつ、(m1+m2)<(M1+m3)
まず、負極集電体1の材料として銅箔や銅合金箔等の金属箔を準備する。金属箔は、例えば50~1000mmの幅を有し、3~150μmの厚さを有するものである。金属箔は、耐熱性を有する圧延箔であることが好ましい。次に、平面視で所定形状を有する複数の凸部が表面に所定間隔で形成されるように、金属箔を加工する。これにより、負極集電体1が得られる。凸部の形状は、平面視で、例えば円形や多角形である。凸部を形成するための加工は、プレス加工のような機械加工であってもよいし、エッチングのような化学的な加工であってもよい。
正極集電体5の材料として、アルミニウム箔またはアルミニウム合金箔等の金属箔を準備する。正極集電体5の幅や厚さは負極集電体1と同じくらいである。正極集電体5の上にドクターブレード法等の公知の方法で正極合剤を例えば10~100μmの厚さで塗布して正極活物質層6を形成する。正極合剤は、正極活物質、導電材、結着材および溶媒を混合することにより得られる。導電材としては、アセチレンブラック等の導電カーボンを使用できる。結着材としては、ポリフッ化ビニリデン(PVdF)、ヘキサフルオロプロピレン(HFP)およびポリテトラフルオロエチレン(PTEF)等のフッ素樹脂を使用できる。溶媒としては、N-メチル-2-ピロリドン(NMP)等の有機溶媒を使用できる。
負極11に負極リード16、正極13に正極リード15をそれぞれ溶接する。正極リード15は、例えば、アルミニウムまたはアルミニウム合金でできている。負極リード16は、例えば、銅、銅合金、ニッケルまたはニッケル合金でできている。負極11および正極13をセパレータ4の左右に配置する。セパレータ4は、典型的には、ポリエチレン製やポリプロピレン製の微多孔膜である。
図6に示すように、本実施形態の方法で製造したリチウム二次電池100を充電すると、負極活物質層3の膨張により応力が発生し、負極集電体1が面内方向に伸びる。図7に示すように、放電すると、負極活物質層3が収縮するとともに、隣接するカラム3aの間に隙間が発生する。放電状態では、負極集電体1において応力が開放されるため、負極集電体1の伸びは最も小さい。また、放電状態では、カラム3aの傾きが充電前よりも小さくなる。
(初期伸び率)=100×(S1-S0)/S0 ・・・(1)
(充電状態での伸び率)=100×(SC-S0)/S0 ・・・(2)
(放電状態での伸び率)=100×(SD-S0)/S0 ・・・(3)
本発明の方法で製造したリチウム二次電池は、充放電を繰り返すと、従来のリチウム二次電池(図8A)と区別がつかないようにも思われる。しかし、以下の方法により、本発明の方法で製造したリチウム二次電池と、従来のリチウム二次電池とを識別できる。
(a)負極集電体の作製
負極集電体の材料として、厚さ26μmの銅合金箔を準備した。10×20μmの対角線の長さを有する平面視で菱形の凸部が30μm間隔で形成されるように、銅合金箔の表面および裏面をプレス加工した。凸部の高さは6μmに設定した。次に、電解銅めっき法により、銅合金箔の表面に厚さ約2μmの銅粗化めっき層を形成した。これにより、負極集電体を得た。銅粗化めっき層の算術平均粗さRa(JIS B 0601(1994))は約0.5μmであった。
次に、図3を参照して説明した斜め蒸着により、シリコンとシリコン酸化物とを含む負極活物質層を負極集電体の上に形成した。同様の蒸着を負極集電体の裏面に対しても行うことにより、負極集電体の両面にも負極活物質層を形成した。負極活物質層の厚さ(図4に示すカラム3aの高さ)は14μmであった。
リチウム金属層を形成する前の負極活物質層と負極集電体との積層体(基礎負極)と、リチウム金属対極とを用いて半電池を作製した。この半電池を充放電することによって、充放電容量および不可逆容量を測定した。具体的には、基礎負極の一部を15×15mmの寸法に切り出し、端部にニッケル製のリードをスポット溶接で接合した。リチウム金属対極として、基礎負極と同じ寸法のリチウム金属板の端部にニッケル製のリードを固定したもの準備した。2枚のリチウム金属対極の間にセパレータ(ポリエチレン微多孔膜、厚さ16μm)を介して基礎負極を挟んだ。基礎負極、セパレータおよびリチウム金属対極で構成された電極群を外装ケースに収納するとともに、1cm3の電解液を外装ケースに入れた。熱シールにより外装ケースを封止して半電池を得た。電解液には、エチレンカーボネート(EC)、エチルメチルカーボネート(EMC)およびジエチルカーボネート(DEC)を3:5:2の体積比で含む溶媒に、LiPF6を1mol/リットルの濃度で溶かしたものを用いた。なお、以下においても同じ組成の電解液を使用した。
本発明者らが行った予備実験によれば、負極活物質層に1μmの厚さでリチウムを蒸着すると、0.2mAh/cm2の不可逆容量を補償できる。不可逆容量が1.5mAh/cm2であったので、7.5μmの厚さでリチウムを蒸着すると、不可逆容量を完全に補償できる。7.5μmの厚さを超える量のリチウムを蒸着すると、リチウム二次電池の組み立て後において、負極から正極にリチウムを供給できる。
次に、作製した基礎負極を15×15mmの寸法に切り出し、その両面に、リチウムを蒸着した。リチウムの入射方向が負極集電体の表面に垂直となるように、基礎負極とリチウムの蒸着源との位置関係を設定した。基礎負極を保持するためのホルダに内蔵されたヒータを用いて、基礎負極の温度を300℃に保持しつつ、リチウムの蒸着を行った。このようにして、リチウムが予め吸蔵された負極活物質層を有する負極を得た。表1に示すように、リチウムの蒸着量を7~28μmの範囲で変化させることで、複数の負極を作製した。
リチウム蒸着後の負極の縦横(面内方向)の長さを測定し、基礎負極の伸び率を0%として、縦方向の伸び率と横方向の伸び率とを別々に算出し、それらの平均値を負極の「初期伸び率」として算出した。縦方向の伸び率と横方向の伸び率は、先に説明した式(1)に基づいて算出した。
平均粒径5μmのコバルト酸リチウム(LiCoO2)100重量部に、アセチレンブラックを3重量部混合した。得られた混合物に、PVdFのNMP溶液をPVdFの重量に換算して4重量部加えて混合し、ペースト状の正極合剤を得た。正極合剤を、アルミニウム箔でできた正極集電体(厚さ15μm)の片面に85μmの厚さで塗布し、乾燥後、圧延した。このようにして、化学量論的組成を持つコバルト酸リチウムを正極活物質として有する正極を得た。以下、この正極のことを「基礎正極」という。
負極と正極とを用いてリチウム二次電池を作製した。まず、負極の端部にニッケル製のリードをスポット溶接によって接合した。リチウムが欠損した正極を15×15mmの寸法に切り出し、その端部にアルミニウム製のリードを超音波溶着で接合した。2枚の正極の間にセパレータ(ポリエチレン微多孔膜、厚さ16μm)を介して負極を挟んだ。正極、セパレータおよび負極で構成された電極群を外装ケースに収納するとともに、1cm3の電解液を外装ケースに入れた。熱シールにより外装ケースを封止した。これにより、リチウム二次電池を得た。充電状態および放電状態での負極の伸び率を算出するために、同一条件で作製した負極および正極を用いて複数のリチウム二次電池を作製した。
作製したリチウム二次電池の可逆充放電容量を測定した。具体的には、1mA/cm2の電流で両極間の電圧が4.2Vになるまで充電した後、1mA/cm2の電流で両極間の電圧が2Vになるまで放電したときの容量(可逆充放電容量)を測定した。結果を表1に示す。
作製したリチウム二次電池を1mA/cm2の電流で両極間の電圧が4.2Vになるまで充電した。充電状態でリチウム二次電池を分解し、充電状態での負極の伸び率を算出した。また、負極の表面にリチウムが析出しているかどうか目視で観察した。また、充電状態のリチウム二次電池を1mA/cm2の電流で両極間の電圧が2Vになるまで放電した。放電状態でリチウム二次電池を分解し、放電状態での負極の伸び率を算出した。また、正極の表面のリチウムが析出しているかどうか目視で観察した。充電状態および放電状態での伸び率は、先に説明した式(2)(3)に基づいて算出した。
Claims (9)
- シリコン、ゲルマニウムおよびスズからなる群より選ばれる少なくとも1つの元素を含む負極活物質層を負極集電体の上に形成する工程と、
前記負極活物質層の上にリチウム金属層を形成することによって負極を準備する工程と、
一般式Li1-xMO2(0.2≦x≦0.6、Mはコバルト、ニッケルおよびマンガンからなる群より選ばれる少なくとも1つの遷移金属を含む)で表される複合酸化物を含む正極活物質層が正極集電体の上に形成された構成を有する正極を準備する工程と、
前記負極、前記正極およびセパレータを用いてリチウム二次電池を組み立てる工程と、
含む、リチウム二次電池の製造方法。 - 前記負極活物質層がシリコンを含む、請求項1に記載のリチウム二次電池の製造方法。
- 前記負極集電体の材料としての金属箔の表面に複数の凸部を形成する工程をさらに含み、
前記複数の凸部を有する前記負極集電体に対して斜め方向から蒸着すべき材料を入射させる斜め蒸着技術によって、前記負極活物質層を前記負極集電体の上に形成する、請求項1に記載のリチウム二次電池の製造方法。 - 前記負極活物質層の上にリチウム金属を蒸着することによって前記リチウム金属層を形成する、請求項1に記載のリチウム二次電池の製造方法。
- 前記負極活物質層を200℃以上400℃未満の範囲の温度に保持しつつ、前記負極活物質の上にリチウム金属を蒸着する、請求項4に記載のリチウム二次電池の製造方法。
- 前記リチウム金属層を形成する前の前記負極集電体の面内の所定方向に関する長さをS0、前記リチウム金属層を形成した時点での前記負極集電体の前記所定方向に関する長さをS1、組み立てられた当該リチウム二次電池の充電状態での前記負極集電体の前記所定方向に関する長さをSC、組み立てられた当該リチウム二次電池の放電状態での前記負極集電体の前記所定方向に関する長さをSDで表し、さらに、下記式(1)~(3)で初期伸び率、充電状態での伸び率および放電状態での伸び率を定義したとき、
前記充電状態での伸び率から前記初期伸び率を減じた値が1%以下で、かつ前記放電状態での伸び率から前記初期伸び率を減じた値が-1%以上となるように、前記リチウム金属層におけるリチウムの量を調整する、請求項1に記載のリチウム二次電池の製造方法。
(初期伸び率)=100×(S1-S0)/S0 …(1)
(充電状態での伸び率)=100×(SC-S0)/S0 …(2)
(放電状態での伸び率)=100×(SD-S0)/S0 …(3) - 前記リチウム金属層を形成する工程において、前記リチウム金属層が、前記負極活物質層の不可逆容量を補償しうるリチウムの量を超える量のリチウムを含むように、前記負極活物質層の上に前記リチウム金属層を形成する、請求項1に記載のリチウム二次電池の製造方法。
- 前記リチウム金属層を形成するべき前記負極活物質層の充電容量および放電容量を測定し、測定された充電容量から放電容量を引いた容量に基づいて、前記不可逆容量を予め算出する、請求項7に記載のリチウム二次電池の製造方法。
- 負極集電体と、前記負極集電体の上に設けられているとともに、シリコン、ゲルマニウムおよびスズからなる群より選ばれる少なくとも1つの元素を含む負極活物質層と、を有する負極と、
正極集電体と、前記正極集電体の上に設けられているとともに、リチウム複合酸化物を含む正極活物質層と、を有する正極と、
前記負極と前記正極との間に配置されたセパレータと、を備え、
前記セパレータの厚さ方向に関して、前記負極活物質層が前記正極活物質層に対向している第1領域と、前記負極活物質層が前記正極活物質層に対向していない第2領域とが存在し、
前記第2領域において単位面積あたりの前記負極に含まれているリチウムの量をM1、単位面積あたりの前記負極の不可逆容量を補償するリチウムの量をM2、前記第1領域において単位面積あたりの前記負極に含まれているリチウムの量をm1、前記第1領域において単位面積あたりの前記正極に含まれているリチウムの量をm2、前記リチウム複合酸化物が化学量論的組成を有すると仮定した場合に前記第1領域において単位面積あたりの前記正極が含むべきリチウムの量をm3としたとき、下記の関係が成立している、リチウム二次電池。
M1>M2、かつ、(m1+m2)<(M1+m3)
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