JP2014017199A - Electrode for lithium secondary battery and method for manufacturing the same, and lithium secondary battery and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for a lithium secondary battery, capable of reducing internal resistance of a battery and improving charge/discharge cycle characteristics.SOLUTION: An electrode for a lithium secondary battery includes a metal collector including a conductive layer made of metal or carbon, and an active material layer formed on a surface of the conductive layer, and the active material layer contains an active material comprising a carbon-coated lithium composite metal oxide particle. Therefore, not only interface resistance between the metal collector and the active material layer, but bulk resistance of the active material layer can be also reduced. Accordingly, internal resistance of the battery can be reduced. Further, charge/discharge cycle characteristics can be improved as compared with a case where a conductive layer is simply provided in a metal collector.

Description

  The present invention relates to an electrode for a lithium secondary battery and a manufacturing method thereof, and a lithium secondary battery and a manufacturing method thereof.

  As a non-aqueous electrolyte secondary battery, a lithium secondary battery has been put into practical use and is widely used. Furthermore, in recent years, lithium secondary batteries are attracting attention not only as small-sized batteries for portable electronic devices but also as large-capacity devices for power storage such as in-vehicle use, solar power generation systems and nighttime power storage. Yes.

  The electrode (positive electrode and negative electrode) of the secondary battery forms a coating film by applying a paste containing an active material and a binder onto a current collector such as a long metal foil on one or both sides. Is dried, and then the dried coating film is pressed and wound, and then cut into a predetermined width or a predetermined length as necessary. The manufactured electrode is laminated via a separator to form a strip-like or wound laminate, and then inserted into the battery container. Moreover, the electrically conductive material is added to the paste as needed.

  In order to use as a large-capacity device, excellent rate characteristics are required, and therefore further reduction of internal resistance and further improvement of charge / discharge cycle characteristics are required.

  In order to reduce the internal resistance of the battery, it has been proposed to form a carbon coat layer on the surface of the metal foil current collector (for example, Patent Documents 1 and 2). According to these documents, it is described that it is possible to prevent the internal resistance from being increased due to the formation of a passive film on the surface of the metal foil current collector.

Japanese Patent Laid-Open No. 2002-298753 JP 2010-212167 A

  However, according to the knowledge of the present inventors, even if a carbon coat layer is formed on the surface of the metal foil current collector, a sufficient effect for improving the charge / discharge cycle characteristics was not recognized.

  Therefore, the present inventors provide a lithium secondary battery electrode capable of reducing the internal resistance of the battery and improving the charge / discharge cycle characteristics, a method for manufacturing the same, and a lithium secondary battery using the electrode. Aimed to do.

  In order to solve the above problems, an electrode for a lithium secondary battery of the present invention has a metal current collector having a conductive layer and an active material layer formed on the surface of the conductive layer, and the active material layer is made of carbon. It contains an active material composed of coated lithium composite metal oxide particles.

  The method for producing an electrode for a lithium secondary battery according to the present invention comprises dissolving a raw material powder of a lithium composite metal oxide and a carbon source in a solvent, firing the mixture obtained by removing the solvent, and carbonizing the mixture. A lithium composite metal oxide coated with carbon with a carbon source is manufactured, and an electrode paste obtained by dispersing the carbon-coated lithium composite metal oxide, a conductive material, a binder, and a thickener in a solvent is made into a metal. It is characterized by being applied to the surface of the conductive layer of the current collector.

  The lithium secondary battery of the present invention is characterized by using the electrode for a lithium secondary battery of the present invention as a positive electrode and / or a negative electrode.

  The method for producing a lithium secondary battery of the present invention is a method for producing a lithium secondary battery in which the electrode for a lithium secondary battery of the present invention is used as a positive electrode and / or a negative electrode. And the carbon source are dissolved in a solvent, and the mixture obtained by removing the solvent is baked to produce a carbon-coated lithium composite metal oxide with the carbonized carbon source, and the carbon-coated lithium composite A positive electrode and / or a negative electrode are manufactured by applying an electrode paste in which a metal oxide, a conductive material, a binder, and a thickener are dispersed in a solvent to the surface of a conductive layer of a metal current collector. .

  ADVANTAGE OF THE INVENTION According to this invention, while being able to reduce the internal resistance of a lithium secondary battery, it becomes possible to improve charging / discharging cycling characteristics. In the present invention, unless otherwise specified, the charge / discharge cycle characteristics refer to the ratio of the battery capacity after a predetermined charge / discharge cycle to the initial battery capacity, and the higher this ratio, the lower the capacity due to repeated charge / discharge. It means less.

Hereinafter, embodiments of the present invention will be described in detail.
Embodiment 1
The electrode for a lithium secondary battery according to the present embodiment is a positive electrode, has a metal current collector having a conductive layer, and a positive electrode active material layer formed on the surface of the conductive layer, and the positive electrode active material layer is It contains a positive electrode active material composed of carbon-coated lithium composite metal oxide particles.

(Positive electrode)
A lithium composite metal oxide is used for the positive electrode active material. Specific examples include LiCoO ₂ , LiNiO ₂ , LiFeO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li ₂ MnO ₃ , LiCoPO ₄ , LiNiPO ₄ , LiMnPO ₄ , LiFePO ₄ (lithium iron phosphate). LiFePO ₄ is preferable. This is because the safety is high and the cost is low. Note that the lithium iron phosphate includes a compound in which the iron site and the phosphorus site are substituted with different elements. Examples of the iron site substitution element include at least one metal element selected from the group consisting of Zr, Sn, Y, and Al, and examples of the phosphorus site substitution element include Si.

  The positive electrode active material can be produced by using any combination of carbonates, hydroxides, chlorides, sulfates, acetates, oxides, oxalates, nitrates, and the like as starting materials. Among these, carbonates, hydroxides, acetates, oxides, and oxalates are preferable from the viewpoint of hardly generating a gas that can affect the synthesis during firing. More preferred are carbonates, hydroxides, acetates and oxalates, which can be synthesized.

  In addition, weak acid salts (carbonates, acetates, oxalates) or strong acid salts (nitrates, chlorides) are preferred from the viewpoint of being easy to produce a uniform solution in the air atmosphere during the liquid phase method and inexpensive. Among these, acetate or nitrate is more preferable.

  As a method for producing the positive electrode active material, methods such as a solid phase method, a sol-gel method, a melt quench method, a mechanochemical method, a coprecipitation method, a hydrothermal method, and a spray pyrolysis method can be used. For single-phase synthesis, it is important that the mixed state before firing is uniform and that the particle size is small, so the sol-gel method, coprecipitation method, hydrothermal method, spray pyrolysis, which are liquid phase methods The method is preferred. From the viewpoint of yield, a sol-gel method, a coprecipitation method, and a hydrothermal method are more preferable. The sol-gel method is more preferable.

  In the present invention, the positive electrode active material made of lithium composite metal oxide particles is coated with carbon. By coating the positive electrode active material with carbon, the electronic conductivity of the positive electrode active material can be improved, and carbon can also suppress the aggregation of the positive electrode active material particles. The coating with carbon may be the entire surface or a part thereof, but it is preferable that the entire surface is uniformly coated in order to obtain good electrode characteristics. Here, “uniform” means a state where the thickness of the coating carbon on the positive electrode active material is constant. This state can be confirmed with a transmission electron microscope. The method of coating the positive electrode active material with carbon is to add a carbon source to a solvent in which the raw material powder of the lithium composite metal oxide is dissolved, remove the solvent, and then fire the resulting mixture in an inert atmosphere or a reducing atmosphere. The method can be used. The carbon source is carbonized during firing and adheres to the surface of the positive electrode active material particles to form a carbon film. As the carbon source, alkylene oxides, saccharides, and polyethers can be used. Examples of the alkylene oxide include ethylene oxide and propylene oxide. Moreover, sucrose and fructose can be mentioned as saccharides. Examples of polyethers include polyethylene glycol and polypropylene glycol. Firing is performed at 400 to 700 ° C., preferably 400 to 600 ° C., for 1 to 24 hours. As an atmosphere during firing, an inert atmosphere (argon, nitrogen, vacuum, etc.) or a reducing atmosphere (hydrogen-containing inert gas, etc.) can be used.

The amount of carbon attached to the surface of the positive electrode active material particles is 0.5 to 10% by weight, preferably 1 to 5% by weight, based on the positive electrode active material. This is because if it is less than 0.5% by weight, the cycle characteristics are not improved, and if it is more than 10% by weight, the capacity decreases.
The amount of carbon is calculated by burning the weighed positive electrode active material particles in an oxygen atmosphere and measuring the amount of carbon-containing gas in the generated gas component. As an example of a measuring apparatus, the carbon and sulfur analyzer EMIA-320V2 by Horiba, Ltd. can be mentioned.

(Production method of positive electrode)
The positive electrode is prepared by kneading and dispersing at least a positive electrode active material, a conductive material, a binder, and a thickener using a solvent to obtain a paste, applying the paste to one or both sides of a current collector, and drying the paste. To do. Examples of the organic solvent include N-methyl-2-pyrrolidone, toluene, cyclohexane, dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, methyl acrylate, diethyltriamine, N, N-dimethylaminopropylamine, ethylene oxide, Tetrahydrofuran or the like can be used. When a water-soluble binder is used, water can be used as a solvent. When water is used as the solvent, the pH of the paste is 5 or higher, preferably 8 or higher. This is because when the pH is less than 5, the battery using the obtained positive electrode does not improve the cycle characteristics.

  As the conductive material, acetylene black, carbon black, natural graphite, artificial graphite or the like can be used alone or in combination.

  Moreover, the ratio of the positive electrode active material and the conductive material contained in the coating film is 2 to 20 parts by weight, preferably 4 to 10 parts by weight of the conductive material with respect to 100 parts by weight of the positive electrode active material. If the conductive material is less than 2 parts by weight, the contact resistance between the positive electrode active material and the current collector is increased, which is not preferable. Further, even if the amount of the conductive material is more than 20 parts by weight, the effect of reducing contact resistance commensurate with the amount added cannot be obtained, and the cost increases.

  The binder includes polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, ethylene propylene diene polymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluorine rubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, Examples of the styrene-butadiene rubber or the water-based binder emulsion include a fluorine-modified styrene-butadiene rubber, an olefin copolymer, and an acid-modified olefin copolymer. When the aqueous binder emulsion is used, a thickener such as carboxymethyl cellulose (hereinafter abbreviated as CMC), polyvinyl alcohol, polyvinyl pyrrolidone and the like can be used as necessary.

  As the metal current collector, a foamed (porous) metal having continuous pores, a metal formed in a honeycomb shape, a sintered metal, an expanded metal, a metal foil, or the like can be used. Moreover, as a material, aluminum, nickel, chromium, and alloys thereof can be used, but aluminum is preferable.

  In the present invention, a metal current collector having a conductive layer is used, and a metal layer or a carbon coating layer can be used for the conductive layer. Platinum, gold, or the like can be used for the metal layer, and these metals can be attached to the metal current collector by a plating method. Moreover, when using a carbon film layer, a carbon film layer can be formed by the method described in Patent Document 1 or 2. For example, it can be produced by applying a carbon paste containing fine carbon to the surface of a metal current collector and drying. In a metal current collector having a metal layer or a carbon film layer, it is possible to prevent an internal resistance from increasing due to the formation of a passive film on the surface of the metal current collector. Further, when a metal current collector having a smooth surface such as a metal foil is used, the contact area between the active material and the current collector is increased, and the adhesive force is increased. As a result, the stripping of the active material from the current collector is suppressed, and an effect of improving the lifetime of the battery can be obtained.

(Negative electrode)
A known material can be used as the negative electrode active material. In order to constitute a high energy density battery, it is preferable that the potential at which lithium is inserted / desorbed is close to the deposition / dissolution potential of metallic lithium. A typical example is a carbon material such as natural or artificial graphite in the form of particles (scale-like, lump-like, fibrous, whisker-like, spherical, pulverized particles, etc.).

  Examples of the artificial graphite include graphite obtained by graphitizing mesocarbon microbeads, mesophase pitch powder, isotropic pitch powder, and the like. Also, graphite particles having amorphous carbon attached to the surface can be used. Among these, natural graphite is preferable because it is inexpensive and close to the redox potential of lithium and can constitute a high energy density battery.

Further, lithium transition metal oxide, lithium transition metal nitride, transition metal oxide, silicon oxide, and the like can be used as the negative electrode active material. Among these, Li ₄ Ti ₅ O ₁₂ is preferable because it has high potential flatness and a small volume change due to charge and discharge.

(Method for producing negative electrode)
The negative electrode can be produced by a known method. For example, a negative electrode active material, a binder, and a conductive material are mixed, the obtained mixed powder is formed into a sheet shape, and the obtained molded body is pressure-bonded to a current collector, for example, a mesh current collector made of stainless steel or copper. Can be produced. Further, as in the case of the positive electrode, it can be prepared using water as a solvent. In that case, at least the negative electrode active material, the conductive material, and the binder are kneaded and dispersed using water to obtain a paste. It can be produced by applying to a current collector. A conductive material may be added as necessary.

(Nonaqueous electrolyte)
As the non-aqueous electrolyte, for example, an organic electrolyte, a gel electrolyte, a polymer solid electrolyte, an inorganic solid electrolyte, a molten salt, or the like can be used.

  Examples of the organic solvent constituting the organic electrolyte include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and butylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate, and dipropyl carbonate. Chain carbonates such as γ-butyrolactone (GBL), lactones such as γ-valerolactone, furans such as tetrahydrofuran and 2-methyltetrahydrofuran, diethyl ether, 1,2-dimethoxyethane, 1,2-diethoxy Examples include ethers such as ethane, ethoxymethoxyethane, dioxane, dimethyl sulfoxide, sulfolane, methyl sulfolane, acetonitrile, methyl formate, methyl acetate, and the like. Can.

  Moreover, since cyclic carbonates such as PC, EC and butylene carbonate are high-boiling solvents, they are suitable as solvents to be mixed with GBL.

Examples of the electrolyte salt constituting the organic electrolyte include lithium borofluoride (LiBF ₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium trifluoroacetate (LiCF ₃ COO) ), Lithium salts such as lithium bis (trifluoromethanesulfone) imide (LiN (CF ₃ SO ₂ ) ₂ ), and a mixture of one or more of these can be used. The salt concentration of the electrolytic solution is preferably 0.5 to 3 mol / L.

(Separator)
As a separator, well-known materials, such as a porous material and a nonwoven fabric, can be used. As a material for the separator, a material that does not dissolve or swell in the organic solvent in the electrolytic solution is preferable. Specific examples include polyester polymers, polyolefin polymers (for example, polyethylene and polypropylene), ether polymers, and glass fibers.

(Other parts)
Various other known materials can be used for other members such as a battery container, and there is no particular limitation.

(Method for manufacturing secondary battery)
The secondary battery includes, for example, a laminate including a positive electrode, a negative electrode, and a separator sandwiched between them. The laminate may have, for example, a strip-like planar shape. In the case of producing a cylindrical or flat battery, the laminate may be wound to form a wound body.

  One or more of the laminates are inserted into the battery container. Usually, the positive electrode and the negative electrode are connected to the external conductive terminal of the battery. Thereafter, the battery container is sealed to block the positive electrode, the negative electrode, and the separator from the outside air.

  In the case of a cylindrical battery, the sealing method is such that a lid having a resin packing is fitted into the opening of the battery container and the battery container and the lid are caulked, or the opening and lid of the battery container are laser welded or the like. A welding method is common. In the case of a square battery, a method of attaching a lid called a metallic sealing plate to the opening and performing welding can be used. In addition to these methods, a method of sealing with a binder and a method of fixing with a bolt via a gasket can also be used. Furthermore, a method of sealing with a laminate film in which a thermoplastic resin is attached to a metal foil can also be used. An opening for electrolyte injection may be provided at the time of sealing. When using an organic electrolyte, the organic electrolyte is injected from the opening, and then the opening is sealed. Gas generated by energization before sealing may be removed. When a large battery having a capacity per battery of 20 Ah or more and 500 Ah or less is manufactured, a plurality of openings for injecting electrolyte may be provided. For example, one opening is for injecting electrolyte. The other is preferably used for removing gas. When the capacity is less than 20 Ah, it is not preferable because it is difficult to reduce the cost as a storage battery system, and when the capacity exceeds 500 Ah, even if lithium iron phosphate is used as the positive electrode active material, safety is lowered, which is not preferable.

  Also, after sealing the battery container, the manufactured battery is charged at 50% or more, preferably 70% or more with respect to full charge, preferably at 40 to 60 ° C., preferably 45 to 55 ° C. for at least 24 hours, preferably Is preferably maintained for at least 72 hours (hereinafter referred to as aging treatment). By performing the aging process, the cycle characteristics can be further improved.

  According to the present embodiment, since the positive electrode active material layer containing the positive electrode active material composed of the lithium composite metal oxide particles coated with carbon is provided on the surface of the conductive layer of the metal current collector, the metal current collector and Not only the interface resistance of the active material layer but also the bulk resistance of the active material layer can be reduced. As a result, the internal resistance of the battery can be reduced. Furthermore, the charge / discharge cycle characteristics can be improved as compared with the case where a conductive layer is simply provided on the metal current collector.

In addition, this embodiment can prevent peeling of the positive electrode active material layer from the metal current collector and increase the internal resistance of the battery even when the thickness of the positive electrode active material layer is increased compared to the conventional case. It has the outstanding effect that an increase can be suppressed. Denoting the thickness of the positive electrode active material layer with a coating amount, the coating amount per unit area of one surface of the metal current collector is 15 mg / cm ² or more, more preferably 15~38mg / cm ^2. In the case of double-sided coating, the coating amount is twice that of the single-side coating, the surfaces of unit area per metal current collector, 30 mg / cm ² or more, more preferably 30~76mg / cm ^2. According to the present embodiment, if the amount of the active material is increased by increasing the thickness of the positive electrode active material layer, a laminate can be manufactured with a smaller number of stacks or turns, and the number of current collectors and separators Therefore, the manufacturing cost can be reduced.

Embodiment 2
The electrode for a lithium secondary battery according to the present embodiment is a negative electrode, and has a metal current collector having a conductive layer and a negative electrode active material layer formed on the surface of the conductive layer, and the negative electrode active material layer is It contains a negative electrode active material composed of carbon-coated lithium composite metal oxide particles.

(Negative electrode)
A lithium composite metal oxide is used for the negative electrode active material. Specific examples include lower oxides of silicon Li _x SiO _y (x ≧ 0, 2>y> 0) and lower oxides of tin Li _x SnO _y and Li ₄ Ti ₅ O ₁₂ . Li ₄ Ti ₅ O ₁₂ is preferable. This is because Li ₄ Ti ₅ O ₁₂ has high potential flatness and a small volume change due to charge and discharge.

(Method for producing negative electrode)
The negative electrode can be produced in the same manner as in Embodiment 1 using the above negative electrode active material. That is, a negative electrode active material, a binder, and a conductive material are mixed, the obtained mixed powder is formed into a sheet shape, and the obtained molded body is pressure-bonded to a current collector, for example, a mesh current collector made of stainless steel or copper. Can be produced. Further, as in the case of the positive electrode, it can be prepared using water as a solvent. In that case, at least the negative electrode active material, the conductive material, and the binder are kneaded and dispersed using water to obtain a paste. It can be produced by applying to a current collector. A conductive material may be added as necessary.

(Positive electrode)
A lithium composite metal oxide can be used for the positive electrode active material. Specific examples include LiCoO ₂ , LiNiO ₂ , LiFeO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li ₂ MnO ₃ , LiCoPO ₄ , LiNiPO ₄ , LiMnPO ₄ , and LiFePO ₄ . LiFePO ₄ (lithium iron phosphate) is preferable. This is because the safety is high and the cost is low. Note that the lithium iron phosphate includes a compound in which the iron site and the phosphorus site are substituted with different elements. Examples of the iron site substitution element include at least one metal element selected from the group consisting of Zr, Sn, Y, and Al, and examples of the phosphorus site substitution element include Si.

(Production method of positive electrode)
The positive electrode can be manufactured in the same manner as in the first embodiment. That is, at least a positive electrode active material, a conductive material, a binder, and a thickener are kneaded and dispersed using a solvent to obtain a paste, and the paste is applied to one or both sides of a current collector and dried. .

(Method for manufacturing secondary battery)
The secondary battery can be manufactured in the same manner as in the first embodiment.

  According to this embodiment, since the negative electrode active material layer containing the negative electrode active material made of carbon-coated lithium composite metal oxide particles is provided on the surface of the conductive layer of the metal current collector, the metal current collector and Not only the interface resistance of the active material layer but also the bulk resistance of the active material layer can be reduced. As a result, the internal resistance of the battery can be reduced. Furthermore, the charge / discharge cycle characteristics can be improved as compared with the case where a conductive layer is simply provided on the metal current collector. In addition, if the thickness of the negative electrode active material layer is increased to increase the amount of active material, a laminate can be produced with a smaller number of laminations or windings, and the number of current collectors and separators can be reduced. Cost can also be reduced.

Embodiment 3
The electrode for a lithium secondary battery according to the present embodiment is a positive electrode and a negative electrode, and the positive electrode and the negative electrode have a metal current collector having a conductive layer, and an active material layer formed on the surface of the conductive layer, The active material layer contains an active material made of carbon-coated lithium composite metal oxide particles.

  In this embodiment, a secondary battery is manufactured in the same manner as in Embodiment 1 except that the positive electrode described in Embodiment 1 is used as the positive electrode and the negative electrode described in Embodiment 2 is used as the negative electrode. can do.

  According to the present embodiment, the internal resistance of the battery can be further reduced, and the charge / discharge cycle characteristics can be further improved as compared with the case where a conductive layer is simply provided on the metal current collector. It becomes possible. In addition, if the amount of the active material is increased by increasing the thickness of the positive electrode active material layer and the negative electrode active material layer, a laminate can be manufactured with a smaller number of layers or windings, and the number of current collectors and separators can be reduced. Since it can be reduced, the manufacturing cost can also be reduced.

  EXAMPLES Hereinafter, although this invention is demonstrated in more detail using an Example, this invention is not limited to a following example.

Example 1
(Synthesis of positive electrode active material)
In this example, LiFePO ₄ was used as the positive electrode active material.
In a sample bottle, weigh out ethanol as a solvent, 15 mmol of Fe (NO ₃ ) ₃ .9H ₂ O as an iron source, 15 mmol of LiCH ₃ COO as a lithium source, and 15 mmol of H ₃ PO ₄ (85%) as a phosphorus source. The solution was stirred until it was completely dissolved and uniform. The molar ratio of the sample was Li: Fe: P = 1: 1: 1. Thereafter, when 3 ml of propylene oxide as a carbon source was added to the solution, the solution lost fluidity and gelled.

Next, the solvent was evaporated by leaving it in an air atmosphere at a temperature of 60 ° C. for 24 hours, and then baked at a temperature of 600 ° C. for 12 hours in a nitrogen atmosphere to obtain LiFePO ₄ .

  A part of the obtained positive electrode active material particles was weighed, burned in an oxygen atmosphere, and the amount of carbon was calculated by measuring the amount of carbon-containing gas in the generated gas component. A carbon / sulfur analyzer EMIA-320V2 manufactured by HORIBA, Ltd. was used as the measuring device. As a result, it was confirmed that 3% by weight of carbon adhered to the surface of the positive electrode active material.

(Preparation of positive electrode)
A predetermined amount of a positive electrode active material powder, a conductive material powder (acetylene black), a binder, a thickener (CMC) aqueous solution, and ion-exchanged water are used at room temperature using filmics 80-50 (manufactured by Primex). The mixture was stirred and mixed to obtain an electrode paste. Here, LiFePO ₄ : acetylene black: binder: CMC = 100: 5: 5: 1 (weight ratio). The pH of the electrode paste was measured and found to be 9.

This electrode paste was applied to both sides using a die coater on a carbon-coated rolled aluminum foil (thickness: 20 μm) (manufactured by Showa Denko Packaging Co., Ltd.), dried in air at 100 ° C. for 30 minutes, and pressed. Thus, a positive electrode plate (coating surface size: 30 cm (vertical) × 15 cm (horizontal)) was obtained. The coating amount per unit area on one side of the metal current collector was 22 mg / cm ² .
Table 1 shows the electrode manufacturing conditions.

(Preparation of negative electrode)
A negative electrode active material powder (natural graphite), a binder, a CMC aqueous solution, and ion-exchanged water were stirred and kneaded at room temperature using a biaxial planetary mixer (manufactured by Primex) to obtain an electrode paste. Here, natural graphite: binder: CMC = 98: 1: 1 (weight ratio).

  This electrode paste was applied to both sides using a die coater on a rolled copper foil (thickness: 10 μm), dried in air at 100 ° C. for 30 minutes, and pressed to form a negative electrode plate (coating surface size: 30.4 cm). (Vertical) × 15.4 cm (Horizontal)) was obtained.

(Production of battery)
The produced positive electrode and negative electrode were dried under reduced pressure at 130 ° C. for 24 hours, and placed in a glove box under an Ar atmosphere. The following battery assembly was all performed in the glove box at room temperature.
A polyethylene (PE) microporous film (30.4 cm (vertical) × 15.4 cm (horizontal) × 25 μm (thickness), porosity: 55%) is placed on the negative electrode, and the positive electrode is stacked thereon, Moreover, the operation | work which piles up PE microporous film was repeated, and the laminated body which pinched | interposed 10 PE microporous films between each electrode of 6 negative electrodes and 5 positive electrodes was produced. Ni leads were ultrasonically welded to six negative electrodes, Al leads were ultrasonically welded from five positive electrodes, inserted into an Al laminated bag, and three sides were heat-sealed. An electrolyte solution in which LiPF ₆ was dissolved in a solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 1: 2 to 1 mol / l was poured into the cell, and each lead was taken out. Meanwhile, the last side of the Al laminate bag was heat-sealed to obtain a battery.

(Evaluation of battery cycle characteristics)
The battery is degassed after 30% charge, and additionally 50% charged. The battery is charged at a total of 80% and held at 45 ° C for 1 week, and then charged and discharged twice at 0.1C. The initial battery capacity was determined. Thereafter, a repeated charge / discharge cycle test of 0.1C charge / discharge once and 1C charge / discharge 199 times was performed. The capacity retention rate was determined from the ratio of the battery capacity after 200 cycles to the initial cycle battery capacity. Table 3 shows the measurement results.

Example 2
A battery was produced in the same manner as in Example 1 except that the amount of propylene oxide serving as the carbon source was increased to 7 ml during the production of the positive electrode, and the cycle characteristics were evaluated. The carbon coating amount for LiFePO ₄ was 7% by weight. The coating amount per unit area on one side of the positive electrode metal current collector was 22 mg / cm ² . The electrode fabrication conditions are shown in Table 1, and the battery evaluation results are shown in Table 3.

Example 3
A battery was produced in the same manner as in Example 1 except that PVDF was used as the binder, N-methyl-2-pyrrolidone was used as the solvent, and CMC was not used. The carbon coating amount for LiFePO ₄ was 3% by weight. The coating amount per unit area on one side of the positive electrode metal current collector was 22 mg / cm ² . The electrode fabrication conditions are shown in Table 1, and the battery evaluation results are shown in Table 3.

Example 4
(Synthesis of positive electrode active material)
In this example, LiCoO ₂ was used as the positive electrode active material.
In an agate mortar, 15 mmol of Li ₂ CO ₃ as a lithium source and 15 mmol of Co (OH) ₂ as a cobalt source were weighed and ground until uniform. The molar ratio of the sample was Li: Co = 1: 1. Furthermore, 10% by weight of sucrose as a carbon source was added to the weight of LiCoO ₂ predicted to be produced, and the raw materials were mixed and pulverized until uniform. Next, the obtained powder was baked in a nitrogen atmosphere at a temperature of 700 ° C. for 12 hours to obtain LiCoO ₂ .

The carbon coating amount for LiCoO ₂ was 1.3% by weight.

In the same manner as in Example 1, a positive electrode, a negative electrode, and a battery were produced, and cycle characteristics were evaluated. The coating amount per unit area on one side of the positive electrode metal current collector was 22 mg / cm ² . The electrode fabrication conditions are shown in Table 1, and the battery evaluation results are shown in Table 3.

Example 5
(Synthesis of positive electrode active material)
In this example, LiMn ₂ O ₄ was used as the positive electrode active material.
In an agate mortar, 5 mmol of Li ₂ CO ₃ as a lithium source and 20 mmol of MnCO ₃ as a manganese source were weighed and ground until uniform. The molar ratio of the sample was Li: Mn = 1: 2. Furthermore, 10% by weight of sucrose was added as a carbon source to the weight of LiMn ₂ O ₄ predicted to be produced, and the raw materials were mixed and pulverized until uniform. Next, the obtained powder was baked in an air atmosphere at a temperature of 700 ° C. for 12 hours to obtain LiMn ₂ O ₄ .

The carbon coating amount with respect to LiMn ₂ O ₄ was 1.5% by weight.

A battery was produced in the same manner as in Example 1, and the cycle characteristics were evaluated. The coating amount per unit area on one side of the positive electrode metal current collector was 22 mg / cm ² . The electrode fabrication conditions are shown in Table 1, and the battery evaluation results are shown in Table 3.

Example 6
A battery was produced in the same manner as in Example 1 except that acetic acid was added to the electrode paste to adjust the pH to 6 when producing the positive electrode, and the cycle characteristics were evaluated. The coating amount per unit area on one side of the positive electrode metal current collector was 22 mg / cm ² . The electrode fabrication conditions are shown in Table 1, and the battery evaluation results are shown in Table 3.

Example 7
(Synthesis of negative electrode active material)
In this example, Li ₄ Ti ₅ O ₁₂ was used as the negative electrode active material.
In an agate mortar, 15 mmol of CH ₃ COOLi as a lithium source and 18.75 mmol of TiO ₂ (anatase) as a titanium source were weighed and ground until uniform. The molar ratio of the sample was Li: Ti = 4: 5. Furthermore, 10% by weight of sucrose as a carbon source was added to the weight of Li ₄ Ti ₅ O ₁₂ predicted to be produced, and the raw materials were mixed and pulverized until uniform. Subsequently, the obtained powder was baked at a temperature of 800 ° C. for 12 hours in a nitrogen atmosphere to obtain Li ₄ Ti ₅ O ₁₂ .

The carbon coating amount with respect to Li ₄ Ti ₅ O ₁₂ was 1.5% by weight.

(Preparation of negative electrode)
A negative electrode active material powder, a binder, a CMC aqueous solution, and ion-exchanged water were stirred and kneaded at room temperature using a biaxial planetary mixer (manufactured by Primex) to obtain an electrode paste. Here, Li ₄ Ti ₅ O ₁₂ : acetylene black: SBR: CMC = 100: 5: 5: 1 (weight ratio). When the pH of the electrode paste was measured, the pH was 10.

This electrode paste was applied to both sides using a die coater on a carbon-coated rolled copper foil (thickness: 10 μm) (manufactured by Showa Denko Packaging Co., Ltd.), dried in air at 100 ° C. for 30 minutes, and pressed. As a result, a negative electrode plate (coating surface size: 30.4 cm (vertical) × 15.4 cm (horizontal)) was obtained. The coating amount per unit area of one surface of the negative electrode metal current collector was 22 mg / cm ² .

  Using the positive electrode of Example 1, a battery was produced in the same manner as in Example 1, and the cycle characteristics were evaluated. The electrode fabrication conditions are shown in Table 2, and the battery evaluation results are shown in Table 3.

Comparative Example 1
A battery was produced in the same manner as in Example 1 except that no carbon source was added during the synthesis of the positive electrode active material and the firing atmosphere was changed to N ₂ + H ₂ (3%) gas, and the cycle characteristics were evaluated. . The coating amount per unit area on one side of the positive electrode metal current collector was 22 mg / cm ² . The electrode fabrication conditions are shown in Table 1, and the battery evaluation results are shown in Table 3.

Comparative Example 2
A battery was produced in the same manner as in Example 4 except that no carbon source was added during the synthesis of the positive electrode active material, and the cycle characteristics were evaluated. The coating amount per unit area on one side of the positive electrode metal current collector was 22 mg / cm ² . The electrode fabrication conditions are shown in Table 1, and the battery evaluation results are shown in Table 3.

Comparative Example 3
A battery was produced in the same manner as in Example 4 except that no carbon source was added and aging was not performed in the synthesis of the positive electrode active material, and the cycle characteristics were evaluated. The coating amount per unit area on one side of the positive electrode metal current collector was 22 mg / cm ² . The electrode fabrication conditions are shown in Table 1, and the battery evaluation results are shown in Table 3.

Comparative Example 4
A battery was prepared in the same manner as in Example 5 except that no carbon source was added during the synthesis of the positive electrode active material, and the cycle characteristics were evaluated. The coating amount per unit area on one side of the positive electrode metal current collector was 22 mg / cm ² . The electrode fabrication conditions are shown in Table 1, and the battery evaluation results are shown in Table 3.

Comparative Example 5
A battery was prepared in the same manner as in Example 1 except that a rolled aluminum foil not coated with carbon was used for the positive electrode current collector, and the cycle characteristics were evaluated. The coating amount per unit area on one side of the positive electrode metal current collector was 22 mg / cm ² . The electrode fabrication conditions are shown in Table 1, and the battery evaluation results are shown in Table 3.

Comparative Example 6
A battery was produced in the same manner as in Example 7 except that no carbon source was added in the synthesis of the positive electrode active material and the negative electrode active material, and the cycle characteristics were evaluated. The coating amount per unit area on one side of the positive electrode metal current collector was 22 mg / cm ² , and the coating amount per unit area on one side of the negative electrode metal current collector was 22 mg / cm ² . The electrode fabrication conditions are shown in Table 2, and the battery evaluation results are shown in Table 3.

(result)
Examples 1 to 3 and 6 show examples in which the present invention is applied to the positive electrode and LiFePO ₄ is used as the positive electrode active material. Comparison with Comparative Examples 1 and 5 shows that the cycle characteristics were improved by using both the carbon-coated aluminum foil and the carbon-coated active material.

In Example 4, the present invention is applied to the positive electrode, and LiCoO ₂ is used as the positive electrode active material. Comparison with Comparative Examples 2 and 3 shows that the cycle characteristics were improved by using both the carbon-coated aluminum foil and the carbon-coated active material.

In Example 5, the present invention is applied to the positive electrode, and LiMn ₂ O ₄ is used as the positive electrode active material. Comparison with Comparative Example 4 shows that the cycle characteristics were improved by using both the carbon-coated aluminum foil and the carbon-coated active material.

Example 7 shows an example in which the present invention is applied to the positive electrode and the negative electrode, LiFePO ₄ is used as the positive electrode active material, and Li ₄ Ti ₅ O ₁₂ is used as the negative electrode active material. Comparison with Comparative Example 6 shows that the cycle characteristics were improved by using both the carbon-coated copper foil and the carbon-coated active material.

Claims (8)

  A lithium collector containing a metal current collector having a conductive layer and an active material layer made of lithium composite metal oxide particles having an active material layer formed on the surface of the conductive layer, the active material layer being carbon-coated. Secondary battery electrode.   The electrode for a lithium secondary battery according to claim 1, wherein the conductive layer is a carbon coating layer.   2. The electrode for a lithium secondary battery according to claim 1, wherein a carbon ratio of the carbon-coated lithium composite metal oxide particles is 0.5 to 10 wt% with respect to a mass of the lithium composite metal oxide particles. A method for producing an electrode for a lithium secondary battery according to claim 1,
A lithium composite metal oxide raw material powder and a carbon source are dissolved in a solvent, and the mixture obtained by removing the solvent is baked to produce a carbon composite lithium composite metal oxide coated with a carbonized carbon source. ,
An electrode for a lithium secondary battery, wherein an electrode paste in which the carbon-coated lithium composite metal oxide, a conductive material, a binder, and a thickener are dispersed in a solvent is applied to the surface of the conductive layer of the metal current collector. Manufacturing method.   The method for producing an electrode for a lithium secondary battery according to claim 4, wherein the solvent is water and the pH of the electrode paste is 5 or more.   The lithium secondary battery which uses the electrode for lithium secondary batteries of Claim 1 for a positive electrode and / or a negative electrode. A method for producing a lithium secondary battery using the electrode for a lithium secondary battery according to claim 1 as a positive electrode and / or a negative electrode,
A lithium composite metal oxide raw material powder and a carbon source are dissolved in a solvent, and the mixture obtained by removing the solvent is baked to produce a carbon composite lithium composite metal oxide coated with a carbonized carbon source. ,
An electrode paste in which the carbon-coated lithium composite metal oxide, a conductive material, a binder, and a thickener are dispersed in a solvent is applied to the surface of the conductive layer of the metal current collector to form a positive electrode and / or a negative electrode. A method for producing a lithium secondary battery to be produced.   The positive electrode, the negative electrode and the electrolyte are accommodated in a battery container, and after the battery container is sealed, the battery container is kept at a temperature of 40 to 60 ° C. for at least 24 hours in a state of being charged at 50% or more with respect to full charge. A method for producing a lithium secondary battery.