WO2014112329A1 - Positive electrode for lithium ion secondary batteries and lithium ion secondary battery - Google Patents

Positive electrode for lithium ion secondary batteries and lithium ion secondary battery Download PDF

Info

Publication number
WO2014112329A1
WO2014112329A1 PCT/JP2014/000035 JP2014000035W WO2014112329A1 WO 2014112329 A1 WO2014112329 A1 WO 2014112329A1 JP 2014000035 W JP2014000035 W JP 2014000035W WO 2014112329 A1 WO2014112329 A1 WO 2014112329A1
Authority
WO
WIPO (PCT)
Prior art keywords
positive electrode
lithium ion
ion secondary
active material
secondary battery
Prior art date
Application number
PCT/JP2014/000035
Other languages
French (fr)
Japanese (ja)
Inventor
達哉 江口
仁 愛清
岡本　亮太
Original Assignee
株式会社豊田自動織機
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 株式会社豊田自動織機 filed Critical 株式会社豊田自動織機
Publication of WO2014112329A1 publication Critical patent/WO2014112329A1/en

Links

Images

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery.
  • Patent Document 1 Japanese Patent Laid-Open No. 2008-53207 describes a technique for forming a coating layer containing filler particles made of inorganic particles containing magnesia and a binder on a positive electrode active material layer. Yes. Patent Document 1 describes that when magnesia is contained in the coating layer, water and magnesia react to become alkaline and hydrofluoric acid is generated, so that it can be neutralized and the elution of cobalt from the positive electrode active material can be suppressed. ing. Patent Document 1 describes that, by having this coating layer, the lithium ion secondary battery is excellent in cycle characteristics and storage characteristics at high potential and high temperature. However, in the technique described in Patent Document 1, the thickness of the coating layer is 1 ⁇ m or more and 4 ⁇ m or less, and if the thickness of the coating layer is less than 1 ⁇ m, a sufficient effect cannot be obtained.
  • the thicker the coating layer the higher the internal resistance of the battery and the lower the charge / discharge capacity of the battery. Further, the thickness of the coating layer is preferably thinner in order to maintain the energy density of the battery.
  • a lithium ion secondary battery having a positive electrode on which a thin coating layer is arranged that improves cycle characteristics at a high potential and does not reduce charge / discharge capacity is desired.
  • the inventors of the present invention have made various studies on the material of the coating layer to be a lithium ion secondary battery having excellent cycle characteristics and high charge / discharge capacity at a high potential.
  • the present invention has been made in view of such circumstances, and provides a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery having excellent cycle characteristics and high charge / discharge capacity at a high potential. Objective.
  • the secondary battery can exhibit excellent cycle characteristics and high charge / discharge capacity at a high potential.
  • the positive electrode for a lithium ion secondary battery of the present invention includes a current collector, a positive electrode active material layer including a positive electrode active material and a binder formed on the surface of the current collector, and a surface of the positive electrode active material layer. And a coating layer having a specific resistance greater than 1.0 ⁇ 10 ⁇ 3 ⁇ cm and less than or equal to 1.0 ⁇ 10 3 ⁇ cm.
  • the covering layer preferably covers 50% or more of the surface of the positive electrode active material layer.
  • the specific resistance of the coating layer is preferably 1 ⁇ cm or less.
  • the coating layer is preferably made of at least one selected from antimony oxide, titanium oxide, tin oxide, zinc oxide, nickel oxide and indium oxide.
  • the thickness of the coating layer is preferably 10 nm or more and less than 1 ⁇ m.
  • the coating layer is made of an aggregate of film-like particles, and the average particle diameter of the particles is preferably 1/10 or less of the average particle diameter of the positive electrode active material.
  • the lithium ion secondary battery of the present invention is characterized by having the above-described positive electrode for a lithium ion secondary battery, a negative electrode, and a non-aqueous electrolyte.
  • the positive electrode for a lithium ion secondary battery of the present invention is a coating formed on at least a part of the surface of the positive electrode active material layer and having a specific resistance greater than 1.0 ⁇ 10 ⁇ 3 ⁇ cm and 1.0 ⁇ 10 3 ⁇ cm or less. Having a layer. That is, a coating layer having a certain degree of electrical conductivity is formed on the surface of the positive electrode active material layer. When an electrically conductive layer is formed on the surface of the positive electrode active material layer, electricity is conducted in the electrically conductive layer, and unevenness in the reaction occurring on the surface of the positive electrode active material layer is suppressed.
  • the specific resistance in the above range of the coating layer is a so-called specific resistance of the semiconductor region.
  • the specific resistance of the coating layer is 1.0 ⁇ 10 ⁇ 3 ⁇ cm or less, electricity flows too much in the coating layer. If electricity flows too much in the coating layer, the substance constituting the coating layer may react with another substance to become another substance. If it becomes another substance, the specific resistance of the coating layer may be larger than the above range. Therefore, the effect of suppressing reaction unevenness on the surface of the positive electrode active material layer by the coating layer cannot be obtained.
  • FIG. 3 is a schematic diagram showing the surface of each negative electrode after a cycle test of the laminated lithium ion secondary battery of Example 1 and Comparative Example 1.
  • 6 is a graph showing cycle test results of laminated lithium ion secondary batteries of Example 2 and Comparative Example 1.
  • a positive electrode for a lithium ion secondary battery includes a current collector, a positive electrode active material layer including a positive electrode active material and a binder formed on the surface of the current collector, and at least a surface of the positive electrode active material layer. And a coating layer having a specific resistance greater than 1.0 ⁇ 10 ⁇ 3 ⁇ cm and not greater than 1.0 ⁇ 10 3 ⁇ cm.
  • a current collector refers to a chemically inert electronic high conductor that keeps a current flowing through an electrode during discharge or charging of a lithium ion secondary battery.
  • the current collector material include metal materials such as stainless steel, titanium, nickel, aluminum, and copper, or conductive resins.
  • the shape of the current collector can take the form of a foil, sheet, film or the like. Therefore, metal foils, such as copper foil, nickel foil, aluminum foil, stainless steel foil, can be used suitably as a collector.
  • the current collector preferably has a thickness of 10 ⁇ m to 100 ⁇ m.
  • the positive electrode active material layer is formed on the surface of the current collector and includes a positive electrode active material and a binder.
  • the positive electrode active material layer may further contain a conductive additive.
  • the positive electrode is prepared by preparing a composition for forming a positive electrode active material layer containing a positive electrode active material and a binder, and if necessary, a conductive additive, and further adding a suitable solvent to the composition to make a paste, After applying to the surface of the current collector, it can be dried and compressed to increase the electrode density as necessary.
  • composition for forming a positive electrode active material layer As a method for applying the composition for forming a positive electrode active material layer, conventionally known methods such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, and a curtain coating method can be used.
  • NMP N-methyl-2-pyrrolidone
  • MIBK methyl isobutyl ketone
  • Examples of the positive electrode active material include lithium-containing compounds or other metal compounds.
  • the positive electrode active material is preferably an olivine type lithium phosphate complex oxide. Since an olivine-based material generally has low conductivity, a positive electrode active material made of an olivine-based material is referred to as a high-resistance positive electrode active material. When such a high-resistance positive electrode active material is used, the effect of the coating layer of the present application becomes remarkable.
  • the olivine type lithium phosphate complex oxide include LiFePO 4 , LiMnPO 4 , LiCoPO 4 , and LiNiPO 4 .
  • the lithium cobalt-containing composite metal oxide preferably has a layered structure.
  • lithium-containing oxide examples include LiCo 1/3 Ni 1/3 Mn 1/3 O 2 , LiNi 0.6 Co 0.2 Mn 0.2 O 2 , LiNi 0.5 Co 0.2 Mn 0. 3 O 2, LiCoO 2, LiNi 0.8 Co 0.2 O 2, LiCoMnO 2 and the like.
  • Lithium-containing oxides are preferably LiCo 1/3 Ni 1/3 Mn 1/3 O 2 and LiNi 0.5 Co 0.2 Mn 0.3 O 2 from the viewpoint of thermal stability.
  • the positive electrode active material is preferably in the form of a powder having an average particle diameter of 1 ⁇ m to 20 ⁇ m.
  • the average particle size of the positive electrode active material is smaller than 1 ⁇ m, the specific surface area of the positive electrode active material is increased, and the reaction area between the positive electrode active material and the electrolytic solution is increased.
  • the average particle diameter of the positive electrode active material is larger than 20 ⁇ m, the resistance of the lithium ion secondary battery increases, and the output characteristics of the lithium ion secondary battery decrease.
  • the average particle size of the positive electrode active material can be measured by a particle size distribution measurement method.
  • the binder serves to bind the positive electrode active material and the conductive additive to the current collector.
  • binders fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene, thermoplastic resins such as polypropylene, polyethylene and polyvinyl acetate resins, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins, Examples thereof include rubbers such as styrene butadiene rubber (SBR) and fluorine rubber.
  • SBR styrene butadiene rubber
  • Conductive aid is added as necessary to increase the conductivity of the electrode.
  • the conductive assistant include carbon black, graphite, acetylene black (AB), ketjen black (registered trademark) (KB), and vapor grown carbon fiber (VGCF) which are carbonaceous fine particles.
  • These conductive assistants can be added to the positive electrode alone or in combination of two or more.
  • the amount of the conductive aid used is not particularly limited, but can be, for example, about 1 to 30 parts by mass with respect to 100 parts by mass of the active material contained in the positive electrode.
  • the coating layer is formed on at least a part of the surface of the positive electrode active material layer. In the positive electrode active material layer coated with the coating layer, reaction unevenness on the surface of the positive electrode active material layer is suppressed.
  • the coating layer preferably covers the surface of the positive electrode active material layer so as to connect adjacent positive electrode active materials. It is preferable that at least 50% or more of the positive electrode active material present on the surface of the positive electrode active material layer is electrically connected by the coating layer. In that case, it is estimated that the reaction nonuniformity of the surface of a positive electrode active material layer can be suppressed more.
  • the coating layer preferably covers 50% or more of the surface of the positive electrode active material layer, and it is particularly preferable that the entire surface of the positive electrode active material layer is covered with the coating layer.
  • the specific resistance of the coating layer is greater than 1.0 ⁇ 10 ⁇ 3 ⁇ cm and 1.0 ⁇ 10 3 ⁇ cm or less. This specific resistance value is a so-called specific resistance region of the semiconductor.
  • the specific resistance of the coating layer is 1.0 ⁇ 10 ⁇ 3 ⁇ cm or less, too much electricity flows on the surface of the positive electrode active material layer. Therefore, the substance forming the coating layer decomposes the substance in the battery, for example, the electrolytic solution, and forms a film on the surface of the coating layer. When the coating is formed, the effect of suppressing the reaction unevenness on the surface of the positive electrode active material layer by the coating layer cannot be obtained. If the specific resistance of the coating layer is greater than 1.0 ⁇ 10 3 ⁇ cm, it is difficult for electricity to pass through the surface of the positive electrode active material layer. Therefore, the effect of suppressing reaction unevenness on the surface of the positive electrode active material layer by the coating layer cannot be obtained.
  • the specific resistance of the coating layer is more preferably 1 ⁇ cm or less.
  • the electrode resistance can be lowered as compared with the case where the coating layer is not formed.
  • the electrode resistance decreases, the charge / discharge capacity of the lithium ion secondary battery can be improved.
  • the covering layer is preferably made of a substance that does not promote decomposition of the electrolytic solution and the electrolyte. If the coating layer is made of a substance that does not promote the decomposition of the electrolytic solution and the electrolyte, the coating layer can suppress the decomposition reaction of the electrolytic solution or the electrolytic salt that easily proceeds in the vicinity of the electrode surface.
  • the coating layer is preferably made of at least one selected from antimony oxide, titanium oxide, tin oxide, zinc oxide, nickel oxide and indium oxide. These materials are difficult to decompose the electrolytic solution and the electrolytic salt. Moreover, even at high potentials, these materials are difficult to cause decomposition reaction of the electrolytic solution and the electrolytic salt.
  • the thickness of the coating layer is preferably 10 nm or more and less than 1 ⁇ m, and more preferably 20 nm to 800 nm. If the coating layer having a thickness of 10 nm or more is formed on the surface of the positive electrode active material layer, uneven reaction on the surface of the positive electrode active material layer is suppressed, and the cycle characteristics of the lithium ion secondary battery can be improved. If the thickness of the coating layer is less than 1 ⁇ m, the volume occupied by the coating layer inside the battery can be made appropriate. If the volume occupied by the coating layer in the battery becomes too large, the positive electrode active material layer and the like must be reduced, leading to a reduction in the charge / discharge capacity of the battery.
  • the coating layer is preferably connected continuously so as to cover the surface of the positive electrode active material layer.
  • the coating layer may be formed by collecting particles or fillers in a film shape. In this case, it is only necessary that adjacent particles and fillers are in contact with each other and have a substantially film shape, and it is not particularly necessary to form a film in which the particles and fillers are integrated.
  • the average particle size of the particles is preferably 1/10 or less of the average particle size of the positive electrode active material. If the average particle diameter of the particles is 1/10 or less of the average particle diameter of the positive electrode active material, the particles can cover the adjacent positive electrode active material along the irregularities on the surface of the positive electrode active material layer.
  • the particles forming the coating layer are preferably nanoparticles. When the particles forming the coating layer are nanoparticles, the thickness of the coating layer can be reduced.
  • FIG. 1 is a schematic diagram for explaining a positive electrode for a lithium ion secondary battery of the present embodiment.
  • a positive electrode active material 3 is bound on a current collector 1 by a binder 2.
  • a positive electrode active material layer 4 is formed from the positive electrode active material 3 and the binder 2.
  • a coating layer 5 is formed on the positive electrode active material layer 4.
  • the coating layer 5 is an aggregate of particles 51, and the plurality of particles 51 are arranged along the unevenness of the surfaces of the positive electrode active material 3 and the binder 2 to form the coating layer 5.
  • Adjacent positive electrode active materials 3 are electrically connected by a coating layer 5. Even if there is uneven electrical reaction in each positive electrode active material 3, electricity flows more evenly across the surface of the positive electrode active material layer 4 by the coating layer 5. Therefore, reaction unevenness as the whole positive electrode is reduced.
  • the positive electrode active material 3 since the positive electrode active material 3 is covered with the coating layer 5, it does not come into direct contact with the electrolytic solution or the like. Therefore, the decomposition reaction of the electrolytic solution that easily proceeds in the vicinity of the electrode surface by the positive electrode active material 3 is suppressed.
  • the method for forming the coating layer on the positive electrode active material layer is not particularly limited.
  • the coating layer can be formed on the positive electrode active material layer by the following method.
  • the coating layer material is dissolved in an organic solvent or water to create a solution, and sprayed onto the coated surface of the positive electrode active material layer using a sprayer, and the organic solvent or water is volatilized and removed to cover the positive electrode active material layer.
  • ethanol, N-methyl-2-pyrrolidone (NMP), methanol, methyl isobutyl ketone (MIBK), or the like can be used as the organic solvent.
  • the water is preferably water from which impurities have been removed, such as distilled water or ion exchange water.
  • the coating layer material is dissolved in an organic solvent or water for viscosity adjustment to prepare a paste-like mixture, the paste-like mixture is applied on the positive electrode active material layer, and dried after the application, whereby the positive electrode active material A coating layer can be formed on the layer.
  • a coating method a conventionally known method such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method may be used.
  • the organic solvent for adjusting the viscosity ethanol, N-methyl-2-pyrrolidone (NMP), methanol, methyl isobutyl ketone (MIBK) and the like can be used.
  • the water is preferably water from which impurities have been removed, such as distilled water or ion exchange water.
  • the lithium ion secondary battery of this invention has the said positive electrode for lithium ion secondary batteries, It is characterized by the above-mentioned.
  • the lithium ion secondary battery which has the said positive electrode for lithium ion secondary batteries has the outstanding cycling performance.
  • the lithium ion secondary battery of the present invention has a negative electrode, a separator, and an electrolytic solution in addition to the above-described positive electrode for a lithium ion secondary battery as battery components.
  • the negative electrode has a current collector and a negative electrode active material layer bound to the surface of the current collector.
  • a negative electrode active material layer contains a negative electrode active material and a binder, and contains a conductive support agent as needed.
  • the current collector, binder and conductive additive are the same as those described for the positive electrode.
  • the negative electrode active material a carbon-based material that can occlude and release lithium, an element that can be alloyed with lithium, a compound that has an element that can be alloyed with lithium, a polymer material, or the like can be used.
  • the carbon-based material examples include non-graphitizable carbon, artificial graphite, coke, graphite, glassy carbon, a fired organic polymer compound, carbon fiber, activated carbon, or carbon black.
  • the organic polymer compound fired body refers to a material obtained by firing and carbonizing a polymer material such as phenols and furans at an appropriate temperature.
  • Elements that can be alloyed with lithium include Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si, Ge, Sn, Pb, Sb, Bi can be exemplified.
  • silicon (Si) or tin (Sn) is preferable as an element that can be alloyed with lithium.
  • Examples of the compound having an element that can be alloyed with lithium include ZnLiAl, AlSb, SiB 4 , SiB 6 , Mg 2 Si, Mg 2 Sn, Ni 2 Si, TiSi 2 , MoSi 2 , CoSi 2 , NiSi 2 , CaSi 2 , CrSi 2, Cu 5 Si, FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 O, SiO v (0 ⁇ v ⁇ 2) SnO w (0 ⁇ w ⁇ 2), SnSiO 3 , LiSiO or LiSnO.
  • a silicon compound or a tin compound is preferable.
  • the silicon compound SiO x (0.5 ⁇ x ⁇ 1.5) is preferable.
  • tin compounds include tin alloys (Cu—Sn alloy, Co—Sn alloy, etc.).
  • polymer material examples include polyacetylene and polypyrrole.
  • the separator separates the positive electrode and the negative electrode and allows lithium ions to pass through while preventing a short circuit of current due to contact between the two electrodes.
  • a porous film made of synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene, or a porous film made of ceramics can be used.
  • the electrolytic solution an electrolytic solution that can be used for a lithium ion secondary battery can be used.
  • the electrolytic solution includes a solvent and an electrolyte dissolved in the solvent.
  • Examples of the solvent include cyclic esters, chain esters, and ethers.
  • Examples of the cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone.
  • Examples of chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester.
  • ethers examples include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane.
  • Examples of the electrolyte dissolved in the electrolytic solution include lithium salts such as LiClO 4 , LiAsF 6 , LiPF 6 , LiBF 4 , LiCF 3 SO 3 , and LiN (CF 3 SO 2 ) 2 .
  • a lithium salt such as LiClO 4 , LiPF 6 , LiBF 4 , LiCF 3 SO 3 or the like in a solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, or diethyl carbonate is 0.5 mol / l to 1.7 mol / l.
  • a solution dissolved at a certain concentration can be mentioned.
  • the lithium ion secondary battery can be mounted on a vehicle. Since the lithium ion secondary battery has excellent cycle performance, a vehicle equipped with the lithium ion secondary battery has high performance in terms of life and output.
  • the vehicle may be a vehicle that uses electric energy from a battery as a whole or a part of a power source.
  • a vehicle that uses electric energy from a battery as a whole or a part of a power source.
  • an electric vehicle a hybrid vehicle, a plug-in hybrid vehicle, a hybrid railway vehicle, an electric forklift, an electric wheelchair, and an electric assist.
  • Bicycles and electric motorcycles are examples.
  • This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to prepare a slurry.
  • NMP N-methyl-2-pyrrolidone
  • An aluminum foil having a thickness of 20 ⁇ m was prepared as a current collector.
  • the slurry was placed on the current collector and applied to the current collector using a doctor blade so that the slurry became a film.
  • the obtained sheet was dried at 80 ° C. for 20 minutes to volatilize and remove NMP. Thereafter, the current collector and the coated material on the current collector were firmly bonded by a roll press. At this time, the electrode density was set to 3.2 g / cm 2 .
  • the bonded product was heated in a vacuum dryer at 120 ° C. for 6 hours.
  • the bonded product after heating was cut into a predetermined shape (rectangular shape of 25 mm ⁇ 30 mm) to obtain a positive electrode A.
  • the thickness of the positive electrode A was about 50 ⁇ m.
  • Patent electrode B Antimony oxide nanoparticles having an average particle size of 20 nm were prepared. Antimony oxide nanoparticles were dispersed in ethanol. Ethanol in which the above-described antimony oxide nanoparticles were dispersed was sprayed on the surface of the positive electrode A using a sprayer. A coating layer of antimony oxide nanoparticles having a thickness of 50 nm was formed on the surface of the positive electrode A by volatilizing and removing ethanol. This is designated as positive electrode B. When the surface of the positive electrode B was observed with a scanning electron microscope (SEM), it was confirmed that the coating layer was formed so as to follow the surface of the positive electrode active material layer.
  • SEM scanning electron microscope
  • Carbon nanoparticles having an average particle diameter of 80 nm were prepared. Carbon nanoparticles were dispersed in ethanol. Ethanol in which the carbon nanoparticles described above were dispersed was sprayed on the surface of the positive electrode A using a sprayer. A 200 nm thick carbon nanoparticle coating layer was formed on the surface of the positive electrode A by volatilizing and removing ethanol. This is designated as positive electrode C. When the surface of the positive electrode C was observed with a scanning electron microscope (SEM), it was confirmed that the coating layer was formed so as to follow the surface of the positive electrode active material layer.
  • SEM scanning electron microscope
  • (Positive electrode D) SnO 2 nanoparticles having an average particle size of 20 nm were prepared. SnO 2 nanoparticles were dispersed in pure water. Pure water in which the above-described SnO 2 nanoparticles were dispersed was sprayed on the surface of the positive electrode A using a sprayer. A coating layer of SnO 2 nanoparticles having a thickness of 50 nm was formed on the surface of the positive electrode A by volatilizing and removing water. This is a positive electrode D. When the surface of the positive electrode D was observed with a scanning electron microscope (SEM), it was confirmed that the coating layer was formed so as to follow the surface of the positive electrode active material layer.
  • SEM scanning electron microscope
  • each of the coating layers of the positive electrodes B, C, and D was used to form a coating layer of 100 nm on glass instead of the positive electrode active material layer.
  • the specific resistance value of each coating layer on the glass was measured by the four probe method. The result was made into each specific resistance value of the coating layer of the said positive electrode B, C, D.
  • the specific resistance value of the coating layer of the positive electrode B was 10 ⁇ cm
  • the specific resistance value of the coating layer of the positive electrode C was 1.0 ⁇ 10 ⁇ 3 ⁇ cm
  • the specific resistance value of the coating layer of the positive electrode D was 1 ⁇ cm.
  • Example 1 A laminated lithium ion secondary battery of Example 1 using the positive electrode B as a positive electrode was produced as follows.
  • the negative electrode was produced as follows. A mixture was prepared by mixing 97 parts by mass of graphite powder, 1 part by mass of acetylene black as a conductive additive, 1 part by mass of styrene-butadiene rubber (SBR) and 1 part by mass of carboxymethyl cellulose (CMC) as a binder. This mixture was dispersed in an appropriate amount of ion-exchanged water to prepare a slurry. This slurry was applied to a copper foil having a thickness of 20 ⁇ m, which is a negative electrode current collector, in a film shape using a doctor blade. The current collector coated with the slurry was dried and pressed, and the bonded product was heated with a vacuum dryer at 120 ° C. for 6 hours. The bonded product after heating was cut into a predetermined shape (rectangular shape of 25 mm ⁇ 30 mm) to obtain a negative electrode. The thickness of the negative electrode was about 45 ⁇ m.
  • a laminate type lithium ion secondary battery was manufactured using the positive electrode B and the negative electrode. Specifically, a rectangular sheet (27 ⁇ 32 mm, thickness 25 ⁇ m) made of polypropylene resin as a separator was sandwiched between the positive electrode B and the negative electrode to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, and the three sides were sealed, and then an electrolyte solution was injected into the bag-like laminated film.
  • the laminated lithium ion secondary battery of Example 1 was produced through the above steps.
  • Example 2 A laminated lithium ion secondary battery of Example 2 was produced in the same manner as in Example 1 except that the positive electrode B in Example 1 was changed to the positive electrode D.
  • Comparative Example 1 A laminated lithium ion secondary battery of Comparative Example 1 was produced in the same manner as in Example 1 except that the positive electrode B in Example 1 was changed to the positive electrode A.
  • Comparative Example 2 A laminated lithium ion secondary battery of Comparative Example 2 was produced in the same manner as in Example 1 except that the positive electrode B in Example 1 was changed to the positive electrode C.
  • the discharge capacity at a current rate of 0.33 C after the cycle test was measured, the discharge capacity at 0.33 C after the cycle test was taken as the post-cycle capacity, and the capacity retention rate was calculated based on the initial capacity.
  • the capacity retention rate was determined by the following formula. The results are shown in Table 1.
  • Capacity retention rate (%) (Capacity after cycle / Initial capacity) x 100
  • the initial capacity of the laminated lithium ion secondary batteries of Example 1, Comparative Example 1 and Comparative Example 2 is slightly higher than the initial capacity of the laminated lithium ion secondary battery of Comparative Example 2.
  • the initial capacity of the laminated lithium ion secondary battery of Example 1 is the initial capacity of the laminated lithium ion secondary battery of Comparative Example 1. Almost no decrease compared to capacity. This indicates that the initial capacity of the lithium ion secondary battery does not decrease even when the antimony oxide coating layer is formed on the surface of the positive electrode active material layer.
  • the capacity retention rates (%) after 200 cycles of the laminated lithium ion secondary batteries of Example 1, Comparative Example 1 and Comparative Example 2 are compared.
  • the capacity retention rate (90.7%) of the laminated lithium ion secondary battery of Example 1 is improved as compared with the capacity retention rate (87.6%) of the laminated lithium ion secondary battery of Comparative Example 1.
  • the laminate type lithium ion secondary battery of Comparative Example 2 has a carbon coating layer formed on the positive electrode active material layer.
  • the capacity retention rate of the laminate type lithium ion secondary battery of Comparative Example 2 (67. 8%) was significantly lower than the capacity retention rate (87.6%) of the laminated lithium ion secondary battery of Comparative Example 1.
  • the laminated lithium ion secondary battery of Example 1 can improve the cycle characteristics without lowering the initial capacity as compared with the laminated lithium ion secondary battery of Comparative Example 1.
  • FIG. 2 is a schematic diagram showing the surface of each negative electrode after the cycle test of the laminated lithium ion secondary battery of Example 1 and Comparative Example 1.
  • FIG. 2 shows that the negative electrode surface of the laminated lithium ion secondary battery of Example 1 has significantly less color unevenness than the negative electrode surface of the laminated lithium ion secondary battery of Comparative Example 1. Therefore, it was found that the reaction unevenness on the surface of the positive electrode could be greatly reduced by forming the antimony oxide coating layer on the positive electrode active material layer. It is estimated that the cycle characteristics of the laminate type lithium ion secondary battery of Example 1 were improved by reducing the reaction unevenness on the surface of the positive electrode.
  • ⁇ Evaluation of cell resistance of laminated lithium ion secondary battery of Example 2 and Comparative Example 1 The cell resistance of the laminate type lithium ion secondary battery of Example 2 and Comparative Example 1 was measured. The cell resistance ( ⁇ ) was measured at a 3C rate and a 10-second discharge at a voltage of 20% SOC (State of charge). A smaller measured value of cell resistance indicates less internal loss of the lithium ion secondary battery. Further, since the cell resistance is measured at a 3C rate, the measured value of the cell resistance is also an index indicating a high rate characteristic.
  • the cell resistance of Comparative Example 1 was 1.29 times that of Example 2. That is, it was found that the internal loss of the lithium ion secondary battery was smaller in the laminated lithium ion secondary battery of Example 2 than in the laminated lithium ion secondary battery of Comparative Example 1. The smaller the internal loss of the lithium ion secondary battery, the higher the charge / discharge capacity of the lithium ion secondary battery. Further, it was found that the internal loss of the lithium ion secondary battery of the laminate type lithium ion secondary battery of Example 2 was smaller than that of the laminate type lithium ion secondary battery of Comparative Example 1 even at a high rate. From the above results, it was found that the internal loss of the electrode can be reduced by forming a coating layer having a specific resistance of 1 ⁇ cm or less on the positive electrode surface.
  • the cycle characteristics of the laminated lithium ion secondary batteries of Example 2 and Comparative Example 1 were evaluated as follows. As an evaluation of the cycle characteristics, a cycle test in which charging and discharging were repeated under the following conditions was performed, and the discharge capacity of each cycle was measured. At the time of charging, CC charging (constant current charging) was performed up to a voltage of 4.5 V at a 1C rate at 60 ° C. When discharging, CC discharge (constant current discharge) was performed at a 1C rate up to 3.0V. This charging / discharging was made into 1 cycle, and the cycle test was done to 50 cycles. The capacity retention rate was calculated based on the initial discharge capacity. The capacity retention rate was determined by the following formula. The results are shown in FIG.
  • Capacity retention rate (%) (discharge capacity of each cycle / initial discharge capacity) x 100
  • the capacity retention rate of each cycle at a high temperature of 60 ° C. was higher in the laminated lithium ion secondary battery of Example 2 than in the laminated lithium ion secondary battery of Comparative Example 1.
  • the capacity retention rate of the laminate type lithium ion secondary battery of Comparative Example 1 was 75%, whereas the capacity retention rate of the laminate type lithium ion secondary battery of Example 2 was 83%.
  • the cycle characteristics of the lithium ion secondary battery can be improved even at a high temperature of 60 ° C. by forming a coating layer having a specific resistance of 1 ⁇ cm on the surface of the positive electrode.

Abstract

Provided are: a positive electrode for lithium ion secondary batteries, which has excellent charge/discharge capacity and excellent cycle characteristics at high potentials; and a lithium ion secondary battery. This positive electrode for lithium ion secondary batteries is characterized by comprising: a collector; a positive electrode active material layer that is formed on the surface of the collector and contains a positive electrode active material and a binder; and a coating layer that is formed on at least a part of the surface of the positive electrode active material layer and has a specific resistance of more than 1.0 × 10-3 Ωcm but 1.0 × 103 Ωcm or less.

Description

リチウムイオン二次電池用正極及びリチウムイオン二次電池Positive electrode for lithium ion secondary battery and lithium ion secondary battery
　本発明は、リチウムイオン二次電池用正極及びリチウムイオン二次電池に関するものである。 The present invention relates to a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery.
　近年、リチウムイオン二次電池の高電位化要求が高まっている。リチウムイオン二次電池の高電位化を実現すべく、より高電位で使用できる正極活物質の検討、高電位駆動の電池の検討など様々な検討が行われている。高電位におけるサイクル特性を上げるために正極に保護膜を形成する検討も行われている。 In recent years, there has been an increasing demand for higher potential lithium ion secondary batteries. In order to realize a higher potential of a lithium ion secondary battery, various studies have been conducted, such as a study of a positive electrode active material that can be used at a higher potential and a study of a battery driven at a high potential. In order to improve cycle characteristics at a high potential, studies have been made to form a protective film on the positive electrode.
　例えば特許文献１（特開２００８－５３２０７号公報）には、正極活物質層の上に、マグネシアを含む無機粒子からなるフィラー粒子とバインダーとが含まれた被覆層を形成する技術が記載されている。特許文献１には、被覆層にマグネシアが含まれると水とマグネシアが反応してアルカリ性となりフッ酸が生じてもこれを中和でき、正極活物質からコバルトが溶出するのを抑制できることが記載されている。そして特許文献１には、この被覆層を有することで、リチウムイオン二次電池は高電位において高温でのサイクル特性、保存特性に優れることが記載されている。しかしながら特許文献１に記載の技術ではこの被覆層の厚みは１μｍ以上４μｍ以下とされ、被覆層の厚みが１μｍ未満であると十分な効果が得られないとされている。 For example, Patent Document 1 (Japanese Patent Laid-Open No. 2008-53207) describes a technique for forming a coating layer containing filler particles made of inorganic particles containing magnesia and a binder on a positive electrode active material layer. Yes. Patent Document 1 describes that when magnesia is contained in the coating layer, water and magnesia react to become alkaline and hydrofluoric acid is generated, so that it can be neutralized and the elution of cobalt from the positive electrode active material can be suppressed. ing. Patent Document 1 describes that, by having this coating layer, the lithium ion secondary battery is excellent in cycle characteristics and storage characteristics at high potential and high temperature. However, in the technique described in Patent Document 1, the thickness of the coating layer is 1 μm or more and 4 μm or less, and if the thickness of the coating layer is less than 1 μm, a sufficient effect cannot be obtained.
　基本的に、被覆層が厚くなるほど、電池の内部抵抗が増大して、電池の充放電容量が低下する。また、電池のエネルギー密度を維持しようとすると被覆層の厚みはより薄い方が好ましい。 Basically, the thicker the coating layer, the higher the internal resistance of the battery and the lower the charge / discharge capacity of the battery. Further, the thickness of the coating layer is preferably thinner in order to maintain the energy density of the battery.
　このことから、高電位におけるサイクル特性を向上し充放電容量を低下させない、厚みの薄い被覆層が配置された正極を有するリチウムイオン二次電池が望まれている。 For this reason, a lithium ion secondary battery having a positive electrode on which a thin coating layer is arranged that improves cycle characteristics at a high potential and does not reduce charge / discharge capacity is desired.
特開２００８－５３２０７号公報JP 2008-53207 A
　本発明者らは、高電位において優れたサイクル特性及び高い充放電容量を有するリチウムイオン二次電池となる被覆層の材料について様々に検討した。 The inventors of the present invention have made various studies on the material of the coating layer to be a lithium ion secondary battery having excellent cycle characteristics and high charge / discharge capacity at a high potential.
　本発明は、このような事情に鑑みて為されたものであり、高電位において優れたサイクル特性及び高い充放電容量を有するリチウムイオン二次電池用正極及びリチウムイオン二次電池を提供することを目的とする。 The present invention has been made in view of such circumstances, and provides a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery having excellent cycle characteristics and high charge / discharge capacity at a high potential. Objective.
　本発明者等が鋭意検討した結果、正極活物質層の表面に比抵抗が１．０×１０－３Ωｃｍより大きく１．０×１０３Ωｃｍ以下である被覆層を形成することにより、リチウムイオン二次電池が高電位において優れたサイクル特性及び高い充放電容量を発揮できることを見いだした。 As a result of intensive studies by the present inventors, by forming a coating layer having a specific resistance greater than 1.0 × 10 −3 Ωcm and 1.0 × 10 3 Ωcm or less on the surface of the positive electrode active material layer, lithium ion It was found that the secondary battery can exhibit excellent cycle characteristics and high charge / discharge capacity at a high potential.
　すなわち、本発明のリチウムイオン二次電池用正極は、集電体と、集電体の表面に形成された、正極活物質及び結着剤を含む正極活物質層と、正極活物質層の表面の少なくとも一部に形成され、比抵抗が１．０×１０－３Ωｃｍより大きく１．０×１０３Ωｃｍ以下である被覆層と、を有することを特徴とする。被覆層は正極活物質層の表面の５０％以上を被覆していることが好ましい。被覆層の比抵抗は１Ωｃｍ以下であることが好ましい。 That is, the positive electrode for a lithium ion secondary battery of the present invention includes a current collector, a positive electrode active material layer including a positive electrode active material and a binder formed on the surface of the current collector, and a surface of the positive electrode active material layer. And a coating layer having a specific resistance greater than 1.0 × 10 −3 Ωcm and less than or equal to 1.0 × 10 3 Ωcm. The covering layer preferably covers 50% or more of the surface of the positive electrode active material layer. The specific resistance of the coating layer is preferably 1 Ωcm or less.
　被覆層は、酸化アンチモン、酸化チタン、酸化錫、酸化亜鉛、酸化ニッケル及び酸化インジウムから選ばれる少なくとも１つからなることが好ましい。 The coating layer is preferably made of at least one selected from antimony oxide, titanium oxide, tin oxide, zinc oxide, nickel oxide and indium oxide.
　被覆層の厚みは１０ｎｍ以上１μｍ未満であることが好ましい。 The thickness of the coating layer is preferably 10 nm or more and less than 1 μm.
　被覆層は、膜状をなす粒子の集合体よりなり、粒子の平均粒径は、正極活物質の平均粒径の１／１０以下であることが好ましい。 The coating layer is made of an aggregate of film-like particles, and the average particle diameter of the particles is preferably 1/10 or less of the average particle diameter of the positive electrode active material.
　本発明のリチウムイオン二次電池は、上記リチウムイオン二次電池用正極と、負極と、非水電解液と、を有することを特徴とする。 The lithium ion secondary battery of the present invention is characterized by having the above-described positive electrode for a lithium ion secondary battery, a negative electrode, and a non-aqueous electrolyte.
　本発明のリチウムイオン二次電池用正極は、正極活物質層の表面の少なくとも一部に形成され、比抵抗が１．０×１０－３Ωｃｍより大きく１．０×１０３Ωｃｍ以下である被覆層を有する。つまり正極活物質層の表面には、ある程度は電気伝導性を有する被覆層が形成されている。正極活物質層の表面に電気伝導性のある層が形成されると、電気伝導性のある層内には電気が伝導し、正極活物質層の表面でおこる反応にムラが生じることが抑制される。正極活物質層の表面における反応ムラが抑制されることによって、正極活物質層の表面における電界集中による正極活物質層の局所劣化が抑制される。そのため、リチウムイオン二次電池のサイクル特性が向上する。 The positive electrode for a lithium ion secondary battery of the present invention is a coating formed on at least a part of the surface of the positive electrode active material layer and having a specific resistance greater than 1.0 × 10 −3 Ωcm and 1.0 × 10 3 Ωcm or less. Having a layer. That is, a coating layer having a certain degree of electrical conductivity is formed on the surface of the positive electrode active material layer. When an electrically conductive layer is formed on the surface of the positive electrode active material layer, electricity is conducted in the electrically conductive layer, and unevenness in the reaction occurring on the surface of the positive electrode active material layer is suppressed. The By suppressing the reaction unevenness on the surface of the positive electrode active material layer, local deterioration of the positive electrode active material layer due to electric field concentration on the surface of the positive electrode active material layer is suppressed. Therefore, the cycle characteristics of the lithium ion secondary battery are improved.
　ここで被覆層の上記範囲の比抵抗はいわゆる半導体領域の比抵抗である。被覆層の比抵抗が１．０×１０－３Ωｃｍ以下になると、被覆層内を電気が流れ過ぎる。被覆層内を電気が流れ過ぎることにより、被覆層を構成する物質が他の物質と反応して別の物質となってしまうおそれがある。別の物質となってしまうと被覆層の比抵抗が上記範囲より大きくなってしまうおそれがある。そのため、被覆層による正極活物質層の表面の反応ムラを抑制する効果が得られなくなる。 Here, the specific resistance in the above range of the coating layer is a so-called specific resistance of the semiconductor region. When the specific resistance of the coating layer is 1.0 × 10 −3 Ωcm or less, electricity flows too much in the coating layer. If electricity flows too much in the coating layer, the substance constituting the coating layer may react with another substance to become another substance. If it becomes another substance, the specific resistance of the coating layer may be larger than the above range. Therefore, the effect of suppressing reaction unevenness on the surface of the positive electrode active material layer by the coating layer cannot be obtained.
本実施形態のリチウムイオン二次電池用正極を説明する模式図である。It is a schematic diagram explaining the positive electrode for lithium ion secondary batteries of this embodiment. 実施例１及び比較例１のラミネート型リチウムイオン二次電池のサイクル試験後の各負極の表面を示す模式図である。FIG. 3 is a schematic diagram showing the surface of each negative electrode after a cycle test of the laminated lithium ion secondary battery of Example 1 and Comparative Example 1. 実施例２及び比較例１のラミネート型リチウムイオン二次電池のサイクル試験結果を表すグラフである。6 is a graph showing cycle test results of laminated lithium ion secondary batteries of Example 2 and Comparative Example 1.
　１：集電体、２：結着剤、３：正極活物質、４：正極活物質層、５：被覆層、５１：粒子。 1: current collector, 2: binder, 3: positive electrode active material, 4: positive electrode active material layer, 5: coating layer, 51: particles.
　＜リチウムイオン二次電池用正極＞
　本発明のリチウムイオン二次電池用正極は、集電体と、集電体の表面に形成された、正極活物質及び結着剤を含む正極活物質層と、正極活物質層の表面の少なくとも一部に形成され、比抵抗が１．０×１０－３Ωｃｍより大きく１．０×１０３Ωｃｍ以下である被覆層と、を有する。 <Positive electrode for lithium ion secondary battery>
A positive electrode for a lithium ion secondary battery according to the present invention includes a current collector, a positive electrode active material layer including a positive electrode active material and a binder formed on the surface of the current collector, and at least a surface of the positive electrode active material layer. And a coating layer having a specific resistance greater than 1.0 × 10 −3 Ωcm and not greater than 1.0 × 10 3 Ωcm.
　集電体は、リチウムイオン二次電池の放電又は充電の間、電極に電流を流し続けるための化学的に不活性な電子高伝導体をいう。集電体の材料として、例えばステンレス鋼、チタン、ニッケル、アルミニウム、銅などの金属材料又は導電性樹脂を挙げることができる。集電体の形状としては、箔、シート、フィルムなどの形態をとることができる。そのため、集電体として、例えば銅箔、ニッケル箔、アルミニウム箔、ステンレス箔などの金属箔を好適に用いることができる。 A current collector refers to a chemically inert electronic high conductor that keeps a current flowing through an electrode during discharge or charging of a lithium ion secondary battery. Examples of the current collector material include metal materials such as stainless steel, titanium, nickel, aluminum, and copper, or conductive resins. The shape of the current collector can take the form of a foil, sheet, film or the like. Therefore, metal foils, such as copper foil, nickel foil, aluminum foil, stainless steel foil, can be used suitably as a collector.
　集電体は、その厚みが１０μｍ～１００μｍであることが好ましい。 The current collector preferably has a thickness of 10 μm to 100 μm.
　正極活物質層は、集電体の表面に形成され、正極活物質及び結着剤を含む。正極活物質層はさらに導電助剤を含んでもよい。正極は、正極活物質及び結着剤、並びに必要に応じて導電助剤を含む正極活物質層形成用組成物を調製し、さらにこの組成物に適当な溶剤を加えてペースト状にしてから、集電体の表面に塗布後、乾燥し、必要に応じて電極密度を高めるべく圧縮して形成することができる。 The positive electrode active material layer is formed on the surface of the current collector and includes a positive electrode active material and a binder. The positive electrode active material layer may further contain a conductive additive. The positive electrode is prepared by preparing a composition for forming a positive electrode active material layer containing a positive electrode active material and a binder, and if necessary, a conductive additive, and further adding a suitable solvent to the composition to make a paste, After applying to the surface of the current collector, it can be dried and compressed to increase the electrode density as necessary.
　正極活物質層形成用組成物の塗布方法としては、ロールコート法、ディップコート法、ドクターブレード法、スプレーコート法、カーテンコート法などの従来から公知の方法を用いることができる。 As a method for applying the composition for forming a positive electrode active material layer, conventionally known methods such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, and a curtain coating method can be used.
　粘度調整のための溶剤としては、Ｎ－メチル－２－ピロリドン（ＮＭＰ）、メタノール、メチルイソブチルケトン（ＭＩＢＫ）などが使用可能である。 As the solvent for adjusting the viscosity, N-methyl-2-pyrrolidone (NMP), methanol, methyl isobutyl ketone (MIBK) and the like can be used.
　正極活物質としては、リチウム含有化合物あるいは他の金属化合物が挙げられる。リチウム含有化合物としては、例えば、層状構造を有するリチウムコバルト複合酸化物、層状構造を有するリチウムニッケル複合酸化物、スピネル構造を有するリチウムマンガン複合酸化物、一般式：ＬｉＣｏｐＮｉｑＭｎｒＤｓＯ２(Ｄはドープ成分であり、Ａｌ、Ｍｇ、Ｔｉ、Ｓｎ、Ｚｎ、Ｗ、Ｚｒ、Ｍｏ、Ｆｅ、Ｎａからなる成分であり、必要に応じて添加される、ｐ＋ｑ＋ｒ＋ｓ＝１、０＜ｐ＜１、０≦ｑ＜１、０≦ｒ＜１、０≦ｓ＜１)で表される層状構造を有するリチウムコバルト含有複合金属酸化物、一般式：ＬｉＭＰＯ４で示されるオリビン型リチウムリン酸複合酸化物（ＭはＭｎ、Ｆｅ、Ｃｏ及びＮｉのうちの少なくとも一種）、一般式：Ｌｉ２ＭＰＯ４Ｆで示されるフッ化オリビン型リチウムリン酸複合酸化物（ＭはＭｎ、Ｆｅ、Ｃｏ及びＮｉのうちの少なくとも一種）、一般式：Ｌｉ２ＭＳｉＯ４で示されるケイ酸塩系型リチウム複合酸化物（ＭはＭｎ、Ｆｅ、Ｃｏ及びＮｉのうちの少なくとも一種）が挙げられる。また他の金属化合物としては、例えば、酸化チタン、酸化バナジウム若しくは二酸化マンガンなどの酸化物、又は硫化チタン若しくは硫化モリブデンなどの二硫化物が挙げられる。 Examples of the positive electrode active material include lithium-containing compounds or other metal compounds. Examples of the lithium-containing compound include a lithium cobalt composite oxide having a layered structure, a lithium nickel composite oxide having a layered structure, a lithium manganese composite oxide having a spinel structure, and a general formula: LiCo p Ni q Mn r D s O 2 (D is a dope component, a component composed of Al, Mg, Ti, Sn, Zn, W, Zr, Mo, Fe, Na, added as necessary, p + q + r + s = 1, 0 <p < Lithium cobalt-containing composite metal oxide having a layered structure represented by 1, 0 ≦ q <1, 0 ≦ r <1, 0 ≦ s <1), an olivine-type lithium phosphate composite represented by the general formula: LiMPO 4 oxide (M is at least one of Mn, Fe, Co and Ni), the general formula: Li 2 MPO 4 fluoride olivine-type lithium phosphate compound oxide represented by F At least one of Li 2 MSiO silicate lithium composite oxide represented by 4 (M is one or more of Mn, Fe, Co and Ni: M at least one), the general formula of Mn, Fe, Co and Ni ). Examples of other metal compounds include oxides such as titanium oxide, vanadium oxide, and manganese dioxide, and disulfides such as titanium sulfide and molybdenum sulfide.
　正極活物質は、オリビン型リチウムリン酸複合酸化物であることが好ましい。オリビン系材料は一般的に導電性が低いため、オリビン系材料からなる正極活物質は高抵抗正極活物質と称される。このような高抵抗の正極活物質を用いると本願の被覆層の効果が顕著となる。オリビン型リチウムリン酸複合酸化物としては、ＬｉＦｅＰＯ４、ＬｉＭｎＰＯ４、ＬｉＣｏＰＯ４、ＬｉＮｉＰＯ４が挙げられる。 The positive electrode active material is preferably an olivine type lithium phosphate complex oxide. Since an olivine-based material generally has low conductivity, a positive electrode active material made of an olivine-based material is referred to as a high-resistance positive electrode active material. When such a high-resistance positive electrode active material is used, the effect of the coating layer of the present application becomes remarkable. Examples of the olivine type lithium phosphate complex oxide include LiFePO 4 , LiMnPO 4 , LiCoPO 4 , and LiNiPO 4 .
　また正極活物質は、化学式：ＬｉＭＯ２（ＭはＮｉ，Ｃｏ及びＭｎから選択される少なくとも１つである）で表されるリチウム含有酸化物よりなることが好ましく、さらに一般式：ＬｉＣｏｐＮｉｑＭｎｒＤｓＯ２(Ｄはドープ成分であり、Ａｌ、Ｍｇ、Ｔｉ、Ｓｎ、Ｚｎ、Ｗ、Ｚｒ、Ｍｏ、Ｆｅ、Ｎａからなる成分であり、必要に応じて添加される、ｐ＋ｑ＋ｒ＋ｓ＝１、０＜ｐ≦１、０≦ｑ＜１、０≦ｒ＜１、０≦ｓ＜１)で表される層状構造を有するリチウムコバルト含有複合金属酸化物よりなることが好ましい。 The positive electrode active material is preferably composed of a lithium-containing oxide represented by the chemical formula: LiMO 2 (M is at least one selected from Ni, Co, and Mn), and further, the general formula: LiCo p Ni q Mn r D s O 2 (D is a doping component, a component consisting of Al, Mg, Ti, Sn, Zn, W, Zr, Mo, Fe, Na, added as required, p + q + r + s = 1 , 0 <p ≦ 1, 0 ≦ q <1, 0 ≦ r <1, 0 ≦ s <1). The lithium cobalt-containing composite metal oxide preferably has a layered structure.
　リチウム含有酸化物としては、例えば、ＬｉＣｏ１／３Ｎｉ１／３Ｍｎ１／３Ｏ２、ＬｉＮｉ０．６Ｃｏ０．２Ｍｎ０．２Ｏ２、ＬｉＮｉ０．５Ｃｏ０．２Ｍｎ０．３Ｏ２、ＬｉＣｏＯ２、ＬｉＮｉ０．８Ｃｏ０．２Ｏ２、ＬｉＣｏＭｎＯ２が挙げられる。リチウム含有酸化物としては、中でもＬｉＣｏ１／３Ｎｉ１／３Ｍｎ１／３Ｏ２、ＬｉＮｉ０．５Ｃｏ０．２Ｍｎ０．３Ｏ２が熱安定性の点で好ましい。 Examples of the lithium-containing oxide include LiCo 1/3 Ni 1/3 Mn 1/3 O 2 , LiNi 0.6 Co 0.2 Mn 0.2 O 2 , LiNi 0.5 Co 0.2 Mn 0. 3 O 2, LiCoO 2, LiNi 0.8 Co 0.2 O 2, LiCoMnO 2 and the like. Lithium-containing oxides are preferably LiCo 1/3 Ni 1/3 Mn 1/3 O 2 and LiNi 0.5 Co 0.2 Mn 0.3 O 2 from the viewpoint of thermal stability.
　正極活物質はその平均粒径が１μｍ～２０μｍである粉末形状であることが好ましい。正極活物質の平均粒径が１μｍより小さいと正極活物質の比表面積が大きくなり正極活物質と電解液との反応面積が増える。正極活物質の平均粒径が２０μｍより大きいとリチウムイオン二次電池の抵抗が大きくなり、リチウムイオン二次電池の出力特性が下がる。正極活物質の平均粒径は粒度分布測定法によって計測できる。 The positive electrode active material is preferably in the form of a powder having an average particle diameter of 1 μm to 20 μm. When the average particle size of the positive electrode active material is smaller than 1 μm, the specific surface area of the positive electrode active material is increased, and the reaction area between the positive electrode active material and the electrolytic solution is increased. When the average particle diameter of the positive electrode active material is larger than 20 μm, the resistance of the lithium ion secondary battery increases, and the output characteristics of the lithium ion secondary battery decrease. The average particle size of the positive electrode active material can be measured by a particle size distribution measurement method.
　結着剤は、上記正極活物質及び導電助剤を集電体に繋ぎ止める役割を果たす。結着剤として、ポリフッ化ビニリデン及びポリテトラフルオロエチレン等の含フッ素樹脂、ポリプロピレン、ポリエチレン及びポリ酢酸ビニル系樹脂等の熱可塑性樹脂、ポリイミド及びポリアミドイミド等のイミド系樹脂、アルコキシシリル基含有樹脂、並びにスチレンブタジエンゴム（ＳＢＲ）及びフッ素ゴム等のゴムを例示できる。 The binder serves to bind the positive electrode active material and the conductive additive to the current collector. As binders, fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene, thermoplastic resins such as polypropylene, polyethylene and polyvinyl acetate resins, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins, Examples thereof include rubbers such as styrene butadiene rubber (SBR) and fluorine rubber.
　導電助剤は、必要に応じて電極の導電性を高めるために添加される。導電助剤として、炭素質微粒子であるカーボンブラック、黒鉛、アセチレンブラック（ＡＢ）、ケッチェンブラック（登録商標）（ＫＢ）、気相法炭素繊維（ＶＧＣＦ）が例示される。これらの導電助剤を単独で又は二種以上組み合わせて正極に添加することができる。導電助剤の使用量については、特に限定的ではないが、例えば、正極に含有される活物質１００質量部に対して、１質量部～３０質量部程度とすることができる。 導電 Conductive aid is added as necessary to increase the conductivity of the electrode. Examples of the conductive assistant include carbon black, graphite, acetylene black (AB), ketjen black (registered trademark) (KB), and vapor grown carbon fiber (VGCF) which are carbonaceous fine particles. These conductive assistants can be added to the positive electrode alone or in combination of two or more. The amount of the conductive aid used is not particularly limited, but can be, for example, about 1 to 30 parts by mass with respect to 100 parts by mass of the active material contained in the positive electrode.
　被覆層は正極活物質層の表面の少なくとも一部に形成される。被覆層が被覆されている正極活物質層では、正極活物質層の表面の反応ムラが抑制される。被覆層は、隣り合う個々の正極活物質同士をつなぐように正極活物質層の表面を被覆していることが好ましい。正極活物質層の表面に存在する正極活物質の少なくとも５０％以上が被覆層によって電気的につながっていることが好ましい。その場合は、正極活物質層の表面の反応ムラはより抑制できると推測される。被覆層は正極活物質層の表面の５０％以上を被覆していることが好ましく、正極活物質層の表面全体に被覆層が被覆されていることが特に好ましい。 The coating layer is formed on at least a part of the surface of the positive electrode active material layer. In the positive electrode active material layer coated with the coating layer, reaction unevenness on the surface of the positive electrode active material layer is suppressed. The coating layer preferably covers the surface of the positive electrode active material layer so as to connect adjacent positive electrode active materials. It is preferable that at least 50% or more of the positive electrode active material present on the surface of the positive electrode active material layer is electrically connected by the coating layer. In that case, it is estimated that the reaction nonuniformity of the surface of a positive electrode active material layer can be suppressed more. The coating layer preferably covers 50% or more of the surface of the positive electrode active material layer, and it is particularly preferable that the entire surface of the positive electrode active material layer is covered with the coating layer.
　またこの被覆層の比抵抗は１．０×１０－３Ωｃｍより大きく１．０×１０３Ωｃｍ以下である。この比抵抗の値はいわゆる半導体の比抵抗領域である。このような電気を通す被覆層が正極活物質層の表面の少なくとも一部を覆うように連続して被覆していることによって、正極活物質層の表面に電気が流れる連続した層ができることとなる。この被覆層により正極活物質層の表面の反応ムラが抑制される。 The specific resistance of the coating layer is greater than 1.0 × 10 −3 Ωcm and 1.0 × 10 3 Ωcm or less. This specific resistance value is a so-called specific resistance region of the semiconductor. By continuously covering at least a part of the surface of the positive electrode active material layer with such a coating layer that conducts electricity, a continuous layer in which electricity flows on the surface of the positive electrode active material layer is formed. . This coating layer suppresses uneven reaction on the surface of the positive electrode active material layer.
　被覆層の比抵抗が１．０×１０－３Ωｃｍ以下であると、正極活物質層の表面に電気が流れ過ぎる。そのため、被覆層を形成する物質は、電池内の物質、例えば電解液を分解して被覆層の表面に被膜を形成してしまう。被膜が形成されると、被覆層による正極活物質層の表面の反応ムラを抑制する効果が得られない。また被覆層の比抵抗が１．０×１０３Ωｃｍより大きいと、正極活物質層の表面に電気が通りにくい。そのため、被覆層による正極活物質層の表面の反応ムラを抑制する効果が得られない。 If the specific resistance of the coating layer is 1.0 × 10 −3 Ωcm or less, too much electricity flows on the surface of the positive electrode active material layer. Therefore, the substance forming the coating layer decomposes the substance in the battery, for example, the electrolytic solution, and forms a film on the surface of the coating layer. When the coating is formed, the effect of suppressing the reaction unevenness on the surface of the positive electrode active material layer by the coating layer cannot be obtained. If the specific resistance of the coating layer is greater than 1.0 × 10 3 Ωcm, it is difficult for electricity to pass through the surface of the positive electrode active material layer. Therefore, the effect of suppressing reaction unevenness on the surface of the positive electrode active material layer by the coating layer cannot be obtained.
　被覆層の比抵抗は１Ωｃｍ以下であるとより好ましい。比抵抗が１Ωｃｍ以下であると被覆層が形成されていないものよりも電極抵抗を下げることができる。電極抵抗が下がると、リチウムイオン二次電池の充放電容量を向上させることができる。 The specific resistance of the coating layer is more preferably 1 Ωcm or less. When the specific resistance is 1 Ωcm or less, the electrode resistance can be lowered as compared with the case where the coating layer is not formed. When the electrode resistance decreases, the charge / discharge capacity of the lithium ion secondary battery can be improved.
　また被覆層は、電解液及び電解質の分解を促進しない物質からなることが好ましい。被覆層が電解液及び電解質の分解を促進しない物質からなれば、この被覆層は、電極表面付近で進行しやすい電解液あるいは電解塩の分解反応を抑制することができる。 The covering layer is preferably made of a substance that does not promote decomposition of the electrolytic solution and the electrolyte. If the coating layer is made of a substance that does not promote the decomposition of the electrolytic solution and the electrolyte, the coating layer can suppress the decomposition reaction of the electrolytic solution or the electrolytic salt that easily proceeds in the vicinity of the electrode surface.
　被覆層は、酸化アンチモン、酸化チタン、酸化錫、酸化亜鉛、酸化ニッケル及び酸化インジウムから選ばれる少なくとも１つからなることが好ましい。これらの材料は電解液及び電解塩の分解反応をおこしにくい。また高電位においてもこれらの材料は電解液及び電解塩の分解反応をおこしにくい。 The coating layer is preferably made of at least one selected from antimony oxide, titanium oxide, tin oxide, zinc oxide, nickel oxide and indium oxide. These materials are difficult to decompose the electrolytic solution and the electrolytic salt. Moreover, even at high potentials, these materials are difficult to cause decomposition reaction of the electrolytic solution and the electrolytic salt.
　被覆層の厚みは１０ｎｍ以上１μｍ未満であることが好ましく、２０ｎｍ～８００ｎｍであることがより好ましい。厚みが１０ｎｍ以上の被覆層が正極活物質層の表面に形成されれば、正極活物質層の表面の反応ムラが抑制され、リチウムイオン二次電池のサイクル特性を向上させることができる。被覆層の厚みが１μｍ未満であれば、電池内部の被覆層の占める体積を適正にすることができる。電池内の被覆層の占める体積が大きくなりすぎると、正極活物質層等を減らさなければならなくなり、電池の充放電容量の低下につながる。 The thickness of the coating layer is preferably 10 nm or more and less than 1 μm, and more preferably 20 nm to 800 nm. If the coating layer having a thickness of 10 nm or more is formed on the surface of the positive electrode active material layer, uneven reaction on the surface of the positive electrode active material layer is suppressed, and the cycle characteristics of the lithium ion secondary battery can be improved. If the thickness of the coating layer is less than 1 μm, the volume occupied by the coating layer inside the battery can be made appropriate. If the volume occupied by the coating layer in the battery becomes too large, the positive electrode active material layer and the like must be reduced, leading to a reduction in the charge / discharge capacity of the battery.
　被覆層は、正極活物質層の表面を覆うように連続的につながっていることが好ましい。被覆層は、膜状に粒子又はフィラーが集合して形成されていてもよい。この場合、隣り合う粒子やフィラーは接触して、実質的に膜状となっていればよく、特に粒子同士やフィラー同士が一体化した膜を形成している必要はない。 The coating layer is preferably connected continuously so as to cover the surface of the positive electrode active material layer. The coating layer may be formed by collecting particles or fillers in a film shape. In this case, it is only necessary that adjacent particles and fillers are in contact with each other and have a substantially film shape, and it is not particularly necessary to form a film in which the particles and fillers are integrated.
　例えば被覆層が粒子の集合体である場合、粒子の平均粒径は、正極活物質の平均粒径の１／１０以下であることが好ましい。粒子の平均粒径が正極活物質の平均粒径の１／１０以下であれば、粒子は正極活物質層の表面の凹凸に沿って隣り合う正極活物質を被覆することができる。 For example, when the coating layer is an aggregate of particles, the average particle size of the particles is preferably 1/10 or less of the average particle size of the positive electrode active material. If the average particle diameter of the particles is 1/10 or less of the average particle diameter of the positive electrode active material, the particles can cover the adjacent positive electrode active material along the irregularities on the surface of the positive electrode active material layer.
　被覆層を形成する粒子はナノ粒子であることが好ましい。被覆層を形成する粒子がナノ粒子であると、被覆層の厚みを小さくすることができる。 The particles forming the coating layer are preferably nanoparticles. When the particles forming the coating layer are nanoparticles, the thickness of the coating layer can be reduced.
　図１に本実施形態のリチウムイオン二次電池用正極を説明する模式図を示す。図１において、集電体１の上に正極活物質３が結着剤２によって結着されている。正極活物質３と結着剤２とから正極活物質層４が形成されている。正極活物質層４の上には被覆層５が形成されている。図１において被覆層５は粒子５１の集合体となっており、複数の粒子５１は正極活物質３及び結着剤２の表面の凹凸に沿って配置され、被覆層５を形成している。 FIG. 1 is a schematic diagram for explaining a positive electrode for a lithium ion secondary battery of the present embodiment. In FIG. 1, a positive electrode active material 3 is bound on a current collector 1 by a binder 2. A positive electrode active material layer 4 is formed from the positive electrode active material 3 and the binder 2. A coating layer 5 is formed on the positive electrode active material layer 4. In FIG. 1, the coating layer 5 is an aggregate of particles 51, and the plurality of particles 51 are arranged along the unevenness of the surfaces of the positive electrode active material 3 and the binder 2 to form the coating layer 5.
　隣り合う正極活物質３は被覆層５によって電気的につながっている。各正極活物質３において電気反応のムラがあっても、被覆層５によって電気がより均等に正極活物質層４の表面全体に流れる。そのため、正極全体としての反応ムラが低減する。 Adjacent positive electrode active materials 3 are electrically connected by a coating layer 5. Even if there is uneven electrical reaction in each positive electrode active material 3, electricity flows more evenly across the surface of the positive electrode active material layer 4 by the coating layer 5. Therefore, reaction unevenness as the whole positive electrode is reduced.
　また正極活物質３は被覆層５によって被覆されているので、電解液などと直接接触しない。そのため、正極活物質３による電極表面付近で進行しやすい電解液の分解反応が抑制される。 In addition, since the positive electrode active material 3 is covered with the coating layer 5, it does not come into direct contact with the electrolytic solution or the like. Therefore, the decomposition reaction of the electrolytic solution that easily proceeds in the vicinity of the electrode surface by the positive electrode active material 3 is suppressed.
　この正極活物質層へ被覆層を形成する方法は、特に限定されない。例えば、以下の方法で正極活物質層へ被覆層を形成できる。被覆層の材料を有機溶媒又は水に溶かして溶液を作成し、噴霧器を用いて正極活物質層の塗布面に噴霧し、有機溶媒又は水を揮発、除去することによって正極活物質層に被覆層を形成することができる。この場合の有機溶媒はエタノール、Ｎ－メチル－２－ピロリドン（ＮＭＰ）、メタノール、メチルイソブチルケトン（ＭＩＢＫ）などが使用できる。水は蒸留水やイオン交換水など、不純物を取り除いたものが好ましい。 The method for forming the coating layer on the positive electrode active material layer is not particularly limited. For example, the coating layer can be formed on the positive electrode active material layer by the following method. The coating layer material is dissolved in an organic solvent or water to create a solution, and sprayed onto the coated surface of the positive electrode active material layer using a sprayer, and the organic solvent or water is volatilized and removed to cover the positive electrode active material layer. Can be formed. In this case, ethanol, N-methyl-2-pyrrolidone (NMP), methanol, methyl isobutyl ketone (MIBK), or the like can be used as the organic solvent. The water is preferably water from which impurities have been removed, such as distilled water or ion exchange water.
　また被覆層の材料を粘度調整のための有機溶媒若しくは水に溶かしてペースト状の混合物を作成し、そのペースト状の混合物を正極活物質層上に塗布し、塗布後に乾燥することによって正極活物質層に被覆層を形成することができる。塗布方法としては、ロールコート法、ディップコート法、ドクターブレード法、スプレーコート法、カーテンコート法などの従来から公知の方法を用いればよい。粘度調整のための有機溶媒としては、エタノール、Ｎ－メチル－２－ピロリドン（ＮＭＰ）、メタノール、メチルイソブチルケトン（ＭＩＢＫ）などが使用可能である。水は蒸留水やイオン交換水など、不純物を取り除いたものが好ましい。 Further, the coating layer material is dissolved in an organic solvent or water for viscosity adjustment to prepare a paste-like mixture, the paste-like mixture is applied on the positive electrode active material layer, and dried after the application, whereby the positive electrode active material A coating layer can be formed on the layer. As a coating method, a conventionally known method such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method may be used. As the organic solvent for adjusting the viscosity, ethanol, N-methyl-2-pyrrolidone (NMP), methanol, methyl isobutyl ketone (MIBK) and the like can be used. The water is preferably water from which impurities have been removed, such as distilled water or ion exchange water.
＜リチウムイオン二次電池＞
　本発明のリチウムイオン二次電池は、上記リチウムイオン二次電池用正極を有することを特徴とする。上記リチウムイオン二次電池用正極を有するリチウムイオン二次電池は、優れたサイクル性能を有する。 <Lithium ion secondary battery>
The lithium ion secondary battery of this invention has the said positive electrode for lithium ion secondary batteries, It is characterized by the above-mentioned. The lithium ion secondary battery which has the said positive electrode for lithium ion secondary batteries has the outstanding cycling performance.
　本発明のリチウムイオン二次電池は、電池構成要素として、上記したリチウムイオン二次電池用正極に加えて、負極、セパレータ、電解液を有する。 The lithium ion secondary battery of the present invention has a negative electrode, a separator, and an electrolytic solution in addition to the above-described positive electrode for a lithium ion secondary battery as battery components.
　負極は、集電体と、集電体の表面に結着させた負極活物質層を有する。負極活物質層は、負極活物質、結着剤を含み、必要に応じて導電助剤を含む。集電体、結着剤、導電助剤は正極で説明したものと同様である。 The negative electrode has a current collector and a negative electrode active material layer bound to the surface of the current collector. A negative electrode active material layer contains a negative electrode active material and a binder, and contains a conductive support agent as needed. The current collector, binder and conductive additive are the same as those described for the positive electrode.
　負極活物質としては、リチウムを吸蔵、放出可能な炭素系材料、リチウムと合金化可能な元素、リチウムと合金化可能な元素を有する化合物、あるいは高分子材料などを用いることができる。 As the negative electrode active material, a carbon-based material that can occlude and release lithium, an element that can be alloyed with lithium, a compound that has an element that can be alloyed with lithium, a polymer material, or the like can be used.
　炭素系材料としては、例えば、難黒鉛化性炭素、人造黒鉛、コークス類、グラファイト類、ガラス状炭素類、有機高分子化合物焼成体、炭素繊維、活性炭あるいはカーボンブラック類が挙げられる。ここで、有機高分子化合物焼成体とは、フェノール類やフラン類などの高分子材料を適当な温度で焼成して炭素化したものをいう。 Examples of the carbon-based material include non-graphitizable carbon, artificial graphite, coke, graphite, glassy carbon, a fired organic polymer compound, carbon fiber, activated carbon, or carbon black. Here, the organic polymer compound fired body refers to a material obtained by firing and carbonizing a polymer material such as phenols and furans at an appropriate temperature.
　リチウムと合金化可能な元素としては、Ｎａ、Ｋ、Ｒｂ、Ｃｓ、Ｆｒ、Ｂｅ、Ｍｇ、Ｃａ、Ｓｒ、Ｂａ、Ｒａ、Ｔｉ、Ａｇ、Ｚｎ、Ｃｄ、Ａｌ、Ｇａ、Ｉｎ、Ｓｉ、Ｇｅ、Ｓｎ、Ｐｂ、Ｓｂ、Ｂｉを例示できる。中でも、リチウムと合金化可能な元素としては、珪素（Ｓｉ）又は錫（Ｓｎ）が好ましい。 Elements that can be alloyed with lithium include Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si, Ge, Sn, Pb, Sb, Bi can be exemplified. Among these, silicon (Si) or tin (Sn) is preferable as an element that can be alloyed with lithium.
　リチウムと合金化可能な元素を有する化合物としては、ＺｎＬｉＡｌ、ＡｌＳｂ、ＳｉＢ４、ＳｉＢ６、Ｍｇ２Ｓｉ、Ｍｇ２Ｓｎ、Ｎｉ２Ｓｉ、ＴｉＳｉ２、ＭｏＳｉ２、ＣｏＳｉ２、ＮｉＳｉ２、ＣａＳｉ２、ＣｒＳｉ２、Ｃｕ５Ｓｉ、ＦｅＳｉ２、ＭｎＳｉ２、ＮｂＳｉ２、ＴａＳｉ２、ＶＳｉ２、ＷＳｉ２、ＺｎＳｉ２、ＳｉＣ、Ｓｉ３Ｎ４、Ｓｉ２Ｎ２Ｏ、ＳｉＯｖ（０＜ｖ≦２）、ＳｎＯｗ（０＜ｗ≦２）、ＳｎＳｉＯ３、ＬｉＳｉＯあるいはＬｉＳｎＯを例示できる。リチウムと合金化可能な元素を有する化合物としては、珪素化合物又は錫化合物が好ましい。珪素化合物としては、ＳｉＯｘ（０．５≦ｘ≦１．５）が好ましい。錫化合物としては、スズ合金（Ｃｕ－Ｓｎ合金、Ｃｏ－Ｓｎ合金等）を例示できる。 Examples of the compound having an element that can be alloyed with lithium include ZnLiAl, AlSb, SiB 4 , SiB 6 , Mg 2 Si, Mg 2 Sn, Ni 2 Si, TiSi 2 , MoSi 2 , CoSi 2 , NiSi 2 , CaSi 2 , CrSi 2, Cu 5 Si, FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 O, SiO v (0 <v ≦ 2) SnO w (0 <w ≦ 2), SnSiO 3 , LiSiO or LiSnO. As the compound having an element that can be alloyed with lithium, a silicon compound or a tin compound is preferable. As the silicon compound, SiO x (0.5 ≦ x ≦ 1.5) is preferable. Examples of tin compounds include tin alloys (Cu—Sn alloy, Co—Sn alloy, etc.).
　高分子材料としては、ポリアセチレン、ポリピロールを例示できる。 Examples of the polymer material include polyacetylene and polypyrrole.
　セパレータは正極と負極とを隔離し、両極の接触による電流の短絡を防止しつつ、リチウムイオンを通過させるものである。セパレータは、例えばポリテトラフルオロエチレン、ポリプロピレン、若しくはポリエチレンなどの合成樹脂製の多孔質膜、又はセラミックス製の多孔質膜が使用できる。 The separator separates the positive electrode and the negative electrode and allows lithium ions to pass through while preventing a short circuit of current due to contact between the two electrodes. As the separator, for example, a porous film made of synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene, or a porous film made of ceramics can be used.
　電解液としては、リチウムイオン二次電池用に用いることのできる電解液が使用できる。電解液は、溶媒とこの溶媒に溶解された電解質とを含んでいる。 As the electrolytic solution, an electrolytic solution that can be used for a lithium ion secondary battery can be used. The electrolytic solution includes a solvent and an electrolyte dissolved in the solvent.
　溶媒として、例えば、環状エステル類、鎖状エステル類、エーテル類が挙げられる。環状エステル類として、例えば、エチレンカーボネート、プロピレンカーボネート、ブチレンカーボネート、ガンマブチロラクトン、ビニレンカーボネート、２－メチル－ガンマブチロラクトン、アセチル－ガンマブチロラクトン、ガンマバレロラクトンが挙げられる。鎖状エステル類として、例えば、ジメチルカーボネート、ジエチルカーボネート、ジブチルカーボネート、ジプロピルカーボネート、メチルエチルカーボネート、プロピオン酸アルキルエステル、マロン酸ジアルキルエステル、酢酸アルキルエステルが挙げられる。エーテル類として、例えば、テトラヒドロフラン、２－メチルテトラヒドロフラン、１，４－ジオキサン、１，２－ジメトキシエタン、１，２－ジエトキシエタン、１，２－ジブトキシエタンが挙げられる。 Examples of the solvent include cyclic esters, chain esters, and ethers. Examples of the cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester. Examples of ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane.
　また上記電解液に溶解させる電解質として、例えばＬｉＣｌＯ４、ＬｉＡｓＦ６、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＣＦ３ＳＯ３、ＬｉＮ（ＣＦ３ＳＯ２）２等のリチウム塩が挙げられる。 Examples of the electrolyte dissolved in the electrolytic solution include lithium salts such as LiClO 4 , LiAsF 6 , LiPF 6 , LiBF 4 , LiCF 3 SO 3 , and LiN (CF 3 SO 2 ) 2 .
　電解液として、例えば、エチレンカーボネート、ジメチルカーボネート、プロピレンカーボネート、ジエチルカーボネートなどの溶媒にＬｉＣｌＯ４、ＬｉＰＦ６、ＬｉＢＦ４、ＬｉＣＦ３ＳＯ３などのリチウム塩を０．５ｍｏｌ／ｌから１．７ｍｏｌ／ｌ程度の濃度で溶解させた溶液が挙げられる。 As the electrolytic solution, for example, a lithium salt such as LiClO 4 , LiPF 6 , LiBF 4 , LiCF 3 SO 3 or the like in a solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, or diethyl carbonate is 0.5 mol / l to 1.7 mol / l. A solution dissolved at a certain concentration can be mentioned.
　上記リチウムイオン二次電池は車両に搭載することができる。上記リチウムイオン二次電池は、優れたサイクル性能を有するため、そのリチウムイオン二次電池を搭載した車両は、寿命、出力の面で高性能となる。 The lithium ion secondary battery can be mounted on a vehicle. Since the lithium ion secondary battery has excellent cycle performance, a vehicle equipped with the lithium ion secondary battery has high performance in terms of life and output.
　車両としては、電池による電気エネルギーを動力源の全部又は一部に使用する車両であればよく、例えば、電気自動車、ハイブリッド自動車、プラグインハイブリッド自動車、ハイブリッド鉄道車両、電動フォークリフト、電気車椅子、電動アシスト自転車、電動二輪車が挙げられる。 The vehicle may be a vehicle that uses electric energy from a battery as a whole or a part of a power source. For example, an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, a hybrid railway vehicle, an electric forklift, an electric wheelchair, and an electric assist. Bicycles and electric motorcycles are examples.
　以上、本発明のリチウムイオン二次電池用正極及びリチウムイオン二次電池の実施形態を説明したが、本発明は、上記実施形態に限定されるものではない。本発明の要旨を逸脱しない範囲において、当業者が行い得る変更、改良等を施した種々の形態にて実施することができる。 As mentioned above, although embodiment of the positive electrode for lithium ion secondary batteries and lithium ion secondary battery of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.
　以下、実施例を挙げて本発明を更に詳しく説明する。 Hereinafter, the present invention will be described in more detail with reference to examples.
＜リチウムイオン二次電池用正極の作成＞
（正極Ａ）
　まず、正極活物質として平均粒子径が５μｍのＬｉＮｉ０．５Ｃｏ０．２Ｍｎ０．３Ｏ２と、導電助剤としてアセチレンブラックと、結着剤としてポリフッ化ビニリデン（ＰＶＤＦ）とを、それぞれ９４質量部、３質量部、３質量部として混合し混合物とした。この混合物を適量のＮ－メチル－２－ピロリドン（ＮＭＰ）に分散させて、スラリーを作製した。 <Creation of positive electrode for lithium ion secondary battery>
(Positive electrode A)
First, LiNi 0.5 Co 0.2 Mn 0.3 O 2 having an average particle diameter of 5 μm as a positive electrode active material, acetylene black as a conductive additive, and polyvinylidene fluoride (PVDF) as a binder, 94 parts by mass, 3 parts by mass, and 3 parts by mass were mixed to obtain a mixture. This mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to prepare a slurry.
　集電体として厚み２０μｍのアルミニウム箔を準備した。集電体にスラリーをのせ、ドクターブレードを用いてスラリーが膜状になるように集電体に塗布した。得られたシートを８０℃で２０分間乾燥してＮＭＰを揮発させて除去した。その後、ロ－ルプレス機により、集電体と集電体上の塗布物を強固に密着接合させた。この時電極密度は３．２ｇ／ｃｍ２となるようにした。接合物を１２０℃で６時間、真空乾燥機で加熱した。加熱後の接合物を、所定の形状（２５ｍｍ×３０ｍｍの矩形状）に切り取り、正極Ａとした。正極Ａの厚さは５０μｍ程度であった。 An aluminum foil having a thickness of 20 μm was prepared as a current collector. The slurry was placed on the current collector and applied to the current collector using a doctor blade so that the slurry became a film. The obtained sheet was dried at 80 ° C. for 20 minutes to volatilize and remove NMP. Thereafter, the current collector and the coated material on the current collector were firmly bonded by a roll press. At this time, the electrode density was set to 3.2 g / cm 2 . The bonded product was heated in a vacuum dryer at 120 ° C. for 6 hours. The bonded product after heating was cut into a predetermined shape (rectangular shape of 25 mm × 30 mm) to obtain a positive electrode A. The thickness of the positive electrode A was about 50 μm.
（正極Ｂ）
　平均粒子径が２０ｎｍの酸化アンチモンのナノ粒子を準備した。酸化アンチモンのナノ粒子をエタノールに分散した。噴霧器を用いて上記した酸化アンチモンのナノ粒子が分散したエタノールを正極Ａの表面に噴霧した。エタノールを揮発、除去することにより正極Ａの表面に厚み５０ｎｍの酸化アンチモンのナノ粒子の被覆層を形成した。これを正極Ｂとする。正極Ｂの表面を走査型電子顕微鏡（ＳＥＭ）で観察すると被覆層は正極活物質層の表面に追随するように形成されていることが確認できた。 (Positive electrode B)
Antimony oxide nanoparticles having an average particle size of 20 nm were prepared. Antimony oxide nanoparticles were dispersed in ethanol. Ethanol in which the above-described antimony oxide nanoparticles were dispersed was sprayed on the surface of the positive electrode A using a sprayer. A coating layer of antimony oxide nanoparticles having a thickness of 50 nm was formed on the surface of the positive electrode A by volatilizing and removing ethanol. This is designated as positive electrode B. When the surface of the positive electrode B was observed with a scanning electron microscope (SEM), it was confirmed that the coating layer was formed so as to follow the surface of the positive electrode active material layer.
（正極Ｃ）
　平均粒子径が８０ｎｍのカーボンのナノ粒子を準備した。カーボンのナノ粒子をエタノールに分散した。噴霧器を用いて上記したカーボンのナノ粒子が分散したエタノールを正極Ａの表面に噴霧した。エタノールを揮発、除去することにより正極Ａの表面に厚み２００ｎｍのカーボンのナノ粒子の被覆層を形成した。これを正極Ｃとする。正極Ｃの表面を走査型電子顕微鏡（ＳＥＭ）で観察すると被覆層は正極活物質層の表面に追随するように形成されていることが確認できた。 (Positive electrode C)
Carbon nanoparticles having an average particle diameter of 80 nm were prepared. Carbon nanoparticles were dispersed in ethanol. Ethanol in which the carbon nanoparticles described above were dispersed was sprayed on the surface of the positive electrode A using a sprayer. A 200 nm thick carbon nanoparticle coating layer was formed on the surface of the positive electrode A by volatilizing and removing ethanol. This is designated as positive electrode C. When the surface of the positive electrode C was observed with a scanning electron microscope (SEM), it was confirmed that the coating layer was formed so as to follow the surface of the positive electrode active material layer.
（正極Ｄ）
　平均粒子径が２０ｎｍのＳｎＯ２のナノ粒子を準備した。ＳｎＯ２のナノ粒子を純水に分散した。噴霧器を用いて上記したＳｎＯ２のナノ粒子を分散した純水を正極Ａの表面に噴霧した。水を揮発、除去することにより正極Ａの表面に厚み５０ｎｍのＳｎＯ２のナノ粒子の被覆層を形成した。これを正極Ｄとする。正極Ｄの表面を走査型電子顕微鏡（ＳＥＭ）で観察すると被覆層は正極活物質層の表面に追随するように形成されていることが確認できた。 (Positive electrode D)
SnO 2 nanoparticles having an average particle size of 20 nm were prepared. SnO 2 nanoparticles were dispersed in pure water. Pure water in which the above-described SnO 2 nanoparticles were dispersed was sprayed on the surface of the positive electrode A using a sprayer. A coating layer of SnO 2 nanoparticles having a thickness of 50 nm was formed on the surface of the positive electrode A by volatilizing and removing water. This is a positive electrode D. When the surface of the positive electrode D was observed with a scanning electron microscope (SEM), it was confirmed that the coating layer was formed so as to follow the surface of the positive electrode active material layer.
＜比抵抗測定＞
　上記正極Ｂ、Ｃ、Ｄの各被覆層材料を用いて正極活物質層上ではなくガラス上に１００ｎｍの各被覆層を形成した。ガラス上の各被覆層の比抵抗値を四探針法にて計測した。その結果を上記正極Ｂ、Ｃ、Ｄの被覆層の各比抵抗値とした。正極Ｂの被覆層の比抵抗値は１０Ωｃｍ、正極Ｃの被覆層の比抵抗値は１．０×１０―３Ωｃｍ、正極Ｄの被覆層の比抵抗値は１Ωｃｍであった。 <Specific resistance measurement>
Each of the coating layers of the positive electrodes B, C, and D was used to form a coating layer of 100 nm on glass instead of the positive electrode active material layer. The specific resistance value of each coating layer on the glass was measured by the four probe method. The result was made into each specific resistance value of the coating layer of the said positive electrode B, C, D. The specific resistance value of the coating layer of the positive electrode B was 10 Ωcm, the specific resistance value of the coating layer of the positive electrode C was 1.0 × 10 −3 Ωcm, and the specific resistance value of the coating layer of the positive electrode D was 1 Ωcm.
　＜ラミネート型リチウムイオン二次電池作製＞
　（実施例１）
　正極Ｂを正極として用いた実施例１のラミネート型リチウムイオン二次電池を次のようにして作製した。 <Production of laminated lithium-ion secondary battery>
(Example 1)
A laminated lithium ion secondary battery of Example 1 using the positive electrode B as a positive electrode was produced as follows.
　負極は以下のように作製した。黒鉛粉末９７質量部と、導電助剤としてアセチレンブラック１質量部と、結着剤としてスチレン－ブタジエンゴム（ＳＢＲ）１質量部及びカルボキシメチルセルロース（ＣＭＣ）１質量部とを混合して混合物とした。この混合物を適量のイオン交換水に分散させてスラリーを作製した。このスラリーを負極用集電体である厚み２０μｍの銅箔にドクターブレードを用いて膜状になるように塗布した。スラリーを塗布した集電体を乾燥後プレスし、接合物を１２０℃で６時間、真空乾燥機で加熱した。加熱後の接合物を所定の形状（２５ｍｍ×３０ｍｍの矩形状）に切り取り、負極とした。負極の厚さは４５μｍ程度であった。 The negative electrode was produced as follows. A mixture was prepared by mixing 97 parts by mass of graphite powder, 1 part by mass of acetylene black as a conductive additive, 1 part by mass of styrene-butadiene rubber (SBR) and 1 part by mass of carboxymethyl cellulose (CMC) as a binder. This mixture was dispersed in an appropriate amount of ion-exchanged water to prepare a slurry. This slurry was applied to a copper foil having a thickness of 20 μm, which is a negative electrode current collector, in a film shape using a doctor blade. The current collector coated with the slurry was dried and pressed, and the bonded product was heated with a vacuum dryer at 120 ° C. for 6 hours. The bonded product after heating was cut into a predetermined shape (rectangular shape of 25 mm × 30 mm) to obtain a negative electrode. The thickness of the negative electrode was about 45 μm.
　正極Ｂ及び負極を用いて、ラミネート型リチウムイオン二次電池を製作した。詳しくは、正極Ｂ及び負極の間に、セパレータとしてポリプロピレン樹脂からなる矩形状シート（２７×３２ｍｍ、厚さ２５μｍ）を挟装して極板群とした。この極板群を二枚一組のラミネートフィルムで覆い、三辺をシールした後、袋状となったラミネートフィルムに電解液を注入した。電解液としてエチレンカーボネート（ＥＣ）とジエチルカーボネー（ＤＥＣ）をＥＣ：ＤＥＣ＝３：７（体積比）で混合した溶媒にＬｉＰＦ6を１モル／ｌとなるように溶解した溶液を用いた。その後、残りの一辺をシールすることで、四辺が気密にシールされ、極板群及び電解液が密閉されたラミネート型リチウムイオン二次電池を得た。なお、正極及び負極は外部と電気的に接続可能なタブを備え、このタブの一部はラミネート型リチウムイオン二次電池の外側に延出している。以上の工程で、実施例１のラミネート型リチウムイオン二次電池を作製した。 A laminate type lithium ion secondary battery was manufactured using the positive electrode B and the negative electrode. Specifically, a rectangular sheet (27 × 32 mm, thickness 25 μm) made of polypropylene resin as a separator was sandwiched between the positive electrode B and the negative electrode to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, and the three sides were sealed, and then an electrolyte solution was injected into the bag-like laminated film. As an electrolytic solution, a solution obtained by dissolving LiPF 6 at 1 mol / l in a solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at EC: DEC = 3: 7 (volume ratio) was used. Thereafter, the remaining one side was sealed to obtain a laminate type lithium ion secondary battery in which the four sides were hermetically sealed and the electrode plate group and the electrolyte were sealed. Note that the positive electrode and the negative electrode each have a tab that can be electrically connected to the outside, and a part of the tab extends to the outside of the laminated lithium ion secondary battery. The laminated lithium ion secondary battery of Example 1 was produced through the above steps.
　（実施例２）
　実施例１における正極Ｂを正極Ｄに変更した以外は実施例１と同様にして実施例２のラミネート型リチウムイオン二次電池を作製した。 (Example 2)
A laminated lithium ion secondary battery of Example 2 was produced in the same manner as in Example 1 except that the positive electrode B in Example 1 was changed to the positive electrode D.
　（比較例１）
　実施例１における正極Ｂを正極Ａに変更した以外は実施例１と同様にして比較例１のラミネート型リチウムイオン二次電池を作製した。 (Comparative Example 1)
A laminated lithium ion secondary battery of Comparative Example 1 was produced in the same manner as in Example 1 except that the positive electrode B in Example 1 was changed to the positive electrode A.
　（比較例２）
　実施例１における正極Ｂを正極Ｃに変更した以外は実施例１と同様にして比較例２のラミネート型リチウムイオン二次電池を作製した。 (Comparative Example 2)
A laminated lithium ion secondary battery of Comparative Example 2 was produced in the same manner as in Example 1 except that the positive electrode B in Example 1 was changed to the positive electrode C.
＜実施例１、比較例１及び比較例２のラミネート型リチウムイオン二次電池の初期容量測定＞
　実施例１、比較例１及び比較例２のラミネート型リチウムイオン二次電池の初期容量を測定した。充電は、２５℃において１Ｃレートで、電圧４．５ＶまでＣＣ充電（定電流充電）をした。その後電圧４．５Ｖにて一時間ＣＶ充電（定電圧充電）をした。放電の際は３．０Ｖまで、０．３３ＣレートでＣＣ放電(定電流放電)を行った。この時の放電容量を測定し、初期容量とした。結果を表１に示した。 <Initial capacity measurement of laminated lithium ion secondary batteries of Example 1, Comparative Example 1 and Comparative Example 2>
The initial capacities of the laminated lithium ion secondary batteries of Example 1, Comparative Example 1 and Comparative Example 2 were measured. The charge was CC charge (constant current charge) up to a voltage of 4.5V at a 1C rate at 25 ° C. Thereafter, CV charging (constant voltage charging) was performed at a voltage of 4.5 V for one hour. When discharging, CC discharge (constant current discharge) was performed at a rate of 0.33 C up to 3.0 V. The discharge capacity at this time was measured and used as the initial capacity. The results are shown in Table 1.
＜実施例１、比較例１及び比較例２のラミネート型リチウムイオン二次電池のサイクル特性評価＞
　実施例１、比較例１及び比較例２のラミネート型リチウムイオン二次電池のサイクル特性を評価した。サイクル特性の評価としては、以下の条件で充放電を繰り返したサイクル試験を行い各サイクルの放電容量を測定した。充電の際は、２５℃において１Ｃレートで、電圧４．５ＶまでＣＣ充電（定電流充電）をした。放電の際は３．０Ｖまで、１ＣレートでＣＣ放電(定電流放電)を行った。この充放電を１サイクルとし、２００サイクルまでサイクル試験を行った。サイクル試験後に電流レートが０．３３Ｃの時の放電容量を測定し、サイクル試験後の０．３３Ｃの時の放電容量をサイクル後容量とし、初期容量を基準にして容量維持率を計算した。容量維持率は次に示す式にて求めた。結果を表１に記す。 <Evaluation of cycle characteristics of laminated lithium ion secondary batteries of Example 1, Comparative Example 1 and Comparative Example 2>
The cycle characteristics of the laminated lithium ion secondary batteries of Example 1, Comparative Example 1 and Comparative Example 2 were evaluated. As an evaluation of the cycle characteristics, a cycle test in which charging and discharging were repeated under the following conditions was performed, and the discharge capacity of each cycle was measured. At the time of charging, CC charging (constant current charging) was performed up to a voltage of 4.5 V at a 1 C rate at 25 ° C. When discharging, CC discharge (constant current discharge) was performed at a 1C rate up to 3.0V. This charging / discharging was made into 1 cycle, and the cycle test was done to 200 cycles. The discharge capacity at a current rate of 0.33 C after the cycle test was measured, the discharge capacity at 0.33 C after the cycle test was taken as the post-cycle capacity, and the capacity retention rate was calculated based on the initial capacity. The capacity retention rate was determined by the following formula. The results are shown in Table 1.
　容量維持率（％）=（サイクル後容量／初期容量）×１００ Capacity retention rate (%) = (Capacity after cycle / Initial capacity) x 100
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　表１に見られるように、実施例１、比較例１及び比較例２のラミネート型リチウムイオン二次電池の初期容量は、比較例２のラミネート型リチウムイオン二次電池の初期容量が若干高いが、ほとんど同等であった。特に比較例１と実施例１のラミネート型リチウムイオン二次電池の初期容量を比較すると実施例１のラミネート型リチウムイオン二次電池の初期容量は比較例１のラミネート型リチウムイオン二次電池の初期容量に比べてほとんど下がらなかった。このことから酸化アンチモンの被覆層が正極活物質層の表面に形成されてもリチウムイオン二次電池の初期容量は低下しないことがわかった。 As can be seen from Table 1, the initial capacity of the laminated lithium ion secondary batteries of Example 1, Comparative Example 1 and Comparative Example 2 is slightly higher than the initial capacity of the laminated lithium ion secondary battery of Comparative Example 2. Was almost equivalent. In particular, comparing the initial capacities of the laminated lithium ion secondary batteries of Comparative Example 1 and Example 1, the initial capacity of the laminated lithium ion secondary battery of Example 1 is the initial capacity of the laminated lithium ion secondary battery of Comparative Example 1. Almost no decrease compared to capacity. This indicates that the initial capacity of the lithium ion secondary battery does not decrease even when the antimony oxide coating layer is formed on the surface of the positive electrode active material layer.
　次に実施例１、比較例１及び比較例２のラミネート型リチウムイオン二次電池の２００サイクル後の容量維持率（％）を比較する。実施例１のラミネート型リチウムイオン二次電池の容量維持率（９０．７％）は比較例１のラミネート型リチウムイオン二次電池の容量維持率（８７．６％）に比べて向上していることがわかった。また比較例２のラミネート型リチウムイオン二次電池は正極活物質層の上にカーボンの被覆層を形成したものであるが、比較例２のラミネート型リチウムイオン二次電池の容量維持率（６７．８％）は比較例１のラミネート型リチウムイオン二次電池の容量維持率（８７．６％）よりも大幅に低下した。このことから比抵抗が小さく、電子伝導性が高い被覆層を形成するとかえってリチウムイオン二次電池のサイクル特性が下がることがわかった。サイクル試験後の比較例２の被覆層をＳＥＭで観察すると、作成時よりも被覆層は膨張しており、サイクル試験中に被覆層が変質してしまったと推測される。 Next, the capacity retention rates (%) after 200 cycles of the laminated lithium ion secondary batteries of Example 1, Comparative Example 1 and Comparative Example 2 are compared. The capacity retention rate (90.7%) of the laminated lithium ion secondary battery of Example 1 is improved as compared with the capacity retention rate (87.6%) of the laminated lithium ion secondary battery of Comparative Example 1. I understood it. The laminate type lithium ion secondary battery of Comparative Example 2 has a carbon coating layer formed on the positive electrode active material layer. However, the capacity retention rate of the laminate type lithium ion secondary battery of Comparative Example 2 (67. 8%) was significantly lower than the capacity retention rate (87.6%) of the laminated lithium ion secondary battery of Comparative Example 1. From this, it was found that the cycle characteristics of the lithium ion secondary battery were lowered when a coating layer having a small specific resistance and high electron conductivity was formed. When the coating layer of Comparative Example 2 after the cycle test is observed with an SEM, the coating layer is expanded more than that at the time of preparation, and it is presumed that the coating layer has been altered during the cycle test.
　以上の結果から実施例１のラミネート型リチウムイオン二次電池は、比較例１のラミネート型リチウムイオン二次電池に比べて初期容量を低下させずにサイクル特性を向上できることがわかった。 From the above results, it was found that the laminated lithium ion secondary battery of Example 1 can improve the cycle characteristics without lowering the initial capacity as compared with the laminated lithium ion secondary battery of Comparative Example 1.
＜実施例１及び比較例１のラミネート型リチウムイオン二次電池の反応ムラ評価＞
　２００サイクル試験後の実施例１及び比較例１のラミネート型リチウムイオン二次電池を解体して、各負極の表面のカラー写真を撮影した。実施例１の負極のカラー写真は、比較例１の負極のカラー写真に比べて虹色の色ムラが大幅に低減した。この色はＬｉとカーボンが反応してできた反応物又は負極表面にできた固体電解質界面被膜（ＳＥＩ：Ｓｏｌｉｄ　Ｅｌｅｃｔｒｏｌｙｔｅ　Ｉｎｔｅｒｐｈａｓｅ）によって発生する色と考えられる。色ムラは、負極の表面にＬｉが偏在して析出することによっておこると考えられる。すなわち色ムラは電界集中による正極の局所劣化がおこっていることを示す。 <Evaluation of reaction unevenness of laminated lithium ion secondary batteries of Example 1 and Comparative Example 1>
The laminated lithium ion secondary batteries of Example 1 and Comparative Example 1 after the 200 cycle test were disassembled, and color photographs of the surface of each negative electrode were taken. The color photograph of the negative electrode of Example 1 significantly reduced iridescent color unevenness compared to the color photograph of the negative electrode of Comparative Example 1. This color is considered to be a color generated by a reaction product formed by reaction of Li and carbon or a solid electrolyte interface film (SEI) formed on the negative electrode surface. The color unevenness is considered to be caused by Li being unevenly distributed on the surface of the negative electrode. That is, color unevenness indicates that local deterioration of the positive electrode due to electric field concentration occurs.
　このカラー写真のデータを白黒のデータにし、白黒データにコントラストをつけてわかりやすくしたものを模式図として図２に示す。図２は実施例１及び比較例１のラミネート型リチウムイオン二次電池のサイクル試験後の各負極の表面を示す模式図である。 2) This color photograph data is converted into black and white data, and the black and white data is contrasted for easy understanding. FIG. 2 is a schematic diagram showing the surface of each negative electrode after the cycle test of the laminated lithium ion secondary battery of Example 1 and Comparative Example 1.
　図２より、実施例１のラミネート型リチウムイオン二次電池の負極表面には比較例１のラミネート型リチウムイオン二次電池の負極表面に比べて大幅に色ムラが少ないことがわかった。従って正極活物質層の上に酸化アンチモンの被覆層を形成することによって正極の表面における反応ムラを大幅に低減できたことがわかった。この正極の表面の反応ムラが減少することによって実施例１のラミネート型リチウムイオン二次電池のサイクル特性が向上したと推測される。 FIG. 2 shows that the negative electrode surface of the laminated lithium ion secondary battery of Example 1 has significantly less color unevenness than the negative electrode surface of the laminated lithium ion secondary battery of Comparative Example 1. Therefore, it was found that the reaction unevenness on the surface of the positive electrode could be greatly reduced by forming the antimony oxide coating layer on the positive electrode active material layer. It is estimated that the cycle characteristics of the laminate type lithium ion secondary battery of Example 1 were improved by reducing the reaction unevenness on the surface of the positive electrode.
＜実施例２及び比較例１のラミネート型リチウムイオン二次電池のセル抵抗評価＞
　実施例２及び比較例１のラミネート型リチウムイオン二次電池のセル抵抗を測定した。セル抵抗（Ω）は、ＳＯＣ（Ｓｔａｔｅ　ｏｆ　ｃｈａｒｇｅ）２０％時の電圧にて３Ｃレート、１０秒放電にて測定した。セル抵抗の測定値が小さい方がリチウムイオン二次電池の内部損失が少ないことを示す。またセル抵抗は３Ｃレートで測定されているので、このセル抵抗の測定値は高レート特性を示す指標ともなる。 <Evaluation of cell resistance of laminated lithium ion secondary battery of Example 2 and Comparative Example 1>
The cell resistance of the laminate type lithium ion secondary battery of Example 2 and Comparative Example 1 was measured. The cell resistance (Ω) was measured at a 3C rate and a 10-second discharge at a voltage of 20% SOC (State of charge). A smaller measured value of cell resistance indicates less internal loss of the lithium ion secondary battery. Further, since the cell resistance is measured at a 3C rate, the measured value of the cell resistance is also an index indicating a high rate characteristic.
　比較例１のセル抵抗は実施例２のセル抵抗の１．２９倍であった。つまり実施例２のラミネート型リチウムイオン二次電池のほうが比較例１のラミネート型リチウムイオン二次電池よりもリチウムイオン二次電池の内部損失が少ないことがわかった。リチウムイオン二次電池の内部損失が少ない方がリチウムイオン二次電池の充放電容量が高くなる。また高レートにおいても実施例２のラミネート型リチウムイオン二次電池が比較例１のラミネート型リチウムイオン二次電池に比べて、リチウムイオン二次電池の内部損失が少ないことがわかった。上記の結果から正極表面に比抵抗が１Ωｃｍ以下の被覆層を形成することにより電極の内部損失を低減できることがわかった。 The cell resistance of Comparative Example 1 was 1.29 times that of Example 2. That is, it was found that the internal loss of the lithium ion secondary battery was smaller in the laminated lithium ion secondary battery of Example 2 than in the laminated lithium ion secondary battery of Comparative Example 1. The smaller the internal loss of the lithium ion secondary battery, the higher the charge / discharge capacity of the lithium ion secondary battery. Further, it was found that the internal loss of the lithium ion secondary battery of the laminate type lithium ion secondary battery of Example 2 was smaller than that of the laminate type lithium ion secondary battery of Comparative Example 1 even at a high rate. From the above results, it was found that the internal loss of the electrode can be reduced by forming a coating layer having a specific resistance of 1 Ωcm or less on the positive electrode surface.
＜実施例２及び比較例１のラミネート型リチウムイオン二次電池のサイクル特性評価＞
　実施例２及び比較例１のラミネート型リチウムイオン二次電池のサイクル特性評価を以下のように行った。サイクル特性の評価としては、以下の条件で充放電を繰り返したサイクル試験を行い各サイクルの放電容量を測定した。充電の際は、６０℃において１Ｃレートで、電圧４．５ＶまでＣＣ充電（定電流充電）をした。放電の際は３．０Ｖまで、１ＣレートでＣＣ放電(定電流放電)を行った。この充放電を１サイクルとし、５０サイクルまでサイクル試験を行った。初期放電容量を基準にして容量維持率を計算した。容量維持率は次に示す式にて求めた。結果を図３に記す。 <Evaluation of cycle characteristics of laminated lithium ion secondary batteries of Example 2 and Comparative Example 1>
The cycle characteristics of the laminated lithium ion secondary batteries of Example 2 and Comparative Example 1 were evaluated as follows. As an evaluation of the cycle characteristics, a cycle test in which charging and discharging were repeated under the following conditions was performed, and the discharge capacity of each cycle was measured. At the time of charging, CC charging (constant current charging) was performed up to a voltage of 4.5 V at a 1C rate at 60 ° C. When discharging, CC discharge (constant current discharge) was performed at a 1C rate up to 3.0V. This charging / discharging was made into 1 cycle, and the cycle test was done to 50 cycles. The capacity retention rate was calculated based on the initial discharge capacity. The capacity retention rate was determined by the following formula. The results are shown in FIG.
　容量維持率（％）=（各サイクルの放電容量／初期放電容量）×１００ Capacity retention rate (%) = (discharge capacity of each cycle / initial discharge capacity) x 100
　図３の結果から、６０℃という高温において各サイクルの容量維持率は実施例２のラミネート型リチウムイオン二次電池のほうが比較例１のラミネート型リチウムイオン二次電池よりも高かった。５０サイクル後において、比較例１のラミネート型リチウムイオン二次電池の容量維持率が７５％であったのに対して、実施例２のラミネート型リチウムイオン二次電池の容量維持率は８３％と大幅に向上した。 3, the capacity retention rate of each cycle at a high temperature of 60 ° C. was higher in the laminated lithium ion secondary battery of Example 2 than in the laminated lithium ion secondary battery of Comparative Example 1. After 50 cycles, the capacity retention rate of the laminate type lithium ion secondary battery of Comparative Example 1 was 75%, whereas the capacity retention rate of the laminate type lithium ion secondary battery of Example 2 was 83%. Greatly improved.
　このことから正極表面に比抵抗が１Ωｃｍの被覆層を形成することにより６０℃という高温においてもリチウムイオン二次電池のサイクル特性を向上させることができることがわかった。 From this, it was found that the cycle characteristics of the lithium ion secondary battery can be improved even at a high temperature of 60 ° C. by forming a coating layer having a specific resistance of 1 Ωcm on the surface of the positive electrode.

Claims (7)

  1. 　集電体と、
    　該集電体の表面に形成された、正極活物質及び結着剤を含む正極活物質層と、
    　該正極活物質層の表面の少なくとも一部に形成され、比抵抗が１．０×１０－３Ωｃｍより大きく１．０×１０３Ωｃｍ以下である被覆層と、
    　を有するリチウムイオン二次電池用正極。     A current collector,
    A positive electrode active material layer including a positive electrode active material and a binder formed on the surface of the current collector;
    A coating layer formed on at least a part of the surface of the positive electrode active material layer and having a specific resistance greater than 1.0 × 10 −3 Ωcm and 1.0 × 10 3 Ωcm or less;
    A positive electrode for a lithium ion secondary battery.
  2. 　前記被覆層は、酸化アンチモン、酸化チタン、酸化錫、酸化亜鉛、酸化ニッケル及び酸化インジウムから選ばれる少なくとも１つからなる請求項１に記載のリチウムイオン二次電池用正極。 The positive electrode for a lithium ion secondary battery according to claim 1, wherein the coating layer is made of at least one selected from antimony oxide, titanium oxide, tin oxide, zinc oxide, nickel oxide and indium oxide.
  3. 　前記被覆層の厚みは１０ｎｍ以上１μｍ未満である請求項１又は２に記載のリチウムイオン二次電池用正極。 The positive electrode for a lithium ion secondary battery according to claim 1 or 2, wherein the coating layer has a thickness of 10 nm or more and less than 1 µm.
  4. 　前記被覆層は、膜状をなす粒子の集合体よりなり、
    　前記粒子の平均粒径は、前記正極活物質の平均粒径の１／１０以下である請求項１～３のいずれか一項に記載のリチウムイオン二次電池用正極。     The coating layer is made of an aggregate of particles that form a film,
    The positive electrode for a lithium ion secondary battery according to any one of claims 1 to 3, wherein an average particle diameter of the particles is 1/10 or less of an average particle diameter of the positive electrode active material.
  5. 　前記被覆層は該正極活物質層の表面の５０％以上に形成されている請求項１～４のいずれか一項に記載のリチウムイオン二次電池用正極。 The positive electrode for a lithium ion secondary battery according to any one of claims 1 to 4, wherein the coating layer is formed on 50% or more of the surface of the positive electrode active material layer.
  6. 　前記比抵抗は１Ωｃｍ以下である請求項１～５のいずれか一項に記載のリチウムイオン二次電池用正極。 The positive electrode for a lithium ion secondary battery according to any one of claims 1 to 5, wherein the specific resistance is 1 Ωcm or less.
  7. 　請求項１～６のいずれか一項に記載のリチウムイオン二次電池用正極と、
    　負極と、
    　非水電解液と、
    　を有するリチウムイオン二次電池。     A positive electrode for a lithium ion secondary battery according to any one of claims 1 to 6;
    A negative electrode,
    A non-aqueous electrolyte,
    A lithium ion secondary battery.
PCT/JP2014/000035 2013-01-15 2014-01-08 Positive electrode for lithium ion secondary batteries and lithium ion secondary battery WO2014112329A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2013-004354 2013-01-15
JP2013004354A JP5557067B1 (en) 2013-01-15 2013-01-15 Positive electrode for lithium ion secondary battery and lithium ion secondary battery

Publications (1)

Publication Number Publication Date
WO2014112329A1 true WO2014112329A1 (en) 2014-07-24

Family

ID=51209430

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/JP2014/000035 WO2014112329A1 (en) 2013-01-15 2014-01-08 Positive electrode for lithium ion secondary batteries and lithium ion secondary battery

Country Status (2)

Country Link
JP (1) JP5557067B1 (en)
WO (1) WO2014112329A1 (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110364697A (en) * 2018-03-26 2019-10-22 丰田自动车株式会社 Positive electrode and the secondary cell for using the positive electrode
CN112670508A (en) * 2020-12-22 2021-04-16 东莞新能源科技有限公司 Positive electrode material, electrochemical device, and electronic device
US11374225B2 (en) 2017-10-06 2022-06-28 Gs Yuasa International Ltd. Electrode plate, energy storage device, and method for manufacturing electrode plate

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH08236114A (en) * 1995-02-27 1996-09-13 Sanyo Electric Co Ltd Lithium secondary battery
JP2007005073A (en) * 2005-06-22 2007-01-11 Sony Corp Positive electrode material, battery, and manufacturing method of positive electrode material
JP2009021134A (en) * 2007-07-12 2009-01-29 Toshiba Corp Nonaqueous electrolyte battery and battery pack
JP2009524707A (en) * 2006-01-26 2009-07-02 イドロ−ケベック Co-crushing mixture of active substance and conductive material, preparation method and use thereof

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH08236114A (en) * 1995-02-27 1996-09-13 Sanyo Electric Co Ltd Lithium secondary battery
JP2007005073A (en) * 2005-06-22 2007-01-11 Sony Corp Positive electrode material, battery, and manufacturing method of positive electrode material
JP2009524707A (en) * 2006-01-26 2009-07-02 イドロ−ケベック Co-crushing mixture of active substance and conductive material, preparation method and use thereof
JP2009021134A (en) * 2007-07-12 2009-01-29 Toshiba Corp Nonaqueous electrolyte battery and battery pack

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US11374225B2 (en) 2017-10-06 2022-06-28 Gs Yuasa International Ltd. Electrode plate, energy storage device, and method for manufacturing electrode plate
CN110364697A (en) * 2018-03-26 2019-10-22 丰田自动车株式会社 Positive electrode and the secondary cell for using the positive electrode
CN110364697B (en) * 2018-03-26 2022-06-28 丰田自动车株式会社 Positive electrode material and secondary battery using the same
CN112670508A (en) * 2020-12-22 2021-04-16 东莞新能源科技有限公司 Positive electrode material, electrochemical device, and electronic device

Also Published As

Publication number Publication date
JP5557067B1 (en) 2014-07-23
JP2014137848A (en) 2014-07-28

Similar Documents

Publication Publication Date Title
JP5757148B2 (en) Negative electrode active material for lithium ion secondary battery and lithium ion secondary battery using the negative electrode active material
JP6044427B2 (en) Current collector for positive electrode of lithium ion secondary battery, positive electrode for lithium ion secondary battery, and lithium ion secondary battery
JP6061143B2 (en) Positive electrode for lithium ion secondary battery and lithium ion secondary battery
JP5664943B2 (en) ELECTRODE FOR LITHIUM ION SECONDARY BATTERY, MANUFACTURING METHOD THEREOF, AND LITHIUM ION SECONDARY BATTERY USING THE ELECTRODE
JP2015011922A (en) Negative electrode for lithium ion secondary battery and lithium ion secondary battery
JP5668845B2 (en) ELECTRODE FOR LITHIUM ION SECONDARY BATTERY, MANUFACTURING METHOD THEREOF, AND LITHIUM ION SECONDARY BATTERY USING THE ELECTRODE
JP6136809B2 (en) Positive electrode for lithium ion secondary battery and lithium ion secondary battery
JP5534377B2 (en) Positive electrode active material for lithium ion secondary battery and lithium ion secondary battery having the same
JP5482858B2 (en) Lithium ion secondary battery
JP6300021B2 (en) Positive electrode for lithium ion secondary battery and lithium ion secondary battery
JP6120087B2 (en) Method for forming protective layer on current collector body, current collector for lithium ion secondary battery, positive electrode for lithium ion secondary battery, and lithium ion secondary battery
JP2014149989A (en) Active material for lithium ion secondary battery, electrode for lithium ion secondary battery including the same, and lithium ion secondary battery
JP5557067B1 (en) Positive electrode for lithium ion secondary battery and lithium ion secondary battery
JP6056685B2 (en) Method for treating positive electrode active material for lithium ion secondary battery, positive electrode active material for lithium ion secondary battery, and lithium ion secondary battery
JP6016029B2 (en) Positive electrode for lithium ion secondary battery and lithium ion secondary battery
JP6011634B2 (en) Nonaqueous electrolyte secondary battery
JP5862490B2 (en) Lithium ion secondary battery
JP6048751B2 (en) Current collector for lithium ion secondary battery, electrode for lithium ion secondary battery, and lithium ion secondary battery
JP5610031B1 (en) Positive electrode for lithium ion secondary battery and lithium ion secondary battery
JP6202191B2 (en) A positive electrode active material layer having a first positive electrode active material and a second positive electrode active material, and a method for producing a positive electrode comprising the positive electrode active material layer
JP2017027772A (en) Lithium ion secondary battery and method for manufacturing the same
JP5999430B2 (en) Positive electrode active material for lithium ion secondary battery and lithium ion secondary battery having the same
JP6048312B2 (en) Negative electrode for lithium ion secondary battery and lithium ion secondary battery
JP6124076B2 (en) Method for forming protective layer on aluminum foil, current collector for lithium ion secondary battery, and lithium ion secondary battery
JP5857943B2 (en) Nonaqueous electrolyte secondary battery

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 14741036

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 14741036

Country of ref document: EP

Kind code of ref document: A1