CN111837263A - Lithium ion secondary battery and method for operating the same - Google Patents

Lithium ion secondary battery and method for operating the same Download PDF

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Publication number
CN111837263A
CN111837263A CN201980018065.XA CN201980018065A CN111837263A CN 111837263 A CN111837263 A CN 111837263A CN 201980018065 A CN201980018065 A CN 201980018065A CN 111837263 A CN111837263 A CN 111837263A
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sulfur
negative electrode
mass
modified polyacrylonitrile
secondary battery
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搅上健二
青山洋平
竹之内宏美
野原雄太
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Adeka Corp
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Adeka Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/137—Electrodes based on electro-active polymers
    • 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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • 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
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/44—Methods for charging or discharging
    • 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
    • H01M4/60—Selection of substances as active materials, active masses, active liquids of organic compounds
    • 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
    • H01M4/60—Selection of substances as active materials, active masses, active liquids of organic compounds
    • H01M4/602—Polymers
    • H01M4/604—Polymers containing aliphatic main chain polymers
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • 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

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Battery Electrode And Active Subsutance (AREA)
  • Secondary Cells (AREA)

Abstract

The present invention is a lithium ion secondary battery having a negative electrode using sulfur-modified polyacrylonitrile as an active material, wherein the negative electrode has a lower charge limit potential of 0.1V (vs. Li/Li)+) Above and below 1.0V (vs. Li/Li)+). The present invention also provides a method for operating a lithium ion secondary battery having a negative electrode containing sulfur-modified polyacrylonitrile as an active material, wherein the negative electrode has a lower charge limit potentialSet to at least 0.1V (vs. Li/Li)+) And less than 1.0V (vs. Li/Li)+). The sulfur content of the sulfur-modified polyacrylonitrile is preferably 25 to 60 mass%.

Description

Lithium ion secondary battery and method for operating the same
Technical Field
The invention relates to a lithium ion secondary battery using sulfur-modified polyacrylonitrile as an electrode active substance and a working method thereof.
Background
Nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries are small and lightweight, have high energy density, and can be repeatedly charged and discharged, and are widely used as power sources for portable electronic devices such as portable personal computers, camcorders, and information terminals. In view of environmental problems, electric vehicles using nonaqueous electrolyte secondary batteries and hybrid vehicles using electric power as a part of motive power have been put to practical use. Therefore, in recent years, further performance improvement of secondary batteries has been demanded.
The characteristics of nonaqueous electrolyte secondary batteries depend on electrodes, separators, electrolytes, and the like as their constituent members, and research and development of each constituent member is being actively performed. In the electrode, an electrode active material is important as well as a binder, a current collector, and the like, and research and development of the electrode active material are actively performed.
Sulfur-modified polyacrylonitrile obtained by heat-treating a mixture of polyacrylonitrile and sulfur in a non-oxidizing atmosphere is known as an electrode active material having a large charge/discharge capacity and little decrease in charge/discharge capacity (hereinafter, sometimes referred to as cycle characteristics) due to repetition of charge/discharge (see, for example, patent documents 1 to 3). Sulfur-modified polyacrylonitrile is used as an active material for a positive electrode, but has also been studied as an active material for a negative electrode (see, for example, patent document 3).
Documents of the prior art
Patent document
Patent document 1: US2011/200875A1
Patent document 2: US2013/029222A1
Patent document 3: US2014/134485A1
Disclosure of Invention
Problems to be solved by the invention
If the lower limit charge potential of the negative electrode active material is low, the charge/discharge capacity can be increased, but if the lower limit charge potential is too low, there is a risk that lithium metal is precipitated in the negative electrode. Therefore, for example, in patent document 3, the average potential at the time of Li insertion of sulfur-modified polyacrylonitrile is set to 1.8V (Li basis), that is, 1.8V (vs. Li/Li)+) Therefore, the lower charge limit potential of the negative electrode having sulfur-modified polyacrylonitrile is assumed to be 1.0V (vs. Li/Li)+) And the left and right (see patent document 3).
A lithium ion secondary battery having high output and excellent cycle characteristics, and further having light weight and small size is required for a nonaqueous electrolyte secondary battery, particularly a nonaqueous electrolyte secondary battery used for an electric vehicle or a hybrid vehicle.
Means for solving the problems
The present inventors have conducted intensive studies and, as a result, have found that: in a non-aqueous electrolyte secondary battery using sulfur-modified polyacrylonitrile as a negative electrode active material, even if the charge lower limit potential of the negative electrode is made lower than 1.0V (vs. Li/Li)+) The deterioration of battery performance was low, and the battery was able to be charged and discharged safely, and the deterioration of cycle characteristics was low, thereby completing the present invention. That is, the present invention is a lithium ion secondary battery having a negative electrode containing sulfur-modified polyacrylonitrile as an active material, wherein the negative electrode has a lower charge limit potential of 0.1V (vs. Li/Li)+) Above and below 1.0V (vs. Li/Li)+)。
The present invention also provides a method for operating a lithium ion secondary battery having a negative electrode containing sulfur-modified polyacrylonitrile as an active material, wherein the lower charge limit potential of the negative electrode is set to 0.1V (vs+) Above and below 1.0V (vs. Li/Li)+)。
Detailed Description
In the present invention, the lower limit potential of charge of the negative electrode of the lithium ion secondary battery is set to 0.1V (vs. Li/Li)+) Above andless than 1.0V (vs. Li/Li)+) This has one of the features. In the present invention, the unit V (vs. Li/Li)+) The potential of the lithium metal reference. The lower charge limit potential of the negative electrode is preferably low but is less than 0.1V (vs. Li/Li)+) In the case of (2), the degradation of the cycle characteristics of the battery becomes large. The lower charge limit potential of the negative electrode in the present invention is preferably 0.15V (vs. Li/Li)+) Above and 0.9V (vs. Li/Li)+) Hereinafter, 0.17V (vs. Li/Li) is more preferable+) Above and 0.85V (vs. Li/Li)+) Particularly preferably 0.25V (vs. Li/Li)+) Above and 0.8V (vs. Li/Li)+) The following. In order to set the lower limit charge potential of the negative electrode within the above range, for example, the weight of the active material per unit area (mg/cm) of the positive electrode and the negative electrode may be adjusted by changing the electrode coating thickness or the like2) The ratio of (a) to (b) is not particularly limited. The lower the ratio of the active material weight per unit area of the negative electrode relative to the positive electrode, the lower the charge lower-limit potential of the negative electrode.
The charge/discharge capacity of the negative electrode using sulfur-modified polyacrylonitrile as an active material is somewhat different depending on the sulfur content of sulfur-modified polyacrylonitrile, but the lower limit potential to charge is 1.0V (vs+) In the case of (2), 0.5V (vs. Li/Li)+) The increase is about 30 to 50 percent and is 0.2V (vs. Li/Li)+) The amount of the sulfur-modified polyacrylonitrile can be increased by about 60 to 80 percent, and the usage amount of the sulfur-modified polyacrylonitrile can be reduced by the increased amount. By reducing the charge lower limit potential and reducing the active material of the negative electrode, the lithium ion secondary battery can be reduced in weight and size. In addition, 1.0V (vs. Li/Li) is used+) The above lower limit charge potential is set to be lower than 1.0V (vs. Li/Li) using the lower limit charge potential+) The lithium ion secondary battery of the above design is not preferable because sufficient charge/discharge capacity cannot be obtained.
The sulfur-modified polyacrylonitrile is a compound obtained by heat-treating polyacrylonitrile and elemental sulfur in a non-oxidizing atmosphere. Polyacrylonitrile can also be a copolymer of acrylonitrile with other monomers such as acrylic acid, vinyl acetate, N-vinylformamide, N-N' methylenebis (acrylamide). Among them, since the battery performance is lowered as the content of acrylonitrile is lowered, in the case of a copolymer of acrylonitrile and another monomer, the content of acrylonitrile in the copolymer is preferably 90 mass% or more. The sulfur content of the sulfur-modified polyacrylonitrile is preferably 25 to 60 mass%, more preferably 27 to 50 mass%, and most preferably 30 to 45 mass% in terms of obtaining a large charge/discharge capacity and reducing a reduction in cycle characteristics in the operation method of the present invention. The sulfur content of the sulfur-modified polyacrylonitrile may be calculated by performing elemental analysis using, for example, a CHN analyzer capable of analyzing sulfur and oxygen.
The ratio of polyacrylonitrile to elemental sulfur in the heating treatment is preferably 100 to 1500 parts by mass, and more preferably 150 to 1000 parts by mass, per 100 parts by mass of polyacrylonitrile. The temperature of the heat treatment is preferably 250 to 550 ℃, and more preferably 350 to 450 ℃. The unreacted elemental sulfur is a factor that degrades the cycle characteristics of the secondary battery, and therefore is preferably removed by, for example, heating, solvent washing, or the like.
When the sulfur-modified polyacrylonitrile of the present invention is used as an electrode active material for an electrode of a secondary battery, for example, the average particle diameter is preferably 0.5 to 100 μm. The average particle size is a 50% particle size measured by a laser diffraction light scattering method. The particle diameter is a volume-based diameter, and the diameter of the secondary particles is measured by a laser diffraction light scattering method. In order to make the average particle size of the sulfur-modified polyacrylonitrile of the present invention smaller than 0.5 μm, a great deal of labor is required for pulverization and the like, but it is desired that a smooth electrode mixture layer is easily obtained by setting the average particle size to 100 μm or less without further improvement in battery performance. The average particle diameter of the sulfur-modified polyacrylonitrile of the present invention is preferably 0.5 to 100. mu.m, more preferably 1 to 50 μm, and still more preferably 2 to 30 μm.
Hereinafter, a preferred configuration of an electrode using sulfur-modified polyacrylonitrile as an electrode active material and a preferred manufacturing method thereof will be described. The electrode is formed by forming an electrode mixture layer having sulfur-modified polyacrylonitrile on a current collector. The electrode material mixture layer is formed by, for example, applying a slurry prepared by adding sulfur-modified polyacrylonitrile, a binder, and a conductive assistant to a solvent on a current collector and drying the slurry.
As the binder for the electrode, known ones can be used, and examples thereof include styrene-butadiene rubber, polyethylene, polypropylene, polyamide, polyamideimide, polyimide, polyacrylonitrile, polyurethane, polyvinylidene fluoride, polytetrafluoroethylene, ethylene-propylene-diene rubber, fluororubber, styrene-acrylate copolymer, ethylene-vinyl alcohol copolymer, acrylonitrile butadiene rubber, styrene-isoprene rubber, polymethyl methacrylate, polyacrylate, polyvinyl alcohol, polyvinyl ether, carboxymethyl cellulose, sodium carboxymethyl cellulose, methyl cellulose, cellulose nanofiber, polyethylene oxide, starch, polyvinyl pyrrolidone, polyvinyl chloride, polyacrylic acid, and the like.
The binder is preferably an aqueous binder, and more preferably styrene-butadiene rubber, sodium carboxymethylcellulose, or polyacrylic acid, because it has a low environmental load and is less likely to cause elution of sulfur. Only 1 kind of the binder may be used, or 2 or more kinds may be used in combination. The content of the binder in the slurry is preferably 1 to 30 parts by mass, and more preferably 1.5 to 20 parts by mass, per 100 parts by mass of the sulfur-modified polyacrylonitrile of the present invention.
As the conductive assistant, those known as conductive assistants for electrodes can be used, and specific examples thereof include Carbon materials such as natural graphite, artificial graphite, Carbon black, ketjen black, acetylene black, channel black, furnace black, lamp black, thermal black, Carbon nanotubes, Vapor phase Carbon fibers (VGCF), exfoliated graphite, graphene, fullerene, and needle coke; metal powders such as aluminum powder, nickel powder, titanium powder, and the like; conductive metal oxides such as zinc oxide and titanium oxide; la2S3、Sm2S3、Ce2S3、TiS2And the like. The average particle diameter of the conductive auxiliary is preferably 0.0001 to 100. mu.m, and more preferably 0.01 to 50 μm. The content of the conductive aid in the slurry is relative to the sulfur-modified polyacrylonitrile 10 of the invention0 part by mass is usually 0.1 to 50 parts by mass, preferably 1 to 30 parts by mass, and more preferably 2 to 20 parts by mass.
Examples of the solvent used for preparing the slurry include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, 1, 2-dimethoxyethane, 1, 2-diethoxyethane, acetonitrile, propionitrile, tetrahydrofuran, 2-methyltetrahydrofuran, dioxane, 1, 3-dioxolane, nitromethane, N-methylpyrrolidone, N-dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N-dimethylaminopropylamine, polyethylene oxide, tetrahydrofuran, dimethyl sulfoxide, sulfolane, γ -butyrolactone, water, and alcohol. The amount of the solvent to be used may be adjusted in accordance with the method of applying the slurry, and in the case of the doctor blade method, for example, the amount is preferably 20 to 300 parts by mass, and more preferably 30 to 200 parts by mass, based on 100 parts by mass of the total amount of the sulfur-modified polyacrylonitrile, the binder, and the conductive assistant.
The slurry sometimes additionally contains other ingredients. Examples of the other components include a viscosity modifier, a reinforcing material, and an antioxidant.
The method for preparing the slurry is not particularly limited, and for example, a usual ball mill, sand mill, bead mill, pigment dispersing machine, beating machine, ultrasonic dispersing machine, homogenizer, rotation and revolution mixer, planetary mixer, fillmix, high-speed dispersing apparatus (JET mill), and the like can be used.
As the current collector, a conductive material such as titanium, a titanium alloy, aluminum, an aluminum alloy, copper, nickel, stainless steel, or nickel-plated steel is used. These conductive materials are sometimes surface coated with carbon. Examples of the shape of the current collector include foil, plate, and mesh. Among them, aluminum, copper, and stainless steel are preferable from the viewpoint of conductivity and price, and the shape is preferably a foil. The foil is usually 1 to 100 μm thick in the case of foil.
The method for applying the slurry to the current collector is not particularly limited, and various methods such as a die coating method, a comma coating method, a curtain coating method, a spray coating method, a gravure coating method, a kiss coating method, a doctor blade method, a reverse roll method, a brush coating method, and a dipping method can be used. From the viewpoint of obtaining a good surface state of the coating layer by comparing physical properties such as viscosity of the slurry and drying property, a die coating method, a doctor blade method, and a blade coating method are preferable. The coating may be performed on one side or both sides of the current collector, and when the coating is performed on both sides of the current collector, the coating may be performed on one side or both sides of the current collector in a stepwise manner. The coating may be performed continuously or intermittently on the surface of the current collector, or may be performed in a stripe pattern. The thickness of the electrode material mixture layer is usually 1 to 500. mu.m, preferably 1 to 300. mu.m, and more preferably 1 to 150. mu.m. The thickness, length or width of the coating layer may be appropriately determined according to the size of the battery.
The method for drying the slurry applied to the current collector is not particularly limited, and various methods such as drying with warm air, hot air, or low-humidity air, vacuum drying, standing in a heating furnace or the like, and irradiation with far infrared rays, electron beams, or the like can be used. By this drying, volatile components such as a solvent are volatilized from the coating film of the slurry, and an electrode mixture layer is formed on the current collector. After that, the electrode may be subjected to a pressing treatment as necessary. Examples of the pressing method include a die pressing method and a roll pressing method.
When the amount of the sulfur-modified polyacrylonitrile in the electrode mixture layer of the negative electrode is set to a certain amount or more, a sufficient charge/discharge capacity is easily obtained, and when the amount of the sulfur-modified polyacrylonitrile is set to a certain amount or less, conductivity and adhesion to the current collector are easily made sufficient. From these points of view, the content of the sulfur-modified polyacrylonitrile in the electrode mixture layer of the negative electrode is preferably 30 to 99.5 mass%, more preferably 40 to 99 mass%, and most preferably 50 to 98 mass%.
The lithium ion secondary battery comprises a negative electrode containing sulfur-modified polyacrylonitrile as an active material, a positive electrode, and a nonaqueous electrolyte, and a separator is provided between the positive electrode and the negative electrode as required. The positive electrode may be an electrode having a known active material as an active material of the positive electrode.
Examples of the known positive electrode active material include a lithium transition metal composite oxide, a lithium-containing transition metal phosphate compound, and a lithium-containing silicate compound. As the transition metal of the lithium transition metal composite oxide, vanadium, titanium, chromium, manganese, iron, cobalt, nickel, copper, and the like are preferable. Specific examples of the lithium transition metal composite oxide include LiCoO2Lithium cobalt composite oxide, LiNiO, etc2Lithium nickel composite oxide and LiMnO2、LiMn2O4、Li2MnO3And lithium manganese complex oxides, and those obtained by substituting a part of transition metal atoms that are the main components of these lithium transition metal complex oxides with another metal such as aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, lithium, nickel, copper, zinc, magnesium, gallium, or zirconium. Specific examples of the substituted compound include, for example, Li1.1Mn1.8Mg0.1O4、Li1.1Mn1.85Al0.05O4、LiNi0.5Co0.2Mn0.3O2、LiNi0.8Co0.1Mn0.1O2、LiNi0.5Mn0.5O2、LiNi0.80Co0.17Al0.03O2、LiNi0.80Co0.15Al0.05O2、LiNi1/3Co1/ 3Mn1/3O2、LiNi0.6Co0.2Mn0.2O2、LiMn1.8Al0.2O4、LiMn1.5Ni0.5O4、Li2MnO3-LiMO2(M ═ Co, Ni, Mn) and the like. The transition metal of the lithium-containing transition metal phosphate compound is preferably vanadium, titanium, manganese, iron, cobalt, nickel, or the like, and specific examples thereof include LiFePO4、LiMnxFe1-xPO4And other iron phosphate compounds, LiCoPO4Cobalt phosphate compounds, lithium transition metal phosphate compounds obtained by using aluminum as a part of transition metal atoms mainly composed of these lithium transition metal phosphate compounds,Substituted with other metals such as titanium, vanadium, chromium, manganese, iron, cobalt, lithium, nickel, copper, zinc, magnesium, gallium, zirconium, and niobium, and Li3V2(PO4)3And vanadium phosphate compounds and the like. Examples of the lithium-containing silicate compound include Li2FeSiO4And the like. These may be used alone in 1 kind, or 2 or more kinds may be used in combination.
Examples of the positive electrode structure and the method for producing the same include those obtained by replacing sulfur-modified polyacrylonitrile with the known positive electrode active material in the preferred structure and the preferred method for producing an electrode using sulfur-modified polyacrylonitrile as an electrode active material.
Examples of the nonaqueous electrolyte include a liquid electrolyte obtained by dissolving an electrolyte in an organic solvent, a polymer gel electrolyte obtained by dissolving an electrolyte in an organic solvent and gelling a polymer, a pure polymer electrolyte obtained by dispersing an electrolyte in a polymer without containing an organic solvent, a boron hydride compound, and an inorganic solid electrolyte.
As the electrolyte used in the liquid electrolyte and the polymer gel electrolyte, for example, a conventionally known lithium salt is used, and examples thereof include LiPF6、LiBF4、LiAsF6、LiCF3SO3、LiCF3CO2、LiN(CF3SO2)2、LiN(C2F5SO2)2、LiN(SO2F)2、LiC(CF3SO2)3、LiB(CF3SO3)4、LiB(C2O4)2、LiBF2(C2O4)、LiSbF6、LiSiF5、LiSCN、LiClO4、LiCl、LiF、LiBr、LiI、LiAlF4、LiAlCl4、LiPO2F2And derivatives thereof, among them, those selected from the group consisting of LiPF are preferably used6、LiBF4、LiClO4、LiAsF6、LiCF3SO3、LiN(CF3SO2)2、LiN(C2F5SO2)2、LiN(SO2F)2And LiC (CF)3SO2)3And LiCF3SO3Derivative of (2), and LiC (CF)3SO2)31 or more of the group consisting of the derivatives of (1). The content of the electrolyte in the liquid electrolyte and the polymer gel electrolyte is preferably 0.5 to 7mol/L, and more preferably 0.8 to 1.8 mol/L.
Examples of the electrolyte used for a pure polymer electrolyte include LiN (CF)3SO2)2、LiN(C2F5SO2)2、LiN(SO2F)2、LiC(CF3SO2)3、LiB(CF3SO3)4、LiB(C2O4)2. Examples of the boron hydride compound include LiBH4-LiI、LiBH4-P2S5。
As the inorganic solid electrolyte, Li may be mentioned1+xAxB2-y(PO4)3(x＝Al、Ge、Sn、Hf、Zr、Sc、Y；B＝Ti、Ge、Zn；0<x<0.5)、LiMPO4(M＝Mn、Fe、Co、Ni)、Li3PO4Phosphoric acid-based materials; li3XO4(X＝As、V)、Li3+xAxB1-xO4(A＝Si、Ge、Ti；B＝P、As、V；0<x<0.6)、Li4+xAxSi1-xO4(A＝B、Al、Ga、Cr、Fe；0<x<0.4)(A＝Ni、Co；0<x<0.1)、Li4-3yAlySiO4(0<y<0.06)、Li4-2yZnyGeO4(0<y<0.25)、LiAlO2、Li2BO4、Li4XO4(X ═ Si, Ge, Ti), lithium titanate (LiTiO)2、LiTi2O4、Li4TiO4、Li2TiO3、Li2Ti3O7、Li4Ti5O12) And lithium composite oxides; LiBr, LiF, LiCl, LiPF6、LiBF4Etc. containing lithium and halogenA compound; LiPON, LiN (SO)2CF3)2、LiN(SO2C2F5)2、Li3N、LiN(SO2C3F7)2And the like lithium and nitrogen containing compounds; la0.55Li0.35TiO3Crystals having a perovskite structure having lithium ion conductivity; li7-La3Zr2O13And crystals having a garnet structure; 50Li4SiO4·50Li3BO3、90Li3BO3·10Li2SO4Glass and the like; 70Li2S·30P2S5、75Li2S·25P2S5、Li6PS5Cl、Li10GeP2S12、Li3.25Ge0.25P0.75S430Li, and the like of lithium-phosphorus sulfide-based crystals2S·26B2S3·44LiI、63Li2S·36SiS2·1Li3PO4、57Li2S·38SiS2·5Li4SiO4、70Li2S·50GeS2、50Li2S·50GeS2Lithium-phosphorus sulfide-based glasses; li7P3S11、Li3.25P0.95S4、Li10GeP2S12、Li9.6P3S12、Li9.54Si1.74P1.44S11.7Cl0.3Etc. glass ceramics, etc.
As the organic solvent used for preparing the liquid nonaqueous electrolyte in the present invention, 1 kind or 2 or more kinds of organic solvents generally used for the liquid nonaqueous electrolyte can be used in combination. Specific examples thereof include saturated cyclic carbonate compounds, saturated cyclic ester compounds, sulfoxide compounds, sulfone compounds, amide compounds, saturated chain carbonate compounds, chain ether compounds, cyclic ether compounds, saturated chain ester compounds, and the like.
Among the above organic solvents, a saturated cyclic carbonate compound, a saturated cyclic ester compound, a sulfoxide compound, a sulfone compound, and an amide compound have a high relative dielectric constant, and therefore, they exert an effect of increasing the dielectric constant of the nonaqueous electrolyte, and a saturated cyclic carbonate compound is particularly preferable. Examples of the saturated cyclic carbonate compound include ethylene carbonate, 1, 2-propylene carbonate, 1, 3-propylene carbonate, 1, 2-butylene carbonate, 1, 3-butylene carbonate, and 1, 1-dimethylethylene carbonate. Examples of the saturated cyclic ester compound include γ -butyrolactone, γ -valerolactone, γ -caprolactone, -caprolactone and-octalactone. Examples of the sulfoxide compound include dimethyl sulfoxide, diethyl sulfoxide, dipropyl sulfoxide, diphenyl sulfoxide, and thiophene. Examples of the sulfone compound include dimethyl sulfone, diethyl sulfone, dipropyl sulfone, diphenyl sulfone, sulfolane (also referred to as tetramethylene sulfone), 3-methylsulfolane, 3, 4-dimethylsulfolane, 3, 4-diphenylmethylsulfolane, sulfolene, 3-methylsulfolane, 3-ethylsulfolene and 3-bromomethylsulfolane, and sulfolane and tetramethylsulfolane are preferable. Examples of the amide compound include N-methylpyrrolidone, dimethylformamide, and dimethylacetamide.
Among the above organic solvents, a saturated chain carbonate compound, a chain ether compound, a cyclic ether compound, and a saturated chain ester compound can reduce the viscosity of the nonaqueous electrolyte, can improve the mobility of electrolyte ions, and the like, and can improve battery characteristics such as output density and the like. In addition, since the viscosity is low, the performance of the nonaqueous electrolyte at low temperature can be improved, and a saturated chain carbonate compound is particularly preferable. Examples of the saturated chain carbonate compound include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethyl butyl carbonate, methyl t-butyl carbonate, diisopropyl carbonate, t-butyl propyl carbonate, and the like. Examples of the chain ether compound or cyclic ether compound include dimethoxyethane, ethoxymethoxyethane, diethoxyethane, tetrahydrofuran, dioxolane, dioxane, 1, 2-bis (methoxycarbonyloxy) ethane, 1, 2-bis (ethoxycarbonyloxy) propane, ethylene glycol bis (trifluoroethyl) ether, propylene glycol bis (trifluoroethyl) ether, ethylene glycol bis (trifluoromethyl) ether, diethylene glycol bis (trifluoroethyl) ether, and dioxolane is preferable.
The saturated chain ester compound is preferably a monoester compound or a diester compound having 2 to 8 carbon atoms in total in the molecule, and specific examples of the compound include methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, isobutyl acetate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl pivalate, ethyl pivalate, methyl malonate, ethyl malonate, methyl succinate, ethyl succinate, methyl 3-methoxypropionate, ethyl 3-methoxypropionate, ethylene glycol diacetyl, and propylene glycol diacetyl, and methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, isobutyl acetate, butyl acetate, methyl propionate, and ethyl propionate are preferable.
As the organic solvent used for preparing the nonaqueous electrolyte, for example, acetonitrile, propionitrile, nitromethane, a derivative thereof, and various ionic liquids may be used.
Examples of the polymer used in the polymer gel electrolyte include polyethylene oxide, polypropylene oxide, polyvinyl chloride, polyacrylonitrile, polymethyl methacrylate, polyethylene, polyvinylidene fluoride, polyhexafluoropropylene, and the like. Examples of the polymer used for the pure polymer electrolyte include polyethylene oxide, polypropylene oxide, and polystyrene sulfonic acid. The mixing ratio in the gel electrolyte and the method of compounding are not particularly limited, and a known mixing ratio or a known compounding method in the art may be used.
The nonaqueous electrolyte may contain other known additives such as an electrode coating film forming agent, an antioxidant, a flame retardant, and an overcharge inhibitor in order to improve the battery life, safety, and the like. When other additives are used, the amount is usually 0.01 to 10 parts by mass, preferably 0.1 to 5 parts by mass, based on the whole nonaqueous electrolyte.
By applying the lithium ion secondary battery and the working method, the charge and discharge capacity of the negative electrode using the sulfur-modified polyacrylonitrile as the active material can be increased, and the usage amount of the sulfur-modified polyacrylonitrile can be reduced. Further, the battery voltage can be increased, and the lithium ion secondary battery can be reduced in weight and size.
Examples
The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to the following examples and the like. In the examples, "part" and "%" are based on mass unless otherwise specified.
[ production example 1]
10 parts by mass of polyacrylonitrile powder (manufactured by Sigma-Aldrich, with an average particle size of 200 μm) and 30 parts by mass of sulfur powder (manufactured by Sigma-Aldrich, with an average particle size of 200 μm) were mixed using a mortar. For the sulfur modification of polyacrylonitrile, the reaction apparatus according to the example of japanese patent laid-open publication No. 2013-054957 was used. The mixture was placed in a cylindrical glass bottle similar to that described in examples of Japanese patent application laid-open No. 2013-054957, and the lower part of the glass bottle was placed in a crucible-type electric furnace and heated at 400 ℃ for 1 hour while removing hydrogen sulfide generated under a nitrogen stream. After cooling, the product was placed in a glass tube oven and elemental sulfur was removed by vacuum suction and heating at 250 ℃ for 3 hours. The obtained sulfur-modified polyacrylonitrile was pulverized with a mortar until the average particle diameter became 10 μm, to obtain sulfur-modified polyacrylonitrile powder PANS 1. The sulfur content of PANS1 was 38% by mass.
[ production example 2]
Sulfur-modified polyacrylonitrile powder PANS2 was obtained in the same manner as in production example 1, except that the temperature for removing elemental sulfur was changed from 250 ℃ to 200 ℃. The sulfur content of the PANS2 was 55% by mass. It is considered that the conditions for removing elemental sulfur in production example 2 are the same as those described in patent document 3, and the sulfur content of PANS2 is the same as that of sulfur-modified polyacrylonitrile described in patent document 3.
[ examples 1 to 6 and comparative examples 1 to 4 ]
[ production of negative electrodes 1 to 10 ]
Slurry was prepared by dispersing 92.0 parts by mass of PANS1 or PANS2 (see Table 1) as an electrode active material, 3.5 parts by mass of acetylene black (manufactured by the electrochemical industry) as a conductive aid, 1.5 parts by mass of carbon nanotubes (manufactured by SHOWA DENKO K.K., trade name VGCF), 1.5 parts by mass of styrene-butadiene rubber (40% by mass aqueous dispersion, manufactured by Zeon Corporation, Japan) as a binder, 1.5 parts by mass of sodium carboxymethylcellulose (manufactured by Daicel Fine Chem Ltd.), and 100 parts by mass of water using a rotation and revolution mixer. This slurry composition was applied to a current collector of a stainless steel foil (thickness: 10 μm) by a doctor blade method so that the thickness of the electrode material mixture layer became the value shown in table 1 below, and dried at 90 ℃ for 3 hours. Then, the electrode was cut into a predetermined size, and vacuum-dried at 120 ℃ for 2 hours to prepare a disk-shaped electrode.
[ Table 1]
Negative electrode active material Thickness of negative electrode mixture layer
Negative electrode 1 PANS1 60μm
Negative electrode 2 PANS2 60μm
Negative electrode 3 PANS1 51μm
Negative electrode 4 PANS2 51μm
Negative electrode 5 PANS1 41μm
Negative electrode 6 PANS2 41μm
Negative electrode 7 PANS1 34μm
Negative electrode 8 PANS2 34μm
Negative electrode 9 PANS1 31μm
Negative electrode 10 PANS2 31μm
[ production of Positive electrode ]
LiNi as a positive electrode active material in an amount of 90 parts by mass1/3Co1/3Mn1/3O2(NCM, manufactured by Nippon chemical industry Co., Ltd.), acetylene black (manufactured by Electrical chemical industry Co., Ltd.) as a conductive aid 5 parts by mass, polyvinylidene fluoride (manufactured by Kureha Corporation) as a binder 5 parts by mass, and a solvent100 parts by mass of N-methylpyrrolidone (A) was dispersed using a rotation/revolution mixer to prepare a slurry. The slurry composition was applied to a current collector of aluminum foil (20 μm in thickness) by a doctor blade method so that the thickness of the electrode material mixture layer became 62 μm, and dried at 90 ℃ for 3 hours. Then, the electrode was cut into a predetermined size, and vacuum-dried at 120 ℃ for 2 hours to prepare a disk-shaped positive electrode. Regarding the positive electrode capacity, when the charge lower limit potential of the negative electrode is any one, the charge upper limit potential of the positive electrode is set to 4.2V (vs. Li/Li)+)。
[ preparation of nonaqueous electrolyte ]
LiPF is dissolved in a mixed solvent of 50 vol% of ethylene carbonate and 50 vol% of diethyl carbonate at a concentration of 1.0mol/L6An electrolyte solution is prepared.
[ Assembly of Battery ]
Negative electrodes 1 to 10 each having PANS1 or 2 as an active material and a positive electrode each having NCM as an active material are held in a case with a separator (product name: Celgard 2325 manufactured by Celgard corporation) interposed therebetween. Then, the nonaqueous electrolyte prepared above was injected into a case, and the case was sealed and sealed to prepare batteries 1 to 10 as nonaqueous electrolyte secondary batteries (coin-shaped batteries having a diameter of 20mm and a thickness of 3.2 mm). In order to confirm the lower potential at the time of initial charging of the negative electrodes 1 to 10, a tripolar cell set (made by TOYO SYSTEM co., ltd.) was used to fabricate a tripolar cell composed of the negative electrodes 1 to 10, an NCM positive electrode, a glass filter separator, a lithium metal reference electrode, and the nonaqueous electrolyte prepared previously.
(Charge and discharge test method)
The tripolar cell was placed in a thermostatic bath at 25 ℃ and charged at a charging rate of 0.1C until the potential of the NCM positive electrode became 4.2V (vs. Li/Li)+) The potentials of the negative electrodes 1 to 10 at this time were confirmed to be the values shown in Table 2.
The nonaqueous electrolyte secondary battery was placed in a thermostatic bath at 25 ℃ and charged and discharged 50 times at a charge rate of 0.1C until the lower limit charge potential of the negative electrode became the value shown in table 2 and at a discharge rate of 0.1C until the battery voltage became 0.8V. Table 2 shows the discharge capacity per unit weight of the PANS negative electrode at the 10 th cycle of charge and discharge, and the ratio of the discharge capacity per unit weight of the PANS negative electrode at the 50 th cycle of charge and discharge to the discharge capacity per unit weight of the PANS negative electrode at the 10 th cycle of charge and discharge. A larger value of this ratio indicates more excellent cycle characteristics.
[ Table 2]
Figure BDA0002672647250000121
From Table 2, the lower limit potential of charge according to the negative electrode was 0.1V (vs. Li/Li)+) Above and below 1.0V (vs. Li/Li)+) The lithium ion secondary batteries of the respective examples of (1) were excellent in both the magnitude of the discharge capacity and the cycle characteristics of the lithium ion secondary batteries. In contrast, the lower limit potential of charge of the negative electrode was set to 1.0V (vs. Li/Li)+) Comparative example 1 is inferior in discharge capacity to examples 1,3 and 5 using PANS having the same sulfur content, and comparative example 3, in which the lower limit charge potential of the negative electrode is set to less than 0.1V, is inferior in cycle characteristics to examples 1,3 and 5. Comparative examples 2 and 4 are similar to examples 2, 4 and 6.
Industrial applicability
According to the present invention, in a lithium ion secondary battery having a negative electrode containing sulfur-modified polyacrylonitrile as an active material, the lower charge limit potential of the negative electrode is set to 0.1V (vs+) Above and below 1.0V (vs. Li/Li)+) Accordingly, the charge/discharge capacity per unit active material and the battery voltage are increased, and the amount of the active material used can be reduced. This makes it possible to reduce the weight and size of the lithium ion secondary battery.

Claims (4)

1. A lithium ion secondary battery having a negative electrode containing sulfur-modified polyacrylonitrile as an active material, wherein the negative electrode has a lower charge limit potential of 0.1V (vs. Li/Li)+) Above and below 1.0V (vs. Li/Li)+)。
2. The lithium ion secondary battery according to claim 1, wherein the sulfur-modified polyacrylonitrile has a sulfur content of 25 to 60 mass%.
3. A method for operating a lithium ion secondary battery having a negative electrode containing sulfur-modified polyacrylonitrile as an active material, wherein the lower charge limit potential of the negative electrode is set to 0.1V (vs. Li/Li)+) Above and below 1.0V (vs. Li/Li)+)。
4. The method according to claim 3, wherein the sulfur-modified polyacrylonitrile has a sulfur content of 25 to 60 mass%.
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