Electrode and lithium ion secondary battery

Abstract

Provided is an electrode comprising a current collector with an active substance layer formed thereon, the active substance containing sulfur-modified polyacrylonitrile and lithium titanium oxide, wherein: the average diameter of secondary particles of the sulfur-modified polyacrylonitrile is larger than the average diameter of secondary particles of the lithium titanium oxide; the sulfur-modified polyacrylonitrile content in the active substance layer is 5 mass% to 85 mass%; and the lithium titanium oxide content in the active substance layer is 5 mass% to 85 mass%.

Description

[Technical field]

[0001] The present invention relates to an electrode containing sulfur-modified polyacrylonitrile and lithium titanium oxide as electrode active materials, and a lithium ion secondary battery including the electrode. [Background technology]

[0002] Lithium-ion secondary batteries have higher cell voltages and higher energy densities than conventional nickel-metal hydride secondary batteries. For this reason, they are being applied to electronic devices such as hybrid and electric vehicles, stationary storage batteries, and laptops, in addition to mobile devices such as smartphones. However, there are issues to be addressed, such as higher capacity, higher output, longer life, improved safety, and lower cost, and the development of electrode materials, electrolytes, and separators is being actively pursued.

[0003] For example, Patent Document 1 proposes a lithium ion secondary battery using at least one selected from the group consisting of lithium nickel cobalt manganese composite oxide, spinel-type lithium manganese nickel composite oxide, lithium phosphate oxide having an olivine structure, lithium cobalt oxide, lithium nickel cobalt composite oxide, and lithium manganese composite oxide for the positive electrode, and using lithium titanium oxide for the negative electrode.

[0004] Patent Document 2 discloses a lithium ion secondary battery that uses lithium iron phosphate for the positive electrode and a carbon-coated LTO electrode for the negative electrode (an electrode using lithium titanium oxide particles in which polyacrylonitrile is formed on the surface and inside of the particles by emulsion polymerization of acrylonitrile monomer, and then the surface of the lithium titanium oxide particles is coated with carbon by carbonization).

[0005] Patent Document 3 discloses a lithium ion secondary battery using sulfur-modified polyacrylonitrile for the positive electrode and metallic lithium foil for the negative electrode. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 3769291 [Patent Document 2] Special Publication No. 2019-521488 [Patent Document 3] International Publication No. 2010 / 044437 Summary of the Invention [Problem to be solved by the invention]

[0007] Conventional lithium ion secondary batteries have a problem that the chargeable and dischargeable electric capacity decreases when they are charged and discharged at high speed. Therefore, the present invention aims to provide an electrode that has a high electric capacity during high speed charging and discharging and also has excellent high temperature stability. Another aim of the present invention is to provide a lithium ion secondary battery that includes the electrode as a positive electrode or a negative electrode. [Means for solving the problem]

[0008] As a result of intensive research, the inventors have found that the above-mentioned problems can be solved by providing an active material layer containing sulfur-modified polyacrylonitrile and lithium titanium oxide in specific ratios whose average secondary particle diameters satisfy a specific relationship, and have thus completed the present invention.

[0009] That is, the present invention is an electrode having an active material layer containing sulfur-modified polyacrylonitrile and lithium titanium oxide formed on a current collector, wherein the average secondary particle diameter of the sulfur-modified polyacrylonitrile is larger than the average secondary particle diameter of the lithium titanium oxide, the content of the sulfur-modified polyacrylonitrile in the active material layer is 5% by mass to 85% by mass, and the content of the lithium titanium oxide in the active material layer is 5% by mass to 85% by mass.

[0010] In the electrode of the present invention, the average secondary particle size of the sulfur-modified polyacrylonitrile is preferably 0.1 μm to 50 μm.

[0011] In the electrode of the present invention, the average secondary particle size of the lithium titanium oxide is preferably 0.05 μm to 30 μm.

[0012] The present invention also relates to a lithium ion secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte containing a lithium salt, in which the positive electrode or the negative electrode is the above-mentioned electrode.

[0013] In the lithium ion secondary battery of the present invention, the nonaqueous electrolyte containing a lithium salt is preferably a liquid nonaqueous electrolyte, a polymer gel nonaqueous electrolyte, a polymer nonaqueous electrolyte, a complex hydride-based solid electrolyte, or an inorganic solid electrolyte.

[0014] In the lithium ion secondary battery of the present invention, the non-aqueous electrolyte containing a lithium salt is a liquid non-aqueous electrolyte, and the liquid non-aqueous electrolyte preferably contains a cyclic carbonate compound.

[0015] In the lithium ion secondary battery of the present invention, the liquid nonaqueous electrolyte more preferably further contains a chain carbonate compound.

[0016] In the lithium ion secondary battery of the present invention, the nonaqueous electrolyte containing a lithium salt is an inorganic solid electrolyte, and the inorganic solid electrolyte is preferably a sulfide-based solid electrolyte or an oxide-based solid electrolyte. Effect of the Invention

[0017] According to the present invention, it is possible to provide a lithium ion secondary battery which has a high electric capacity during high-rate charging and discharging and is also excellent in high-temperature stability. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a longitudinal sectional view that illustrates an example of the structure of a coin-type lithium ion secondary battery of the present invention. [Diagram 2] FIG. 1 is a schematic diagram showing a basic configuration of a cylindrical battery of a lithium ion secondary battery of the present invention. [Diagram 3] FIG. 2 is a perspective view showing a cross section of the internal structure of a cylindrical battery of the lithium ion secondary battery of the present invention. [Figure 4] FIG. 2 is an exploded perspective view showing a stacked electrode group inside a laminated battery of the lithium ion secondary battery of the present invention. [Diagram 5] FIG. 1 is an exploded perspective view showing a laminated type battery of a lithium ion secondary battery according to the present invention. [Figure 6] FIG. 1 is an external plan view showing a schematic view of a laminated type lithium ion secondary battery of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, the electrode and lithium ion secondary battery of the present invention will be described in detail based on preferred embodiments.

[0020] The electrode of the present invention is characterized in that an active material layer containing sulfur-modified polyacrylonitrile and lithium titanium oxide is formed on a current collector. <Sulfur-modified polyacrylonitrile> Sulfur-modified polyacrylonitrile (hereinafter sometimes referred to as "SPAN") can be produced by mixing a polyacrylonitrile compound with sulfur and modifying the mixture by heat treatment at 250° C. to 600° C. in a non-oxidizing atmosphere. The non-oxidizing atmosphere refers to an atmosphere having an oxygen concentration of less than 5% by volume, preferably less than 2% by volume, and more preferably substantially free of oxygen, and examples of such an atmosphere include an inert gas atmosphere such as nitrogen, helium, or argon, and a sulfur gas atmosphere. In addition, SPAN may be produced by adding other active materials and conductive assistants when mixing the polyacrylonitrile compound and sulfur.

[0021] The polyacrylonitrile compound may be a homopolymer of acrylonitrile or a copolymer of acrylonitrile and another monomer. If the content of acrylonitrile in the polyacrylonitrile compound is low, the capacity of the battery cannot be increased by the active material, and the battery performance is deteriorated. From this viewpoint, the content of acrylonitrile in the copolymer of acrylonitrile and another monomer is preferably at least 90 mass%, and polyacrylonitrile homopolymer is more preferable. Examples of the other monomer include acrylic acid, vinyl acetate, N-vinylformamide, and N,N'-methylenebis(acrylamide).

[0022] It is preferable that SPAN is pulverized to a desired particle size by a method such as pulverization or granulation. The pulverization may be a dry pulverization carried out in a gas or a wet pulverization carried out in a liquid such as water. Examples of industrial pulverization methods include a ball mill, a roller mill, a turbo mill, a jet mill, a cyclone mill, a hammer mill, a pin mill, a rotary mill, a vibration mill, a planetary mill, an attritor, and a bead mill.

[0023] The pulverized SPAN is preferably further classified. The classification method is not particularly limited, but may be a dry classification method such as gravity classification, inertial classification, or centrifugal classification; a wet classification method such as sedimentation classification, mechanical classification, or hydraulic classification; or a sieve classification method using a sieve net such as a vibrating sieve or an in-plane motion sieve. Among these, the sieve classification method is preferred. By carrying out the pulverization and classification steps, SPAN having a particle size suitable for the electrode of the present invention can be efficiently produced.

[0024] As the SPAN, primary particles, secondary particles which are aggregates of primary particles, or both primary and secondary particles can be used. The average secondary particle diameter (D50) of the SPAN is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less. On the other hand, if the average secondary particle diameter of the SPAN is too small, the handling property deteriorates, and side reactions tend to occur due to an increase in the specific surface area of ​​the particles, which adversely affects the charge and discharge stability of the lithium ion secondary battery. Therefore, the average secondary particle diameter (D50) of the SPAN is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more.

[0025] The average secondary particle size of SPAN is the 50% particle size measured by the laser diffraction light scattering method. In the laser diffraction light scattering method, the particle size is the volume-based diameter, and the secondary particle size of SPAN is measured. When measuring the average secondary particle size of SPAN by the laser diffraction light scattering method, SPAN is dispersed in a dispersion medium such as water or alcohol and then measured.

[0026] In the present invention, the shape of the SPAN may be fibrous. When fibrous SPAN is used, the preferred average fiber diameter is 0.05 μm or more and 10 μm or less. Although a smaller fiber diameter is preferable, it is difficult to obtain industrial products of polyacrylonitrile, which is the raw material of SPAN, having an average fiber diameter of less than 0.05 μm. In addition, when the average fiber diameter is greater than 10 μm, a large charge / discharge capacity may not be obtained. From the viewpoint of obtaining a larger charge / discharge capacity and easy availability, the average fiber diameter of the fibrous SPAN is preferably 0.1 μm to 5 μm, and more preferably 0.15 μm to 2 μm.

[0027] When the aspect ratio of the fibrous SPAN is expressed as the ratio of fiber length / fiber diameter, the average aspect ratio of the fibrous SPAN is preferably 3 or more, more preferably 5 or more. Since a larger aspect ratio leads to a larger charge / discharge capacity, a larger fiber length is preferable, but if the fiber length is too large, the surface of the active material layer containing the SPAN may not be smooth. The average fiber length of the fibrous SPAN is preferably 300 μm or less, more preferably 150 μm or less. From the same viewpoint, the average aspect ratio of the fibrous SPAN is preferably 5000 or less, more preferably 1000 or less. The fiber length and fiber diameter of the fibrous SPAN can be obtained from a scanning electron microscope image (SEM image). The fiber length represents the length of the fiber, and the fiber diameter represents the diameter of the circle when the cross section perpendicular to the longitudinal direction of the fiber is circular, and represents the average of the short diameter and long diameter of the cross section when the cross section is not circular. The fiber diameter of one fibrous SPAN can be measured at any point.

[0028] The average aspect ratio of fibrous SPAN is the calculated value of average fiber length / average fiber diameter, and the average fiber length and average fiber diameter represent the arithmetic average of fiber diameters and fiber lengths measured from SEM images of 10 or more fibrous SPANs.

[0029] The sulfur content in SPAN is preferably from 30% by mass to 45% by mass, and more preferably from 35% by mass to 43% by mass, since large charge / discharge capacity and excellent cycle characteristics can be obtained. In this specification, the sulfur content of SPAN represents a value calculated from the results of elemental analysis using a CHN analyzer capable of analyzing sulfur and oxygen, such as vario MICRO cube manufactured by Elementor.

[0030] In the active material layer containing SPAN and lithium titanium oxide, the SPAN content is in the range of 5% by mass to 85% by mass, preferably in the range of 10% by mass to 80% by mass. If the SPAN content exceeds 85% by mass, the rate characteristics of the lithium ion secondary battery are significantly reduced. On the other hand, if the SPAN content is less than 5% by mass, the discharge capacity during high-speed charging of the lithium ion secondary battery is reduced.

[0031] <Lithium titanium oxide> The lithium titanium oxide may be a compound represented by the following general formula (1). Li a Ti b O c M d (1) (In the formula, M represents one or a mixture of two or more elements selected from the group consisting of Zr, B, Sn, S, Be, Ge, and Zn, and a, b, c, and d represent 0.5≦a≦5, 1≦b≦5, 2≦c≦12, and 0≦d<0.1, respectively.)

[0032] Examples of lithium titanium oxide suitable for the electrode of the present invention include spinel-structure lithium titanium oxide and ramsdellite-structure lithium titanium oxide. The spinel-structure lithium titanium oxide is, for example, Li 4+e Ti 5 O 12 Ramsdellite-structure lithium titanium oxides include, for example, Li 2+e Ti 3 O 7 , Li 1+f Ti 2 O 4 , Li 1.1+f Ti 1.8 O 4 , Li 1.07+f Ti 1.86 O 4 Here, e and f represent -1≦e≦1 and 0≦f≦1, respectively. In the electrode of the present invention, a spinel-structure lithium titanium oxide is preferred because it undergoes little volume change during charging.

[0033] The lithium titanium oxide may be in the form of primary particles, secondary particles which are aggregates of primary particles, or a mixture of primary particles and secondary particles.

[0034] The average primary particle size (D50) of the lithium titanium oxide is preferably 0.01 μm or more and 10 μm or less, and more preferably 0.05 μm or more and 1 μm or less. It is difficult to manufacture lithium titanium oxide having an average primary particle size of less than 0.01 μm. On the other hand, if the average primary particle size of the lithium titanium oxide exceeds 10 μm, the unevenness of the electrode surface increases, the surface area decreases, and the affinity of the electrode with the non-aqueous electrolyte decreases, which may shorten the discharge cycle life.

[0035] The average primary particle size of the lithium titanium oxide is represented by the arithmetic average of the major axes measured for 10 or more lithium titanium oxide particles using SEM images.

[0036] The average secondary particle diameter (D50) of the lithium titanium oxide is preferably 0.05 μm or more and 30 μm or less, more preferably 0.5 μm or more and 10 μm or less. If the average secondary particle diameter of the lithium titanium oxide is less than 0.05 μm, it is difficult to handle, a large amount of binder is required, and the aggregation of the primary particles becomes significant, which may reduce the affinity between the electrode and the non-aqueous electrolyte, increase the resistance at the electrode interface, and deteriorate the output characteristics and charge / discharge cycle characteristics of the lithium ion secondary battery. On the other hand, if the average secondary particle diameter of the lithium titanium oxide exceeds 30 μm, the diffusion resistance increases, which may adversely affect the output characteristics and charge / discharge cycle characteristics. However, in the active material layer of the electrode of the present invention, it is necessary to select SPAN and lithium titanium oxide so that the average secondary particle diameter of SPAN is larger than that of lithium titanium oxide. If the average secondary particle diameter of SPAN is equal to or smaller than that of lithium titanium oxide, high-speed charging and discharging becomes difficult.

[0037] The average secondary particle size of the lithium titanium oxide can be adjusted, for example, by pulverizing the particles using a pulverizer such as a ball mill or a jet mill, granulating the particles, or classifying the particles by sieving or the like.

[0038] The average secondary particle size (D50) of lithium titanium oxide is the 50% particle size measured by a laser diffraction light scattering method, and in the laser diffraction light scattering method, the particle size is a volume-based diameter. When measuring the average secondary particle size of lithium titanium oxide by the laser diffraction light scattering method, the lithium titanium oxide is dispersed in a dispersion medium such as water or alcohol and then measured.

[0039] The specific surface area of ​​lithium titanium oxide is 1 m 2 / g~200m 2 / g is preferred, and 3m 2 / g~50m 2 / g is more preferable. 2 When the specific surface area of ​​the lithium titanium oxide is less than 200 m / g, the lithium ions may not be sufficiently incorporated into the active material layer. 2 If it exceeds 1 / g, the distribution of the non-aqueous electrolyte becomes uneven, which may adversely affect the output characteristics and cycle characteristics of the lithium ion secondary battery.

[0040] In the electrode of the present invention, when at least a part of the surface of the lithium titanium oxide is coated with a carbon material, the electrode resistance can be reduced, so the lithium titanium oxide may be coated with a carbon material. A method for producing the lithium titanium oxide coated with a carbon material includes, for example, mixing the lithium titanium oxide, a precursor of the carbon material, and a dispersion medium such as water, and baking the mixture at 500° C. or higher in an inert atmosphere.

[0041] In the active material layer containing SPAN and lithium titanium oxide, the content of lithium titanium oxide is in the range of 5% by mass to 85% by mass, preferably in the range of 10% by mass to 80% by mass. If the content of lithium titanium oxide is less than 5% by mass, the rate characteristics of the lithium ion secondary battery are significantly reduced. On the other hand, if the content of lithium titanium oxide exceeds 85% by mass, the discharge capacity during high-speed charging of the lithium ion secondary battery is reduced.

[0042] A lithium ion secondary battery in which the nonaqueous electrolyte containing a lithium salt is a liquid nonaqueous electrolyte or a polymer gel nonaqueous electrolyte is a liquid battery. The active material layer in the electrode of the liquid battery refers to an electrode mixture layer obtained by volatilizing volatile components such as a solvent from a coating film formed by applying an electrode mixture paste containing an active material, a binder, and a conductive assistant onto a current collector.

[0043] A lithium ion secondary battery in which the non-aqueous electrolyte containing a lithium salt is a polymer non-aqueous electrolyte, a complex hydride solid electrolyte, or an inorganic solid electrolyte is a solid-state battery. The active material layer in the electrode of the solid-state battery may contain such a non-aqueous electrolyte. In the present invention, the solid-state battery includes an all-solid-state battery and a semi-solid-state battery.

[0044] The total amount of SPAN and lithium titanium oxide contained in the active material layer in the electrode of the liquid battery is preferably 55 mass % or more, and more preferably 70 mass % or more, relative to the active material layer, from the viewpoint of fully exerting battery performance.

[0045] The total amount of SPAN and lithium titanium oxide contained in the active material layer in the electrode of a solid-state battery is preferably 40 mass % or more, and more preferably 70 mass % or more, relative to the active material layer, from the viewpoint of fully exerting battery performance.

[0046] <Electrode manufacturing method> The electrode of the present invention can be manufactured according to a known method. For example, an electrode mixture paste is manufactured by forming a slurry of an active material containing SPAN and lithium titanium oxide, a binder, and a conductive assistant with an organic solvent or water, and the electrode mixture paste is applied onto a current collector and dried to manufacture an electrode having an active material layer formed on the current collector.

[0047] The binder is not particularly limited, but known binders can be used. Specific examples of binders include, for example, styrene-butadiene rubber, butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene rubber, styrene-isoprene rubber, fluororubber, polyethylene, polypropylene, polyacrylamide, polyamide, polyamideimide, polyimide, polyacrylonitrile, polyurethane, polyvinylidene fluoride, polytetrafluoroethylene, styrene-acrylic acid ester copolymer, ethylene-vinyl alcohol copolymer, polymethyl methacrylate, polyacrylate, polyvinyl alcohol, polyethylene oxide, polyvinylpyrrolidone, polyvinyl ether, polyvinyl chloride, acrylic acid, polyacrylic acid, methylcellulose, carboxymethylcellulose, sodium carboxymethylcellulose, cellulose nanofiber, starch, etc. Only one type of binder may be used, or two or more types may be used in combination.

[0048] The content of the binder is preferably 0.5 parts by mass to 30 parts by mass relative to 100 parts by mass of the active material containing SPAN and lithium titanium oxide, and from the viewpoint of improving the stability of the working electrode, it is more preferably 1 part by mass to 20 parts by mass.

[0049] The conductive assistant may be a known conductive assistant for electrodes. Specific examples of the conductive assistant include carbon materials such as natural graphite, artificial graphite, coal tar pitch, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, roller black, disc black, carbon nanotubes, vapor grown carbon fiber (VGCF), exfoliated graphite, graphene, fullerene, and needle coke; metal powders such as aluminum powder, nickel powder, and titanium powder; conductive metal oxides such as zinc oxide and titanium oxide; La 2 S 3 , Sm 2 S 3 , Ce 2S 3 , TiS 2 and the like sulfides.

[0050] The average primary particle size of the conductive assistant is preferably 0.0001 μm to 100 μm, and more preferably 0.001 μm to 50 μm.

[0051] The content of the conductive assistant is usually 0.1 to 50 parts by mass, preferably 0.5 to 30 parts by mass, and more preferably 1 to 20 parts by mass, per 100 parts by mass of the active material containing SPAN and lithium titanium oxide.

[0052] Examples of the organic solvent 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,N-dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N,N-dimethylaminopropylamine, polyethylene oxide, tetrahydrofuran, dimethyl sulfoxide, sulfolane, γ-butyrolactone, and alcohol. The amount of organic solvent or water used can be adjusted according to the application method selected when applying the electrode mixture paste. For example, in the case of application by a doctor blade method, the amount is preferably 10 parts by mass to 300 parts by mass, and more preferably 20 parts by mass to 200 parts by mass, per 100 parts by mass of the total amount of the active material, binder, and conductive assistant.

[0053] In the production of the electrode mixture paste, other components such as a viscosity adjuster, a reinforcing material, an antioxidant, a pH adjuster, a dispersant, etc. may be contained in the electrode mixture paste within a range that does not impair the effects of the present invention. As these other components, known ones can be used in known blending ratios.

[0054] In the manufacture of the electrode mixture paste, when SPAN and lithium titanium oxide as active materials, a binder, and a conductive assistant are dispersed or dissolved in an organic solvent or water, they may be added all at once to the organic solvent or water and dispersed, or they may be added separately. It is preferable to add the binder, conductive assistant, and active material in order to the organic solvent or water and disperse them, because they can be uniformly dispersed in the solvent. When the electrode mixture paste contains other components, the other components can be added all at once and dispersed, but it is preferable to disperse each time one of the other components is added.

[0055] The method for the dispersion treatment is not particularly limited, but as an industrial method, for example, a normal ball mill, sand mill, bead mill, cyclone mill, zero mill, pigment disperser, crusher, ultrasonic disperser, homogenizer, disperser, rotation-revolution mixer, planetary mixer, film mix, jet paste, etc. can be used.

[0056] Examples of the current collector include conductive materials such as titanium, titanium alloys, aluminum, aluminum alloys, copper, nickel, stainless steel, nickel-plated steel, carbon, and conductive resins. The shape of the current collector includes foil, plate, mesh, three-dimensional mesh, foam, nonwoven fabric, and the like, and the current collector may be either porous or nonporous. In addition, these conductive materials may be surface-treated to improve adhesion and electrical properties. Among these conductive materials, aluminum is preferred from the viewpoints of conductivity and cost, and aluminum foil is particularly preferred. The thickness of the current collector is not particularly limited, but is usually 5 μm to 30 μm in the case of a foil.

[0057] The method for applying the electrode mixture paste onto the current collector is not particularly limited, and examples thereof include a die coater method, a comma coater method, a curtain coater method, a spray coater method, a gravure coater method, a flexo coater method, a knife coater method, a doctor blade method, a reverse roll method, a brush coating method, a dipping method, etc. The die coater method, the knife coater method, the doctor blade method, and the comma coater method are preferred in that they make it possible to obtain a good surface condition of the coating film in accordance with the viscosity and drying property of the electrode mixture paste.

[0058] The electrode mixture paste may be applied to one side or both sides of the current collector. When applying to both sides of the current collector, the paste may be applied to each side sequentially or simultaneously. The paste may be applied to the surface of the current collector continuously, intermittently, or in stripes. The thickness, length, and width of the coating film may be appropriately determined depending on the size of the battery, etc.

[0059] The method for drying the coating film of the electrode mixture paste applied on the current collector is not particularly limited, and a known method can be used. Examples of the drying method include drying with warm air, hot air, or low humidity air, vacuum drying, leaving the electrode mixture paste in a heating furnace, or drying by irradiating far infrared rays, infrared rays, or electron beams. These drying methods may be performed in combination. The temperature when heating is generally about 50°C to 180°C, but the conditions such as temperature can be appropriately set depending on the amount of electrode mixture paste applied, the boiling point of the solvent used, the type of binder, and the like. This drying causes volatile components such as the solvent to volatilize from the coating film of the electrode mixture paste, and an electrode mixture layer is formed on the current collector.

[0060] Although SPAN is a material that does not originally contain lithium, it may be doped with lithium in advance because it has an irreversible capacity. Examples of methods for doping SPAN with lithium include a method of inserting lithium by electrolytic doping, in which a half cell is assembled using metallic lithium as a counter electrode and lithium is electrochemically doped, a method of inserting lithium by pasting metallic lithium foil onto an electrode, leaving it in an electrolyte, and doping by utilizing the diffusion of lithium into the electrode, a mechanical doping method of mechanically colliding an active material layer containing SPAN with lithium metal to insert lithium, and a chemical doping method of immersing an electrode in a lithium naphthalenide solution to insert lithium, but the present invention is not limited to these methods.

[0061] Next, the lithium ion secondary battery of the present invention will be described. The lithium ion secondary battery of the present invention is characterized in that it comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte containing a lithium salt, and uses the above-mentioned electrode for the positive electrode or the negative electrode.

[0062] <Manufacturing method of counter electrode> In the lithium ion secondary battery of the present invention, examples of the counter electrode to the electrode of the present invention include metal lithium, or an electrode containing a lithium-containing composite oxide, silicon, silicon oxide, graphite, carbon, or the like as an active material.

[0063] When metallic lithium is used as the counter electrode, the counter electrode can be made of metallic lithium and / or a lithium alloy. Alternatively, the counter electrode may be provided with a current collector made of a conductive material such as metallic lithium and / or a lithium alloy. In this case, an active material layer containing lithium metal may be formed. The active material layer can be formed, for example, by attaching foil-shaped metallic lithium, or by electrolytic deposition or vapor deposition of metallic lithium.

[0064] The above lithium-containing composite oxide is selected from the group consisting of lithium transition metal composite oxides, lithium transition metal silicate compounds, and lithium transition metal sulfate compounds. The transition metals contained in these compounds are not particularly limited. However, since the charge-discharge stability of the lithium-ion secondary battery is good, aluminum, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, magnesium, gallium, zirconium, niobium, boron, calcium, molybdenum, and tungsten are preferred. Aluminum, vanadium, titanium, chromium, manganese, iron, cobalt, nickel, and copper are preferred because the effects of the present invention are remarkable, and aluminum, manganese, iron, cobalt, and nickel are preferred because the effects of the present invention are more remarkable.

[0065] Examples of the lithium transition metal composite oxide include, for example, LiCoO 2 , LiNiO 2 , LiMnO 2 , compounds represented by the following general formula (2) and compounds represented by the following general formula (3). Li g Ni h Co i M1 j O 2 (2) Li (1+x) Mn (2-x-y) M1 y O 4 (3) In the formulas, g, h, i, and j satisfy 0.9 ≦ g ≦ 1.2, 0.3 < h < 1, 0 ≦ i ≦ 0.5, 0 ≦ j ≦ 0.5, and h + i + j = 1. x satisfies 0 ≦ x < 0.5, and y satisfies 0 ≦ y < 0.5. M1 is preferably at least one selected from the group consisting of aluminum, titanium, vanadium, chromium, manganese, iron, copper, zinc, magnesium, gallium, zirconium, niobium, boron, calcium, molybdenum, and tungsten.

[0066] Specific examples of the compound represented by the general formula (2) or the compound represented by the general formula (3) include, for example, LiMn 2 O 4 , LiNi0.5 Co 0.2 Mn 0.3 O 2 , LiNi 0.8 Co 0.1 Mn 0.1 O 2 , LiNi 0.5 Mn 1.5 O 4 , LiNi 0.80 Co 0.15 Al 0.05 O 2 , LiNi 0.80 Co 0.17 Al 0.03 O 2 , LiNi 0.90 Co 0.05 Al 0.05 O 2 , LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 , LiNi 0.6 Co 0.2 Mn 0.2 O 2 , LiNi 0.9 Co 0.05 Mn 0.05 O 2 , LiMn 1.8 Al 0.2 O 4 , Li 1.1 Mn 1.8 Mg 0.1 O 4 , Li 1.1 Mn 1.85 Al 0.05 O 4 , Li 2 MnO 3 -LiMO 2 (M=cobalt, nickel, manganese) etc.

[0067] As the lithium transition metal composite oxide, for example, LiCoO 2 , LiMn 2 O 4 , LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 , LiNi 0.5 Co 0.2Mn 0.3 O 2 、LiNi 0.6 Co 0.2 Mn 0.2 O 2 、LiNi 0.8 Co 0.1 Mn 0.1 O 2 、LiNi 0.8 Co 0.15 Al 0.05 O 2 is preferred.

[0068] Examples of the lithium transition metal phosphate compound include, for example, a compound represented by the following general formula (4). Li k M2 m (PO 4 ) n F p (4) In the formula, k satisfies 0 < k ≤ 3, m satisfies 0.5 ≤ m ≤ 2, n satisfies 1 ≤ n ≤ 3, and p satisfies 0 ≤ p ≤ 1. M2 is at least one selected from the group consisting of iron, cobalt, nickel, manganese, copper, titanium, tungsten, molybdenum, chromium, vanadium, and vanadium(II) monoxide. Since it has good charge-discharge stability, at least one selected from the group consisting of iron, cobalt, nickel, manganese, copper, vanadium, and vanadium(II) monoxide is more preferred. Also, a part of M2 may be substituted with one or more other metals such as aluminum, zinc, magnesium, zirconium, gallium, niobium, etc.

[0069] Specific examples of the lithium transition metal phosphate compound include, for example, LiFePO 4 、LiMn X Fe 1-X PO 4 、LiCuPO 4 、LiNiPO 4 、LiCoPO 4 、LiMnPO 4 、LiVOPO 4 、Li 2 FePO 4 、Li 2 NiPO 4 、Li2 CoPO 4 , Li 2 MnPO 4 , Li 2 NiPO 4 F, Li 2 CoPO 4 F, Li 2 MnPO 4 F, Li 2 FePO 4 F, Li 3 V 2 (PO 4 ) 3 , LiMn 7 / 8 Fe 1 / 8 PO 4 , LiMn 2 / 3 Fe 1 / 3 PO 4 , Life 0.9 Mn 0.1 PO 4 , Life 0.2 Mn 0.8 PO 4 , Life 0.15 Mn 0.75 Mg 0.1 PO 4 , Life 0.19 Mn 0.75 Zr 0.03 PO 4 etc.

[0070] As the lithium transition metal phosphate compound, LiFePO 4 , LiCuPO 4 , LiNiPO 4 , LiCoPO 4 , LiMnPO 4 , LiVOPO 4 is preferred, and LiFePO 4 , LiNiPO 4 , LiCoPO 4 , LiMnPO 4 is more preferred.

[0071] The counter electrode active material is preferably pulverized, granulated, or the like to have a desired particle size, and is preferably further classified. Methods for pulverization and classification include the same methods as those described in the SPAN pulverization and classification methods.

[0072] The average secondary particle diameter (D50) of the active material of the counter electrode is preferably 0.1 μm to 50 μm, more preferably 0.5 μm to 50 μm, and even more preferably 1 μm to 30 μm. If the average secondary particle diameter of the active material of the counter electrode exceeds 50 μm, a uniform and smooth active material layer may not be formed. On the other hand, if the average secondary particle diameter of the active material of the counter electrode is smaller than 0.1 μm, the handling property may deteriorate, and side reactions may easily occur due to an increase in the specific surface area, which may adversely affect the charge and discharge stability.

[0073] The counter electrode can be manufactured according to a known method. An electrode mixture paste is manufactured by slurriedly preparing a mixture containing the active material, binder, and conductive assistant of the counter electrode with an organic solvent or water, and the electrode mixture paste is applied to a current collector and dried to manufacture a counter electrode having an active material layer formed on the current collector.

[0074] The binder used in the counter electrode may be the same as those described above, but polyvinylidene fluoride, polyimide, polyacrylonitrile, polytetrafluoroethylene, polyacrylic acid, and sodium carboxymethylcellulose are preferred because of their good charge-discharge stability.

[0075] The content of the binder is preferably 0.5 to 30 parts by mass, and more preferably 1 to 20 parts by mass, relative to 100 parts by mass of the active material of the counter electrode.

[0076] The conductive assistant used in the counter electrode may be the same as those described above.

[0077] The content of the conductive assistant is preferably 0.1 to 50 parts by mass, more preferably 0.5 to 30 parts by mass, and further preferably 1 to 20 parts by mass, relative to 100 parts by mass of the active material of the counter electrode.

[0078] The solvent for preparing the electrode mixture paste of the counter electrode can be the same as the solvent for preparing the electrode mixture paste. The amount of the solvent used can be adjusted according to the application method selected when applying the electrode mixture paste. For example, in the case of application by the doctor blade method, the amount of the solvent is preferably 10 parts by mass to 300 parts by mass, more preferably 20 parts by mass to 200 parts by mass, relative to 100 parts by mass of the total amount of the active material, binder, and conductive assistant of the counter electrode.

[0079] The electrode mixture paste for the counter electrode may contain, in addition to the above-mentioned components, other components such as a viscosity adjuster, a reinforcing material, an antioxidant, a pH adjuster, a dispersant, etc. These other components may be known and may be used in known blending ratios, provided that the effects of the present invention are not impaired.

[0080] In the manufacture of the electrode mixture paste for the counter electrode, when dispersing or dissolving the active material, binder, and conductive assistant in an organic solvent or water, they may be added to the solvent all at once and dispersed, or may be added separately and dispersed. It is preferable to add the binder, conductive assistant, and active material of the counter electrode in this order to the organic solvent or water and disperse them, because they can be uniformly dispersed in the solvent. When the electrode mixture paste for the counter electrode contains other components, the other components can be added all at once and dispersed, but it is preferable to disperse each time one of the other components is added.

[0081] The dispersion treatment method and the current collector in the production of the electrode mixture paste for the counter electrode may be the same as those described in the production of the electrode mixture paste above.

[0082] The method of applying the electrode mixture paste of the counter electrode onto the current collector and the method of drying the electrode mixture paste of the counter electrode can be the same as those described above for the method of applying the electrode mixture paste onto the current collector and the method of drying the electrode mixture paste.

[0083] <Method of manufacturing lithium-ion secondary battery> The lithium ion secondary battery of the present invention can be manufactured by a known method for manufacturing a lithium ion secondary battery, except that an electrode containing SPAN and lithium titanium oxide is used as the working electrode. For example, the working electrode and the counter electrode are sandwiched between a separator and held in a battery cell, and a non-aqueous electrolyte is introduced into the battery cell, followed by sealing and sealing. Each material of the lithium ion secondary battery will be described below.

[0084] <Non-aqueous electrolyte> Examples of non-aqueous electrolytes that can be used in the lithium ion secondary battery of the present invention include liquid non-aqueous electrolytes obtained by dissolving a lithium salt in an organic solvent, polymer gel non-aqueous electrolytes obtained by dissolving or dispersing a lithium salt in a polymer gel obtained by dissolving a polymer compound in an organic solvent as a solvent or dispersion medium, polymer non-aqueous electrolytes obtained by dispersing a lithium salt using a polymer as a dispersion medium without using a solvent (in this specification, an electrolyte obtained by dispersing a lithium salt in a polymer as a dispersion medium without using a solvent is defined as a polymer electrolyte), complex hydride-based solid electrolytes, inorganic solid electrolytes, and the like.

[0085] <Lithium salt> The lithium salt used in the non-aqueous electrolyte is not particularly limited, and any known lithium salt that can be used as a lithium salt for a lithium ion secondary battery can be used. Specific examples of lithium salts include LiPF 6 , LiBF 4 , LiAsF 6 , LiCF 3 SO 3 , LiCF 3 CO 2 , LiN(CF 3 SO2 ) 2 , LiN(C 2 F 5 SO 2 ) 2 , LiN(SO 2 F) 2 , LiC(CF 3 SO 2 ) 3 , LiB(CF 3 SO 3 ) 4 , LiB(C 2 O 4 ) 2 , LiBF 2 (C 2 O 4 ), LiSbF 6 , LiSiF 5 , LiSCN, LiClO 4 , LiCl, LiF, LiBr, LiI, LiAlF 4 , LiAlCl 4 , LiPO 2 F 2 and derivatives thereof.

[0086] The lithium salt used in the liquid electrolyte and polymer gel electrolyte is LiPF 6 , LiBF 4 , LiClO 4 , LiCF 3 SO 3 , LiN(CF 3 SO 2 ) 2 , LiN(C 2 F 5 SO 2 ) 2 , LiN(SO 2 F) 2 , LiPO 2 F 2 , LiC(CF 3 SO 2 ) 3 and LiCF 3 SO 3 Derivatives of LiC(CF 3 SO 2 ) 3 It is preferable to use one or more selected from the group consisting of the derivatives of the following:

[0087] The lithium salt used in the polymer electrolyte (or the polymer electrolyte obtained by dispersing the lithium salt without using a solvent) is LiPF 6 , LiBF 4 , LiClO 4 , LiN(CF 3 SO 2 ) 2 , LiN(C 2 F 5 SO 2 ) 2 , LiN(SO 2 F) 2 , LiC(CF 3 SO 2 ) 3 , LiB(CF 3 SO 3 ) 4 , LiB(C 2 O 4 ) 2 It is preferable to use one or more selected from the group consisting of:

[0088] If the concentration of the lithium salt in the non-aqueous electrolyte is too low, a sufficient current density may not be obtained, whereas if the concentration is too high, the stability of the non-aqueous electrolyte may be impaired. Therefore, the concentration of the lithium salt is preferably 0.5 mol / L to 7 mol / L, and more preferably 0.8 mol / L to 1.8 mol / L.

[0089] <Liquid non-aqueous electrolyte> When a liquid nonaqueous electrolyte is used as the nonaqueous electrolyte, it preferably contains at least one compound selected from cyclic carbonate compounds. Examples of the cyclic carbonate compound include saturated cyclic carbonate compounds such as ethylene carbonate, 1,2-propylene carbonate, 1,3-propylene carbonate, 1,2-butylene carbonate, 1,3-butylene carbonate, and 1,1-dimethylethylene carbonate, and unsaturated cyclic carbonate compounds such as vinylene carbonate, vinylethylene carbonate, propylidene carbonate, ethylene ethylidene carbonate, and ethylene isopropylidene carbonate. These cyclic carbonate compounds may have some of the hydrogen atoms substituted with fluorine atoms.

[0090] When the non-aqueous electrolyte contains a cyclic carbonate compound, it is preferable to further contain a chain carbonate compound, since the viscosity is reduced and the ion conductivity is improved. Examples of the chain carbonate compound include saturated chain carbonate compounds such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate, and unsaturated chain carbonate compounds such as dipropargyl carbonate, propargyl methyl carbonate, ethyl propargyl carbonate, bis(1-methylpropargyl) carbonate, and bis(1-dimethylpropargyl) carbonate. In these chain carbonate compounds, a part of the hydrogen atoms may be replaced by fluorine atoms.

[0091] From the viewpoints of performance and storage stability of the lithium ion secondary battery, the liquid nonaqueous electrolyte is preferably propylene carbonate, a mixed solvent of ethylene carbonate and dimethyl carbonate, a mixed solvent of ethylene carbonate and ethyl methyl carbonate, a mixed solvent of ethylene carbonate and diethyl carbonate, a mixed solvent of propylene carbonate and dimethyl carbonate, a mixed solvent of propylene carbonate and diethyl carbonate, or a mixed solvent of propylene carbonate, ethylene carbonate and ethyl methyl carbonate, and more preferably propylene carbonate, a mixed solvent of ethylene carbonate and ethyl methyl carbonate, a mixed solvent of ethylene carbonate and diethyl carbonate, a mixed solvent of propylene carbonate and diethyl carbonate, or a mixed solvent of propylene carbonate, ethylene carbonate and ethyl methyl carbonate.

[0092] When the liquid non-aqueous electrolyte further contains a chain carbonate compound, the mixing ratio of the cyclic carbonate compound and the chain carbonate compound is preferably 10 to 1000 parts by volume of the chain carbonate compound per 100 parts by volume of the cyclic carbonate compound. If the amount of the chain carbonate compound is less than 10 parts by volume, the performance of the lithium ion secondary battery may be reduced. On the other hand, if the amount of the chain carbonate compound is more than 1000 parts by volume, the charge / discharge stability of the lithium ion secondary battery at high temperatures may be reduced.

[0093] The liquid non-aqueous electrolyte may contain an organic solvent that is commonly used in non-aqueous electrolytes for lithium ion secondary batteries. Specific examples of the organic solvent include saturated cyclic ester compounds, sulfoxide compounds, sulfone compounds, amide compounds, chain ether compounds, cyclic ether compounds, and saturated chain ester compounds. Only one of these organic solvents may be added, or two or more of them may be added.

[0094] Examples of the saturated cyclic ester compound include γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-hexanolactone, and δ-octanolactone.

[0095] Examples of the sulfoxide compound include dimethyl sulfoxide, diethyl sulfoxide, dipropyl sulfoxide, diphenyl sulfoxide, and thiophene.

[0096] Examples of sulfone compounds include dimethyl sulfone, diethyl sulfone, dipropyl sulfone, diphenyl sulfone, sulfolane (also called tetramethylene sulfone), 3-methyl sulfolane, 3,4-dimethyl sulfolane, 3,4-diphenylmethyl sulfolane, sulfolene, 3-methyl sulfolene, 3-ethyl sulfolene, 3-bromomethyl sulfolene, etc. Among these, sulfolane and tetramethyl sulfolane are preferred.

[0097] Examples of the amide compound include N-methylpyrrolidone, dimethylformamide, and dimethylacetamide.

[0098] Examples of chain ether compounds and cyclic ether compounds include dimethoxyethane, ethoxymethoxyethane, diethoxyethane, tetrahydrofuran, dioxolane, dioxane, 1,2-bis(methoxycarbonyloxy)ethane, 1,2-bis(ethoxycarbonyloxy)ethane, 1,2-bis(ethoxycarbonyloxy)propane, ethylene glycol bis(trifluoroethyl)ether, propylene glycol bis(trifluoroethyl)ether, ethylene glycol bis(trifluoromethyl)ether, and diethylene glycol bis(trifluoroethyl)ether. Of these, dioxolane is preferred.

[0099] The saturated chain ester compound is preferably a monoester compound or a diester compound having 2 to 8 carbon atoms in the molecule in total. 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 trimethylacetate, ethyl trimethylethylacetate, methyl malonate, ethyl malonate, methyl succinate, ethyl succinate, methyl 3-methoxypropionate, ethyl 3-methoxypropionate, ethylene glycol diacetyl, and propylene glycol diacetyl. Of these, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, isobutyl acetate, butyl acetate, methyl propionate, and ethyl propionate are preferred.

[0100] Other organic solvents that can be used include, for example, acetonitrile, propionitrile, nitromethane, and derivatives thereof, and various ionic liquids.

[0101] <Polymer gel-type non-aqueous electrolyte> Examples of polymers that can be used as the polymer gel include polyethylene oxide, polypropylene oxide, polyvinyl chloride, polyacrylonitrile, polymethyl methacrylate, polyethylene, polyvinylidene fluoride, polyhexafluoropropylene, polystyrene sulfonic acid, etc. There are no particular limitations on the organic solvent that dissolves the polymer to gel, the blending ratio of the lithium salt and the polymer gel, and the method for producing the polymer gel, and any organic solvent, lithium salt, and production method known in the art can be used.

[0102] <Polymer nonaqueous electrolyte> Examples of polymers that can be used as the polymer nonaqueous electrolyte obtained by dispersing a lithium salt using a polymer as a dispersion medium without using a solvent include polyethylene oxide, polypropylene oxide, and polystyrene sulfonic acid. There are no particular limitations on the blending ratio of the lithium salt and the polymer in the polymer nonaqueous electrolyte, and on the method for producing the polymer nonaqueous electrolyte, and any blending ratio and production method known in the art can be used.

[0103] <Complex hydride-based solid electrolyte> As a complex hydride solid electrolyte, Li(CB 9 H 10 ), Li(CB 11 H 12 ), Li 2 (B 12 H 12 ), Li(BH 4 ), 3(LiBH 4 )-LiI, Li(NH 2 ), Li(AlH 4 ), Li 3 (AlH 6 ), 3(LiBH 4 )-Li(NH 2 ), Li(BH 4 )-Li(NH 2 ), 0.7Li(CB 9 H 10 )-0.3Li(CB 11 H 12 ), Li(BH 4 )-3KI, Li(BH 4 )-P 2 I 4 , Li(BH 4 )-P 2 S 5 , Li 2 (NH 2 ), Li(BH 4 )-GdCl 3 , Li(BH 4 )-NaI, Li(BH 4 )-3Li(NH 2 ) etc.

[0104] <Inorganic solid electrolyte> Examples of inorganic solid electrolytes include sulfide-based solid electrolytes, oxide-based solid electrolytes, and phosphoric acid-based solid electrolytes.

[0105] As a sulfide-based solid electrolyte, Li 2SP 2 S 5 based compounds, Li 2 S-SiS 2 based compounds, Li 2 S-GeS 2 based compounds, Li 2 S.B. 2 S 3 based compounds, Li 2 SP 2 S 3 based compounds, LiI-Si 2 SP 2 S 5 , LiI-Li 2 SP 2 O 5 , LiI-Li 3 PO 4 -P 2 S 5 , Li 10 GeP 2 S 12 In this specification, the term "compound based on Li" is used in conjunction with the term "compound based on Li 2 S" "P 2 S 5 It is used as a general term for solid electrolytes that mainly contain raw materials such as Li. 2 SP 2 S 5 Li 2 S and P 2 S 5 The solid electrolyte mainly contains Li and may further contain other raw materials. 2 SP 2 S 5 Li 2 S and P 2 S 5 Also included are solid electrolytes having different mixture ratios of

[0106] Li 2 SP 2 S 5 Li-based compounds include 2 SP 2 S 5 , Li 2 SP 2 S 5 - LiI, Li 2SP 2 S 5 -LiCl, Li 2 SP 2 S 5 -LiBr, Li 2 SP 2 S 5 -Li 2 O, Li 2 SP 2 S 5 -Li 2 O-LiI, Li 2 SP 2 S 5 -Z m S n (Z is Ge, Zn or Ga, and m and n are positive numbers).

[0107] Li 2 S-SiS 2 Li-based compounds include 2 S-SiS 2 , Li 2 S-SiS 2 - LiI, Li 2 S-SiS 2 -LiBr, Li 2 S-SiS 2 -LiCl, Li 2 S-SiS 2 -B 2 S 3 - LiI, Li 2 S-SiS 2 -P 2 S 5 - LiI, Li 2 S-SiS 2 -Li 3 PO 4 , Li 2 S-SiS 2 -Li 2 SO 4 , Li 2 S-SiS 2 -Li x MO y (M is P, Si, Ge, B, Al, Ga, or In, and x and y are positive numbers).

[0108] Li 2 S-GeS2 Li-based compounds include 2 S-GeS 2 , Li 2 S-GeS 2 -P 2 S 5 etc. can be mentioned.

[0109] Examples of oxide-based solid electrolytes include perovskite-type oxides, Nasicon-type oxides, Lisicon-type oxides, garnet-type oxides, and β-alumina oxides.

[0110] Examples of perovskite oxides include Li a La 1-a TiO 3 Li-La-Ti perovskite oxides, which are expressed as b La 1-b TaO 3 Li-La-Ta perovskite oxides, which are expressed as c La 1-c NbO 3 Examples of perovskite oxides include Li-La-Nb-based oxides represented as follows (0 <a<1、0<b<1、0<c<1である)。

[0111] As an example of Nasicon-type oxide, Li d+l Al d Ti 2-d (PO 4 ) 3 Li, which has the crystals represented by e X f Y g P h O j (X is B, Al, Ga, In, C, Si, Ge, Sn, Sb or Se, Y is Ti, Zr, Ge, In, Ga, Sn or Al, 0≦d≦1, e, f, g, h and j are positive numbers). 2 (PO 4 ) 3 Examples include:

[0112] Examples of the lithiated oxide include Li 4 XO 4 -Li 3 YO 4 (X is Si, Ge or Ti, and Y is P, As or V), and the like.

[0113] Garnet-type oxides include, for example, Li 7 La 3 Zr 2 O 12 Li-La-Zr oxides and their derivatives are typified by the following:

[0114] In the lithium ion secondary battery of the present invention, the form of the non-aqueous electrolyte is not particularly limited, but it is preferable to use a liquid non-aqueous electrolyte because the production process is simple.

[0115] The non-aqueous electrolyte may further contain known electrolyte additives such as an electrode film forming agent, an antioxidant, a flame retardant, an overcharge inhibitor, etc., in order to improve the battery life and safety. When an electrolyte additive is used, the concentration of the electrolyte additive is preferably 0.01% by mass to 10% by mass, and more preferably 0.1% by mass to 5% by mass, relative to the non-aqueous electrolyte. If the concentration is less than 0.01% by mass, the effect of the addition may not be exhibited, and if the concentration exceeds 10% by mass, the characteristics of the lithium ion secondary battery may be adversely affected.

[0116] <separator> In the lithium ion secondary battery of the present invention, when a liquid non-aqueous electrolyte is used as the non-aqueous electrolyte, it is preferable to interpose a separator between the working electrode and the counter electrode. The separator can be selected from polymer films, nonwoven fabrics, and glass filters that are usually used in lithium ion secondary batteries without any particular limitation. Specific examples of polymer films include films made of polyethylene, polypropylene, polyvinylidene fluoride, polyvinylidene chloride, polyacrylonitrile, polyacrylamide, polytetrafluoroethylene, polysulfone, polyethersulfone, polycarbonate, polyamide, polyimide, polyethers such as polyethylene oxide and polypropylene oxide, various celluloses such as carboxymethyl cellulose and hydroxypropyl cellulose, polymer compounds mainly composed of poly(meth)acrylic acid and various esters thereof, derivatives thereof, copolymers or mixtures thereof, etc., and these polymer films may be coated with ceramic materials such as alumina and silica, magnesium oxide, aramid resin, and polyvinylidene fluoride. These polymer films may be used alone, or these films may be stacked together to form a multilayer film. Furthermore, various additives may be used in these polymer films, and the type and content of the additives are not particularly limited. Among these polymer films, films selected from polyethylene, polypropylene, polyvinylidene fluoride, and polysulfone are preferably used.

[0117] These polymer films are used in a microporous state so that the nonaqueous electrolyte can penetrate and ions can easily pass through. Methods for making the polymer film microporous include the "phase separation method" in which a solution of a polymer compound and a solvent is subjected to microphase separation to form a film, and the solvent is extracted and removed to make the film porous, and the "stretching method" in which a molten polymer compound is extruded at a high draft to form a film, and then heat-treated to align the crystals in one direction, and then stretched to form gaps between the crystals to make the film porous. The method is appropriately selected depending on the polymer film to be used.

[0118] When a polymer gel electrolyte, a polymer electrolyte (or a polymer electrolyte obtained by dispersing a lithium salt without using a solvent), a complex hydride-based solid electrolyte, or an inorganic solid electrolyte is used as the non-aqueous electrolyte, a separator may not be included.

[0119] <External packaging> The shape of the lithium ion battery of the present invention is not particularly limited, and it can be a battery of various shapes such as a coin type battery, a cylindrical battery, a square battery, a laminated battery, etc., and a metal container or a laminate film can be used as the external packaging material. The thickness of the external packaging material is usually 0.5 mm or less, preferably 0.3 mm or less. The shape of the external packaging material can be a flat type (thin type), a square type, a cylindrical type, a coin type, a button type, etc.

[0120] Examples of metal containers include those made of stainless steel, aluminum, aluminum alloys, etc. The aluminum alloy is preferably an alloy containing elements such as magnesium, zinc, silicon, etc. In aluminum or aluminum alloys, by making the content of transition metals such as iron, copper, nickel, chromium, etc. 1% or less, it is possible to dramatically improve long-term reliability and heat dissipation properties in high-temperature environments.

[0121] The laminate film may be a multi-layer film having a metal layer between resin films. The metal layer is preferably an aluminum foil or an aluminum alloy foil for weight reduction. The resin film may be made of a polymer material such as polypropylene, polyethylene, nylon, or polyethylene terephthalate. The laminate film may be sealed by heat fusion to form an exterior member.

[0122] FIG. 1 shows an example of a coin-type lithium ion secondary battery of the present invention, FIGS. 2 and 3 show examples of a cylindrical battery, and FIGS. 4 to 6 show examples of a laminated battery.

[0123] In the coin-type lithium-ion secondary battery 10 shown in FIG. 1, reference numeral 1 denotes a positive electrode capable of releasing lithium ions, 1a denotes a positive electrode current collector, 2 denotes a negative electrode capable of absorbing and releasing lithium ions released from the positive electrode, 2a denotes a negative electrode current collector, 3 denotes a non-aqueous electrolyte, 4 denotes a stainless steel positive electrode case, 5 denotes a stainless steel negative electrode case, 6 denotes a polypropylene gasket, and 7 denotes a polyethylene separator.

[0124] In a cylindrical lithium-ion secondary battery 10′ shown in FIGS. 2 and 3, 11 is a negative electrode, 12 is a negative electrode current collector, 13 is a positive electrode, 14 is a positive electrode current collector, 15 is a nonaqueous electrolyte, 16 is a separator, 17 is a positive electrode terminal, 18 is a negative electrode terminal, 19 is a negative electrode plate, 20 is a negative electrode lead, 21 is a positive electrode plate, 22 is a positive electrode lead, 23 is a case, 24 is an insulating plate, 25 is a gasket, 26 is a safety valve, and 27 is a PTC element.

[0125] 4 is an exploded perspective view showing a schematic diagram of an electrode group 29 of a laminated lithium ion secondary battery 28. In the embodiment described later, a laminated lithium ion secondary battery will be used for explanation, but the present invention is not limited thereto. The electrode group 29 has a structure in which, for example, a sheet-shaped negative electrode 11, a sheet-shaped positive electrode 13, and a sheet-shaped separator 16 separating the negative electrode 11 and the positive electrode 13 are alternately laminated. 17 is a positive electrode terminal, and 18 is a negative electrode terminal.

[0126] Fig. 5 is an exploded perspective view showing a laminated type lithium ion secondary battery 28, and Fig. 6 is an external plan view showing a laminated type lithium ion secondary battery 28. Reference numeral 17 denotes a positive electrode terminal, 18 denotes a negative electrode terminal, 29 denotes an electrode group, 30 denotes a case-side laminate film, and 31 denotes a lid-side laminate film.

[0127] Although the embodiment of the present invention has been described above, the present invention is not limited to the above-mentioned embodiment. The present invention can be embodied in various forms including modifications and improvements that can be made by those skilled in the art without departing from the gist of the present invention. EXAMPLES

[0128] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[0129] [Production Example 1] Production of SPAN A mixture of 200 parts by mass of sulfur (Sigma-Aldrich, particle size 200 μm, powder) and 100 parts by mass of polyacrylonitrile powder (Sigma-Aldrich, classified using a sieve with an opening diameter of 30 μm) was placed in an alumina Tammann tube, and the opening of the alumina Tammann tube was then covered with a rubber plug equipped with a thermocouple, a gas inlet tube, and a gas outlet tube. The mixture was heated at a temperature increase rate of 5° C. / min while introducing argon gas into the alumina Tammann tube at a flow rate of 100 cc / min, and heating was stopped when the temperature reached 360° C., but the temperature had risen to 400° C. After cooling to room temperature by natural cooling, the reaction product was taken out from the alumina Tammann tube. The obtained reaction product was heated to remove elemental sulfur, and then pulverized to obtain SPAN. The average secondary particle diameter of the obtained SPAN was 9 μm, and the sulfur content was 38% by mass.

[0130] [Production Example 2] Production of carbon-coated LTO In a 250 ml round-bottom flask, add lithium titanium oxide (Li 4 Ti 5 O 12 ) (Ishihara Sangyo Kaisha, Ltd., average particle size: 7 μm) and 100 ml of pure water were added, stirred for 1 hour, and then irradiated with ultrasonic waves for 6 minutes. The resulting slurry was cooled in an ice bath, and then 3 g of acrylonitrile and 25 mg of 2,2'-azobis(isobutyronitrile) were added, followed by irradiating with ultrasonic waves for 6 minutes. Next, the slurry was degassed for 30 minutes under nitrogen reflux, and then heated to 70°C and heated for 12 hours. The resulting slurry was vacuum dried and then allowed to stand at room temperature (25°C). The temperature was raised from 25°C to 240°C at a rate of 5°C / min under air and held at 240°C for 1 hour. The temperature was then raised to 700°C at a rate of 5°C / min under nitrogen reflux to produce carbon-coated LTO, in which the surface of the lithium titanium oxide was coated with carbon. The average particle size of the obtained carbon-coated LTO was 8μm.

[0131] [Example 1] Production of electrode A As the electrode active material, 45.0 parts by mass of SPAN produced in Production Example 1 and lithium titanium oxide (Li 4 Ti 5 O 12 ) (manufactured by Ishihara Sangyo Kaisha, Ltd., average secondary particle diameter 7 μm) 45.0 parts by mass, as a conductive assistant acetylene black (manufactured by Denka Co., Ltd.), as a binder 3.0 parts by mass (solids content) of styrene-butadiene rubber (40 mass% aqueous dispersion, manufactured by Zeon Corporation), and 2.0 parts by mass of sodium carboxymethylcellulose (manufactured by Daicel FineChem Corporation) were added to 110 parts by mass of water as a solvent, and these were mixed for 30 minutes using a rotation-revolution mixer under conditions of revolution of 1600 rpm and rotation of 640 rpm to prepare an electrode mixture paste.

[0132] The obtained electrode mixture paste was applied to one side of a current collector made of carbon-coated aluminum foil (thickness 22 μm) by a doctor blade method, left to stand for 1 hour to dry at 80° C., and then pressed to form an active material layer on the current collector. Thereafter, the aluminum foil on which the active material layer was formed was cut to a predetermined size (circular shape), and further vacuum dried at 130° C. for 2 hours just before use to produce electrode A.

[0133] [Example 2] Production of electrode B The electrode active material in Example 1 was prepared by mixing 72 parts by mass of SPAN prepared in Preparation Example 1 and lithium titanium oxide (Li 4 Ti 5 O 12 An electrode B was produced in the same manner as in Example 1, except that the amount of ruthenium oxide was changed to 18 parts by mass of ruthenium oxide (manufactured by Ishihara Sangyo Kaisha, Ltd., average secondary particle diameter 7 μm).

[0134] [Example 3] Production of electrode C The electrode active material in Example 1 was prepared by mixing 18 parts by mass of SPAN produced in Production Example 1 and lithium titanium oxide (Li 4 Ti 5 O 12 An electrode C was produced in the same manner as in Example 1, except that the amount of ruthenium oxide was changed to 72 parts by mass of ruthenium oxide (manufactured by Ishihara Sangyo Kaisha, Ltd., average secondary particle diameter 7 μm).

[0135] [Comparative Example 1] Manufacture of electrode D The electrode active material in Example 1 was prepared by mixing 45 parts by mass of SPAN produced in Production Example 1 and lithium titanium oxide (Li 4 Ti 5 O 12 An electrode D was produced in the same manner as in Example 1, except that the amount of 45 parts by mass of ruthenium oxide (manufactured by Ishihara Sangyo Kaisha, Ltd., average secondary particle diameter 15 μm) was changed to 45 parts by mass.

[0136] [Comparative Example 2] Production of Electrode E An electrode E was produced in the same manner as in Example 1, except that the electrode active material in Example 1 was changed to only 90 parts by mass of SPAN produced in Production Example 1.

[0137] [Comparative Example 3] Production of electrode F The electrode active material in Example 1 was lithium titanium oxide (Li 4 Ti 5 O 12 An electrode F was produced in the same manner as in Example 1, except that only 90 parts by mass of SiO2 (manufactured by Ishihara Sangyo Kaisha, Ltd., average secondary particle diameter 7 μm) was used.

[0138] [Comparative Example 4] Production of electrode G An electrode G was produced in the same manner as in Example 1, except that the electrode active material in Example 1 was changed to only 90 parts by mass of the carbon-coated LTO produced in Production Example 2.

[0139] [Comparative Example 5] Production of Electrode H The electrode active material in Example 1 was prepared by mixing 88 parts by mass of SPAN prepared in Preparation Example 1 and lithium titanium oxide (Li 4 Ti 5 O 12 An electrode H was produced in the same manner as in Example 1, except that the amount of the sintered material was changed to 2 parts by mass of sintered material (manufactured by Ishihara Sangyo Kaisha, Ltd., average secondary particle diameter 7 μm).

[0140] [Comparative Example 6] Production of Electrode I The electrode active material in Example 1 was prepared by mixing 2 parts by mass of SPAN produced in Production Example 1 and lithium titanium oxide (Li4 Ti 5 O 12 An electrode I was produced in the same manner as in Example 1, except that the amount of ruthenium oxide was changed to 88 parts by mass of ruthenium oxide (manufactured by Ishihara Sangyo Kaisha, Ltd., average secondary particle diameter 7 μm).

[0141] [Example 4] Production of lithium ion secondary battery A Electrode A was used as the working electrode, and a 500 μm thick circular lithium metal was used as the counter electrode. A glass filter was sandwiched between the working electrode and the counter electrode as the separator, and the electrodes were held in the case. LiPF 6 A non-aqueous electrolyte solution adjusted to a concentration of 1.0 ml / L was enclosed in the case, and the case was sealed using a crimping machine to produce a coin-type lithium-ion secondary battery A with a diameter of 20 mm and a thickness of 3.2 mm. The capacity of the battery was 3 mAh. A schematic diagram of this coin-type lithium-ion secondary battery is shown in Figure 1.

[0142] [Example 5] Production of lithium ion secondary battery B A lithium ion secondary battery B was produced in the same manner as in Example 4, except that the electrode A as the working electrode was changed to the electrode B. The capacity of the battery was 3 mAh.

[0143] [Example 6] Production of lithium ion secondary battery C A lithium ion secondary battery C was produced in the same manner as in Example 4, except that the electrode A as the working electrode was changed to the electrode C. The capacity of the battery was 3 mAh.

[0144] Comparative Example 7: Manufacture of lithium ion secondary battery D A lithium ion secondary battery D was produced in the same manner as in Example 4, except that the electrode A as the working electrode was changed to the electrode D. The capacity of the battery was 3 mAh.

[0145] [Comparative Example 8] Manufacture of lithium-ion secondary battery E A lithium ion secondary battery E was produced in the same manner as in Example 4, except that the electrode A as the working electrode was changed to the electrode E. The capacity of the battery was 3 mAh.

[0146] Comparative Example 9: Manufacture of lithium ion secondary battery F A lithium ion secondary battery F was produced in the same manner as in Example 4, except that the electrode A as the working electrode was changed to the electrode F. The capacity of the battery was 3 mAh.

[0147] Comparative Example 10: Manufacture of lithium ion secondary battery G A lithium ion secondary battery G was produced in the same manner as in Example 4, except that the electrode A as the working electrode was changed to the electrode G. The capacity of the battery was 3 mAh.

[0148] Comparative Example 11: Manufacture of lithium ion secondary battery H A lithium ion secondary battery H was produced in the same manner as in Example 4, except that the electrode A as the working electrode was changed to the electrode H. The capacity of the battery was 3 mAh.

[0149] [Comparative Example 12] Production of lithium ion secondary battery I A lithium ion secondary battery I was produced in the same manner as in Example 4, except that the electrode A as the working electrode was changed to the electrode I. The capacity of the battery was 3 mAh.

[0150] The lithium ion secondary batteries A to I produced in Examples 4 to 6 and Comparative Examples 7 to 12 were used to carry out the following evaluations.

[0151] (1) Rate characteristics The lithium-ion secondary battery was placed in a thermostatic chamber at 25°C, and the charge end voltage was set to 3.0V, the discharge end voltage was set to 1.0V, and the charge and discharge tests were performed five times in succession under the conditions of a charge rate of 0.1C and a discharge rate of 0.1C. Then, a charge test was performed three times in succession under the conditions of a charge rate of 0.1C and a discharge rate of 5.0C. Furthermore, a charge and discharge test was performed three times in succession under the conditions of a charge rate of 0.1C and a discharge rate of 0.1C. A total of 11 charge and discharge tests were performed to measure the discharge capacity. The fifth discharge capacity and the eighth discharge capacity, and the ratio of the eighth discharge capacity to the fifth discharge capacity were calculated as the rate characteristic (%). These results are shown in Table 1. The unit of discharge capacity is mAh / g.

[0152] [Table 1]

[0153] (2) High temperature storage stability test (calendar life) The lithium ion secondary battery thus prepared was placed in a thermostatic chamber at 25°C, and a charge / discharge test was carried out five times in succession under the conditions of a charge cut-off voltage of 3.0V, a discharge cut-off voltage of 1.0V, a charge rate of 0.1C, and a discharge rate of 0.1C. Then, only charging at a charge rate of 0.1C was carried out. The charged non-aqueous electrolyte secondary battery was stored at 80°C for 10 days, and then a charge / discharge test was carried out three times under the conditions of a charge rate of 0.1C and a discharge rate of 0.1C, for a total of eight charge / discharge tests, and the discharge capacity was measured. The fifth discharge capacity, the eighth discharge capacity, and the ratio of the eighth discharge capacity / fifth discharge capacity were calculated as the calendar life (%). These results are shown in Table 2. The unit of discharge capacity is mAh / g.

[0154] [Table 2]

[0155] From the results of Comparative Examples 7 to 12 shown in Tables 1 and 2, it was found that the lithium ion secondary batteries different from the configuration of the present invention were unable to achieve both high levels of rate characteristics and calendar life. In contrast, from the results of Examples 4 to 6, it was confirmed that the lithium ion secondary batteries of the present invention were able to achieve both high levels of rate characteristics and calendar life.

[0156] [Example 7] Production of all-solid-state secondary battery J As the electrode active material, 25.0 parts by mass of SPAN produced in Production Example 1 and lithium titanium oxide (Li 4 Ti 5 O 12 ) (manufactured by Ishihara Sangyo Kaisha, Ltd., average secondary particle diameter 7 μm) 25.0 parts by mass, as a conductive additive, acetylene black (manufactured by Denka Co., Ltd.) 5.0 parts by mass, and as a solid electrolyte, 75Li 2 S·25P 2 S 5 (Li 2 S:P 2 S 5 The mixture was pressed to form a circular working electrode mixture layer having a diameter of 10 mm. 2 S·25P 2 S 5 ) / In-Li alloy / SUS foil, which were then press molded under a load of 20 kN and sealed in an all-solid-state battery evaluation cell (manufactured by Hosen Co., Ltd., model KP-SolidCell), to produce all-solid-state secondary battery J.

[0157] [Comparative Example 13] Manufacture of all-solid-state secondary battery K An all-solid-state secondary battery K was produced in the same manner as in Example 7, except that the electrode active material in Example 7 was changed to only 50.0 parts by mass of SPAN produced in Production Example 1.

[0158] [Comparative Example 14] Production of all-solid-state secondary battery L The electrode active material in Example 7 was lithium titanium oxide (Li 4 Ti 5 O 12An all-solid-state secondary battery L was produced in the same manner as in Example 7, except that only 50.0 parts by mass of 1,2-dichlorophenyl ether (manufactured by Ishihara Sangyo Kaisha, Ltd., average secondary particle diameter 7 μm) was used.

[0159] The all-solid-state secondary batteries J to L produced in Example 7, Comparative Example 13, and Comparative Example 14 were used to carry out the following evaluations.

[0160] (1) Rate characteristics The all-solid-state secondary battery was placed in a thermostatic chamber at 60°C, and a charge / discharge test was performed five times in succession under the conditions of a charge cut-off voltage of 2.38V, a discharge cut-off voltage of 0.38V, a charge rate of 0.05C, and a discharge rate of 0.05C. Furthermore, a charge / discharge test was performed three times in succession under the conditions of a charge rate of 0.05C and a discharge rate of 1.0C. A total of eight charge / discharge tests were performed to measure the discharge capacity. The ratio of the eighth discharge capacity to the fifth discharge capacity was calculated as the rate characteristic (%). These results are shown in Table 3.

[0161] [Table 3] [Explanation of symbols]

[0162] 1 positive electrode 1a Positive electrode current collector 2 negative electrode 2a Negative electrode current collector 3. Nonaqueous electrolyte 4 Positive electrode case 5 Negative electrode case 6 Gasket 7 Separator 10. Coin-type lithium-ion secondary battery 10' Cylindrical lithium-ion secondary battery 11 Negative electrode 12 Negative electrode current collector 13 Positive electrode 14 Positive electrode current collector 15. Nonaqueous electrolytes 16 Separator 17 Positive terminal 18 Negative terminal 19 Negative plate 20 Negative lead 21 Positive electrode plate 22 Positive lead 23 cases 24 Insulating plate 25 Gasket 26 Safety valve 27 PTC element 28 Laminated lithium-ion secondary battery 29 Electrode group 30 Case side lamination film 31 Lid side lamination film

Claims

1. An electrode having an active material layer containing sulfur-modified polyacrylonitrile and lithium titanium oxide formed on a current collector, An electrode in which the average secondary particle diameter of the sulfur-modified polyacrylonitrile is larger than the average secondary particle diameter of the lithium titanium oxide, the content of the sulfur-modified polyacrylonitrile in the active material layer is 5% by mass to 85% by mass, and the content of the lithium titanium oxide in the active material layer is 5% by mass to 85% by mass.

2. The electrode according to claim 1, wherein the average secondary particle diameter of the sulfur-modified polyacrylonitrile is 0.1 μm to 50 μm.

3. 3. The electrode according to claim 1, wherein the average secondary particle size of the lithium titanium oxide is 0.05 μm to 30 μm.

4. A positive electrode and A negative electrode; A non-aqueous electrolyte containing a lithium salt; A lithium ion secondary battery comprising: A lithium ion secondary battery, wherein the positive electrode or the negative electrode is the electrode according to any one of claims 1 to 3.

5. 5. The lithium ion secondary battery according to claim 4, wherein the non-aqueous electrolyte containing a lithium salt is a liquid non-aqueous electrolyte, a polymer gel non-aqueous electrolyte, a polymer non-aqueous electrolyte, a complex hydride-based solid electrolyte, or an inorganic solid electrolyte.

6. 5. The lithium ion secondary battery according to claim 4, wherein the non-aqueous electrolyte containing the lithium salt is a liquid non-aqueous electrolyte, and the liquid non-aqueous electrolyte contains a cyclic carbonate compound.

7. The lithium ion secondary battery according to claim 6 , wherein the liquid nonaqueous electrolyte further contains a chain carbonate compound.

8. 5. The lithium ion secondary battery according to claim 4, wherein the non-aqueous electrolyte containing a lithium salt is an inorganic solid electrolyte, and the inorganic solid electrolyte is a sulfide-based solid electrolyte or an oxide-based solid electrolyte.

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