JP2015201335A - lithium ion battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion battery excellent in preserving property at high temperature.SOLUTION: The lithium ion battery includes: a positive electrode; a negative electrode; and an electrolyte. The positive electrode includes: a collector; and a positive electrode mixture coated at least on one surface of the collector. The positive electrode mixture contains a positive electrode conductive material and a lithium manganese nickel complex oxide, having BET specific surface area of less than 0.3 m2/g as a positive electrode active material. The negative electrode contains a negative electrode conductive material and a lithium titanium complex oxide as a negative electrode active material.

Description

  The present invention relates to a lithium ion battery.

  Lithium ion batteries are secondary batteries with high energy density, and are used as power sources for portable devices such as notebook computers and mobile phones, taking advantage of their characteristics.

  In recent years, lithium-ion batteries excellent in input / output characteristics, energy density, and charge / discharge cycle characteristics have been required as power supplies for electronic devices, power storage power supplies, and electric vehicle power supplies that are becoming smaller in size.

  As means for improving output characteristics and charge / discharge cycle characteristics, the following Patent Document 1 discloses a technique related to a lithium ion battery using a spinel-structure lithium titanium composite oxide having a specific surface area as a negative electrode active material. ing.

JP 2005-317512 A

  Incidentally, lithium ion batteries are also required to improve storage characteristics at high temperatures.

  This invention is made | formed in view of the said situation, and it aims at providing the lithium ion battery which is excellent in the storage characteristic at high temperature.

A lithium ion battery according to the present invention is a lithium ion battery comprising a positive electrode, a negative electrode, and an electrolyte solution, wherein the positive electrode is a positive electrode mixture coated on at least one surface of a current collector and the current collector. The positive electrode mixture includes a lithium manganese nickel composite oxide having a BET specific surface area of less than 0.3 m ² / g and a positive electrode conductive material as a positive electrode active material, and the negative electrode is lithium as a negative electrode active material. Includes titanium composite oxide and negative electrode conductive material.
According to the lithium ion battery of the present invention, the storage characteristics at high temperatures are excellent.

The positive electrode conductive material is preferably acetylene black. In this case, the input / output characteristics can be further improved.

  Moreover, it is preferable that content of the said positive electrode electrically conductive material is 4-10 mass% on the basis of the whole quantity of positive electrode compound material. In this case, input / output characteristics can be further improved.

  ADVANTAGE OF THE INVENTION According to this invention, the lithium ion battery excellent in the storage characteristic at high temperature can be provided.

It is a perspective view which shows one Embodiment of the lithium ion secondary battery of this invention. It is a perspective view which shows the positive electrode plate, negative electrode plate, and separator which comprise an electrode group.

  Hereinafter, embodiments of the lithium ion battery of the present invention will be described in the order of a lithium manganese nickel composite oxide serving as a positive electrode active material, a lithium titanium composite oxide serving as a negative electrode active material, and an overall configuration of the lithium ion battery.

<Lithium manganese nickel composite oxide>
The lithium manganese nickel composite oxide serving as the positive electrode active material of the lithium ion battery of this embodiment is preferably a lithium manganese nickel composite oxide having a spinel structure. The spinel type lithium manganese nickel composite oxide is represented by LiNi _X Mn _{2 -X} O ₄ (0.3 <X <0.7). From the viewpoint of stability, LiNi _0.5 Mn _1.5 O ₄ is More preferred. In order to further stabilize the crystal structure of LiNi _0.5 Mn _1.5 O _{4 having} the spinel structure, a part of the Mn / Ni site of the spinel structure lithium manganese nickel composite oxide was replaced with another metal. It can also be used as a positive electrode active material.

  Moreover, what made excess lithium exist in a crystal | crystallization, or what produced the defect | deletion in O site can also be used. Examples of other metals that can substitute the Mn / Ni site include Ti, V, Cr, Fe, Co, Zn, Cu, W, Mg, Al, and Ru. These can be substituted with one or more metal elements. Of these substitutable metal elements, Ti is preferably used as the substitution element from the viewpoint of stabilizing the crystal structure.

From the viewpoint of high energy density, the lithium manganese nickel composite oxide is preferably used with a potential in a charged state of 4.5 V or more and 5 V or less with respect to Li / Li ⁺ , and 4.6 or more and 4.9 V or less. It is more preferable to use in.

BET specific surface area of the lithium-manganese-nickel composite oxide is less than 0.3 m ² / g, from the viewpoint of further improving the storage characteristics at high temperatures, preferably less than 2.9 m ² / g, More preferably, it is less than 2.8 m ² / g. Input-output characteristic (hereinafter, sometimes referred rate characteristics) from the point of view that can improve, BET specific surface area is preferably at 0.05 m ² / g or more, more not less 0.08 m ² / g or more Preferably, it is more preferably 0.1 m ² / g or more.
The BET specific surface area can be measured from the nitrogen adsorption capacity according to, for example, JIS Z 8830. As the evaluation device, for example, AUTOSORB-1 (trade name) manufactured by QUANTACHROME can be used. When measuring the BET specific surface area, it is considered that the moisture adsorbed on the sample surface and structure affects the gas adsorption capacity. Therefore, it is preferable to first perform pretreatment for moisture removal by heating. . In the pretreatment, the measurement cell charged with 0.05 g of the measurement sample is depressurized to 10 Pa or less with a vacuum pump, heated at 110 ° C., held for 3 hours or more, and kept at a normal temperature while maintaining the depressurized state. It is preferable to naturally cool to (25 ° C.). After performing this pretreatment, it is preferable that the evaluation temperature is 77K and the evaluation pressure range is less than 1 in relative pressure (equilibrium pressure with respect to saturated vapor pressure).
The median diameter D50 of the lithium manganese nickel composite oxide particles (secondary particle median diameter D50 when primary particles are aggregated to form secondary particles) is the dispersibility of the mixture slurry. In view of the above, it is preferably 0.5 μm or more and 100 μm or less, and more preferably 1 μm or more and 50 μm or less. The median diameter D50 can be obtained from the particle size distribution obtained by the laser diffraction / scattering method.

  The positive electrode active material in the lithium ion battery of this embodiment may include a positive electrode active material other than the lithium manganese nickel composite oxide.

Examples of positive electrode active materials other than lithium manganese nickel composite oxide include Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x Co _y Ni _1-y O ₂ , and Li _x Co _y M _1-y O. _{z, Li x Ni 1-y} M y O z, Li x Mn 2 O 4 and _{Li x Mn 2-y M y} O 4 ( in each of the formulas above, M is Na, Mg, Sc, Y, Mn, Fe, It represents at least one element selected from the group consisting of Co, Cu, Zn, Al, Cr, Pb, Sb, V and B. x = 0 to 1.2, y = 0 to 0.9, z = 2. 0.0 to 2.3.). Here, x value which shows the molar ratio of lithium increases / decreases by charging / discharging.

  From the viewpoint of improving the battery capacity, the content of the lithium manganese nickel composite oxide is preferably 60 to 100% by mass, more preferably 70 to 100% by mass, and 85 to 100% by mass in the total amount of the positive electrode active material. More preferably it is.

<Lithium titanium composite oxide>
The lithium titanium composite oxide serving as the negative electrode active material of the lithium ion battery of the present embodiment is preferably a lithium titanium composite oxide having a spinel structure. The basic composition formula of the spinel structure lithium titanium composite oxide is represented by Li [Li _1/3 Ti _5/3 ] O ₄ , and in order to further stabilize the crystal structure, the spinel structure lithium titanium composite oxide A material in which a part of the Li or Ti site is substituted with another metal, a material in which excess lithium is present in the crystal, or a material in which a part of the O site is substituted with another element can also be used. Examples of other metals that can be substituted include F, B, Nb, V, Mn, Ni, Cu, Co, Zn, Sn, Pb, Al, Mo, Ba, Sr, Ta, Mg, and Ca. Can do. These can be substituted with one or more metal atoms.

The potential in the charged state of the lithium titanium composite oxide is preferably 1 V or more and 2 V or less with respect to Li / Li ⁺ .

  The negative electrode active material in the lithium ion battery of the present embodiment may include a negative electrode active material other than the lithium titanium composite oxide.

  Examples of the negative electrode active material other than the lithium titanium composite oxide include a carbon material.

  The content of the lithium titanium composite oxide is preferably 70 to 100% by mass, more preferably 80 to 100% by mass, and more preferably 90 to 100% by mass in the total amount of the negative electrode active material from the viewpoint of improving safety and cycle characteristics. More preferably.

<Overall configuration of lithium-ion battery>
The positive electrode of the lithium ion battery uses the above lithium manganese nickel composite oxide as a positive electrode active material, and a conductive material is mixed therewith, and an appropriate binder and solvent are added as necessary to obtain a paste-like positive electrode mixture. A thing is apply | coated to the collector surface of metal foils, such as aluminum foil, it dries, and it forms after that, after that, raises the density of positive mix by a press etc. as needed. In addition, although the positive electrode active material can be constituted only by the present lithium manganese nickel composite oxide, for the purpose of improving the characteristics of the lithium ion battery, etc., known LiCoO ₂ , LiNiO ₂ , LiMn are known for the lithium manganese nickel composite oxide. A lithium composite oxide such as ₂ O ₄ , LiFePO ₄ , or Li (Co _1/3 Ni _1/3 Mn _1/3 ) O ₂ may be mixed to obtain a positive electrode active material.

From the viewpoint of energy density and input / output characteristics, the single-side coating amount of the positive electrode mixture on the current collector is preferably 10 g / m ² or more and 250 g / m ² or less, and 50 g / m ² or more and 200 g / m ² or less. It is more preferable that
The density of the positive electrode mixture is preferably 1.8 g / cm ³ or more and 3.2 g / cm ³ or less from the viewpoint of energy density. 2.0 g / cm ³ or more and 3.0 g / cm ³ or less is more preferable.

  For the negative electrode, the lithium titanium composite oxide is used as a negative electrode active material, and a conductive material and a binder are mixed therein, and an appropriate solvent is added as necessary to obtain a paste-like negative electrode mixture such as copper. It is applied to a current collector of the metal foil, dried, and then formed by increasing the density of the negative electrode mixture by pressing or the like as necessary. In addition, the negative electrode active material can be composed only of the lithium titanium composite oxide, but for the purpose of improving the characteristics of the lithium ion battery, a known carbon material or the like is already mixed with the lithium titanium composite oxide, and the negative electrode active material. It may be.

The amount of the negative electrode mixture applied to the current collector is preferably 10 g / m ² or more and 200 g / m ² or less, and 50 g / m ² or more and 150 g / m ² or less from the viewpoint of energy density and input / output characteristics. More preferably.
The density of the negative electrode mixture is preferably 1.0 g / cm ³ or more and 2.8 g / cm ³ or less from the viewpoint of energy density. 1.2 g / cm ³ or more and 2.6 g / cm ³ or less is more preferable.

  From the viewpoint of improving the electrical conductivity of the positive electrode and the negative electrode, the conductive material is used by mixing one or more of carbon powders such as acetylene black and ketjen black, and carbon material powders such as graphite. be able to. In addition, a small amount of carbon nanotubes, graphene, or the like can be added as a conductive material to increase the electrical conductivity of the positive electrode and / or the negative electrode.

As the conductive material used for the positive electrode (hereinafter referred to as the positive electrode conductive material), acetylene black is preferable from the viewpoint of improving the rate characteristics.
From the viewpoint of rate characteristics, the content of the positive electrode conductive material is preferably 4% by mass or more, more preferably 5% by mass or more, and still more preferably 5.5% by mass or more, based on the total amount of the positive electrode mixture. The upper limit is preferably 10% by mass or less, more preferably 9% by mass or less, and still more preferably 8.5% by mass or less from the viewpoint of battery capacity.

Moreover, as a electrically conductive material (henceforth a negative electrode electrically conductive material) used for a negative electrode, from a viewpoint which can improve a rate characteristic more, acetylene black is preferable.
From the viewpoint of rate characteristics, the content of the negative electrode conductive material is preferably 1% by mass or more, more preferably 4% by mass or more, and still more preferably 6% by mass or more, based on the total amount of the negative electrode mixture. From the viewpoint of battery capacity, the upper limit is preferably 15% by mass or less, more preferably 12% by mass or less, and still more preferably 10% by mass or less.

The binder is not particularly limited, and a material having good solubility or dispersibility in the dispersion solvent is selected. Specific examples include resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluorine Rubbery polymers such as rubber, isoprene rubber, butadiene rubber, ethylene-propylene rubber; styrene / butadiene / styrene block copolymer or hydrogenated product thereof, EPDM (ethylene / propylene / diene terpolymer), styrene / Thermoplastic elastomeric polymers such as ethylene / butadiene / ethylene copolymers, styrene / isoprene / styrene block copolymers or hydrogenated products thereof; syndiotactic-1, 2-polybutadiene, polyvinyl acetate , Ethylene / vinyl acetate copolymer, propylene / α-olefin copolymer and other soft resinous polymers; polyvinylidene fluoride (PVdF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene / ethylene copolymer Polymers, fluorinated polymers such as polytetrafluoroethylene / vinylidene fluoride copolymers, copolymers obtained by adding acrylic acid and linear ether groups to the polyacrylonitrile skeleton, ion conduction of alkali metal ions (especially lithium ions) And a polymer composition having the property. Of these, one type may be used alone, or two or more types may be used in combination. For both the positive electrode and the negative electrode, from the viewpoint of high adhesion, it is preferable to use a polyvinylidene fluoride (PVdF) or a copolymer obtained by adding acrylic acid and a linear ether group to a polyacrylonitrile skeleton.

  Regarding the content of the binder, the range of the content of the binder relative to the mass of the positive electrode mixture is as follows. The lower limit of the range is preferably 0.1% by mass or more from the viewpoint of sufficiently binding the positive electrode active material to obtain sufficient mechanical strength of the positive electrode and stabilizing battery performance such as cycle characteristics. The above is more preferable, and 2% by mass or more is more preferable. From the viewpoint of improving battery capacity and conductivity, the upper limit is preferably 30% by mass or less, more preferably 20% by mass or less, and still more preferably 10% by mass or less. The content of the binder with respect to the total amount of the negative electrode mixture is as follows. The lower limit of the range is preferably 0.1% by mass or more from the viewpoint of sufficiently binding the negative electrode active material to obtain sufficient mechanical strength of the negative electrode and stabilizing battery performance such as cycle characteristics. More preferably, it is more preferably 1% by mass or more. The upper limit is preferably 40% by mass or less, more preferably 25% by mass or less, and still more preferably 15% by mass or less from the viewpoint of improving battery capacity and conductivity.

  An organic solvent such as N-methyl-2pyrrolidone can be used as a solvent for dispersing these active materials, conductive materials, binders and the like.

  In addition to the positive electrode and the negative electrode, the lithium ion battery of this embodiment preferably has a separator, a non-aqueous electrolyte, or the like that is sandwiched between the positive electrode and the negative electrode.

  The separator is not particularly limited as long as it has ion permeability while electronically insulating between the positive electrode and the negative electrode, and has resistance to oxidation on the positive electrode side and reducibility on the negative electrode side. As a material (material) of the separator satisfying such characteristics, a resin, an inorganic material, glass fiber, or the like is used.

As the resin, olefin polymer, fluorine polymer, cellulose polymer, polyimide, nylon and the like are used. Specifically, it is preferable to select from materials that are stable with respect to non-aqueous electrolytes and have excellent liquid retention properties. For example, porous sheets or nonwoven fabrics made from polyolefins such as polyethylene and polypropylene may be used. preferable. In addition, considering that the potential of the positive electrode may be as high as 4.7 to 4.8 V with respect to Li / Li ⁺ , three types of polypropylene / polyethylene / polypropylene in which polyethylene is sandwiched between polypropylenes having high potential resistance. Those including a layer structure are preferred.

  As the inorganic material, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate are used. For example, what made the said inorganic substance of fiber shape or particle shape adhere to thin film-shaped base materials, such as a nonwoven fabric, a woven fabric, and a microporous film, can be used as a separator. As a thin film-shaped substrate, a substrate having a pore diameter of 0.01 to 1 μm and a thickness of 5 to 50 μm is preferably used. In addition, for example, a separator in which a composite porous layer is formed using the above-described inorganic material in a fiber shape or a particle shape by using a binder such as a resin can be used as a separator. Furthermore, this composite porous layer may be formed on the surface of the positive electrode or the negative electrode to form a separator. For example, a composite porous layer in which alumina particles having a 90% average particle diameter (D90) of less than 1 μm are bound using a fluororesin as a binder may be formed on the surface of the positive electrode or the surface facing the positive electrode of the separator. Good.

  In addition, positive and negative electrode current collectors are used for the positive and negative electrode active materials, and the material for the positive electrode is aluminum, titanium, stainless steel, nickel, calcined carbon, conductive polymer, conductive glass, etc. In addition, the surface of aluminum, copper, etc. treated with carbon, nickel, titanium, silver, etc. can be used for the purpose of improving adhesion, conductivity, oxidation resistance, and the negative electrode is copper, stainless steel, nickel, aluminum In addition to titanium, baked carbon, conductive polymer, conductive glass, aluminum-cadmium alloy, etc., carbon, nickel, titanium, etc. on the surface of copper, aluminum, etc. for the purpose of improving adhesion, conductivity, reduction resistance Those treated with silver or the like can be used. The positive and negative electrode current collector thickness is preferably 1 to 50 μm from the viewpoint of electrode strength and energy density.

  The electrolytic solution of the present embodiment includes a lithium salt (electrolyte) and a non-aqueous solvent that dissolves the lithium salt. You may add an additive as needed.

Lithium salts include LiPF ₆ , LiBF ₄ , LiFSI (lithium bisfluorosulfonylimide), LiTFSI (lithium bistrifluoromethanesulfonylimide), LiClO ₄ , LiB (C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN (SO ₂ F) ₂ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₂ CF ₃ ) _{2 and the} like. These lithium salts may be used alone or in combination of two or more. Among these, lithium hexafluorophosphate (LiPF ₆ ) is preferable when comprehensively judging solubility in a solvent, charge / discharge characteristics in the case of a lithium ion battery, input / output characteristics, cycle characteristics, and the like.

  The concentration of the lithium salt is preferably 0.5 mol / L to 1.5 mol / L, more preferably 0.7 mol / L to 1.3 mol / L with respect to the nonaqueous solvent. More preferably, it is 8 mol / L to 1.2 mol / L. By setting the concentration of the lithium salt to 0.5 mol / L to 1.5 mol / L, the charge / discharge characteristics can be further improved.

  Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate and propylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate, γ-butyllactone, acetonitrile, 1,2-dimethoxyethane, dimethoxymethane, Tetrahydrofuran, dioxolane, methylene chloride and methyl acetate. These may be used alone or in combination of two or more, but it is preferable to use a mixed solvent in which a cyclic carbonate and a chain carbonate are mixed.

  When the cyclic carbonate is contained, the content is preferably 10 to 70% by volume, more preferably 20 to 60% by volume, and still more preferably 35 to 55% by volume with respect to the total amount of the nonaqueous solvent.

  The additive is not particularly limited as long as it is an additive for a non-aqueous electrolyte solution of a lithium ion battery. For example, nitrogen, sulfur or a heterocyclic compound containing nitrogen and sulfur, a cyclic carboxylic acid ester, a fluorine-containing cyclic Examples thereof include carbonates and other compounds having an unsaturated bond in the molecule. In addition to the above additives, other additives such as an overcharge prevention material, a negative electrode film forming material, a positive electrode protective material, and a high input / output material may be used depending on the required function.

  With the other additives, it is possible to improve storage characteristics at high temperatures, cycle characteristics, and input / output characteristics.

The lithium ion battery configured as described above can have various shapes such as a cylindrical shape, a stacked shape, and a coin shape. Regardless of which shape is used, a separator is sandwiched between the positive electrode and the negative electrode to form an electrode body, and the space between the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal is used for current collection. Connection is made using a lead or the like, and this electrode body is sealed in a battery case together with a non-aqueous electrolyte to complete a lithium ion battery.
As an embodiment of the present invention, a laminated lithium ion battery in which a positive electrode plate and a negative electrode plate are laminated via a separator will be described, but the embodiment of the present invention is not limited thereto. Other embodiments include, for example, a wound lithium ion battery in which a laminate formed by laminating a positive electrode plate and a negative electrode plate via a separator is wound.

  FIG. 1 is a perspective view showing an embodiment of the lithium ion secondary battery of the present invention. The lithium ion secondary battery 10 is one in which the electrode group 20 and the electrolyte solution are accommodated in the battery container of the laminate film 6, and the positive electrode current collecting tab 2 and the negative electrode current collecting tab 4 are taken out of the battery container. Yes.

As shown in FIG. 2, the electrode group 20 is formed by laminating a positive electrode plate 1 to which a positive electrode current collecting tab 2 is attached, a separator 5, and a negative electrode plate 3 to which a negative electrode current collecting tab 4 is attached.
In addition, the magnitude | size, shape, etc. of a positive electrode plate, a negative electrode plate, a separator, an electrode group, and a battery can be made into arbitrary things, and are not necessarily limited to what is shown by FIG.1 and FIG.2.

The lithium ion battery used in the present embodiment preferably has a BET specific surface area of less than 0.3 m ² / g from the viewpoint of storage characteristics at high temperatures. The reason why the storage property at high temperature is good when the BET specific surface area is less than 0.3 m ² / g is considered to be because the oxidative decomposition of the electrolytic solution on the surface of the positive electrode active material is reduced.

  In the lithium ion battery used in the present embodiment, the capacity ratio (negative electrode capacity / positive electrode capacity) between the positive electrode and the negative electrode is preferably 0.7 or more and less than 1 from the viewpoint of input characteristics. When the capacity ratio is 0.7 or more, the battery capacity is improved and a high energy density tends to be obtained. On the other hand, when the capacity ratio is less than 1, the decomposition reaction of the electrolytic solution due to the positive electrode being at a high potential hardly occurs, and the cycle characteristics of the lithium ion battery tend to be good. From the viewpoint of energy density and input characteristics, the capacity ratio is more preferably 0.75 or more and 0.95 or less.

The "positive electrode capacity" and the "negative electrode capacity" are the maximum reversibly available when a constant current constant voltage charge-constant current discharge is performed with an electrochemical cell having a counter electrode made of metallic lithium. Means capacity. In the present specification, the “positive electrode capacity” and the “negative electrode capacity” are the current densities during constant current charging and constant current discharging in the electrochemical cell, respectively, with voltage ranges of 4.95 V to 3.5 V and 2 V to 1 V, respectively. The capacity obtained when the above charging / discharging is evaluated to 0.1 mA / cm ² .

  As mentioned above, although the embodiment of the lithium ion battery of the present invention has been described, the above embodiment is only one embodiment, and the lithium ion battery of the present invention includes various embodiments based on the knowledge of those skilled in the art including the above embodiment. The present invention can be implemented in various forms with modifications and improvements.

  Hereinafter, the present embodiment will be described in more detail based on examples. The present invention is not limited to the following examples.

[Example 1]
The positive electrode is 88 parts by mass of lithium manganese nickel composite oxide (LiNi _0.5 Mn _1.5 O ₄ ) having a BET specific surface area of 0.1 m ² / g and an average particle diameter (D50) of 28.8 μm, conductive 6 parts by mass of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a material, and a copolymer obtained by adding acrylic acid and a linear ether group to a polyacrylonitrile skeleton as a binder (manufactured by Hitachi Chemical Co., Ltd., trade name: LSR7) 6 parts by mass, and an appropriate amount of N-methyl-2-pyrrolidone was added and kneaded to obtain a paste-like positive electrode mixture slurry. This slurry was applied to one side of a 20 μm-thick aluminum foil, which is a positive electrode current collector, so as to be substantially uniformly and uniformly 140 g / m ² . Thereafter, drying treatment was performed, and consolidation was performed by pressing to a density of 2.3 g / cm ³ to produce a sheet-like positive electrode. This was cut into a width of 30 mm and a length of 45 mm to form a positive electrode plate, and a positive electrode current collecting tab was attached to the positive electrode plate as shown in FIG.

The negative electrode was mixed with 87 parts by mass of lithium titanium composite oxide, 8 parts by mass of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material, and 5 parts by mass of polyvinylidene fluoride as a binder, and an appropriate amount of N-methyl. A paste-like negative electrode mixture slurry was obtained by adding -2-pyrrolidone and kneading. This slurry was applied to one side of a 10 μm-thick copper foil, which is a negative electrode current collector, at 110 g / m ² . Thereafter, a drying treatment was performed, and the sheet was consolidated by pressing to a density of 1.7 g / cm ³ to produce a sheet-like negative electrode. This was cut into a width of 31 mm and a length of 46 mm to form a negative electrode plate, and a negative electrode current collecting tab was attached to the negative electrode plate as shown in FIG.

(Production of electrode group)
The produced positive electrode plate and the negative electrode plate were opposed to each other through a separator made of a polyethylene microporous film having a thickness of 30 μm, a width of 35 mm, and a length of 50 mm to produce a laminated electrode group.

(Production of lithium ion battery)
As shown in FIG. 1, the electrode group is housed in a battery container made of an aluminum laminate film, and 1 ml of a nonaqueous electrolyte is injected into the battery container, and then the positive electrode current collecting tab is used. The lithium ion batteries of Examples 1 to 5 and Comparative Examples 1 to 3 were fabricated by sealing the opening of the battery container so that the negative electrode current collecting tab and the negative electrode current collecting tab were taken out. As the non-aqueous electrolyte, a solution obtained by dissolving LiPF ₆ at a concentration of 1M in a mixed solvent in which ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 3: 7 was used. The aluminum laminate film is a laminate of polyethylene terephthalate (PET) film / aluminum foil / sealant layer (polypropylene, etc.).

(Initial discharge capacity)
The above lithium ion battery was charged with a constant current at 25 ° C. with a current value of 0.2 C and a charge end voltage of 3.4 V using a charging / discharging device (BATTERY TEST UNIT, manufactured by IEM Co., Ltd.), and then a charging voltage of 3. Constant voltage charging was performed until the current value reached 0.01 C at 4V. C used as a unit of current value means “current value (A) / battery capacity (Ah)”. After resting for 15 minutes, constant current discharge was performed at a current value of 0.2 C and a discharge end voltage of 2.0 V. Charging / discharging was repeated four times under the above-mentioned charging / discharging conditions, and the initial discharge capacity was determined by measuring the discharge capacity in a constant current discharge test at a fourth current value of 0.2 C and a final discharge voltage of 2.0 V.

(Input characteristics)
Using the lithium ion battery whose initial discharge capacity was measured, after the discharge was stopped for 15 minutes, it was charged with a constant current at 25 ° C. with a current value of 0.5 C and a charge end voltage of 3.4 V, and then a charge end voltage of 3 Constant voltage charging was performed until the current value reached 0.01 C at 4 V, and the charge capacity was measured (charge capacity at 0.5 C). After resting for 15 minutes, a constant current discharge was performed at 25 ° C. with a current value of 0.5 C and a final voltage of 2 V. Next, after resting for 15 minutes, a constant current charge was performed at 25 ° C. with a current value of 5 C and a charge end voltage of 3.4 V, and the charge capacity was measured (charge capacity at 5 C). And the input characteristic was computed from the following formula | equation.
Input characteristics (%) = (charge capacity at 5C / charge capacity at 0.5C) × 100

(Output characteristics)
Using the lithium ion battery in which the input characteristics were measured, after charging was stopped for 15 minutes, a constant current discharge with a current value of 0.5 C and a final voltage of 2 V was performed at 25 ° C. After a 15-minute pause, charge at a constant current of 0.5 C and a charge end voltage of 3.4 V at 25 ° C., and then charge at a constant voltage until the current value reaches 0.01 C at a charge end voltage of 3.4 V. Went. After resting for 15 minutes, a constant current discharge was performed at 25 ° C. with a current value of 0.5 C and a final voltage of 2 V, and the discharge capacity was measured (discharge capacity at 0.5 C). Next, 15 minutes later, constant current charging was performed at 25 ° C. with a current value of 0.5 C and a charge end voltage of 3.4 V, and then with a charge end voltage of 3.4 V, constant voltage charge was performed until the current value reached 0.01 C. It was. After resting for 15 minutes, a constant current discharge was performed at 25 ° C. with a current value of 5 C and a final voltage of 2 V, and the discharge capacity was measured (discharge capacity at 5 C). And the output characteristic was computed from the following formula | equation.
Output characteristics (%) = (discharge capacity at 5 C / discharge capacity at 0.5 C) × 100

(Storage characteristics)
Using the lithium ion battery whose output characteristics were measured, a constant current charge was performed at 25 ° C. with a current value of 0.2 C and a charge end voltage of 3.4 V, and then a current value of 0.01 C at a charge end voltage of 3.4 V. Constant voltage charging was performed until Thereafter, the lithium ion battery was kept in a thermostat at 50 ° C. for 20 days. After storage for 20 days, the lithium ion battery was held at 25 ° C. for 1 hour. Thereafter, constant current discharge at a current value of 0.2 C and a final voltage of 2 V was performed at 25 ° C. After a 15-minute pause, charge at constant current at 25 ° C with a current value of 0.2C and a charge end voltage of 3.4V, and then charge at a constant voltage until the current value reaches 0.01C at a charge end voltage of 3.4V. Went. After resting for 15 minutes, a constant current discharge with a current value of 0.2 C and a final voltage of 2 V was performed at 25 ° C., and the discharge capacity was measured (discharge capacity after storage for 20 days). And the preservation | save characteristic was computed from the following formula | equation.
Storage characteristics (%) = (discharge capacity after 20 days storage / initial discharge capacity) × 100

[Example 2]
A lithium manganese nickel composite oxide (LiNi _0.5 Mn _1.5 O ₄ ) having a BET specific surface area of 0.1 m ² / g and an average particle size (D50) of 28.8 μm shown in Example 2 of Table 1 86 parts by mass, 8 parts by mass of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material, and a copolymer obtained by adding acrylic acid and a linear ether group to a polyacrylonitrile skeleton as a binder (Hitachi Chemical Co., Ltd.) Manufactured, trade name: LSR7) was mixed, and an appropriate amount of N-methyl-2-pyrrolidone was added and kneaded to obtain a paste-like positive electrode mixture slurry. This slurry was applied to both surfaces of a 20 μm-thick aluminum foil as a positive electrode current collector in an amount of 140 g / m ² substantially uniformly and uniformly. Thereafter, drying treatment was performed, and consolidation was performed by pressing to a density of 2.3 g / cm ³ to produce a sheet-like positive electrode. This was cut into a width of 30 mm and a length of 45 mm to form a positive electrode plate, and a positive electrode current collecting tab was attached to the positive electrode plate as shown in FIG. Then, the negative electrode and the lithium ion secondary battery were produced by the same method as shown in Example 1, and the initial discharge capacity, input characteristics, output characteristics, and storage characteristics were measured.

[Example 3]
A lithium manganese nickel composite oxide (LiNi _0.5 Mn _1.5 O ₄ ) having a BET specific surface area of 0.1 m ² / g and an average particle size (D50) of 28.8 μm shown in Example 2 of Table 1 90 parts by mass, 4 parts by mass of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material, and a copolymer obtained by adding acrylic acid and a linear ether group to a polyacrylonitrile skeleton as a binder (Hitachi Chemical Co., Ltd.) Manufactured, trade name: LSR7) was mixed, and an appropriate amount of N-methyl-2-pyrrolidone was added and kneaded to obtain a paste-like positive electrode mixture slurry. This slurry was applied to both surfaces of a 20 μm-thick aluminum foil as a positive electrode current collector in an amount of 140 g / m ² substantially uniformly and uniformly. Thereafter, drying treatment was performed, and consolidation was performed by pressing to a density of 2.3 g / cm ³ to produce a sheet-like positive electrode. This was cut into a width of 30 mm and a length of 45 mm to form a positive electrode plate, and a positive electrode current collecting tab was attached to the positive electrode plate as shown in FIG. Then, the negative electrode and the lithium ion secondary battery were produced by the same method as shown in Example 1, and the initial discharge capacity, input characteristics, output characteristics, and storage characteristics were measured.

[Examples 4 to 5]
A lithium manganese nickel composite oxide having a BET specific surface area of 0.22 m ² / g and an average particle diameter (D50) of 17.9 μm shown in Examples 4 to 5 in Table 1, and a BET specific surface area of 0.25 g / m ² A lithium ion secondary battery was prepared in the same manner as in Example 1 except that the lithium manganese nickel composite oxide having an average particle size of 13.5 μm was changed to an initial discharge capacity, input characteristics, output characteristics, and storage. Characteristics were measured.

[Comparative Examples 1-3]
A lithium ion secondary battery was fabricated in the same manner as in Example 1, except that the lithium manganese nickel composite oxide having a BET specific surface area of 0.4 m ² / g or more shown in Comparative Examples 1 to 3 in Table 1 was changed. The initial discharge capacity, input characteristics, output characteristics, and storage characteristics were measured.

  Table 1 shows the measurement results of the BET specific surface area of the positive electrode active material, the average particle size of the positive electrode active material, the positive electrode conductive agent amount, the initial discharge capacity, the input characteristics, the output characteristics, and the storage characteristics.

In the examples, it can be confirmed that the storage characteristics at high temperatures are excellent as compared with the comparative examples.

  ADVANTAGE OF THE INVENTION According to this invention, the lithium ion battery excellent in the storage characteristic at high temperature can be provided.

  DESCRIPTION OF SYMBOLS 1 ... Positive electrode plate, 2 ... Positive electrode current collection tab, 3 ... Negative electrode plate, 4 ... Negative electrode current collection tab, 5 ... Separator, 6 ... Laminate film, 10 ... Lithium ion secondary battery, 20 ... Electrode group.

Claims (3)

A lithium ion battery comprising a positive electrode, a negative electrode, and an electrolyte solution,
The positive electrode includes a current collector and a positive electrode mixture applied to at least one surface of the current collector, and the positive electrode mixture is a lithium having a BET specific surface area of less than 0.3 m 2 / g as a positive electrode active material. Containing manganese nickel composite oxide and positive electrode conductive material,
The negative electrode is a lithium ion battery including a lithium titanium composite oxide and a negative electrode conductive material as a negative electrode active material.   The lithium ion battery according to claim 1, wherein the positive electrode conductive material is acetylene black.   The lithium ion battery according to claim 1 or 2, wherein the content of the positive electrode conductive material is 4 to 10% by mass based on the total amount of the positive electrode mixture.

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