JP2017010716A - Lithium ion battery and lithium ion battery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion battery and a lithium ion battery system which have excellent cycle characteristic at high temperatures.SOLUTION: A lithium ion battery includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode has a collector and a positive electrode mixture applied to at least one surface of the collector. The positive electrode mixture contains a lithium-manganese-nickel composite oxide as a cathode active material, and contains acetylene black and graphene as a positive electrode conductive material. The negative electrode contains a lithium titanium composite oxide and a negative electrode conductive material as an anode active material.SELECTED DRAWING: None

Description

  The present invention relates to a lithium ion battery and a lithium ion battery system.

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 having excellent input / output characteristics, energy density, and charge / discharge cycle characteristics have been required as power supplies for electronic devices, power supplies for power storage, and power supplies for electric vehicles, which have been improved in performance and 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. Yes.

JP 2005-317512 A

Incidentally, lithium ion batteries are also required to improve cycle characteristics at high temperatures.
This invention is made | formed in view of the said situation, and it aims at providing the lithium ion battery and lithium ion battery system which are excellent in an output characteristic and the cycling characteristics in high temperature.

  The present inventors provide a lithium ion battery comprising a positive electrode, a negative electrode, and an electrolyte solution, the positive electrode having a current collector and a positive electrode mixture applied to at least one surface of the current collector. The positive electrode mixture includes lithium / manganese / nickel composite oxide, acetylene black and graphene, and the negative electrode uses a lithium ion battery including a lithium titanium composite oxide and a negative electrode conductive material as a negative electrode active material. It has been found that the above problems can be solved.

  That is, the present invention is a lithium ion battery comprising a positive electrode, a negative electrode, and an electrolyte solution, wherein the positive electrode has a current collector and a positive electrode mixture applied to at least one surface of the current collector. The positive electrode mixture includes a lithium / manganese / nickel composite oxide as a positive electrode active material, acetylene black and graphene as a positive electrode conductive material, and the negative electrode includes a lithium titanium composite oxide and a negative electrode conductive material as a negative electrode active material. Including lithium ion batteries.

  The present invention also relates to the above lithium ion battery, wherein a capacity ratio (negative electrode capacity / positive electrode capacity) between the positive electrode and the negative electrode is 0.7 or more and less than 1.

  Furthermore, the present invention relates to a lithium ion battery system comprising the above lithium ion battery and charge control means for controlling the charge end voltage Vf within a range of 3.6V ≦ Vf ≦ 4.0V.

  The lithium ion battery according to the present invention is excellent in output characteristics and high temperature cycle characteristics due to the above configuration.

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

It is a perspective view which shows one Embodiment of the lithium ion 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, an embodiment of a lithium ion battery system 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 according to the present embodiment is preferably a lithium / manganese / nickel composite oxide having a spinel structure. Spinel type lithium-manganese-nickel composite oxide represented by _{LiNi X Mn 2-X O 4} (0.3 <X <0.7), preferably LiNi _0.5 Mn _1.5 O ₄ from the viewpoint of stability. In order to further stabilize the crystal structure of the spinel structure LiNi _0.5 Mn _1.5 O ₄ , a positive electrode active material obtained by substituting a part of the Mn / Ni site of the spinel structure lithium / manganese / nickel composite oxide with another metal is used. It can also be used as a substance.

  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 above lithium / manganese / nickel composite oxide preferably has a potential in a charged state of 4.5 V or more and 5 V or less with respect to Li / Li ⁺ . More preferably, it is 9 V or less.

The positive electrode active material in the lithium ion battery of the present 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 oxides 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 And at least one element selected from the group consisting of Fe, Co, Cu, Zn, Al, Cr, Pb, Sb, V and B. x = 0 to 1.2, y = 0 to 0.9, z = 2.0 to 2.3.). Here, x value which shows the molar ratio of lithium increases / decreases by charging / discharging.

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

<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 make the crystal structure more stable, the spinel structure lithium titanium composite oxide Li Alternatively, a material in which a part of the 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 be used. Examples of other elements that can be substituted include F, B, Nb, V, Mn, Ni, Cu, Co, Zn, Sn, Pb, Al, Mo, Ba, Sr, Ta, Mg, and Ca. be able to. These can be substituted with one or more elements.

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 of the present embodiment uses the above lithium-manganese-nickel composite oxide as a positive electrode active material, mixes a positive electrode conductive material and a binder, and adds an appropriate solvent as necessary, and pastes It can be formed by applying to the surface of a current collector made of a metal foil such as an aluminum foil, drying, and then increasing the density of the positive electrode mixture by pressing or the like as necessary. it can. The positive electrode active material can be composed of only the above lithium / manganese / nickel composite oxide. However, for the purpose of improving the characteristics of the lithium ion battery, the well-known LiCoO ₂ is already used for the lithium / manganese / nickel composite oxide. , LiNiO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , Li (Co _1/3 Ni _1/3 Mn _1/3 ) O ₂ or the like may be mixed to form a positive electrode active material. .

  The negative electrode of the lithium ion battery of this embodiment uses the above lithium-titanium composite oxide as a negative electrode active material, and a negative electrode conductive material and a binder are mixed with this, and an appropriate solvent is added as necessary, to form a paste-like negative electrode The mixture can be formed by applying and drying a current collector made of a metal foil such as copper and then increasing the density of the negative electrode mixture by pressing or the like as necessary. Although the negative electrode active material can be composed of only the above lithium titanium composite oxide, a known carbon material or the like is already mixed with the lithium titanium composite oxide for the purpose of improving the characteristics of the lithium ion battery. It may be a negative electrode active material.

The positive electrode conductive material is characterized by using a mixture of acetylene black and graphene from the viewpoint of improving electrical conductivity and improving cycle characteristics at high temperatures.
The mixing ratio of acetylene black and graphene is preferably 0.1% by mass or more and 85% by mass or less, and more preferably 1% by mass or more and 50% by mass or less with respect to the whole positive electrode conductive material. . Within the above range, the output characteristics and cycle characteristics can be improved in a balanced manner.

  From the viewpoint of improving electrical conductivity, the negative electrode conductive material can be used by mixing one or more of carbon blacks such as acetylene black and ketjen black and carbonaceous powders such as graphite. . Further, as a conductive material, a small amount of carbon nanotubes, graphene, or the like can be added to increase electrical conductivity. As said negative electrode electrically conductive material, acetylene black is preferable from a viewpoint which can improve a rate characteristic more.

The range of the content of the positive electrode conductive material relative to the mass of the positive electrode mixture is as follows. The lower limit of the range is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and still more preferably 1% by mass or more from the viewpoint of excellent conductivity, and the upper limit is a viewpoint that can improve the battery capacity. Preferably, it is 50 mass% or less, More preferably, it is 30 mass% or less, More preferably, it is 15 mass% or less.
The range of the content of the negative electrode conductive material with respect to the mass of the negative electrode mixture is as follows. The lower limit of the range is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and still more preferably 1% by mass or more from the viewpoint of excellent conductivity, and the upper limit is a viewpoint that can improve the battery capacity. Preferably, it is 45 mass% or less, More preferably, it is 30 mass% or less, More preferably, it is 15 mass% or less.

  The binder is not particularly limited, and a material having good solubility and 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, fluoropolymers such as polytetrafluoroethylene / vinylidene fluoride copolymers, resins having structural units derived from nitrile group-containing monomers, and high ion conductivity of alkali metal ions (especially lithium ions) A molecular composition is mentioned. 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, a resin having a structural unit derived from polyvinylidene fluoride (PVdF) or a nitrile group-containing monomer is preferably used from the viewpoint of high adhesion.

Regarding the content of the binder, the range of the content of the binder with respect 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, more preferably from the viewpoint of sufficiently binding the positive electrode active material to obtain sufficient positive electrode mechanical strength and stabilizing battery performance such as cycle characteristics. 1% by mass or more, more preferably 2% by mass or more, and the upper limit is preferably 30% by mass or less, more preferably 20% by mass or less, and still more preferably 10% by mass from the viewpoint of improving battery capacity and conductivity. It is as follows. The range of the binder content with respect to the mass of the negative electrode mixture is as follows. The lower limit of the range is preferably 0.1% by mass or more, more preferably 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. It is 0.5 mass% or more, More preferably, it is 1 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 the active material, conductive material, and binder.

  Like the general lithium ion battery, the lithium ion battery according to the present embodiment can include a separator, a non-aqueous electrolyte, and the like that are sandwiched between the positive electrode and the negative electrode in addition to 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 can be 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, a porous sheet or nonwoven fabric made of polyolefin such as polyethylene or polypropylene may be used. preferable. Considering that the average potential of the positive electrode is as high as 4.7 to 4.8 V with respect to Li / Li ⁺ , it has a three-layer structure of polypropylene / polyethylene / polypropylene in which polyethylene is sandwiched between polypropylenes having a high potential resistance. Those are also 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 can be 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% particle size 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.

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

  The electrolyte solution used for the lithium ion battery of this embodiment can use what is comprised from lithium salt (electrolyte) and the non-aqueous solvent which melt | dissolves this. 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 them, lithium hexafluorophosphate (LiPF ₆ ) is preferable when comprehensively judging the solubility in a solvent, charge / discharge characteristics in the case of a secondary battery, output characteristics, cycle characteristics, and the like.

  The concentration of the lithium salt is preferably 0.5 to 1.5 mol / L, more preferably 0.7 to 1.3 mol / L with respect to the nonaqueous solvent, and 0.8 to 1. More preferably, it is 2 mol / L. Charge / discharge characteristics can be further improved by setting the concentration of the lithium salt to 0.5 to 1.5 mol / L.

  The non-aqueous solvent is not particularly limited as long as it is a non-aqueous solvent that can be used as an electrolyte solvent for lithium ion batteries. For example, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ- Examples include butyl lactone, 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 two or more compounds are used in combination.

  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.

  Although there is no limitation in particular in the ratio of the additive in a non-aqueous electrolyte solution, the range is as follows. In addition, when using a some additive, the ratio of each additive is meant. The lower limit of the ratio of the additive to the non-aqueous electrolyte is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.2% by mass or more, and the upper limit is preferably 5%. It is not more than mass%, more preferably not more than 3 mass%, still more preferably not more than 2 mass%.

  By using the other additives, it is possible to improve capacity maintenance characteristics and cycle characteristics after high-temperature storage, and to improve 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. A battery is completed by connecting with a lead or the like and sealing the electrode body together with a non-aqueous electrolyte in a battery case.

  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 a lithium ion battery of the present invention. The lithium ion battery 10 is one in which the electrode group 20 and an electrolytic solution are accommodated in a battery container of a 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.

  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 end-of-charge voltage Vf of the lithium ion battery system of the present embodiment is preferably 3.6V ≦ Vf ≦ 4.0V. When Vf is 3.6 V or higher, high input characteristics can be obtained. When Vf is 4.0 V or less, the positive electrode does not become too high, and the decomposition reaction with the electrolytic solution is suppressed. Characteristics are obtained. In order to obtain a lithium ion battery with a better balance between input characteristics and life characteristics, it is more preferable to set 3.7V ≦ Vf ≦ 3.9V.

  The charge control means of the lithium ion battery system according to the present embodiment is not particularly limited as long as the charge end voltage Vf can be controlled within the range of 3.6 V ≦ Vf ≦ 4.0 V. For example, a control IC is used. First, a control method (constant current / constant voltage method) in which charging is performed up to a preset upper limit voltage with a constant current and then charging is performed while maintaining the voltage can be used.

  The lithium ion battery used in this embodiment preferably has a positive electrode / negative electrode capacity ratio (negative electrode capacity / positive electrode capacity) of 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, a decomposition reaction of the electrolytic solution due to the positive electrode being at a high potential hardly occurs, and the life 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 0.8 or more and 0.95 or less.

The “positive electrode capacity” and “negative electrode capacity” are the maximum reversibly available when a constant current, constant voltage charge-constant current discharge is performed by forming 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 carried out and evaluated at 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]
In the positive electrode, 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 diameter (D50) of 28.8 μm as a positive electrode active material is 93.0. 4.0 parts by mass of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) and 1.0 part by mass of graphene having a BET specific surface area of 750 m ² / g as a positive electrode conductive material, and a nitrile group-containing single amount as a binder 2.0 parts by mass of a resin having a structural unit derived from the body (trade name: LSR7, manufactured by Hitachi Chemical Co., Ltd.), and an appropriate amount of N-methyl-2-pyrrolidone is added and kneaded to form a paste-like positive electrode A mixture slurry was obtained. This slurry was applied to both surfaces of an aluminum foil having a thickness of 20 μm, which is a current collector for the positive electrode, 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 2.4 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.
In addition, a BET specific surface area can be measured from nitrogen adsorption capacity according to JISZ8830, for example. As an evaluation apparatus, the product name: AUTOSORB-1 by the QUANTACHROME company can be used, for example. 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. Cool naturally to (25 ° C). After this pretreatment, the evaluation temperature is 77K (−196 ° C.), and the evaluation pressure range is measured as a relative pressure (equilibrium pressure relative to the saturated vapor pressure) of less than 1.
The average particle diameter (D50) can be determined from the particle size distribution determined by the laser diffraction / scattering method.

The negative electrode is 91.0 parts by mass of lithium titanium composite oxide as the negative electrode active material, 4.0 parts by mass of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) as the negative electrode conductive material, and 5. polyvinylidene fluoride as the binder. A paste-like negative electrode mixture slurry was obtained by mixing 0 part by mass, adding an appropriate amount of N-methyl-2-pyrrolidone and kneading. This slurry was applied to both surfaces of a 10 μm-thick copper foil as a negative electrode current collector so as to be substantially uniformly and uniformly 85 g / m ² . Thereafter, a drying process was performed, and the sheet was consolidated by pressing to a density of 1.9 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 20 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 nonaqueous electrolytic solution, a solution obtained by dissolving LiPF ₆ at a concentration of 1.2 M in a mixed solvent in which ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 1: 3 was used. The aluminum laminate film is a laminate of polyethylene terephthalate (PET) film / aluminum foil / sealant layer (polypropylene, etc.).

(First charge / discharge)
The above lithium-ion battery was charged at a constant current of 25 C at a current value of 0.2 C and a charge end voltage of 3.8 V using a charge / discharge device (trade name: BATTERY TEST UNIT, manufactured by IEM Co., Ltd.), and then charged. Constant voltage charging was performed until the current value reached 0.01 C at a voltage of 3.8 V. 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 3 times under the above charging / discharging conditions.

(Output characteristics)
Using the lithium ion battery that was charged and discharged as described above, after charging 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. Table 1 shows the calculated output characteristics.
Output characteristics (%) = (discharge capacity at 5C / discharge capacity at 0.5C) x 100

(Cycle characteristics)
Using the lithium ion battery having the above output characteristics measured, a constant current charge is performed at a current value of 1 C and a charge end voltage of 3.8 V at 50 ° C., and then the current value becomes 0.01 C at a charge end voltage of 3.8 V. Until constant voltage charging. After resting for 15 minutes, a constant current discharge with a current value of 1 C and a final voltage of 2 V was performed at 25 ° C., and the discharge capacity was measured (discharge capacity at the first cycle). The above charging / discharging was performed 200 cycles, and the discharge capacity after 200 cycles (discharge capacity after 200 cycles) was measured. And the cycle characteristic was computed from the following formula | equation. Table 1 shows the calculated cycle characteristics.
Cycle characteristics (%) = (discharge capacity after 200 cycles / discharge capacity at the first cycle) × 100

[Examples 2 and 3]
Example 1 and Example 1 except that acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) and graphene having a specific surface area of 750 m ² / g were mixed as a positive electrode conductive material in the proportions shown in Examples 2 and 3 of Table 1. A lithium ion battery was prepared by the same method, and the output characteristics and cycle characteristics were measured. Table 1 shows the measurement results of output characteristics and cycle characteristics.

[Comparative Examples 1-3]
Example 1 except that acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) and graphite (manufactured by Nippon Graphite Industry Co., Ltd.) were mixed as the positive electrode conductive material in the proportions shown in Comparative Examples 1 to 3 in Table 1. A lithium ion battery was prepared by the same method, and the output characteristics and cycle characteristics were measured. Table 1 shows the measurement results of output characteristics and cycle characteristics.

[Comparative Examples 4 to 6]
Similar to Example 1 except that graphite (manufactured by Nippon Graphite Industry Co., Ltd.) and graphene with a specific surface area of 750 m ² / g were mixed as a positive electrode conductive material in the proportions shown in Comparative Examples 4 to 6 in Table 1. A lithium ion battery was prepared by the method described above, and the output characteristics and cycle characteristics were measured. Table 1 shows the measurement results of output characteristics and cycle characteristics.

[Comparative Example 7]
As shown in Comparative Example 7 in Table 1, a lithium ion battery was prepared in the same manner as in Example 1 except that only 5 parts by mass of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd.) was mixed as the positive electrode conductive material. Output characteristics and cycle characteristics were measured. Table 1 shows the measurement results of output characteristics and cycle characteristics.

[Comparative Example 8]
As shown in Comparative Example 8 in Table 1, a lithium ion battery was produced in the same manner as in Example 1 except that only 5 parts by mass of graphene having a specific surface area of 750 m ² / g was mixed as the positive electrode conductive material. Characteristics and cycle characteristics were measured. Table 1 shows the measurement results of output characteristics and cycle characteristics.

  Comparing Examples 1 to 3 and Comparative Examples 1 to 3 in Table 1, when acetylene black and graphene are used as the positive electrode conductive material, the cycle characteristic shows a high value of 65% or more, whereas the positive electrode conductive material It can be seen that when acetylene black and graphite are used, the cycle characteristics are reduced to 55% or less.

  Comparing Examples 1 to 3 and Comparative Examples 4 to 6 in Table 1, when acetylene black and graphene are used as the positive electrode conductive material, the output characteristics are as high as 80% or more, and the cycle characteristics are as high as 65% or more. On the other hand, when graphite and graphene are used as the positive electrode conductive material, it can be seen that the output characteristics are reduced to 75% or less and the cycle characteristics to 50% or less.

  When Examples 1 to 3 and Comparative Example 7 in Table 1 are compared, when acetylene black and graphene are used as the positive electrode conductive material, the cycle characteristics show a high value of 65% or more, whereas acetylene as the positive electrode conductive material. It can be seen that when only black is used, the cycle characteristics are reduced to 55%.

  When Examples 1 to 3 in Table 1 are compared with Comparative Example 8, when acetylene black and graphene are used as the positive electrode conductive material, the output characteristics are as high as 80% or more and the cycle characteristics are as high as 65% or more. On the other hand, when only graphene is used as the positive electrode conductive material, it can be seen that the output characteristics are reduced to 75% and the cycle characteristics to 30%.

  From the above results, it was found that a battery having excellent output characteristics and cycle characteristics can be obtained by including acetylene black and graphene as the positive electrode conductive material in the lithium ion battery.

  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 battery, 20 ... Electrode group.

Claims (3)

A lithium ion battery comprising a positive electrode, a negative electrode, and an electrolyte solution,
The positive electrode has a current collector and a positive electrode mixture applied to at least one surface of the current collector, and the positive electrode mixture includes a lithium / manganese / nickel composite oxide as a positive electrode active material and a positive electrode conductive material. Including acetylene black and graphene,
The negative electrode includes a lithium titanium composite oxide and a negative electrode conductive material as a negative electrode active material,
Lithium ion battery.   The lithium ion battery according to claim 1, wherein a capacity ratio (negative electrode capacity / positive electrode capacity) between the positive electrode and the negative electrode is 0.7 or more and less than 1. The lithium ion battery according to claim 1 or 2,
Charge control means for controlling the end-of-charge voltage Vf within a range of 3.6 V ≦ Vf ≦ 4.0 V,
Lithium ion battery system.

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