WO2017068985A1

WO2017068985A1 - Lithium-ion cell

Info

Publication number: WO2017068985A1
Application number: PCT/JP2016/079737
Authority: WO
Inventors: 賢匠星; 美枝阿部
Original assignee: 日立化成株式会社
Priority date: 2015-10-22
Filing date: 2016-10-06
Publication date: 2017-04-27
Also published as: JPWO2017068985A1

Abstract

Provided is a lithium-ion cell having excellent input characteristics, lifetime characteristics, and overcharging resistance. In order to achieve these objectives, the lithium-ion cell has a negative electrode that includes graphite and amorphous carbon, and a positive electrode that includes a lithium transition metal composite oxide. The content of graphite included in the negative electrode is 10-70 mass% in relation to the total amount of graphite and amorphous carbon included in the negative electrode, and the capacitance ratio, which is the ratio of the capacitance of the negative electrode to the capacitance of the positive electrode, is 1.3-2.2.

Description

Lithium ion battery

The present invention relates to a lithium ion battery.

A lithium ion battery (lithium ion secondary battery) is a lightweight, high energy density secondary battery, and is used as a power source for portable devices such as notebook computers and mobile phones, taking advantage of its characteristics.

In recent years, it has been developed not only for consumer use such as portable devices, but also for on-vehicle use or large-scale power storage systems for natural energy such as solar and wind power generation. Lithium ion batteries for use in vehicles and for large-scale power storage systems are required to have higher input / output, and the negative electrode active material and the positive electrode active material are improved. For negative electrode active materials, carbon materials are widely used. For example, Patent Document 1 proposes a negative electrode active material using a mixture of graphite and graphitizable carbon in order to improve output characteristics at low temperatures. .

Patent Document 2 discloses a lithium secondary battery having high output and long life by selecting graphitizable carbon among graphite and amorphous carbon and determining the weight ratio of graphite and graphitizable carbon. .

JP 2007-335360 A JP 2009-70598 A

However, it has been found that the lithium secondary battery described in Patent Document 1 has room for further improvement in terms of safety such as overcharge resistance. Moreover, in the lithium secondary battery currently disclosed by patent document 2, the density of the negative mix layer containing a negative electrode active material was high, and it turned out that sufficient input characteristics are not acquired. This invention is made | formed in view of the said subject, and is providing the lithium ion battery excellent in an input characteristic, a lifetime characteristic, and an overcharge tolerance.

A lithium ion battery according to a typical embodiment includes a negative electrode including graphite and amorphous carbon, and a positive electrode including a lithium transition metal composite oxide. The content of graphite contained in the negative electrode is 10 to 70% by mass with respect to the total amount of graphite and amorphous carbon contained in the negative electrode, and the capacity ratio, which is the ratio of the negative electrode capacity to the positive electrode capacity, is 1. 3 to 2.2.

Also, a lithium ion battery according to a typical embodiment includes a negative electrode including graphite and amorphous carbon, and a positive electrode including a lithium transition metal composite oxide. The state of charge of the negative electrode at a potential of 0.1 V with respect to the lithium potential is 42 to 60%, and the capacity ratio, which is the ratio of the negative electrode capacity to the positive electrode capacity, is 1.3 to 2.2. .

In the lithium ion battery, the lithium transition metal composite oxide may be a layered lithium / nickel / manganese / cobalt composite oxide.

According to the present invention, it is possible to provide a lithium ion battery excellent in input characteristics, life characteristics and overcharge resistance.

It is sectional drawing of the lithium ion battery of embodiment which can apply this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description shows specific examples of the contents of the present invention, and the present invention is not limited to these descriptions. Various modifications by those skilled in the art are within the scope of the technical idea disclosed in this specification. Changes and modifications are possible.

In the following embodiments, when ranges are shown as A to B, A or more and B or less are shown unless otherwise specified.
(Embodiment)

First, the outline of the lithium ion battery will be briefly described. The lithium ion battery has a positive electrode, a negative electrode, a separator, and an electrolytic solution in a battery container. A separator is disposed between the positive electrode and the negative electrode.

When charging the lithium ion battery, connect a charger between the positive electrode and the negative electrode. At the time of charging, lithium ions inserted into the positive electrode active material are desorbed and released into the electrolytic solution. The lithium ions released into the electrolytic solution move in the electrolytic solution, pass through a separator made of a microporous film, and reach the negative electrode. The lithium ions that have reached the negative electrode are inserted into the negative electrode active material constituting the negative electrode.

When discharging, connect an external load between the positive and negative electrodes. At the time of discharging, the lithium ions inserted into the negative electrode active material are desorbed and released into the electrolytic solution. At this time, electrons are emitted from the negative electrode. Then, the lithium ions released into the electrolytic solution move in the electrolytic solution, pass through a separator made of a microporous film, and reach the positive electrode. The lithium ions reaching the positive electrode are inserted into the positive electrode active material constituting the positive electrode. At this time, when lithium ions are inserted into the positive electrode active material, electrons flow into the positive electrode. In this way, discharge is performed by the movement of electrons from the negative electrode to the positive electrode.

Thus, charging and discharging can be performed by inserting and desorbing lithium ions between the positive electrode active material and the negative electrode active material. A configuration example of an actual lithium ion battery will be described later (see, for example, FIG. 1).

Next, a positive electrode, a negative electrode, an electrolytic solution, a separator, and other components that are components of the lithium ion battery according to the present embodiment will be sequentially described.
1. Positive electrode

In this embodiment, the following positive electrode is applicable to a high-capacity, high-input / output lithium-ion battery. The positive electrode (positive electrode plate) of the present embodiment is composed of a current collector and a positive electrode mixture formed thereon. The positive electrode mixture is a layer including at least a positive electrode active material provided on the current collector.

The positive electrode active material includes a layered lithium / nickel / manganese / cobalt composite oxide (hereinafter sometimes referred to as NMC). NMC has a high capacity and excellent safety.

From the viewpoint of further improving safety, it is preferable to use a mixed active material with NMC and a spinel-type lithium manganese composite oxide (hereinafter sometimes referred to as sp-Mn).

The content of NMC is preferably 65% by mass or more, more preferably 70% by mass or more, and more preferably 80% by mass or more with respect to the total amount of the positive electrode mixture, from the viewpoint of increasing the capacity of the battery. Is more preferable.
As said NMC, it is preferable to use what is represented by the following compositional formula (Formula 1).
Li _{(1 + δ)} Mn _x Ni _y Co _(1-xyz) M _z O ₂ (Formula 1)

In the above composition formula (Formula 1), (1 + δ) is a composition ratio of Li (lithium), x is a composition ratio of Mn (manganese), y is a composition ratio of Ni (nickel), and (1-xyz) Indicates the composition ratio of Co (cobalt). z represents the composition ratio of the element M. The composition ratio of O (oxygen) is 2.

The elements M are Ti (titanium), Zr (zirconium), Nb (niobium), Mo (molybdenum), W (tungsten), Al (aluminum), Si (silicon), Ga (gallium), Ge (germanium), and Sn. It is at least one element selected from the group consisting of (tin).

-0.15 <δ <0.15, 0.1 <x ≦ 0.5, 0.6 <x + y + z ≦ 1.0, 0 ≦ z ≦ 0.1.

Further, as the sp-Mn, it is preferable to use one represented by the following composition formula (Formula 2).
Li _{(1 + η)} Mn _(2-λ) M ′ _λ O ₄ (Chemical formula 2)

In the above composition formula (Formula 2), (1 + η) represents the composition ratio of Li, (2-λ) represents the composition ratio of Mn, and λ represents the composition ratio of the element M ′. The composition ratio of O (oxygen) is 4.

The element M ′ is at least one element selected from the group consisting of Mg (magnesium), Ca (calcium), Sr (strontium), Al, Ga, Zn (zinc), and Cu (copper). preferable.
0 ≦ η ≦ 0.2 and 0 ≦ λ ≦ 0.1.

Mg or Al is preferably used as the element M ′ in the composition formula (Chemical Formula 2). By using Mg or Al, the battery life can be extended. In addition, the safety of the battery can be improved. Furthermore, since the elution of Mn can be reduced by adding the element M ′, storage characteristics and charge / discharge cycle characteristics can be improved.
Further, as the positive electrode active material, materials other than the above NMC and sp-Mn may be used.

As the positive electrode active material other than NMC and sp-Mn, those commonly used in this field can be used, and lithium transition metal composite oxides other than NMC and sp-Mn, olivine type lithium salts, chalcogen compounds, manganese dioxide, etc. Is mentioned. The lithium transition metal composite oxide is a metal oxide containing lithium and a transition metal or a metal oxide in which a part of the transition metal in the metal oxide is substituted with a different element. Here, examples of the different elements include Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, V, and B. Mn, Al, Co, Ni and Mg are preferable. One kind or two or more kinds of different elements can be used. Examples of lithium transition metal composite oxides other than NMC and sp-Mn 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 _{1-1. y} Oz, Li _x Ni _1-y M _y O _z (wherein M is Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, V And at least one element selected from the group consisting of B 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. Examples of the olivine type lithium salt include LiFePO ₄ . Examples of the chalcogen compound include titanium disulfide and molybdenum disulfide. A positive electrode active material can be used individually by 1 type, or can use 2 or more types together.

Next, the positive electrode mixture and the current collector will be described in detail. The positive electrode mixture contains a positive electrode active material, a binder, and the like, and is formed on the current collector. Although there is no restriction | limiting in the formation method, For example, it forms as follows. A positive electrode active material, a binder, and other materials such as a conductive agent and a thickener used as needed are mixed in a dry form to form a sheet, which is then pressure-bonded to a current collector (dry method). In addition, a positive electrode active material, a binder, and other materials such as a conductive agent and a thickener used as necessary are dissolved or dispersed in a dispersion solvent to form a slurry, which is applied to a current collector and dried. (Wet method).

The dispersion solvent for forming the slurry may be any solvent that can dissolve or disperse the positive electrode active material, the binder, and the conductive agent or thickener used as necessary. Preferable examples include N-methylpyrrolidone (NMP) which is an organic solvent.

As described above, the layered lithium-nickel-manganese-cobalt composite oxide (NMC) is used as the positive electrode active material. These are used in powder form (granular) and mixed.

As the positive electrode active material particles such as NMC and sp-Mn, particles having a lump shape, polyhedron shape, spherical shape, elliptical spherical shape, plate shape, needle shape, columnar shape, and the like can be used.

The average particle size (d50) of the positive electrode active material particles such as NMC and sp-Mn (when the primary particles are aggregated to form secondary particles, the average particle size (d50) of the secondary particles) is: From the viewpoint of tab density (fillability) and miscibility with other materials during electrode formation, it is preferably 1 to 30 μm, more preferably 3 to 25 μm, and even more preferably 5 to 15 μm. The average particle diameter d50 (median diameter) means the particle diameter at an integrated value of 50% in the particle size distribution determined by the laser diffraction / scattering method.

The range of the BET specific surface area of the particles of the positive electrode active material such as NMC or sp-Mn is preferably 0.2 to 4.0 m ² / g, more preferably 0.3 to 2.5 m ² / g, 0.4 More preferably, ˜1.5 m ² / g.

If it is 0.2 m ² / g or more, excellent battery performance can be obtained. Further, when it is 4.0 m ² / g or less, the tap density is easily increased, and the mixing property with other materials such as a binder and a conductive agent is good. The BET specific surface area is a specific surface area (area per unit g) determined by the BET method.

Examples of the conductive agent for the positive electrode include metal materials such as copper and nickel; graphite such as natural graphite and artificial graphite (graphite); carbon black such as acetylene black; and carbonaceous materials such as amorphous carbon such as needle coke. It is done. Of these, one type may be used alone, or two or more types may be used in combination.

The range of the content of the conductive agent with respect to the mass of the positive electrode mixture is preferably 0.01 to 50% by mass, more preferably 0.1 to 30% by mass, and further preferably 1 to 15% by mass. Sufficient electroconductivity can be acquired as it is 0.1 mass% or more, and the fall of battery capacity can be suppressed if it is 50 mass% or less.

The binder for the positive electrode active material is not particularly limited, and when the positive electrode mixture is formed by a coating method, a material having good solubility or dispersibility in the dispersion solvent is selected. Specifically, resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polyimide, and cellulose; rubbery polymers such as SBR (styrene-butadiene rubber) and NBR (acrylonitrile-butadiene rubber); polyvinylidene fluoride (PVdF) Fluorine polymers such as polytetrafluoroethylene and fluorinated polyvinylidene fluoride; polymer compositions having alkali metal ion (especially lithium ion) ion conductivity, and the like. Of these, one type may be used alone, or two or more types may be used in combination.

From the viewpoint of the stability of the positive electrode, it is preferable to use a fluorine-based polymer such as polyvinylidene fluoride (PVdF) or a polytetrafluoroethylene / vinylidene fluoride copolymer.

The range of the content of the binder with respect to the mass of the positive electrode mixture is preferably 0.1 to 60% by mass, more preferably 1 to 40% by mass, and further preferably 3 to 10% by mass.

When the content of the binder is 0.1% by mass or more, the positive electrode active material can be sufficiently bound, sufficient mechanical strength of the positive electrode active material is obtained, and battery performance such as excellent cycle characteristics is obtained. It is done. Sufficient battery capacity and electroconductivity are acquired as it is 60 mass% or less.

The layer formed on the current collector using the above wet method or dry method is preferably consolidated by a hand press or a roller press in order to improve the packing density of the positive electrode active material.

The density of the positive electrode mixture consolidated as described above is preferably in the range of 2.5 to 2.8 g / cm ³ from the viewpoint of further improving input / output characteristics and safety, and is preferably 2.55 to 2.75 g. / Cm ³ is more preferable, and 2.6 to 2.7 g / cm ³ is still more preferable.

The amount of the single-sided coating of the positive electrode mixture to the positive electrode current collector is preferably 110 to 170 g / m ² and more preferably 120 to 160 g / m ² from the viewpoint of energy density and input / output characteristics. Preferably, it is 130 to 150 g / m ² .

Considering the amount of single-sided application of the positive electrode mixture to the positive electrode current collector and the positive electrode mixture density, the thickness of the single-sided coating film of the positive electrode mixture on the positive electrode current collector ([positive electrode thickness−positive electrode current collector] The thickness] / 2) is preferably 39 to 68 μm, more preferably 43 to 64 μm, and still more preferably 46 to 60 μm.

The material of the current collector for the positive electrode is not particularly limited, but a metal material, particularly aluminum, is particularly preferable. There is no restriction | limiting in particular as a shape of an electrical power collector, The material processed into various shapes can be used. Examples of the metal material include a metal foil, a metal plate, a metal thin film, and an expanded metal. Among these, it is preferable to use a metal thin film. In addition, you may form a thin film suitably in mesh shape.

The thickness of the thin film is arbitrary, but from the viewpoint of obtaining strength required for the current collector and good flexibility, it is preferably 1 μm to 1 mm, more preferably 3 to 100 μm, and even more preferably 5 to 100 μm.
2. Negative electrode

The negative electrode in the present embodiment includes graphite and amorphous carbon as the negative electrode active material. The state of charge of the negative electrode at a potential of 0.1 V with respect to the lithium potential (State of charge) is 42 to 60%. Here, the state of charge may be referred to as SOC. Note that the higher the SOC at a potential of 0.1 V with respect to the lithium potential, the less affected by the IR drop (voltage drop) at the positive electrode, and the charging load characteristics are improved.

First, the graphite contained in the negative electrode will be described. The graphite in the present invention has, for example, a carbon network surface interlayer (d002) in an X-ray wide angle diffraction method of less than 0.34 nm.

Since the pulverized mass of natural graphite may contain impurities, it is preferable to purify it by a purification treatment. The purity of the natural graphite is preferably 99.8% or more (ash content 0.2% or less), more preferably 99.9% or more (ash content 0.1% or less) on a mass basis. When the purity is 99.8% or more, the safety of the battery is further improved, and the battery performance is further improved.

Artificial graphite obtained by firing using a resin raw material such as epoxy or phenol or a pitch-based material obtained from petroleum or coal as a raw material may be used.

The method for obtaining the artificial graphite is not particularly limited. For example, a thermoplastic resin, naphthalene, anthracene, phenanthrolen, coal tar, tar pitch, etc. are calcined in an inert atmosphere at 800 ° C. or higher. Then, it can be produced by pulverizing by a known method such as jet mill, vibration mill, pin mill, hammer mill and the like, and adjusting the particle size to 5 to 40 μm. Further, heat treatment may be performed in advance before the above calcination. When heat treatment is performed, for example, the heat treatment is performed in advance by an autoclave or the like, coarsely pulverized by a known method, and then calcined in an inert atmosphere at 800 ° C. or higher and pulverized to adjust the particle size. You can get it.

Graphite may be modified with other materials. For example, the ratio of the carbon layer to the graphite having a low crystalline carbon layer on the surface of graphite as a nucleus (mass ratio) is preferably 0.005 to 0.1, preferably 0.005 to 0.09. More preferably, it is more preferably 0.005 to 0.08. If the ratio (mass ratio) of the carbon layer to the carbon material is 0.005 or more, the initial efficiency and life characteristics are excellent. Moreover, if it is 0.1 or less, the input / output characteristics are excellent.

The graphite contained in the negative electrode preferably has the physical properties shown in the following (1) and (2).

(1) Intensity ratio between the peak intensity (ID) in the range of 1300 to 1400 cm ⁻¹ measured with the Raman spectrum and the peak intensity (IG) in the range of 1580 to 1620 cm ⁻¹ measured with the Raman spectrum. The R value (IG / ID) is preferably 3 or more, more preferably 10 or more, and still more preferably 50 or more.

The Raman spectrum can be measured using a Raman spectrometer (for example, DXR manufactured by Thermo Fisher Scientific).

(2) The average particle diameter (d50) is preferably 2 to 20 μm, more preferably 2.5 to 15 μm, and still more preferably 3 to 10 μm. When it is 20 μm or less, the discharge capacity and the discharge characteristics are improved. Moreover, it exists in the tendency which initial stage charge / discharge efficiency improves that it is 2 micrometers or more.

The average particle diameter (d50) is a value measured as d50 (median diameter) using, for example, a particle size distribution measuring apparatus using a laser light scattering method (for example, SALD-3000, manufactured by Shimadzu Corporation). It is.

The method for the purification treatment is not particularly limited, and can be appropriately selected from commonly used purification treatment methods. Examples thereof include flotation, electrochemical treatment, chemical treatment, and the like.
Next, the amorphous carbon contained in the negative electrode will be described.

The amorphous carbon preferably has a carbon network plane interlayer (d002) in the X-ray wide angle diffraction method of 0.34 to 0.39 nm, more preferably 0.341 to 0.385 nm, and 0 More preferably, the thickness is from 342 to 0.37 nm. When the amorphous carbon is graphitizable carbon, the carbon network plane interlayer (d002) in the X-ray wide angle diffraction method is preferably 0.34 to 0.36 nm, and 0.341 More preferably, it is ˜0.355 nm, and further preferably 0.342 to 0.35 nm.

In addition, as the amorphous carbon, the mass at 550 ° C. in the air stream is 70% by mass or more with respect to the mass at 25 ° C., and the mass at 650 ° C. is the mass at 25 ° C. It is preferable to use a material that is 20% by mass or less. The thermogravimetry can be measured, for example, with a TG analysis (Thermo Gravimetry Analysis) apparatus (for example, TG / DTA6200, manufactured by SII Nanotechnology Co., Ltd.). For example, a sample of 10 mg can be collected, and measurement can be performed under a flow condition of dry air of 300 mL / min and using alumina as a reference and a heating rate of 1 ° C./min.

From the viewpoint of further improving the input / output characteristics, the mass at 550 ° C. in the air stream is 90% or more of the mass at 25 ° C., and the mass at 650 ° C. is 10% or less of the mass at 25 ° C. Some amorphous carbon is more preferred.

The average particle diameter (d50) of the amorphous carbon is preferably 5 to 30 μm, more preferably 10 to 25 μm, and still more preferably 12 to 23 μm. If the average particle diameter is 5 μm or more, the specific surface area can be in an appropriate range, the initial charge / discharge efficiency of the lithium ion battery is excellent, and the contact between the particles is good and the input / output characteristics tend to be excellent.

On the other hand, if the average particle diameter is 30 μm or less, unevenness on the electrode surface is unlikely to occur and the short circuit of the battery can be suppressed, and the Li diffusion distance from the particle surface to the inside becomes relatively short, so Properties tend to improve.

For example, the particle size distribution can be measured with a laser diffraction particle size distribution analyzer (for example, SALD-3000J, manufactured by Shimadzu Corporation) by dispersing a sample in purified water containing a surfactant. The diameter is calculated as d50 (median diameter).

By mixing the graphite and the amorphous carbon, output characteristics and energy density can be further improved while maintaining input characteristics. The content ratio of graphite to amorphous carbon ((graphite) / (amorphous carbon)) is preferably 10/90 to 70/30, more preferably 15/85 to 65/35, 80 to 50/50 is more preferable. If the compounding ratio of graphite is 10% or more, the output density and overcharge resistance are improved because the electrode density is increased and the battery voltage is increased, and if it is 70% or less, both retention of input characteristics and overcharge resistance are achieved. it can.

In addition, as the negative electrode active material, amorphous carbon, carbonaceous materials other than graphite, metal oxides such as tin oxide and silicon oxide, metal composite oxide, lithium simple substance, lithium alloys such as lithium aluminum alloy, Sn, Si, etc. A material capable of forming an alloy with lithium may be used in combination. These may be used alone or in combination of two or more. The metal composite oxide is not particularly limited as long as it can occlude and release lithium, but it contains Ti (titanium), Li (lithium) or both Ti and Li in terms of discharge characteristics. Is preferable.

The configuration of the negative electrode mixture formed using the negative electrode active material is not particularly limited, but the negative electrode mixture density is preferably in the range of 0.7 to 2 g / cm ³ , and 0.8 to 1.9 g / cm ^3. More preferably, it is 0.9 to 1.8 g / cm ³ .

When it is 0.7 g / cm ³ or more, the conductivity between the negative electrode active materials is improved, an increase in battery resistance can be suppressed, and the capacity per unit volume can be improved. When it is 2 g / cm ³ or less, there is less possibility of incurring deterioration in discharge characteristics due to an increase in initial additional reverse capacity and a decrease in permeability to the electrolyte near the interface between the current collector and the negative electrode active material.

As the conductive agent, natural graphite, graphite such as artificial graphite (graphite), carbon black such as acetylene black, and amorphous carbon such as needle coke can be used. These may be used alone or in combination of two or more. Thus, there exists an effect of reducing the resistance of an electrode by adding a conductive agent.

The range of the content of the conductive agent relative to the weight of the negative electrode mixture is preferably in the range of 1 to 45% by weight, preferably 2 to 42% by weight, from the viewpoint of improving the conductivity and reducing the initial irreversible capacity. More preferred is 3 to 40% by weight.

The material of the current collector for the negative electrode is not particularly limited, and specific examples include metal materials such as copper, nickel, stainless steel, and nickel-plated steel. Among these, copper is preferable from the viewpoint of ease of processing and cost.

The shape of the current collector is not particularly limited, and materials processed into various shapes can be used. Specific examples include metal foil, metal plate, metal thin film, expanded metal, and the like. Especially, metal foil is preferable and copper foil is more preferable. The copper foil includes a rolled copper foil formed by a rolling method and an electrolytic copper foil formed by an electrolytic method, both of which are suitable for use as a current collector.

The thickness of the current collector is not limited, but if the thickness is less than 25 μm, its strength can be increased by using a strong copper alloy (phosphor bronze, titanium copper, Corson alloy, Cu—Cr—Zr alloy, etc.) rather than pure copper. Can be improved.

The binder for the negative electrode active material is not particularly limited as long as it is a material that is stable with respect to the dispersion solvent used when forming the electrolytic solution and the electrode. Specifically, resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, cellulose, and nitrocellulose; rubbery polymers such as SBR (styrene-butadiene rubber) and NBR (acrylonitrile-butadiene rubber); polyvinylidene fluoride (PVdF) ), Fluorine-based polymers such as polytetrafluoroethylene and fluorinated polyvinylidene fluoride; polymer compositions having ion conductivity of alkali metal ions (particularly lithium ions), and the like. Of these, one type may be used alone, or two or more types may be used in combination.

In addition, when the fluorine-based polymer typified by polyvinylidene fluoride is used as the main component as the binder, the range of the binder content relative to the mass of the negative electrode mixture is 1 to 15% by mass. It is preferably 2 to 10% by mass, more preferably 3 to 8% by mass.

Thickener is used to adjust the viscosity of the slurry. The thickener is not particularly limited, and specific examples include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof. These may be used alone or in combination of two or more.

The range of the content of the binder with respect to the mass of the negative electrode mixture is preferably 0.1 to 20% by mass, more preferably 0.5 to 15% by mass, and still more preferably 0.6 to 10% by mass.

When the content of the binder is 0.1% by mass or more, the negative electrode active material can be sufficiently bound, and sufficient mechanical strength of the negative electrode active material can be obtained. Sufficient battery capacity and electroconductivity are obtained as it is 20 mass% or less.

As the dispersion solvent for forming the slurry, any kind of solvent can be used as long as it can dissolve or disperse the negative electrode active material, the binder, and the conductive agent or thickener used as necessary. There is no restriction, and either an aqueous solvent or an organic solvent may be used. Examples of the aqueous solvent include water, alcohol, and a mixed solvent with water. Examples of the organic solvent include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, Examples include methyl acrylate, tetrahydrofuran (THF), toluene, acetone, diethyl ether, dimethylacetamide, dimethyl sulfoxide, benzene, xylene, and hexane. In particular, when an aqueous solvent is used, it is preferable to use a thickener. A dispersion solvent or the like is added to the thickener and slurried using a latex such as SBR. In addition, the said dispersion solvent may be used individually by 1 type, or may be used in combination of 2 or more type.
The range of the content of the thickener relative to the mass of the negative electrode mixture when using the thickener is the rate characteristics and

From the viewpoint of battery capacity, it is preferably 0.1 to 5% by mass, more preferably 0.5 to 3% by mass, and still more preferably 0.6 to 2% by mass.
3. Electrolyte

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

The lithium salt is not particularly limited as long as it is a lithium salt that can be used as an electrolyte for a lithium ion battery, and examples thereof include the following inorganic lithium salts, fluorine-containing organic lithium salts, and oxalatoborate salts.

Examples of the inorganic lithium _{_{_{salt, LiPF 6, LiBF 4, LiAsF}}} 6, inorganic fluoride salts LiSbF ₆ or the _like, perhalogenate such as LiClO 4, Libro _4, such as an inorganic chloride salts such as LiAlCl ₄ and the like.

Fluorine-containing organic lithium salt, fluoroalkyl fluorophosphate, etc. may be used. Examples of the oxalatoborate salt include lithium bis (oxalato) borate and lithium difluorooxalatoborate.

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 the solubility in a non-aqueous solvent, charge / discharge characteristics in the case of a secondary battery, output characteristics, cycle characteristics, and the like.

The concentration of the electrolyte in the electrolytic solution is not particularly limited, but the electrolyte concentration range is preferably 0.5 mol / L to 2 mol / L, more preferably 0.6 mol / L to 1.8 mol / L. Preferably, it is 0.7 mol / L to 1.8 mol / L.

When the concentration is 0.5 mol / L or more, sufficient electric conductivity of the electrolytic solution can be obtained. Moreover, since a viscosity does not become high too much that a density | concentration is 2 mol / L or less, the fall of electrical conductivity can be suppressed.

There is no particular limitation as long as it is a non-aqueous solvent that can be used as an electrolyte solvent for lithium ion batteries, and examples thereof include cyclic carbonates, chain carbonates, chain esters, cyclic ethers, and chain ethers.

Examples include ethylene carbonate, propylene carbonate, butylene carbonate, dialkyl carbonate, dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, ethyl methyl carbonate, methyl-n-propyl carbonate, ethyl-n-propyl carbonate, and the like.

These may be used alone or in combination of two or more, but it is preferable to use a nonaqueous solvent in which two or more compounds are used in combination. For example, it is preferable to use a high dielectric constant solvent of cyclic carbonates in combination with a low viscosity solvent of chain carbonates or chain esters.

The additive is not particularly limited as long as it is an additive for an 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 carbonate, Other compounds having an unsaturated bond in the molecule are exemplified. From the viewpoint of extending the life of the battery, fluorine-containing cyclic carbonates and other compounds having an unsaturated bond in the molecule are preferred.

Examples of the fluorine-containing cyclic carbonate include fluoroethylene carbonate, difluoroethylene carbonate, trifluoroethylene carbonate, and tetrafluoroethylene carbonate.

Examples of the other compound having an unsaturated bond in the molecule include vinylene carbonate.

In addition to the above additives, other additives such as an overcharge inhibitor, a negative electrode film forming agent, a positive electrode protective agent, and a high input / output agent may be used depending on the required function.

By using the other additives, it is possible to suppress a rapid electrode reaction at the time of abnormality due to overcharge, to improve capacity maintenance characteristics after storage at high temperature, to improve cycle characteristics, and to improve input / output characteristics.
4). Separator

The separator is not particularly limited as long as it has ion permeability while electronically insulating 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 or the like is used. It is preferable to select from materials that are stable with respect to the electrolytic solution and have excellent liquid retention properties, and it is preferable to use a porous sheet or a nonwoven fabric made of a polyolefin such as polyethylene or polypropylene.

As the inorganic material, oxides such as alumina and silicon dioxide, and nitrides such as aluminum nitride and silicon nitride 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 the thin film-shaped substrate, those having a pore diameter of 0.01 to 1 μm and a thickness of 5 to 50 μm are preferably used. Moreover, what made the said inorganic substance of fiber shape or particle shape the composite porous layer using binders, such as 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.
5). Other components

A cleavage valve may be provided as another component of the lithium ion battery. By opening the cleavage valve, it is possible to suppress an increase in pressure inside the battery and to improve safety.

Moreover, you may provide the structure part which discharge | releases inert gas (for example, carbon dioxide etc.) with a temperature rise. By providing such a component, when the temperature inside the battery rises, the cleavage valve can be opened quickly due to the generation of inert gas, and safety can be improved. As a material used for the said structural part, lithium carbonate, polyethylene carbonate, and polypropylene carbonate are preferable.
(Discharge capacity of lithium-ion battery)

The lithium ion battery of the present invention is suitable for a large capacity discharge capacity of 30 Ah or more and less than 100 Ah. From the viewpoint of high input / output and high energy density while ensuring safety, it is preferably 35 Ah or more and less than 100 Ah, more preferably 40 Ah or more and less than 95 Ah.
(Capacity ratio of the negative electrode to the positive electrode of the lithium ion battery)

In the present invention, the capacity ratio of the negative electrode to the positive electrode (negative electrode capacity / positive electrode capacity) is preferably 1.3 to 2.2 from the viewpoint of safety and energy density, and preferably 1.3 to 2.0. Is more preferable. In the conventional technique, when the capacity ratio is 1.2 or more, the positive electrode potential may be higher than 4.2 V during charging, which may reduce safety (the positive electrode potential at this time is According to the present invention, it is possible to provide a lithium ion battery excellent in overcharge resistance and cycle characteristics at the time of abnormality without sacrificing safety even when the capacity ratio is 2.0 or more. On the other hand, since an excessive capacity ratio leads to a decrease in energy density, the capacity ratio is preferably set to 2.2 or less.

In other words, when the capacity ratio (negative electrode capacity / positive electrode capacity) is 1.3 or more, Li deposition on the negative electrode can be suppressed during overcharge, and thus safety is improved. On the other hand, when the capacity ratio is high, there is a negative electrode that is not used during normal operation, and the energy density decreases. Therefore, the capacity ratio is preferably 1.3 to 2.2, and more preferably 1.3 to 2.0.

The negative electrode capacity refers to [negative electrode discharge capacity], and the positive electrode capacity refers to [positive charge initial charge capacity—negative electrode or positive electrode, whichever is greater]. Here, the “negative electrode discharge capacity” is defined to be calculated by the charge / discharge device when the lithium ions inserted into the negative electrode active material are desorbed. Further, the “initial charge capacity of the positive electrode” is defined as that calculated by the charge / discharge device when lithium ions are desorbed from the positive electrode active material.

The capacity ratio between the negative electrode and the positive electrode can also be calculated from, for example, “negative electrode discharge capacity / lithium ion battery discharge capacity”. The discharge capacity of the lithium ion battery is, for example, 4.2 V, 0.1 to 0.5 C, 0.1 to 0.00 after performing constant current and constant voltage (CCCV) charging with a termination time of 2 to 5 hours. It can be measured under conditions when a constant current (CC) discharge is performed up to 2.7 V at 5C. The discharge capacity of the negative electrode is obtained by cutting a negative electrode obtained by measuring the discharge capacity of the lithium ion battery into a predetermined area, using lithium metal as a counter electrode, and producing a single electrode cell through a separator impregnated with an electrolyte, Discharge per predetermined area under the conditions of constant current (CCCV) charging at 0V, 0.1C, and final current 0.01C, followed by constant current (CC) discharging to 1.5V at 0.1C It can be calculated by measuring the capacity and converting this to the total area used as the negative electrode of the lithium ion battery. In this single electrode cell, the direction in which lithium ions are inserted into the negative electrode active material is defined as charging, and the direction in which lithium ions inserted into the negative electrode active material are desorbed is defined as discharging. C means “current value (A) / battery discharge capacity (Ah)”.

Hereinafter, the present embodiment will be described in more detail based on examples. The present invention is not limited to the following examples.
(Examples 1 to 5)
[Production of positive electrode plate]

The positive electrode plate was produced as follows. Layered lithium / nickel / manganese / cobalt composite oxide (positive BET surface area of 0.4 m ² / g, average particle size (d50) of 6.5 μm) as positive electrode active material, and acetylene black (trade name: HS) as conductive agent -100, average particle diameter 48 nm (Denki Kagaku Kogyo Co., Ltd.), Denki Kagaku Kogyo Co., Ltd.) and polyvinylidene fluoride as a binder were sequentially added and mixed to obtain a mixture of positive electrode materials. The mass ratio was active material: conductive agent: binder = 90: 5: 5. Further, N-methyl-2-pyrrolidone (NMP) as a dispersion solvent was added to the above mixture and kneaded to form a slurry. This slurry was applied to both surfaces of a 20 μm thick aluminum foil as a positive electrode current collector. Then, the drying process was performed and it consolidated by the press to the predetermined density. The density of the positive electrode mixture was 2.7 g / cm ^3, and the coating amount on one side of the positive electrode mixture was 140 g / m ² .

In the examples, a positive electrode active material represented by the composition formula LiMn _1/3 Ni _1/3 Co _1/3 O ₂ was used. However, when NMC and sp-Mn are used as the positive electrode active material, for example, when the composition formula (Formula 1) and the composition formula (Formula 2) are satisfied, similar results are obtained.
[Production of negative electrode plate]

The negative electrode plate was produced as follows. Table 1 shows the mixing ratio of graphitizable carbon (d002 = 0.35 nm, average particle size (d50) = 10 μm) and graphite (d002 = 0.337 nm, average particle size (d50) = 20 μm) as the negative electrode active material. Mixed with (graphite / amorphous carbon). Polyvinylidene fluoride was added as a binder to this negative electrode active material. These mass ratios were negative electrode active material: binder = 92: 8. A dispersion solvent N-methyl-2-pyrrolidone (NMP) was added thereto and kneaded to form a slurry. This slurry was applied to both surfaces of a rolled copper foil having a thickness of 10 μm, which is a current collector for a negative electrode, so that the negative electrode capacity / positive electrode capacity were as shown in Table 1. The negative electrode mixture density was 1.15 g / cm ³ .
[Production of battery]

Wrapping with a separator made of polyethylene having a thickness of 30 μm so that the positive electrode plate and the negative electrode plate are not in direct contact with each other. At this time, the lead piece of the positive electrode plate and the lead piece of the negative electrode plate are respectively positioned on the opposite end surfaces of the electrode group. Further, the lengths of the positive electrode plate, the negative electrode plate, and the separator were adjusted, and the electrode group diameter was set to 65 ± 0.1 mm.

Next, as shown in FIG. 1, the lead pieces 9 led out from the positive electrode plate are deformed, and all of them are gathered near the bottom of the flange 7 on the positive electrode side and brought into contact with each other. The flange portion 7 on the positive electrode side is formed so as to protrude from the periphery of the pole column (positive electrode external terminal 1) substantially on the extension line of the axis of the electrode group 6, and has a bottom portion and a side portion. Thereafter, the lead piece 9 is connected and fixed to the bottom of the flange 7 by ultrasonic welding. The lead piece 9 led out from the negative electrode plate and the bottom of the flange 7 on the negative electrode side are similarly connected and fixed. The negative electrode side flange portion 7 is formed so as to protrude from the periphery of the pole column (negative electrode external terminal 1 ′) substantially on the extension line of the axis of the electrode group 6, and has a bottom portion and a side portion.

Then, using an adhesive tape, an insulating coating 8 was formed by covering the side of the flange 7 on the positive electrode external terminal 1 side and the side of the flange 7 of the negative electrode external terminal 1 ′. Similarly, an insulating coating 8 was formed on the outer periphery of the electrode group 6. For example, this adhesive tape is stretched from the side of the flange 7 on the positive electrode external terminal 1 side to the outer peripheral surface of the electrode group 6, and further from the outer periphery of the electrode group 6 to the flange 7 on the negative electrode external terminal 1 ′ side. The insulating coating 8 is formed by winding several times over the side. As the insulating coating (adhesive tape) 8, an adhesive tape in which the base material was polyimide and a methacrylate adhesive material was applied on one surface thereof was used. The thickness of the insulating coating 8 (the number of windings of the adhesive tape) is adjusted so that the maximum diameter portion of the electrode group 6 is slightly smaller than the inner diameter of the stainless steel battery container 5, and the electrode group 6 is inserted into the battery container 5. did. The battery container 5 had an outer diameter of 67 mm and an inner diameter of 66 mm.

Next, as shown in FIG. 1, the ceramic washer 3 ′ is fitted into the pole column whose tip constitutes the positive electrode external terminal 1 and the pole column whose tip constitutes the negative electrode external terminal 1 ′. The ceramic washer 3 ′ is made of alumina, and the thickness of the portion in contact with the back surface of the battery lid 4 is 2 mm, the inner diameter is 16 mm, and the outer diameter is 25 mm. Next, with the ceramic washer 3 placed on the battery lid 4, the positive external terminal 1 is passed through the ceramic washer 3, and with the other ceramic washer 3 placed on the other battery lid 4, the negative external terminal Pass 1 'through another ceramic washer 3. The ceramic washer 3 is made of alumina and has a flat plate shape with a thickness of 2 mm, an inner diameter of 16 mm, and an outer diameter of 28 mm.

Thereafter, the peripheral end surface of the battery lid 4 is fitted into the opening of the battery container 5 and the entire area of both contact portions is laser welded. At this time, the positive electrode external terminal 1 and the negative electrode external terminal 1 ′ pass through a hole (hole) in the center of the battery lid 4 and project outside the battery lid 4. The battery lid 4 is provided with a cleavage valve 10 that cleaves in response to an increase in the internal pressure of the battery. The cleavage pressure of the cleavage valve 10 was 13 to 18 kgf / cm ² (1.27 to 1.77 MPa).

Next, as shown in FIG. 1, the metal washer 11 is fitted into the positive external terminal 1 and the negative external terminal 1 '. Thereby, the metal washer 11 is disposed on the ceramic washer 3. The metal washer 11 is made of a material smoother than the bottom surface of the nut 2.

Next, the metal nut 2 is screwed to the positive electrode external terminal 1 and the negative electrode external terminal 1 ′, and the battery lid 4 is connected to the flange portion 7 and the nut 2 via the ceramic washer 3, the metal washer 11, and the ceramic washer 3 ′. Secure by tightening between. The tightening torque value at this time was 70 kgf · cm (6.86 N · m). The metal washer 11 did not rotate until the tightening operation was completed. In this state, the power generation element inside the battery container 5 is shielded from the outside air by the compression of the rubber (EPDM) O-ring 12 interposed between the back surface of the battery lid 4 and the flange 7.

Thereafter, a predetermined amount of electrolyte was injected into the battery container 5 from the injection port 13 provided in the battery lid 4, and then the injection port 13 was sealed to complete the cylindrical lithium ion battery 20.

As an electrolytic solution, 1.2 mol / L of lithium hexafluorophosphate (LiPF ₆ ) was dissolved in a mixed solution in which ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed at a volume ratio of 2: 3: 2. And what added 1.0 mass% of vinylene carbonate (VC) as an additive was used.
[SOC at a potential of 0.1 V with respect to the lithium potential]

The measurement of SOC at a potential of 0.1 V with respect to the lithium potential was performed by punching the prepared sample negative electrode into a size of φ15 mm, punching out a counter electrode (metallic lithium) punched into a size of φ16 mm, and punching into a size of φ19 mm The separator and the electrolytic solution were incorporated into a CR2032-type coin cell under an argon atmosphere and performed in an environment of 25 ° C. For the counter electrode, metallic lithium whose surface was polished to remove the oxide film was used.

The electrolyte is an electrolyte (0.8% by mass of vinylene carbonate is added to ethylene carbonate / methyl ethyl carbonate / dimethyl carbonate = 2/2/3 mixed solution (volume ratio) containing 1M LiPF ₆ with respect to the total amount of the mixed solution). 0.2 mL of a product name, Sollite, manufactured by Mitsubishi Chemical Corporation) was used. As the separator, a polyethylene porous sheet separator (trade name: Hypore, manufactured by Asahi Kasei Co., Ltd., thickness: 30 μm) was used.

Using the obtained coin cell, the sample electrode is charged to 0 V (V vs Li / Li ⁺ ) with a constant current of 0.1 C between the sample electrode and the counter electrode, and the current density becomes 0.01 C with a constant voltage of 0 V. Charged up to. The discharge was performed at a constant current of a current density of 0.1 C up to 1.5 V (V vs Li / Li ⁺ ). This charge and discharge test was performed for 3 cycles. “V vs Li / Li ⁺ ” is the potential of the sample negative electrode with respect to the potential of the counter electrode (metal lithium).

The charge capacity in the third cycle was set at 100% SOC. The SOC at 0.1 V, that is, the SOC at a potential of 0.1 V with respect to the lithium potential, was calculated from the charge capacity up to 0.1 V in the same third cycle.

SOC = CC charge capacity up to 0.1V in the third cycle / CCCV charge capacity up to 0V in the third cycle

That is, a test battery including a test negative electrode formed by cutting a part of a negative electrode of a lithium ion battery and a counter electrode made of metallic lithium was produced, and a constant current with a current density of 0.1 C was passed. In this state, after the test battery is charged until the potential of the test negative electrode with respect to the potential of the counter electrode becomes 0 V, the test is performed until the current density becomes 0.01 C with the potential of the negative electrode for test with respect to the potential of the counter electrode being 0 V. The charging operation for charging the battery for charging and the discharging operation for discharging the test battery after the charging operation are alternately repeated. The charge state at a potential of 0.1 V with respect to the lithium potential is such that the potential of the negative electrode for testing with respect to the potential of the counter electrode is 0.3 in the third charge operation for the charge capacity after the third charge operation is completed. It is the ratio of the charge capacity when it becomes 1V.

Note that the SOC at a potential of 0.1 V with respect to the lithium potential as described above is also referred to as a CC / CCCV total capacity.
[Evaluation of battery characteristics (discharge capacity, input characteristics, life characteristics)]

In a 25 ° C. environment, the current value was 0.5 C for both charging and discharging. Charging was constant current constant voltage (CCCV) charging with 4.2 V as the upper limit voltage, and the termination condition was 3 hours. The discharge was a constant current (CC) discharge with 2.7 V as the end condition. Further, a pause of 30 minutes was put between charge and discharge. This was carried out for three cycles, and the charge capacity at the third cycle was defined as “charge capacity at a current value of 0.5 C”, and the discharge capacity at the third cycle was defined as “discharge capacity at a current value of 0.5 C”.

Here, the negative electrode capacity / positive electrode capacity was calculated from “discharge capacity at a current value of 0.5 C / negative electrode discharge capacity”. The discharge capacity of the negative electrode was calculated from the “discharge capacity per predetermined area of the negative electrode (1.7671 cm ² )” in terms of the total area of the negative electrode produced by the lithium ion battery.
(Input characteristics)

After measuring the discharge capacity at the third cycle, the input characteristics were charged at a constant current and constant voltage (CCCV) with a current value of 3C and 4.2V as the upper limit voltage, and with a termination condition of 3 hours. The charge capacity was “charge capacity at a current value of 3 C”, and the input characteristics were calculated by the following formula. Thereafter, constant current discharge with a final voltage of 2.7 V was performed at a current value of 0.5 C.
Input characteristics = Charge capacity at a current value of 3C / Charge capacity at a current value of 0.5C

The input characteristics of 80% or more were evaluated as “A”, 75% or more and less than 80% as “B”, and less than 75% as “C”.
(Life characteristics)

Lifetime characteristics are as follows: In a 50 ° C environment, the battery is charged at a constant current and a constant voltage up to 4.2V at a current value of 0.5C, then rested for 30 minutes and discharged at a constant current of 0.5C at a current value of 2.7V. And rested for 30 minutes. This was repeatedly evaluated 200 times. The ratio of the discharge capacity after 200 cycles based on the discharge capacity at the first cycle is 80% or more as “A”, 70% or more and less than 80% as “B”, and less than 70% as “B”. Evaluated as “C”.
(Overcharge resistance)

In a 25 ° C. environment, the current value was 0.5 C for both charging and discharging. Charging was constant current constant voltage (CCCV) charging with 4.2 V as the upper limit voltage, and the termination condition was 3 hours. The discharge was a constant current (CC) discharge with 2.7 V as the end condition. Further, a pause of 30 minutes was put between charge and discharge. After performing this two cycles, only the discharge of the third cycle was discharged to 2.7 V at a current value of 0.2C.

This battery was charged at a constant current up to a set voltage of 10 V at a current value of 3 C under an environment of 50 ° C. The case where no thermal runaway occurred was designated as “A”, and the case where thermal runaway occurred was designated as “C”.
(Example 6)

The production of the negative electrode plate was performed in the same manner as in Example 1 except that the capacity ratio of the negative electrode to the positive electrode (negative electrode capacity / positive electrode capacity) was 1.5.
(Example 7)

The production of the negative electrode plate was performed in the same manner as in Example 1 except that the capacity ratio of the negative electrode to the positive electrode (negative electrode capacity / positive electrode capacity) was 1.8.
(Example 8)

Production of the negative electrode plate was performed in the same manner as in Example 1 except that the capacity ratio of the negative electrode to the positive electrode (negative electrode capacity / positive electrode capacity) was set to 2.0.
Example 9

The production of the negative electrode plate was performed in the same manner as in Example 1 except that the capacity ratio of the negative electrode to the positive electrode (negative electrode capacity / positive electrode capacity) was set to 2.2.
(Example 10)

The production of the negative electrode plate was performed in the same manner as in Example 1 except that the negative electrode active material was changed from graphitizable carbon to non-graphitizable carbon.
(Example 11)

The negative electrode plate was produced in the same manner as in Example 1 except that the negative electrode active material was changed from natural graphite to artificial graphite (d002 = 0.337 nm, average particle size (d50) = 18 μm).
Example 12

In preparation of the negative electrode plate, graphitizable carbon (d002 = 0.35 nm, average particle size (d50) = 10 μm) as a negative electrode active material and polyvinylidene fluoride as a binder are mixed and applied onto a copper foil, and then dried. , Natural graphite (d002 = 0.337 nm, average particle size (d50) = 20 μm) as the negative electrode active material, carboxymethylcellulose (Daicel Finechem # 2200) and styrene as the binder on the pressed graphitizable carbon coated copper foil Butadiene (SBR) was mixed and applied, then dried and pressed (also called double coating). Otherwise, the same procedure as in Example 1 was performed.
(Example 13)

In the production of the negative electrode plate, a predetermined natural graphite as a negative electrode active material and carboxymethyl cellulose and styrene butadiene as a binder are mixed and applied onto a copper foil, and then dried and pressed on a graphite-coated copper foil as a negative electrode active material. Graphitizable carbon (d002 = 0.35 nm, average particle size (d50) = 10 μm) and polyvinylidene fluoride as a binder were mixed, applied onto a copper foil, dried and pressed (also called double coating) ). Otherwise, the same procedure as in Example 1 was performed.
(Comparative Example 1)
The production of the negative electrode plate was performed in the same manner as in Example 1, except that the negative electrode active material was only natural graphite.
(Comparative Example 2)

The production of the negative electrode plate was performed in the same manner as in Comparative Example 1 except that the capacity ratio of the negative electrode to the positive electrode (negative electrode capacity / positive electrode capacity) was set to 2.2.
(Comparative Example 3)

The production of the negative electrode plate was performed in the same manner as in Example 1 except that only the graphitizable carbon was used as the negative electrode active material.
(Comparative Example 4)

The production of the negative electrode plate was performed in the same manner as in Comparative Example 3 except that the capacity ratio of the negative electrode to the positive electrode (negative electrode capacity / positive electrode capacity) was set to 2.2.
(Comparative Example 5)

Production of the negative electrode plate was performed in the same manner as in Example 3 except that the mixing ratio of graphite and amorphous carbon (graphite / amorphous carbon) was 80/20.
(Comparative Example 6)

Production of the negative electrode plate was performed in the same manner as in Example 1 except that the capacity ratio of the negative electrode to the positive electrode (negative electrode capacity / positive electrode capacity) was 1.2.
The results of the above examples and comparative examples are shown in Table 1 below.

As shown in Table 1, in Examples 1 to 13, the content of graphite contained in the negative electrode was 10 to 70% by mass with respect to the total amount of graphite and amorphous carbon contained in the negative electrode. The capacity ratio (negative electrode capacity / positive electrode capacity), which is the ratio of the capacity of the negative electrode to the capacity, is 1.3 to 2.2. In Examples 1 to 13, the evaluation result is “A” or “B” in any of the input characteristics, overcharge resistance, and life characteristics. Among these, the content of graphite contained in the negative electrode is 10 to 50% by mass with respect to the total amount of graphite and amorphous carbon contained in the negative electrode, and the capacity ratio (negative electrode capacity / positive electrode capacity) is 1.3. In Examples 2 to 5, the evaluation result is “A” in any of the input characteristics, overcharge resistance, and life characteristics. Further, the content of graphite contained in the negative electrode is 70% by mass with respect to the total amount of graphite and amorphous carbon contained in the negative electrode, and the capacity ratio (negative electrode capacity / positive electrode capacity) is 2.0-2. In Examples 8 and 9, which are 2, the evaluation result is “A” in any of the input characteristics, overcharge resistance, and life characteristics.

In Examples 1 to 13, the state of charge of the negative electrode at a potential of 0.1 V with respect to the lithium potential is 42 to 60%. Here, the state of charge of the negative electrode at a potential of 0.1 V with respect to the lithium potential depends on the graphite content. This is because the charge curves of graphitizable carbon, non-graphitizable carbon, and graphite are different from each other, and the “CCCV charge capacity up to 0 V in the third cycle” is different from that of graphitizable carbon, non-graphitizable carbon, and graphite. This is because they are different. Therefore, the mixing ratio of graphite to the total amount of graphite and amorphous carbon can be determined by determining the state of charge (CC / CCCV total capacity) of the negative electrode at a potential of 0.1 V with respect to the lithium potential.

On the other hand, in Comparative Examples 1, 2 and 5, the capacity ratio (negative electrode capacity / positive electrode capacity) is 1.3 to 2.2, but the graphite content contained in the negative electrode is different from that contained in the negative electrode. It exceeds 70 mass% with respect to the total amount of crystalline carbon. In Comparative Examples 3 and 4, the capacity ratio (negative electrode capacity / positive electrode capacity) is 1.3 to 2.2, but the graphite content in the negative electrode is graphite and amorphous in the negative electrode. It is less than 10 mass% with respect to the total amount of carbon. In Comparative Example 6, the content of graphite contained in the negative electrode was 10 to 70% by mass with respect to the total amount of graphite and amorphous carbon contained in the negative electrode, but the capacity ratio (negative electrode capacity / positive electrode capacity) Is less than 1.3. In Comparative Examples 1 to 6, the evaluation result is “C” in any one of the input characteristics, overcharge resistance, and life characteristics. In Comparative Examples 1, 2, and 5, the state of charge of the negative electrode at a potential of 0.1 V with respect to the lithium potential is 41% or less, and in Comparative Examples 3 and 4, the negative electrode has a lithium potential with respect to the lithium potential. The charge state at a potential of 0.1 V exceeds 60%.

Thus, by mixing the graphite and the amorphous carbon, it is possible to further improve the output characteristics and energy density while maintaining the input characteristics. The content ratio of graphite to amorphous carbon ((graphite) / (amorphous carbon)) is preferably 10/90 to 70/30, more preferably 15/85 to 65/35, More preferred is 20/80 to 50/50. This is because the output characteristics and the overcharge resistance are improved when the blending ratio of graphite is 10% or more, and the maintenance of the input characteristics and the overcharge resistance can be achieved at 70% or less.

That is, the content of graphite contained in the negative electrode is 10 to 70% by mass with respect to the total amount of graphite and amorphous carbon contained in the negative electrode, and the capacity ratio (negative electrode When the capacity / positive electrode capacity is 1.3 to 2.2, it is possible to provide a lithium ion battery excellent in input characteristics, life characteristics and overcharge resistance.

DESCRIPTION OF SYMBOLS 1 Positive electrode external terminal 1 'Negative electrode external terminal 2 Nut 3 Ceramic washer 3' Ceramic washer 4 Battery cover 5 Battery container 6 Electrode group 7 buttock 8 Insulation coating 9 Lead piece 10 Cleavage valve 11 Metal washer 12 O-ring 13 Injection port 20 Lithium ion battery

Claims

A negative electrode comprising graphite and amorphous carbon;
A positive electrode comprising a lithium transition metal composite oxide;
An electrolyte,
With
The content of the graphite contained in the negative electrode is 10 to 70% by mass with respect to the total amount of the graphite and the amorphous carbon contained in the negative electrode,
A lithium ion battery, wherein a capacity ratio, which is a ratio of a capacity of the negative electrode to a capacity of the positive electrode, is 1.3 to 2.2.
A negative electrode comprising graphite and amorphous carbon;
A positive electrode comprising a lithium transition metal composite oxide;
An electrolyte,
With
The state of charge of the negative electrode at a potential of 0.1 V with respect to the lithium potential is 42 to 60%,
A lithium ion battery, wherein a capacity ratio, which is a ratio of a capacity of the negative electrode to a capacity of the positive electrode, is 1.3 to 2.2.
The lithium ion battery according to claim 1 or 2,
The lithium transition metal composite oxide is a lithium ion battery, which is a layered lithium / nickel / manganese / cobalt composite oxide.
The lithium ion battery according to any one of claims 1 to 3,
The electrolytic solution is a lithium ion battery including ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.
The lithium ion battery according to any one of claims 1 to 4,
The lithium ion battery, wherein the positive electrode is made of a positive electrode mixture, and the density of the positive electrode mixture is 2.5 to 2.8 g / cm 3 .