JP6344470B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery.

A lithium ion secondary battery is a high energy density secondary battery, and is used as a power source for portable devices such as notebook computers and mobile phones by taking advantage of its characteristics. There are various types of lithium ion secondary batteries. Cylindrical lithium ion secondary batteries employ a wound structure of a positive electrode, a negative electrode, and a separator. For example, a positive electrode material and a negative electrode material are respectively applied to two strip-shaped metal foils, a separator is sandwiched therebetween, and these laminated bodies are wound in a spiral shape to form a wound group. The wound group is housed in a cylindrical battery can serving as a battery container, and after injecting an electrolytic solution, the cylindrical lithium ion secondary battery is formed.
As the cylindrical lithium ion secondary battery, a 18650 type lithium ion battery is widely used as a consumer lithium ion battery. The outer diameter of the 18650 type lithium ion battery is 18 mm in diameter and is small with a height of about 65 mm. As the positive electrode active material of the 18650 type lithium ion secondary battery, lithium cobaltate characterized by high capacity and long life is mainly used, and the battery capacity is approximately 1.0 Ah to 2.0 Ah (3.7 Wh to 7.4 Wh).

In recent years, lithium ion secondary batteries are expected to be used not only for consumer applications such as portable devices but also for large-scale power storage systems for natural energy such as solar power and wind power generation. In a large-scale power storage system, the amount of power per system is required on the order of several MWh.
For example, Patent Literature 1 below discloses a cylindrical lithium ion secondary battery having an electrode winding group in which a positive electrode, a negative electrode, and a separator are wound around a cylindrical battery container. This battery has a discharge capacity of 30 Ah or more, a positive electrode active material mixture containing lithium manganese composite oxide is used for the positive electrode, and a negative electrode active material mixture containing amorphous carbon is used for the negative electrode. Yes.

International Publication No. 2013/128677

In recent years, lithium ion secondary batteries have attracted attention as high input / output power sources used in electric vehicles, hybrid electric vehicles, and the like. In such an application to the automobile field, in addition to high output, high capacity, and long life, excellent input characteristics and life characteristics are required to improve energy utilization efficiency by regeneration.
However, the lithium ion secondary battery described in Patent Document 1 reveals that the input characteristics are not sufficient from the examination results of the present inventors.
This invention is made | formed in view of the said subject, and is providing the lithium ion secondary battery excellent in an input characteristic and a lifetime characteristic.

Specific means for solving the above problems are as follows.
When the ratio of the charge capacity in the constant current region in 10 hour rate charge is X% with respect to the total capacity of the negative electrode, a negative electrode satisfying the following formula (1), a lithium / nickel / manganese / cobalt composite oxide ( A lithium ion secondary battery including a positive electrode including NMC and having a capacity ratio (negative electrode capacity / positive electrode capacity) Y between the positive electrode and the negative electrode satisfying the following formula (2).
70 ≦ X ≦ 95 (1)
1 ≦ Y ≦ 1 + (1−X / 100) (2)
In the above, X in the formula (1) is preferably in the range of the following formula (3).
80 ≦ X ≦ 90 (3)
In the above, it is preferable that the negative electrode contains graphitizable carbon and the graphitizable carbon is contained in an amount of 20% by mass or more based on the total amount of the negative electrode active material.
Further, in the above, the negative electrode contains graphitizable carbon and non-graphitizable carbon, and the mixing ratio of graphitizable carbon and non-graphitizable carbon is graphitizable carbon / non-graphitizable carbon (mass ratio) = 100/0. 10/90 is preferable.

  ADVANTAGE OF THE INVENTION According to this invention, the lithium ion secondary battery excellent in an input characteristic and a lifetime characteristic can be provided.

It is sectional drawing of the lithium ion secondary battery of embodiment which can apply this invention. It is the graph which put together the relationship of capacity | capacitance ratio (negative electrode capacity / positive electrode capacity) and the constant current area | region charge capacity / negative electrode total capacity | capacitance of a negative electrode.

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 secondary battery will be briefly described. The lithium ion secondary 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 secondary battery, a charger is connected 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, an external load is connected between the positive electrode and the negative electrode. 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.

In this manner, charging / 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 secondary battery will be described later (see, for example, FIG. 1).
Next, a positive electrode, a negative electrode, an electrolytic solution, a separator, and other constituent members that are constituent elements of the lithium ion secondary battery of the present embodiment will be sequentially described.

1. Positive electrode

In this embodiment mode, the positive electrode shown below is applicable to a high-capacity, high-input / output lithium ion secondary battery. The positive electrode (positive electrode plate) of the present embodiment is composed of a current collector and a positive electrode mixture (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 also 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 of NMC and 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 based on 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), (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.

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. Lithium-containing composite metal oxides other than NMC and sp-Mn, olivine type lithium salts, chalcogen compounds, manganese dioxide, etc. Is mentioned. The lithium-containing composite metal 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 the lithium-containing composite metal oxide other than NMC and sp-Mn include LixCoO ₂ , LixNiO ₂ , LixMnO ₂ , LixCoyNi ₁ -yO ₂ , LixCoyM ₁ -yOz, LixNi ₁ -yMyOz (wherein M is Na , Mg, Sc, Y, Mn, Fe, Co, Ni, 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. 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 material and a thickener used as needed are mixed in a dry form to form a sheet, which is pressure-bonded to a current collector (dry method). In addition, a positive electrode active material, a binder, and other materials such as a conductive material 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).
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 particles of the positive electrode active material such as NMC or sp-Mn, particles having a lump shape, a polyhedron shape, a spherical shape, an elliptical spherical shape, a plate shape, a needle shape, a columnar shape, or the like can be used.
The median diameter d50 of the positive electrode active material particles such as NMC and sp-Mn (when the primary particles aggregate to form secondary particles, the median diameter d50 of the secondary particles) can be adjusted within the following range. It is. The lower limit of the range is 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and the upper limit is 30 μm or less, preferably 25 μm or less, more preferably 15 μm or less.
If it is less than the above lower limit, the tap density (fillability) may be lowered, and a desired tap density may not be obtained. If the upper limit is exceeded, it takes time to diffuse lithium ions in the particles, so that the battery performance is lowered. May be incurred. Moreover, when the said upper limit is exceeded, the mixing property with other materials, such as a binder and a conductive material, may fall at the time of formation of an electrode. Therefore, when this mixture is slurried and applied, it may not be applied uniformly, which may cause problems such as streaking. The median diameter d50 can be obtained from the particle size distribution obtained by the laser diffraction / scattering method.

  The range of the average particle size of the primary particles in the case where the primary particles are aggregated to form secondary particles is as follows. The lower limit of the range is 0.01 μm or more, preferably 0.05 μm or more, more preferably 0.08 μm or more, particularly preferably 0.1 μm or more, and the upper limit is 3 μm or less, preferably 2 μm or less, more preferably 1 μm. Hereinafter, it is particularly preferably 0.6 μm or less. When the above upper limit is exceeded, it is difficult to form spherical secondary particles, and battery performance such as output characteristics may be reduced due to a decrease in tap density (fillability) and a decrease in specific surface area. Moreover, if it is less than the said lower limit, problems, such as deterioration of the reversibility of charging / discharging, may arise by crystallinity fall.

The ranges of the BET specific surface area of the positive electrode active material particles such as NMC and sp-Mn are as follows. The lower limit of the range is 0.2 m ² / g or more, preferably 0.3 m ² / g or more, more preferably 0.4 m ² / g or more, and the upper limit is 4.0 m ² / g or less, preferably 2 .5m ² / g, more preferably not more than 1.5 m ² / g. If it is less than the said minimum, battery performance may fall. When the above upper limit is exceeded, it is difficult to increase the tap density, and there is a possibility that the miscibility with other materials such as a binder and a conductive material is lowered. Therefore, there is a possibility that the applicability when the mixture is slurried and applied is deteriorated. The BET specific surface area is a specific surface area (area per unit g) determined by the BET method.

Examples of the conductive material 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.
About the content (addition amount, ratio, amount) of the conductive material, the range of the content of the conductive material with respect to the mass of the positive electrode mixture is as follows. The lower limit of the range is 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 1% by mass or more, and the upper limit is 50% by mass or less, preferably 30% by mass or less, more preferably 15%. It is below mass%. If it is less than the said minimum, electroconductivity may become inadequate. Moreover, when the said upper limit is exceeded, battery capacity may fall.

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 and dispersibility in the dispersion solvent is selected. Specifically, resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, 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 Examples thereof include fluorine polymers such as polymers and polytetrafluoroethylene / vinylidene fluoride copolymers; 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. 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.
Regarding the content (addition amount, ratio, amount) 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 0.1% by mass or more, preferably 1% by mass or more, more preferably 3% by mass or more, and the upper limit is 80% by mass or less, preferably 60% by mass or less, more preferably 40% by mass. Hereinafter, it is particularly preferably 10% by mass or less. If the content of the binder is too low, the positive electrode active material cannot be sufficiently bound, the positive electrode has insufficient mechanical strength, and battery performance such as cycle characteristics may be deteriorated. Conversely, if it is too high, the battery capacity and conductivity may be reduced.

In order to improve the packing density of the positive electrode active material, the layer formed on the current collector using the wet method or the dry method is preferably consolidated by a hand press, a roller press, or the like. The density of the positive electrode mixture is preferably 2.5 to 2.8 g / cm ³ . If the positive electrode mixture density is less than 2.5 g / cm ³ , the resistance of the positive electrode is increased, and input / output characteristics may be deteriorated. On the other hand, when the density of the positive electrode mixture exceeds 2.8 g / cm ³ , there is a concern that the safety may be lowered, and it may be necessary to strengthen other safety measures. From this point of view, positive electrode density, 2.55 g / cm ³ or more, 2.75 g / cm ³ or less is more preferable. Moreover, it is preferable that the single-sided coating amount to the positive electrode electrical power collector of positive electrode compound material is 110-170 g / m < ² >.
When the coating amount of the positive electrode mixture is less than 110 g / m ² , the amount of the active material that contributes to charging / discharging decreases, and the energy density of the battery may decrease. On the other hand, when the coating amount of the positive electrode mixture exceeds 170 g / m ² , the resistance of the positive electrode mixture increases, and the input / output characteristics may deteriorate. From the above viewpoint, the single-sided coating amount of the positive electrode mixture to the positive electrode current collector is more preferably 120 g / m ² or more and 160 g / m ² or less, and 130 g / m ² or more and 150 g / m ^2. More preferably, it is as follows.
Considering the amount of single-sided application of the positive electrode mixture to the positive electrode current collector and the density of the positive electrode mixture, 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, and examples thereof include metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and carbonaceous materials such as carbon cloth and carbon paper. Of these, metal materials, particularly aluminum, are preferred.
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 metal foil, metal cylinder, metal coil, metal plate, metal thin film, expanded metal, punch metal, and foam metal. Examples of the carbonaceous material include carbon plate, carbon thin film, and carbon cylinder. It is done. 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 the range is as follows. The lower limit of the range is 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and the upper limit is 1 mm or less, preferably 100 μm or less, more preferably 50 μm or less. If it is less than the said minimum, intensity | strength required as a collector may be insufficient. Moreover, when the said upper limit is exceeded, flexibility will fall and workability may deteriorate.

2. Negative electrode

The negative electrode of the present embodiment is particularly limited as long as it satisfies the following formula (1) when the ratio of the charge capacity in the constant current region in 10 hour rate charge is X% with respect to the total capacity of the negative electrode. Not.
70 ≦ X ≦ 95 (1)
The negative electrode comprises a current collector and a negative electrode mixture (negative electrode mixture) formed on both surfaces (or one surface) of the current collector. The negative electrode mixture contains a negative electrode active material that can electrochemically occlude and release lithium ions.
The negative electrode active material used in the present invention preferably contains graphitizable carbon (hereinafter sometimes referred to as soft carbon) so as to be within the range of the formula (1). In addition, as long as it exists in the range of said Formula (1), carbon materials other than graphitizable carbon may be included.
Carbon materials are broadly divided into graphite materials with a uniform crystal structure and non-graphite materials with a disordered crystal structure. The former includes natural graphite and artificial graphite, and the latter has a disordered crystal structure. However, there are easily graphitized carbon that is likely to become graphite by heating at 2000 to 3000 ° C. and non-graphitizable carbon that is difficult to become graphite (hereinafter sometimes referred to as hard carbon). Specific examples include graphite, cokes (petroleum coke, pitch coke, needle coke, etc.), resin film fired carbon, fiber fired carbon, vapor grown carbon, and the like. The non-graphite-based carbon material can be produced by heat-treating petroleum pitch, polyacene, polyparaphenylene, polyfurfuryl alcohol, polysiloxane, etc., and by changing the firing temperature, hard carbon can be obtained, It is possible to use soft carbon. For example, a firing temperature of about 500 ° C. to 800 ° C. is suitable for producing hard carbon, and a firing temperature of about 800 ° C. to 1000 ° C. is suitable for producing soft carbon. The non-graphitizable carbon is defined as having a surface spacing d002 value in the C-axis direction obtained by an X-ray wide angle diffraction method of 0.36 nm or more and 0.40 nm or less.
The graphitizable carbon preferably has a surface spacing d002 value in the C-axis direction obtained by an X-ray wide-angle diffraction method of 0.34 nm or more and less than 0.36 nm, and is 0.341 nm or more and 0.355 nm or less. More preferably, it is 0.342 nm or more and 0.35 nm or less.

As the negative electrode active material satisfying 70 ≦ X ≦ 95 when the ratio of the charge capacity in the constant current region in 10 hour rate charge to the total capacity of the negative electrode is X%, graphitizable carbon (soft carbon) is used. It is preferable to include. The content of graphitizable carbon (soft carbon) is preferably 20% by mass or more, more preferably 50% by mass or more, and still more preferably 70% by mass or more based on the total amount of the negative electrode active material. Further, graphitizable carbon (soft carbon) and non-graphitizable carbon (hard carbon) may be used in combination. The mixing ratio (mass ratio) of graphitizable carbon (soft carbon) and non-graphitizable carbon (hard carbon) is graphitizable carbon (soft carbon) / non-graphitizable carbon (hard carbon) = 100 / 0-10 / 90 is preferable, 100/0 to 20/80 is more preferable, 100/0 to 50/50 is further preferable, and 100/0 to 70/30 is particularly preferable.
The average particle diameter (d50) of the graphitizable carbon (soft carbon) is preferably 2 to 50 μm. When the average particle diameter is 2 μm or more, the specific surface area can be in an appropriate range, the initial charge / discharge efficiency of the lithium ion secondary battery is excellent, and the contact between particles tends to be excellent and the input / output characteristics tend to be excellent. On the other hand, when the average particle diameter is 50 μm or less, unevenness on the electrode surface hardly occurs, and the short circuit of the battery can be suppressed, and the diffusion distance of Li from the particle surface to the inside becomes relatively short, so that the insertion of the lithium ion secondary battery The output characteristics tend to improve. From this viewpoint, the average particle diameter is more preferably 5 to 30 μm, and further preferably 10 to 20 μm. For example, the particle size distribution can be measured with a laser diffraction particle size distribution measuring device (for example, SALD-3000J manufactured by Shimadzu Corporation) by dispersing a sample in purified water containing a surfactant, and the average particle size Is calculated as the median diameter (d50).

In addition, as the negative electrode active material, a metal oxide such as tin oxide or silicon oxide, a metal composite oxide, a lithium alloy such as lithium alone or a lithium aluminum alloy, or a material capable of forming an alloy with lithium such as Sn or Si is used in combination. May be. 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 Ti (titanium), Li (lithium), or a material containing both Ti and Li has a high current density. This is preferable from the viewpoint of discharge characteristics.

There is no restriction | limiting in particular as a material of the collector for negative electrodes, Metal materials, such as copper, nickel, stainless steel, nickel plating steel, are mentioned. Among these, copper is preferable from the viewpoint of ease of processing and cost.
There is no restriction | limiting in particular as a shape of an electrical power collector, The material processed into various shapes can be used. Specific examples include metal foil, metal cylinder, metal coil, metal plate, metal thin film, expanded metal, punch metal, and foam metal. Among these, a metal thin film is preferable, and a 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 when 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 single-sided coating amount of the negative electrode mixture on the current collector is preferably 50 g / m ² or more and 120 g / m ² or less, and preferably 60 g / m ² or more and 100 g / m from the viewpoint of energy density and input / output characteristics. More preferably, it is ² or less.
Although there is no restriction | limiting in particular in the structure of the negative electrode compound material formed using the negative electrode active material, The range of the negative electrode compound material density is as follows. The lower limit of the negative electrode composite density is preferably 0.7 g / cm ³ or more, more preferably 0.8 g / cm ³ , still more preferably 0.9 g / cm ³ or more, and the upper limit is 2 g / cm ³ or less. Preferably it is 1.9 g / cm ³ or less, more preferably 1.8 g / cm ³ or less, and even more preferably 1.7 g / cm ³ or less.
When the above upper limit is exceeded, particles of the negative electrode active material are likely to be destroyed, and a high current is generated due to an increase in the initial irreversible capacity and a decrease in the permeability of the non-aqueous electrolyte solution near the interface between the current collector and the negative electrode active material. There is a possibility of deteriorating the density charge / discharge characteristics. In addition, if it is less than the above lower limit, the conductivity between the negative electrode active materials decreases, so the battery resistance increases, and the capacity per unit volume may decrease.

  The binder for the negative electrode active material is not particularly limited as long as it is a material that is stable to the non-aqueous electrolyte and the dispersion solvent used when forming the electrode. Resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, cellulose, nitrocellulose; SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber, fluorine rubber, NBR (acrylonitrile-butadiene rubber) Rubber polymers such as ethylene-propylene rubber; Styrene / butadiene / styrene block copolymers or hydrogenated products thereof; EPDM (ethylene / propylene / diene terpolymer), styrene / ethylene / butadiene / styrene copolymer Polymers, thermoplastic elastomeric polymers such as styrene / isoprene / styrene block copolymers or hydrogenated products thereof; syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene / vinyl acetate Polymers, soft resinous polymers such as propylene / α-olefin copolymers; fluorinated polymers such as polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene / ethylene copolymers; Examples thereof include a polymer composition having ion conductivity of alkali metal ions (particularly lithium ions). These may be used alone or in combination of two or more.

As the dispersion solvent for forming the slurry, any type of solvent can be used as long as it can dissolve or disperse the negative electrode active material, the binder, and the conductive material and the 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, a mixed solvent of alcohol and water, and examples of the organic solvent include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, and acrylic. Methyl acid, diethyltriamine, N, N-dimethylaminopropylamine, tetrahydrofuran (THF), toluene, acetone, diethyl ether, dimethylacetamide, hexamethylphosphalamide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methyl Naphthalene and hexane are mentioned. In particular, when an aqueous solvent is used, it is preferable to use a thickener. A dispersing agent or the like is added to the thickener, and a slurry such as SBR is made into a slurry. In addition, the said dispersion solvent may be used individually by 1 type, or may be used in combination of 2 or more type.
Regarding the content (addition amount, ratio, amount) of the binder, the range of the content of the binder 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 0.5% by mass or more, and further preferably 0.6% by mass or more. The upper limit is 20% by mass or less, preferably 15% by mass or less, more preferably 10% by mass or less, and still more preferably 8% by mass or less.
When the upper limit is exceeded, the proportion of the binder that does not contribute to the battery capacity increases, which may lead to a decrease in battery capacity. Moreover, if it is less than the said minimum, the fall of the intensity | strength of a negative electrode compound material may be caused.
In particular, the range of the content of the binder with respect to the mass of the negative electrode mixture when a rubbery polymer typified by SBR is used as the main component as the binder is as follows. The lower limit of the range is 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and the upper limit is 5% by mass or less, preferably 3% by mass or less, more preferably. Is 2% by mass or less.
The range of the binder content with respect to the mass of the negative electrode mixture when a fluorine-based polymer typified by polyvinylidene fluoride is used as the main component as the binder is as follows. The lower limit of the range is 1% by mass or more, preferably 2% by mass or more, more preferably 3% by mass or more, and the upper limit is 15% by mass or less, preferably 10% by mass or less, more preferably 8% by mass or less. is there.

The thickener is used to adjust the viscosity of the slurry. The thickener is not particularly limited, and examples thereof 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 thickener relative to the mass of the negative electrode mixture when the thickener is used is as follows. The lower limit of the range is 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and the upper limit is 5% by mass or less, preferably 3% by mass or less, more preferably. Is 2% by mass or less.
If it is less than the said minimum, the applicability | paintability of a slurry may fall. Moreover, when the said upper limit is exceeded, the ratio of the negative electrode active material to a negative electrode compound material will fall, and there exists a possibility of the fall of battery capacity and the raise between resistances of a negative electrode active material.

3. Electrolyte

The electrolytic solution of the present embodiment includes a lithium salt (electrolyte) and a non-aqueous solvent that dissolves the lithium salt. You may add an additive as needed.
The lithium salt is not particularly limited as long as it is a lithium salt that can be used as an electrolyte of a non-aqueous electrolyte solution for a lithium ion battery, but the following inorganic lithium salt, fluorine-containing organic lithium salt, oxalate borate salt, and the like can be used. Can be mentioned.
Examples of the inorganic lithium _salt, LiPF _6, and LiBF _4, inorganic fluoride salts LiAsF 6, LiSbF _{6, etc.,} LiClO _4, Libro 4, and perhalogenate of LiIO ₄ or the like, and inorganic chloride salts such as LiAlCl ₄ Is mentioned.
Examples of the fluorine-containing organic lithium salt include perfluoroalkane sulfonates such as LiCF ₃ SO ₃ ; LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C Perfluoroalkanesulfonylimide salt such as ₄ F ₉ SO ₉ ); perfluoroalkanesulfonylmethide salt such as LiC (CF ₃ SO ₂ ) ₃ ; Li [PF ₅ (CF ₂ CF ₂ CF ₃ )], Li [PF ₄ (CF ₂ CF ₂ CF ₃ ) ₂ ], Li [PF ₃ (CF ₂ CF ₂ CF ₃ ) ₃ ], Li [PF ₅ (CF ₂ CF ₂ CF ₂ CF ₃ )], Li [PF ₄ (CF ₂ CF ₂ CF ₂ CF ₃ ) ₂ ], Li [PF ₃ (CF ₂ CF ₂ CF ₂ CF ₃ ) ₃ ] and other fluoroalkyl fluorophosphates.
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 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.
Although there is no restriction | limiting in particular in the density | concentration of the electrolyte in a non-aqueous electrolyte solution, The density | concentration range of an electrolyte is as follows. The lower limit of the concentration is 0.5 mol / L or more, preferably 0.6 mol / L or more, more preferably 0.7 mol / L or more. Further, the upper limit of the concentration is 2 mol / L or less, preferably 1.8 mol / L or less, more preferably 1.7 mol / L or less. If the concentration is too low, the electrical conductivity of the electrolyte may be insufficient. On the other hand, if the concentration is too high, the viscosity increases and the electrical conductivity may decrease. Such a decrease in electrical conductivity may reduce the performance of the lithium ion secondary battery.

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 a lithium ion secondary battery, and examples thereof include cyclic carbonates, chain carbonates, chain esters, cyclic ethers, and chain ethers. Can be mentioned.
As the cyclic carbonate, those having 2 to 6 carbon atoms of the alkylene group constituting the cyclic carbonate are preferable, and those having 2 to 4 are more preferable. Specific examples include ethylene carbonate, propylene carbonate, and butylene carbonate. Of these, ethylene carbonate and propylene carbonate are preferable.
As the chain carbonate, dialkyl carbonate is preferable, and the number of carbon atoms of the two alkyl groups is preferably 1 to 5, and more preferably 1 to 4. Specific examples include symmetric chain carbonates such as dimethyl carbonate, diethyl carbonate, and di-n-propyl carbonate; and asymmetric chain carbonates such as ethyl methyl carbonate, methyl-n-propyl carbonate, and ethyl-n-propyl carbonate. It is done. Of these, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferable.
Examples of chain esters include methyl acetate, ethyl acetate, propyl acetate, and methyl propionate. Among them, it is preferable to use methyl acetate from the viewpoint of improving the low temperature characteristics.
Examples of the cyclic ether include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran and the like. Of these, tetrahydrofuran is preferably used from the viewpoint of improving input / output characteristics.
Examples of chain ethers include dimethoxyethane and dimethoxymethane.
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. 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. One of the preferable combinations is a combination mainly composed of cyclic carbonates and chain carbonates. Among them, the total of the cyclic carbonates and the chain carbonates in the non-aqueous solvent is 80% by volume or more, preferably 85% by volume or more, more preferably 90% by volume or more, and the cyclic carbonates and the chain carbonates. It is preferable that the cyclic carbonates have a capacity in the following range with respect to the total of the above. The lower limit of the capacity of the cyclic carbonates is 5% by volume or more, preferably 10% by volume or more, more preferably 15% by volume or more, and the upper limit is 50% by volume or less, preferably 35% by volume or less, more preferably 30%. The capacity is less than%. By using such a combination of non-aqueous solvents, battery cycle characteristics and high-temperature storage characteristics (particularly, remaining capacity and high-load discharge capacity after high-temperature storage) are improved.

  The additive is not particularly limited as long as it is an additive for a non-aqueous electrolyte solution of a lithium ion secondary battery. For example, nitrogen, sulfur or a heterocyclic compound containing nitrogen and sulfur, a cyclic carboxylic acid ester, fluorine Examples thereof include cyclic carbonates and other compounds having an unsaturated bond in the molecule. 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, tetrafluoroethylene carbonate, and trifluoropropylene carbonate.
Examples of the compound having an unsaturated bond in the other molecule include vinylene carbonate.
In addition to the above additives, other additives such as an overcharge preventing 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.
By using the other additives, it is possible to suppress a rapid electrode reaction at the time of abnormality due to overcharge, improve capacity maintenance characteristics and cycle characteristics after high temperature storage, and improve input / output characteristics.

4). Separator

The separator is not particularly limited as long as it has electronic permeability while electrically 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, an olefin polymer, a fluorine polymer, a cellulose polymer, polyimide, nylon, or the like is used. It is preferable to select from materials that are stable with respect to the non-aqueous electrolyte 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, nitrides such as aluminum nitride and silicon nitride, sulfates such as barium sulfate and calcium sulfate, and the like are used. For example, what made the said inorganic substance of fiber shape or particle shape adhere to thin film-shaped base materials, such as a nonwoven fabric, a woven fabric, and a microporous film, can be used as a separator. As a thin film-shaped substrate, a substrate having a pore diameter of 0.01 to 1 μm and a thickness of 5 to 50 μm is preferably used. 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. 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.

5. Other components

A cleavage valve may be provided as another component of the lithium ion secondary 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. Examples of the material used for the above components include lithium carbonate and polyalkylene carbonate resin. Examples of the polyalkylene carbonate resin include polyethylene carbonate, polypropylene carbonate, poly (1,2-dimethylethylene carbonate), polybutene carbonate, polyisobutene carbonate, polypentene carbonate, polyhexene carbonate, polycyclopentene carbonate, polycyclohexene carbonate, and polycycloheptene. Examples include carbonate, polycyclooctene carbonate, and polylimonene carbonate. As a material used for the said structural part, lithium carbonate, polyethylene carbonate, and polypropylene carbonate are preferable.

(Discharge capacity of lithium ion secondary battery)
The lithium ion secondary battery of the present invention is suitable for a large capacity discharge capacity of 30 Ah or more and less than 99 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 99 Ah, and more preferably 45 Ah or more and less than 95 Ah.

(Capacity ratio of negative electrode to positive electrode of lithium ion secondary battery)
In the present invention, when the ratio of the charge capacity in the constant current region in 10 hour rate charge is X% with respect to the total capacity of the negative electrode, the capacity ratio between the negative electrode satisfying the following formula (1) and the positive electrode (negative electrode) (Capacity / positive electrode capacity) Y needs to satisfy the following formula (2). The lower limit of X is 70, but 75 or more is preferable from the viewpoint of input characteristics, and 80 or more is preferable from the viewpoint of input characteristics and life characteristics. The upper limit of X is 95, but 92 or less is preferable and 90 or less is more preferable from a practical viewpoint.
Here, 10 hour rate charging means that constant current charging is performed at a current value of 0.1 C.
The lower limit of Y is 1, but is preferably 1.05 or more from the viewpoint of safety. The upper limit of Y is 1+ (1−X / 100). When Y exceeds 1+ (1−X / 100), the potential of the positive electrode tends to increase before the negative electrode reaches the constant voltage charging region during charging. In such a case, it becomes easier for the negative electrode to reach the specified voltage (for example, 4.2 V) of the battery before the negative electrode reaches the constant voltage charging region during charging. That is, when Y exceeds 1+ (1−X / 100), for example, when the specified voltage of the battery is set to 4.2V, the potential of the positive electrode (lithium reference) exceeds 4.2V. Capacity deterioration occurs, and the battery life may be shortened.
70 ≦ X ≦ 95 (1)
1 ≦ Y <1+ (1−X / 100) (2)

The negative electrode capacity refers to [negative electrode discharge capacity], and the positive electrode capacity refers to [positive charge capacity of positive electrode minus 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 be calculated from, for example, “discharge capacity of negative electrode / discharge capacity of lithium ion secondary battery”. The lithium ion secondary battery has a discharge capacity of, for example, 4.2 V, 0.1 to 0.5 C, and a constant current and constant voltage (CCCV) charge with an end time of 2 to 5 hours. It can be measured under conditions when a constant current (CC) is discharged to 2.7 V at ˜0.5 C. The discharge capacity of the negative electrode was prepared by cutting a negative electrode having a measured discharge capacity of the lithium ion secondary battery into a predetermined area, using lithium metal as a counter electrode, and preparing a single electrode cell through a separator impregnated with an electrolyte. After constant current constant voltage (CCCV) charging at 0 V, 0.1 C, and a final current of 0.01 C, a constant current (CC) discharge at a constant current (CC) of up to 1.5 V at 0.1 C It can be calculated by measuring the discharge 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.
[Production of positive electrode plate]
The positive electrode plate was produced as follows. Layered lithium / nickel / manganese / cobalt composite oxide as positive electrode active material (BET specific surface area is 0.4 m ² / g, average particle size (d50) is 6.5 μm), and acetylene black as a conductive material (trade name: HS -100, average particle size 48 nm (Denki Kagaku Kogyo Co., Ltd. catalog), Denki Kagaku Kogyo Co., Ltd.), and polyvinylidene fluoride (trade name: Kureha KF Polymer # 1120, Kureha Co., Ltd.) as a binder. , To obtain a mixture of positive electrode materials. The mass ratio was active material: conductive material: 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 substantially evenly and uniformly 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 .

[Production of negative electrode plate]

The negative electrode plate was produced as follows. Easily graphitized carbon (d002 = 0.35 nm, average particle size (d50) = 10 μm) and non-graphitizable carbon (d002 = 0.37-0.38 nm, average particle size (d50) = 9 μm) as the negative electrode active material Were mixed at a predetermined active material mass ratio (easily graphitized carbon / non-graphitizable carbon). Table 1 shows the compounding ratio of non-graphitizable carbon. To this negative electrode active material, polyvinylidene fluoride (trade name: Kureha KF Polymer # 1120, Kureha Co., Ltd.) was added as a binder. 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 negative electrode current collector, substantially uniformly and uniformly so that the negative electrode capacity / positive electrode capacity had the values shown in Table 1. The density of the negative electrode mixture was 1.15 g / cm ³ .

[Production of battery]

The positive electrode plate and the negative electrode plate are wound with a polyethylene separator having a thickness of 30 μm interposed therebetween so that they 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 winding group. Further, the lengths of the positive electrode plate, the negative electrode plate, and the separator were adjusted, and the wound 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 positive electrode side flange portion 7 is integrally 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 wound 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 integrally 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 wound group 6, and has a bottom portion and a side portion.
Then, the insulating coating 8 was formed using an adhesive tape to cover 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 wound 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 winding group 6 and further from the outer periphery of the winding group 6 to the negative electrode external terminal 1 ′ side. Insulating coating 8 is formed by winding several times over the side of 7. 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 wound group 6 is slightly smaller than the inner diameter of the stainless steel battery container 5, and the wound group 6 is placed in the battery container 5. Inserted into. 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 a pole column whose tip constitutes the positive electrode external terminal 1 and a 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 cover 4 and project outside the battery cover 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 set to 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 ′, respectively. 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 through 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 is injected into the battery container 5 from the injection port 13 provided in the battery lid 4, and then the injection port 13 is sealed to complete the cylindrical lithium ion secondary battery 20. It was.

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 0.8 mass% of vinylene carbonate (VC) as an additive was used.

[Ratio of charge capacity in constant current region in 10 hour rate charge X% of total capacity of negative electrode]
The measurement of the ratio of the charge capacity in the constant current region (hereinafter sometimes referred to as the CC capacity of the negative electrode) in 10 hour rate charging with respect to the total capacity of the negative electrode was calculated as follows. First, the negative electrode plate produced above was punched into a diameter of 15 mm, and the negative electrode mixture layer on one side was removed.
Next, a CR2032-type coin cell was produced in an argon atmosphere through a separator and electrolyte solution obtained by punching the negative electrode plate and a counter electrode (metallic lithium) punched to a diameter of 16 mm into a diameter of 19 mm. The counter lithium metal lithium was used after polishing the surface to remove the oxide film. The electrolyte was a non-aqueous electrolyte (ethylene carbonate / methyl ethyl carbonate / dimethyl carbonate = 2/2/3 mixed solution (volume ratio) containing 1M LiPF ₆ ), and 0.8 mass of vinylene carbonate relative to the total amount of the mixed solution. % Of the product (trade name: Sollite, manufactured by Mitsubishi Chemical Co., Ltd., “Sollite” is a registered trademark) was used.The separator was a polyethylene porous sheet separator (trade name: Hypore, Asahi Kasei Corporation). “Hypore” is a registered trademark with a thickness of 30 μm.).

  Using the obtained coin cell, the sample electrode and the counter electrode are charged to 0 V (V vs Li / Li +) at a constant current of 0.1 C, and until the current density reaches 0.01 C at a constant voltage of 0 V. Charged. Discharging was performed up to 1.5 V (V vs Li / Li +) at a constant current of a current density of 0.1 C. This charge and discharge test was performed for 3 cycles.

The charge capacity at the third cycle was defined as the total capacity of the negative electrode. The discharge capacity at the third cycle was defined as “discharge capacity per predetermined area of negative electrode (1.7671 cm ² )”.
In addition, the charge capacity in the constant current region in 10 hour rate charge was the capacity when charged to 0 V (V vs Li / Li +) with a constant current of a current density of 0.1 C.

[Evaluation of battery characteristics (discharge capacity, input characteristics, life characteristics)] (discharge capacity)

Under an environment of 25 ° C., 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 “negative electrode discharge capacity / discharge capacity at a current value of 0.5 C”. 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 secondary 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 characteristic = Charge capacity at current value 3C / Charge capacity input characteristic at current value 0.5C is 80% or more as “A”, 75% or more and less than 80% as “B”, and less than 75% as “C” evaluated.

(Life characteristics)
The life characteristics are as follows: the battery is charged to 4.2 V at a current value of 0.5 C in an environment of 25 ° C., then left for 3 months in an environment of 50 ° C., and the discharge capacity after being left in an environment of 25 ° C. Measured and evaluated the discharge capacity ratio before and after being left. The discharge capacity ratio before and after standing was evaluated as “A” when 80% or more by volume, “B” when 75% or more and less than 80% by volume, and “C” when less than 75% by volume. The results of the above examples and comparative examples are shown in Table 1.

As shown in FIG. 2 and Table 1, Examples 1 to 8 satisfying the expressions (1) and (2) are excellent in input characteristics and life characteristics. In particular, it is excellent when X is 80 ≦ X ≦ 90.
On the other hand, Comparative Example 1 not included in 70 ≦ X ≦ 95 of Formula (1) and Comparison included in Formula (1) but not included in 1 ≦ Y ≦ 1 + (1−X / 100) of Formula 2 Examples 2 to 5 tend to be inferior in input characteristics and inferior in life characteristics.

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 ... Winding group, 7 ... Ridge part, 8 DESCRIPTION OF SYMBOLS ... Insulation coating, 9 ... Lead piece, 10 ... Cleavage valve, 11 ... Metal washer, 12 ... O-ring, 13 ... Injection hole, 20 ... Cylindrical lithium ion secondary battery

Claims (2)

When the ratio of the charging capacity in the constant current region in 10 hour rate charging is X% with respect to the total capacity of the negative electrode, the negative electrode satisfying the following formula (1) and the lithium / nickel / manganese / cobalt composite oxide: a positive electrode wherein the volume ratio of the positive electrode and the negative electrode (negative electrode capacity / positive electrode capacity) Y is meets the following formula (2), including,
As the negative electrode active material in the negative electrode, lithium ion two-phase is used, which is a graphitizable carbon or a mixture of graphitizable carbon and non-graphitizable carbon and containing at least 20% by mass of the graphitizable carbon. Next battery.
70 ≦ X ≦ 95 (1)
1 ≦ Y ≦ 1 + (1−X / 100) (2) The lithium ion secondary battery according to claim 1, wherein X in the formula (1) is in the range of the following formula (3).
80 ≦ X ≦ 90 (3)

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