JP2016152112A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery superior in life.SOLUTION: A lithium ion secondary battery comprises, in a battery container, a wound electrode group arranged by winding a positive electrode, a negative electrode and a separator and an electrolyte, and has a discharge capacity of 30 Ah or larger, but under 99 Ah. The positive electrode has a current collector and a positive electrode mixture applied to each face of the current collector. The positive electrode mixture includes a lithium-nickel-manganese-cobalt composite oxide as a positive electrode active material. As to the lithium-nickel-manganese-cobalt composite oxide, the median diameter (d50) is 5-7 μm, and 90% diameter (d90) is 8-14 μm. The positive electrode mixture has a density of 2.5-2.8 g/cm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lithium ion secondary battery.

Lithium ion secondary batteries are used as power sources for portable devices such as notebook computers and mobile phones. 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, an 18650 type lithium ion secondary battery is widely used as a consumer lithium ion secondary battery. The outer diameter of the 18650 type lithium ion secondary 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, which is characterized by high capacity and long life, is mainly used, and the battery capacity is approximately 1.0 to 2.0 Ah (3.7 to 7.4 Wh).
In recent years, lithium ion secondary batteries are expected to be used not only for 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 may be 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 (mixture) containing lithium manganese composite oxide is used for the positive electrode, and a negative electrode active material mixture containing amorphous carbon for the negative electrode. Is used.

International Publication No. 2013/128677

Lithium ion secondary batteries for large-scale power storage systems are required to have a product life and reliability of 10 years or longer, which is longer than consumer lithium ion secondary batteries, in combination with input / output characteristics. It became clear from the examination result of the present inventors that the life of the lithium ion secondary battery described in Patent Document 1 is not sufficient.
This invention is made | formed in view of the said subject, and is providing the long-life lithium ion secondary battery.

Specific means for solving the above problems are as follows.
<1> A lithium ion secondary battery comprising an electrode winding group in which a positive electrode, a negative electrode, and a separator are wound, and an electrolyte solution, and a discharge capacity of 30 Ah or more and less than 99 Ah,
The positive electrode has a current collector and a positive electrode mixture applied on both sides of the current collector, the positive electrode mixture includes a lithium-nickel-manganese-cobalt composite oxide as a positive electrode active material, The median diameter (d50) of the lithium / nickel / manganese / cobalt composite oxide is 5 to 7 μm and the 90% diameter (d90) is 8 to 14 μm, and the density of the positive electrode mixture is 2.5 to 2.8 g / lithium ion secondary battery is cm ^3.

  ADVANTAGE OF THE INVENTION According to this invention, the lithium ion secondary battery which is excellent in lifetime can be provided.

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

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, the following positive electrode is used as an electrode 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 on both surfaces of the current collector. 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 layered lithium / nickel / manganese / cobalt composite oxide (NMC) having a specific particle size described later. The layered lithium / nickel / manganese / cobalt composite oxide (NMC) has a high capacity and excellent safety.
The content of the layered lithium / nickel / manganese / cobalt composite oxide (NMC) is preferably 65% by mass or more, more than 70% by mass with respect to the total amount of the positive electrode mixture, from the viewpoint of increasing the capacity of the battery. It is more preferable that it is 80 mass% or more.

Further, as the positive electrode active material, materials other than the above NMC may be used. As the positive electrode active material other than the NMC, those commonly used in this field can be used, and examples thereof include lithium-containing composite metal oxides such as sp-Mn, olivine type lithium salts, chalcogen compounds, and manganese dioxide. 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 element include Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, V, and B, and Mn, Al, Co, and the like. Ni, Mg are preferable. One kind or two or more kinds of different elements may be used. Among these, lithium-containing composite metal oxides are preferable. The lithium-containing composite metal oxide, for _{example, LixCoO 2, LixNiO 2, LixMnO} 2, LixCoyNi 1 -yO 2, LixCoyM 1 -yOz, LixNi 1 -yMyOz, LixMn 2 O 4, LixMn 2 -yMyO 4, LiMPO 4, Li ₂ MPO ₄ F (wherein M is selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, V, and B) And at least one element, where x = 0 to 1.2, y = 0 to 0.9, and z = 2.0 to 2.3. Here, x value which shows the molar ratio of lithium increases / decreases by charging / discharging. Further, as the olivine type lithium salts, for example, LiFePO _4, and the like. 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.

In the present invention, the density of the positive electrode mixture constituting the lithium ion secondary battery is 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.
In order to obtain such a positive electrode mixture density, it is preferable that the single-sided coating amount of the positive electrode mixture to the positive electrode current collector is 110 to 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 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 or less. It is more preferable that
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.
Thus, in the positive electrode mixture, in order to set the positive electrode mixture density to 2.5 to 2.8 g / cm ³ , the amount of single-sided application of the positive electrode mixture to the positive electrode current collector and the positive electrode current collector of the positive electrode mixture to By setting the thickness of the single-side coated film in the above range, a high-capacity lithium ion secondary battery having a discharge capacity of 30 Ah or more and less than 99 Ah can be realized.

Further, as the layered lithium / nickel / manganese / cobalt composite oxide (NMC) having a specific particle size described later used in the present invention, it is preferable to use one represented by the following composition formula (1).
Li _{(1 + δ)} Mn _x Ni _y Co _(1-xyz) M _z O ₂ (1)
In the composition 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) is The composition ratio of Co (cobalt) is shown. z represents the composition ratio of the element M. The composition ratio of O (oxygen) is 2.
The element M includes 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.
Thus, by using layered lithium / nickel / manganese / cobalt composite oxide (NMC) as the positive electrode active material (positive electrode active material), it is possible to provide a battery with high capacity and excellent safety. it can.

  Hereinafter, 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, it forms as follows, for example. 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 the layered lithium / nickel / manganese / cobalt composite oxide (NMC) particles, particles having a lump shape, polyhedron shape, spherical shape, elliptical spherical shape, plate shape, needle shape, columnar shape, or the like can be used. .
Among them, it is preferable that the primary particles are aggregated to form secondary particles, and the shape of the secondary particles is spherical or elliptical.
In an electrochemical element such as a battery, the active material in the electrode expands and contracts as it is charged / discharged, so that the active material is easily damaged by the stress or the conductive path is broken. For this reason, it is preferable to use particles in which primary particles are aggregated to form secondary particles, rather than using single particles of only primary particles, because the stress of expansion and contraction can be relieved and the above deterioration can be prevented. In addition, it is preferable to use spherical or oval spherical particles rather than plate-like particles having axial orientation, since the orientation in the electrode is reduced, so that the expansion and contraction of the electrode during charge / discharge is reduced. Further, it is preferable because other materials such as a conductive material are easily mixed uniformly when forming the electrode.

The median diameter d50 of the layered lithium / nickel / manganese / cobalt composite oxide (NMC) particles (when the primary particles are aggregated to form secondary particles, the median diameter d50 of the secondary particles) is 5 to 5 7 μm. Further, the 90% diameter (d90) of the layered lithium / nickel / manganese / cobalt composite oxide (NMC) particles (d90 of the secondary particles when the primary particles are aggregated to form secondary particles) is 8-14 μm.
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 and 90% diameter (d90) can be calculated from the particle size distribution obtained by the laser diffraction / scattering method. A volume cumulative particle size distribution curve measured using a laser diffraction / scattering method with the particle diameter on the horizontal axis and the volume cumulative on the vertical axis. The median diameter (d50) is the cumulative from the small particle size side. The 90% diameter (d90) is the particle diameter at which the accumulation from the small particle diameter side becomes 90%.

The range of the BET specific surface area of the positive electrode active material particles of layered lithium / nickel / manganese / cobalt composite oxide (NMC) is 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 at most 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. Can be mentioned. Of these, one type may be used alone, or two or more types may be used in combination.
Regarding the content (addition amount, ratio, amount) of the conductive material, the range of the content of the conductive material relative to the weight 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. Specific examples include resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluorine Rubbery polymers such as rubber, isoprene rubber, butadiene rubber, ethylene-propylene rubber; styrene / butadiene / styrene block copolymer or hydrogenated product thereof, EPDM (ethylene / propylene / diene terpolymer), styrene / Thermoplastic elastomeric polymers such as ethylene / butadiene / ethylene copolymers, styrene / isoprene / styrene block copolymers or hydrogenated products thereof; syndiotactic-1,2-polybutadiene, polyacetic acid Soft resinous polymers such as Nyl, ethylene / vinyl acetate copolymer, propylene / α-olefin copolymer; polyvinylidene fluoride (PVdF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, polytetrafluoroethylene / ethylene Fluoropolymers such as copolymers 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 relative to the weight 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 more 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 material of the current collector for the positive electrode is not particularly limited, and specific examples 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. Specific examples of the metal material include a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, an expanded metal, a punch metal, and a foam metal, and the carbonaceous material includes a carbon plate, a carbon thin film, A carbon cylinder etc. are mentioned. Among these, it is preferable to use a metal thin film or a metal foil. In addition, you may form a thin film and metal foil in mesh shape suitably. Although the thickness of a thin film and metal foil is arbitrary, 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 In this embodiment, the negative electrode shown below is applicable to a long-life, high-capacity lithium ion secondary battery. The negative electrode (negative electrode plate) of the present embodiment is composed of a current collector and a negative electrode mixture (negative electrode mixture) formed on both sides (or one side) thereof. The negative electrode mixture contains a negative electrode active material that can electrochemically occlude and release lithium ions.
The negative electrode active material preferably contains a carbon material. The carbon material is roughly classified into a graphite material having a uniform crystal structure and a non-graphite material having a disordered crystal structure. In the graphite system, there are natural graphite and artificial graphite, in the non-graphite system there is amorphous carbon, and although the crystal structure is disordered, graphitizable carbon that easily becomes graphite by heating at 2000 to 3000 ° C., There is non-graphitizable carbon that is difficult to become graphite. The amorphous carbon can be produced, for example, by heat-treating petroleum pitch, polyacene, polyparaphenylene, polyfurfuryl alcohol, or polysiloxane. Or graphitizable carbon. For example, a firing temperature of about 500 to 800 ° C. is suitable for producing non-graphitizable carbon, and a firing temperature of about 800 to 1000 ° C. is suitable for producing graphitizable 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.
The graphite preferably has an interplanar spacing d002 value in the C-axis direction obtained by an X-ray wide-angle diffraction method of 0.33 nm or more and less than 0.34 nm, preferably 0.335 nm or more and 0.337 nm or less. More preferred.

20 mass% or more is preferable with respect to the total amount of a negative electrode active material, as for the content rate of a carbon material, 50 mass% or more is more preferable, and 70 mass% or more is still more preferable.
The average particle diameter (d50) of the negative electrode active material is preferably 2.0 to 50 μm. When the average particle size is 5 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, the particles are in good contact, and the input / output characteristics tend to be excellent. . On the other hand, when the average particle diameter is 30 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. In this respect, the average particle size is more preferably 5 to 30 μm, and still more 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 a 50% diameter (d50).

Moreover, as a negative electrode active material, negative electrode active materials other than a carbonaceous material can also be used. Examples of negative electrode active materials other than carbonaceous materials include metal oxides such as tin oxide and silicon oxide, metal composite oxides, lithium alloys such as lithium alone and lithium aluminum alloys, and materials that can be alloyed with lithium such as Sn and Si. Etc. 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. However, a material containing both Ti (titanium), Li (lithium), and Ti and Li has a high current density. This is preferable from the viewpoint of discharge characteristics.
In addition, lithium metal that can occlude and release lithium by forming a compound with lithium, or a group 4 element such as silicon, germanium, and tin that can occlude and release lithium by forming a compound with lithium and inserting it in a crystal gap. Oxides or nitrides may be used in combination with the above graphite or graphitizable carbon.
In addition, as a preferred form, there is a form in which a carbonaceous material that is not symmetric when the volume-based particle size distribution is centered on the median diameter is used as the second carbonaceous material (conductive material). Further, as the second carbonaceous material (conductive material), a form using a carbonaceous material having a different Raman R value from the carbonaceous material used as the negative electrode active material, or as the second carbonaceous material (conductive material), as the negative electrode active material There is a form using a carbonaceous material having a different X-ray parameter from the first carbonaceous material used.
As the second carbonaceous material (conductive material), a highly conductive carbonaceous material such as graphite, amorphous, activated carbon or the like can be used. Specifically, graphite (graphite) such as natural graphite and artificial 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, by adding the second carbonaceous material (conductive material), there are effects such as reducing the resistance of the electrode.

There is no restriction | limiting in particular as a material of the electrical power collector for negative electrodes, As a specific example, 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 and a metal foil are 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.

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. Negative electrode composite lower limit of the density is preferably 0.7 g / cm ³ or more, more preferably 0.8 g / cm ³ or more, more preferably 0.9 g / cm ³ or more, the upper limit is 2 g / cm ³ or less , preferably 1.9 g / cm ³ or less, more preferably 1.8 g / cm ³ or less, further 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. Specifically, resin-based 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-like polymers such as ethylene-propylene rubber; styrene / butadiene / styrene block copolymer or hydrogenated product thereof; EPDM (ethylene / propylene / diene terpolymer), styrene / ethylene / Thermoplastic elastomeric polymers such as butadiene / styrene copolymer, styrene / isoprene / styrene block copolymer or hydrogenated products thereof; syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene Soft resinous polymers such as vinyl acetate copolymer and propylene / α-olefin copolymer; Fluorine-based polymers such as polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene / ethylene copolymer Polymers: Polymer compositions having ionic conductivity of alkali metal ions (particularly lithium ions), and the like. 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, etc., and examples of the organic solvent include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, Methyl acrylate, diethyltriamine, N, N-dimethylaminopropylamine, tetrahydrofuran (THF), toluene, acetone, diethyl ether, dimethylacetamide, hexamethylphosphalamide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, Examples include methylnaphthalene and hexane. 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.

  The content of the binder is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and still more preferably 0.6% by mass or more with respect to the total amount of the negative electrode composite material. The upper limit of the binder content 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 binder content with respect to the weight 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.

  In addition, the range of the binder content relative to the weight 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 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 thickener relative to the weight 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, there exists a possibility that the applicability | paintability of a slurry may fall. On the other hand, when the above upper limit is exceeded, the ratio of the negative electrode active material to the negative electrode mixture decreases, and there is a risk that the battery capacity decreases and the resistance between the negative electrode active materials increases.

3. Electrolytic Solution 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 of a non-aqueous electrolyte solution for a lithium ion secondary battery. For example, the following inorganic lithium salt, fluorine-containing organic lithium salt, or oxalate borate Salt.
Examples of the inorganic lithium _{salt, LiPF 6, LiBF 4, LiAsF} 6, LiSbF inorganic fluoride salts and the like _6, LiClO _4, Libro 4, LiIO and perhalogenate such as _4, an inorganic chloride salts such as LiAlCl _4, etc. 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 salts such as ₄ F ₉ SO ₂ ); perfluoroalkanesulfonylmethide salts 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] fluoroalkyl hexafluorophosphate salts such like.
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 nonaqueous 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. For example, the following cyclic carbonate, chain carbonate, chain ester, cyclic ether, and chain And ethers.
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, butylene carbonate, and the like. 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. Specifically, symmetrical chain carbonates such as dimethyl carbonate, diethyl carbonate, and di-n-propyl carbonate; asymmetric chain carbonates such as ethyl methyl carbonate, methyl-n-propyl carbonate, and ethyl-n-propyl carbonate Is mentioned. 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 such as 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, Examples thereof include fluorine-containing cyclic carbonate and 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.
Although there is no limitation in particular in the ratio of the additive in a non-aqueous electrolyte solution, the range is as follows. In addition, when using a some additive, the ratio of each additive is meant. The lower limit of the ratio of the additive to the non-aqueous electrolyte is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.2% by mass or more, and the upper limit is preferably 5%. It is not more than mass%, more preferably not more than 3 mass%, still more preferably not more than 2 mass%.
By using the other additives, it is possible to 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 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, an olefin polymer, a fluorine polymer, a cellulose polymer, polyimide, nylon, or the like is used. Specifically, it is preferable to select from materials that are stable with respect to non-aqueous electrolytes and have excellent liquid retention properties, and porous sheets or nonwoven fabrics made from polyolefin polymers such as polyethylene and polypropylene are used. It is preferable.
As the inorganic material, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate are used. For example, what made the said inorganic substance of fiber shape or particle shape adhere to thin film-shaped base materials, such as a nonwoven fabric, a woven fabric, and a microporous film, can be used as a separator. As a thin film-shaped substrate, a substrate having a pore diameter of 0.01 to 1 μm and a thickness of 5 to 50 μm is preferably used. In addition, for example, a separator in which a composite porous layer is formed using the above-described inorganic material in a fiber shape or a particle shape by using a binder such as a resin can be used as a separator. Furthermore, this composite porous layer may be formed on the surface of the positive electrode or the negative electrode to form a separator. For example, a composite porous layer in which alumina particles having a 90% 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 constituent members As other constituent members of the lithium ion secondary battery, a cleavage valve may be provided. 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 polycyclohexane. Examples include heptene 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, the capacity ratio of the negative electrode to the positive electrode (negative electrode capacity / positive electrode capacity) is preferably 1 or more and less than 1.5 from the viewpoint of safety and energy density, more preferably 1.05 to 1.3. 1.1 to 1.2 are more preferable. If it exceeds 1.3, the positive electrode potential may be higher than 4.2 V during charging, and safety may be reduced (the positive electrode potential at this time refers to the Li potential).
Here, the negative electrode capacity indicates [negative electrode discharge capacity], and the positive electrode capacity indicates [positive electrode initial charge capacity-negative electrode or positive electrode, whichever is greater, irreversible capacity]. 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 the lithium ion secondary battery / discharge capacity of the negative electrode”. The discharge capacity of the lithium ion secondary battery is, for example, 4.2 V, 0.1 to 0.5 C, and after performing constant current constant voltage (CCCV) charging 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.
For the discharge capacity of the negative electrode, the negative electrode whose discharge capacity was measured for the lithium ion secondary battery was cut into a predetermined area, lithium metal was used as the counter electrode, and a single electrode cell was prepared via a separator impregnated with an electrolyte. , 0V, 0.1C, constant current constant voltage (CCCV) charge at a final current of 0.01C, then discharge per predetermined area under the condition of constant current (CC) discharge 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 secondary 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 (NMC) having a median diameter of d50 = 6 μm and d90 = 11 μm as the positive electrode active material, acetylene black as the conductive material, and polyvinylidene fluoride as the binder By adding and mixing, a mixture of positive electrode materials was obtained. The weight ratio was positive electrode 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 120 g / m ² .

[Production of negative electrode plate]
The negative electrode plate was produced as follows. Graphite carbon (d002 = 0.35 nm, average particle size (d50) = 10 μm) as negative electrode active material, SOC (State Of Charge, charging rate) at a potential of 0.1 V with respect to lithium potential is 70%. Polyvinylidene fluoride was added as a binder to the negative electrode active material, and the weight ratio thereof was negative electrode active material: binder = 92: 8, and N-methyl-2-2, which is a dispersion solvent, was added thereto. Pyrrolidone (NMP) was added and kneaded to form a slurry, which was applied in a predetermined amount substantially uniformly and uniformly to both surfaces of a rolled copper foil having a thickness of 10 μm, which is a current collector for a negative electrode. The negative electrode mixture density was 1.15 g / cm ³ .

[Production of lithium ion secondary 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 64 ± 0.5 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 an 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 1.27 to 1.77 MPa (13 to 18 kgf / cm ² ).
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 686 N · cm (70 kgf · cm). 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.

<Examples 1-4>
In each of the examples, batteries were prepared with the median diameter of the layered lithium / nickel / manganese / cobalt composite oxide (NMC) and the density of the positive electrode mixture shown in Table 1 as Examples 1 to 4.

<Comparative Examples 1-2>
In the said Example, the battery was produced as the median diameter of the layered type lithium-nickel-manganese-cobalt composite oxide (NMC) and the positive electrode mixture density shown in Table 1, respectively, and Comparative Examples 1 and 2 were obtained.

[Evaluation of battery characteristics (initial discharge capacity, life test)]
(Initial discharge capacity)
In an environment of 25 ° C., the current value was 25 A for both charging and discharging. Charging was constant current and constant voltage charging with 4.2 V as the upper limit voltage, and the termination condition was 3 hours. The discharge was a constant current discharge, and 2.7 V was set as a termination condition. Further, a pause of 30 minutes was put between charge and discharge. This was carried out for three cycles, and the discharge capacity at the third cycle was defined as “initial discharge capacity (Ah)”.

(Life test)
In the life test, after measuring the discharge capacity at the third cycle, the battery was charged at a constant current and constant voltage with an upper limit voltage of 4.2 V at a current value of 50 A, and the termination condition was 3 hours. The battery was discharged at a constant current of 50 A with 2.7 V as the end condition, and rested for 30 minutes. This charging / discharging was made into 1 cycle, and 1000 cycles of charging / discharging was implemented. After 1000 cycles, charge at a constant current constant voltage with a current value of 25A and 4.2V as the upper limit voltage, and a termination condition of 3 hours. After a 30-minute pause, stop at 2.7V with a constant current of 25A Discharge as a condition, pause for 30 minutes, and calculate the discharge capacity at this time as “post-cycle discharge capacity (Ah)” and the post-cycle discharge capacity relative to the initial discharge capacity as “cycle capacity maintenance rate (%)” did.
Cycle capacity retention rate (%) = [discharge capacity after cycle (Ah) / initial discharge capacity (Ah)] × 100
The results of the above examples and comparative examples are shown in Table 1 below.

Examples 1 to 5 and Comparative Examples 1 and 2 using the positive electrode mixture of the same material, but the median diameter (d50) of the lithium / nickel / manganese / cobalt composite oxide used as the positive electrode active material is 5 to 7 μm In Comparative Examples 1 and 2 in which the 90% diameter (d90) deviates from 8 to 14 μm, the initial discharge capacity is 1 to 2% lower than the Examples using particles in the above range, and it is clear in the cycle capacity maintenance rate. The difference is seen, and the maintenance rate after the 1000 cycle test at 50 A charge / discharge is lower than that of the example. On the other hand, the density of the positive electrode mixture is in the range of 2.5 to 2.8 g / cm ³ , the median diameter (d50) of the lithium / nickel / manganese / cobalt composite oxide is 5 to 7 μm, and the diameter is 90%. Examples 1 to 5 in which (d90) is in the range of 8 to 14 μm can provide a long-life lithium ion secondary battery having a high initial discharge capacity and a high cycle capacity maintenance rate.

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 鍔 part 8 Insulation coating 9 Lead piece 10 Cleavage valve 11 Metal washer 12 O ring 13 Injection port 20 Cylindrical lithium ion secondary battery

Claims (1)

An electrode winding group in which a positive electrode, a negative electrode, and a separator are wound, and an electrolyte solution are provided in a battery container, and the discharge capacity is a lithium ion secondary battery having a discharge capacity of 30 Ah or more and less than 99 Ah,
The positive electrode has a current collector and a positive electrode mixture applied on both sides of the current collector, the positive electrode mixture includes a lithium-nickel-manganese-cobalt composite oxide as a positive electrode active material, The median diameter (d50) of the lithium / nickel / manganese / cobalt composite oxide is 5 to 7 μm and the 90% diameter (d90) is 8 to 14 μm, and the density of the positive electrode mixture is 2.5 to 2.8 g / lithium ion secondary battery is cm ^3.

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