JP2001351627A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery that prevents a rapid temperature rise by obstructing a rapid reaction of oxygen gas generated from oxidization dissolution of the positive electrode active material with the compounds inside lithium and graphite layer at over-charging. SOLUTION: In the lithium ion secondary battery in which the electrode body having a positive electrode 1 and a negative electrode 2 piled over each other through a separator 3 is arranged in the battery case 4 together with electrolyte, the graphite material of the negative electrode is composed of hexagonal system and rhombohedral system. The size Lc of the crystal cell in the direction of 'c' axis as calculated in the diffraction line (112) is 200 (Å) to 400 (Å) and the average particle size is 20 (μm) to 30 (μm), and the existence ratio of the above rhombohedral system as specified in the formula r(101)×12/15}/ r(101)×15/12+h(101)} is made to be in the range 15% and more and 25% or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium ion secondary battery, and more particularly to an improvement in a graphite material used as a negative electrode mixture.

[0002]

_2. Description of the Related Art A lithium-containing composite metal oxide represented by lithium cobalt oxide represented by the general formula LiCoO ₂ is used as a positive electrode active material, and a carbon material and a lithium salt capable of occluding and releasing lithium are used as a negative electrode material. Lithium ion secondary batteries using a non-aqueous electrolyte solution containing hydrogen are attracting attention because of their high electromotive force, little capacity degradation during charge / discharge cycles, and excellent durability. This is because a material capable of inserting and extracting lithium reversibly is used for the positive electrode and the negative electrode, and utilizes the fact that a complex compound with lithium is reversibly formed in the charging and discharging process.

For example, when a battery is formed together with a non-aqueous electrolyte by facing a negative electrode using a carbon material and a positive electrode using lithium cobalt oxide via a separator, the battery is required to be assembled in a discharged state. become. For this reason, this type of battery cannot be discharged unless it is charged after assembly. When the battery is charged in the first cycle, lithium contained in the lithium cobalt oxide is released, the positive electrode potential shifts to a noble direction, and is doped between layers of the negative electrode carbon material. When the discharge is performed, the lithium doped in the carbon material is undoped, and is occluded again in the lithium cobalt oxide of the positive electrode, and the positive electrode potential shifts to a lower direction.

[0004] The charging upper limit voltage of this type of battery is from 4.1 V to
When set to about 4.2 V, the positive electrode potential does not usually reach a noble potential of 4.3 V or more with respect to the lithium potential, and the negative electrode potential does not reach a lower level than the lithium metal potential. The weight ratio of the positive electrode material and the negative electrode material filled in the battery is arbitrarily determined. However, when charging a battery, a large current may flow temporarily to the battery due to a sudden failure of the charger, or the power-on state may continue even if the battery reaches the charge end voltage. When the battery is exposed to such an overcharged state, gas is generated in the battery, causing a problem that the internal pressure increases and the battery ruptures.

In a secondary battery such as a nickel-cadmium battery or a nickel-hydrogen battery, when gas is generated inside the battery as described above, the gas can be absorbed by the electrode.
Burst can be prevented beforehand. However, in this type of lithium secondary battery, since the generated gas is not absorbed by the electrode, a safety valve that operates by increasing the internal pressure of the battery, that is, an explosion-proof valve is provided, and when the internal pressure exceeds a predetermined value, The above gas is discharged to prevent explosion.

For example, JP-A-2-112151 and JP-A-2-288063 propose an explosion-proof lithium-ion secondary battery in which current is cut off as the internal pressure of the battery increases. This explosion-proof lithium-ion secondary battery is
The explosion-proof valve, which deforms in the direction of internal pressure as the internal pressure rises, is installed by contacting the stopper for reed shut-off. To cut off the current and prevent the explosion.

[0007]

However, even in the above-mentioned conventional lithium ion secondary battery, there is a type in which the temperature rises rapidly when the battery is overcharged. The present inventors have investigated this cause in detail, and found that rapid heat generation occurs before the internal pressure of the battery rises so much, and that the temperature may rise rapidly before the current interruption mechanism functions effectively. There was found. One of the main causes of this phenomenon is that when the lithium cobalt oxide, which is the positive electrode active material, is overcharged, it releases oxygen gas before all the lithium is released, and rapidly decomposes. It has been found that the generated oxygen gas reacts rapidly with the lithium-graphite intercalation compound of the negative electrode to generate heat with a rapid temperature rise.

The present invention is intended to improve the safety of a battery that has fallen into such an overcharged state, and an object of the present invention is to provide an oxygen gas, which is generated by oxidative decomposition of a positive electrode active material during overcharge, and a lithium battery. It is an object of the present invention to provide a lithium ion secondary battery that can inhibit a rapid reaction with a graphite intercalation compound and thereby prevent a rapid temperature rise.

[0009]

In order to achieve the above object, in the lithium ion secondary battery of the present invention, a lithium-containing composite metal oxide capable of reversibly inserting and extracting lithium is used as a positive electrode active material. A positive electrode part in which a positive electrode mixture containing the same is formed into a sheet shape on a metal foil, and a negative electrode part in which a negative electrode mixture mainly containing a graphite material capable of absorbing and releasing lithium is formed into a sheet shape on a metal foil. And a non-aqueous electrolyte containing a lithium salt in a closed container, wherein the graphite material is hexagonal and rhombohedral. When measured by the X-ray wide-angle diffraction method,
(112) The crystallite size Lc (112) in the c-axis direction calculated from the diffraction line is from 200 (Å) to 400 (Å),
In addition, the average particle diameter is 20 (μm) to 30 (μm), the peak area of the (101) diffraction line belonging to the rhombohedral crystal is defined as r (101), and the peak area is attributed to the hexagonal crystal. (101) The peak area of the diffraction line is h (101)
｛R (101) × 12/15｝ / ｛r (10
1) The existence ratio of the rhombohedral crystal system defined by the formula of × 15/12 + h (101)} is in the range of 15% or more and 25% or less.

[0010] In graphite, in addition to crystals belonging to hexagonal system (ABAB ... lamination period), rhombohedral system (ABCABC.
・ ・ Lamination cycle). FIG. 1 shows a unit cell of hexagonal graphite, and FIG. 2 shows a unit cell of rhombohedral graphite. As shown in FIG. 1, the hexagonal graphite has a stack of carbon hexagonal mesh planes.
(3/3) and the third layer just overlaps the first layer. That is, ABAB repeated every two layers
・ It has a structure. On the other hand, in rhombohedral graphite, the second layer is shifted by (2/3, 1/3) with respect to the first layer as shown in FIG.
The third layer is further shifted by (1/3, 2/3) and the fourth layer overlaps the first layer.

The rhombohedral graphite is a plane direction (a-axis) and a vertical lamination (c-axis) of crystallites such as artificial graphite in which crystals are highly developed or natural graphite having a very high degree of graphitization.
This is a form of crystals introduced into a part of a hexagonal graphite material having an extremely small lattice strain in the direction by grinding. Very weak bonds between the graphite layers at the initial stage of grinding,
Alternatively, a very small value of the elastic constant (C44 = 4.5G)
Reflecting Pa), it is considered that shear deformation mainly occurs along the layer surface, and a rhombohedral structure appears. The stacking fault energy for generating the rhombohedral structure calculated using the anisotropic elasticity theory is 5.1 to 5.8 × 10E (−
2) Since it is as small as J / m ² , a large number of strong carbon-carbon bonds in the layer surface are not broken to introduce a large amount of defects, and the rhombohedral structure is used as a part of storing mechanical energy given by grinding. Is understood to be introduced. However, if the grinding is continued further, it becomes impossible to store the mechanical energy given by the grinding, and a large amount of defects are introduced into the graphite layer surface, which may lead to the destruction of the layer surface simultaneously with the introduction of rhombohedral crystals. . As described above, the rhombohedral structure is a form caused by stacking faults of a hexagonal structure,
It is qualitatively understood that the structure itself is destroyed when its abundance ratio increases.

The existence ratio of the rhombohedral structure and the hexagonal structure can be verified by examining the intensity ratio of diffraction peaks obtained by the X-ray wide-angle diffraction method. When measuring with a Geiger-flex type powder X-ray wide-angle diffractometer using copper for the tube, the diffraction angle (2θ / θ) may be scanned in the vicinity of 40 to 50 ° (hereinafter the state of the diffraction operation is expressed). In this case, and when simply expressed as a diffraction angle, it is assumed that the expression refers to a case where measurement is performed using a Geiger flex type powder X-ray wide-angle diffractometer using copper as a tube). Here, the proportion of the rhombohedral graphite within the range of the present invention is specified to be 15 to 25%. However, since this value slightly changes depending on the measurement conditions, it is particularly measured by the following method. It is limited to the value calculated in the case where it is performed.

First, a graphite sample is filled in a measuring cell, and a wide angle X-ray diffraction curve is measured by a reflection type diffractometer method using a CuKα ray monochromatized by a graphite monochromator as a radiation source. The applied voltage and current to the X-ray tube are 4
0 kV and 40 mA, the divergence slit was set to 1 °, the scattering slit was set to 1 °, and the light receiving slit was set to 0.15 mm.
Scanning is performed at a speed of 0.25 ° per minute from 2θ of 41 ° to 48 °.

FIG. 3 shows a diffraction pattern of a commercially available natural graphite having an average particle size of 100 (μm), which was measured by the above-mentioned operation, and which was pulverized in an agate mortar. In particular, in the case of a sample obtained by pulverizing graphite having high crystallinity, usually four diffraction lines can be observed in this spectral band. Each diffraction line has a hexagonal (100) plane and a (101) plane near 42.3 ° and 44.4 °, and a rhombohedral (100) plane near 43.3 ° and 46.0 °. 101) plane and (01)
2) A surface appears. The surface index of the rhombohedral system is expressed by indexing when a unit lattice similar to that of the hexagonal system is taken as shown in FIG. 2, and in the present invention, the surface index is assigned according to this unit lattice. I will do it.

The graphite powder used as the negative electrode part of the present invention has a rhombohedral content of 15% or more and 25% or less, and has a rhombohedral structure as shown in the following formula 1. This is a value obtained by the ratio of the characteristic area of the (101) diffraction line to the total area of the diffraction lines of the hexagonal (101) plane.
01) The area of the diffraction line is multiplied by the correction coefficient 15/12. Since this ratio relates to the same element, it may be expressed by an atomic ratio, a molar ratio, or a mass ratio.

(Equation 1) {r (101) × 12/15} / Δr (101) × 15
/ 12 + h (101)} where r (101) is the peak area of the (101) diffraction line belonging to the rhombohedral crystal measured by the X-ray wide-angle diffraction method, and h (101) is measured in the same manner. The peak area of the (101) diffraction line attributed to the hexagonal crystal is shown.

If the crystallinity of the raw graphite powder to be pulverized is low, the peak attributed to the rhombohedral system cannot be confirmed even if the degree of pulverization is increased.
This is presumably because rhombohedral graphite is a form caused by stacking faults, as described above, and graphite with low crystallinity originally did not sufficiently develop a stacked structure. The crystallinity is low when Lc (112) is 100 ° or less, and when it is more than 100 ° C., the average particle diameter is 20 ° or less.
(Μm) to 30 (μm), and when the Lc (112) after pulverization is from 200 (Å) to 400 (Å), 25% or more of rhombohedral is usually introduced. is there.

However, the graphite material according to the present invention has an Lc (112) after pulverization of 200 (Å) to 400.
(Å), characterized in that the average particle size is from 20 (μm) to 30 (μm), and the ratio of the rhombohedral system is 15% or more and 25% or less. Therefore, it can be said that it is a graphite material into which rhombohedral crystals are hardly introduced despite high crystallinity. In general, the graphite material develops a crystal with the heat treatment temperature, and its lattice strain decreases.However, the graphite material according to the present invention still has a lattice strain even when the crystal develops, so that the crystallite is large despite the crystallite being large. The reason is that the hexagonal mesh plane has low symmetry, and it is difficult for shear deformation to occur along the layer plane, so that it is difficult to introduce rhombohedral crystals. Hereinafter, a specific method for obtaining graphite powder containing rhombohedral crystals in such a proportion will be described.

The graphite material according to the present invention is obtained by pulverizing a raw material A and a raw material B described below so that each has an average particle diameter of 10 (μm) or less, and a weight ratio of about 80:20 to 99: 1. More preferably, it is obtained by mixing at a weight ratio of about 95: 5 to 99: 1 and then graphitizing at a high temperature of 2800 ° C. or more in an inert atmosphere. The reason that the mixing ratio is limited as described above is that when the mixing ratio of the raw material A is higher than 99%, the lattice strain introduced into the crystal after graphitization is small, and the average particle diameter is 20 (μm) to 30%. (Lm) is from 200 (Å) to 400 (Å) after pulverization to have a rhombohedral crystal content of 25%.
This is not preferable because of the above. Conversely, when the mixing ratio of the raw material A is 80% or less, the amount of introduced lattice strain is too large, and the Lc (112) after graphitization and pulverization is unlikely to be 200 ° or more, and the reversibility of the graphite material itself is reduced. In addition to a reduction in the capacity capable of occluding and releasing lithium, a battery to which the graphite material is applied is also not preferable because load characteristics also deteriorate.

Here, the raw material A is 500 ° C. in an inert atmosphere.
When the fired body obtained by heat-treating to １1700 ° C. is observed under a deflection microscope, a mosaic constituent unit has a fibrous shape of several tens μm or more, and gives a flow structure having an anisotropic region over a wide range. When the fired body obtained in the same manner is observed under a deflection microscope, the fine structure is a so-called “granular mosaic structure”, and the raw material B has a mosaic constituent unit of several μm to a dozen or more. μm
Organic compounds that give a degree. The organic compounds usable as the raw materials A and B are as follows.

(1) Coal coke The formation of coke structure is largely determined during the softening process. In coal that softens and melts well, the molecular orientation tends to advance,
A directional structure (anisotropic structure) is generated. Conversely, coal that is difficult to soften and melt has a random molecular isotropic structure. Specifically, a mosaic constituent unit of a structure (reactive-derived structure) formed by melting and deforming during carbonization of the coal structure components is a fine mosaic shape or a medium coarse mosaic shape of about several μm to 10 μm, Coke structure intact (inert-derived structure) that is not softened and melted during carbonization and exists in the coal without anisotropy, for example, high volatile low flow coal, high volatile high flow coal, It is desirable that medium volatile volatile fluid carbon or the like is used as the raw material B.
Conversely, there are several tens of mosaic constituent units of reactive origin tissue
(Μm) or more leaf-shaped, high-volatile low-flow coal, high-volatile high-flow coal, medium-volatile high-flow coal that gives a flow structure with an anisotropic region over a wide range And the like are desirably used as the raw material A. On the other hand, if too much inert-derived tissue component not having anisotropy is contained, the degree of crystallinity is low even if graphitization is performed, and Lc (112) does not become 200 (Å) or more. It is not preferable because it may occur.

(2) quinoline-insoluble matter (QI component), quinoline-soluble
Relatively high softening point containing a lot of benzene-insoluble matter (BI / QS component = β resin), specifically, petroleum pitch having an H / C atomic ratio of about 0.6 or less and a softening point of about 90 ° C. or more Is preferred. Contains a large amount of benzene-soluble / carbon tetrachloride-insoluble, carbon tetrachloride-soluble / heptane-insoluble, and QI, BI.
Low content of QS component, relatively low softening point,
That is, a feedstock oil containing an early caulking component and having a relatively high viscosity can be used as the feedstock B. A fired body obtained by heat-treating this type of raw oil at 500 ° C. to 1700 ° C. in an inert atmosphere has many granular mosaic structures, a complicated fine structure, and characteristics close to optical isotropy. I have. A modified pitch in which a process such as air blowing is performed on the pitch and a functional group containing oxygen is introduced (so-called oxygen cross-linking) can also be used as the raw material B. Here, the functional group containing oxygen refers to an atom or an atomic group composed of oxygen chemically bonded to a base material such as pitch. For example, quinone group, ether bond, lactone bond, hydroxyl group,
There are ester bonds and carboxyl groups.

Such an operation is achieved by an insoluble / infusible treatment. The specific means of the insoluble / infusible treatment is not limited to the following methods, for example, nitric acid, mixed acid, sulfuric acid, wet method with an aqueous solution of hypochlorous acid, etc.
Alternatively, a dry method using an oxidizing gas (air or oxygen), and a reaction using a solid reagent such as sulfur, ammonium nitrate, and ferric chloride are used. The carbonized petroleum pitch modified by the insoluble / infusible treatment has many fine mosaic structures, has a complicated fine structure, and has characteristics close to optical isotropy. However, if the amount of oxygen introduced into the petroleum pitch is too large, Lc (112)
Is not preferably 200 (Å) or more. Further, since the structure cannot be modified even if the amount of oxygen introduced is too small, the amount of oxygen introduced by the insoluble / infusible treatment is 0.5% by weight to 1.0% by weight.
A degree is desirable.

On the other hand, asphaltene and resin components that cause early coking from the raw material oil, and impurities (sulfur, oxygen, nitrogen, metals, catalysts, free carbon), etc., are harmful when arranging crystallites. Remove such components,
Alternatively, the viscosity is relatively low even in the raw material oil or pitch obtained by reducing the amount, and quinoline-insoluble matter (QI component), quinoline-soluble / benzene-insoluble matter (BI ·
(QS component = β resin), etc., and contains a large amount of benzene-soluble / carbon tetrachloride-insoluble matter, carbon tetrachloride-soluble / heptane-insoluble matter, and has a relatively low softening point. Can be used as A fired body obtained by heat-treating such a pitch to 500 ° C. to 1700 ° C. in an inert atmosphere has optical anisotropy when observed under a deflection microscope, and its structure is mainly composed of a flow pattern. It has become.

(3) Condensable polycyclic polynuclear aromatics The condensable polycyclic polynuclear aromatics refer to macromolecules of polycondensates of condensed polycyclic aromatic hydrocarbons. For example, pyrene, perylene,
An organic compound such as isoviolanthrone (also referred to as a main agent) and an organic compound such as benzaldehyde and 9,10-dihydroanthracene (also referred to as a cross-linking material) are converted into paratoluenesulfonane, maleic anhydride, and the like. Heating and mixing at about 100 ° C to 200 ° C under the organic acid catalyst of
It is obtained by subjecting the obtained polymer to a neutralization treatment as necessary, and removing the residual solution by means such as suction filtration. The texture of the carbon material obtained by carbonizing such a condensable polycyclic polynuclear aromatic, which is observed under a polarizing microscope, depends on the selection of the base material and the binder. Also in this case, the texture is a granular mosaic structure, and the mosaic constituent unit is several μm.
If a combination of a base material and a binder that gives about 10 to several tens of μm is selected, it can be used as a raw material B. The raw material A can be used by selecting a combination of a base material and a binder that gives a fired body having a flow structure having the following. Examples of the main agent for providing the raw material B include naphthalene, phenanthrene, and perylene, and examples of the main agent for providing the raw material A include anthracene, pyrene, and isobiolanthrone.

(4) Organic high molecular compound starting from a specific organic compound The organic high molecular compound obtained by heat-treating a 2- to 4-ring aromatic hydrocarbon or a derivative thereof under pressure with an inert gas is also used as raw material A. Or it can be used as B. Examples of the 2- to 4-ring aromatic hydrocarbon or a derivative thereof include naphthalene, phenanthrene, chrysene, anthracene, benzanthrene, triphenylene, pixelne, acenaphthylene, pyrene and the like. Among them, the organic polymer compound using naphthalene or phenanthrene as a raw material is particularly preferable as the raw material B because the texture is a granular mosaic structure and the mosaic constituent unit is about several μm to about several tens μm. On the other hand, since the texture of an organic polymer compound using anthracene, acenaphthylene or pyrene as a raw material is a fibrous structure having mosaic constituent units of several tens of μm or more and exhibits a flow structure having an anisotropic region over a wide range, the raw material A Can be used as

The raw material A and the raw material B as described above are pulverized so that each has an average particle diameter of 10 (μm) or less, mixed in a weight ratio of about 99: 1 to 95: 5, and then mixed with an inert atmosphere. The graphite material according to the present invention can be obtained by graphitization at a high temperature of 2800 ° C. or higher and further pulverization. For grinding graphite materials, ball mills,
A jet mill and a colloidal mill are mainly used. Ball mill pulverization means that a predetermined amount of raw graphite powder and a pulverizing medium preliminarily pulverized to an average particle size of about 100 (μm) are put into a pot mill, and the pot is covered. The gas is sealed, the valve of the sealing line is closed, the pot is closed, and the pot is rotated at a predetermined rotation speed for a desired time to perform pulverization. In this case, generally, balls made of metal or ceramics are used as a grinding medium, and an inert gas such as nitrogen or argon gas, helium gas, carbon dioxide or the like is used as an atmospheric gas. Jet mill pulverization means that powder is continuously supplied to an ultrasonic nozzle, and at the same time as the graphite particles collide with each other due to the disturbance of the pressurized air flow in the nozzle, a solid-gas mixture flow is applied to the collision plate installed in front of the nozzle. Are forcibly collided to perform pulverization. Colloidal milling is a method based on the millstone principle.
This is a method of adjusting the distance between dies made of metal or ceramics and grinding them by rotating them in opposite directions.

In order to obtain graphite powder within the scope of the present invention even among the above-mentioned pulverization methods, jet mill pulverization is particularly preferable. This is because although there is a difference depending on the pulverization method and the pulverization time, the crystallites of the graphite particles are usually reduced and the crystallinity is reduced by the pulverization operation. This is because the degree of reduction in crystallinity is remarkably small as compared with the case of the pulverization method. This is considered to be because the force acting perpendicular to the carbon layer surface in jet mill pulverization is stronger than in other pulverizers. However, even when pulverized by a jet mill, care must be taken because the reduction in crystallinity due to pulverization is strongly affected by atmospheric gas. For example, if oxygen or moisture is present in the atmosphere, the particles are liable to be cleaved by cleavage, and the particles are crushed into flakes and the crystallites are apt to be reduced, but helium, nitrogen,
This is because, in a vacuum, the particles are three-dimensionally and pulverized into ultrafine powder, the crystallites are three-dimensional, and the crystallinity is not significantly changed as compared to before the pulverization. Therefore, it is preferable to reduce the amount of moisture or oxygen mixed in the pulverizing atmosphere as much as possible. This phenomenon is explained by the difference in the coefficient of friction of the graphite particles when pulverized.

In the graphite material according to the present invention, the content ratio of the rhombohedral after the above-mentioned pulverization treatment is limited to 15 to 25%. If it is 15% or less, the average particle diameter of the graphite material may be large, or the crystallinity of the original graphite material may be low, and it may be difficult to introduce rhombohedral particles even when pulverized. When the average particle diameter is large, the safety of the battery exposed to the overcharged state is improved, but the load characteristics are remarkably reduced, which is not preferable. If the crystallinity is low, the lithium
It is not preferable because the reversible capacity that can be released is low and the battery capacity decreases. On the other hand, if it is 25% or more, the average particle diameter of the graphite material may be small, or the graphite material having extremely small lattice distortion inside the crystal may be crushed. In any case, it is not preferable because the safety of the battery exposed to the overcharged state is reduced.

The graphite material according to the present invention has an Lc (112) of 200 to 50 after the above-mentioned pulverization.
0 (Å). The reason for this is that the higher the crystallinity, the greater the lithium storage / release capacity of the graphite material, and a capacity closer to the theoretical value can be obtained. Lc
When (112) is 200 (以下) or less, Lc (112)
(Reduced crystallinity) decreases the chargeable / dischargeable capacity, which is not preferable. Lc (112) is 500
As far as the present inventors have performed, graphite materials exceeding (等)
Lc (112) is limited to 200 to 500 (Å) because it could not be obtained by the manufacturing method described in the present invention.

Lc (112) is the Japan Society for the Promotion of Science 11
7 Committee established method (literature name: Japan Society for the Promotion of Science No. 11
7 committee, carbon, 25, (No. 36), 1963). First, about 10% by weight of X
High-purity silicon powder for X-ray standard was added as an internal standard substance, mixed, filled in a sample cell, and a wide angle X-ray diffraction curve was measured by a reflection type diffractometer method using a CuKα ray monochromatized with a graphite monochromator as a source. . X
The voltage and current applied to the tube were set to 40 kV and 40 mA, the divergence slit was set to 2 °, the scattering slit was set to 2 °, and the light receiving slit was set to 0.3 mm. Scanning was performed at a speed of 25 °. According to document (1), the obtained diffraction pattern shows the diffraction angle and half width of the (112) diffraction line of the graphite material whose 2θ appears around 83.6 °, and the 2θ appears around 88.1 °. Correction was performed using the (422) diffraction line of the silicon powder, and the crystallite size Lc (112) in the c-axis direction was calculated.

Further, the graphite material according to the present invention is limited to an average particle diameter of 20 to 30 (μm) after the above pulverization.
When the average particle diameter is 20 (μm) or less, Lc (11
Even if the percentage of the rhombohedral system contained in 2) and the graphite material is within the scope of the present invention, it is not preferable because the safety of the battery in the event of an overcharged state is significantly reduced.
If the average particle size is small, the surface area increases, the reaction area with oxygen gas generated from the positive electrode during overcharge increases, and heat is generated with a rapid temperature rise. This is because the reaction cannot be effectively stopped. When the average particle diameter is 30 (μm) or more, the safety of the battery exposed to the overcharged state is improved, but the load characteristics are remarkably reduced, which is not preferable. It is considered that when the particle diameter is large, the contact area with the electrolyte decreases, and it becomes difficult for lithium occluded in the graphite material to diffuse into the electrolyte during discharge.

A slurry prepared by dispersing the graphite powder obtained as described above in a solvent together with a binder is subjected to various treatments, coated and dried on a copper foil, and the resulting laminate is bound on the copper foil. A sheet electrode of the negative electrode of the lithium ion secondary battery to which the present invention is applied is obtained by preparing the sheet electrode thus formed and compressing and molding the sheet electrode.

On the other hand, for the positive electrode portion, the method used for this type of cylindrical and prismatic batteries can be applied as it is. Here, as the positive electrode material, a Li-containing composite oxide represented by LiCoO ₂ is mainly used, but since the conductivity of the oxide itself is very small, it is represented by graphites and acetylene black as a conductive agent. Usually, such carbon blacks are used in combination as a conductive aid. That is, the positive electrode portion is configured as a positive electrode mixture in which a conductive material and a conductive auxiliary are further added to the Li-containing composite oxide and the binder. For example, the positive electrode used in this type of cylindrical and prismatic batteries is prepared by mixing a positive electrode active material powder and a conductive agent, dispersing the slurry together with a binder in a solvent, performing various treatments, applying the slurry to an aluminum foil, and drying. A sheet electrode obtained by binding the laminated body produced as described above to an aluminum foil, and then compression and molding is used. In addition, the positive electrode active material,
As the binder, any material commonly used in this type of lithium ion secondary battery can be used. For example, it is particularly preferable to use a material containing a sufficient amount of lithium as the positive electrode active material from the viewpoint of achieving a high capacity of the battery. For example, LiMn ₂ O ₄ or the general formula LiMO
₂ (where M represents at least one of Co and Ni. Therefore, for example, LiCoO ₂ or LiCo _0.8 Ni _0.2
Intercalation compound containing composite metal oxide and lithium represented by O ₂ or the like) is preferable. Further, as the binder, fluorine-based resins such as polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride, etc., carboxymethyl cellulose, polyacrylic acid are used because they do not dissolve in the electrolytic solution and have excellent solvent resistance. Organic polymer compounds such as soda are suitable.

The positive electrode portion and the negative electrode portion configured as described above are placed in a closed container in a state where a non-aqueous electrolytic solution in which a lithium salt is dissolved is poured into an electrode body configured with a separator interposed therebetween. By doing so, a lithium ion secondary battery to which the present invention is applied is completed. The non-aqueous electrolyte is adjusted by appropriately combining an organic solvent and an electrolyte, and any of these organic solvents and electrolytes can be used as long as they are used for this type of battery. For example, as the organic solvent, propylene carbonate, ethylene carbonate, vinylene carbonate, dimethyl carbonate,
Diethyl carbonate, methyl ethyl carbonate,
1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolan, 4-
Methyl-1,3-dioxolan, diethyl ether, sulfolane, and mixtures thereof. As the electrolyte _{LiClO 4, LiAsF 6, LiBF 4} , LiP
F ₆ , LiCF ₃ SO ₃ , LiCl and the like, and these electrolytes may be used alone or in combination of two or more.

==== Action ==== As described above, the present inventors have found that during overcharging, the lithium cobalt oxide, which is the positive electrode active material, releases oxygen gas before releasing all lithium. It is considered that heat is generated with rapid temperature rise due to rapid reaction between oxygen gas, which is rapidly decomposed and rapidly generated at this time, and the lithium-graphite intercalation compound of the negative electrode. Therefore, if the reaction rate between the lithium occluded in graphite and the oxygen gas is reduced,
It was thought that both did not react rapidly and did not lead to a thermal runaway reaction. The rate-determining step in the reaction process of oxygen gas and lithium is a diffusion process in which graphite moves from inside the crystal to the particle surface. As means for further reducing the diffusion rate, the present inventors have attempted to reduce the symmetry of adjacent hexagonal mesh planes of the graphite crystal and introduce lattice strain without reducing the crystallite size, and have completed the present invention. Was. In the present invention, as a means for evaluating the lattice strain, the correlation between the average particle diameter and the existing ratio of rhombohedral graphite is used. As described above, Lc (112) is increased from 200 (Å) to 400.
(Å) If the average particle system is a graphite material of 20 to 30 (μm), usually 25% or more of rhombohedral is introduced, but the graphite material according to the present invention is the same. Lc
Even with (112) and the average particle size, the proportion of the rhombohedral system is 15% or more and 25% or less. This means that despite the high degree of crystallinity and large crystallites, lattice distortion still remains, the symmetry of the adjacent hexagonal mesh plane is low, and shear deformation is unlikely to occur along the layer plane. Because it is hard to be done. Even a graphite material having such a lattice strain has large crystallites, so it has a reversible occlusion / release capacity equivalent to that of highly crystalline flaky graphite represented by conventional natural graphite, and is suitable. Since it has a large average particle size, it is possible to secure load characteristics equivalent to those of conventional graphite materials.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS ==== Preparation of Battery ==== FIG. 4 shows the structure of an AA wound lithium secondary battery according to the present invention. In FIG. 1, reference numeral 1 denotes a positive electrode plate, which includes LiCoO _{2 as} a positive electrode active material, graphite powder as a conductive material (nitrogen adsorption specific surface area 270 m ² / g), acetylene black powder as a conductive additive, and polyvinylidene fluoride resin as a binder. Were mixed at a weight ratio of 94: 2: 1: 3, and a mixture obtained by adding an N-methyl-2-pyrrolidinone solvent and kneading the mixture into a paste was applied to both surfaces of an aluminum foil 4 having a thickness of 20 (μm). After drying, rolling, and cutting into a predetermined size, a belt-shaped positive electrode sheet was produced. In the rolling step, the mixture density of the sheet electrode was controlled to be 3.4 g / cm ³ . The electrode thickness is 70 (μm). The mixture was scraped off a part of the sheet perpendicularly to the longitudinal direction of the sheet, and an aluminum positive electrode lead plate 18 was attached to the current collector by ultrasonic welding. For the active material LiCoO ₂ , an aqueous solution of potassium sulfate and an aqueous solution of potassium hydroxide are added to an aqueous solution of cobalt sulfate.
H was dropped until 11.2, and cobalt hydroxide (Co
(OH) ₂ ) is precipitated, and the hydroxide
Heat treatment at 00 ° C. gave tricobalt tetroxide. This tricobalt tetroxide and lithium carbonate are combined with Li / C
o Mixing was performed so that the atomic ratio became 1.05, and the mixture was fired in a stream of air at a predetermined temperature (4) for 10 hours to prepare lithium cobalt oxide. The obtained lithium cobaltate was lightly pulverized without pulverizing by applying a compressive force and an impact force as in a ball mill or a jet mill pulverizer to break up agglomerated particles. Reference numeral 2 denotes a negative electrode carbon material electrode in which graphite powder obtained by various methods and carboxymethylcellulose as a binder were mixed at a weight ratio of 97: 3, ion-exchanged water was added, and the mixture was kneaded into a paste. After coating on both sides of a 14 (μm) copper foil 5, it was dried, rolled, and cut into a predetermined size to produce a strip-shaped negative electrode sheet. The mixture was scraped off a part of the sheet perpendicularly to the longitudinal direction of the sheet, and a nickel negative electrode lead plate 7 was spot-welded onto the current collector.

In the rolling step, the mixture density of the sheet electrode was controlled to be 1.2 g / cm ³ . The electrode thickness is 66 (μm). The positive electrode and the negative electrode are spirally wound through three polypropylene porous film separators, and inserted into the case 17. After the above operation, an electrolyte is injected. The used electrolyte solution was dissolved in a mixed solvent in which ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate were mixed at a volume ratio of 2: 1: 7 so that LiPF ₆ was 1.3 (mol / l). Was used. After the insertion, an explosion-proof lid element having a current interrupting mechanism is fitted together with the gasket 13,
Seal the power generating element. The cover element includes a metal positive electrode terminal plate 8, an intermediate pressure-sensitive plate 14, and an upwardly projecting projection 10.
The positive electrode terminal plate 8 and the fixing plate 12 are provided with a gas vent hole, and the conductive member (10, 11) including the base member 11 and the conductive member (10, 11). 10 and 11) are provided on the upper surface of the fixing
The lower surface of the base 11 is exposed on the lower surface side of the fixing plate 12 and the lower surface of the base plate 11 is exposed. The gasket 13 is fitted into the inner periphery of the opening of the battery case 4. The fixing plate 12 is fitted, the intermediate pressure-sensitive plate 14 and the positive electrode terminal plate 8 are laminated on the fixing plate 12, and the conductive agent (10, 11) and the intermediate pressure-sensitive plate 14 are connected to the conductive portion. Both are connected at the projecting portion 10 of the agent (10, 11), and both are conductive only at the contact portion including the connecting portion 15,
The tip of the positive electrode lead plate 5 is connected to the base 11 of the conductive agent (10, 11), and the opening of the battery case 4 is crimped inward to compress the gasket 13 to compress the battery case 13. 4 is sealed with the lid element. When the inside of the battery case 4 reaches a predetermined internal pressure, the conductive member (1) is formed by the intermediate terminal plate 14 bulging outward.
The conductive path between the positive electrode lead plate 18 and the positive electrode terminal plate 8 is cut off by breaking the periphery of the connection portion 15 of the protruding portion 10 of (0, 11). Reference numeral 6 denotes an insulating bottom plate made of polypropylene, which has a hole so as to have the same area as the space A generated at the time of winding. Reference numeral 16 denotes an insulating plate inserted so that the wound electrode group and the positive electrode lead plate are not short-circuited. The size of the completed battery is AA (14.5φm
mx 50 mm).

==== Measurement of Lc (112) of Graphite Material ==== About 10% by weight of high purity silicon powder for X-ray standard is added to the sample as an internal standard substance, mixed and packed in a sample cell. , CuKα monochromated by graphite monochromator
Using a line as a radiation source, a wide-angle X-ray diffraction curve was measured by a reflection type diffractometer method. The applied voltage and current to the X-ray tube were 40 kV and 40 mA, and the divergence slit was 2
°, the scattering slit was set to 2 °, and the light receiving slit was set to 0.3 mm, and scanning was performed at a speed of 0.25 ° per minute from 2 ° to 81 ° to 89 °. The obtained diffraction pattern is based on (1) of the graphite material in which 2θ appears around 83.6 ° according to the literature (1).
12) The diffraction angle and half width of the diffraction line are 28.1 = 88.1 °.
Correction was made by the (422) diffraction line of the silicon powder appearing in the vicinity, and the crystallite size Lc (112) in the c-axis direction was calculated.

==== Calculation of Existence Ratio of Rhombohedral Graphite ==== Using the aforementioned X-ray wide-angle diffractometer, only the graphite powder was packed in the sample holder without adding any internal standard material, and the measurement was performed. went. The applied voltage and current to the X-ray tube were 40 kV and 40 kV.
mA, the separation slit is 1 °, the divergence slit is 1 °,
The light receiving slit is set to 0.15 mm, the scanning speed is set to 0.25 ° per minute, and (2θ / θ) is scanned from low to high angles from 41 ° to 48 ° to obtain an X-ray diffraction pattern. Was. If any rhombohedral graphite is present, four diffraction lines can be observed within this measurement range.
Each diffraction line has a (2θ / θ) of 42.3 ° from the low angle side.
A hexagonal (100) diffraction line near 43.3 °, a rhombohedral (101) diffraction line near 43.3 °, a hexagonal (101) diffraction line near 44.4 °, and 46. A rhombohedral (012) diffraction line appears around 0 °. Since the results of X-ray diffraction vary significantly depending on the measurement conditions, the existence ratio of rhombohedral crystals defined within the scope of the present invention is limited to the case where the ratio is calculated from the results obtained under the above measurement conditions. I do. A base line was arbitrarily set for the obtained diffraction pattern, and these diffraction lines were separated on the figure to calculate the peak area of each diffraction line. Peak area r (101) of (101) diffraction line attributed to rhombohedral crystal and peak area h (1) of (101) diffraction line attributed to hexagonal crystal
01) was substituted into Equation 1 below, and the abundance ratio of rhombohedral graphite was calculated.

(Equation 1) {r (101) × 15/12} / Δr (101) × 15
/ 12 + h (101)｝

==== Measurement of Average Particle Size ==== The average particle size of the graphite powder was measured by a laser diffraction particle size distribution analyzer (HELOS, manufactured by JEOL Ltd.). In the present specification, the cumulative 50% diameter measured by this measuring device will be referred to as the average particle diameter. The measurement lens was appropriately changed according to the measured average particle diameter.

==== Preparation of Graphite Material ==== (Graphite 1) Acenaphthylene was put in an autoclave,
A nitrogen gas of 50 kg / cm ² was sealed and heated to 700 ° C. to carbonize. At this time, the heating rate is from room temperature to 250 ° C.
Up to 100 ° C / hour, 250 ° C to 550 ° C
100 ° C / hour from 550 ° C to 700 ° C. The coke thus obtained was placed in an electric furnace, heated to 2800 ° C. in a nitrogen stream, kept for 5 hours, and allowed to cool to room temperature.

(Graphite 2) Acenaphthylene and phenanthrene were each pulverized so that the average particle diameter became 5 (μm), and both were mixed so that the ratio became 90:10. The mixture was placed in an autoclave, filled with 50 kg / cm ² of nitrogen gas, and heated to 700 ° C. to carbonize. At this time, the heating rate is 100 ° C./hour from room temperature to 250 ° C., 50 ° C./hour from 250 ° C. to 550 ° C., and 550 ° C.
100 ° C./hour up to ７００700 ° C. The coke thus obtained was placed in an electric furnace, heated to 2800 ° C. in a nitrogen stream, kept for 5 hours, and allowed to cool to room temperature.

(Graphite 3) Acenaphthylene and phenanthrene were each pulverized so that the average particle diameter was 5 (μm), and both were mixed so that the weight ratio was 97: 3. The mixture was placed in an autoclave, filled with 50 kg / cm ² of nitrogen gas, and heated to 700 ° C. to carbonize. At this time, the heating rate is 100 ° C./hour from room temperature to 250 ° C., 50 ° C./hour from 250 ° C. to 550 ° C., and 550 ° C.
100 ° C./hour up to ７００700 ° C. The coke thus obtained was placed in an electric furnace, heated to 2800 ° C. in a nitrogen stream, kept for 5 hours, and allowed to cool to room temperature.

(Graphite 4) Phenanthrene was charged into an autoclave, and nitrogen gas at 50 kg / cm ² was charged.
It was heated to 00 ° C and carbonized. At this time, the heating rate is from room temperature to 250 ° C. at 100 ° C./hour, and 250 ° C. to 550.
50 ° C / hour to 550 ° C to 10 ° C
0 ° C./hour. The coke thus obtained was placed in an electric furnace, heated to 2800 ° C. in a nitrogen stream, kept for 5 hours, and allowed to cool to room temperature.

(Graphite 5) Anthracene and benzaldehyde are mixed in a molar ratio of 0.198: 0.304, and paratoluenesulfonic acid is added to this mixture in 5.1.
The mixture was added to 9% by weight and stirred sufficiently. In this state, it was heated to 160 ° C. and kept for 1 hour. Thereafter, water and unreacted benzaldehyde were removed by vacuum distillation and dried. The condensable polycyclic polynuclear aromatic thus obtained was pulverized by a ball mill until the average particle diameter became 5 (μm). This pulverized material is used as a raw material B. Meanwhile, pyrene,
Benzaldehyde and p-toluenesulfonic acid were mixed at a molar ratio of 0.126: 0.157: 0.011, and sufficiently stirred. 150 ° C. with continuous stirring
, And kept in this state for 2 hours to cool. The condensable polycyclic polynuclear aromatic thus obtained was pulverized by a ball mill until the average particle diameter became 5 (μm). This pulverized product is referred to as a raw material A. Raw material A and raw material B are in a weight ratio of 95:
The mixture was heated to 700 ° C. and carbonized. At this time, the heating rate is from room temperature to 250 ° C.
50 ° C / hour, from 250 ° C to 550 ° C,
100 ° C / hour from 50 ° C to 700 ° C. The coke thus obtained is placed in an electric furnace and placed in a nitrogen stream at 280.
The temperature was raised to 0 ° C., maintained for 5 hours, and allowed to cool to room temperature.

(Graphite 6) A highly purified flaky natural graphite powder produced in Madagascar (average particle diameter 100 (μm)
m)) was used as is.

These graphites 1 to 5 were subjected to jet milling using an argon gas as a gas stream to have an average particle size of about 40, 30, 2
Each was pulverized by appropriately adjusting to 5, 20, and 10 (μm).

==== Test Method for Battery ==== Lc (112) of the graphite powder obtained as described above,
The average particle diameter and the abundance ratio of rhombohedral graphite are shown in Table 1 together with the corresponding example numbers.

[0051]

[Table 1]

A battery corresponding to the example number was manufactured according to (battery manufacturing method). When the battery voltage reaches a constant charge current of 50 mA and the battery voltage reaches a charge end voltage of 4.2 V, the charging operation is temporarily stopped.
After a pause of one minute, the discharge operation is suspended when the battery voltage reaches a discharge end voltage of 3.0 V with a constant discharge current of 50 mA, and the charge operation is paused for 15 minutes to perform a charge / discharge cycle of five cycles. After that, a load characteristic test described later was performed, and an overcharge test described later was performed after the test.

(1) Load Characteristics Test The battery was charged by a constant current / constant voltage method. The charging current is 400 mA, the charging voltage is 4.2 V, and the charging time is 5 hours. After the end of the above charging operation, pause for 15 minutes,
Discharge was performed by a constant current method with a discharge current of 200 mA, and the discharge operation was temporarily stopped when the battery voltage reached a discharge end voltage of 2.5 V. Further, after performing the same charging operation and rest, discharging was performed by a constant current method with a discharging current of 600 mA, and the discharging operation was terminated when the same discharge termination voltage of 2.5 V was reached. Table 1 shows the apparent discharge capacities obtained at each discharge current. The ratio (%) of the apparent discharge capacity obtained when the discharge current was 600 mA to that obtained when the discharge current was 200 mA was expressed as the load characteristic. Table 3 also shows the load characteristics obtained for each battery.

(2) Overcharge Test The battery having completed the load characteristics was continuously charged at a constant current of 400 mA to artificially create an overcharged state, and the safety of the battery was confirmed. Table 3 shows the results. The pass / fail judgment of the overcharge test was made based on whether or not excessive heat generation occurred during the test. For batteries that did not generate excessive heat, the safety valve with the current cutoff mechanism operated normally, and the charging current was cut off during overcharge.Batteries that generated excessive heat had normal current cutoff mechanisms. It is considered that the cause is that some abnormal condition has occurred before the operation is performed.

(3) Results of Examples Regardless of the type of graphite used, the average particle size was reduced and the load characteristics were improved. However, no clear correlation was found between the load characteristics and the results of the safety test.

Batteries using graphite 1 and graphite 6 failed the overcharge test regardless of the average particle size. Since both graphites have a relatively high ratio of rhombohedral crystals even if the average particle diameter is about 40 (μm), the lattice strain inside the crystals is originally small, and the diffusion rate of occluded lithium in the solid phase is low. It is presumed that this was due to the large size, and it was presumed that a rapid thermal runaway reaction occurred during overcharge.

Graphite 2 and graphite 5 have an average particle diameter of 10 (μ
In cases other than m), the overcharge test was passed. However, when the average particle diameter was 40 (μm) and 30 (μm), the load characteristics were less than 80%. Since both graphites have a lower ratio of rhombohedral crystals than those of graphite 1 and graphite 4, it is considered that the lattice strain inside the crystals was relatively large and the diffusion rate of the stored lithium in the solid phase was low. . Unless the average particle diameter is at least less than 30 (μm), it is presumed that it is difficult to achieve a load characteristic of 80% or more.

When the average particle diameter of graphite 3 was other than 10 (μm), it passed the overcharge test. However, the average particle size is 40
(Μm), the load characteristics were less than 80%. When graphites having similar particle diameters are compared with each other, the ratio of the rhombohedral crystal of graphite 2 is lower than that of graphite 1 and graphite 6, and that of graphite 2
And 5 higher. Therefore, it is inferred that the lattice strain is smaller than at least graphite 2 and graphite 5. For this reason, even when the average particle diameter is 30 (μm), the load characteristics are 80%.
That was all. In the case of graphite 3, it is presumed that it is difficult to achieve a load characteristic of 80% or more unless the average particle diameter is at least less than 40 (μm).

The graphite 4 passed the overcharge test when the average particle size was other than 10 (μm), but the battery capacity was less than 450 mAh regardless of the particle size. It is considered that the reason why the battery capacity is small is that the reversible lithium storage / release capacity is small due to the small crystallite size Lc (112) of graphite. Even if this graphite is pulverized to reduce the average particle diameter, it is presumed that the proportion of rhombohedral crystals is lower than that of other graphite materials, and that the lattice strain inside the crystal is large. For this reason, it is considered that the load characteristics also showed lower values as compared with the case of other graphite materials.

As described above, a battery using a graphite material within the scope of the present invention has a capacity of 450 mAh or more and a load characteristic of 80 mAh.
% And passed the overcharge test.

[0061]

According to the lithium ion secondary battery using the graphite material according to the present invention, overcharge resistance, that is, safety in overcharge can be improved without lowering capacity and load characteristics. Was.

[Brief description of the drawings]

FIG. 1 is a diagram showing a unit cell structure of hexagonal graphite according to the present invention.

FIG. 2 is a diagram showing a unit cell structure of rhombohedral graphite according to the present invention.

FIG. 3 is a diffraction diagram of graphite powder obtained by pulverizing natural graphite according to the present invention.

FIG. 4 is a longitudinal sectional view showing the structure of an AA wound lithium secondary battery according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode plate 2 Negative electrode carbon material 3 Polypropylene porous film separator 4 Battery case 6 Polypropylene insulating bottom plate 7 Nickel negative electrode lead plate 8 Positive electrode terminal plate 10 Protrusion 11 Base 12 Fixing plate 13 Gasket 14 Intermediate pressure sensing plate 15 Connection part 16 wound electrode group 17 case 18 aluminum positive electrode lead plate

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Yoshiro Harada Inventor 5-36-11 Shimbashi, Minato-ku, Tokyo Fuji Electric Chemical Co., Ltd. F-term (reference) 5H029 AJ01 AJ12 AK03 AL07 AM03 AM04 AM05 AM07 BJ02 DJ16 DJ17 HJ01 HJ05 5H050 AA03 AA15 BA17 CA08 CA09 CB08 EA10 EA24 FA17 FA19 HA02 HA05 HA13

Claims (1)

[Claims] 1. A positive electrode part comprising a positive electrode mixture containing a lithium-containing composite metal oxide capable of reversibly occluding and releasing lithium as a positive electrode active material formed in a sheet shape on a metal foil; A non-aqueous electrolyte containing a lithium salt is formed by laminating a negative electrode mixture composed mainly of a releasable graphite material as a sheet on a metal foil and a negative electrode part via a separator. And a lithium ion secondary battery arranged in a closed container, wherein the graphite material is composed of hexagonal and rhombohedral, and X
When measured by the line wide angle diffraction method, the crystallite size Lc (11) in the c-axis direction calculated from the (112) diffraction line
2) is 200 (Å) to 400 (Å), the average particle size is 20 (μm) to 30 (μm), and the peak area of the (101) diffraction line attributed to the rhombohedral is r ( 1
01) and belonging to the hexagonal crystal (10)
1) Assuming that the peak area of the diffraction line is h (101), Δr
(101) × 12/15｝ / ｛r (101) × 15/1
The lithium ion secondary battery, wherein the proportion of the rhombohedral system defined by the formula of 2 + h (101)} is in the range of 15% or more and 25% or less.