JP2002216758A - Lithium ion secondary battery, positive electrode active material and sheath for synthesizing compound oxide containing lithium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery of high safety and a long life, capable of easily arranging particle size distribution of positive electrode active material and of eliminating burst ignition in nailing test. SOLUTION: In a lithium ion secondary battery provided with a positive electrode containing active material, an negative electrode and nonaqueous electrolyte, the positive electrode active material contains compound oxide containing lithium provided by sintering raw material powder 47 under a condition of storing in a sheath containing a compound component composed of at least one kind selected from a group comprising MgO and MgAl2O4 spinel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises a sheath used for synthesizing a lithium-containing composite oxide, a positive electrode active material containing a lithium-containing composite oxide, and a positive electrode active material containing a lithium-containing nickel oxide. The present invention relates to a lithium ion secondary battery.

[0002]

2. Description of the Related Art In recent years, as portable personal computers and mobile phones have become smaller and lighter, there has been a demand for smaller and lighter secondary batteries as power supplies for these electronic devices. I have.

As such a secondary battery, a lithium ion secondary battery using a material capable of occluding and releasing lithium ions, such as a carbon material, as a negative electrode material has been developed and has been put to practical use as a power source for small electronic devices. The demand for this secondary battery is increasing because it is smaller and lighter than conventional lead storage batteries and nickel-cadmium batteries and has a high energy density.

As a positive electrode active material of this lithium ion secondary battery, a lithium-containing cobalt oxide (LiCoO ₂ ) having a high discharge potential and a high energy density has been put to practical use. However, cobalt, which is a raw material for this composite oxide, is scarce as a resource and is ubiquitous in countries where commercially available mineral deposits are scattered in a few countries. It is accompanied by supply anxiety.

[0005] Therefore, researches on positive electrode active materials other than lithium-containing cobalt oxides have been actively conducted in recent years. As an example, various compounds have been reported as composite oxides of lithium and manganese synthesized from various manganese raw materials and lithium raw materials. Specifically, a lithium manganese composite oxide represented by LiMn ₂ O ₄ having a spinel-type crystal structure has a potential of 3 V with respect to lithium due to electrochemical oxidation, and has a theoretical charge / discharge capacity of 148 mAh / g. Have.

However, a lithium ion secondary battery using a manganese oxide or a lithium manganese composite oxide as a positive electrode active material has a disadvantage that the capacity is significantly deteriorated when used in an environment at room temperature or higher. This is because manganese oxide and lithium manganese composite oxide are destabilized by high temperature, and Mn is eluted in the non-aqueous electrolyte. Particularly in recent years, large-sized lithium ion secondary batteries for electric vehicles or road leveling have been developed in various fields. In this large-sized lithium ion secondary battery, heat generation during use cannot be ignored as the battery becomes larger, and the inside of the battery tends to become relatively high even when the ambient environmental temperature is around room temperature. In addition, even a relatively small battery used for a small portable device or the like may be used in a high-temperature environment such as a cabin of a car in the middle of summer, and the temperature inside the battery may be relatively high. is there. From such a problem, it is very difficult to put a positive electrode active material using manganese as a raw material into practical use.

By the way, nickel composite oxides have been actively studied as post-cobalt composite oxides. For example, a nickel composite oxide such as LiNiO ₂ has a theoretical capacity of 180 to 200 mAh / g, which is larger than that of a LiCoO ₂ -based active material or a LiMn ₂ O ₄ -based active material, and has an optimum discharge potential of about 3.6 V on average. Therefore, it is a very promising cathode active material. However, since the crystal structure of LiNiO ₂ is unstable, the initial discharge capacity in the charge / discharge cycle test decreases significantly with the number of times of charge / discharge,
In a nail penetration test of a lithium ion secondary battery manufactured using LiNiO ₂ , there is a problem in safety leading to rupture and ignition.

[0008] As a method for synthesizing these lithium-containing composite oxides, the starting raw material powder is made of Saya having alumina (Al ₂ O ₃ ) as a main component or mullite (3Al ₂ O ₃ .2Si).
A method of baking in a sheath containing O ₂ ) as a main component is common.

However, when a sheath containing alumina or mullite as a main component is used, the sheath and the starting material powder are liable to react with each other, and a by-product generated in this reaction is mixed into the lithium-containing composite oxide. Not only does the charge / discharge cycle characteristic of the secondary battery deteriorate, but also the risk of explosion or fire when short-circuited as in a nail penetration test increases. In addition, lithium-containing composite oxide powder synthesized using a sheath containing alumina or mullite as a main component is a broad powder containing a wide variety of particles ranging from small particles having a submicron diameter to aggregated particles having a particle diameter of about 100 microns. Has a good particle size distribution. With such a particle size distribution, not only the charge / discharge cycle characteristics and safety may be further deteriorated, but also the active material filling density of the positive electrode may be reduced. It is desirable to make the distribution uniform. However, since the dispersion of the particle size distribution is inherently large, sieving for uniforming the particle size distribution must be repeated many times, which causes a problem that not only the yield of the positive electrode active material decreases but also the manufacturing process becomes complicated.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a lithium ion having a high safety and a long life, which can easily make the particle size distribution of the positive electrode active material uniform, does not rupture and fire in a nail penetration test. It is intended to provide a secondary battery.

It is another object of the present invention to provide a positive electrode active material which is easy to make uniform in particle size distribution, has no burst ignition in a nail penetration test, has high safety, and can realize a long-life battery. It is intended to provide.

[0012] Furthermore, the object of the present invention is to make it easy to make the particle size distribution uniform, and to cause no burst ignition in a nail penetration test.
An object of the present invention is to provide a sheath for synthesizing a lithium-containing composite oxide used when synthesizing a lithium-containing composite oxide capable of realizing a battery having high safety and a long life.

[0013]

A lithium ion secondary battery according to the present invention is a lithium ion secondary battery including a positive electrode containing an active material, a negative electrode, and a non-aqueous electrolyte. A lithium-containing composite oxide obtained by firing the raw material powder in a state of being housed in a sheath containing at least one compound component selected from the group consisting of MgO and MgAl ₂ O ₄ spinel, Lithium ion secondary battery.

In the lithium ion secondary battery according to the present invention, when the sheath contains MgO,
It is desirable to further include at least one component selected from the group consisting of i, Ca, Y and Zr.

In the lithium ion secondary battery according to the present invention, when the sheath contains MgAl ₂ O ₄ spinel, at least one kind of component selected from the group consisting of Si, Ca, Y, Zr and Hf. It is desirable to further include

In the lithium ion secondary battery according to the present invention, the lithium-containing composite oxide preferably has a particle size distribution defined by the following formula (I).

S ≦ 2D (I) Here, S is the half-value width of the particle size distribution of the lithium-containing composite oxide, and D is the particle size showing the maximum peak in the particle size distribution of the lithium-containing composite oxide.

The cathode active material according to the present invention comprises:
A positive electrode active material comprising a lithium-containing composite oxide obtained by firing in a state of being housed in a sheath containing at least one compound component selected from the group consisting of MgO and MgAl ₂ O ₄ spinel. is there.

The sheath for synthesizing a lithium-containing composite oxide according to the present invention is characterized by containing at least one compound component selected from the group consisting of MgO and MgAl ₂ O ₄ spinel.

According to the present invention, the raw material powder is
A positive electrode comprising a step of synthesizing a lithium-containing composite oxide by firing in a state of being housed in a sheath containing at least one compound component selected from the group consisting of O and MgAl ₂ O ₄ spinel. A method for producing an active material can be provided.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a positive electrode active material according to the present invention will be described.

This positive electrode active material is a lithium-containing composite obtained by firing the raw material powder in a sheath containing at least one compound component selected from the group consisting of MgO and MgAl ₂ O ₄ spinel. Contains oxide.

The sheath is also called a firing tray, and its shape is not particularly limited as long as the desired lithium-containing composite oxide is obtained, but an example is shown in FIG. Figure 1
(A) shows a bottom sheath-integrated square sheath 41,
FIG. 1B shows a round sheath 42 integrated with the bottom trunk. On the other hand, FIG. 1C shows a rectangular cylindrical body 4.
3 and a rectangular bottom plate 44 having a rectangular bottom plate 44, and a cylindrical trunk 4 is shown in FIG.
5 and a bottom shell separated type round sheath having a circular bottom plate 46 are shown. The powder stored in each sheath is the raw material powder 47. In particular, according to the bottom-body-separated type sheath, oxygen gas is supplied from above the sheath at the time of firing, and is also supplied from the gap between the body and the bottom plate. Therefore, oxygen gas is uniformly supplied to the raw material powder. And a firing reaction can be uniformly generated.

FIG. 2 shows a state in which four square sheaths of the separated bottom body type in which the raw material powder 47 is stored are set in an electric furnace 48. The atmosphere (sintering atmosphere) in the furnace 48 is preferably an oxygen gas (O ₂ ) atmosphere or an atmosphere containing oxygen gas (O ₂ ). Further, the number of sheaths accommodated in the electric furnace is not limited to four, and can be set to any number.
For example, as shown in FIG. 3, the sheath may be housed in the electric furnace 48 in two stages. Further, a tunnel pot may be used as an electric furnace in order to enhance mass productivity.

When a sheath containing MgO is used as the sheath, it is preferable that MgO is a main component of the sheath. Here, the main component means a component having the highest abundance ratio among components constituting the sheath. The sheath has a MgO content of 99%
It is preferable to be within the range of 100%. Sheath MgO
If the content is less than 99%, components other than MgO contained in the sheath may react with the raw material powder, which may make it difficult to obtain high safety and charge / discharge characteristics. Among them, MgO content is 99% or more, and Al, Si, C
at least one selected from the group consisting of a, Y and Zr
Sheaths containing different types of elements are preferred. Since such a sheath can improve thermal shock resistance, it is difficult to crack when the sheath is forcibly taken out of the furnace at high temperature to room temperature, and the sheath can be taken out of the furnace immediately after firing. , Can improve productivity. In addition, since the sheath is expensive, if it is difficult to break, the production cost of the positive electrode active material can be reduced. Regarding the content of each element in the sheath, the Al content is preferably 30 ppm or more and 2000 ppm or less, and the Si content is 30 ppm or more and 10,000 pp.
m or less, the Ca content is 30 ppm
It is preferable that the content is not less than 10,000 ppm.
The content is preferably 30 ppm or more and 2000 ppm or less, and the Zr content is 30 ppm or more and 3 ppm or less.
It is preferred that the content be 0000 ppm or less. By setting the content of each element in the sheath in the above range, it is possible to improve the thermal shock resistance of the sheath while improving the characteristics of the positive electrode active material.

[0026] As sheath, when using those containing MgAl ₂ O ₄ spinel, it is desirable MgAl ₂ O ₄ spinel is the main component of the sheath. Here, the main component means a component having the highest abundance ratio among components constituting the sheath.
The MgAl ₂ O ₄ spinel content of the sheath is 95% to 100%
Is preferably within the range. If the MgAl ₂ O ₄ content of the sheath is less than 95%, components other than the MgAl ₂ O ₄ contained in the sheath may react with the raw material powder, making it difficult to obtain high safety and charge / discharge characteristics. Because there is. Above all, a sheath having a MgAl ₂ O ₄ spinel content of 95% or more and containing at least one element selected from the group consisting of Si, Ca, Y, Zr and Hf is preferable. Since such a sheath can improve thermal shock resistance, it is difficult to crack when the sheath is forcibly taken out of the furnace at high temperature to room temperature, and the sheath can be taken out of the furnace immediately after firing. , Can improve productivity. In addition, since the sheath is expensive, if it is difficult to break, the production cost of the positive electrode active material can be reduced. Regarding the content of each element in the sheath, the Si content was 30 ppm or more and 10,000 pp.
m or less, the Ca content is 30 ppm
It is preferable that the content is not less than 10,000 ppm.
The content is preferably 30 ppm or more and 2000 ppm or less, and the Zr content is 30 ppm or more and 3000 ppm or less.
The Hf content is preferably 0 ppm or less, and the Hf content is preferably 30 ppm or more and 2000 ppm or less. By setting the content of each element in the sheath in the above range, it is possible to improve the thermal shock resistance of the sheath while improving the characteristics of the positive electrode active material.

The components of the sheath include MgO and MgAl ₂ O ₄
Both spinels may be contained.

The firing is performed at a temperature of 450 to 550 ° C. for 2 to 2 hours.
It is desirable to carry out a two-stage firing in which firing is performed for 0 hour, and then at 630 to 730 ° C. for 2 to 50 hours.

The present invention can be applied to lithium-containing composite oxides having various compositions. In particular, the composition of the lithium-containing composite oxide is a composite oxide containing Li and Co such as LiCoO _2. Material, LiMnO ₂ or Li
A composite oxide containing Li and Mn, such as Mn ₂ O ₄ , L
It is preferable to use a composite oxide containing Li and Ni, such as iNiO ₂ . In particular, the composition of the lithium-containing composite oxide may be a composite oxide containing Li and Ni, a lithium-containing composite oxide in which some of the oxygen atoms are replaced by fluorine atoms, a hydroxyl group (OH) or H _This is effective when a raw material powder containing a starting compound containing ₂ O molecules is used.

The composition of the composite oxide containing Li and Ni can be, for example, a composition represented by the following formulas (1) to (4).

Li _{1 + x} Ni _1-x O _uy F _y (1) where the molar ratios x, y and u are expressed as ｛(y + 0.05) /
2｝ ≦ x <{(y + 1) / 3}, y> 0, 1.9 ≦ u ≦
2.1 is shown.

Li _{1 + x} Ni _1-x O _uy F _y + cC (2) However, the molar ratios x, y and u are represented by ｛(y + 0.05) /
2｝ ≦ x <{(y + 1) / 3}, y> 0, 1.9 ≦ u ≦
2.1 is shown. C is at least one element selected from the group consisting of Na, K, Ca, S, Si and Fe, and the content c of the element C in the composite oxide is 20 to
It is in the range of 3000 ppm.

Li _x (Ni _1-y Me1 _y ) (O _2-z X _z ) (3) where Me1 is B, Mg, Al, Sc, Ti, V, C
r, Mn, Co, Cu, Zn, Ga, Y, Zr, Nb,
Mo, Tc, Ru, Sn, La, Hf, Ta, W, R
e, at least one element selected from the group consisting of Pb and Bi, and X is at least one type of halogen element selected from the group consisting of F, Cl, Br and I;
The molar ratios x, y and z are respectively 0.02 ≦ x ≦ 1.
3, 0.005 ≦ y ≦ 0.5 and 0.01 ≦ z ≦ 0.5.

[0034] _{Li x (Ni 1-y Me1} y) (O 2-z X z) + cC (4) where said Me1 is B, Mg, Al, Sc, Ti, V, C
r, Mn, Co, Cu, Zn, Ga, Y, Zr, Nb,
Mo, Tc, Ru, Sn, La, Hf, Ta, W, R
e, at least one element selected from the group consisting of Pb and Bi, and X is at least one type of halogen element selected from the group consisting of F, Cl, Br and I;
The molar ratios x, y and z are respectively 0.02 ≦ x ≦ 1.
3, 0.005 ≦ y ≦ 0.5, 0.01 ≦ z ≦ 0.5, wherein C is at least one element selected from the group consisting of Na, K, Ca, S, Si and Fe The content c of the element C in the composite oxide is 20 to 3000 p.
pm.

The reason why the molar ratios x, y and z in the composition formulas (3) and (4) are set in the above ranges will be described below.

The molar ratio x of lithium will be described. If the molar ratio x is less than 0.02, the crystal structure of the composite oxide becomes extremely unstable, and the cycle characteristics and safety of the secondary battery may be insufficient. On the other hand, when the molar ratio x exceeds 1.3, the discharge capacity and safety of the secondary battery may be insufficient. A more preferable range of the molar ratio x is 0.05 ≦ x ≦ 1.2.

The molar ratio y of the element Me1 will be described. If the molar ratio y is less than 0.005, the safety of the secondary battery may be insufficient. On the other hand, if the molar ratio y exceeds 0.5, a high discharge capacity may not be obtained.
A more preferable range of the molar ratio y is 0.01 ≦ y ≦ 0.3
5 Further, among the elements Me1, Al, Ti, M
n, Nb and Ta are preferred.

The molar ratio z of the halogen element X will be described. If the molar ratio z is less than 0.01, the cycle characteristics and safety of the secondary battery may be insufficient. On the other hand, when the molar ratio z exceeds 0.5, a high discharge capacity may not be obtained. A more preferable range of the molar ratio z is 0.02 ≦ z ≦ 0.3. The halogen element X is preferably F.

The element C contained in the composite oxide having the composition represented by (2) or (4) will be described.
By including the element C in the composite oxide, it is possible to suppress a rapid rise in battery temperature when a large current flows through the secondary battery due to a short circuit or the like, thereby improving the safety of the secondary battery. can do. If the content c of the element C in the composite oxide is less than 20 ppm, it may be difficult to sufficiently suppress rapid heat generation of the battery when a large current flows. On the other hand, when the content c of the element C in the composite oxide is 3
If it exceeds 000 ppm, the charge / discharge cycle characteristics may be significantly deteriorated.

The optimum content c of the element C in the composite oxide tends to vary depending on the type of the element C, and is desirably set as described below.

When the element C is at least one selected from the group consisting of Na, K and S, the content c of the element C is 20
It is preferable to be within the range of -3000 ppm. A more preferable range of the content c is 20 ppm ≦ c ≦ 1500 ppm, and a more preferable range is 20 ppm ≦ c ≦ 1000 ppm. Further, the lower limit of the content c is more preferably set to 50 ppm.

On the other hand, when Ca is used as the element C, the content c of the element C is preferably in the range of 20 to 500 ppm. A more preferable range of the content c is 20 ppm
≤ c ≤ 300 ppm.

When at least one element selected from the group consisting of Si and Fe is used as the element C, the element C
Is preferably in the range of 20 to 500 ppm. A more preferable range of the content c of the element C is 20
ppm ≦ c ≦ 250 ppm.

In the above-mentioned composition formulas (1) to (4),
(2) to (4) are preferable because the safety and cycle characteristics of the secondary battery can be further improved. Most preferred is a lithium-containing composite oxide represented by the composition formula (4), which can dramatically improve safety and cycle characteristics.

The lithium-containing composite oxide powder preferably has a particle size distribution defined by the following formula (I).

S ≦ 2D (I) Here, S is the half width of the particle size distribution of the lithium-containing composite oxide powder, and D is the particle size showing the maximum peak in the particle size distribution of the lithium-containing composite oxide powder.

FIG. 4 shows an example of the particle size distribution of the lithium-containing composite oxide powder. The particle size D having the maximum peak in this particle size distribution is, for example, 10 μm. On the other hand, since the half width S of this particle size distribution is, for example, 5 μm, the particle size D
0.5 times as large as Therefore, this particle size distribution
It satisfies the relationship of the above-mentioned formula (I).

If the half value width S exceeds the value obtained by doubling the particle diameter D, the dispersion of the particle size distribution becomes large, so that the dispersion of discharge capacity and the cycle deterioration may occur, and the safety may be impaired. is there. The particle size distribution is S ≦ 1.
5D, more preferably, S
<D. The half width S is 0.01D.
If it is smaller, a high discharge capacity may not be obtained, so the minimum value of the half width S is preferably set to 0.01D.

When the raw material powder is fired while housed in a sheath containing at least one compound component selected from the group consisting of MgO and MgAl ₂ O ₄ spinel, a lithium-containing composite oxide powder having a uniform particle size distribution is obtained. Since it is easy to obtain, it is possible to obtain a lithium-containing composite oxide having a particle size distribution that satisfies the above-described formula (I) without performing particle size selection after firing. If the particle size distribution after calcination is out of the above-mentioned formula (I), classification after calcination or crushing and classification is performed to obtain a particle size satisfying the above-mentioned formula (I). It is good to set to distribution. According to the present invention, aggregation of particles hardly occurs during firing and the particle size distribution after firing is relatively uniform, so that the number of classifications can be reduced and the particle size can be easily sorted.

Next, a lithium ion secondary battery using the positive electrode active material according to the present invention will be described.

The lithium ion secondary battery according to the present invention
A positive electrode including the positive electrode active material described above, a negative electrode, and a non-aqueous electrolyte are provided.

Examples of the non-aqueous electrolyte include a liquid non-aqueous electrolyte (non-aqueous electrolyte) prepared by dissolving an electrolyte in a non-aqueous solvent, and a non-aqueous solvent and an electrolyte held in a polymer material. Examples thereof include a polymer gel nonaqueous electrolyte, a solid polymer electrolyte mainly composed of an electrolyte, and an inorganic solid nonaqueous electrolyte having lithium ion conductivity. As the non-aqueous solvent and the electrolyte contained in each non-aqueous electrolyte, those described in a liquid non-aqueous electrolyte described later can be used.

Examples of the polymer material contained in the gelled nonaqueous electrolyte include polyacrylonitrile, polyacrylate, polyvinylidene fluoride (PVdF), polyethylene oxide (PEO), or acrylonitrile, acrylate, vinylidene fluoride or ethylene oxide. Examples of the polymer include monomers. Examples of the polymer material contained in the polymer solid electrolyte include polyacrylonitrile, polyvinylidene fluoride (PVdF), polyethylene oxide (PEO), and polymers containing acrylonitrile, vinylidene fluoride, or ethylene oxide as a monomer. And the like. On the other hand, examples of the inorganic solid nonaqueous electrolyte include a ceramic material containing lithium. Specifically, Li ₃ N,
It can be mentioned _{Li 3 PO 4 -Li 2 S-} SiS glass.

Hereinafter, an example of the lithium ion secondary battery according to the present invention will be described.

The lithium ion secondary battery comprises a positive electrode containing the positive electrode active material according to the present invention, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and at least a liquid non-aqueous liquid impregnated in the separator. And an electrolyte.

The positive electrode, separator, negative electrode and liquid non-aqueous electrolyte will be described in detail.

1) Positive Electrode The positive electrode is prepared, for example, by mixing the positive electrode active material according to the present invention, an electric conduction aid and a binder, and pressing the mixture on a current collector, or , An electric conduction aid and a binder are suspended in an appropriate solvent, and this suspension is applied to a current collector and dried.

Examples of the electric conduction aid include acetylene black, carbon black, graphite and the like.

Examples of the binder include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVd).
F), ethylene-propylene-diene copolymer (EPD
M), styrene-butadiene rubber (SBR) and the like can be used.

The mixing ratio of the positive electrode active material, the electric conduction aid and the binder ranges from 80 to 95% by weight of the positive electrode active material, 3 to 20% by weight of the electric conduction aid and 2 to 7% by weight of the binder. Is preferable. As the current collector, a conductive substrate having a porous structure or a non-porous conductive substrate can be used. Examples of the material constituting the current collector include aluminum, stainless steel, and nickel.

2) Separator As the separator, for example, a synthetic resin nonwoven fabric,
A polyethylene porous film, a polypropylene porous film, or the like can be used.

3) Negative Electrode This negative electrode contains a material capable of occluding (doping) and releasing (undoping) lithium.

As such a material, for example, lithium metal, a Li-containing alloy capable of inserting and extracting lithium, a metal oxide capable of inserting and extracting lithium, and an oxide storing and releasing lithium can be used. Metal sulfides, metal nitrides capable of storing and releasing lithium, chalcogen compounds capable of storing and releasing lithium, and carbon materials capable of storing and releasing lithium ions. it can. In particular, the negative electrode containing the chalcogen compound or the carbon material has high safety, and can improve the cycle life of the secondary battery,
desirable.

Examples of the carbon material that occludes / releases lithium ions include coke, carbon fiber, pyrolysis gas phase carbon material, graphite, resin fired body, mesophase pitch-based carbon fiber, mesophase pitch spherical carbon, and the like. Can be. Carbon materials of the type described above are desirable because they can increase the electrode capacity.

Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, niobium selenide, tin oxide and the like. When such a chalcogen compound is used for the negative electrode, the capacity of the negative electrode is increased although the battery voltage is reduced, so that the capacity of the secondary battery is improved.

The negative electrode containing the carbon material is produced, for example, by kneading the carbon material and the binder in the presence of a solvent, applying the obtained suspension to a current collector, and drying the resultant. You.

In this case, as the binder, for example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), ethylene-propylene-diene copolymer (EP
DM), styrene-butadiene rubber (SBR) and the like can be used. Further, the mixing ratio of the carbon material and the binder is 90 to 98% by weight of the carbon material and 2 to 10% by weight of the binder.
It is preferable to be within the range. Further, as the current collector, for example, a conductive substrate of aluminum, stainless steel, nickel, or the like can be used. The current collector may have a porous structure or a non-porous structure.

4) Liquid Non-Aqueous Electrolyte (Non-Aqueous Electrolyte) This liquid non-aqueous electrolyte is prepared by dissolving the electrolyte in a non-aqueous solvent.

Examples of the non-aqueous solvent include cyclic carbonates and chain carbonates (eg, ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, etc.), cyclic ethers and chain ethers (eg, , 2−
Dimethoxyethane, 2-methyltetrahydrofuran, etc.), cyclic ester or chain ester (for example, γ-butyrolactone, γ-valerolactone, σ-valerolactone, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, methyl propionate, propion) Ethylate, propyl propionate, etc.). The non-aqueous solvent includes one or two selected from the types described above.
Up to five types of mixed solvents can be used, but the present invention is not necessarily limited to these.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ) and lithium hexafluorophosphate (Li
PF ₆ ), lithium borofluoride (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), lithium trifluoromethylsulfonylimide (LiCF ₃ SO ₃ ), lithium bistrifluoromethylsulfonylimide [LiN (CF ₃
SO ₂ ) ₂ ]. As such an electrolyte, one or two or three lithium salts selected therefrom can be used, but the electrolyte is not limited to these.

The amount of the electrolyte dissolved in the non-aqueous solvent is desirably in the range of 0.5 to 2 mol / L.

One example of the lithium ion secondary battery according to the present invention is shown in FIGS.

FIG. 5 is a partially cutaway perspective view showing a cylindrical lithium ion secondary battery which is an example of the lithium ion secondary battery according to the present invention. FIG. 6 is an example of the lithium ion secondary battery according to the present invention. FIG. 7 is a cross-sectional view showing a portion A of FIG. 6.

As shown in FIG. 5, a bottomed cylindrical container 1 made of, for example, stainless steel has an insulator 2 disposed at the bottom. The electrode group 3 is housed in the container 1.
The electrode group 3 has a structure in which a band formed by laminating a positive electrode 4, a separator 5 and a negative electrode 6 in this order is spirally wound.

The container 1 contains a non-aqueous electrolyte. A PTC element 7 having an opening in the center,
A safety valve 8 disposed on the TC element 7 and a hat-shaped positive terminal 9 disposed on the safety valve 8 are caulked and fixed to an upper opening of the container 1 via an insulating gasket 10. The positive electrode terminal 9 has a built-in safety mechanism serving as a gas vent hole (not shown). One end of a positive electrode lead 11 is connected to the positive electrode 4 and the other end is connected to the PTC element 7.
Connected to each other. The negative electrode 6 is connected to the container 1 as a negative terminal via a negative lead (not shown).

As shown in FIG. 6, an electrode group 22 is housed in a housing 21 made of, for example, a film material. Examples of the film material include a metal film, a resin sheet such as a thermoplastic resin, and a sheet in which one or both surfaces of a metal layer are covered with a resin layer such as a thermoplastic resin. The electrode group 22 has a structure in which a laminate including a positive electrode, a separator, and a negative electrode is wound into a flat shape. 7, the separator 23, the positive electrode layer 24, the positive electrode current collector 25, and the positive electrode 26 including the positive electrode layer 24, the separator 23, the negative electrode layer 27, the negative electrode current collector 28, and the negative electrode layer 27 from below. Negative electrode 29 provided with the separator 2
3, positive electrode layer 24, positive electrode current collector 25, positive electrode 26 including positive electrode layer 24, separator 23, negative electrode layer 27, and negative electrode current collector 2
A negative electrode 29 provided with a negative electrode 8 is laminated in this order. A negative electrode current collector 28 is located at the outermost periphery of the electrode group 22. One end of the strip-shaped positive electrode lead 30 is
Is connected to the positive electrode current collector 25 of the
Has been extended from. On the other hand, the strip-shaped negative electrode lead 31
One end is connected to the negative electrode current collector 28 of the electrode group 22, and the other end extends from the storage container 21.

The positive electrode active material according to the present invention described above comprises:
It contains a lithium-containing composite oxide obtained by firing the raw material powder in a state of being housed in a sheath containing at least one compound component selected from the group consisting of MgO and MgAl ₂ O ₄ spinel. According to such a positive electrode active material, the reaction between the raw material powder and the sheath at the time of firing can be suppressed, so that the amount of impurities in the positive electrode active material can be reduced. Further, the particle size distribution of the lithium-containing composite oxide can be sharpened. Therefore,
A lithium ion secondary battery including a positive electrode including the positive electrode active material can reduce variation in discharge capacity,
It can improve the charge-discharge cycle characteristics, and can suppress sudden heat generation when a large current flows due to a short circuit condition like a nail penetration test, and prevent rupture and ignition before it occurs. it can.

By setting the particle size distribution of the lithium-containing composite oxide to satisfy the above-mentioned relational expression (I), it is possible to further reduce the variation in discharge capacity while ensuring a high positive electrode active material packing density. In addition, the charge / discharge cycle characteristics can be improved, and the battery temperature when a large current flows due to a short circuit state as in a nail penetration test can be further reduced.

In the present invention, the MgO content is 9
Al, Si, Ca, Y and Zr
A sheath further containing at least one component selected from the group consisting of: MgAl ₂ O ₄ spinel content of 95% or more, and Si, Ca, Y, Zr and H
By using a sheath further containing at least one component selected from the group consisting of f, a positive electrode active material capable of realizing a secondary battery excellent in discharge capacity, charge / discharge cycle characteristics and safety is produced. It becomes possible to manufacture with good efficiency.

[0080]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

Example 1 A detachable bottom shell having the shape shown in FIG. 1C was prepared. This horn sheath
99.5% of MgO component and 160p of Al component
pm, the Si content is 140 ppm, and the Ca content is 1
At 000 ppm, the amount of the Y component was 140 ppm, and the amount of the Zr component was 2000 ppm. The analysis of the elements constituting the sheath was performed by the method described below.

Components other than MgO contained in the sheath (subcomponents)
About glow discharge mass spectrometry (GDMS: Glow Dis
charge Mass Spectrometry). The purity of MgO, which is the main component, is defined as 100% for all constituent components of the sheath.
It was calculated by subtracting the concentration of the accessory component from 100%.

As starting materials, LiOH, Ni _0.78 Co
_The composition is Li using _0.22 (OH) ₂ · H ₂ O and LiF.
After mixing so as to be _1.1 Ni _0.78 Co _0.22 O _1.95 F _0.05 , a mixed powder (raw material powder) was prepared by mixing with a Henschel mixer for 30 minutes. The mixed powder was stored in a square sheath, and four such square sheaths were set in an electric furnace as shown in FIG. The firing was maintained at 480 ° C. for 15 hours while flowing oxygen at 5 liter / min, and then performed at 700 ° C. for 20 hours to obtain a lithium-containing composite oxide powder.

The obtained lithium-containing composite oxide powder was measured by a laser diffraction particle size distribution analyzer, and as a result, as shown in FIG. 8, the particle diameter D that accounted for the maximum ratio in the particle size distribution was 5 μm. On the other hand, the half width S is 3 μm and 0.6D
Was a value corresponding to Therefore, the particle size distribution of the lithium-containing composite oxide powder satisfied the relationship of the above-described formula (I).

<Preparation of Positive Electrode> Polyvinylidene fluoride was converted to N
To a solution dissolved in -methyl-2-pyrrolidone, lithium-containing composite oxide powder as a positive electrode active material, acetylene black and artificial graphite as a conductive agent were added and mixed by stirring, and 92.2% by weight of a positive electrode active material was obtained. A positive electrode mixture comprising 1.8% by weight of acetylene black, 2.2% by weight of artificial graphite, and 3.8% by weight of polyvinylidene fluoride was prepared. This positive electrode mixture was applied to both surfaces of an aluminum foil (thickness: 20 μm), dried, and then pressure-formed using a roller press to produce a positive electrode.

<Preparation of Negative Electrode> Mesophase pitch carbon fiber using mesophase pitch as a raw material was carbonized at 1000 ° C. in an argon atmosphere, and then the average fiber length was 30 μm.
After appropriately pulverizing so that 90 volume% is present in an average fiber diameter of 11 μm and a particle diameter of 1 to 80 μm, and particles having a particle diameter of 0.5 μm or less are reduced (5% or less), 3000 ° C. in an argon atmosphere To produce a carbonaceous material.

The polyvinylidene fluoride was converted to N-methyl-2-
The carbonaceous material and artificial graphite are added to the solution dissolved in pyrrolidone, and the mixture is stirred and mixed. The negative electrode mixture is composed of 86.5% by weight of carbonaceous material, 9.5% by weight of artificial graphite, and 4% by weight of polyvinylidene fluoride. An agent was prepared. This is copper foil (thickness 1
(5 μm), dried and then pressed under a roller press to produce a negative electrode. On this occasion,
The packing density and the electrode length were adjusted such that the ratio (capacity balance) of the designed capacity of the negative electrode to the designed capacity of the positive electrode after molding was 1.03 or more and 1.1 or less.

<Preparation of non-aqueous electrolyte (liquid non-aqueous electrolyte)>
Ethylene carbonate (EC) and methyl ethyl carbonate
(MEC) was mixed such that the volume ratio was 1: 2.
Lithium hexafluorophosphate (LiPF) ₆) To 1
By dissolving M, a non-aqueous electrolyte was prepared.

<Assembly of Battery> After welding a positive electrode lead made of aluminum and a negative electrode lead made of nickel to the positive electrode and the negative electrode, respectively, the positive electrode, a separator made of a porous film made of polyethylene, and the negative electrode were respectively attached. The electrodes were stacked in this order, and spirally wound so that the negative electrode was located outside, to produce an electrode group.

This electrode group is housed in a bottomed cylindrical container,
The negative electrode lead was welded to the bottom of the bottomed cylindrical container, and the positive electrode lead was welded to a safety valve arranged at the opening of the bottomed cylindrical container. Subsequently, 4 mL of a non-aqueous electrolyte was injected into the bottomed cylindrical container, and the electrode group was sufficiently impregnated with the non-aqueous electrolyte. After the positive electrode terminal was arranged on the safety valve, it was fixed by caulking. As described above, a cylindrical lithium ion secondary battery (18650 size) having a designed rated capacity of 1600 mAh was assembled.

Example 2 The firing conditions in the synthesis of the positive electrode active material were set to 48 while flowing oxygen at 5 L / min.
A lithium-containing composite oxide powder was obtained in the same manner as in Example 1 except that the temperature was maintained at 0 ° C. for 15 hours and then changed to 720 ° C. for 25 hours.

As a result of measuring the obtained lithium-containing composite oxide powder with a laser diffraction particle size distribution analyzer, it was found that S = between the particle size D and the half width S, which occupy the largest ratio in the particle size distribution.
The relational expression of 1.2D was established.

A cylindrical lithium ion secondary battery was manufactured in the same manner as described in Example 1 except that such a positive electrode active material was used.

Example 3 The firing conditions in the synthesis of the positive electrode active material were set to 48 while flowing oxygen at 5 L / min.
A lithium-containing composite oxide powder was obtained in the same manner as in Example 1 except that the temperature was maintained at 0 ° C. for 15 hours and then changed to 730 ° C. for 30 hours.

As a result of measuring the obtained lithium-containing composite oxide powder with a laser diffraction particle size distribution analyzer, it was found that S = between the particle size D and the half width S that occupy the largest ratio in the particle size distribution.
The relational expression of 1.7D was established.

A cylindrical lithium ion secondary battery was manufactured in the same manner as described in Example 1 except that such a positive electrode active material was used.

(Example 4) A bottom-body-separated type square sheath having the shape shown in FIG. 1C was prepared. This horn sheath
The content of the MgAl ₂ O ₄ spinel component is 98.0%, the content of the Si component is 410 ppm, and the content of the Ca component is 1100 ppm.
The amount of the Y component is 500 ppm, and the amount of the Zr component is 8100.
In ppm, the amount of the Hf component was 210 ppm. In addition,
The elements constituting the sheath were analyzed by the method described below.

The components (subcomponents) other than the MgAl ₂ O ₄ spinel contained in the sheath were analyzed by glow discharge mass spectrometry (GDMS: Glow Discharge Mass Spectrometry). The purity of the main component MgAl ₂ O ₄ spinel is
The calculation was made by setting the total constituent components of the sheath to 100% and subtracting the concentration of the subcomponent from 100%.

Using such a square sheath and setting the firing conditions to 5
10 at 480 ° C while flowing oxygen per minute
A lithium-containing composite oxide powder was synthesized in the same manner as described in Example 1 except that the temperature was changed to 700 ° C. for 15 hours after the holding.

As a result of measuring the obtained lithium-containing composite oxide powder with a laser diffraction particle size distribution analyzer, the particle diameter D which accounts for the maximum ratio in the particle size distribution was 6 μm. On the other hand, the half width S was 3 μm, a value corresponding to 0.5D. Therefore, the particle size distribution of the lithium-containing composite oxide powder satisfied the relationship of the above-described formula (I).

A cylindrical lithium ion secondary battery was manufactured in the same manner as described in Example 1 except that such a positive electrode active material was used.

(Comparative Example 1) A square sheath made of alumina (Al ₂ O ₃ ) was prepared from a bottom-body separated type having the shape shown in FIG. A lithium-containing composite oxide powder was synthesized in the same manner as described in Example 1 except that such a square sheath was used.

As a result of measuring the obtained lithium-containing composite oxide powder with a laser diffraction particle size distribution analyzer, it showed a broad particle size distribution ranging from submicron to several hundred μm as shown in FIG. Particle size is about 100μm
Giant particles were also present. In addition, the particle diameter D that accounts for the maximum ratio in the particle size distribution was 4.5 μm. On the other hand, the half width S was 13.5 μm, which was a value corresponding to 3D.
Therefore, the particle size distribution of the lithium-containing composite oxide powder deviated from the relationship of the above-described formula (I).

A cylindrical lithium ion secondary battery was manufactured in the same manner as described in Example 1 except that such a positive electrode active material was used.

Comparative Example 2 Fine particles and coarse particles of the lithium-containing composite oxide synthesized in Comparative Example 1 were classified to make the particle size distribution the same as in Example 1 described above. A cylindrical lithium ion secondary battery was manufactured in the same manner as described in Example 1 except that such a positive electrode active material was used.

About 20 obtained secondary batteries of Examples 1 to 4 and Comparative Examples 1 and 2 were prepared at 20 ° C.
Was measured, and the results are shown in Table 1 below. The charging was performed at a current value corresponding to the design rated capacity of 0.2 C up to 4.2 V, and then maintained at a constant voltage of 4.2 V for a total of 8 hours. Discharge was performed up to 2.7 V at the same current value.

Further, three secondary batteries were prepared for each of Examples 1 to 4 and Comparative Examples 1 and 2, and a charge / discharge cycle test was performed at room temperature. The average reduction rate of the discharge capacity after 500 cycles was determined. And the results are shown in Table 1 below. The charge / discharge cycle test was performed at a current value corresponding to the designed rated capacity of 0.5 C up to 4.2 V, and then maintained at a constant voltage of 4.2 V for a total of 5 hours. Discharge was performed up to 2.7 V at the same current value. There was a 30-minute pause between charging and discharging.

Further, with respect to the secondary batteries of Examples 1 to 4 and Comparative Examples 1 and 2, three batteries were prepared, and
After charging, safety was examined by a nail penetration test. The nail used in the test had a diameter of 2 mm and a nail speed of 135 mm / s.
The temperature rise of the battery in the nail penetration test was measured using a thermocouple attached to the outer surface of the battery. Table 1 below shows the presence or absence of rupture / ignition in the nail penetration test and the battery temperature in the nail penetration test.

[0109]

[Table 1]

As is clear from Table 1, the raw material powder was
Secondary of Examples 1 to 4 containing gO and lithium-containing composite oxide obtained by firing in a state of being accommodated in a sheath comprising a compound component composed of at least one kind selected from MgAl ₂ O ₄ group consisting spinel The battery has a higher initial capacity, a smaller capacity variation, and a shorter cycle life than the secondary batteries of Comparative Examples 1 and 2, which include the positive electrode active material synthesized using a sheath made of alumina (Al ₂ O ₃ ). It is long, the rate of temperature rise during the nail penetration test is low, and it can be seen that there is no rupture or ignition by the nail penetration test.

Example 5 LiOH.H as starting material
Oxide of ₂ O, Ni (OH) ₂ and element Me1 (Co),
Carbonate, nitrate, NaOH, KOH, Ca
(OH) ₂ and sodium sulfide (Na ₂
S.9H ₂ O) and sulfuric acid compound (NiSO ₄ .6H ₂ O)
If, oxides of Si, sulfide, alkoxide and an oxide of Fe, sulfide, prepared with alkoxide composition of these compounds powder _{Li 1.1 Ni 0.7 8 Co 0.22 O} 1.95 F
_0.05 + cC), and after mixing, mixed with a Henschel mixer for 30 minutes to obtain a mixed powder (raw material powder)
Was prepared. This mixed powder was accommodated in the same square sheath as that described in Example 1 described above, and four such square sheaths were set in an electric furnace as shown in FIG. 2 described above and fired.
Baking is performed at 480 while flowing oxygen at 5 L / min.
After holding at 10 ° C. for 10 hours, the reaction was performed at 700 ° C. for 15 hours to obtain a lithium-containing composite oxide powder. The type of the element C in the composition formula of the lithium-containing composite oxide and the content c (ppm) of the element C in the oxide are shown in Table 2 below.

As a result of measuring the obtained lithium-containing composite oxide powder with a laser diffraction particle size distribution analyzer, the particle diameter D which accounts for the maximum ratio in the particle size distribution was 5.0 μm. On the other hand, the half width S was 3.5 μm, which was a value corresponding to 0.7D. Therefore, the particle size distribution of the lithium-containing composite oxide powder satisfied the relationship of the above-described formula (I).

The composition of the positive electrode active material was analyzed by glow discharge mass spectrometry (GDMS: Glow Discharge Mass Spectrom).
etry). Here, GDMS is an Ar atmosphere of about 1 Torr, a voltage of several kV is applied to one electrode as a sample, the sample surface is sputtered by the formed glow discharge, and the generated sample ions are extracted from an aperture in the electrode. It is a method of mass spectrometry. The content of each element constituting the composite oxide was determined by the glow discharge mass spectrometry.
To obtain the desired chemical formula. The composition analysis of the positive electrode active material obtained in the following examples is also performed by glow discharge mass spectrometry.

A cylindrical lithium ion secondary battery was manufactured in the same manner as described in Example 1 except that such a positive electrode active material was used.

Examples 6 to 8 Except that the type of the element C in the composition of the lithium-containing composite oxide and the content c (ppm) of the element C in the oxide were changed as shown in Table 2 below, A lithium-containing composite oxide powder was obtained in the same manner as described in Example 5 described above.

A cylindrical lithium ion secondary battery was manufactured in the same manner as described in Example 1 except that such a positive electrode active material was used.

Example 9 LiOH.H was used as a starting material.
Oxide of ₂ O, Ni (OH) ₂ and element Me1 (Co),
Carbonate, nitrate, NaOH, KOH, Ca
(OH) ₂ and sodium sulfide (Na ₂
S.9H ₂ O) and sulfuric acid compound (NiSO ₄ .6H ₂ O)
If, oxides of Si, sulfide, alkoxide and an oxide of Fe, sulfide, prepared with alkoxide composition of these compounds powder _{Li 1.1 Ni 0.7 8 Co 0.22 O} 1.95 F
_0.05 + cC), and after mixing, mixed with a Henschel mixer for 30 minutes to obtain a mixed powder (raw material powder)
Was prepared. This mixed powder was accommodated in a square sheath similar to that described in Example 4 described above, and four such square sheaths were set in an electric furnace as shown in FIG. 2 described above and fired.
Baking is performed at 480 while flowing oxygen at 5 L / min.
After holding at 10 ° C. for 10 hours, the reaction was performed at 700 ° C. for 15 hours to obtain a lithium-containing composite oxide powder. The type of the element C in the composition formula of the lithium-containing composite oxide and the content c (ppm) of the element C in the oxide are shown in Table 2 below.

As a result of measuring the obtained lithium-containing composite oxide powder with a laser diffraction particle size distribution analyzer, the particle diameter D that accounts for the maximum ratio in the particle size distribution was 6.5 μm. On the other hand, the half width S was 3.3 μm, a value corresponding to 0.5D. Therefore, the particle size distribution of the lithium-containing composite oxide powder satisfied the relationship of the above-described formula (I).

A cylindrical lithium ion secondary battery was manufactured in the same manner as described in Example 1 except that such a positive electrode active material was used.

(Examples 10 to 12) The type of the element C in the composition of the lithium-containing composite oxide and the element C in the oxide
Was obtained in the same manner as described in Example 9 above, except that the content c (ppm) of was changed as shown in Table 2 below.

A cylindrical lithium ion secondary battery was manufactured in the same manner as described in Example 1 except that such a positive electrode active material was used.

For the obtained secondary batteries of Examples 5 to 12, the initial capacity, the average reduction rate of the discharge capacity after 500 cycles, the battery temperature in the nail penetration test, and the presence or absence of rupture and ignition during the nail penetration test were determined as described above. The measurement was performed in the same manner as described in Example 1 and the results are shown in Table 2 below. Table 2 also shows the results of Comparative Examples 1 and 2 described above.

[0123]

[Table 2]

As apparent from Table 2, Examples 5 to 12
Of the secondary batteries of Comparative Examples 1 and 2, the variation in the initial capacity is small, the discharge capacity decrease rate after 500 cycles is small, the temperature rise during the nail penetration test is suppressed, and the battery is ruptured. It turns out that there is no ignition.

[0125] The component of the horn sheath was changed to an amount of 9 MgO.
At 9.0%, the Al content is 520 ppm, the Si content is 350 ppm, the Ca content is 2000 ppm,
Component amount is 160ppm, Zr component amount is 1600ppm
A lithium-ion secondary battery was manufactured in the same manner as described in Example 1 except that the battery was changed to that described above. As a result, the same excellent battery characteristics and safety as in Example 1 were obtained. I was able to.

The components of the horn sheath were 99.0% of the MgAl ₂ O ₄ spinel component and 210 ppm of the Si component.
And the Ca component amount is 600 ppm and the Y component amount is 320 p.
pm, except that the Zr component amount was 2000 ppm and the Hf component amount was 160 ppm, except that the lithium ion secondary battery was manufactured in the same manner as described in Example 4 above. The same excellent battery characteristics and safety as in Example 4 could be obtained.

Example 13 <Preparation of Positive Electrode> 91% by weight of a lithium-containing composite oxide powder having the same composition as that described in Example 1 was added to 2.5% by weight of acetylene black, 3% by weight of graphite, 4% by weight of polyvinylidene fluoride (PVdF) and an N-methylpyrrolidone (NMP) solution were added and mixed to obtain a thickness of 15%.
The resultant was applied to a current collector of aluminum foil having a thickness of μm, dried, and pressed to produce a band-shaped positive electrode having an electrode density of 3.0 g / cm ³ .

<Preparation of Negative Electrode> 94% by weight of powder of mesophase pitch-based carbon fiber (average particle size 25 μm, average fiber length 30 μm) heat-treated at 3000 ° C., 6% by weight of polyvinylidene fluoride (PVdF), and N-methyl A pyrrolidone (NMP) solution was added and mixed, applied to a copper foil having a thickness of 12 μm, dried, and pressed to obtain an electrode density of 1.4.
A strip-shaped negative electrode of g / cm ³ was produced.

<Preparation of Electrode Group> The positive electrode, thickness 16 μm
With a porosity of 50% and an air permeability of 200 seconds / 100 cm
After laminating in order of the separator made of the polyethylene porous film of No. ^3, the negative electrode, and the separator, they were spirally wound. This was hot-pressed at 90 ° C. to produce a flat electrode group having a width of 30 mm and a thickness of 3.0 mm. The obtained electrode group was housed in a 0.1 mm-thick laminated film pack composed of an aluminum foil having a thickness of 40 μm and polypropylene layers formed on both sides of the aluminum foil. Vacuum drying was performed for hours.

<Preparation of non-aqueous electrolyte (liquid non-aqueous electrolyte)>
1.5 mol / L lithium tetrafluoroborate (LiBF ₄ ) as an electrolyte in a mixed solvent (volume ratio 24: 75: 1) of ethylene carbonate (EC), γ-butyrolactone (BL) and vinylene carbonate (VC) A non-aqueous electrolyte was prepared by dissolving.

After injecting the non-aqueous electrolyte into the laminate film pack containing the electrode group, the laminate film pack was completely sealed by heat sealing.
A thin lithium-ion secondary battery having the structure shown in FIGS. 6 and 7 described above and having a width of 35 mm, a thickness of 3.2 mm, and a height of 65 mm was manufactured.

Example 14 The same procedure as described in Example 13 was performed except that a lithium-containing composite oxide having the same composition as that described in Example 4 was used as the positive electrode active material. A thin lithium ion secondary battery was manufactured.

(Example 15) [0133] Except that a lithium-containing composite oxide having the same composition as that described in Example 5 was used as the positive electrode active material, the same procedure as described in Example 13 was performed. A thin lithium ion secondary battery was manufactured.

(Example 16) A lithium-containing composite oxide having the same composition as that described in Example 9 was used as the positive electrode active material in the same manner as described in Example 13 above. A thin lithium ion secondary battery was manufactured.

With respect to the obtained secondary batteries of Examples 13 to 16, the average reduction rate of the discharge capacity after 500 cycles, the battery temperature by the nail penetration test, and the presence or absence of rupture and ignition during the nail penetration test were determined by the above-described Examples. The measurement was performed in the same manner as described in Example 1, and the results are shown in Table 3 below.

[0136]

[Table 3]

As is clear from Table 3, even when the form of the secondary battery is changed from cylindrical to thin, as long as the positive electrode active material according to the present invention is used, excellent cycle characteristics and high safety can be obtained. I understand.

[0138]

As described above in detail, according to the present invention, it is possible to provide a lithium ion secondary battery having a small variation in discharge capacity, a long cycle life, and improved safety. Further, according to the present invention, there is provided a cathode active material and a sheath for synthesizing a lithium-containing composite oxide capable of realizing a battery having a small variation in discharge capacity, a long cycle life, and improved safety. be able to.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a sheath used when synthesizing a positive electrode active material according to the present invention.

FIG. 2 is a schematic perspective view showing an example of a firing step for synthesizing a positive electrode active material according to the present invention.

FIG. 3 is a schematic perspective view showing still another example of a firing step for synthesizing a positive electrode active material according to the present invention.

FIG. 4 is a characteristic diagram showing an example of a particle size distribution of a lithium-containing composite oxide powder.

FIG. 5 is a partially cutaway perspective view showing a cylindrical lithium ion secondary battery as an example of the lithium ion secondary battery according to the present invention.

FIG. 6 is a cross-sectional view showing a thin lithium ion secondary battery which is an example of the lithium ion secondary battery according to the present invention.

FIG. 7 is a sectional view showing a part A in FIG. 6;

FIG. 8 is a characteristic diagram showing a particle size distribution of a positive electrode active material in Example 1 and Comparative Example 1.

[Explanation of symbols]

 41: Bottom-body-integrated square sheath, 42: Bottom-body-integrated round sheath, 43, 45 ... Body, 44, 46 ... Bottom plate, 47 ... Raw material powder.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) CB09 CB12 DA00 DA09 EA12 EA14 GA02 GA27

Claims (5)

[Claims] 1. A lithium ion secondary battery comprising a positive electrode containing an active material, a negative electrode, and a non-aqueous electrolyte, wherein the active material of the positive electrode comprises a raw material powder of MgO and MgAl.
A lithium ion secondary battery comprising a lithium-containing composite oxide obtained by baking in a state of being housed in a sheath containing at least one compound component selected from the group consisting of ₂ O ₄ spinels. 2. The method according to claim 1, wherein the sheath contains MgO.
2. The lithium ion secondary battery according to claim 1, further comprising at least one component selected from the group consisting of 1, Si, Ca, Y and Zr. 3. When the sheath contains MgAl ₂ O ₄ spinel, the sheath further comprises at least one component selected from the group consisting of Si, Ca, Y, Zr and Hf. Item 7. The lithium ion secondary battery according to Item 1. 4. A lithium-containing composite oxide obtained by firing the raw material powder in a state of being housed in a sheath containing at least one compound component selected from the group consisting of MgO and MgAl ₂ O ₄ spinel. A positive electrode active material, characterized in that: 5. A sheath for synthesizing a lithium-containing composite oxide, comprising at least one compound component selected from the group consisting of MgO and MgAl ₂ O ₄ spinel.