JP2003022805A - Positive active material for lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive active material which reduces generation of gases in a lithium ion secondary battery and enhancing battery characteristics (cycle characteristics and heavy load characteristic) and thermal stability. SOLUTION: This positive active material for the lithium ion secondary battery is represented by the general formula Liv Co1-w-x Alw Mx Oy Sz (M is at least one selected from among Mg and Ba; 0.95<=v<=1.05; 0<w<=0.10; 0<x<=0.10; 1<=y<=2.5; and 0<z<=0.015).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode active material used in a lithium ion secondary battery, and in particular, it has little gas generation and is excellent in battery characteristics (cycle characteristics, high load characteristics) and thermal stability. It relates to a positive electrode active material.

[0002]

2. Description of the Related Art In recent years, lithium ion secondary batteries having a high energy density have been adopted as batteries incorporated in electronic equipment such as portable personal computers and video cameras.
This lithium ion secondary battery includes a positive electrode plate in which a positive electrode active material such as lithium cobalt composite oxide is held on a positive electrode current collector which is a support thereof, and a negative electrode active material such as lithium metal which is a negative electrode which is a support thereof. A negative electrode plate held by a current collector, Li
It is composed of a non-aqueous electrolytic solution composed of an organic solvent in which a lithium salt such as PF ₆ is dissolved, and a separator interposed between the positive electrode plate and the negative electrode plate to prevent a short circuit between both electrodes. Among them, the positive electrode plate, the negative electrode plate, and the separator formed into a thin sheet are wound, and the laminated battery housed in the battery case of the metal laminated resin film or the battery housed in the thin metal case has the same thickness as the conventional one. As compared with a battery housed in a metal case of a mold, there is a problem that the battery easily expands due to gas generation in the battery, heat generation, or external heating, and the battery pack case housing the battery also expands and deforms.

Conventionally, when LiCoO ₂ is used as the positive electrode active material of a lithium ion secondary battery, when the charging voltage is increased for the purpose of improving the discharge capacity, the crystals of the positive electrode active material are transferred or the positive electrode active material is decomposed. Then, oxygen from cobalt acid is released, and this oxygen oxidizes and decomposes the non-aqueous electrolyte solution, and as a result, gas is generated in the battery, which causes the above problem in a laminated battery or the like, and therefore a countermeasure is required.

Similarly, when the charging voltage was increased for the purpose of improving the discharge capacity, the battery characteristics (cycle characteristics, high load characteristics) and thermal stability were also deteriorated due to crystal transition or decomposition of the positive electrode active material. In addition, LiCoO _{2 as} a positive electrode active material has low conductivity, and therefore conductivity is improved by coating conductive carbon. However, when contact with carbon is poor, it causes cycle deterioration. It was

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and reduces gas generation of a lithium ion secondary battery to improve battery characteristics (cycle characteristics, high load characteristics) and thermal stability. It is an object to provide a positive electrode active material that can be improved.

[0006]

Means for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the present inventor has found that the general formula of Li _v Co as a positive electrode active material of a lithium ion secondary battery is
_1-w-x Al _w M _x O _y S _z (where M is Mg, Ba
At least one selected from 0.95 ≦ v ≦
1.05, 0 <w ≦ 0.10, 0 <x ≦ 0.10, 1 ≦
y ≦ 2.5 and 0 <z ≦ 0.015. It was found that the above problem can be solved by using the positive electrode active material represented by (4), and the present invention has been completed.

That is, the positive electrode active material for a lithium ion secondary battery of the present invention has a general formula of Li _v Co _1-w Al _w M
_x O _y S _z (where M is at least one selected from Mg and Ba, and 0.95 ≦ v ≦ 1.05, 0 <w ≦
0.10, 0 <x ≦ 0.10, 1 ≦ y ≦ 2.5, 0 <z
≦ 0.015. ), The amount of Li (v value) in the composition affects the discharge capacity and the high load capacity of the lithium ion secondary battery, and 0.95 ≦ v ≦
The range of 1.05 is preferable. Also, the amount of Al in the composition (w
Value), M content (x value) and S content (z value) have a great influence on the gas generation and battery characteristics (cycle characteristics, high load characteristics) of the lithium ion secondary battery, and 0 <w ≦ 0.10. , 0 <x
The range of ≦ 0.10, 0 <z ≦ 0.015 is preferable, and 0.0001 ≦ w ≦ 0.05, 0.0001 ≦ x ≦
The range of 0.05 and 0.003 ≦ z ≦ 0.009 is more preferable. The amount of O (y value) in the composition varies depending on the method of introducing the S element into the positive electrode active material and the like, and 1 ≦ y ≦
It is in the range of 2.5.

The positive electrode active material for a lithium ion secondary battery of the present invention is characterized by having a specific surface area of 0.2 to 2.0 m ² / g. The specific surface area of the positive electrode active material has a great influence on the gas generation of the lithium ion secondary battery, and particularly in the case of the positive electrode active material of the present invention represented by the above general formula, the specific surface area is 0.2 to 2.0 m ² / Gas generation can be significantly reduced in the range of g. More preferably 0.4 to 0.8
It is in the range of m ² / g.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The synthesis of the positive electrode active material for a lithium ion secondary battery of the present invention is carried out by the following method, as shown in the following: a lithium compound, a cobalt compound, an aluminum compound and Mg,
It is performed by firing a raw material mixture obtained by mixing sulfur or a sulfur compound with a compound containing at least one element of Ba, and then pulverizing the raw material mixture.

Lithium compound, cobalt compound, aluminum
A nickel compound and at least one of Mg and Ba
Compounds containing elements include oxides, hydroxides and carbonic acid
Use salts, nitrates, sulfates, acetates, oxalates, etc.
You can Preferably, as the lithium compound, Li
_TwoO, LiOH, Li_TwoCO_Three, LiHCO_Three, LiN
O_Three, Li_TwoSO_Four・ H_TwoO, Li (CH_ThreeCOO), L
i_TwoC_TwoO_FourAs a cobalt compound, Co_ThreeO_Four,
Co_TwoO_Three, Co (OH)_Two, CoCO_Three, Co (NO_Three)
_Two・ 6H_TwoO, CoC_TwoO_FourEtc. with aluminum compounds
And then Al_TwoO _Three, Al (OH)_Three, Al (NO_Three)_Three・ 9
H_TwoO, Al (CH_ThreeCOO)_ThreeEtc. Of Mg, Ba
As a compound containing at least one element, MgO, M
g (OH) _Two, MgCO_Three, Mg (NO_Three)_Two・ 6H_TwoO,
MgC_TwoO_Four・ 2H_TwoO, BaO, Ba (OH)_Two・ 8H
_TwoO, BaCO_Three, Ba (NO_Three)_Two, BaC_TwoO_Four・ H
_TwoO etc. can be used.

Sulfur compounds include oxides, sulfides and sulfur compounds.
Acid salt, hydrogen sulfate, pyrosulfate, sulfite, peroxo
It is possible to use sulfates, thiosulfates, alkyl sulfates, etc.
it can. Preferably, (NH_Four)_TwoS, Li_TwoSO_Four・
H_TwoO, CoSO_Four, (NH _Four)_TwoSO_Four, (NH_Four)_Two
S_TwoO₈Etc. can be used.

The raw materials in powder form may be mixed as they are, or may be mixed in the form of a slurry using water or an organic solvent. The slurry-like mixture is dried to obtain a raw material mixture.

The raw material mixture thus obtained is fired in the air or in a weakly oxidizing atmosphere in the temperature range of 500 to 1000 ° C. for 1 to 24 hours. Preferably 800-100
Baking at a temperature range of 0 ° C. for 6 to 12 hours. Firing temperature is 5
When the temperature is lower than 00 ° C, unreacted raw materials remain in the positive electrode active material, and the original characteristics of the positive electrode active material cannot be utilized. Conversely, 1000
If the temperature exceeds ℃, the particle size of the positive electrode active material becomes too large and the battery characteristics deteriorate. If the firing time is less than 1 hour, the diffusion reaction between the raw material particles does not proceed, and after 24 hours, the diffusion reaction is almost completed. Therefore, it is not necessary to further fire.

The calcined product obtained by the above calcining is pulverized by using a raider to give a specific surface area of 0.2 to 2.0 m ² /
g, the positive electrode active material of the present invention having an average particle size of 1.0 to 12.0 μm is obtained.

In the lithium ion secondary battery using the positive electrode active material of the present invention, the oxidative decomposition reaction of the electrolytic solution is suppressed and the amount of gas generated in the battery is reduced. The characteristics (cycle characteristics, high load characteristics) and thermal stability are also improved.

Next, the results of measuring a gas generation, battery characteristics (cycle characteristics, high load characteristics) and thermal stability by producing a lithium ion secondary battery using the positive electrode active material of the present invention will be described.

(Production of Lithium Ion Secondary Battery) 90 parts by weight of a positive electrode active material powder, a conductive agent (for example, graphite such as natural graphite, flake graphite, artificial graphite, expanded graphite, acetylene black, Ketjen black, 5 parts by weight of carbon black such as channel black, furnace black, lamp black, thermal black and the like, or conductive fibers such as carbon fiber and metal fiber are used alone or in combination, and 5 parts by weight of polyvinylidene fluoride. And kneading to prepare a paste, which is applied to the positive electrode current collector,
It is dried to obtain a positive electrode plate. Further, carbon (for example, natural graphite, artificial graphite, non-graphite carbon, etc.) is used for the negative electrode, a porous propylene film is used for the separator, and LiPF is used as an electrolytic solution in a mixed solvent of ethylene carbonate: diethyl carbonate = 1: 1 (volume ratio). _A lithium ion secondary battery is produced using a solution in which ₆ is dissolved at a concentration of 1 mol / l. Here, a positive electrode plate, a negative electrode plate, and a separator, which are formed into a thin sheet shape, are wound, and a laminated battery housed in a battery case of a metal laminated resin film is manufactured.

(Evaluation of Gas Generation) The general formula is LiCo
_0.989Al_0.01Mg_0.001O_TwoS_z, Li
Co _0.99Al_0.01O_TwoS_z, LiCo
_0.999Mg_0.001O_TwoS_zAnd LiCoO_TwoS
_zLaminated battery using various positive electrode active materials represented by
Created and charged at constant current up to 4.2V with a charging load of 0.5C
Then, store at 80 ° C for 2 days to expand the battery due to gas generation.
Calculate the rate (%) from the following formula (where 1C is 1 hour
It is a current load that ends charging or discharging.) Expansion coefficient of battery = {(battery thickness after storage at 80 ° C-before measurement
Thickness of battery) / thickness of battery before measurement} × 100

FIG. 1 shows the amount of S (z value) in the positive electrode active material.
And the expansion coefficient of the battery is shown. As is clear from this figure, the positive electrode active material of the present invention LiCo _0.989 Al
The expansion coefficient of the battery using _0.01 Mg _0.001 O ₂ S _z (1a) is low in the range of z value 0 <z ≦ 0.015,
Particularly, it is extremely low in the range of 0.003 ≦ z ≦ 0.009, and it can be seen that the amount of gas generated in the battery is reduced. In addition, the positive electrode active material LiC containing no Mg element
o _0.99 Al _0.01 O ₂ S _z (1b), positive electrode active material containing no Al element LiCo _0.999 Mg
_It can be seen that the expansion coefficient is extremely low as compared with the battery using _0.001 O ₂ S _z (1c) and the positive electrode active material LiCoO ₂ S _z (1d) that does not contain both Mg element and Al element. Thus, in the positive electrode active material, Al element, Mg element,
By including all three types of S elements, the coefficient of expansion of the battery is greatly reduced.

Next, various positive electrode active materials having different specific surface areas
Laminated battery is manufactured using
Calculate (%). In FIG. 2, the general formula is LiCo_0.989
Al _0.01Mg_0.001O_TwoS_0.005Represented by
2 shows the relationship between the specific surface area of the positive electrode active material and the expansion coefficient of the battery.
As is clear from this figure, the positive electrode active material of the present invention was used.
The expansion rate of the battery has a specific surface area of 2.0 m^TwoLess than / g
None, especially 0.8 m^Two/ G or less is very low
It can be seen that the amount of gas generated in the battery is reduced.
It Specific surface area is 2.0m^Two/ G, the positive electrode
Oxidative decomposition reaction of the electrolyte that occurs on or near the surface of the active material
Reaction, which increases the amount of gas generated in the battery.
It is expected to increase. Specific surface area is 0.2m^Two/ G
If it is too small, the particle size of the positive electrode active material will become too large and
The specific surface area is 0.2-2.0 m because the characteristics are deteriorated.^Two/
The range of g is preferable, and 0.4 to 0.8 m^TwoThe range of / g
More preferable.

(Evaluation of cycle characteristics) The general formula is LiCo.
_0.999-w Al _w Mg _0.001 O
₂ S _0.005 , LiCo _1-w Al _w O ₂ S
_0.005 , LiCo _0.999-w Al _w Mg _0.
Laminated batteries were made using various positive electrode active materials represented by ₀₀₁ O ₂ and LiCo _1-w Al _w O ₂ , and were charged at a constant current at room temperature (25 ° C.) with a charging load of 0.5 C to 4.2 V. After that, charge and discharge to discharge to 2.75V at 1.0C is 5
After carrying out 00 cycles, the capacity retention rate (%) at the 500th cycle is obtained from the following formula. Capacity retention rate = (500th cycle discharge capacity / first cycle discharge capacity) × 100

FIG. 3 shows the amount of Al (w in the positive electrode active material).
Value) and capacity retention rate. According to FIG.
Very active material LiCo_0.999-wAl_wMg_0.001
O_TwoS _0.005Capacity retention rate of battery using (3a)
Has a high w value in the range of 0 <w ≦ 0.05, and is particularly 0.0
It is extremely high in the range of 001 ≦ w ≦ 0.05.
I understand. In addition, the positive electrode active material L containing no Mg element
iCo_1-wAl_wO_TwoS _0.005(3b), S element
-Free positive electrode active material LiCo_0.999-wAl_w
Mg_0.001O_Two(3c) and Mg element and S element together
Positive electrode active material not containing LiCo_1-wAl_wO_Two(3
The capacity retention rate is much higher than that of the battery using d).
I understand. Thus, in the positive electrode active material, Al element, M
By including all three elements of g element and S element
Thus, the cycle characteristics of the battery are greatly improved.

(Evaluation of high load characteristics) The general formula is LiCo.
_0.99-xAl_0.01Mg_xO_TwoS_0.005, L
iCo_1-xMg_xO_TwoS_0.005, LiCo
_0.99-xAl_0.01Mg_xO _TwoAnd LiCo
_1-xMg_xO_TwoUsing various positive electrode active materials represented by
Produce a laminated battery, 4.2V at a charging load of 2.0C
After constant current charging up to, discharged at 2.0C to 2.75V
The discharge capacity at this time was calculated as the high load capacity (mAh / g)
It

FIG. 4 shows the amount of Mg (x
Value) and high load capacity. From FIG. 4, the positive electrode active material of the present invention LiCo _0.99-x Al _0.01 Mg _x O ₂
S _0. The high load capacity of the battery using ₀₀₅ (4a) is x
Values are high in the range of 0 <x ≦ 0.10, especially 0.0001
It can be seen that the value is extremely high in the range of ≦ x ≦ 0.05. In addition, the positive electrode active material LiCo containing no Al element
_{1-x Mg x O 2 S} 0. ₀₀₅ (4b), positive electrode active material LiCo _0.99-x Al _{0. 01} M
It can be seen that the high load capacity is much higher than that of the battery using g _x O ₂ (4c) and the positive electrode active material LiCo _1-x Mg _x O ₂ (4d) that does not contain both Al element and S element. Thus, in the positive electrode active material, Al element, Mg element,
By including all three types of S elements, the high load characteristics of the battery are greatly improved.

As described above, by including all three elements of Al element, Mg element, and S element in the positive electrode active material, the crystal transition or decomposition of the positive electrode active material is further suppressed as a synergistic effect. The expansion coefficient of the battery is significantly reduced, and the battery characteristics (cycle characteristics, high load characteristics) are greatly improved.

Similarly, the general formula is Li _v Co _0.989 A
l _0.01 Mg _0.001 O ₂ S _{0 .} Laminated batteries are manufactured using various positive electrode active materials represented by ₀₀₅ , and high load capacity (mAh / g) is determined. FIG. 5 shows the relationship between the amount of Li (v value) in the positive electrode active material and the high load capacity. From this figure, it can be seen that the high load capacity decreases as the v value becomes larger than 1.05.

FIG. 6 shows the relationship between the Li amount (v value) in the positive electrode active material and the discharge capacity when discharged at a normal current density (0.25 C). From this figure, it can be seen that the discharge capacity decreases when the v value becomes smaller than 0.95.

Therefore, considering both the high load capacity and the discharge capacity under normal conditions, it is necessary to set the v value within the range of 0.95≤v≤1.05.

Examples of the present invention will be described below, but it goes without saying that the present invention is not limited to specific examples.

[0030]

EXAMPLES Example 1 Lithium carbonate (Li ₂ C
O ₃ ), cobalt trioxide (Co ₃ O ₄ ), aluminum oxide (Al ₂ O ₃ ), magnesium carbonate (MgC
O ₃ ), lithium sulfate (Li ₂ SO ₄ .H ₂ O), v
= 1.0, w = 0.01, x = 0.001, z = 0.0
Weigh to 05 and dry mix. The obtained raw material mixture was fired in air at 900 ° C. for 10 hours and then pulverized using a raider to give a specific surface area of 0.62 m ² /
positive electrode active material powder LiCo having an average particle size of 3.5 μm
_0.989 Al _{0 . 01} Mg _0.001 O ₂ S
We get _0.005 .

The specific surface area is measured by a constant pressure BET one-point method using nitrogen gas adsorption. The average particle diameter is obtained by measuring the specific surface area by the air permeation method and determining the average value of the particle diameter of primary particles, and is measured using a Fisher subsieve sizer (FSSS). The composition analysis is measured by the following method. That is, Li is a flame photometric method,
Co is measured by a titration method, and Al, Mg, Ba and S are measured by ICP emission spectroscopy.

Example 2 The specific surface area is 0.62 m ² / g in the same manner as in Example 1 except that w = 0.001.
Positive electrode active material powder LiCo having an average particle size of 3.5 μm
_{0.998 Al 0.00 1 Mg 0.001 O 2} S
We get _0.005 .

Example 3 A positive electrode active material powder LiCo having a specific surface area of 0.62 m ² / g and an average particle size of 3.5 μm was prepared in the same manner as in Example 1 except that w = 0.05.
_0.949 Al _0.05 Mg _0.001 O ₂ S
We get _0.005 .

[Example 4] The specific surface area was 0.64 m ² / g in the same manner as in Example 1 except that x = 0.005.
Positive electrode active material powder LiCo having an average particle size of 3.3 μm
_0.985 Al _0.01 Mg _0.005 O ₂ S
We get _0.005 .

[Embodiment 5] Except that x = 0.01
Similar to Example 1, specific surface area is 0.65 m^Two/ G, flat
Positive electrode active material powder LiCo having a uniform particle size of 3.3 μm_0.98
Al_0.01Mg _0.01O_TwoS_0.005To get

Example 6 The specific surface area is 0.63 m ² / g in the same manner as in Example 1 except that z = 0.003.
Positive electrode active material powder LiCo having an average particle size of 3.5 μm
_0.989 Al _0.01 Mg _0.001 O ₂ S
We get _0.003 .

[Embodiment 7] The specific surface area is 0.64 m ² / g in the same manner as in Embodiment 1 except that z = 0.09.
Positive electrode active material powder LiCo having an average particle size of 3.4 μm
_0.989 Al _0.01 Mg _0.001 O ₂ S
We get _0.009 .

Example 8 The specific surface area is 0.64 m ² / g in the same manner as in Example 1 except that z = 0.0012.
Positive electrode active material powder LiCo having an average particle size of 3.4 μm
_0.989 Al _0.01 Mg _0.001 O ₂ S
_0.012 is obtained.

[Embodiment 9] A specific surface area of 0.65 m ² / g was obtained in the same manner as in Embodiment 1 except that z = 0.015.
Positive electrode active material powder LiCo having an average particle size of 3.4 μm
_0.989 Al _0.01 Mg _0.001 O ₂ S
To obtain _0.015 .

[Example 10] Aluminum oxide (Al_Two
O_Three) Instead of aluminum hydroxide (Al (OH) _Three)
In the same manner as in Example 1 except that
0.63m^Two/ G, positive electrode active material with an average particle size of 3.5 μm
Powder LiCo_0.989Al_0.01Mg_{0. 001}O
_TwoS_0.005To get

Example 11 Aluminum oxide (Al_Two
O_Three) Instead of aluminum nitrate (Al (NO_Three) _Three・
9H_TwoO) was used in the same manner as in Example 1, except that
Surface area is 0.63m ^Two/ G, average particle size 3.5μm positive
Extremely active material powder LiCo_0.989Al_{0.0 1}Mg
_0.001O_TwoS_0.005To get

Example 12 Aluminum oxide (Al ₂
Instead of O ₃ ), aluminum acetate (Al (CH ₃ CO
O) ₃ ) except that the positive electrode active material powder LiCo _0.989 Al _0.01 Mg having a specific surface area of 0.64 m ² / g and an average particle diameter of 3.4 μm was prepared in the same manner as in Example 1.
_0.001 O ₂ S _0.005 is obtained.

Example 13 Lithium Sulfate (Li ₂ SO
Positive electrode active material powder LiCo having a specific surface area of 0.64 m ² / g and an average particle diameter of 3.4 μm in the same manner as in Example 1 except that sulfur (S) is used instead of ₄ · H ₂ O).
_0.989 Al _0.01 Mg _0.001 O ₂ S _{0.0
Get 05} .

Example 14 Lithium Sulfate (Li_TwoSO
_Four・ H_TwoO) instead of ammonium sulfide ((NH _Four)
_TwoThe specific surface is the same as in Example 1 except that S) is used.
Product is 0.63m^Two/ G, positive electrode active material with an average particle size of 3.5 μm
Substance powder LiCo_0.989Al_0.01Mg
_0.001O_TwoS_0.005To get

Example 15 Lithium Sulfate (Li ₂ SO
But using ammonium peroxodisulfate in place of _{4 · H 2 O) ((} NH 4) 2 S 2 O 8) in the same manner as in Example 1, a specific surface area of 0.63 m ² / g, average particle size 3.5 μm positive electrode active material powder LiCo _{0.9 89} Al
_0.01 Mg _0.001 O ₂ S _0.005 is obtained.

[Example 16] Magnesium carbonate (MgC)
O_Three) Instead of barium carbonate (BaCO_Three)
The specific surface area is 0.64 m in the same manner as in Example 1 except that
^Two/ G, positive electrode active material powder LiC having an average particle size of 3.4 μm
o_0.989Ba_0.01Mg_0.001O _TwoS
_0.005To get

[Comparative Example 1] Aluminum oxide (Al_TwoO
_Three), Magnesium carbonate (MgCO_Three), Lithium sulfate
(Li_TwoSO_Four・ H_TwoExample 1 except that O) is not used
The specific surface area is 0.61m^Two/ G, average particle size
Positive electrode active material powder LiCoO 3 having a particle size of 3.6 μm _TwoTo get

[Comparative Example 2] Magnesium carbonate (MgCO)
₃ ) and a specific surface area of 0.61 in the same manner as in Example 1 except that lithium sulfate (Li ₂ SO ₄ .H ₂ O) is not used.
m ² / g, positive electrode active material powder Li having an average particle size of 3.6 μm
Co _0.99 Al _0.01 O ₂ is obtained.

Comparative Example 3 Aluminum oxide (Al ₂ O
₃ ) and a specific surface area of 0.61 in the same manner as in Example 1 except that lithium sulfate (Li ₂ SO ₄ .H ₂ O) is not used.
m ² / g, positive electrode active material powder Li having an average particle size of 3.6 μm
Co _0.999 Mg _0.001 O ₂ is obtained.

[Comparative Example 4] Aluminum oxide (Al ₂ O
₃ ) and magnesium carbonate (MgCO ₃ ) in the same manner as in Example 1 except that the specific surface area is 0.61 m ² /
g, positive electrode active material powder LiCoO 2 having an average particle size of 3.6 μm
₂ S _0.005 is obtained.

[Comparative Example 5] Lithium sulfate (Li ₂ SO ₄
.H ₂ O) in the same manner as in Example 1 except that
Positive electrode active material powder LiCo _0.989 Al _0.01 Mg having a specific surface area of 0.61 m ² / g and an average particle diameter of 3.6 μm
_0.001 O ₂ is obtained.

Comparative Example 6 Magnesium carbonate (MgCO
_Three) Was used in the same manner as in Example 1 except that
Product is 0.61m^Two/ G, positive electrode active material with an average particle size of 3.6 μm
Substance powder LiCo _0.99Al_0.01O_TwoS
_0.005To get

[Comparative Example 7] Aluminum oxide (Al_TwoO
_Three) Was used in the same manner as in Example 1 except that
Product is 0.61m^Two/ G, positive electrode active material with an average particle size of 3.6 μm
Substance powder LiCo _0.999Mg_0.001O_TwoS
_0.005To get

(Evaluation) Examples 1 to 16 and Comparative Examples 1 to 7
Table 1 shows the results of measurements of gas generation, battery characteristics (cycle characteristics, high load characteristics), and thermal stability of a laminated battery prepared using the positive electrode active material powder obtained in the above. The expansion coefficient, capacity retention rate at room temperature (25 ° C.) and high load capacity of the battery are measured in the same manner as above. The capacity retention rate at high temperature (60 ° C.) is measured in the same manner as the capacity retention rate at room temperature (25 ° C.) except that it is measured in a 60 ° C. high temperature tank. Regarding the thermal stability, differential scanning calorimetry is performed as follows, and the heat generation start temperature is evaluated.

(Evaluation of Thermal Stability) 90 parts by weight of the positive electrode active material powder, 5 parts by weight of carbon as a conductive agent, and 5 parts by weight of polyvinylidene fluoride were kneaded to prepare a paste, and the paste was unipolarly evaluated. It is applied to a possible demantable cell positive electrode current collector, and ethylene carbonate is used as an electrolytic solution to prepare a secondary battery. After charging and discharging with a constant current and acclimatizing, the battery is charged with a constant current until the battery voltage becomes 4.3V. After charging, the positive electrode is taken out from the secondary battery, washed and dried to scrape off the positive electrode active material. 5 mg of the positive electrode active material scraped off from the positive electrode and 2 mg of ethylene carbonate are put into an Al cell, and a differential scanning calorimetric analysis is performed to determine the heat generation start temperature.

The differential scanning calorimetry is a method of analyzing the thermal characteristics of the sample substance by measuring the temperature difference between the reference substance and the sample while heating them simultaneously at a constant rate, and analyzing the thermal characteristics of the sample substance. When the substance is measured, the differential scanning calorific value does not change in the low temperature part, but the differential scanning calorific value greatly increases at a certain temperature or higher. The temperature at this time is taken as the heat generation start temperature, and it can be said that the higher this temperature, the better the thermal stability.

From Table 1, as compared with Comparative Examples 1 to 7, Example 1
Nos. 15 to 15 include all three elements of Al element, Mg element, and S element in the positive electrode active material, so that the expansion coefficient of the battery is reduced, the capacity maintenance ratio and the high load capacity are high, and the battery characteristics (cycle characteristics , High load characteristics) are excellent.
Regarding the cycle characteristics, not only the cycle characteristics at room temperature (25 ° C.) but also the cycle characteristics at high temperature (60 ° C.) are excellent, and it can be seen that excellent battery characteristics are exhibited even when the operating environment of the battery is high. Further, it can be seen that the heat generation start temperature is higher than that of the comparative example, and the thermal stability is also excellent. For example, A
Comparative Example 1 containing none of three kinds of elements, ie, 1 element, Mg element, and S element, Comparative Examples 2 to 4 containing only one kind of element,
Compared with Comparative Examples 5 to 7 containing two kinds of elements, in the case of Example 1 containing all three kinds of elements, the expansion coefficient of the battery was low, and the capacity maintenance ratio and the high load capacity were high. Further, the heat generation start temperature is also high. As described above, by including all three elements of Al element, Mg element, and S element in the positive electrode active material, the crystal transition or decomposition of the positive electrode active material is further suppressed as a synergistic effect. The generation is remarkably reduced, and the battery characteristics (cycle characteristics, high load characteristics) and thermal stability are greatly improved.

[0058]

[Table 1]

[0059]

As a positive electrode active material of a lithium ion secondary battery, the general formula is Li _v Co _1-w-x Al _w M _x O _y S _z.
(However, M is at least one selected from Mg and Ba, and 0.95 ≦ v ≦ 1.05, 0 <w ≦ 0.10, 0
<X ≦ 0.10, 1 ≦ y ≦ 2.5, 0 <z ≦ 0.015
Is. By using the positive electrode active material represented by
Gas generation in the battery is reduced and battery characteristics (cycle characteristics,
It is possible to improve high load characteristics) and thermal stability.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing the relationship between the amount of S (z value) in a positive electrode active material and the expansion coefficient of a battery.

FIG. 2 is a characteristic diagram showing the relationship between the specific surface area of the positive electrode active material and the expansion coefficient of the battery.

FIG. 3 is a characteristic diagram showing the relationship between the amount of Al (w value) in the positive electrode active material and the capacity retention rate.

FIG. 4 is a characteristic diagram showing the relationship between the amount of Mg (x value) in the positive electrode active material and the high load capacity.

FIG. 5 is a characteristic diagram showing the relationship between the amount of Li (v value) in the positive electrode active material and the high load capacity.

FIG. 6 is a characteristic diagram showing the relationship between the amount of Li (v value) in the positive electrode active material and the discharge capacity.

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 4G048 AA04 AA05 AA07 AB05 AC06                       AD04 AE05                 5H029 AJ01 AJ05 AK03 AL06 AL07                       AM03 AM05 AM07 EJ04 EJ12                       HJ02 HJ07                 5H050 AA01 AA08 BA17 CA08 CB07                       CB08 EA02 EA09 EA10 HA02                       HA07

Claims (2)

[Claims] 1. The general formula is Li _v Co _1-w-x Al _w M.
_x O _y S _z (where M is at least one selected from Mg and Ba, and 0.95 ≦ v ≦ 1.05, 0 <w ≦
0.10, 0 <x ≦ 0.10, 1 ≦ y ≦ 2.5, 0 <z
≦ 0.015. ) A positive electrode active material for a lithium ion secondary battery, characterized in that 2. The positive electrode active material for a lithium ion secondary battery according to claim 1, which has a specific surface area of 0.2 to 2.0 m ² / g.