JPH1116573A - Lithium cobalt double oxide for lithium ion secondary battery and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the capacity keeping performance at high temperature by specifying the X-ray diffraction pattern ratio of plane (101) to plane (003) in hexagonal system and lattice constants thereof, and the half-value width and crystal element diameter of plane (003). SOLUTION: This lithium cobalt double oxide has a ratio I(101)/I(003) of 0.200-0.350 when the intensity in X-ray diffraction pattern of plane (101) in hexagonal system is I(101), and the intensity in X-ray diffraction pattern of plane (003) is I(003). The lattice constants (a) and (c) thereof are taken as 2.8/30-2.8/60 Å and 14.040-14.060 Å, respectively. The half-value width of the X-ray diffraction pattern of plane (003) is 0.160 or less, and the crystal element diameter determined from the X-ray diffraction pattern of plane (003) is 700.0 Åor more. Thus, a double oxide for secondary battery having a volume of unit cell of 0.09600-0.09650 nm<3> can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium-cobalt double oxide used as a positive electrode active material in a lithium ion secondary battery and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, with the spread of portable devices such as portable telephones and notebook personal computers, there is a strong demand for the development of small, lightweight, high capacity secondary batteries having a high energy density. As such a device, there is a lithium ion secondary battery, and research and development thereof have been actively conducted.

A lithium ion secondary battery uses a lithium-cobalt double oxide (LiCoO ₂ ) as a positive electrode active material and lithium, a lithium alloy, carbon fiber, carbon such as graphite as a negative electrode, and obtains a high voltage of 4V class. Therefore, it is expected as a battery having a high energy density, and its practical use is progressing. Many results have already been reported in the development of lithium ion secondary batteries having excellent cycle characteristics and electron conductivity.

In order to produce a lithium cobalt double oxide used as a positive electrode active material in such a lithium ion secondary battery, for example, lithium carbonate (Li ₂ CO ₃ ) powder and cobalt oxide (Co ₃ O ₄ ) powder A method of weighing the mixture, adding a binder to the lithium carbonate powder and the cobalt oxide powder by a mixing granulator to prepare a granulated product, and firing the granulated product in an oxygen-containing atmosphere is known. I have.

By the way, when considering actual use, the power consumption of portable equipment tends to increase as the capacity of the battery increases, and the battery is constantly at a high temperature (about 60 ° C.). Therefore, the deterioration characteristics of the discharge capacity at such a high temperature, that is, the high-temperature storage characteristics of the battery are important in actual use.

[0006] However, the lithium-cobalt double oxide produced by the above method cannot supply a lithium-ion secondary battery having excellent high-temperature storage characteristics.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium-cobalt double oxide capable of supplying a lithium-ion secondary battery having excellent high-temperature storage characteristics, and a method for producing the same. It is in.

The present inventor has made intensive studies to solve the above problems. That is, in order to find out the cause of the difference in the capacity deterioration rate of the battery, various lithium-cobalt double oxides were repeatedly synthesized, XRD measurement was performed, and the battery was manufactured and the capacity deterioration rate was measured. Furthermore, the obtained diffraction pattern was examined in detail using Rietveld analysis. As a result, they found that there was a correlation between the crystal structure of the lithium-cobalt double oxide, that is, the X-ray diffraction pattern and the capacity deterioration rate, and reached the lithium-cobalt double oxide of the present invention.

Further, in order to supply a lithium ion secondary battery having a low capacity deterioration rate, that is, to produce a lithium-cobalt double oxide having a desired crystal structure,
It has been found that the particle size of the lithium carbonate powder and the cobalt oxide powder, which are the raw material powders, the mixing ratio of the two powders, and the sintering conditions of the granulated material are important factors.

[0010]

The lithium-cobalt double oxide for a lithium ion secondary battery according to the present invention comprises (a) the intensity I (101) of the X-ray diffraction pattern of the (101) plane in the hexagonal system.
And the ratio I (101) / I (003) of the intensity (I) of the X-ray diffraction pattern of the (003) plane is 0.200 to 0.350.
Lattice constants a and c are respectively 2.8130 to 2.81
(C) the half-width of the X-ray diffraction pattern of the (003) plane is 0.160 ° or less, and (d) the (00)
3) The crystallite diameter determined from the X-ray diffraction pattern of the plane is 700.0
Angstrom or more.

The method for producing a lithium-cobalt double oxide for a lithium-ion secondary battery according to the present invention is a method for producing the lithium-cobalt double oxide for a lithium-ion secondary battery according to the present invention. (1) The lithium carbonate powder has an average particle size of 10 μm or less and a specific surface area of 1.0 m ² / g or more. (2) The cobalt oxide powder has a specific surface area of 1.0 to 3 μm. assume the .5m ² / g, (3) lithium carbonate acid powder and oxidizing the cobalt powder, Li / Co molar ratio of from 0.980 to 1.00
5 and weighed (4)
It is carried out at 0 ° C. for 5 to 20 hours.

[0012]

Embodiments of the present invention will be described below.

(1) Lithium Cobalt Double Oxide for Lithium Ion Secondary Battery As a characteristic representing the crystal structure of lithium cobalt double oxide for a lithium ion secondary battery, in the present invention, (a) (101) in hexagonal system X-ray diffraction pattern intensity I (101)
And the intensity I (003) of the X-ray diffraction pattern of the (003) plane, I (101) / I (003), (b) lattice constants a and c,
(C) The half width of the X-ray diffraction pattern of the (003) plane and (d) the crystallite diameter determined from the X-ray diffraction pattern of the (003) plane were taken up. If the lithium-cobalt double oxide does not satisfy any of the above characteristic value ranges, a battery having an excellent capacity deterioration rate cannot be obtained.

The crystal system of the lithium-cobalt double oxide of the present invention is a hexagonal system. The hexagonal plane index is 4
Generally written as (hkil) by book axis. However, h +
Since there is a relationship k = −i, in this specification,
Write (hkl).

(A) X-ray diffraction pattern intensity ratio I (101) / I
(003) The intensity ratio (I (101) / I (003)) between the (101) plane X-ray diffraction pattern and the (003) plane X-ray diffraction pattern is 0.200.
０．３0.350, preferably 0.220 to 0.300
It is. This is because when the intensity ratio is in the above range, a
This is probably because the crystal structure formed by crystal growth in the axial and c-axis directions is more stable at the time of charging (Li is desorbed). The intensity ratio is less than 0.200 or 0.3
If it exceeds 50, the capacity degradation at high temperatures becomes large.

(B) Lattice constants a and c The lattice constant a is 2.8130 to 2.8160 angstroms, and the lattice constant c is 14.40 to 14.060.
In the case of angstrom, the capacity deterioration rate is low.
Outside of these ranges, the capacity deterioration rate deteriorates.

(C) Half-width of X-ray diffraction pattern of (003) plane When the half-width of X-ray diffraction pattern of (003) plane is 0.160 ° or less, the capacity deterioration rate is low. If it exceeds 0.160 °, the capacity deterioration rate will deteriorate.

(D) The crystallite diameter determined from the X-ray diffraction pattern of the (003) plane The crystallite diameter determined from the X-ray diffraction pattern of the (003) plane is 70
When it is 0.0 Å or more, the capacity deterioration rate is low. If the crystallite diameter is less than 700.0 angstroms and the crystal growth in the c-axis direction is poor, the capacity deterioration rate will deteriorate and good cycle characteristics will not be obtained.

Incidentally, the crystallite diameter (ε) was determined by [Equation 1].

[0020]

(Equation 1)

Here, λ is the wavelength (angstrom) of the CuKα ray, β is (integrated intensity) / (peak intensity) of the (003) plane, and θ is the Bragg angle (°) of the diffraction line.

(E) Volume of the unit cell The volume of the unit cell of the lithium-cobalt double oxide is 0.096.
It is preferable that the 00~0.09650nm ^3. Although the reason for this is not clear, it is considered that when the volume is within the above range, the reversibility of the crystal structure during charge / discharge is improved, and the cycle characteristics are improved.

The unit cell volume (V) was determined by [Equation 2].

[0024]

(Equation 2)

Here, a and c are lattice constants (angstrom).

When the lithium-cobalt double oxide of the present invention is used as an active material of a lithium secondary battery, a battery having high high-temperature storage performance can be obtained.

(2) Method for producing lithium-cobalt double oxide for lithium ion secondary battery (a) Raw material In the production method according to the present invention, the average particle diameter is 10 μm or less and the specific surface area is 1.0 m ² / g or more. Use lithium carbonate powder. When the raw material lithium carbonate particles are coarse, variation in the Li / Co molar ratio (variation in composition) of the lithium-cobalt double oxide occurs, so that the capacity deterioration rate deteriorates.

Also, the specific surface area is 1.0 to 3.5 m ² / g
Using cobalt oxide powder. If the specific surface area of the raw material cobalt oxide powder is smaller than 1.0 m ² / g and the particles are coarse, abrasion of stirring blades and balls of a ball mill is likely to occur in the subsequent mixing / granulation process. On the other hand, 3.5 m ² /
If the particle size is larger than g and the particles are fine, a lithium-cobalt double oxide which has a large particle size, has good handling properties, and stabilizes the capacity deterioration rate of the battery at a low level cannot be obtained.

(B) Weighing Lithium carbonate and cobalt oxide are weighed such that the Li / Co molar ratio is 0.980 to 1.005. Outside this range, the lithium / cobalt double oxide Li / Co
A deviation (composition deviation) from the desired value of the molar ratio (stoichiometrically, 1) is likely to occur, so that the capacity deterioration rate is deteriorated.

(C) Granulation The binder may be a conventional binder such as an aqueous vinyl alcohol solution. The amount of the vinyl alcohol aqueous solution to be added is preferably 20 to 30 parts by weight based on 100 parts by weight of the total amount of the lithium carbonate powder and the cobalt oxide powder. By granulation, a granulated product having a diameter of about 1 to 3 mm is obtained.

(D) Firing The firing conditions were an oxygen-containing atmosphere and a temperature of 850-850.
1000 ° C., the time is 5 to 20 hours. Firing temperature 8
When the temperature is 50 to 1000 ° C., the capacity deterioration rate is low.
When the ratio is out of this range, the capacity deterioration rate is deteriorated. The firing time is from 5 to 5 in order to efficiently perform firing at the above temperature.
20 hours.

It is preferable that the lithium-cobalt double oxide obtained by the above-mentioned method is pulverized and used so that the average particle size is 30 μm or less.

[0033]

【Example】

[Example 1] (Synthesis of active material) Synthesis of an active material was performed as follows.

Lithium carbonate (Li ₂ CO ₃ , purity: 99% by weight, average particle size: 10 μm or less, specific surface area: 1.3 m ² / g) so that the Li / Co molar ratio becomes 1.000.
3.788 kg, cobalt oxide (Co ₃ O ₄ , Co content: 73.3% by weight, specific surface area: 3.4 m ² / g)
261 kg was precisely weighed.

After preliminarily mixing the precisely weighed lithium carbonate and cobalt oxide for 5 minutes using a mixing granulator (high speed mixer manufactured by Fukae Kogyo KK), 4% by weight of P
3.012 kg of VA (polyvinyl alcohol) aqueous solution
In addition, granulation was performed for 15 minutes to produce a granulated product of 1 to 3 mm.

After the granules were dried at 100 ° C. for 2 hours, they were fired as follows. That is, using a magnesia setter, an oxygen flow rate of 3 liter / min (furnace volume:
0.5 m ³ ), the temperature was raised to 900 ° C. at a heating rate of 5 ° C./min, and held for 20 hours.

The thus-burned lithium-cobalt double oxide was pulverized to a particle size of 30 μm or less.

From the produced lithium cobalt double oxide, X
A sample for RD was prepared, and (a) the ratio I (101) of the intensity I (101) of the X-ray diffraction pattern of the (101) plane to the intensity I (003) of the X-ray diffraction pattern of the (003) plane. / I (003), (b) lattice constants a and c, (c) half-width of X-ray diffraction pattern of (003) plane,
(D) The crystallite diameter determined from the X-ray diffraction pattern of the (003) plane and (e) the volume of the unit cell were measured.

(Evaluation of Battery) Using the obtained active material, a battery was prepared as follows, and the charge / discharge capacity was measured. That is, 5% by weight of acetylene black and 8% by weight of PVDF (polyvinylidene fluoride) were added to 87% by weight of the active material powder.
And NMP (n-methylpyrrolidone) is added,
Pasted. Next, the weight of the active material after drying was 0.07 g / cm ^{2 on} an expanded metal mesh made of aluminum.
Was applied and dried. Further, vacuum drying was performed at 120 ° C. to obtain a positive electrode.

A Li metal was used as a negative electrode.

As the electrolytic solution, a mixed solution of equivalent amounts of ethylene carbonate (EC) and diethyl carbonate (DEC) using 1 mol of LiPF ₆ as a supporting salt was used.

As the separator, three polyethylene porous films each having a thickness of 25 μm were used in a stacked state.

FIG. 1 is a longitudinal sectional view of the assembled battery. A separator 5 is interposed between a positive electrode 2 to which a lead wire 1 is attached and a negative electrode 4 to which a lead wire 3 is attached. Fixed. This fixed material is placed in a beaker 6
After being immersed in the electrolyte solution 7 accommodated in the beaker 6, the inside of the beaker 6 was sealed with a Teflon stopper 8. In addition, the lead wire 9 is used so that the potential of the positive electrode 2 can be measured for confirmation at the time of charging and discharging.
The reference electrode (Li metal) 10 provided with was also immersed. The lead wires 1, 3, and 9 pass through the Teflon stopper 8,
Pulled out of the beaker 6. The above assembly was performed in a glove box in an Ar atmosphere.

The fabricated battery was left for about 10 hours,
Is stabilized, the current density with respect to the positive electrode is increased to 1.0 mA / c.
m ^2, and a charge / discharge test was performed at a cutoff of 4.3 to 3.0 V. The discharge capacity at this time is defined as the initial capacity.

Further, the current density with respect to the positive electrode was 1.0 m
After charging to 4.3 V as A / cm ² ,
Environmental tester (Tabayespec Co., Ltd., P
L-2SPH) for 3 days and subjected to aging treatment. Thereafter, the battery was discharged once, and the discharge capacity after the aging treatment was measured under the same conditions as the initial capacity.

From the obtained capacity, the aging effect (capacity deterioration rate) was obtained by [Equation 3].

[0047]

(Equation 3)

Example 2 The firing temperature and the holding time were
The test was performed in the same manner as in Example 1 except that the temperature was changed to 925 ° C. for 15 hours.

Example 3 A test was conducted in the same manner as in Example 1 except that the holding time was changed to 15 hours.

Comparative Example 1 A test was conducted in the same manner as in Example 1 except that the sintering temperature was 800 ° C.

[Comparative Example 2] The lithium / cobalt ratio was 1.
Mixing was performed to 100, and the firing temperature was 1050 ° C.
The test was conducted in the same manner as in Example 1 except that the test was performed.

Comparative Example 3 When the lithium / cobalt ratio was 1.
The test was performed in the same manner as in Example 1 except that the mixing was performed so as to reach 050.

Example 4 The lithium / cobalt ratio was set to 1.
The test was performed in the same manner as in Example 1 except that mixing was performed so as to obtain 005.

Example 5 A test was performed in the same manner as in Example 1 except that the firing temperature was 950 ° C.

Comparative Example 4 The lithium / cobalt ratio was set to 1.
After performing mixing so as to be 010, granulation was performed, and a test was performed in the same manner as in Example 1 except that the firing temperature was set to 800 ° C.

Comparative Example 5 A test was conducted in the same manner as in Example 1 except that the firing temperature was changed to 1050 ° C.

Comparative Example 6 A lithium / cobalt ratio of 1.
After performing mixing so as to be 080, the mixture was granulated, and a test was performed in the same manner as in Example 1 except that the firing temperature was set to 950 ° C.

Table 1 shows the main production conditions of the lithium-cobalt double oxide in the above Examples and Comparative Examples, and Tables 2 and 3 show the measurement results.

[0059]

[Table 1]

[0060]

[Table 2]

[0061]

[Table 3]

As described above, it can be seen that when the lithium-cobalt double oxide according to the present invention is used as an active material of a lithium secondary battery, a battery having high high-temperature storage performance can be obtained.

[0063]

According to the lithium-cobalt double oxide and the method for producing the same of the present invention, it is possible to provide a positive electrode active material for a non-aqueous secondary battery having excellent capacity retention at high temperatures.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view of a beaker battery used in Examples and Comparative Examples.

[Explanation of symbols]

 1, 3, 9 Lead wire 2 Positive electrode 4 Negative electrode 5 Separator 6 Beaker 7 Electrolyte 8 Teflon stopper 10 Reference electrode

Claims (5)

[Claims] (1) The ratio I (101) of the intensity I (101) of the X-ray diffraction pattern of the (101) plane and the intensity I (003) of the X-ray diffraction pattern of the (003) plane in the hexagonal system. 101) / I (003) is 0.
(B) lattice constants a and c are 2.8130 to 2.8160 Å, respectively;
4.040 to 14.060 angstroms, (c) a crystal whose half-width of the (003) plane X-ray diffraction pattern is 0.160 ° or less, and (d) a crystal obtained from the (003) plane X-ray diffraction pattern Lithium-cobalt double oxide for lithium ion secondary batteries having a diameter of 700.0 angstroms or more. 2. The unit cell volume is 0.09600 to 0.09.
9650Nm ³ a lithium ion secondary battery for a lithium cobalt complex oxide according to claim 1. 3. A lithium carbonate (Li ₂ CO ₃ ) powder and a cobalt oxide (Co ₃ O ₄ ) powder are weighed, and a binder is added to the lithium carbonate powder and the cobalt oxide powder by a mixing granulator. After producing the granulated material, the method of firing the granulated material in an oxygen-containing atmosphere includes the following steps: (1) The lithium carbonate powder has an average particle diameter of 10 μm or less and a specific surface area of 1.0 m ² / g or more. (2) the cobalt oxide powder has a specific surface area of 1.0 to 3.5 m ² / g, and (3) the lithium carbonate powder and the cobalt oxide powder have a Li / Co molar ratio of It is weighed so as to be 0.980 to 1.005, and (4) firing is performed at 850 to 1000 ° C.
A method for producing a lithium-cobalt double oxide for a lithium ion secondary battery, wherein the method is performed under conditions of 5 to 20 hours. 4. The method for producing a lithium-cobalt double oxide for a lithium ion secondary battery according to claim 3, wherein the binder is an aqueous vinyl alcohol solution. 5. The vinyl alcohol aqueous solution is added in a total amount of lithium carbonate powder and cobalt oxide powder of 100.
The method for producing a lithium-cobalt double oxide for a lithium ion secondary battery according to claim 4, wherein the amount is 20 to 30 parts by weight with respect to part by weight.