JPH09270257A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery with high discharging capacity by having a positive electrode using a lithium-containing composite oxide whose unit cell volume is specified as the active material and a negative electrode capable of absorbing/releasing lithium. SOLUTION: A nonaqueous electrolyte secondary battery has a positive electrode using a lithium-containing composite oxide represented by the general formula, Lix Ni1-y Coy O2 , (0<=x<=1.2, 0<y<=0.5), and having a unit cell volume of 100.5-102 cubic angstrom as the active material and a negative electrode capable of absorbing/releasing lithium. The lithium-containing composite oxide is preferable to have a crystallite size ε in the direction of (c) axis calculated from Scherrer equation by using 003 reflection obtained by powder X-ray diffraction of 300-1800Å.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a positive electrode active material thereof.

[0002]

2. Description of the Related Art Nickel-cadmium batteries or small sealed lead-acid batteries are widely used as power sources for driving consumer electronic devices. In recent years, portable and cordless electronic devices have been rapidly developed, and along with this, high energy density of a secondary battery serving as a driving power source,
The demand for smaller size and lighter weight is increasing. Under such circumstances, as disclosed in, for example, Japanese Patent Application Laid-Open No. 63-59507, LiCoO ₂ or the like is used as a positive electrode active material, and a composite oxide of lithium and a transition metal showing a high operating voltage is used. A non-aqueous electrolyte secondary battery utilizing insertion / removal of a battery has been proposed. However, although the lithium cobalt composite oxide as described above has a high operating voltage, it is scarce in terms of resources, is relatively expensive in terms of cost, and has a small discharge capacity.
To solve this problem, a non-aqueous electrolyte secondary battery using a lithium nickel composite oxide, which is rich in resources, has been proposed.

Lithium-nickel composite oxide is inexpensive, but its discharge capacity is not sufficient. Further, there is a problem of cycle deterioration in which the capacity is gradually reduced by repeating the charge / discharge cycle. Further, the lithium nickel composite oxide has a larger irreversible capacity, which is the difference between the charge capacity and the discharge capacity, as compared with the lithium cobalt composite oxide. Therefore,
In order to obtain a sufficient discharge capacity, it is necessary to increase the capacity and reduce the irreversible capacity. To solve this problem, U.S. Pat. No. 4,980,080 and Japanese Patent Laid-Open No. 5-3259.
In Japanese Patent Publication No. 66, it is reported that cycle characteristics are improved by using Li _x Ni _1-y Co _y O _{2 in} which a part of nickel in the lithium nickel composite oxide is replaced with cobalt as a positive electrode active material. ing. However, also in this case, it cannot be said that the discharge capacity is still sufficient.

In order to solve this problem, powder X
Various studies have been made on the correlation between the crystalline state of the lithium nickel composite oxide and the discharge capacity by using the line diffraction method. For example, in JP-A-6-60887, JP-A-5-290845, and JP-A-6-215773, in the powder X-ray diffraction method using CuKα as a radiation source, 2θ = about 18 ° to 20 ° or so. Crystal plane detected at 0
It has been reported that the intensity ratio between the diffraction peak on the 03 plane and the diffraction peak on the 104 plane detected near 2θ = 44 ° to 46 ° has a certain correlation with the discharge capacity. Further, JP-A-6-267539 reports that there is a certain correlation between the full width at half maximum and the discharge capacity. Also,
As disclosed in JP-A-6-275274,
The correlation between the size of the crystallite of the lithium nickel composite oxide in the c-axis direction, the average particle size, or the unit cell volume of the crystal and the discharge capacity has also been studied.

[0005]

However, the effects obtained by these are small, and further increase in discharge capacity is desired. An object of the present invention is to solve the problems caused by the positive electrode active material and to provide a non-aqueous electrolyte secondary battery having a large discharge capacity.

[0006]

The present invention is based on the general formula Li _x
A non-aqueous material provided with a positive electrode using a lithium nickel composite oxide represented by Ni _1-y Co _y O ₂ as an active material, and a negative electrode containing a compound that absorbs and releases lithium such as lithium and a lithium alloy as a main material. The present invention relates to an electrolyte secondary battery, wherein a lithium nickel composite oxide has a unit cell volume of 100.5 to
It is 102 cubic angstroms, and the size of the crystallite in the c-axis direction is 300 to 1800 angstroms.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The non-aqueous electrolyte secondary battery of the present invention
The general formula Li _x Ni _1-y Co _y O ₂ (where 0 ≦ x ≦ 1.
2, 0 <y ≦ 0.5) and a positive electrode using a lithium-containing composite oxide having a unit cell volume of 100.5 to 102 cubic angstroms as an active material, and a negative electrode that absorbs and releases lithium. It is equipped with.

Further, the lithium-containing composite oxide is powder X
Using 003 reflection obtained by the line diffraction method, Scherrer's formula: ε = λ / (β cos θ) where ε: crystallite size (angstrom) λ: measured X-ray wavelength (angstrom) β: integration Width (= integrated intensity / peak intensity) θ: The size ε of the crystallite in the c-axis direction calculated from the Bragg angle (°) of the diffraction line is 300 to
It is preferably 1800 Å. Li
Among lithium nickel composite oxides represented by _x Ni _1-y Co _y O ₂ , the unit cell volume is 100.5 to 102 cubic angstroms, and from the 003 reflection by the powder X-ray diffraction method, using the Scherrer's formula. A discharge capacity of 150 mAh / g or more can be obtained and a irreversible capacity of 30 mAh / g or less can be obtained by using a crystallite having a calculated c-axis direction size of 300 to 1800 Å for the positive electrode active material. Can be suppressed.

Further, it is preferable that the lithium-containing composite oxide is _one synthesized by firing a mixture of Ni _1-y Co _y (OH) ₂ obtained by the coprecipitation method and a lithium compound. This cobalt-containing lithium nickel composite oxide is obtained, for example, by substituting a part of nickel of the lithium nickel composite oxide with Co. For example, by a coprecipitation method in which an alkaline solution is added to a solution in which a nickel salt and a cobalt salt are saturated and dissolved to precipitate the Ni _{1 -y} Co
_y (OH) ₂ is synthesized, and this nickel cobalt hydroxide is mixed with a lithium compound at a predetermined ratio and then baked. At this time, a lithium composite oxide having a desired unit cell volume and crystallite size can be obtained by changing the firing temperature, firing time, and cooling rate after firing. Ni _{1- y} Co _y (OH) ₂ synthesized by the coprecipitation method has a uniform composition, and by mixing this with a lithium compound, Li _x Ni _1-y having high crystallinity and excellent properties is obtained. Co _y O ₂ can be obtained.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

The positive electrode active material was synthesized as follows. First, nickel hydroxide was synthesized by the coprecipitation method. Nickel sulfate (NiSO ₄ ) aqueous solution and cobalt sulfate (Co
The SO ₄₎ aqueous solution were mixed at a predetermined ratio by controlling the temperature and pH, some of the nickel to precipitate a substituted nickel hydroxide _{[Ni 0.85 Co 0. 15 (OH} ) 2] in Co. The obtained cobalt-containing nickel hydroxide and lithium hydroxide monohydrate (LiOH.H ₂ O) were mixed with (Ni + Co) and Li.
Were mixed so that the ratio of the number of atoms was 1: 1, and this mixture was heat-treated at 700 ° C. for 15 hours in an air atmosphere. Then, cool it to room temperature at a cooling rate of 1 ° C./min,
Lithium nickel composite oxide (LiNi _0.85 Co _0.15 O
₂ ) was synthesized. This lithium nickel composite oxide
It was crushed using a ball mill, and those having a particle size of 45 μm or less were separated to obtain a positive electrode active material.

The unit cell volume of the obtained positive electrode active material and the size of the crystallite in the c-axis direction were determined by the powder X-ray diffraction method. CuKα ray was used as the radiation source. From the obtained X-ray diffraction pattern, JCPDS card 9-63 (LiNi
The lattice constant was determined based on the Miller index shown in O ₂ ) and the unit cell volume was calculated. The crystallite size is 2θ = 18 in the diffraction pattern obtained by the powder X-ray diffraction method.
It was calculated based on the Scherrer's formula below from the integral width of the 003 reflection peak detected in the vicinity of 20 ° to 20 °.

Ε = λ / (β cos θ) where ε: average of crystallite size (angstrom) λ: measured X-ray wavelength (angstrom) β: integral width (= integral intensity / peak intensity) θ: diffraction line Bragg angle (°)

To 100 parts by weight of the lithium nickel composite oxide powder obtained as above, 5 parts by weight of acetylene black and 5 parts by weight of polyvinylidene fluoride were added and mixed, and this mixture was mixed with N-methyl-2-. The mixture paste was prepared by suspending it in pyrrolidone. This paste
It is applied on both sides of 0.025 mm thick aluminum foil, dried and rolled to a thickness of 0.15 mm, and further 37 mm wide,
It was cut into a length of 380 mm to obtain a positive electrode plate.

As the negative electrode mixture, a paste prepared by suspending 100 parts by weight of carbon powder obtained by heat-treating coke and 3.5 parts by weight of styrene-butadiene rubber in an aqueous carboxymethyl cellulose solution was used. This paste is applied to both sides of a copper foil having a thickness of 0.015 mm, dried, and then rolled with a roller press to a thickness of 0.2 mm, and a width of 39 mm.
mm and a length of 425 mm were cut out to obtain a negative electrode plate.

FIG. 1 is a vertical sectional view of the cylindrical battery used in this embodiment. Inside the battery case 1 made of stainless steel whose inner wall surface has been treated with an organic electrolytic solution, a positive electrode plate 5 and a negative electrode plate 6 are superposed with a separator 7 in between, and a spirally wound electrode plate group 4 is provided. Is stored. A positive electrode lead 5a made of aluminum is drawn out from the positive electrode plate 5 and connected to the sealing plate 2, and a negative electrode lead 6b made of nickel is drawn from the negative electrode plate 6.
Are drawn out and connected to the bottom of the battery case 1.
The insulating rings 8 are provided on the upper and lower portions of the electrode plate group 4, respectively. The opening of the battery case 1 is fitted with a sealing plate 2 provided with a safety valve with an insulating packing 3 interposed therebetween, and the inside of the battery case 1 is sealed. Lithium hexafluorophosphate (LiPF ₆ ) was dissolved in an equal volume mixed solvent of ethylene carbonate and diethyl carbonate at a ratio of 1.5 mol / liter to prepare an electrolytic solution. Diameter 16.3mm, height 50.7m
The spirally wound electrode group 4 was housed in the battery case 1 of m, the electrolyte was injected, and then the opening of the battery case 1 was sealed to obtain a non-aqueous electrolyte secondary battery. This is called battery A.

Using the same cobalt-containing nickel hydroxide and lithium hydroxide monohydrate used in Battery A, the firing temperature, firing time, and cooling rate were changed as shown in Table 1 to obtain lithium nickel. Complex oxide powder LiNi _0.85 C
o _0.15 O ₂ was synthesized, and these were used as the positive electrode active materials to prepare a non-aqueous electrolyte secondary battery similar to the battery A.
These are referred to as batteries B to H, respectively.

[0018]

[Table 1]

The unit cell volume of the lithium nickel composite oxide powder used in each battery was determined by the powder X-ray diffraction method. Further, from the obtained 003 reflection, the size in the direction perpendicular to the crystal plane 003, that is, the size of the crystallite in the c-axis direction was determined from the above Scherrer's equation. Table 2 shows the results.

[0020]

[Table 2]

500 m for all batteries A to H
After charging to 4.2 V with the constant current of A, further 4.
The battery was charged at a constant voltage of 2 V for a total of 2 hours, and discharged up to 3.0 V at a constant current of 750 mA.

FIG. 2 shows the positive electrode active material L used in the batteries AH.
The relationship between the unit cell volume of iNi _0.85 Co _0.15 O ₂ and the discharge capacity is shown, the horizontal axis shows the unit cell volume (cubic angstrom), and the vertical axis shows the discharge capacity per unit weight of the positive electrode active material (mAh /
g) is shown. According to the figure, it can be seen that the discharge capacity exceeds 150 mAh / g in the unit cell volume range of 100.5 to 102 cubic angstroms.

FIG. 3 shows the relationship between the unit cell volume and the irreversible capacity (mAh / g) per unit weight of the positive electrode active material. The figure shows that the irreversible capacity is 30 mAh / g or less in the unit cell volume range of 100.5 to 102 cubic angstroms.

As described above, the unit cell volume is 100.5 to
102 cubic Å LiNi _0.85 Co
_{When 0.15} O ₂ is used as the positive electrode active material, a non-aqueous electrolyte secondary battery having a large discharge capacity and a small irreversible capacity can be obtained.

FIG. 4 shows the relationship between the size of the crystallite in the c-axis direction and the discharge capacity (mAh / g) per unit weight of the positive electrode active material. According to the figure, the size of the crystallite in the c-axis direction is 30
It can be seen that in the case of 0 Å or more, the discharge capacity exceeds 150 mAh / g.

FIG. 5 shows the relationship between the crystallite size in the c-axis direction and the discharge capacity, the abscissa axis represents the crystallite size, and the ordinate axis represents the irreversible capacity per unit weight of the positive electrode active material (mAh / g). Take and show. According to the figure, the size of the crystallite in the c-axis direction is 3
In case of 00 angstrom or more, irreversible capacity is 30m
It turns out that it becomes Ah / g or less.

Although the synthesis conditions have been studied earnestly, a lithium nickel composite oxide having a crystallite size in the c-axis direction exceeding 1800 Å has not been obtained.
According to the previously reported powder X-ray diffraction pattern, it is 0
It is known that the integrated widths of the 03 reflection peaks are all 0.05 ° or more, and the size of the crystallite in the c-axis direction calculated by Scherrer's formula is 1800 angstroms or less, which exceeds 1800 angstroms. It is considered difficult to synthesize a lithium nickel composite oxide.

In the above examples, the positive electrode active material was synthesized using lithium hydroxide, but the same effect was obtained by using a lithium salt such as lithium carbonate or lithium nitrate. Furthermore, cobalt-containing nickel hydroxide [Ni _0.85 C
o _0.15 (OH) ₂ ], for example, Co (N
It is also possible to use other cobalt salts such as O ₃ ) ₂ .
In addition, in the above-mentioned embodiment, Li _x Ni used for the positive electrode active material is used.
LiNi _0.85 Co _0.15 O ₂ has been described as an example of _1-y Co _y O ₂ , but 0 ≦ x ≦ 1.2 and 0 ≦ y ≦ 0.5.
Therefore, the same effect can be obtained by using any of the composite oxides for the positive electrode active material. In the above embodiment,
The evaluation was performed using a cylindrical battery, but the same effect can be obtained even if the battery shape such as a prismatic shape is different. Furthermore, although a carbon material is used for the negative electrode in the above-described examples, the effect of the present invention works on the positive electrode plate, so any substance that can store and release lithium ions can be used without particular limitation. For example, metallic lithium, lithium alloys, Fe
Similar effects can be obtained by using other negative electrode materials such as oxides such as ₂ O ₃ and WO ₂ and sulfides such as TiS ₂ .

Although lithium hexafluorophosphate (LiPF ₆ ) is used as the electrolytic solution in the above embodiment, other lithium-containing salts such as lithium perchlorate (LiCl) are used.
O ₄ ), lithium trifluoromethylsulfonate (Li
CF ₃ SO _3), hexafluoride arsenate lithium (LiAsF ₆₎
Etc., the same effect was obtained. Furthermore, although a mixed solvent of ethylene carbonate and diethyl carbonate was used in the above examples, other non-aqueous solvents, for example, cyclic esters such as propylene carbonate,
The same effect can be obtained by using a cyclic ether such as tetrahydrofuran, a chain ether such as dimethoxyethane, a nonaqueous solvent such as a chain ester such as methyl propionate, or a multi-component mixed solvent thereof.

[0030]

According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery having a large discharge capacity.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a cylindrical battery according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a relationship between a discharge capacity and a unit cell volume of a positive electrode active material LiNi _0.85 Co _0.15 O ₂ .

FIG. 3 is a characteristic diagram showing a relationship of irreversible capacity with respect to the same unit cell volume.

FIG. 4 is a characteristic diagram showing the relationship of the discharge capacity to the size of the crystallite in the c-axis direction.

FIG. 5 is a characteristic diagram showing the relationship between the size of the crystallite in the c-axis direction and the irreversible capacity.

[Explanation of symbols]

 1 Battery Case 2 Sealing Plate 3 Insulation Packing 4 Electrode Plate Group 5 Positive Electrode Plate 5a Positive Electrode Lead 6 Negative Electrode Plate 6b Negative Electrode Lead 7 Separator 8 Insulating Ring

Claims (3)

[Claims] 1. The general formula Li _x Ni _1-y Co _y O ₂ (where
0 ≦ x ≦ 1.2, 0 <y ≦ 0.5) and a lithium-containing composite oxide having a unit cell volume of 100.5 to 102 cubic angstroms as an active material, and lithium. A non-aqueous electrolyte secondary battery provided with a negative electrode that occludes and releases hydrogen. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the crystallite of the lithium-containing composite oxide has a size in the c-axis direction of 300 to 1800 angstroms. 3. The lithium-containing composite oxide is synthesized by calcining a mixture of Ni _{1 -y} Co _y (OH) ₂ and a lithium compound obtained by a coprecipitation method. The non-aqueous electrolyte secondary battery described.