JP2003317720A - Lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery using a positive electrode material synthesized by a lithium compound and Co<SB>3</SB>O<SB>4</SB>, wherein discharging rate characteristics are not impaired, gas production under a high temperature environment is suppressed, and no malfunction is caused in a current blocking mechanism. <P>SOLUTION: Co<SB>3</SB>O<SB>4</SB>whereof the half-value width of its 311 face in X-ray diffraction by CuKα rays is 0.366 deg. or less is used, and its particle size distribution is preferably in the range of D(30%)=2.5-6.0 μm, D(50%)=4.0-7.5 μm, and D(90%)=13.0-16.0 μm. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery which is free from malfunction of a current interruption mechanism in a high temperature environment and has excellent discharge rate characteristics.

[0002]

2. Description of the Related Art In recent years, lithium ion batteries which absorb and release lithium have been put to practical use as high capacity non-aqueous electrolyte secondary batteries. A lithium-containing composite metal oxide is used as the positive electrode active material, and metallic lithium, a carbon material such as lithium alloy, carbon fiber, or graphite is used as the negative electrode active material, and it is put into practical use as a battery having a high voltage of 4V class and a high energy density. Has been done. The power consumption tends to increase with the sophistication of mobile devices, which are the main applications of this battery, and the components are mounted in high density as the device becomes smaller. May be exposed to the environment.

When exposed to a high temperature environment for a long time, the crystal structure of the positive electrode active material becomes unstable inside the battery, and oxygen gas is generated to form an oxidizing atmosphere, so that the non-aqueous electrolyte is decomposed and further gas is generated. If it occurs, the current cutoff mechanism, which should normally operate during overcharge, may malfunction.

Therefore, Japanese Patent Laid-Open No. 7-134985 discloses a method in which a predetermined amount of nickel oxide and / or cobalt oxide is added to the positive electrode active material.
000-200605 discloses that by adhering titanium particles and / or titanium compounds to the surface of lithium cobalt oxide particles of a positive electrode active material, it is possible to suppress gas generation during long-term storage or high-temperature storage. There is.

[0005]

However, since these methods employ the method of lowering the reactivity of the positive electrode active material, they have the effect of suppressing gas generation in a high temperature environment, but the discharge rate characteristics It was causing a decline.

By the way, in Japanese Unexamined Patent Publication (Kokai) No. 11-49519, the half-value width of the diffraction peak corresponding to the 311 plane of Co ₃ O ₄ is larger than 0.31 degree in X-ray diffraction using CuKα rays, and cobalt having poor crystallinity is disclosed. A solid-phase reaction proceeds satisfactorily when a compound is used, and a method for efficiently producing a lithium-cobalt composite oxide is disclosed, but stability in a high temperature environment is not described.

The present invention has been made in view of these problems, and provides a lithium secondary battery that does not impair discharge rate characteristics, suppresses gas generation in a high temperature environment, and has no malfunction of a current cutoff mechanism. The purpose is to provide.

[0008]

In order to solve the above-mentioned problems, the present invention provides a positive electrode active material synthesized from a lithium compound and Co ₃ O ₄ , which is an X-ray diffraction pattern of the above-mentioned Co ₃ O ₄ by CuKα ray. The full width at half maximum of the 311 surface at 0.366 deg. It is characterized by the following.

The full width at half maximum is 0.366 deg. Co ₃ below
Since the lithium-containing cobalt oxide obtained from O ₄ and the lithium compound can form a skeleton with high crystallinity, gas generation is suppressed even in a high temperature environment, and a lithium secondary battery having excellent discharge rate characteristics is obtained. be able to.

The particle size distribution of Co ₃ O ₄ is D (3
0%) = 2.5 μm to 6.0 μm, D (50%) = 4.
0 μm to 7.5 μm, D (90%) = 13.0 μm to 1
It is preferable to use a material having a thickness in the range of 6.0 μm because the effect of suppressing gas generation in a high temperature environment and the discharge rate characteristic are further improved.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings to provide an understanding of the present invention. still,
The embodiments described below are examples embodying the present invention and do not limit the technical scope of the present invention.

FIG. 1 shows a vertical sectional view of a cylindrical lithium secondary battery. The battery case 1 contains a positive electrode plate 5 and a negative electrode plate 6 which are spirally wound with a separator 7 in between, and a non-aqueous electrolyte solution.
The blade 6a is welded via the insulating plate 8. The insulating plate 8 is inserted in the upper part of the electrode plate group 4, and the positive electrode lead 5a and the sealing plate 2 are welded. The inside of the battery case 1 of the sealing plate 2 is sealed by bending the upper end of the battery case 1 inward through the insulating gasket 3 and caulking.

The positive electrode plate 5 is made of an aluminum foil or a lathed or etched foil having a thickness of 10 μm to 60 μm, and a positive electrode active material, a binder and, if necessary, a conductive agent on one or both sides of the current collector. , A paste in which a thickener is kneaded and dispersed in a solvent is applied, dried and rolled to form an active material layer,
The active material layer is provided with a plain portion and the positive electrode lead 5a is welded.

As the positive electrode active material, X by CuKα ray is used.
The full width at half maximum of the 311 plane in the line diffraction is 0.366 deg. A lithium-containing cobalt oxide obtained by mixing the following Co ₃ O ₄ and a lithium compound and firing is used.

The half-value width of the 311 plane in X-ray diffraction with CuKα rays is 0.366 deg. The following Co ₃ O ₄ is Co
(OH) ₂ is preheated at 100 ° C. to 120 ° C. for 2 hours to 15 hours and then at 1 ° C./min. ~ 4 ° C / min. Which is the dehydration temperature of Co (OH) _{2 at} a temperature rising rate of 150 ° C. to 1
It can be obtained by heating to 80 ° C. and dehydrating in an air atmosphere for 2 hours to 24 hours, preferably 5 hours to 15 hours.

The atomic ratio of Li ₃ and Co ₃ O ₄ to the lithium compound is preferably 0.97: 1 to 1: 1.05 from the viewpoint of battery characteristics.

The full width at half maximum is 0.366 deg. Co ₃ below
Since the lithium-containing cobalt oxide obtained from O ₄ and the lithium compound can form a skeleton with high crystallinity, gas generation is suppressed even in a high temperature environment, and a lithium secondary battery having excellent discharge rate characteristics is obtained. be able to.

The full width at half maximum is 0.366 deg. If it exceeds 1.0, since the crystallinity of Co ₃ O ₄ is lowered, the crystallinity of the portion forming the skeleton of the obtained lithium-containing cobalt oxide is lowered, so that it becomes unstable in a high temperature environment, and This is not preferable because it reacts with the water electrolyte to increase the amount of gas generated and causes the current cutoff mechanism to malfunction.

On the contrary, the full width at half maximum is 0.350 deg. If it is less than the above range, the reactivity with the lithium compound is lowered and the productivity is lowered, which is not preferable.

By the way, the particle size distribution of Co ₃ O ₄ is D (30
%) = 2.5 μm to 6.0 μm, D (50%) = 4.0
μm to 7.5 μm, D (90%) = 13.0 μm to 1
It is preferable to use one having a range of 6.0 μm.

When the particle size distribution D (30%) is less than 2.5 μm, the lithium-containing cobalt oxide obtained has a small skeleton, a large specific surface area, high reactivity with a non-aqueous electrolyte, and gas generation. It is not preferable because the effect of suppressing is reduced. On the other hand, when it exceeds 6.0 μm, the reactivity is lowered and the discharge rate characteristic is lowered, which is not preferable.

When the particle size distribution D (50%) is less than 4.0 μm, the skeleton of the lithium-containing cobalt oxide obtained is small, the specific surface area is large, the reactivity with the non-aqueous electrolyte is high, and gas is generated. It is not preferable because the effect of suppressing is reduced. On the other hand, when it exceeds 7.5 μm, the reactivity is lowered and the discharge rate characteristic is lowered, which is not preferable.

When the particle size distribution D (90%) is less than 13.0 μ, the skeleton of the lithium-containing cobalt oxide obtained is small, the specific surface area is large, the reactivity with the non-aqueous electrolyte is high, and gas is generated. It is not preferable because the effect of suppressing is reduced. On the other hand, when it exceeds 16.0 μm, the reactivity is lowered and the discharge rate characteristic is lowered, which is not preferable.

The lithium compound is not particularly limited, but LiCO ₃ , LiOH, LiNO ₃ , L
At least one selected from i ₂ SO ₄ can be used.

The binder is not particularly limited as long as it can be kneaded and dispersed in a solvent, and examples thereof include a fluorine-based binder, acrylic rubber, modified acrylic rubber, styrene-butadiene rubber (SBR), and acrylic heavy binder. A united material, a vinyl-based polymer or the like can be used alone or as a mixture or copolymer of two or more kinds. As the fluorine-based binder, for example, polyvinylidene fluoride, a copolymer of vinylidene fluoride and propylene hexafluoride, or a dispersion of polytetrafluoroethylene resin is preferable.

If desired, a conductive agent and a thickener can be added. As the conductive agent, acetylene black, graphite, carbon fiber or the like is preferably used alone or in a mixture of two or more kinds. Are preferably ethylene-vinyl alcohol copolymer, carboxymethyl cellulose, methyl cellulose and the like.

As the solvent, a solvent in which the binder can be dissolved is suitable, and in the case of an organic binder, N-methyl-2-pyrrolidone, N, N-dimethylformamide, tetrahydrofuran, dimethylacetamide, dimethylsulfoxide. , Hexamethylsulforamide, tetramethylurea,
An organic solvent such as acetone or methyl ethyl ketone is preferably used alone or as a mixed solvent thereof, and in the case of an aqueous binder, water or warm water is preferred.

It is also possible to add various dispersants, surfactants, stabilizers, and the like, if necessary, at the time of kneading and dispersing the pasty mixture.

The coating and drying is not particularly limited, and the paste mixture prepared by kneading and dispersing as described above can be used, for example, in a slit die coater, a reverse roll coater, a lip coater, a blade coater, a knife coater, a gravure. Using a coater, dip coater, etc.
It can be easily applied and is preferably close to natural drying, but in view of productivity, it is preferable to dry at 70 ° C. to 200 ° C. for 5 hours to 10 minutes.

Rolling is carried out by a roller press until a predetermined thickness is reached and a linear pressure of 1000 kg / cm to 2000 k is applied.
The rolling is performed several times at g / cm, but it is preferable to perform the rolling while changing the linear pressure.

The negative electrode plate 6 has a negative electrode active material on one surface of the current collector.
Binder, and if necessary, a conductive additive is kneaded and dispersed in an organic solvent to apply a paste-like mixture, which is then dried, and then applied to the other surface of the current collector as well, followed by drying and rolling. To be done.

The collector of the negative electrode plate 6 is made of copper foil, lathed foil, or etched foil, and the thickness is preferably in the range of 10 μm to 50 μm.

The negative electrode active material is not particularly limited, but for example, a carbon material obtained by firing an organic polymer compound (phenol resin, polyacrylonitrile, cellulose, etc.), coke or pitch is fired. The shape of the carbon material thus obtained, or artificial graphite, natural graphite, or the like, may be spherical, scaly, or massive.

The same binder and thickener as those used for the positive electrode plate can be used.

The separator 7 has a thickness of 15 μm to 3 μm.
A 0 μm polyethylene resin, a microporous polyolefin resin such as a polypropylene resin, or a laminated body thereof can be used.

The non-aqueous electrolytic solution is prepared by dissolving an electrolyte in a non-aqueous solvent. The non-aqueous solvent, ethylene carbonate, propylene carbonate,
Butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-dichloroethane, 1,3-dimethoxypropane, 4-methyl-2-pentanone, 1,4-
Dioxane, acetonitrile, propionitrile, butyronitrile, valeronitrile, benzonitrile, sulfolane, 3-methyl-sulfolane, tetrahydrofuran,
2-Methyltetrahydrofuran, dimethylformamide, dimethylsulfoxide, dimethylformamide, trimethyl phosphate, triethyl phosphate and the like can be used alone or as a mixed solvent of two or more kinds.

As the electrolyte to be added to the non-aqueous solvent, a lithium salt having a strong electron withdrawing property is used, and LiPF ₆ , Li
BF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ ,
LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , L
iC (SO ₂ CF ₃ ) _{3 and the} like can be used alone or in combination of two or more kinds. The amount of these electrolytes is 0.5 mol / l to 2.0 mol with respect to the non-aqueous solvent.
It is preferable to dissolve at a concentration of / l.

[0038]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples. However, the present invention is not limited to the following examples, and various modifications may be made without departing from the scope of the invention. It is possible. In this embodiment, FIG.
The cylindrical lithium secondary battery shown in was prepared and evaluated.

Example First, a positive electrode active material was prepared as follows.

Co ₃ O ₄ is prepared by preheating Co (OH) ₂ at 100 ° C. for 10 hours, and then C at a temperature rising rate of 3 ° C./min.
Raise the dehydration temperature of o (OH) _{2 to} 180 ° C.,
It was obtained by dehydration in an air atmosphere for 10 hours. Co ₃ obtained
By crushing and classifying O ₄ , various C shown in Table 1
Co ₃ O ₄ , a1 to a7 having a full width at half maximum of 311 plane and a particle size distribution in X-ray diffraction by uKα ray were obtained.

[0041]

[Table 1]

Next, various Co ₃ O ₄ and Li ₂ shown in Table 1 were used.
CO ₃ is precisely weighed and the atomic ratio of Li and Co is 1: 1.
And mixed to obtain a lithium-containing cobalt oxide LiCoO ₂ by firing in air at 900 ° C. for 6 hours.

LiCoO ₂ 10 thus obtained
0 parts by weight of acetylene black 3 as a conductive agent
Parts by weight, polytetrafluoroethylene (P
4 parts by weight of a dispersion of TFE) and 0.8 parts by weight of an aqueous solution of carboxymethyl cellulose as a thickener were kneaded and dispersed in a mixer to obtain a positive electrode mixture paste. This positive electrode mixture paste has a thickness of 20 μm
The aluminum alloy foil current collector was continuously coated and dried on both sides, and then rolled with a roller press to a thickness of 180 μm and cut into a predetermined size to prepare a positive electrode plate 5.

The negative electrode plate 6 is an artificial graphite 1 which is a negative electrode active material.
4 parts by weight of a water-soluble dispersion of styrene-butadiene rubber (SBR) as a binder as a solid content and 0.8 parts by weight of an aqueous carboxymethyl cellulose solution as a thickener as a solid content were kneaded with 00 parts by weight. A negative electrode material mixture paste was obtained. This negative electrode mixture paste is 14 μm thick
After continuously and intermittently applying the copper foil current collector of m to both surfaces, the dried product was rolled with a roller press to a thickness of 195 μm and cut into a predetermined size to prepare a negative electrode plate 6.

The positive electrode plate 5 and the negative electrode plate 6 obtained in this manner were spirally wound with a separator 7 made of a microporous polyethylene film having a thickness of 25 μm interposed therebetween to prepare an electrode plate group 4.

The electrode plate group 4 was housed in a bottomed cylindrical battery case 1 made of stainless steel which also serves as a negative electrode terminal, and the negative electrode lead 6
a was welded to the bottom of the battery case 1. Further, after injecting into the battery case 1 an electrolyte solution in which 1.25 mol / l LiPF ₆ was dissolved as an electrolyte in a mixed solvent of ethylene carbonate and ethyl methyl carbonate, the sealing plate 2 welded to the positive electrode lead 5a was attached. The battery case 1 and the sealing plate 2 were hermetically sealed via the insulating gasket 3. Furthermore, after charging the battery voltage at a constant current up to 4.1 V, it was stored in a constant temperature bath kept at 45 ° C. for 1 week and then subjected to aging treatment, and the diameter corresponding to Co ₃ O _{4 of} a1 to a7 was 18 mm and high. 65 mm in size, batteries A1 to A7 with a battery capacity of 2000 mAh
Got

(Comparative Example) Various CuKα rays shown in Table 1
X-ray diffraction analysis of the 311 surface FWHM and grain size distribution of Co₃
O_FourSame as the example except that b1 to b5 were used.
b1 to b5 of Co ₃O_FourComparative batteries B1 to B5 corresponding to
Was produced.

The discharge rate characteristics and the storage test under a high temperature environment were evaluated by using each of the five batteries A1 to A7 and B1 to B6 of the examples and comparative examples thus obtained, and the results are shown in a table. 2 shows.

The discharge rate characteristic is 1 until the battery voltage reaches 4.2V after the residual discharge of each battery at a constant current of 2000mA (1.0ItA) to the final voltage of 3.0V.
A constant current of 400 mA (0.7 ItA) was charged, and then the battery was charged until the current value was attenuated to 100 mA (0.05 ItA), and the battery was fully charged.

Then, the fully charged battery was discharged at a discharge current of 400 mA (0.2 ItA) at 20 ° C. to a final voltage of 3.0 V, and the discharge current was 4 with respect to the battery capacity.
Discharge rate ratio = (2.0 ItA discharge capacity) / (0.2 ItA discharge capacity) × 100 (%), which is the ratio of the battery capacity when discharged at 000 mA (2.0 ItA), and calculated the average value. I asked.

In the storage test under a high temperature environment, the above fully charged battery was stored in a constant temperature bath maintained at 85 ° C. for 3 days, and then the presence or absence of malfunction of the current interruption mechanism was evaluated by fluorescent X-ray. .

[0052]

[Table 2]

As is clear from the results of Table 2, CuKα
X-ray diffraction by X-rays has a half-value width of 311 plane of 0.366d
eg. Battery A using the following lithium-containing cobalt oxide obtained from Co ₃ O ₄ and a lithium compound as a positive electrode active material
Nos. 1 to A7 form a skeleton with high crystallinity, so they are stable in a high temperature environment, and there is no malfunction of the current interruption mechanism, but Comparative Examples B1 to B6 cause malfunctions of the current interruption mechanism. was there.

The particle size distribution of Co ₃ O ₄ is D (30%).
= 2.5 to 6.0 μm, D (50%) = 4.0 to 7.5
The batteries A1 to A4 in the range of μm, D (90%) = 13.0 to 16.0 μm can obtain a more uniform and firm positive electrode active material with high crystallinity as compared with the batteries A5 to A7. It was revealed that the discharge rate characteristics were better.

[0055]

As is apparent from the above description, the lithium secondary battery using the positive electrode active material synthesized from Co ₃ O ₄ and the lithium compound of the present invention does not impair the discharge rate characteristics and is high in temperature. It is possible to obtain a lithium secondary battery that suppresses gas generation under the environment and has no malfunction of the current interruption mechanism, and its industrial value is extremely high.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention.

[Explanation of symbols]

1 battery case 2 Seal plate 3 Insulation gasket 4 electrode group 5 Positive plate 5a Positive lead 6 Negative plate 6a Negative electrode lead 7 separator 8 insulating plates

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] March 12, 2003 (2003.3.1)
2)

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

From the viewpoint of battery characteristics, the atomic ratio of Co ₃ O ₄ to Li and Co of the lithium compound is preferably in the range of 1: 0.97 to 1: 1.05 .

Continued front page    (72) Inventor Toyoji Sugimoto             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F-term (reference) 4G048 AA04 AB06 AC06 AD04 AD06                       AE05                 5H029 AJ02 AJ12 AK03 AL06 AL07                       AM02 AM03 AM04 AM05 AM07                       BJ02 BJ14 BJ27 DJ16 EJ04                       EJ12 HJ05 HJ13                 5H050 AA02 AA15 BA17 CA08 CB07                       CB08 EA09 EA28 FA17 HA05                       HA13

Claims (2)

[Claims] 1. A lithium secondary battery using a positive electrode active material synthesized from a lithium compound and Co ₃ O ₄ , wherein the full width at half maximum of the 311 plane in the X-ray diffraction of Co ₃ O ₄ by CuKα rays is 0.366 deg. The lithium secondary battery is characterized in that: 2. The Co ₃ O ₄ particle size distribution is D (30%).
= 2.5 μm to 6.0 μm, D (50%) = 4.0 μm
˜7.5 μm, D (90%) = 13.0 μm to 16.0
The lithium secondary battery according to claim 1, which is in the range of μm.