JPH11185822A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a good load performance and long charging/discharging cycles by using lithium manganese oxide as a positive electrode material, and specifying the weight ratio of a positive depolarizing mix and a negative depolarizing mix to the specified range, the thickness ratio of a positive deporizing mix layer and a positive current collector, and the thickness ratio of a negative depovizing mix layer and a negative current collector both to the specified range. SOLUTION: This nonaqueous electrolyte secondary battery is formed in such a way that a negative electrode formed by arranging a negative depolarizing mix layer 15 on both surfaces of a negative current collector 10, and a positive electrode 2 formed by arranging a positive depolarizing mix layer 16 containing lithium manganese oxide on both surfaces of a positive current collector 11 are spirally wound through a microporous film separator 3, an insulator 4 is placed on the top and bottom of the winding body, then they are housed in a battery can 5. In the battery, the ratio of the positive mix layer 16 and the negative mix layer 15 is specified to the range of 3:1-4:1, the thickness ratio of the positive mix layer 16 and the positive current collector 11 and that of the negative mix layer 15 and the negative current collector 10 are specified to the range of 2:1-4:1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to an improvement in load performance and charge / discharge cycle characteristics.

[0002]

2. Description of the Related Art In recent years, as electronic devices have become smaller and lighter,
A secondary battery serving as a power supply has been required to have a high energy density. Non-aqueous electrolyte secondary batteries are expected as secondary batteries that meet such demands.

As a non-aqueous battery liquid secondary battery, one using lithium metal or lithium alloy as a negative electrode material and using a lithium-containing compound as a positive electrode material has been proposed.

[0004] However, when lithium metal or lithium alloy is used for the negative electrode, the lithium metal tends to precipitate in a dendrite shape on the negative electrode during the charging process. At the tip of this dendrite crystal, the current density becomes very high, so that the non-aqueous electrolyte is decomposed and the cycle life is reduced, or the dendrite crystal deposited from the negative electrode reaches the positive electrode,
There is a problem that an internal short circuit occurs in the battery.

On the other hand, lithium ions are doped.
Non-aqueous electrolyte secondary batteries using a undoped carbon material as a negative electrode material have been proposed. As the carbon material, graphitizable carbon, non-graphitizable carbon, and graphites are used. In a non-aqueous electrolyte secondary battery using such a carbon material, since lithium does not exist in a metal state in the battery system, formation of dendrites is suppressed, and good cycle characteristics are obtained. Therefore, it has been put to practical use as a power source for video cameras and mobile phones.

By the way, LiCoO ₂ and LiNiO ₂ are often used as a positive electrode material of a non-aqueous electrolyte secondary battery. However, resources such as cobalt and nickel are scarce. Cobalt compounds and nickel compounds containing these are more expensive than lead and manganese compounds, making it unreasonable to use them in large batteries that use a large amount of positive electrode material.

Therefore, the use of lithium manganese oxide containing Mn, which is relatively rich in resources, has been studied. For example, US Pat. No. 4,366,215, US Pat. No. 4,828,834,
U.S. Pat. No. 4,980,251 and JP-A-7-192768 propose the use of a spinel-type lithium manganese oxide as a positive electrode material.

When an electrode is formed using such a carbon material or a lithium-containing compound as an electrode material, for example, a negative electrode is formed by applying a powder of a carbon material and a binder to a negative electrode current collector. Is formed by applying a lithium-containing compound powder, a conductive agent and a binder to a positive electrode current collector.

[0009]

However, when lithium manganese oxide is used as the cathode material, Li
The battery performance is inevitably inferior to the case where CoO ₂ or LiNiO ₂ is used as the cathode material.

That is, in a battery using lithium manganese oxide as a positive electrode material, reversibility is lost with charging and discharging, and the capacity is significantly reduced. In addition, when charging and discharging are continuously performed in a high-temperature environment, the capacity is significantly reduced with the progress of the charging and discharging cycle. Furthermore, in charging and discharging under a large current condition, there is a problem that the inflow and out of lithium do not follow the charging and discharging cycle, resulting in poor load performance.

Accordingly, the present invention has been proposed in view of such a conventional situation, and is a secondary battery using lithium manganese oxide as a positive electrode material, which is excellent in load performance and charge / discharge cycle characteristics. And a non-aqueous electrolyte secondary battery.

[0012]

In order to achieve the above-mentioned object, a non-aqueous electrolyte secondary battery of the present invention comprises a negative electrode comprising a negative electrode mixture layer containing a carbon material held by a negative electrode current collector. When,
The positive electrode mixture layer comprising a positive electrode in which a positive electrode mixture layer containing lithium manganese oxide is held by a positive electrode current collector, and a nonaqueous electrolyte in which an electrolyte salt is dissolved in a nonaqueous solvent. And a weight ratio of the negative electrode mixture layer to the negative electrode mixture layer is 3: 1 to 4: 1.

In a non-aqueous electrolyte secondary battery using lithium manganese oxide as a cathode material, if the weight ratio of the cathode mixture layer to the anode mixture layer is in the range of 3: 1 to 4: 1, Load performance and charge / discharge cycle characteristics are improved.
Further, the ratio of the thickness of the positive electrode mixture layer to the thickness of the positive electrode current collector and the ratio of the thickness of the negative electrode mixture layer to the thickness of the negative electrode current collector are both in the range of 2: 1 to 4: 1. , Load performance and charge / discharge cycle characteristics are further improved.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described.

The nonaqueous electrolyte secondary battery according to the present invention comprises a negative electrode comprising a carbon material-containing negative electrode mixture layer held by a negative electrode current collector, and a positive electrode mixture layer comprising lithium manganese oxide comprising a positive electrode mixture layer. It comprises a positive electrode held by a current collector and a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent.

First, in the negative electrode, the negative electrode mixture layer is a layer containing a carbon material to be doped / dedoped with lithium ions, and holds at least the carbon material and the carbon material on a negative electrode current collector. Composed of a binder for

As the carbon material, for example, a non-graphitizable carbon material is used. This non-graphitizable carbon material has a (002) plane spacing d determined by X-ray diffraction measurement of 0.3.
It indicates 6 nm or more, and a region having a crystal structure and an amorphous region coexist. With such a structure, a smooth occlusion / release reaction of lithium ions is performed.

Such a non-graphitizable carbon material is obtained by heat-treating petroleum pitch, a polymer resin, and various organic compounds. Used as a material.

The non-graphitizable carbon material powder used as the negative electrode material preferably has a particle diameter of 1 μm or more and 50 μm or less, and an average particle diameter of 15 μm or less. Also, B
It is desirable that the specific surface area by the ET method is 0.1 to ²⁰ m ² / g.

Other examples of the negative electrode material include graphite powder, mesophase microbeads, pyrolytic carbon fiber, mesophase pitch-based carbon fiber, and high-temperature-processable graphitizable carbon. It is desirable to use the above non-graphitizable carbon material because a discharge potential can be obtained.

As the binder and the negative electrode current collector for holding the carbon material on the negative electrode current collector, those commonly used can be used. For example, a fluorine-based resin such as polyvinylidene fluoride is used as the binder, and a copper foil or the like is used as the current collector.

On the other hand, in the positive electrode, the positive electrode mixture layer is a layer containing lithium manganese oxide serving as a positive electrode active material, and holds at least the lithium manganese oxide, a conductive agent, and these on a positive electrode current collector. Composed of a binder for

Examples of the lithium manganese oxide include LiMn ₂ O _{4 and} LiMn having a spinel structure.
A substance obtained by adding a predetermined amount of Li to ₂ O ₄ , for example, Li _x Mn
O _y (where x is 0.50 to 0.52, y is 1.
96 to 2.00).
Among them, Li _{x obtained} by adding a predetermined amount of Li to LiMn ₂ O ₄
MnO _y is observed by powder X-ray diffraction measurement after performing heat treatment at 700 to 750 ° C. for 8 hours or more (31).
1) Peak ratio between diffraction plane and (400) diffraction plane [(311)
Diffractive surface: (400) diffractive surface].
Preferably, it is 20. L whose peak ratio is in this range
i _x MnO _y has a spinel type crystal structure similar. When the peak ratio is out of this range, a lower manganese compound is generated as the charge / discharge cycle is repeated, and the capacity may be reduced as the charge / discharge cycle progresses. In addition,
Li ₄ Mn ₅ O ₁₂ can also be used as a material for the positive electrode.

Such a lithium manganese oxide is prepared by mixing a lithium source such as lithium hydroxide and a manganese source,
It is synthesized by heat treatment in an oxygen-containing atmosphere.

As the manganese source, manganese carbonate, manganese nitrate, manganese sulfate, manganese acetate or those obtained by heating / oxidizing them, electrolytic manganese dioxide, chemically synthesized manganese dioxide, Mn ₂ O ₃ , Mn ₃ O _{4 and the} like can be used. .

As the conductive agent for imparting conductivity to the positive electrode, the binder for holding the positive electrode active material on the positive electrode current collector, and the positive electrode current collector, those commonly used can be used.
For example, graphite is used as the conductive agent, fluorine resin such as polyvinylidene fluoride is used as the binder, and aluminum foil is used as the positive electrode current collector.

The negative electrode and the positive electrode are configured as described above. In the nonaqueous electrolyte secondary battery of the present invention, in particular, the weight of the positive electrode mixture:
It is regulated at 3: 1 to 4: 1.

When the weight ratio of the positive electrode mixture and the negative electrode mixture is within the above range, lithium can smoothly enter and leave the electrode during charging and discharging, and good load performance and good charge / discharge cycle characteristics can be obtained. Will be obtained. In addition, high-temperature storage performance is also improved. Furthermore, the more preferable range of the weight ratio of the positive electrode mixture and the negative electrode mixture is 3.2: 1 to 3.9: 1,
Further, the ratio is 3.4: 1 to 3.7: 1.

In addition to this, the thickness of the positive electrode mixture layer: the thickness of the positive electrode current collector and the thickness of the negative electrode mixture layer: the thickness of the negative electrode current collector are both 2: 1 to 4: When the range is 1, the load performance and the charge / discharge cycle characteristics are further improved. Further, the thickness of the positive electrode: the thickness of the negative electrode also affects the battery performance, and is 1.1: 1 to 1.8: 1, and further 1.3: 1 to 1.3: 1.
Preferably, the ratio is 1.5: 1.

In this non-aqueous electrolyte secondary battery, the following are used as the non-aqueous solvent and the electrolyte salt of the non-aqueous electrolyte.

Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate, ethylene carbonate and butylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate and ethyl methyl carbonate; ether compounds such as dimethoxyethane and tetrahydrofuran; -Cyclic esters such as butyrolactone, sulfolane and the like are used alone or in combination.

As the electrolyte salt, LiPF ₆ , LiPF
Lithium salts such as BF ₄ , LiCF ₃ SO ₃ , LiClO ₄ and LiAsF ₆ are used. These electrolyte salts are 0.5 to
It is dissolved in a non-aqueous solvent at a concentration of 2 mol / l.

The present invention can be applied to various types of non-aqueous electrolyte secondary batteries. In particular, a cylindrical battery using a wound electrode body obtained by laminating and winding a strip-shaped positive electrode and a strip-shaped negative electrode via a separator, and a plate-shaped battery It is suitable to be applied to a prismatic battery or the like using a laminated electrode body in which a positive electrode and a strip-shaped negative electrode are laminated with a separator interposed therebetween.

FIG. 1 shows an example of a cylindrical non-aqueous electrolyte secondary battery.

As shown in FIG. 1, this non-aqueous electrolyte secondary battery has a negative electrode 1 in which a negative electrode mixture layer 15 is formed on both surfaces of a negative electrode current collector 9, and a positive electrode current collector 10 Positive electrode mixture layer 16
Is wound through a microporous membrane separator 3 made of polypropylene, polyethylene, or the like,
With the insulator 4 placed above and below the wound body, the battery can 5
It is to be stored in.

A battery lid 7 is attached to the battery can 5 by caulking via a sealing gasket 6, and is electrically connected to the negative electrode 1 or the positive electrode 2 via a negative electrode lead 11 and a positive electrode lead 12, respectively. Is configured to function as a negative electrode or a positive electrode.

In this battery, the positive electrode lead 1
2 is welded and attached to the current interrupting thin plate 8, and the battery cover 7 is connected to the current interrupting thin plate 8 via the thermal resistance element 13.
Electrical connection with the device.

In a battery having such a configuration,
When the pressure inside the battery rises, the thin plate 8 such as the current interrupter is pushed up and deformed. Then, the positive electrode lead 12 is cut leaving a portion welded to the current interrupting thin plate 8, and the current is interrupted.

In this battery, in particular, the weight ratio of the positive electrode mixture layer to the negative electrode mixture layer is 3: 1 to 4: 1, furthermore, the ratio of the thickness of the positive electrode mixture layer to the current collector and the negative electrode mixture layer The thickness ratio between the layer and the negative electrode current collector is both in the range of 2: 1 to 4: 1. Thereby, good load performance and charge / discharge cycle characteristics can be obtained. In this battery, the positive electrode mixture layer and the negative electrode mixture layer are formed on both sides of the current collector. When the mixture layer is thus formed on both sides of the current collector, the both sides are combined. The weight ratio of the positive electrode mixture to the negative electrode mixture, and the ratio of the total thickness of the mixture layers on both surfaces and the thickness of the current collector are regulated to predetermined ranges.

[0040]

Embodiments of the present invention will be described below based on experimental results.

Example 1 Thickness of positive electrode mixture layer: thickness of positive electrode current collector = 3.1: 1, thickness of negative electrode mixture layer: thickness of negative electrode current collector = 3.0: 1, This is an example of a non-aqueous electrolyte secondary battery in which the weight of the positive electrode mixture layer: the weight of the negative electrode mixture layer = 3.5: 1.

[0042] Such a non-aqueous electrolyte secondary battery was manufactured as follows.

First, a positive electrode was manufactured as follows.

Lithium hydroxide and electrolytic manganese dioxide pulverized to a particle size of 30 μm or less were weighed so that the Li: Mn (atomic ratio) became 1.04: 2, and charged into a mortar.

After sufficiently mixing them, the mixture was put into an alumina crucible and placed in an electric furnace in an atmosphere containing oxygen.
Heat treatment was performed at 350 ° C. for 6 hours, further heat treatment at 780 ° C. for 12 hours, and after cooling to room temperature, the mixture was coarsely ground to obtain a positive electrode material.

When the positive electrode material was measured by a powder X-ray diffraction method, the observed peak coincided with the peak of spinel type LiMn ₂ O ₄ . (31
1) Peak ratio between diffraction plane and (400) diffraction plane [(311)
Diffraction plane: (400) diffraction plane] was 1: 1.12.

90 parts by weight of this positive electrode material, 6 parts by weight of graphite serving as a conductive material, and 4 parts by weight of polyvinylidene fluoride (PVDF) serving as a binder are mixed, and N is used as a solvent.
-Methyl-2-pyrrolidone was added and mixed to prepare a positive electrode mixture. Next, this positive electrode mixture mix is uniformly applied to both surfaces of a 20 μm-thick aluminum foil (positive electrode current collector) except for a lead welding portion, and dried to form a 62 μm-thick positive electrode mixture layer. It was formed and cut into a predetermined size. Then, a positive electrode was manufactured by welding an aluminum lead body to the lead welding portion of the positive electrode current collector. Here, the thickness of the positive electrode mixture layer: the thickness of the positive electrode current collector was 3.1: 1.

A negative electrode was manufactured as follows.

The petroleum pitch was heat-treated at 1000 ° C. in an electric furnace in an oxygen-containing atmosphere to produce a non-graphitizable carbon powder having an oxygen cross-link.

When the particle size distribution of this non-graphitizable carbon powder was measured, it was found that the 50% cumulative diameter was 9 μm and the particle size was 1 to 30 μm. The (002) plane spacing measured by the X-ray diffraction method was 0.37 nm.

A mixture of negative electrodes was prepared by mixing 90 parts by weight of this carbon powder and 10 parts by weight of polyvinylidene fluoride as a binder, and further adding and mixing N-methyl-2-pyrrolidone as a solvent. . Next, this negative electrode mixture mix is uniformly applied to both surfaces of a copper foil (negative electrode current collector) having a thickness of 10 μm except for a lead welding portion, and dried to form a negative electrode mixture layer having a thickness of 30 μm. It was formed and cut into a predetermined size. Then, a negative electrode was manufactured by welding a nickel lead body to the lead welded portion of the negative electrode current collector. Here, the thickness of the negative electrode mixture layer: the thickness of the negative electrode current collector is 3:
1, and the weight ratio of the positive electrode mixture layer to the negative electrode mixture layer was 3.5:
It was one.

The positive electrode and the negative electrode thus produced were
The laminate was laminated via a microporous polypropylene membrane serving as a separator, and wound many times to produce a spiral electrode element.

Then, an insulating plate was attached to the spiral electrode element and inserted into a battery can. The negative electrode lead was welded to the battery can and the positive electrode lead was welded to a current interrupting thin plate. Next, L was added to a mixture of propylene carbonate and dimethyl carbonate.
An electrolytic solution in which iPF ₆ was dissolved at a concentration of 1 mol / l was poured into a battery can, and the battery lid was placed on a current interrupting thin plate.
Then, the upper part of the battery can was caulked using a caulking machine to seal the can, and a cylindrical battery having an outer diameter of 18 mm and a height of 65 mm was produced.

Examples 2 to 5 Example 1 was repeated except that the thickness of the positive electrode mixture layer and the positive electrode current collector and the thickness of the negative electrode mixture layer and the negative electrode current collector were changed as shown in Table 1. This is an example of a battery having the same configuration as that of FIG.

Comparative Examples 1 and 2 The thicknesses of the positive electrode mixture layer and the positive electrode current collector, and the thicknesses of the negative electrode mixture layer and the negative electrode current collector were changed as shown in Table 1, and the thickness ratio and This is an example of a battery having the same configuration as in Example 1 except that one of the weight ratios is out of the predetermined range.

[0056]

[Table 1]

Thickness of positive electrode mixture layer of these batteries: thickness of positive electrode current collector, thickness of negative electrode mixture layer: thickness of negative electrode current collector, weight of positive electrode mixture layer: weight of negative electrode mixture layer The weight is shown in Table 2.

[0058]

[Table 2]

With respect to the battery thus manufactured,
The battery was charged at 0.3 A to an upper limit voltage of 4.2 V for 8 hours, and then discharged at 0.5 A to a final voltage of 2.5 V. And
Five charge / discharge cycles were performed in which the battery was charged at 1 A to an upper limit voltage of 4.2 V for 3 hours and then discharged at 1 A to a final voltage of 2.5 V for 3 hours.

Thereafter, the following discharge load test and charge / discharge cycle test were performed to evaluate the performance of the battery.

Discharge load test: 1 A current and upper limit voltage 4.2
After charging to V for 3 hours, the battery was discharged to a final voltage of 2.5V. In addition, the electric current at the time of discharge was changed in the range of 0.1 to 10A.

Charge / discharge cycle test: A charge / discharge cycle was performed 200 times in which the battery was charged with a current of 1 A to an upper limit voltage of 4.2 V for 3 hours and then discharged with a current of 0.5 A to a final voltage of 2.5 V.

FIG. 2 shows the discharge load characteristics, and FIG. 3 shows the charge / discharge cycle characteristics.

As shown in FIG. 2, the ratio of the thickness of the positive electrode mixture layer to the thickness of the positive electrode current collector, the ratio of the thickness of the negative electrode mixture layer to the thickness of the negative electrode current collector, The batteries of Examples 1 to 5 in which the weight ratio is within the predetermined range can obtain a sufficient discharge capacity even when the discharge current is increased to 10 A, and are excellent in the discharge as compared with the batteries of Comparative Examples 1 and 2. Load characteristics can be obtained.

The charge / discharge characteristics shown in FIG.
The batteries of Examples 1 to 5 showed a small decrease in capacity due to repeated charge / discharge cycles, and were superior to the batteries of Comparative Examples 1 and 2.

From this, the weight of the positive electrode mixture layer: the weight of the negative electrode mixture layer was set to 3: 1 to 4: 1, and the thickness of the positive electrode mixture layer: the thickness of the positive electrode current collector and the thickness of the negative electrode mixture layer. It was found that the charge / discharge performance and the charge / discharge cycle characteristics at a large current of the battery were improved by setting the thickness of the agent layer: the thickness of the negative electrode current collector to 2: 1 to 4: 1.

[0067]

As is clear from the above description, the nonaqueous electrolyte secondary battery of the present invention uses lithium manganese oxide as the positive electrode material, and the weight ratio of the positive electrode mixture to the negative electrode mixture Is regulated to 3: 1 to 4: 1, and the ratio of the thickness of the positive electrode mixture layer to the thickness of the positive electrode current collector and the ratio of the thickness of the negative electrode mixture layer to the thickness of the negative electrode current collector are both 2: 1 to 1 Since the ratio is 4: 1, good load performance and charge / discharge cycle characteristics can be obtained. Also,
Lithium manganese oxide used as a cathode material in this non-aqueous electrolyte secondary battery is a rare resource such as lithium cobalt composite oxide and lithium nickel composite oxide.
Since it does not contain o and Ni, it is easy to obtain. Therefore, the nonaqueous electrolyte secondary battery of the present invention is also suitable as a large battery using a large amount of the positive electrode material.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view showing an example of a non-aqueous electrolyte secondary battery to which the present invention is applied.

FIG. 2 is a characteristic diagram showing a discharge load characteristic of a nonaqueous electrolyte secondary battery.

FIG. 3 is a characteristic diagram showing charge / discharge cycle characteristics of a nonaqueous electrolyte secondary battery.

[Explanation of symbols]

Reference Signs List 1 negative electrode, 2 positive electrode, 10 negative electrode current collector, 11 positive electrode current collector, 15 negative electrode mixture layer, 16 positive electrode mixture layer

Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H01M 4/58 H01M 4/58 (72) Inventor Masashi Kumakawa 1-1-1 Shimosugishita, Takakura, Hiwadacho, Koriyama-shi, Fukushima 1 Sony Energy Corporation・ Tech

Claims (4)

[Claims] 1. A negative electrode in which a negative electrode mixture layer containing a carbon material is held on a negative electrode current collector, and a positive electrode in which a positive electrode mixture layer containing lithium manganese oxide is held on a positive electrode current collector And a non-aqueous electrolyte obtained by dissolving an electrolyte salt in a non-aqueous solvent, wherein the weight ratio of the positive electrode mixture layer and the negative electrode mixture layer is 3: 1 to 4:
1. A non-aqueous electrolyte secondary battery, wherein 2. The ratio of the thickness of the positive electrode mixture layer to the thickness of the positive electrode current collector and the ratio of the thickness of the negative electrode mixture layer to the thickness of the negative electrode current collector are both 2: 1.
The non-aqueous electrolyte secondary battery according to claim 1, wherein the ratio is up to 4: 1. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the carbon material is a non-graphitizable carbon material. 4. The lithium manganese oxide is Li _x Mn
2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is represented by O _y (where x is 0.505 to 0.525 and y is 1.96 to 2.00). .