JPH11219731A - Organic electrolyte secondary battery - Google Patents

Abstract

(57) [Problem] To provide a rectangular organic electrolyte secondary battery excellent in initial capacity and cycle characteristics. A negative electrode (1) and a positive electrode (2) are sandwiched between polypropylene film separators (3), and a pressing plate (12) and a spring plate (13) are integrally fixed with an element adhesive tape (9) to form an electrode body (20). The insulating sheets 10 are arranged above and below the electrode body 20 and inserted into the battery case 11, the positive lead 4 is welded to the positive terminal 7, and the negative lead 5 is welded to the battery case 11. An electrolyte obtained by dissolving LiPF ₆ at a rate of 1 mol / liter in a mixed solvent of propylene carbonate and dimethyl carbonate is poured into the battery case 11, and the battery lid 8 is fixed to the battery case 11 by laser welding, and Fabricate an ion secondary battery. The shape of the spring plate 13 is a flat bowl shape with a central portion protruding, and the peripheral portion is a battery case 11.
Is inserted into the battery case 11 such that the central portion thereof presses the electrode body 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electrolyte secondary battery, and more particularly, to a rectangular organic electrolyte secondary battery having improved initial adhesion and cycle characteristics by improving the adhesion of an electrode body having a laminated structure. .

[0002]

2. Description of the Related Art In recent years, electronic devices such as laptop computers, cellular horns, 8 mm video and audio devices have been remarkably developed, and these electronic devices have become smaller, lighter and thinner with advances in electronic technology. Along with this, the demand for a secondary battery as a portable power source has been increasing, and research and development have been promoted to obtain a higher energy density.

Under such circumstances, a lithium ion secondary battery using a non-aqueous electrolyte has been proposed as a secondary battery having a higher energy density than an aqueous electrolyte secondary battery such as a lead battery or a nickel cadmium battery. Practical use is progressing.

[0004] As the battery form of the lithium ion battery,
There are a cylindrical battery in which a spirally wound electrode is inserted into a cylindrical case, a folded battery and a rectangular laminated electrode, and a rectangular battery in which an elliptically wound electrode is inserted into a rectangular case.
The latter square battery has better space efficiency when mounted on an electronic device as compared with a cylindrical battery, and has been increasingly required in recent years as electronic devices have become thinner.

In this lithium ion battery, the adhesion between the electrodes greatly affects the battery performance, for example, capacity, load characteristics, and cycle characteristics, and high adhesion is required. On the other hand, in order to facilitate the insertion of the electrode body into the battery case, it is necessary to provide a certain clearance between the internal dimensions of the battery case and the electrode body, which are conflicting requirements.

Therefore, conventionally, as a countermeasure, a spring plate is inserted between the electrode body and the inner wall of the battery case to press the electrode body,
Attempts have been made to improve the cycle characteristics and the like by ensuring the adhesion between the electrodes. However, at present, a sufficient effect cannot be obtained with the conventional shape of the spring plate.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a rectangular organic electrolyte secondary battery having a laminated electrode by inserting a suitably shaped spring plate between a battery case and an electrode body. The purpose is to increase the initial capacity of the battery and to improve the cycle characteristics.

[0008]

The present invention SUMMARY OF] has been made in view of the above problems, a positive electrode having a lithium composite oxide LixMO ₂ or LixM ₂ O _4, (M is one or more transition metals) as a positive electrode active material And a flat bowl-shaped elastic body is disposed between the electrode body and the inner wall of the battery case in an organic electrolyte secondary battery comprising a negative electrode having a carbon material capable of being doped with lithium and dedoped as lithium as a negative electrode active material. The organic electrolyte secondary battery is provided. Further, the above problem is solved by setting the diameter of the flat bowl-shaped elastic body to be at least half the width of the battery case.

According to the present invention, the adhesion between the electrodes of the laminate is improved.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention.
This will be described with reference to FIG. FIG. 1 is a cross-sectional view of a rectangular organic electrolyte secondary battery according to the present invention, and FIG. 2 is a spring plate used in the organic electrolyte secondary battery shown in FIG. And (b) is A- of (a).
It is sectional drawing in the A line. 3 and 4 are perspective views of a spring plate formed for comparison.

The prismatic organic electrolyte secondary battery according to the present invention has a lithium composite oxide LixMO as a positive electrode active material.
₂ or LixM ₂ O ₄ (M is one or more transition metals)
And a lithium ion secondary battery having a carbon material capable of doping and dedoping lithium as a negative electrode active material.

Although a carbon material is used as the negative electrode active material, any material capable of doping and undoping lithium can be used.
Pyrolytic carbons, cokes (pitch coke, needle coke, petroleum coke, etc.), natural graphites, artificial graphites, glassy carbons, organic polymer compound fired bodies, carbon fibers, activated carbon and the like can be used. Preferably, (00
2) The plane spacing is 0.37 nm or more, and the true density is 1.70.
less than g / cm ^3, and, using a carbon material having no exothermic peak at 700 ° C. or higher in differential thermal analysis in air stream.

As the positive electrode active material, lithium composite oxide L
ixMO ₂ or LixM ₂ O ₄ (M is one or more transition metals) is used. This lithium composite oxide is obtained by, for example, using carbonates of lithium, cobalt, and nickel as starting materials, mixing these carbonates according to the composition, and calcining the mixture in a temperature range of 600 to 1000 ° C. in an oxygen-containing atmosphere. Can be The starting material is not limited to carbonate, but may be synthesized from oxides and hydroxides.

As the electrolyte, an electrolyte obtained by dissolving a lithium salt in an organic solvent is used. Here, the organic solvent is not particularly limited, but propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, tetrahydrofuran, γ-butyrolactone, methyl ethyl carbonate, or a single solvent or a mixture of two or more solvents can be used. It is.

As the electrolyte, LiPF ₆ , LiPF
BF ₄ , LiClO ₄ , LiAsF _{6 and the} like can be used.

Example 1 First, the production of the negative electrode 1 will be described. Petroleum pitch selected from the range of H / C atomic ratio of 0.6 to 0.8 was pulverized and oxidized in an air stream to obtain a carbon precursor. Quinoline-insoluble matter of this carbon precursor (JIS centrifugation: K24
25-1983) was 80% and the oxygen content (by organic elemental analysis) was 15.4% by weight. The carbon precursor was heated to 1000 ° C. in an air stream and heat-treated, and then pulverized to obtain a non-graphitizable carbon material powder having an average particle size of 10 μm. Incidentally, as a result of performing X-ray diffraction measurement on the non-graphitizable carbon material obtained at this time, the (002) plane spacing was 0.381 nm, and the true specific gravity was 1.54.

90 parts by weight of this carbon material powder and 10 parts by weight of polyvinylidene fluoride as a binder are mixed, and this negative electrode mixture is dispersed in N-methyl-2-pyrrolidone to form a slurry, thereby preparing a negative electrode slurry. did. The negative electrode slurry thus obtained was uniformly applied to both surfaces of a 10 μm-thick strip-shaped copper foil serving as a negative electrode current collector, dried, and then compression-molded by a roll press to produce a strip-shaped electrode.

Next, the production of the positive electrode 2 will be described. Lithium carbonate and cobalt carbonate are mixed at a ratio of 0.5 mol: 1.0 mol and calcined in air at 900 ° C. for 5 hours to obtain LiC
oO ₂ was obtained. 91 parts by weight of this LiCoO ₂ powder,
6 parts by weight of graphite as a conductive agent and 3 parts by weight of polyvinylidene fluoride as a binder are mixed, and this positive electrode mixture is dispersed in N-methyl-2-pyrrolidone to form a slurry, which is formed into a 20 μm-thick strip. It was applied to both sides of an aluminum foil, dried, and then compression-molded by a roll press to produce a strip electrode.

A negative electrode 1 and a positive electrode 2 are sandwiched between separators 3 made of a microporous polypropylene film, and a pressing plate 12 and a spring plate 13 are integrally fixed with an element adhesive tape 9 to produce an electrode body 20. The insulating sheets 10 were arranged above and below the electrode body 20 and inserted into the battery case 11. Next, the positive electrode lead 4 is connected to the battery cover 8
Was welded to the positive electrode terminal 7 attached to. Further, the negative electrode lead 5 was assembled and welded to the battery case 11.

Then, L was added to a mixed solvent of 50% by volume of propylene carbonate and 50% by volume of dimethyl carbonate.
An electrolyte prepared by dissolving iPF ₆ at a rate of 1 mol / liter is injected into the battery case 11, and the battery lid 8 is fixed to the battery case 11 by laser welding to produce a prismatic lithium ion secondary battery. did. The size of the battery case 11 was 34 mm in width, 48 mm in height, and 8 mm in thickness.

As shown in FIG. 2, the spring plate 13 used in this embodiment has a flat bowl shape with a central portion protruding, and its peripheral portion is in contact with the inner wall of the battery case 11. The central part is inserted into the battery case 11 so as to press the electrode body 20.

Comparative Example 1 A battery was manufactured in the same manner as in Example 1 except that the spring plate 13 was replaced with a spring plate 14 having the shape shown in FIG. still,
The spring plate 14 has a structure in which three convex portions have a spring property.

Comparative Example 2 A battery was manufactured in the same manner as in Example 1 except that the spring plate 15 having the shape shown in FIG. still,
The spring plate 15 has a convex portion at the center, and has a structure having the maximum spring property at this portion.

The batteries prepared in Example 1 and Comparative Examples 1 and 2 were measured for charge / discharge at 23 ° C. The charging voltage was set to 4.2V and 700
The battery was charged at a constant current of 2 hours and 30 minutes at a constant current of mA, and discharged at 40 mA.
The operation was performed at a constant current of 0 mA to a final voltage of 2.75 V, which was used as the initial capacity of the battery. Table 1 shows the results.

[0025]

[Table 1]

Further, charging and discharging are repeated under the above conditions,
Capacity A at the 10th cycle and Capacity B at the 200th cycle
And the capacity retention B / A (%) were determined. Table 2 shows the results.

[0027]

[Table 2]

From the measurement results, it is found that the rectangular organic electrolyte secondary battery using the spring plate 13 according to the present invention is superior in initial capacity and cycle characteristics to those using the spring plates 14 and 15 of other shapes. You can see that there is. Also, it was recognized that the same effect was obtained when the diameter of the spring plate 13 was equal to or more than の of the width of the battery case 11.

The material of the spring plate used here may be any material as long as it can withstand the electrolytic solution of the battery. For example, a metal plate such as iron, nickel, copper, stainless steel, and titanium, a plastic plate such as polypropylene, polyethylene, polycarbonate, polytetrafluoroethylene, and polyvinylidene fluoride, a ceramic plate, a graphite plate, and the like can be given. In particular, a stainless steel material which is thin, has high strength, is low in cost, and has excellent corrosion resistance is preferable.

The present invention is not limited to the above-described embodiment, but may have other configurations that embody the technical idea of the present invention.

[0031]

Effect of the Invention] above, use the LixMO _2, or LixM ₂ O ₄ (M is one or more transition metals) used, a carbon material capable of doping and dedoping negative electrode as a positive electrode active material as described in detail In the conventional rectangular organic electrolyte secondary battery, the initial capacity and the cycle characteristics can be improved by inserting a flat bowl-shaped spring plate between the electrode body and the battery case.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a rectangular organic electrolyte secondary battery according to the present invention.

2A and 2B are spring plates used in the organic electrolyte secondary battery shown in FIG. 1, wherein FIG. 2A is a plan view and FIG. 2B is a cross-sectional view taken along line AA of FIG.

FIG. 3 is a perspective view of a spring plate used in Comparative Example 1.

FIG. 4 is a perspective view of a spring plate used in Comparative Example 2.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Negative electrode, 2 ... Positive electrode, 3 ... Separator, 4 ... Positive electrode lead, 5 ... Negative electrode lead, 6 ... Gasket, 7 ... Positive electrode terminal,
8 ... battery lid, 9 ... element adhesive tape, 10 ... insulating sheet,
11 ... battery case, 12 ... holding plate, 13, 14, 15
... spring plate, 20 ... electrode body

Claims (2)

[Claims] 1. A lithium composite oxide L as a positive electrode active material
In an organic electrolyte secondary battery comprising a positive electrode having ixMO ₂ or LixM ₂ O ₄ (M is one or more transition metals) and a negative electrode having a carbon material capable of being doped with lithium and dedoped as a negative electrode active material, An organic electrolyte secondary battery characterized in that a flat bowl-shaped elastic body is disposed between the battery and the inner wall of the battery case. 2. The flat bowl-shaped elastic body has a diameter equal to or more than の of a battery case width.
The organic electrolyte secondary battery according to claim 1.