JPH07122301A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To enhance charge/discharge cycle performance by covering part of the surface of an electrode plate group comprising a positive plate, a negative plate, and a separator with a heat-shrinkable resin film. CONSTITUTION:A negative electrode 2 and a positive electrode 1 are arranged through a separator so that the negative electrode locates outside. A heat- shrinkable tube 9 is put on the electrode group, then heat-shrunken to physically compress the electrode group, and the electrode group is put into a case 4. An electrolyte is poured into the case 4, and a sealing plate 8 is bonded to the case 4 to form a battery. Since the electrode group is physically compressed from the outside, the looseness of the electrode plates attendant on charge/ discharge cycles is suppressed.

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 having a high energy density.

[0002]

2. Description of the Related Art Non-aqueous electrolyte secondary batteries having lithium or a lithium compound as a negative electrode are expected to have a high voltage and a high energy density, and have been actively studied. So far,
V ₂ O ₅ , Cr ₂ as a positive electrode active material of a non-aqueous electrolyte secondary battery
O ₅ , MnO ₂ , TiS _{2 and the} like are known. In recent years, LiMn ₂ O ₄ and LiCo have been used as positive electrode active materials for 4-volt class non-aqueous electrolyte secondary batteries having higher energy density.
O _2, such as LiNiO _2, LiFeO ₂ has been attracting attention. In particular, LiMn ₂ O ₄ , LiNiO ₂ and LiFeO ₂ are low in cost and the supply of raw materials is stable, and active research is being carried out as an active material for a large capacity non-aqueous electrolyte secondary battery. On the other hand, as the negative electrode active material, a carbon material has attracted attention in place of metallic lithium in terms of safety and rate characteristics. In particular, graphite powder with a high degree of graphitization has a high capacity and a discharge potential of about 0.1 compared to metallic lithium.
It is V-noble and has a characteristic that the battery voltage does not drop so much that it has been actively researched.

[0003]

However, when a material that intercalates lithium ions, such as graphite powder, is used for the negative electrode, the expansion and contraction of the electrode plate is accompanied by the absorption and desorption of lithium during charge and discharge of the battery. By repeating the process, the electrode plate becomes loose, and the contact between the negative electrode active materials (carbon materials) deteriorates. As a result, there has been a problem that the current collecting ability of the electrode plate is lowered and the capacity is lowered with charge / discharge cycles of the battery. As a countermeasure to this problem, fibrous graphite or the like is added to the negative electrode to form a current collecting network of the electrode plate to improve the current collecting ability of the electrode plate. In the case of adding, the amount of the binder needs to be increased in order to increase the strength of the electrode plate, and there remains a problem that the absolute capacity of the battery is lowered. Furthermore, addition of fibrous graphite or the like does not suppress expansion and contraction of the negative electrode plate, and a problem still remains in a long-term charge / discharge cycle. Therefore, an object of the present invention is to improve charge / discharge cycle characteristics of a non-aqueous electrolyte secondary battery using a carbon material for a negative electrode.

[0004]

In order to solve the above-mentioned problems, the present invention covers a part of the surface of an electrode plate group consisting of a positive electrode plate, a negative electrode plate and a separator with a heat-shrinkable resin film. . As the heat-shrinkable resin, polypropylene, polyethylene, crosslinked polyolefin, polyvinyl chloride, polyethylene terephthalate or the like can be used. The thickness of the resin film used is 20 to 4
It is suitable that the shrinkage in the vertical direction is 5 μm, the shrinkage in the vertical direction is 5 to 15%, and the shrinkage in the horizontal direction is 40 to 60%.

[0005]

According to the present invention, a part of the surface of an electrode plate group consisting of a positive electrode plate, a negative electrode plate and a separator is covered with a heat-shrinkable resin film, and the film is heat-shrinked so that the electrode plate group is physically exposed from the outside. Can be oppressed. Therefore, it is possible to prevent the electrode plate from loosening due to expansion / contraction of the battery during charging / discharging, and to suppress a decrease in capacity due to charging / discharging cycles. Further, by subjecting the heat-shrinkable resin film to hydrophilic treatment with a surfactant, variations in battery capacity can be reduced. As this surfactant, oleic acid amide, oleic acid amide ethylene oxide adduct, oleic acid diethanolamide, oleic acid diethanolamine and the like are used. Further, since the electrode plate group is covered with the film, workability when inserting the electrode plate group into the battery case can be improved.

[0006]

EXAMPLES Examples of the present invention will be described below. [Example 1] A battery was manufactured by the following procedure. LiMn _1.8 Co _0.2 O ₄ , which is the positive electrode active material, contains Li ₂ CO ₃ and M
n ₃ O ₄ and CoCO ₃ are mixed in a molar ratio of 5: 6: 2,
It was synthesized by heating at 900 ° C. Further, this was classified into 100 mesh or less to obtain a positive electrode active material. To 100 g of the positive electrode active material, 10 g of carbon powder as a conductive agent and 20 g of an aqueous dispersion of polytetrafluoroethylene as a binder in a resin component were added, kneaded to form a paste, and applied to a titanium core material, It is dried and rolled into a positive electrode. The negative electrode was prepared by adding 20 g of polyvinylidene fluoride to 100 g of graphite powder as a negative electrode active material, further adding dimethylformamide as a solvent, kneading to form a paste, coating on a nickel core material, drying and rolling. Create.

FIG. 1 is a vertical sectional view of the prismatic battery used in this example. To assemble this battery, first of all, as shown in FIG.
And the positive electrode 1 are arranged so that the negative electrode is outside. A 20 μm-thick polyvinyl chloride resin heat-shrinkable tube 9 is covered on the electrode plate group, and then the electrode plate group is thermally shrunk and physically pressed to produce an electrode plate group. Next, the lead connected to the positive collector plate 6 is spot-welded to the positive terminal, and the lead connected to the negative collector plate 7 is spot-welded to the negative terminal 5. These electrode plate groups are put in a case 4 having a length of 110 mm, a width of 70 mm and a width of 25 mm. Next, 1 mol / min was added to a solvent in which propylene carbonate and ethylene carbonate were mixed at a volume ratio of 1: 1.
An electrolyte solution in which 1 of lithium perchlorate is dissolved is injected, and the sealing plate 8 is adhered to the case to form a battery.

[Comparative Example 1] In the battery manufacturing process of Example 1,
A battery is manufactured in the same manner as in Example 1 except for the step of covering with a heat-shrinkable resin tube.

A charging / discharging cycle test was conducted on these manufactured batteries at a charging / discharging current of 2 A and a charging / discharging voltage range of 4.3V to 3.0V. The results are shown in Table 1. here,
The capacity retention rate is defined as follows. Assuming that the discharge capacity at the first cycle is C0 and the discharge capacity at the nth cycle is Cn, the capacity retention rate (%) = (C0-Cn) / C0 × 100 In the battery of the comparative example, the capacity decrease due to the charge / discharge cycle is severe. The capacity retention rate in 100 cycles is 30%. On the other hand, the battery of this example has much better cycleability than the battery of the comparative example, and the capacity retention rate at 100 cycles is 95%.

[0010]

[Table 1]

[Example 2] Next, a case was investigated in which a heat-shrinkable film of the same kind as that used in Example 1 was subjected to hydrophilic treatment. First, a heat-shrinkable tube made of polyvinyl chloride resin is dipped in a 3 wt% ethyl alcohol solution of oleic acid amide as a surfactant, pulled up, and then vacuum dried to remove ethyl alcohol. Using a heat-shrinkable tube treated with a surfactant like this,
100 batteries are prepared in the same manner as in Example 1.

[Comparative Example 2] [Comparative Example 2]
Make 0 batteries.

These batteries were charged / discharged under the conditions of a charging / discharging current of 2 A and a charging / discharging voltage range of 4.3 V to 3.0 V, and the variation of the initial capacity was confirmed. The results are shown in Table 2. When the resin film covering the electrode plate group is not subjected to the hydrophilic treatment, the initial capacity of the battery varies by ± 15% as shown in Table 2. However, when the film is subjected to the hydrophilic treatment, the variation in battery capacity is reduced to 5%. It is considered that this is because the electrolyte solution does not penetrate well into the electrode group when a film that has not been subjected to the hydrophilic treatment is used when injecting the solution into the battery.

[0014]

[Table 2]

In the above examples, the case where a system in which 1 mol / l of lithium perchlorate was dissolved in an equal volume mixed solvent of propylene carbonate and ethylene carbonate was used as the non-aqueous electrolytic solution was used. Besides this, propylene carbonate, ethylene carbonate,
When carbonates such as diethoxy carbonate, gamma-butyrolactone, esters such as methyl acetate are used alone or as a mixture of one or more, and lithium perchlorate, lithium borofluoride or lithium hexafluorophosphate is used as a solute. However, the same result can be obtained. Although in the embodiment described with reference to LiMn _1.8 Co _0.2 O ₄ as a cathode active material, In addition as a positive electrode active material, V
₂ O ₅ , Cr ₂ O ₅ , MnO ₂ , TiS ₂ , LiMn ₂ O ₄ , L
iCoO _2, LiNiO _2, LiFeO is of course obtained similar results using ₂ or the like. further,
In the examples, the prismatic battery is used for explanation, but not only the prismatic battery but also the cylindrical battery, the cycle characteristics are improved by pressing the electrode plate group with the heat-shrinkable resin film.

[0016]

As described above, according to the present invention, the charge / discharge cycle characteristics of a non-aqueous electrolyte secondary battery having a carbon material as a negative electrode can be remarkably improved.

[Brief description of drawings]

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode plate 2 Negative electrode plate 3 Separator 4 Battery case 5 Negative electrode terminal 6 Positive electrode current collector plate 7 Negative electrode current collector plate 8 Sealing plate 9 Heat shrinkable resin film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiko Mito 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Within the corporation

Claims (1)

[Claims] 1. An electrode plate group comprising a positive electrode having reversibility to charge and discharge, a negative electrode containing a carbon material as a main active material, and a separator, wherein a part of the surface of the electrode plate group is a heat-shrinkable resin. A non-aqueous electrolyte secondary battery characterized by being covered with a film.