JPH0773899A - Non-aqueous secondary battery and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a non-aqueous electrolyte secondary battery having an improved electric charging/discharging cycle characteristic by filling an electrode group consisting of positive and negative electrode plates alternately laminated via separators and expansible materials interposing the electrodes. CONSTITUTION:Positive electrode plates 1 having reversibility with respect to electric charging/discharging and negative electrode plates 2 made of a carbon material as a main active material are alternately laminated via separators 3 made of polypropylene. A filter 9 expansible toward both sides is disposed in such a manner as to interpose the electrodes, and they are tightly inserted into a battery jar 4. An electrolyte, in which lithium perchlorate is dissolved into a solvent obtained by mixing propylene carbonate with ethylene carbonate is injected, and then, a port sealing plate 8 is bonded to the battery jar 4. A core material of the negative plate 2 and a core material of the positive plate 1 are connected to a negative electrode terminal 5 of the port sealing plate 8 via leads 7, 6, followed by spot welding. Consequently, it is possible to provide a non-aqueous electrolyte secondary battery which can restrain loosening of the electrode plates due to expansion or contraction caused by electric charging/ discharging of the battery.

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 and a method for manufacturing the same.

[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 a 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 decrease in battery voltage is small, and it is actively researched.

[0004]

When a material for intercalating lithium ions such as graphite powder is used for the negative electrode, lithium is inserted and discharged during charge and discharge of the battery,
By repeating expansion and contraction of the electrode plate, the electrode plate loosens,
The contact between the negative electrode active materials (carbon materials) deteriorates. As a result, the current collecting ability of the electrode plate is lowered, and the capacity is lowered with the charge / discharge cycle of the battery. As a countermeasure for this, it has been attempted to add a fibrous graphite or the like 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. further,
The addition of fibrous graphite does not suppress the expansion and contraction of the negative electrode plate, and a problem still remains in a long-term charge / discharge cycle.

As another countermeasure, it has been proposed to press the electrode plate group using a pressing member such as a leaf spring (Japanese Patent Laid-Open No. 294071/1992). However, according to this method, it is necessary to apply pressure when the electrode plate group and the pressure member are housed in the battery case, and it is difficult to apply sufficient pressure structurally. In addition, when a leaf spring is used as the pressing member, it is difficult to apply pressure evenly to the surface of the electrode plate, and the leaf spring deteriorates after long-term use and cannot be used for a long time.
Therefore, an object of the present invention is to improve the electrode plate group pressurizing means in a non-aqueous electrolyte secondary battery using a carbon material for the negative electrode to improve the charge / discharge cycle characteristics.

[0006]

In order to solve the above-mentioned problems, the present invention is to fill a material that expands in parallel with an electrode plate group in which positive electrode plates and negative electrode plates are alternately stacked with a separator interposed therebetween. is there. As this material, a material that expands by absorbing an electrolytic solution or a material that expands by heating is used. When the liquid absorbing expansive material is used, the expansive material can absorb and expand in the step of injecting the electrode plate group before sealing. When the latter heat-expandable material is used, it is expanded by heating after sealing the battery.

Examples of the liquid-absorbent material include liquid-swellable resins such as polyacrylic acid salt, polyethylene oxide, and acrylic acid-acrylonitrile copolymer, in addition to polyacrylamide used in Examples described later. Further, as the latter thermally expandable material, other than those shown in the examples,
Acrylonitrile-vinylidene chloride copolymer resin, acrylonitrile-a variety of thermoplastic resins such as methyl methacrylate copolymer resin as a core, inside which is gasified at a temperature below the softening point of the resin, such as propane, butane, For example, microcapsules enclosing a low boiling point liquid such as pentane can be used. Filling the thermosetting resin with the above-mentioned heat-expandable resin so as to be parallel to the electrode plate group,
When the former is expanded and the latter is cured by heating, it is advantageous because the pressed state of the electrode by the expanded resin can be maintained regardless of changes in the surrounding environment.

[0008]

According to the present invention, the expansive material is arranged in parallel to the electrode plates in which the positive electrode plates and the negative electrode plates are alternately stacked with the separators interposed therebetween, and the expansive material is expanded after being housed in the battery case. , The electrode plate group can be mechanically pressed. Therefore, it is possible to suppress loosening of the electrode plate due to expansion and contraction due to charge and discharge of the battery, and it is possible to suppress a decrease in capacity due to charge and discharge cycles. Further, since the compression of the electrode plate continues semipermanently after the filled expansive material is expanded, it is effective in long-term charge / discharge cycle characteristics.

[0009]

EXAMPLES Examples of the present invention will be described below. Example 1 A battery having the structure shown in FIG. 1 is manufactured by the following procedure. LiMn _1.8 Co _0.2 O which is a positive electrode active material
₄ is 5: 6: 2 of Li ₂ CO ₃ , Mn ₃ O _4, and CoCO _3.
Are mixed at a molar ratio of 100 ° C. and heated at 900 ° C. to synthesize. This is classified to 100 mesh or less, 10
To 0 g, 10 g of carbon powder as a conductive agent and an aqueous dispersion of polytetrafluoroethylene as a binder in solid content of 2
0 g is added and kneaded to form a paste, which is applied to a titanium core material, dried, and rolled to form a positive electrode plate. On the other hand, the negative electrode plate is
20 g of polyvinylidene fluoride as a binder is added to 100 g of graphite powder as an active material, dimethylformamide is further added, and the mixture is kneaded to form a paste, which is applied to a nickel core material, dried and rolled.

The positive electrode plate 1 and the negative electrode plate 2 are alternately laminated with a separator 3 made of polypropylene interposed therebetween to form an electrode plate group in which the negative electrode plates are arranged outside, and the electrode plate group is sandwiched. Filler 9 is placed on both sides, 110 mm long and 70 m wide
It is densely inserted in the battery case 4 having a width of 25 mm and a width of 25 mm. Next, an electrolyte solution in which 1 mol / l of lithium perchlorate is dissolved is poured into a solvent in which propylene carbonate and ethylene carbonate are mixed at a volume ratio of 1: 1 and the sealing plate 8 is bonded to the case.

The sealing plate 8 is provided with a negative electrode terminal 5 and a positive electrode terminal (not shown), and leads 7 and 6 connected to the negative electrode core material and the positive electrode core material are spotted on these terminals, respectively. It is welded. As the filler 9, polyacrylamide, which is a liquid-swellable resin, is packed in a polypropylene bag made of the same material as the separator, and inserted so as to sandwich the electrode plate group. The battery produced as described above is designated as A.

[Comparative Example 1] A liquid absorbing expansive material was not filled,
A battery is manufactured in the same manner as in Example 1 except that a case whose width is reduced to 20 mm is used. This battery is a1
And [Comparative Example 2] 5 g of fibrous graphite and 10 g of polyvinylidene fluoride were added to 100 g of graphite powder to form a paste using dimethylformamide, which was applied to a nickel core material, dried, and rolled to obtain a negative electrode. A battery is manufactured in the same manner as in Comparative Example 1 except that This battery is designated as a2.

The batteries thus produced were subjected to a charge / discharge cycle test under the conditions of a charge / discharge current of 2 A and a charge / discharge voltage range of 4.3 V to 3.0 V. The result is shown in FIG. Here, the discharge capacity at the first cycle is C0, and the discharge capacity at the nth cycle is Cn.
Then, the capacity retention rate is defined as follows. Capacity retention rate (%) = (C0−Cn) / C0 × 100 The capacity of the battery a1 of the comparative example is drastically decreased due to charge / discharge cycles, and the capacity retention rate at 50 cycles is 48%. In addition, the battery a2 of the comparative example does not have a capacity decrease as much as the battery a1, but the capacity retention ratio at 100 cycles is 75.
%. On the other hand, the battery A of the present embodiment is the battery a
Compared with 1 and a2, the cycle performance is very good and 100
The capacity retention rate in the cycle is 93%.

Example 2 In this example, a thermally expansive resin is used as the filler. As the heat-expandable material, microcapsules having an acrylonitrile-vinyl acetate copolymer resin as a core and propane enclosed therein are used. As the microcapsules, those whose volume increases by about 3 to 5% by heating are used. When a microcapsule having a volume expansion coefficient of more than 10% is used, the expansion of the microcapsule may damage the battery. A battery is manufactured in the same manner as in Example 1, and instead of polyacrylamide, which is a liquid-swellable resin, the thermally expandable microcapsules are packed and filled in a polypropylene bag.
After sealing the battery, the battery is heated at a temperature between 80 ° C and 90 ° C for about 20 minutes. The battery thus manufactured is designated as B.
However, since heating at this temperature may deteriorate the performance of the battery itself, it is preferable that the heating be as short as possible.

The result of the charge / discharge cycle test of the battery B under the same conditions as above is shown in FIG. The capacity retention rate of Battery B in 100 cycles is about 96%. It can be seen that the cycleability of the battery B of this example is better than that of the battery A of Example 1. That is, since the filler of this example has a higher hardness than the filler used in Example 1, it is considered that the loosening of the electrode due to the expansion and contraction of the negative electrode can be more effectively suppressed.

[Embodiment 3] An example in which a mixture of a thermosetting resin and a thermally expansive resin is used as a filler will be described. An epoxy resin is used as the thermosetting resin, and a microcapsule having an acronitrile-vinyl acetate copolymer resin as a core and propane enclosed therein is used as the heat-expandable resin, as in Example 2. A battery is prepared in the same manner as in Example 2, and is filled with microcapsules, which are heat-expandable spheres, and epoxy resin at a mixing ratio of 50:50 by volume. After sealing the battery, keep the battery at 80 ° C to 90 ° C.
Heat at a temperature between about 20 minutes. The battery thus manufactured is designated as C. The charge / discharge cycle test result of the battery C is shown in FIG.
Is shown in. The capacity retention rate of Battery C in 100 cycles is about 96%.

Next, a high temperature cycle test was conducted on the batteries B and C. The test conditions are a temperature atmosphere of 60 ° C., a charge / discharge current of 2 A, and a charge / discharge voltage range of 4.3 V to 3.0 V. The result is shown in FIG. As is clear from FIG.
It can be seen that the battery B has a larger capacity decrease with charge / discharge cycles than the battery C. This is considered to be a result of the fact that the microcapsules filled in the battery B at a temperature of 60 ° C. were unable to press the electrodes due to a slight softening. That is, since the battery C is also filled with the thermosetting resin at the same time, it is considered that the electrodes cannot be pressed under the high temperature cycle unlike the battery B and the high temperature cycle characteristics are improved.

Although the specific non-aqueous electrolyte and the positive electrode active material are used in the above examples, it goes without saying that the present invention is not limited to these. Furthermore, in the example, the expansion material was filled so as to sandwich the electrode group, but it is not necessary to fill the expansion material on both sides, and it is sufficient if pressure is applied in the vertical direction of the electrode plate group, and one side is also sufficiently effective. is there.

[0019]

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.

FIG. 2 is a diagram showing cycle characteristics of a battery of an example and a battery of a comparative example.

FIG. 3 is a diagram showing high-temperature cycle characteristics of batteries of Examples.

[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 lead 7 Negative electrode lead 8 Sealing plate 9 Expansion material

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

Claims (4)

[Claims] 1. An electrode plate group, a non-aqueous electrolyte, and the electrode plate group, wherein positive electrodes having reversibility to charge and discharge and negative electrodes containing a carbon material as a main active material are alternately stacked with a separator interposed therebetween. A non-aqueous electrolyte secondary battery comprising a material that expands in parallel. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the material that expands is a liquid-swellable resin. 3. An electrode plate group, a non-aqueous electrolyte, and the electrode plate group, wherein positive electrodes having reversibility to charge and discharge and negative electrodes containing a carbon material as a main active material are alternately stacked with a separator interposed therebetween. A method for manufacturing a non-aqueous electrolyte secondary battery, which comprises a step of housing thermally expandable materials filled in parallel in a battery case, heating after sealing, and heating. 4. The method for manufacturing a non-aqueous electrolyte secondary battery according to claim 3, wherein a thermosetting resin is filled together with the thermally expandable material in parallel with the electrode plate group.