JP3263198B2 - Non-aqueous electrolyte secondary battery and manufacturing method thereof - Google Patents

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 producing the same.

[0002]

2. Description of the Related Art Non-aqueous electrolyte secondary batteries using lithium or a lithium compound as a negative electrode are expected to have a high voltage and a high energy density, and are being actively studied. So far,
V ₂ O ₅ , Cr ₂ as a positive electrode active material of a nonaqueous electrolyte secondary battery
O ₅ , MnO ₂ , TiS _{2 and the} like are known. In recent years, LiMn ₂ O ₄ , LiCo as a positive electrode active material of a 4 volt class non-aqueous electrolyte secondary battery having a higher energy density
O ₂ , LiNiO ₂ , LiFeO _{2 and the} like have been attracting attention. In particular, LiMn ₂ O ₄ , LiNiO ₂ and LiFeO ₂ are inexpensive, have a stable supply of raw materials, and are being actively studied as active materials for large-capacity non-aqueous electrolyte secondary batteries.

On the other hand, as a negative electrode active material, a carbon material has been attracting attention instead of lithium metal in view 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 times that of metallic lithium.
It has the feature of being V-noble and has a small decrease in battery voltage, and has been actively studied.

[0004]

In the case where a material that intercalates lithium ions such as graphite powder is used for the negative electrode, it involves the occlusion and release of lithium during charging and discharging of the battery.
By repeating expansion and contraction of the electrode plate, the electrode plate becomes loose,
The contact between the negative electrode active materials (carbon materials) becomes poor. As a result, the current collecting ability of the electrode plate is reduced, and the capacity is reduced due to the charge / discharge cycle of the battery. As a countermeasure, fibrous graphite and the like are 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, it is necessary to increase the amount of the binder in order to increase the strength of the electrode plate, and there remains a problem that the absolute capacity of the battery is reduced. further,
Even if fibrous graphite or the like is added, expansion and shrinkage of the negative electrode plate are not suppressed, and a long-term charge / discharge cycle still has a problem.

As another countermeasure, it has been proposed to press the electrode plate group by using a pressing member such as a leaf spring (Japanese Patent Laid-Open No. 4-294707). However, according to this method, when the electrode group and the pressurizing member are stored in the battery case, it is necessary to apply pressure, and it is difficult to apply a sufficient pressure due to the structure. In addition, when a leaf spring is used as the pressing member, it is difficult to uniformly apply pressure to the electrode plate surface, and the leaf spring deteriorates when used for a long time, and cannot be used for a long time.
Therefore, an object of the present invention is to improve the electrode group pressurizing means in a non-aqueous electrolyte secondary battery using a carbon material for the negative electrode, and to improve charge / discharge cycle characteristics.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a heat-expandable material and a thermosetting material in parallel with a group of electrode plates in which a positive electrode plate and a negative electrode plate are alternately stacked via a separator.
The conductive resin is filled in a battery case . The heat-expandable material is
It is expanded by heating after sealing the battery.

[0007] Examples of the thermally expandable material include those shown in the examples.
Acrylonitrile-vinylidene chloride copolymer tree
Fatty, acrylonitrile-methyl methacrylate copolymer tree
The core is made of various thermoplastic resins such as fats,
Substances that gasify at temperatures below the softening point of fats, e.g.
Microphone containing low-boiling liquid such as butane, butane, pentane, etc.
A capsule or the like can be used. Thermal expansion of the former
Thermosetting resin along with resin so that it is parallel to the electrode group
Filling and heating to expand the former and harden the latter
And the compression of the electrodes by the expanding resin
It is advantageous because it can be maintained regardless.

[0008]

According to the present invention, an inflatable material is arranged in parallel with an electrode plate group in which a positive electrode plate and a negative electrode plate are alternately stacked with a separator interposed therebetween. The electrode group can be mechanically pressed. Therefore, it is possible to suppress the slack of the electrode plate due to expansion and contraction accompanying the charge and discharge of the battery, and it is possible to suppress a decrease in capacity due to a charge and discharge cycle. Furthermore, since the pressing of the electrode plate continues semipermanently from the time when the filled expandable material is expanded, it is effective in long-term charge / discharge cycle characteristics.

[0009]

Embodiments 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 as the positive electrode active material
₄ is a mixture of Li ₂ CO ₃ , Mn ₃ O ₄ and CoCO _{3 in a} ratio of 5: 6: 2.
And the mixture is heated at 900 ° C. to synthesize. This is classified into 100 mesh or less, and 10
0 g, 10 g of carbon powder as a conductive agent, and an aqueous dispersion of polytetrafluoroethylene as a binder in a solid content of 2 g.
0 g is added and kneaded to form a paste, applied to a titanium core material, dried and rolled to obtain a positive electrode plate. On the other hand, the negative electrode plate
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. The paste is applied to a nickel core material, dried, and rolled.

The above-mentioned positive electrode plate 1 and negative electrode plate 2 are alternately laminated with a polypropylene separator 3 interposed therebetween to form an electrode plate group in which the negative electrode plate is disposed outside, and further sandwich the electrode plate group. Filling material 9 on both sides, 110mm long, 70m wide
m, 25 mm in width. Next, an electrolyte in which 1 mol / l of lithium perchlorate is dissolved in a solvent in which propylene carbonate and ethylene carbonate are mixed at a volume ratio of 1: 1 is injected, and the sealing plate 8 is adhered to the case.

The sealing plate 8 is provided with a negative electrode terminal 5 and a positive electrode terminal (not shown), and these terminals are provided with spots of leads 7 and 6 connected to the core material of the negative electrode and the core material of the positive electrode, respectively. Welded. As the filler 9, polyacrylamide as a liquid-swelling 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 prepared as described above is designated as A.

[Comparative Example 1] No liquid-absorbing expandable material was 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] To a negative electrode obtained by adding 5 g of fibrous graphite and 10 g of polyvinylidene fluoride to 100 g of graphite powder, forming a paste using dimethylformamide, applying the paste to a nickel core material, drying and rolling. A battery was fabricated in the same manner as in Comparative Example 1 except for the above. This battery is referred to as a2.

These batteries 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 results are shown in Figure 2. Here, the discharge capacity at the first cycle is C0, and the discharge capacity at the nth cycle is Cn.
And the capacity retention ratio is defined as follows. Capacity maintenance rate (%) = (C0−Cn) / C0 × 100 The battery a1 of the comparative example has a sharp decrease in capacity due to charge / discharge cycles, and the capacity maintenance rate in 50 cycles is 48%. In addition, the battery a2 of the comparative example does not decrease in capacity as much as the battery a1, but has a capacity retention ratio of 75 in 100 cycles.
%. On the other hand, the battery A of the present embodiment is a battery a
Cycleability is very good as compared with 1, a2, 100
The capacity retention in the cycle is 93%.

Embodiment 2 In this embodiment, a heat-expandable resin is used as a filler. As the thermally expandable material, microcapsules having an acrylonitrile-vinyl acetate copolymer resin as a core and propane encapsulated therein are used. The microcapsules whose volume increases by about 3 to 5% by heating are used. When a microcapsule having a volume expansion rate exceeding 10% is used, the battery may be damaged due to expansion of the microcapsule. The battery is manufactured in the same manner as in Example 1, and the above-mentioned heat-expandable microcapsules are packed in a polypropylene bag instead of polyacrylamide as a liquid-swelling resin.
After sealing the battery, the battery is heated at a temperature between 80C and 90C for about 20 minutes. The battery fabricated in this manner is designated as B.
However, heating at this temperature may decrease the performance of the battery itself, so that it is better to be as short as possible.

FIG. 2 shows the result of the charge / discharge cycle test of the battery B under the same conditions as described above. The capacity retention rate of the battery B in 100 cycles is about 96%. It can be seen that the cycle performance of the battery B of this example is even better than that of the battery A of Example 1. That is, since the filler of the present example has 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.

Example 3 An example using a mixture of a thermosetting resin and a heat-expandable resin as a filler will be described. As the thermosetting resin, an epoxy resin is used, and as the thermally expandable resin, microcapsules having an acrylonitrile-vinyl acetate copolymer resin as a core and propane encapsulated therein are used as in Example 2. A battery was prepared in the same manner as in Example 2, and filled with a mixture of microcapsules, which are thermally expandable spheres, and epoxy resin in a volume ratio of 50:50. After sealing the battery, the battery is heated at a temperature between 80C and 90C for about 20 minutes. The battery fabricated in this manner is designated as C. FIG. 2 shows the results of the charge / discharge cycle test of the battery C. The capacity retention of the battery C in 100 cycles is about 96%.

Next, the batteries B and C were subjected to a high-temperature cycle test. The test conditions are a charge / discharge current of 2 A and a charge / discharge voltage range of 4.3 V to 3.0 V in a 60 ° C. temperature atmosphere. The results are shown in Figure 3. As apparent from FIG. 3,
It can be seen that the capacity of the battery B greatly decreases with the charge / discharge cycle as compared to the battery C. This is considered to be a result of the fact that the microcapsules filled at the temperature of 60 ° C. in the battery B softened slightly, so that the electrodes could not be pressed. That is, since the battery C is also filled with the thermosetting resin at the same time, unlike the battery B, the electrodes cannot be pressed even in the high-temperature cycle, and the high-temperature cycle characteristics are considered to be improved.

In the above embodiments, specific non-aqueous electrolytes and positive electrode active materials were used, but it goes without saying that the present invention is not limited to these. Further, in the embodiment, the inflation material is filled so as to sandwich the electrode group. However, it is not necessary to fill the inflation material on both sides, and it is sufficient that pressure is applied in the vertical direction of the electrode plate group. is there.

[0019]

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

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a prismatic nonaqueous electrolyte secondary battery according to an embodiment 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 a battery of an example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode plate 2 Negative electrode plate 3 Separator 4 Battery case 5 Negative terminal 6 Positive electrode lead 7 Negative electrode lead 8 Sealing plate 9 Expansion material

Continuing on the front page (72) Inventor Yasuhiko Mito 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. In-company (56) References JP-A-4-294701 (JP, A) JP-A-5-121101 (JP, A) JP-A-59-158070 (JP, A) (58) Fields investigated (Int. . ^7, DB name) H01M 10/40

Claims (2)

(57) [Claims] 1. An electrode plate group comprising a positive electrode having reversibility to charge and discharge and a negative electrode containing a carbon material as a main active material alternately stacked via a separator, a non-aqueous electrolyte, a battery case , and the electrode Thermo-expandable material and thermosetting filled in battery case in parallel with plate group
A non-aqueous electrolyte secondary battery comprising a resin . 2. An electrode group in which a positive electrode having reversibility to charge and discharge and a negative electrode having a carbon material as a main active material are alternately stacked via a separator, and a nonaqueous electrolyte is housed in a battery case.
As well as, in parallel with the electrode plate group, Oyo intumescent material
A method for producing a non-aqueous electrolyte secondary battery, comprising a step of filling a battery case with a thermosetting resin and heating after sealing.