Nonaqueous electrolyte secondary battery

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Industrial application field]

The present invention relates to a non-aqueous electrolyte secondary battery having a high energy density and high safety as a power source for driving an electronic device, a power source for holding a memory, or a battery for an electric vehicle.

【0002】

[Conventional technology and its problems]

With the rapid reduction in size and weight of electronic devices, there is an increasing demand for the development of a secondary battery that is small in size, lightweight, has a high energy density, and can be repeatedly charged and discharged. As a secondary battery that meets these requirements, a non-aqueous electrolyte secondary battery is the most promising.

【0003】

As the positive electrode active material of the non-aqueous electrolyte secondary battery, various materials such as titanium disulfide, lithium cobalt composite oxide, spinel type lithium manganese oxide, vanadium pentoxide and molybdenum trioxide have been studied. Among them, lithium cobalt composite oxide (LixCoO)₂) Is 4V (Li / Li)⁺) Since charging and discharging are performed at the above extremely noble potential, a battery having a high discharge voltage can be realized by using it as a positive electrode.

【0004】

As the negative electrode active material of non-aqueous electrolyte secondary batteries, various materials such as metallic lithium, Li-Al alloy capable of occluding and releasing lithium, and carbon materials have been studied. Among them, carbon materials are safe. There is an advantage that a battery having high properties and a long cycle life can be obtained.

【0005】

As the lithium salt, lithium perchlorate, lithium trimethanesulfonate trifluoride, lithium hexafluoride phosphate and the like are generally used. Among them, lithium hexafluoride phosphate has been widely used in recent years because of its high safety and high ionic conductivity of the dissolved electrolytic solution.

【0006】

Battery cases include cylindrical type, gum type, square type, and oval type. The cylindrical type is the most versatile, but less space efficient. The gum type and the square type are the most space efficient, and the oval type is between the cylindrical type and the square type.

【0007】

However, lithium cobalt composite oxide (Li_X CoO₂) A battery in which a power generation element consisting of a positive electrode, a carbon material negative electrode, and a non-aqueous electrolyte containing a lithium salt is housed in a space-efficient battery case such as a gum type, a square type, or an oval type is a battery after charging. There was a problem of swelling. The swelling of the battery causes the destruction of peripheral parts and the destruction of the battery storage case in electronic devices that have been highly concentrated in recent years. Further, in the assembled battery, various problems such as disconnection of the connection reed between the batteries and deformation of the terminal connecting the reed are caused.

【0008】

As countermeasures, we examined a method of increasing the plate thickness of the case and a method of using high-strength stainless steel or titanium as the material of the case. As a result, although the problem of swelling is slightly improved, the former method has a problem that the energy density per weight and capacity is lowered, and the latter method has a problem that the manufacturing cost of the battery is high.

【0009】

[Means for solving problems]

According to the present invention, a power generation element composed of a negative electrode made of a substance that occludes and releases lithium, a positive electrode, and a non-aqueous electrolyte containing lithium salt is housed in a battery case having an arched or S-shaped cross section. It tries to solve the problem.

【0010】

[Action]

Lithium cobalt composite oxide (Li), which is a positive electrode active material_X CoO₂) Has a layered structure, but it is known that the cobalt-oxygen layer expands and the crystal expands with the progress of the charging reaction accompanied by the desorption of lithium ions. It is known that the carbon material used for the negative electrode also has a layered structure and the crystals expand as the charging reaction proceeds with the insertion of lithium. That is, the volume of the power generation element composed of these positive and negative electrodes expands in the charge reaction and contracts in the discharge reaction. It is considered that the reason why the batteries in which these power generation elements are housed in the battery cases such as gum type, square type and oval type, which are excellent in space efficiency, swell during charging is because the case withstand voltage strength is low.

【0011】

On the other hand, a battery in which a power generation element in which electrodes are spirally wound is housed in a cylindrical case has a high withstand voltage of the case, so that there is no problem of swelling during charging, but space efficiency is inferior. However, a battery in which a power generation element is housed in an arch-shaped or S-shaped battery case like the battery of the present invention has a high withstand voltage of the case, so that the swelling of the battery during charging is solved and the space efficiency is excellent. It has characteristics.

【0012】

[Example]

Hereinafter, the present invention will be described with reference to suitable examples.

【0013】

The positive electrode is a lithium cobalt composite oxide (LixCoO).₂), Carbon powder as a conductive agent, and polyvinylidene fluoride as a binder in a weight ratio of 91: 2: 7, and a paste prepared using an organic solvent is uniformly applied to both sides of a stainless steel foil having a thickness of 15 μm. It is coated and then dried.

【0014】

For the negative electrode, graphite and fluororesin powder as a binder were mixed at a weight ratio of 91: 9, and a paste prepared using an organic solvent was uniformly applied to both sides of a stainless steel foil having a thickness of 15 μm and then dried. It is a thing.

【0015】

FIG. 1 is a vertical cross-sectional view and a cross-sectional view of the battery. In this figure, 1 is an arched case made by punching a steel plate (thickness 0.4 mm) with nickel plating on iron, and 2 is a sealing plate made by punching stainless steel (SUS304). Positive electrode terminal 3 (SUS304) and negative electrode Terminal 4 (SUS304) is fixed by a glass hermetic seal. Reference numeral 5 is a separator made of polypropylene, and 6 is a positive electrode, which is electrically connected to the positive electrode terminal 3 by a lead. Reference numeral 7 is a negative electrode, which is electrically connected to the negative electrode terminal 4. The separator, positive electrode, and negative electrode are spirally wound and inserted into the battery case, the electrolytic solution is injected, and then the joint between the case 1 and the sealing plate 2 is welded by a laser to seal the battery. The degree of compression of the above battery (inner dimension of battery case ÷ thickness of electrode plate) was 0.9.

【0016】

The organic electrolyte is a solvent in which ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) are mixed at a volume ratio of 2: 2: 1, and 1 mol / liter lithium hexafluoride phosphate and 0.05 mol. A solution prepared by dissolving / liter of lithium perchlorate was used.

【0017】

The organic electrolyte secondary battery of the present invention using the above-mentioned positive electrode plate, negative electrode plate, electrolytic solution and battery case is (A), except that the S-shaped battery case shown in FIG. 2 is used (A). The battery of the present invention having the same configuration is referred to as (B). The battery sizes of both of these are 100 mm in height, 10 mm in thickness, and 50 mm in width.

【0018】

In addition, as shown in FIGS. 3 and 4, the power generation element formed by laminating the strip-shaped separator 5, the positive electrode plate 6 and the negative electrode plate 7 is stored in an arch-shaped or S-shaped battery case. The batteries of the present invention having the same configuration as the battery of the invention (A) are called (C) and (D), respectively. Both batteries have a height of 100 mm, a thickness of 10 mm, and a width of 50 mm.

【0019】

For comparison, the configuration is the same as that of the battery (A) of the present invention, except that the separator 5, the positive electrode 6, and the negative electrode 7 are spirally wound and inserted into the oval battery case as shown in FIG. As shown in FIG. 6, the comparative battery is referred to as (a), and as shown in FIG. 6, the power generation element formed by laminating the strip-shaped separator 5, the positive electrode plate 6 and the negative electrode plate 7 is housed in a gum-shaped battery case. Outside, a comparative battery having the same configuration as the battery (A) of the present invention is called (a). The sizes of the batteries (a) and (b) are 100 mm in height, 10 mm in thickness, and 50 mm in width.

【0020】

Next, a charge / discharge cycle test was conducted in which these batteries were charged with a constant current of 500 mA until the terminal voltage reached 4.1 V, and then discharged with a constant current of 2.0 mA until the terminal voltage reached 3 V. 10 cycles were performed at room temperature. After stopping in the charged state, the swelling of the battery was measured. Table 1 shows the partial thickness of each battery before and after charging.

【0021】

[table 1]

<img file="JPH06181069A_D0001.tif" />As is clear from the results in Table 1, the battery thickness of the comparative batteries (A) and (B) is increased, whereas the thickness of the batteries (A), (B), (C) and (D) of the present invention is increased. Can not be seen. Next, the space efficiency of the assembled battery was compared between the cylindrical battery having a height of 100 mm and a diameter of 10 mm and the batteries (A) (B) (C) (C) of the present invention. Fig. 7 shows the filling method when the batteries are stored upright on a rectangular floor with a width of 50 mm and a depth of 100 mm, and Fig. 8 shows the filling method when the batteries are stored upright on a rectangular floor with a width of 50 mm and a depth of 105 mm. .. Table 2 summarizes the total projected area of the assembled batteries.

【0022】

[Table 2]

<img file="JPH06181069A_D0002.tif" />As is clear from the results, the battery of the present invention is 10% to 18% more space efficient than the cylindrical battery.

【0023】

In the above embodiment, the case where lithium cobalt composite oxide is used as the positive electrode active material has been described, but manganese dioxide including titanium disulfide and spinel-type lithium manganese oxide (LixMn) have been described.₂ O₄), Vanadium pentoxide and molybdenum trioxide can be used. Further, although a carbon material is used as the negative electrode, when using the positive electrode of the present invention, the negative electrode active material is not basically limited, and the negative electrode active material used in the conventional non-aqueous electrolyte secondary battery, for example, pure Lithium, lithium alloy and the like can be used.

【0024】

Further, the electrolytic solution which is a lithium ion conductive substance and the solid ion conductor are not basically limited, and those used in the conventional organic electrolytic solution secondary battery can be used. For example, examples of the organic solvent include cyclic esters such as ethylene carbonate, which is an aprotic solvent, and ethers such as tetrahydrofuran and dioxolane, and a solvent using these alone or a mixture of two or more thereof can be used. As the solid ion conductor, any one having lithium ion conductivity can be used. A typical example thereof is polyethylene oxide. Further, the supporting electrolyte dissolved in such a non-aqueous solvent or a solid ionic conductor is not basically limited. For example, LiAsF₆, LiPF₆, LiCF₃SO₃One or more such as can be used.

【0025】

[Effect of the invention]

As described above, a power generation element composed of a negative electrode made of a substance that occludes and releases lithium, a positive electrode, and a non-aqueous electrolyte containing a lithium salt is housed in an arch-shaped or S-shaped battery case. The non-aqueous electrolyte secondary battery can effectively suppress the swelling of the battery during charging and can effectively use the battery storage space, and its industrial value is extremely large.

[Simple explanation of drawings]

[Figure 1]

The figure which showed the internal structure of the arch type battery (swirl type).

[Figure 2]

The figure which showed the internal structure of the S-shaped battery (swirl type).

[Fig. 3]

The figure which showed the internal structure of the arch type battery (stacked type).

[Fig. 4]

The figure which showed the internal structure of the S-shaped battery (stacked type).

[Fig. 5]

The figure which showed the internal structure of an oval battery (swirl type).

[Fig. 6]

The figure which showed the internal structure of the gum type battery (stacked type).

[Fig. 7]

The figure which showed the assembly battery filling style of a cylindrical type, an arch type (swirl type and a laminated type), and an S-shaped type (swirl type and a laminated type) battery (space width 50 mm × depth 100 mm).

[Fig. 8]

The figure which showed the assembly battery filling style of a cylindrical type, an arch type (swirl type and a laminated type), and an S-shaped type (swirl type and a laminated type) battery (space width 50 mm × depth 105 mm).

[Explanation of symbols]

1 Battery case 2 Seal plate 3 Positive electrode terminal 4 Negative electrode terminal 5 Separator 6 Positive electrode 7 Negative electrode