JPH06181069A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To restrain bulging of a battery at charging time, and use space effectively by forming a case in an arch shape or an S shape when power generating elements composed of a negative electrode composed of a material to store and release lithium, a positive electrode and nonaqueous electrolyte containing lithium salt are housed in the battery case. CONSTITUTION:A positive electrode is formed of mixture of lithium cobalt composite oxide, carbon power as an electrically conductive agent and polyvinylidene fluoride as a binding agent. A negative electrode is formed of graphite and fluororesin powder as a binding agent. When an organic electrolyte secondary battery obtained in this way is housed in a case, a cross-sectional structure of a housing case 1 to a battery composed of a sealing plate 2, a positive electrode terminal 3, a negative electrode terminal 4, a separator 6, the positive electrode 6 and the negative electrode 7, is formed in an arch shape or an S shape.

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 high safety as a power source for driving electronic devices or a memory holding power source or a battery for electric vehicles.

[0002]

2. Description of the Related Art With the rapid miniaturization and weight reduction of electronic equipment, the development of a secondary battery that is smaller, lighter in weight and high in energy density, and that can be repeatedly charged and discharged with respect to the power source battery The demand is increasing. Non-aqueous electrolyte secondary batteries are the most promising secondary batteries that meet these requirements.

Various positive electrode active materials for non-aqueous electrolyte secondary batteries such as titanium disulfide, lithium cobalt composite oxide, spinel type lithium manganese oxide, vanadium pentoxide and molybdenum trioxide have been investigated. ing. Among them, lithium cobalt composite oxide (Li
Since xCoO ₂ ) charges and discharges at an extremely noble potential of 4 V (Li / Li ⁺ ) or more, a battery having a high discharge voltage can be realized by using it as a positive electrode.

As a negative electrode active material for a non-aqueous electrolyte secondary battery, various materials such as metallic lithium, Li-Al alloys capable of inserting and extracting lithium, and carbon materials have been studied. Among them, carbon materials are particularly preferable. Has the advantage that a battery with high safety and long cycle life can be obtained.

As the lithium salt, lithium perchlorate, lithium trifluorotrimethanesulfonate, lithium hexafluorophosphate, etc. are generally used. Among them, lithium hexafluorophosphate has been widely used in recent years because of its high safety and high ionic conductivity of the dissolved electrolyte.

The battery case includes a cylindrical type, a gum type, a square type, an oval type and the like. The cylindrical type is most commonly used, but it is not space efficient. The gum type and the square type have the highest space efficiency, and the oval type is between the cylindrical type and the square type.

However, lithium cobalt composite oxide (Li
_X CoO ₂ ) A positive electrode, a carbon material negative electrode, and a non-aqueous electrolyte containing a lithium salt in a power generating element housed in a gum-shaped, square-shaped, or oval-shaped battery case with excellent space efficiency. There was a problem that the battery swells after charging. The swelling of the battery causes destruction of peripheral parts, destruction of the battery storage case, and the like in electronic devices which have been highly concentrated in recent years. Further, in the assembled battery, various problems such as disconnection of connection leads between the batteries and deformation of terminals connecting the leads are caused.

As measures against this, a method of increasing the plate thickness of the case and a method of using stainless steel or titanium having high strength as a material of the case were examined. 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]

According to the present invention, a power generation element comprising a negative electrode made of a substance capable of occluding and releasing lithium, a positive electrode, and a non-aqueous electrolyte containing a lithium salt is used. The above problem is solved by housing the battery in the battery case.

[0010]

[Function] The lithium cobalt composite oxide (Li _X CoO ₂ ) that is the positive electrode active material has a layered structure, but with the progress of the charging reaction accompanying the desorption of lithium ions, cobalt-
It is known that the oxygen layer extends and the crystal expands.
It is known that the carbon material used for the negative electrode also has a layered structure and the crystal expands as the charging reaction proceeds with the insertion of lithium. That is, the power generation element including these positive and negative electrodes expands in volume during the charge reaction and contracts during the discharge reaction. It is considered that the reason why a battery in which these power generating elements are housed in a gum-shaped, square-shaped, or oval-shaped battery case having excellent space efficiency swells during charging is that the case pressure resistance is low.

On the other hand, a battery in which a power generating element formed by spirally winding an electrode is housed in a cylindrical case does not have a problem of swelling at the time of charging because of a high withstand voltage of the case, but is inferior in space efficiency. However, a battery in which a power generating 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 swelling of the battery at the time of charging is solved and space efficiency is excellent. It has characteristics.

[0012]

EXAMPLES The present invention will be described below with reference to preferred examples.

The positive electrode is a lithium cobalt composite oxide (Li
xCoO ₂ ), carbon powder as a conductive agent, and polyvinylidene fluoride as a binder were mixed at a weight ratio of 91: 2: 7, and a paste prepared by using an organic solvent was applied to both sides of a stainless steel foil having a thickness of 15 μm. Is uniformly applied and then dried.

For the negative electrode, graphite and fluororesin powder as a binder were mixed in a weight ratio of 91: 9, and a paste prepared by using an organic solvent was uniformly applied to both surfaces of a 15 μm-thick stainless steel foil and dried. It has been processed.

FIG. 1 is a vertical sectional view and a horizontal sectional view of a battery. In this figure, 1 is an arch-shaped case made by punching a steel plate (thickness 0.4 mm) made of nickel plated with iron, 2 is a sealing plate made by punching stainless steel (SUS304), and the positive electrode terminal 3 (SUS304) and Negative electrode terminal 4 (SU
S304) is fixed by a glass hermetic seal. 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. A negative electrode 7 is electrically connected to the negative electrode terminal 4. The separator, the positive electrode, and the negative electrode are spirally wound and inserted into the battery case, and after the electrolytic solution is injected, the junction between the case 1 and the sealing plate 2 is welded with a laser to hermetically seal the battery. The degree of compression of the battery (inner dimension of battery case / electrode plate thickness) was 0.9.

Ethylene carbonate (E
C), dimethyl carbonate (DMC) and diethyl carbonate (DEC) mixed in a volume ratio of 2: 2: 1 to 1 mol / liter of lithium hexafluorophosphate and 0.0
What melt | dissolved 5 mol / liter lithium perchlorate was used.

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

Further, as shown in FIGS. 3 and 4, the power generating element formed by stacking the strip-shaped separator 5, the positive electrode plate 6 and the negative electrode plate 7 may be housed in an arch-shaped or S-shaped battery case. Outside, the batteries of the present invention having the same structure as the battery of the present invention (A) are referred to as (C) and (D), respectively. The battery size is 100 mm in height, 10 mm in thickness, and 50 mm in width.

For comparison, as shown in FIG. 5, except that the separator 5, the positive electrode 6 and the negative electrode 7 were spirally wound and inserted into the elliptical battery case, the battery (A) of the present invention was used. A comparative battery having the same structure is referred to as (A), and as shown in FIG. 6, a power generating element formed by stacking a strip-shaped separator 5, a positive electrode plate 6 and a negative electrode plate 7 is housed in a gum type battery case. Other than that, the comparative battery having the same structure as the battery (A) of the present invention is referred to as (A). The size of the batteries (a) and (a) is 100 mm in height, 10 mm in thickness, and 50 mm in width.

Next, these batteries are charged at a constant current of 500 mA until the terminal voltage reaches 4.1 V, and then discharged at the same constant current of 2.0 mA until the terminal voltage reaches 3 V. The charge / discharge cycle test was performed at room temperature for 10 cycles. 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] As is clear from the results in Table 1, the comparative batteries (a) and (a) have an increased battery thickness, while the batteries of the present invention (A), (B), (C) and (D) have an increased thickness. Can't 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) and (C) of the present invention. Width 50 mm, depth 10
FIG. 7 shows a filling mode when the battery is stood upright on a 0 mm rectangular floor and stored, and FIG. 8 shows a filling mode when the battery is stood upright on a rectangular floor with a width of 50 mm and a depth of 105 mm. Table 2 shows the total projected area of the assembled battery.

[0022]

[Table 2] As is clear from the results, the battery of the present invention has a space efficiency of 10% to 18% higher than that of the cylindrical battery.

In the above embodiment, the case where the lithium cobalt composite oxide is used as the positive electrode active material has been described.
Various materials such as manganese dioxide, spinel-type lithium manganese oxide (LixMn ₂ O ₄ ), vanadium pentoxide, and molybdenum trioxide can be used as well as titanium disulfide. Although a carbon material was used as the negative electrode, the negative electrode active material is basically not limited when using the positive electrode of the present invention, and the negative electrode active material used in the conventional non-aqueous electrolyte secondary battery, for example, pure Lithium, a lithium alloy, or the like can be used.

Further, the electrolytic solution which is a lithium ion conductive material and the solid ionic conductor are basically not limited, and those used in the conventional organic electrolytic solution secondary battery can be used. Examples of the organic solvent include cyclic esters such as ethylene carbonate which is an aprotic solvent and ethers such as tetrahydrofuran and dioxolane. These can be used alone or in a mixture of two or more kinds. As the solid ionic conductor, any substance having lithium ion conductivity can be used. A typical example thereof is polyethylene oxide. Also, the supporting electrolyte dissolved in such a non-aqueous solvent or solid ionic conductor is not basically limited. For example, L
One or more of iAsF ₆ , LiPF ₆ and LiCF ₃ SO ₃ can be used.

[0025]

As described above, the power generating element composed of the negative electrode made of a substance capable of inserting and extracting lithium, the positive electrode, and the non-aqueous electrolyte containing a lithium salt is formed into an arch type or an S type.
The non-aqueous electrolyte secondary battery, which is characterized by being housed in a V-shaped battery case, is capable of effectively suppressing the swelling of the battery during charging and effectively utilizing the battery storage space. The target value is extremely large.

[Brief description of drawings]

FIG. 1 is a diagram showing an internal structure of an arch-type battery (spiral type).

FIG. 2 is a diagram showing an internal structure of an S-shaped battery (spiral type).

FIG. 3 is a diagram showing an internal structure of an arch-type battery (stacked type).

FIG. 4 is a diagram showing an internal structure of an S-shaped battery (stacked type).

FIG. 5 is a view showing the internal structure of an oval battery (spiral type).

FIG. 6 is a diagram showing an internal structure of a gum type battery (laminated type).

FIG. 7: Cylindrical type, arch type (spiral type and laminated type), S
The figure (space width 50mm x depth 100mm) which showed the assembled battery filling mode of a character type (spiral type and a laminated type) battery.

FIG. 8: Cylindrical type, arch type (spiral type and laminated type), S
The figure (space width 50mm x depth 105mm) which showed the assembled battery filling mode of a character type (spiral type and a laminated type) battery.

[Explanation of symbols]

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

Claims (1)

[Claims] 1. A power generation element comprising a negative electrode made of a substance capable of occluding and releasing lithium, a positive electrode, and a non-aqueous electrolyte containing a lithium salt is housed in a battery case having an arch-shaped or S-shaped cross section. And a non-aqueous electrolyte secondary battery.