JP3143951B2 - Non-aqueous electrolyte secondary battery - 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, and more particularly to a non-aqueous electrolyte secondary battery whose electrodes are spiral electrodes.

[0002]

2. Description of the Related Art In recent years, remarkable progress in electronic technology has realized a reduction in size and weight of electronic devices one after another. Along with this, there is an increasing demand for batteries as mobile power sources that are smaller, lighter and have higher energy density.

Conventionally, aqueous secondary batteries such as lead batteries and nickel-cadmium batteries have been the mainstream as secondary batteries for general use. However, although these secondary batteries have excellent cycle characteristics, they cannot be said to be sufficiently satisfactory in terms of battery weight and energy density.

Therefore, recently, nonaqueous electrolyte secondary batteries using lithium or a lithium alloy as a negative electrode as a secondary battery replacing such an aqueous secondary battery such as a lead battery, and further, such as a carbonaceous material, have been proposed. A non-aqueous electrolyte secondary battery using a material capable of doping / dedoping lithium for a negative electrode has been proposed. These non-aqueous electrolyte secondary batteries have high energy density, low self-discharge, and are lightweight and have excellent characteristics as a mobile power supply, such as video cameras and laptop computers. Is expected to be used as a power supply for equipment.

[0005] By the way, devices such as video cameras consume a relatively large amount of current. Therefore, it is required that a power source used in these devices can cope with the current consumption. As a non-aqueous electrolyte secondary battery that meets such demands, a non-aqueous electrolyte secondary battery using a spiral electrode has been proposed.

A spiral electrode used in this non-aqueous electrolyte secondary battery has a structure in which, for example, a strip-shaped positive electrode and a negative electrode are interposed via a separator, and the negative electrode, the separator, the positive electrode, and the separator are sequentially arranged in the order of 4
The four-layered laminated electrode body is spirally wound around the winding core many times, and then the winding core is removed. This spiral electrode is
Since the electrode area is large and can withstand heavy loads, it is suitable as an electrode of a battery requiring a large supply current.

However, the non-aqueous electrolyte secondary battery in which the electrode has a spiral electrode structure has a problem that an internal short circuit may occur at the center of the battery with repeated charging and discharging. That is, in the non-aqueous electrolyte secondary battery, a phenomenon is seen in which the volume of the electrode increases due to repeated charging and discharging. Here, the spiral electrode is
Since it is housed in a metal can, it cannot expand outward, but the central part has a void after removing the winding core, so the volume increase is concentrated in the central part with this void. Will be done. In such a case, the electrode near the center of the electrode is deformed and breaks through the separator. As a result, a problem occurs in that the positive electrode plate and the negative electrode plate come into contact with each other to cause an internal short circuit.

In order to prevent an internal short circuit caused by deformation of the electrode center of such a non-aqueous electrolyte secondary battery, for example, in Japanese Patent Application Laid-Open No. 1-175176, a rod-shaped insulator made of an insulator is provided in the center void. A non-aqueous electrolyte secondary battery in which a center pin is provided to suppress deformation of the center portion has been proposed. However, the non-aqueous electrolyte secondary battery has a problem in that the electrolyte may overflow when the center pin is inserted into the center gap, resulting in poor workability.

In order to prevent such overflow of the electrolyte, a non-aqueous electrolyte secondary battery using a hollow cylindrical center pin made of an insulator is disclosed in Japanese Utility Model Laid-Open No. 1-155262. . In this non-aqueous electrolyte secondary battery, since the center pin has a hollow cylindrical shape, the electrolyte does not overflow when the center pin is inserted, and good workability can be obtained.

[0010]

However, the hollow cylindrical insulator is deformed by pressurization or heat to bend, or a gate burr occurs during manufacturing, so that the insulator is misaligned when inserted. Or, it often happens that it gets stuck on the separator. For this reason, the insertion of the center pin causes the separator to be wrinkled or folded back, and the clearance between the center pin and the separator is lost, so that the insertion of the center pin is not easily completed, so that a poor insertion is likely to occur. Further, the hollow cylindrical center pin made of an insulator is not inserted into the center gap portion by its own weight due to its light weight, and it is necessary to press the center pin in the insertion direction when inserting. For this reason, the insertion operation becomes complicated, and it becomes difficult to increase the productivity of the battery. Furthermore, the hollow cylindrical center pin made of an insulator is
Since the strength is insufficient, the battery is damaged or deformed when a high pressure is applied to the battery from outside. As a result, the sealing portion of the battery is deformed and the electrolyte leaks.

Therefore, the present invention has been proposed in view of such a conventional situation, in which the frequency of occurrence of defective insertion when inserting a center pin is low, high productivity is obtained, and high pressure is applied from the outside. It is hard to be deformed even if it hangs,
It is an object to provide a non-aqueous electrolyte secondary battery with high safety.

[0012]

In order to solve the above-mentioned problems, a non-aqueous electrolyte secondary battery according to the present invention comprises a housing in which a negative electrode and a positive electrode are spirally laminated with a separator interposed therebetween. In a non-aqueous electrolyte secondary battery containing a wound body formed as described above and a hollow cylindrical center pin provided in a central void portion of the wound body, the positive electrode includes lithium as a positive electrode active material. It contains a composite oxide, the negative electrode contains a carbonaceous material as a negative electrode active material, the center pin is made of metal, and the length is smaller than the width of the separator. It is assumed that.

In the non-aqueous electrolyte secondary battery of the present invention, the center pin is made of a metal in order to secure the insertability into the center of the electrode and the strength of the battery. The metal is not particularly limited, and various metals can be used. However, stainless steel, nickel, titanium, steel, and the like are desirably used because they are excellent in productivity, workability, hardness, and corrosion resistance.

The shape of the center pin made of the above metal is a hollow cylinder in order to prevent overflow of the electrolyte. Note that the cylindrical shape does not necessarily have to be a complete cylindrical shape, and may be, for example, a cylindrical shape having a gap 8a equal to or less than 10% of the outer periphery of the battery as shown in FIG. Here, the tip of the hollow cylindrical center pin is desirably tapered to facilitate insertion into the center of the electrode. Further, the length of the center pin is preferably shorter than the separator width in order to prevent an internal short circuit. Further, in order to insulate the center pin from the electrode, it is desirable to arrange an insulator such as a separator on the innermost periphery of the spiral electrode.

As the negative electrode used in the non-aqueous electrolyte secondary battery, there can be used an alkali metal such as lithium, or a material which is doped / dedoped with an alkali metal such as lithium during a charge / discharge reaction. As an example of the latter,
A conductive polymer such as polyacetylene or polypyrrole, or a carbon material such as coke, polymer charcoal, or carbon fiber can be used. However, it is desirable to use a carbonaceous material because of its high energy density per unit volume. As the carbonaceous material, pyrolytic carbons, cokes (petroleum coke, pitch coke, coal coke, etc.), carbon black (acetylene black, etc.),
Glassy carbon, an organic polymer material fired body (an organic polymer material fired at an appropriate temperature of 500 ° C. or more in an inert gas stream or in a vacuum), carbon fiber, and the like are used.

On the other hand, as the positive electrode, a transition metal oxide such as manganese dioxide or vanadium pentoxide, a transition metal chalcogenide such as iron sulfide or titanium sulfide, or a composite compound of these and lithium is used. Can be. In particular, a lithium-cobalt composite oxide or a lithium-cobalt-nickel composite oxide is preferable because a high voltage, a high energy density can be obtained, and cycle characteristics are excellent.

As the electrolytic solution, for example, an electrolytic solution in which a lithium salt is used as an electrolyte and this is dissolved in an organic solvent is used. Here, the organic solvent is not particularly limited. For example, propylene carbonate, ethylene carbonate, diethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3 -Dioxolan,
A single solvent such as 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, cetonitrile, propionitrile, or a mixture of two or more solvents can be used. As the electrolyte, any of those conventionally known can be used, and LiClO ₄ , LiAsF ₆ , LiPF ₆ ,
LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , LiCl, LiB
r, CH ₃ SO ₃ LI, CF ₃ SO ₃ Li and the like.

[0018]

The non-aqueous electrolyte secondary battery of the present invention contains a spirally wound electrode and a metallic hollow cylindrical center pin disposed in the center gap of the spirally wound electrode in a storage can. . In a battery, the strength largely depends on the material of a center pin serving as a core of the battery. If the center pin is a hard metal, the strength of the battery is secured and deformation is suppressed. In addition, the center pin made of metal has high processing accuracy even after the metal is processed into the center pin shape.
Since a deformation due to heat and pressure hardly occurs, a predetermined shape is maintained during insertion. Therefore, when the center pin is inserted into the center gap, the center pin does not catch on the separator, and the occurrence frequency of the center pin insertion failure can be suppressed low. Further, the center pin is heavier than the center pin made of synthetic resin or the like, and is dropped and inserted into the electrode core by its own weight. For this reason, pressurization when inserting the center pin is almost unnecessary, and the operation of inserting the center pin is simplified.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below based on experimental results.

Example 1 FIG. 1 shows a schematic longitudinal section of a non-aqueous electrolyte secondary battery of this example . This battery was prepared as follows.

First, the negative electrode 1 was manufactured as follows.
A petroleum pitch was used as a starting material, and was calcined to obtain coarse-grained pitch coke. This coarse-grained pitch coke was pulverized to obtain a powder having an average particle diameter of 40 μm. Subsequently, the powder was refired at 1,000 ° C. in an inert gas to remove impurities, thereby obtaining a coke material powder. The coke material powder thus obtained was used as a negative electrode active material carrier, and 90 parts by weight of the coke material powder and 10 parts by weight of polyvinylidene fluoride (PVDF) as a binder were mixed to prepare a negative electrode mixture. . This negative electrode mixture is dispersed in N-methyl-2-pyrrolidone as a solvent to form a slurry (paste).
I made it. Next, this negative electrode mixture slurry was applied to both surfaces of a negative electrode current collector, which is a strip-shaped copper foil having a thickness of 10 μm, and the solvent was dried.
I got The thickness of the negative electrode mixture after molding was 10 on both sides.
The width of the strip-shaped negative electrode was 41.5 mm,
The length was 635 mm.

Next, the positive electrode 2 was manufactured as follows.
0.5 mol of lithium carbonate and 1 mol of cobalt carbonate are mixed and calcined in air at 900 ° C. for 5 hours to obtain L
iCoO ₂ was obtained. This LiCoO ₂ was used as a positive electrode active material, and 91 parts by weight of this LiCoO ₂ , 6 parts by weight of graphite as a conductive agent, and 3 parts by weight of polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture. This positive electrode mixture was dispersed in a solvent N-methylpyrrolidone to form a slurry (paste). Then, this positive electrode mixture was applied to a thickness of 20 μm.
m, a band-shaped aluminum foil was uniformly coated on both sides of the positive electrode current collector and dried. After drying, compression molding was performed to obtain a band-shaped positive electrode 2. The thickness of the mixture after molding was 80 μm on both sides.
m, and the width of the belt-shaped positive electrode was 39.5 mm and the length was 605 mm.

Next, a separator 3 made of a microporous polypropylene film having a thickness of 25 μm and a width of 44 mm was placed on a separator 2.
After winding twice around a pin having a diameter of 4 mm, the strip-shaped negative electrode 1 and the strip-shaped positive electrode 2 produced as described above are stacked so as to face each other with a separator interposed therebetween, and the stacked electrode body is spirally wound many times. Then, the final end of the outermost peripheral separator was fixed with a tape to produce a spiral electrode. In addition, of this spiral type electrode,
The inner diameter of the hollow part at the center is 3.6 mm, and the outer diameter is 19.7
mm.

The spiral electrode manufactured as described above was housed in a nickel-plated iron battery can 5. Also,
An insulating plate 4 is disposed on both upper and lower surfaces of the spiral electrode, and an aluminum positive electrode lead is led out of the positive electrode current collector to collect the negative electrode and the positive electrode. It was taken out of the current collector and welded to the battery can 5.
Thereafter, 4.9 ml of a non-aqueous electrolyte obtained by dissolving LiPF ₆ at a ratio of 1 mol / l in a mixed solvent of propylene carbonate and diethyl carbonate in an equal volume was injected into the battery can 5 and the spiral electrode was formed. Impregnated.

After injecting the electrolyte in this manner, FIG.
3.5mm outer diameter, 2.5mm inner diameter, 40mm length
The stainless steel (SUS304) tapered hollow center pin 8 is used for the insertion space shown in FIG. 3 in the spiral space of the spiral electrode 33. First, the center pin 8 is passed through the pin guide 31 so that the electrode hollow is vertical. Drop it to the part 34,
The electrode was completely inserted into the electrode hollow portion using the insertion rod 32.
The weight of the center pin 8 was 1.37 g.

The battery lid 5 was fixed by caulking the battery can 5 through an insulating sealing gasket whose surface was coated with asphalt, and the confidentiality inside the battery was maintained. With the above configuration, a cylindrical nonaqueous electrolyte battery (Example Battery 1) having a diameter of 20.5 mm and a height of 50 mm as shown in FIG. 1 was produced.

Example 2 The center pin to be inserted has an outer diameter of 3.5 mm and an inner diameter of 2.5 m
m, a stainless steel (SUS304) hollow member having a length of 40 mm and a gap 8 having a maximum width of 1 mm as shown in FIG.
A cylindrical nonaqueous electrolyte battery (Example battery 2) was produced in the same manner as in Example 1 except that the battery containing a was used. The weight of the center pin was 1.30 g.

Comparative Example 1 The center pin to be inserted has an outer diameter of 3.5 mm and an inner diameter of 2.5 m
A cylindrical nonaqueous electrolyte battery (Comparative Battery 1) was prepared in the same manner as in Example 1 except that a polypropylene hollow center pin having a length of 40 mm and a length of 40 mm was used. The center pin weighed 0.16 g.

The batteries 1 and 2 of the embodiment thus prepared
Regarding the battery of Example 2 and the battery of Comparative Example 1, the failure rate when the center pin was inserted into the center of the electrode was examined. Table 1 shows the results.

[Table 1]

As can be seen from Table 1, the batteries of Examples 1 and 2 had a low defect rate when the center pin was inserted and exhibited good insertability, while the batteries of Comparative Example 1 and 2 exhibited good insertability.
In this case, poor insertion occurs due to the center pin being hooked on the separator, and sufficient insertability cannot be obtained. Therefore, from these results, it was shown that, in the non-aqueous electrolyte secondary battery, configuring the center pin with a metal is effective in reducing poor insertion of the center pin.

Here, in the comparative example battery 1 using the center pin made of polypropylene, the center pin is as light as 0.16 g, so that the center pin does not drop by its own weight and must be pressurized when inserted. However, in each of Example Battery 1 and Example Battery 2 using the stainless steel center pin, since the center pin was as heavy as about 1.3 g, the center pin was dropped on the electrode core by its own weight, and the pressure was reduced. Almost unnecessary. Therefore, this indicates that if a metal center pin is used, the pressing step at the time of inserting the center pin can be omitted, and the battery manufacturing operation can be simplified. .

Next, the strength of the example battery 1, the example battery 2 and the comparative example battery 1 against external pressure was examined.

In order to examine the strength of each battery against external pressure, first, a metal flat plate 5 as shown in FIG.
A battery 51 serving as a sample is sandwiched between the metal flat plates 52 and 53 by using a pressurizing device provided with the metal plates 2 and 53 facing each other, and a direction in which the battery 51 is sandwiched (the direction of the arrow P in the figure).
Was pressurized by 0.5 ton with a hydraulic press. Then, the strength of the battery was evaluated by measuring the height of the battery in the pressing direction. Table 2 shows the height of the battery after pressurization and the amount of change in height due to pressurization (battery height before pressurization-battery height after pressurization).

[Table 2]

As shown in Table 2, in Comparative Example Battery 1 using a center pin made of polypropylene, the amount of change in height due to pressurization was as large as 1.7 mm. In the battery 1 and the example battery 2, the height change amount was about 1 / of that of the comparative example battery 1.
About 2 and almost no deformation

Therefore, the use of the metal center pin is effective in increasing the strength of the battery, thereby preventing leakage of the electrolyte due to deformation of the sealing portion and the like. It was found that safety could be improved. In addition, at this time, the same strength was obtained in Example Battery 1 and Example Battery 2, indicating that the battery strength was not affected even if a gap of 10% or less existed on the outer periphery of the center pin. As a result, it was found that the center pin could be easily processed.

[0036]

As is clear from the above description, in the present invention, the spiral electrode and the metallic hollow cylindrical center pin disposed on the core of the spiral electrode are provided in the storage can. In the stored non-aqueous electrolyte secondary battery, since the center pin is made of metal, the rate of defective insertion when the center pin is inserted into the electrode core can be reduced, and the number of battery manufacturing steps can be reduced. It can be reduced, and the productivity of the battery can be improved. Also, since the strength is increased, deformation when high pressure is applied from the outside,
Electrolyte leakage is prevented, and high safety can be ensured.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view showing an example of a non-aqueous electrolyte secondary battery of the present invention.

FIG. 2 is a perspective view showing an example of a center pin.

FIG. 3 is a schematic diagram showing a process of inserting a center pin into an electrode core.

FIG. 4 is a perspective view showing another example of the center pin.

FIG. 5 is a schematic diagram showing a pressurizing device used to measure the strength of the battery against pressurization.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Negative electrode 2 ... Positive electrode 3 ... Separator 4 ... Insulating plate 5 ... Battery can 6 ... Sealing gasket 7 ... Battery cover 9 ... Negative electrode collector 10 ...・ Positive electrode collector 11 ・ ・ ・ Negative electrode lead 12 ・ ・ ・ Positive electrode lead

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-61-104561 (JP, A) JP-A-60-41772 (JP, A) JP-A-3-93162 (JP, A) JP-A-3-103 84872 (JP, A) JP-A-3-49155 (JP, A) JP-A-4-71170 (JP, A) JP-A-2-220360 (JP, A) Japanese Utility Model Laid-Open No. 59-61468 (JP, U) (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 10/40 H01M 4/02 H01M 4/58 H01M 2/20-2/34 H01M 10/04

Claims (3)

(57) [Claims] 1. A wound body in which a negative electrode and a positive electrode are spirally stacked and wound in a storage can with a separator interposed therebetween, and a hollow cylindrical member provided in a central gap portion of the wound body. In a nonaqueous electrolyte secondary battery containing a center pin , the positive electrode contains a lithium composite oxide as a positive electrode active material.
A, the negative electrode, to contain a carbonaceous material as an anode active material
In both cases, the center pin is made of metal , and
A nonaqueous electrolyte secondary battery, wherein the length is smaller than the width of the separator . 2. The tip of the center pin is tapered.
The non-aqueous electrolysis according to claim 1, wherein
Liquid secondary battery. 3. The method according to claim 1, wherein the positive electrode active material is on both sides of a belt-shaped positive electrode current collector.
Are formed on, the negative electrode active material formed on both surfaces of the strip-shaped negative electrode current collector, equipped with a non-aqueous electrolyte prepared by dissolving lithium salt in a nonaqueous solvent
The non-aqueous electrolyte secondary battery according to claim 1, wherein: