JPH05314977A - Nonaqueous electrolytic secondary battery - Google Patents

Abstract

PURPOSE:To increase capacity and improve cycle characteristics by using a carbon material with a Fulleren crystal structure of nodular molecules as a negative electrode. CONSTITUTION:An electrode plate group 4 in a case 1 comprises positive and negative electrodes spirally wound by a plurality of turns via a separator. A carbon material of a Fulleren crystal structure of nodular molecules constituted of a hexagon having six carbon atoms and a pentagon having five carbon atoms, is used as a negative electrode. Consequently, a lithium amount intercalated and de-intercalated with carbon increases. Also, as the carbon has a nodular crystal structure, the negative electrode becomes strong, compared with the case of a laminar structure, and a battery having large capacity and excellent cycle characteristics can be provided. Also, the nodular molecules are constituted of 60, 70, 76 and 84 carbon atoms.

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 having an improved negative electrode.

[0002]

2. Description of the Related Art In recent years, portable electronic devices for consumer use,
Cordless is advancing rapidly. Along with this, there is an increasing demand for a small-sized, lightweight secondary battery having a high energy density, which serves as a driving power source. From this point of view, non-aqueous secondary batteries, especially lithium secondary batteries, have great expectations as batteries having high voltage and high energy density, and their development is urgently needed.

Conventionally, manganese dioxide, vanadium pentoxide, titanium disulfide and the like have been used as positive electrode active materials for such lithium secondary batteries. A battery was constituted by these positive electrodes, a lithium negative electrode and an organic electrolytic solution, and charging and discharging were repeated.

However, generally, in a secondary battery using lithium metal for the negative electrode, problems such as an internal short circuit due to dendrite-like lithium generated during charging and a side reaction between an active material and an electrolytic solution are major obstacles to the secondary battery. Was there. In addition, recently, the safety of lithium batteries has been pointed out severely,
In a battery system using lithium metal or lithium alloy for the negative electrode, it is very difficult to ensure safety.

On the other hand, a new type of electrode active material utilizing the intercalation reaction of a layered compound has attracted attention, and a graphite intercalation compound is considered as an electrode material for secondary batteries.

In particular, graphite intercalation compounds incorporating anions such as ClO ₄ , PF ₅ and BF ₄ ions can be used as positive electrodes, while graphite intercalation compounds incorporating cations such as Li ⁺ and Na ⁺ can be used as negative electrodes. It is believed that it can be used.

[0007]

However, the graphite intercalation compound incorporating a cation is extremely unstable, and when natural graphite or artificial graphite is used as the negative electrode, it usually lacks stability as a battery and has a low capacity. There was a problem. Further, since the electrolyte solution is decomposed, it cannot be used as a substitute for the lithium negative electrode.

Further, in the conventional constitution, when the amounts of lithium intercalate and deintercalate were determined, when a pseudographite material having insufficient graphitization was used for the negative electrode, the capacity of 100 to 150 mAh carbon 1 g was obtained. There was a problem that it could only be obtained.

On the other hand, when a highly crystalline graphite material is used for the negative electrode, a high temperature calcined product of coke or the like has a relatively high capacity of 200 to 250 mAh / g. However, there has been a problem that the molded body swells due to the large expansion and contraction of graphite in the C-axis direction with charge and discharge, and the original shape cannot be maintained.

Therefore, an object of the present invention is to provide a non-aqueous electrolyte secondary battery which solves the above-mentioned problems of the prior art, ensures safety, has a high capacity, and is excellent in cycle characteristics. Especially.

[0011]

Such objects are achieved by the present invention described in (1) and (2) below.

(1) In a non-aqueous electrolyte secondary battery provided with a non-aqueous electrolyte, a chargeable / dischargeable positive electrode, and a negative electrode, the negative electrode is a hexagon having 6 carbon atoms and 5 carbon atoms.
A non-aqueous electrolyte secondary battery comprising a carbon material having a spherical molecule fullerene crystal structure composed of individual pentagons.

(2) 60, 70 and 7 spherical molecules
The non-aqueous electrolyte secondary battery according to (1) above, which is composed of 6 or 84 carbon atoms.

[0014]

When a carbon material having a spherical molecule fullerene crystal structure according to the present invention is used for the negative electrode, the amount of lithium intercalating and deintercalating to this carbon increases, and the carbon crystal structure is spherical, resulting in a layered structure. As a result, it is possible to realize a non-aqueous electrolyte secondary battery that is stronger, has higher capacity, and has excellent cycle characteristics.

[0015]

Concrete Structure The present invention will be described below with reference to the drawings.

FIG. 1 shows a schematic diagram of a molecule having a fullerene crystal structure of 60 carbon atoms used in the present invention.

As can be seen from FIG. 1, in such a carbon material, a spherical molecule is composed of a hexagon having 6 carbon atoms and a pentagon having 5 carbon atoms.

This fullerene crystal structure is a new discovery of the recently announced crystal type of carbon (graphite) (see “Functional Material” February 1992 Vol. 12 No. 2). Graphite having a fullerene structure has its carbon atoms arranged in an equivalent and symmetrical form to form a soccer ball-shaped molecule.

This crystal structure can be grown on the negative electrode by placing two carbon electrodes in an argon atmosphere, causing an arc discharge, and decomposing and crystallization of carbon under high temperature and high magnetic field.

For the negative electrode, for example, a carbonaceous material having such a spherical molecule fullerene crystal structure is mixed with a resin adhesive,
It can be manufactured by suspending in an aqueous solution to form a paste, applying this paste to both surfaces of a copper foil, drying and rolling.

As the positive electrode, the electrolytic solution and the like, those conventionally known in the field of non-aqueous electrolytic solution secondary batteries can be used and are not particularly limited.

The reason why graphite having a spherical molecule fullerene crystal structure has a high capacity is as follows.

Theoretically, graphite having a planar layered structure intercalates one lithium with six carbon atoms, but in an actual battery, only two-thirds of the lithium intercalates. .. However, when the crystal structure is spherical, interstitial doping is performed on the outside of the sphere, and lithium is likely to enter, so that a high capacity is considered to be possible.

Further, the reason why the cycle characteristics are improved is considered to be that the crystal structure is spherical and the crystal structure is hardly broken by intercalation and deintercalation of lithium.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. Example FIG. 2 shows a vertical sectional view of a cylindrical battery used in this example.
In FIG. 2, 1 is a battery case formed by processing an organic electrolytic solution resistant stainless steel plate, 2 is a sealing plate provided with a safety valve, and 3 is an insulating packing. Reference numeral 4 denotes an electrode plate group, in which the positive electrode and the negative electrode are spirally wound a plurality of times with a separator interposed therebetween and housed.

A positive electrode lead 5 is drawn out from the positive electrode and connected to the sealing plate 2, while a negative electrode lead 6 is drawn from the negative electrode.
Is drawn out and connected to the bottom portion 1 of the battery case.
Insulating rings 7 are provided on the upper and lower portions of the electrode plate group, respectively. Hereinafter, the positive and negative electrode plates, the electrolytic solution and the like will be described in detail.

In order to manufacture the positive electrode, first, Li ₂ CO
₃ and CoCO ₃ were mixed, and 100 parts by weight of LiCoO ₂ powder synthesized by firing at 900 ° C. for 10 hours was mixed with 3 parts by weight of acetylene black, 4 parts by weight of graphite and 7 parts by weight of fluororesin adhesive. Then, this was suspended in an aqueous solution of carboxymethyl cellulose to form a paste. The paste was applied to both sides of an aluminum foil having a thickness of 0.03 mm, dried and rolled to a thickness of 0.19 mm, a width of 40 mm,
The electrode plate was 250 mm long. The mixture weight was 5 g.

The production of the negative electrode is carried out by first performing a heat treatment on a carbon material 1 having a fullerene crystal structure of spherical molecules and having 60 carbon atoms.
10 parts by weight of a fluororesin-based adhesive was mixed with 00 parts by weight, and this was suspended in an aqueous carboxymethylcellulose solution to form a paste. Then, this paste was applied to both sides of a copper foil having a thickness of 0.02 mm, dried and rolled to form an electrode plate having a thickness of 0.20 mm, a width of 40 mm and a length of 260 mm. The weight of the mixture was 2.5 g. there were.

Next, a lead is attached to each of the negative electrode plates and spirally wound through a polypropylene separator having a thickness of 0.025 mm, a width of 46 mm and a length of 700 mm, which has a diameter of 13.8 mm and a height of 50 mm. Stored in the battery case. As the electrolytic solution, a solution prepared by dissolving lithium perchlorate in a mixed solvent of equal volume of propylene carbonate and ethylene carbonate at a ratio of 1 mol / 1 was used. Comparative Example 1 A battery of Comparative Example 1 was prepared under the same conditions as those of the battery of Example except that the non-graphitized mesocarbon microbeads heat-treated at 1200 ° C. were used for the negative electrode. Comparative Example 2 A battery of Comparative Example 2 was prepared under the same conditions as those of the batteries of Examples except that the negative electrode was made of the graphite having a layered structure with high graphitization of the coke calcined body which was heat-treated at 2800 ° C.

A constant current charge / discharge test was conducted on the batteries of the above-mentioned examples and the batteries of Comparative Examples 1 and 2 under the conditions of a charge / discharge current of 100 mA, a charge end voltage of 4.1 v, and a discharge end voltage of 3.0 v, respectively. .. FIG. 3 shows a comparison of charge / discharge curves at the 10th cycle, and FIG. 4 shows a comparison of cycle characteristics.

As is clear from FIG. 3, the battery of this example using a carbon material having a fullerene crystal structure of a spherical molecule having 60 carbon atoms exhibited a high capacity of 640 mAh.
On the other hand, the comparative battery 2 had a capacity of 450 to 500 mAh, while the battery of Comparative Example 1 using the non-graphitized negative electrode material had a very low value of 350 mAh.

Further, as is clear from FIG. 4, the batteries of Examples have good cycle flatness and can be charged and discharged for 500 cycles or more. On the other hand, the battery of Comparative Example 2 using coke was significantly deteriorated with cycles, and was less than half of the initial capacity at 50 cycles.

Further, as another embodiment, carbon atom 6
A carbon material having a fullerene crystal structure of 70, 76 and 84 spherical molecules other than 0 was also examined, and in this case as well, the same discharge capacity and cycle characteristics as those of the above-mentioned Examples were obtained.

As described above, in the present embodiment, by using the carbon material having the spherical molecule fullerene structure for the negative electrode, a lithium secondary battery having a high capacity and excellent cycle characteristics could be realized.

[0035]

EFFECTS OF THE INVENTION By using a carbon material having a fullerene crystal structure of a spherical molecule composed of a hexagon having 6 carbon atoms and a pentagon having 5 carbon atoms as a negative electrode of the present invention, it is possible to cycle at a high capacity. It is possible to obtain the effect of becoming a non-aqueous electrolyte secondary battery having good characteristics.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a fullerene crystal structure of a spherical molecule having 60 carbon atoms.

FIG. 2 is a vertical cross-sectional view of a cylindrical non-aqueous electrolyte secondary battery used in this example.

FIG. 3 is a graph showing a comparison of charge / discharge curves at the 10th cycle between the example battery of the present invention and the batteries of Comparative Examples 1 and 2.

FIG. 4 is a graph showing a comparison of cycle characteristics of an example battery of the present invention and batteries of Comparative Examples 1 and 2.

[Explanation of symbols]

 1 Battery case 2 Seal plate 3 Insulation packing 4 Electrode plate group 5 Positive electrode lead 6 Negative electrode lead 7 Insulation ring

Front page continuation (72) Inventor Yoshiaki Nitta 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Takahiro Teraoka, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial

Claims (2)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte, a chargeable / dischargeable positive electrode, and a negative electrode, wherein the negative electrode comprises a hexagon having 6 carbon atoms and 5 carbon atoms. A non-aqueous electrolyte secondary battery comprising a carbon material having a spherical molecule fullerene crystal structure composed of the following pentagon. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the spherical molecule is composed of 60, 70, 76 or 84 carbon atoms.