JP3008638B2 - Non-aqueous electrolyte secondary battery and its negative electrode active material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery and its negative electrode active material.

[0002] In recent years, portable and cordless consumer electronic devices have been rapidly advancing. Accordingly, there has been a growing demand for a small, lightweight, and high energy density secondary battery that serves as a driving power supply. From such a viewpoint, non-aqueous secondary batteries, particularly lithium secondary batteries, are particularly expected to be batteries having a high voltage and a high energy density, and their development is urgent.

[0003]

2. Description of the Related Art Conventionally, manganese dioxide, vanadium pentoxide, titanium disulfide and the like have been used as a positive electrode active material of the above-mentioned lithium secondary battery. A battery was composed of these positive electrodes, a lithium negative electrode and an organic electrolyte, and charging and discharging were repeated. However, in such secondary batteries using lithium metal as the negative electrode active material, problems such as an internal short circuit due to dendritic lithium generated during charging and side reactions between the active material and the electrolyte are major obstacles to the creation of secondary batteries. Had become.

For this reason, a new type of electrode active material utilizing an intercalation reaction of a layered compound has attracted attention, and a highly crystalline graphite intercalation compound has been used as a negative electrode active material of a non-aqueous electrolyte secondary battery. Have been.

[0005]

However, when high-crystalline graphite is used as the negative electrode active material as in the above-mentioned conventional example, for example, a high-temperature fired body of coke is 200 mA.
Only a discharge capacity as low as h / g was obtained. Further, there is a problem in that when the battery is configured, highly crystalline graphite comes into contact with the electrolyte, the electrolyte is decomposed, gas is generated, and the internal pressure of the battery increases.

The present invention solves the above-mentioned conventional problems, and has a high capacity by using graphite made of a carbon material having a surface activated as an anode active material.
Moreover, it is an object of the present invention to provide a non-aqueous electrolyte secondary battery in which the decomposition of the electrolyte is small.

[0007]

In order to solve these problems, a non-aqueous electrolyte secondary battery according to the present invention comprises a non-aqueous electrolyte comprising a non-aqueous electrolyte, a chargeable and dischargeable positive electrode and a negative electrode. The secondary battery is characterized in that graphite made of a carbon material having a surface activated is used as a negative electrode active material.

Further, the negative electrode active material for a non-aqueous electrolyte secondary battery of the present invention is a negative electrode active material for a non-aqueous electrolyte secondary battery comprising graphite, wherein the graphite comprises a carbon material whose surface has been activated. Is used.

It is preferable to use spherical graphite as the carbon material. Further, there is a relationship described below between the activation processing conditions and the discharge capacity. FIG. 3 shows a relationship curve between the carbon yield and the discharge capacity. The yield is a factor indicating the degree of the activation treatment and is determined by the type and composition of the activation gas, the activation temperature and the activation time. That is, carbon monoxide and hydrogen are generated by the reaction between carbon and the activation gas, and the weight of carbon is reduced.
The remaining amount of carbon is expressed in yield. From FIG. 3, yield 8
It can be seen that the discharge capacity is excellent if it is 0 to 95%. The capacity on the vertical axis is a discharge result obtained by the battery configuration of the example described later. The reason why the yield of 80 to 95% is excellent is that if the yield is less than 80%, the layered structure of graphite is destroyed and the portion where lithium intercalates is reduced, while 95%
This is because, when it exceeds, the growth of the fine structure on the surface is small.

FIG. 4 shows the relationship between the yield and the activation time. FIG.
Shows the relationship between the yield and the activation time in a mixed gas atmosphere of carbon dioxide containing 5 to 10% by volume of water vapor. A hatched portion A is a portion having a high discharge capacity. That is, the hatched portion has a discharge capacity of 550.
The area is equal to or larger than mAh. From this figure, it is clear that the activation treatment conditions show a high capacity at an activation temperature of 750 to 900 ° C. and an activation time of 30 minutes to 1 hour.

[0011]

When the activated graphite is used for the negative electrode, the amount of lithium intercalated and deintercalated in the graphite increases, and a high-capacity nonaqueous electrolyte secondary battery can be realized. In addition, it is possible to realize a nonaqueous electrolyte secondary battery in which the decomposition of the electrolyte due to the contact between graphite and the electrolyte is reduced and the internal pressure of the battery is less increased.

The graphite of the present invention has a high capacity because the carbon surface is eroded by activation and a microporous structure is formed on the surface, so that lithium can be easily intercalated and deintercalated between layers of the graphite layered structure. Because the amount increases.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

First, a method of activating a carbon material was performed as follows to obtain a negative electrode active material. As the activated carbon material, spheroidal graphite fired at 2800 ° C. and having a highly graphitized layered structure was used. As the activation gas, carbon dioxide containing 10% by volume of water vapor was used. The activation treatment was performed at a treatment temperature of 800 ° C. and a treatment time of 1 hour.

FIG. 1 is a longitudinal sectional view of a cylindrical battery used in this embodiment. In the figure, reference numeral 1 denotes a battery case processed from a stainless steel sheet having resistance to organic electrolyte, 2 denotes a sealing plate provided with a safety valve, and 3 denotes an insulating packing. Reference numeral 4 denotes an electrode group, in which a positive electrode and a negative electrode are spirally wound a plurality of times via a separator and housed. A positive electrode lead 5 is drawn out from the positive electrode and connected to the sealing plate 2, and a negative electrode lead 6 is drawn out from the negative electrode and connected to the bottom 1 of the battery case. Reference numeral 7 denotes an insulating ring provided on the upper and lower portions of the electrode group. Hereinafter, the positive and negative electrode plates, the electrolytic solution and the like will be described in detail.

The positive electrode is LiCoO ₂ synthesized by mixing Li ₂ CO ₃ and CoCO ₃ and firing at 900 ° C. for 10 hours.
100 parts by weight of powder, 3 parts by weight of acetylene black,
4 parts by weight of graphite and 7 parts by weight of a fluororesin-based binder were mixed and suspended in an aqueous solution of carboxymethylcellulose to form a paste. 0.03m thick paste
m, dried and rolled after drying.
The electrode plate was 19 mm, 40 mm in width, and 250 mm in length.
The mixture weight was 5 g.

For the negative electrode, spherical graphite which has been subjected to the above-described activation treatment of the present invention is used. 10 parts by weight of a fluororesin binder was mixed with 100 parts by weight of the graphite of the present invention, and suspended in an aqueous solution of carboxymethyl cellulose to form a paste. This paste was applied to both sides of a copper foil having a thickness of 0.02 mm, dried and rolled, and then dried to a thickness of 0.20 mm, a width of 40 mm, and a length of 26.
A 0 mm electrode plate was used. The mixture weight was 2.5 g.

Then, a lead was attached to each of the positive and negative electrode plates, and the thickness was 0.025 mm, the width was 46 mm, and the length was 700.
It was spirally wound via a polypropylene separator of 1 mm and housed in a battery case having a diameter of 13.8 mm and a height of 50 mm. As the electrolytic solution, a solution prepared by dissolving lithium perchlorate at a ratio of 1 mol / liter in a mixed solvent of equal volumes of propylene carbonate and ethylene carbonate was used.

Comparative Example A battery according to a comparative example was prepared under the same conditions as the battery of the above example, except that the negative electrode was subjected to a heat treatment at 2800 ° C. and used spherical graphite having a highly graphitized layered structure.

A constant current charge / discharge test was performed on the batteries of the above-described examples and the comparative example 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. FIG. 2 shows a comparison of the charge and discharge curves at the tenth cycle.

As is clear from FIG. 2, the battery of this example exhibited a high capacity of 650 mAh. In contrast, the battery of the comparative example exhibited a small capacity of 450 mAh.

Further, when the battery of the present invention and the battery of the comparative example were compared, there was a large difference in battery internal pressure during battery assembly.
That is, the internal pressure of the battery of the present invention did not increase at 1 atm, but the internal pressure of the comparative example was as high as 13 atm.

As described above, according to this embodiment, by using graphite made of a carbon material whose surface has been activated for the negative electrode, the secondary battery of the non-aqueous electrolyte having a high capacity and less generation of gas due to contact with the electrolyte can be obtained. A battery can be realized.

[0024]

According to the present invention, a non-aqueous electrolyte secondary battery having a high capacity and little gas generation due to contact with an electrolyte can be provided by using graphite made of a carbon material whose surface has been activated as the negative electrode. It has the effect of.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a cylindrical non-aqueous electrolyte secondary battery of the present invention and a conventional example.

FIG. 2 is a diagram showing a comparison of charge / discharge curves at the 10th cycle between the batteries of the present invention and a conventional example.

FIG. 3 is a diagram showing the relationship between battery discharge capacity and yield.

FIG. 4 is a diagram showing the relationship between the yield and the activation time in a steam mixed gas atmosphere.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Insulation packing 4 Electrode group 5 Positive electrode lead 6 Negative electrode lead 7 Insulation ring

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Sho Ota 1006 Kazuma Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-5-139712 (JP, A) JP-A 64- 48371 (JP, A) JP-A-64-45057 (JP, A) JP-A-64-1219 (JP, A) JP-A-60-194514 (JP, A) JP-A-60-170172 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01M 4/58 H01M 4/02 H01M 10/40

Claims (6)

(57) [Claims] 1. A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte, a chargeable / dischargeable positive electrode and a negative electrode, characterized in that graphite comprising a carbon material whose surface has been activated is used as a negative electrode active material. Non-aqueous electrolyte secondary battery. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein spheroidal graphite is used as said carbon material. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the graphite is a graphite made of a carbon material that has been activated at a yield of 95 to 80%. 4. A method according to claim 1, wherein said graphite is water vapor of 5 to 15% by volume.
750-900 ° C, 30 min-1
The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein graphite made of a carbon material that has been activated under a treatment condition of time is used. 5. A negative electrode active material for a non-aqueous electrolyte secondary battery, characterized by using spherical graphite whose surface has been activated . 6. Activation of the graphite with a yield of 95 to 80%.
6. The negative electrode active material for a non-aqueous electrolyte secondary battery according to claim 5, wherein treated spherical graphite is used.