JP2000251879A - Non-aqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery having high capacity and superior cycle characteristic by providing a positive electrode made of a sintered body formed of a positive electrode active material, and a negative electrode that is made of a sintered body containing silicon and carbon material, contains a specific quantity of silicon in the sintered body and stores a specific quantity of lithium when fully charged. SOLUTION: Silicon content in a negative electrode sintered body is 50-99 wt.%, and the sintered body stores lithium equivalent to 200-800 mAh per gram of silicon when fully charged. Thereby, irreversible capacity is lowered and a cycle characteristic is improved, while securing high capacity as compared with a conventional carbon material. The breakdown in the structure of the negative electrode containing silicon considered as a cause of the irreversible capacity and the production of a substance not participating in a charge-discharge reaction are restrained, and high conductivity is imparted to the negative electrode. The silicon may be crystalline or amorphous, and as a silicic compound, an inorganic silicon compound such as silicon oxide or an organic silicon compound such as a silicon-containing high polymer compound, which is a material to be changed into silicon by being decomposed or reduced in a non-oxidative atmosphere can be cited, and silicon (elemental substance) is particularly preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonaqueous secondary battery having a high capacity and excellent cycle characteristics using a sintered body containing silicon as a negative electrode active material as a negative electrode.

[0002]

2. Description of the Related Art With the spread of mobile phones and notebook personal computers, high-capacity lithium secondary batteries containing a positive electrode active material and a negative electrode active material capable of inserting and extracting lithium ions have been receiving attention.

As the negative electrode active material, an attempt has been made to construct a negative electrode using silicon or a compound thereof, which can be expected to increase in capacity per unit volume as compared with a carbon material, as the negative electrode active material. For example, Japanese Unexamined Patent Publication No. Hei 7-29602 discloses that Li _x Si (0 ≦ x ≦ 5, which corresponds to storing up to 4800 mAh of lithium per gram of silicon) is used as a negative electrode active material, and a conductive material is used. A method of manufacturing a negative electrode as a pellet by adding graphite and a binder and forming a negative electrode is disclosed in Japanese Patent Application Laid-Open No. Hei 5-74463. Is disclosed.

[0004]

To occlude lithium in silicon, for example, a method of supplying lithium from a positive electrode by charging is used. The initial charge loses the crystallinity of silicon and changes to an amorphous structure, thereby enabling reversible occlusion and release of lithium ions. However, silicon can occlude more lithium than conventional carbon materials, but the difference between the amount of lithium absorbed and released during the first charge (irreversible capacity) is large, and the volume of the electrode increases with repeated charging and discharging. There is a problem that the electric resistance of the electrode increases due to a large change, and the capacity decreases with an increase in the number of charge / discharge cycles.

In order to ensure the conductivity of the negative electrode, a large amount of a carbon material must be added as a conductive material.
There is a problem that the capacity per volume of the battery is reduced.

The present invention relates to a non-aqueous secondary battery having a negative electrode made of a sintered body containing silicon as a negative electrode active material, and has a high capacity and excellent cycle characteristics and a non-aqueous secondary battery used therefor. An object is to provide a negative electrode for a non-aqueous secondary battery.

[0007]

The present invention relates to a non-aqueous secondary battery having a positive electrode and a negative electrode containing an active material capable of inserting and extracting lithium ions, wherein the negative electrode is a sintered body containing silicon and a carbon material. The silicon content in the sintered body is 50 to 99% by weight
And between 200 and 800 per gram of silicon when fully charged.
Provided is a non-aqueous secondary battery obtained by absorbing mAh of lithium.

[0008] A sintered body containing silicon and a carbon material is used for the negative electrode, the silicon content is in the range of 50 to 99% by weight, and the amount of lithium stored in silicon is limited to 200 to 800 mAh per gram of silicon. The amount of lithium absorbed at the time of full charge is 200 to 8 per gram of silicon.
By setting it to 00 mAh, the irreversible capacity can be reduced and the cycle characteristics can be improved while securing a higher capacity than the conventional carbon material. In the above range, it is presumed that the collapse of the structure of the negative electrode containing silicon, which is considered to be the cause of the irreversible capacity, and the generation of substances not involved in the charge / discharge reaction are suppressed, and that the negative electrode is provided with high conductivity. You.

The negative electrode for a non-aqueous secondary battery of the present invention is a sintered body containing silicon and a carbon material, and has a silicon content of 50 to 50%.
99% by weight, and 20 g / g of silicon when fully charged.
It is formed by storing 0 to 800 mAh of lithium.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The sintered body containing silicon and a carbon material of the present invention can be produced by firing silicon or a compound thereof and a carbon material or a material to be carbonized by heat treatment in a non-oxidizing atmosphere.

As silicon, either crystalline or amorphous silicon can be used, and a compound containing silicon may be used. Examples of the silicon compound include materials that can be decomposed or reduced in a non-oxidizing atmosphere, such as an inorganic silicon compound such as silicon oxide or an organic silicon compound such as a silicone resin or a silicon-containing polymer compound, to be converted into silicon. Among these, silicon (simple) is particularly preferred.

[0012] Examples of the carbon material include coke, glassy carbon, carbides of graphite and pitch, and mixtures thereof.

As a material to be carbonized by the heat treatment, pheno-
Resins, epoxy resins, unsaturated polyester resins, furan resins, urea resins, melamine resins, alkyd resins, thermosetting resins such as xylene resins, naphthalene, acenaphthylene, phenanthrene, anthracene, triphenylene, pyrene, chrysene, naphthacene, picene, Pitches mainly containing a condensed polycyclic hydrocarbon compound such as perylene, pentaphene, and pentacene or a derivative thereof, or a mixture of the above compounds as a main component, are preferred.

The negative electrode used in the present invention is prepared by mixing silicon powder in the presence of a carbon material or a material carbonized by heat treatment, in a non-oxidizing atmosphere, in a range where silicon is not melted,
After heat treatment at 0 to 1400 ° C., preferably 800 to 1200 ° C. to prepare a treatment powder, a binder and a solvent are added to the treatment powder to prepare a coating liquid, and this coating liquid is applied to a conductive substrate to prepare a coating film. Further, this coating film is formed in a range in which the conductive substrate does not melt under a non-oxidizing atmosphere, for example, 400 to 1000.
It can be manufactured by heat-treating at a temperature of ° C. to be integrated with the conductive substrate and sintering. Alternatively, the treated powder may be formed into a predetermined shape together with a binder or the like, and then sintered in a non-oxidizing atmosphere to form an electrode.

A coating liquid is prepared by adding a binder and a solvent to a mixture of silicon powder and a carbon material or a material to be carbonized by a heat treatment without prior heat treatment, and after applying this coating liquid to a conductive substrate, A negative electrode manufactured by heating under a non-oxidizing atmosphere in a range in which the conductive substrate does not melt to integrate with the conductive substrate and sintering may be used.

As the binder, a thermosetting resin such as a urethane resin, a phenol resin, or an epoxy resin, a thermoplastic resin or an elastomer such as polyethylene or polypropylene, further, vinylidene fluoride, ethylene fluoride, acrylonitrile, ethylene oxide, propylene oxide, A homo- or copolymer such as methyl methacrylate can be used.

The silicon content of the negative electrode used in the present invention is 50 to 50%.
99% by weight, more preferably 70-99% by weight,
The balance is substantially carbon. Within this range, a negative electrode having high conductivity can be obtained.

The positive electrode used as the positive electrode active material of the present invention
The material is Li_xCoO_Two, Li _xNiO_Two, Mn
O_Two, Li_xMnO_Two, Li_xMn_TwoO_Four, Li_xMn
_2-yO_Four, Α-V_TwoO_Five, TiS_TwoEtc. can be used
You.

The non-aqueous electrolyte used in the present invention is a non-aqueous electrolyte in which a lithium compound such as LiPF ₆ is dissolved in an organic solvent such as ethylene carbonate or dimethyl carbonate, or a solid solution of a lithium compound in a polymer. A polymer solid electrolyte holding an organic solvent in which a lithium compound is dissolved can be used.

The occlusion of lithium into the negative electrode active material is as follows:
This is performed for a battery assembled using the above-described negative electrode, positive electrode, and electrolyte. That is, the first charge was performed with silicon 1
200-800 mAh per g, preferably 400-8
Lithium is absorbed within the range of 00 mAh until a predetermined charge capacity value set according to the amount of the positive electrode active material for supplying lithium is reached. It is preferable that the second and subsequent charging be performed with the charging capacity value lower than the first charging value.

[0021]

[Embodiment 1] Purity 100.0%, average particle size 7
90 parts by weight of polycrystalline silicon powder of 90 μm (hereinafter, parts by weight are abbreviated as “parts”) and 10 parts of acetylene black (Denki Kagaku Kogyo Co., Ltd.) as a carbon material are uniformly mixed in advance with a Henschel mixer. N-methyl-2-pyrrolidone solution of vinylidene chloride (Kureha Chemical Industry Co., Ltd.) (12
(% By weight) and mixed with a vibration mill to prepare a uniform coating liquid for a negative electrode. This coating solution was applied on both sides of a 35-μm-thick copper foil using an applicator, dried at 80 ° C. for 30 minutes, punched out into a disk having a diameter of 20 mm, and pressed by a flat plate press. This coating film was fired at 800 ° C. for 3 hours in a nitrogen atmosphere, and a sintered body having a thickness of 100 μm on one side obtained as a negative electrode. The silicon content of the negative electrode was 88% by weight according to a fluorescent X-ray analysis.

Li ₂ CO ₃ and CoCO ₃ are mixed in a molar ratio of Li /
Co was mixed so that Co = 1/1, isopropyl alcohol was added, and the mixture was wet-mixed with a ball mill, and then the solvent was evaporated and calcined at 800 ° C. for 5 hours. Next, this was pulverized, press-molded into a disk having a diameter of 20 mm and a thickness of 200 μm, and then fired again at 800 ° C. for 10 hours to obtain a sintered body as a positive electrode.

The electrolytic solution is prepared by adding Li to a mixed solvent of propylene carbonate and dimethyl carbonate (1: 1 by volume).
The PF ₆ was prepared by dissolving 1mol / L.

A coin-type battery is assembled by sandwiching a negative electrode having a separator made of a polyethylene porous film on both sides in a sandwich manner between two positive electrodes, and allowed to stand at room temperature for 24 hours. Then, the amount of lithium absorbed by the negative electrode is determined per 1 g of silicon. 600m
Ah was set, and the charge and discharge cycle test was performed at 2.0 mA for the first charge and discharge and 10 mA for the subsequent charge and discharge. Table 1 shows the results.

Embodiment 2 FIG. 80 parts of polycrystalline silicon powder,
20 parts of graphite pitch granulated product (Osaka Chemical Co., Ltd.) was used as a carbon material, and a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio 1:
A battery was prepared in the same manner as in Example 1 except that 1 mol / L of LiPF ₆ was dissolved in 1), and a charge / discharge cycle test was performed. Table 1 shows the results. The negative electrode had a silicon content of 75% by weight.

Embodiment 3 FIG. 80 parts of polycrystalline silicon powder,
A battery was prepared in the same manner as in Example 1 except that 50 parts of natural graphite (Kansai Thermochemical Co., Ltd.) was used as the carbon material, and the electrolyte used in Example 2 was used. The test was performed. Table 1 shows the results. The negative electrode had a silicon content of 58% by weight.

Embodiment 4 FIG. 95 parts of polycrystalline silicon powder,
A battery was prepared in the same manner as in Example 1 except that 5 parts of acetylene black was used as the carbon material, and a charge / discharge cycle test was performed. Table 1 shows the results. The silicon content of the negative electrode was 90% by weight.

[0028]

[Table 1]

[0029]

As is apparent from the above description, according to the present invention, a sintered body containing silicon and a carbon material is used for a negative electrode, the silicon content is regulated within a predetermined range, and the amount of lithium absorbed by silicon is controlled. By controlling the amount within a predetermined range, it is possible to provide a non-aqueous secondary battery and a negative electrode for a non-aqueous secondary battery in which high conductivity and mechanical strength are imparted to the negative electrode, high capacity and improved cycle characteristics.

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[Procedure amendment]

[Submission Date] June 19, 2000 (2006.1.
9)

[Procedure amendment 1]

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[Claims]

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[Correction target item name] 0007

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[0007]

SUMMARY OF THE INVENTION The present invention relates to a non-aqueous secondary battery having a cathode and an anode containing an active material capable of inserting and extracting lithium ions. Is a sintered body containing silicon and carbon material,
Provided is a non-aqueous secondary battery having a sintered body having a silicon content of 50 to 99% by weight and absorbing 200 to 800 mAh of lithium per gram of silicon when fully charged.

[Procedure amendment 3]

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Claims (2)

[Claims] 1. A non-aqueous secondary battery having a positive electrode and a negative electrode containing an active material capable of inserting and extracting lithium ions,
The negative electrode is a sintered body containing silicon and a carbon material, the silicon content of the sintered body is 50 to 99% by weight, and 200 to 800 mAh of lithium per 1 g of silicon is absorbed when fully charged. Water-based secondary battery. 2. A sintered body containing silicon and a carbon material, which has a silicon content of 50 to 99% by weight and absorbs 200 to 800 mAh of lithium per gram of silicon when fully charged. Negative electrode.