JPH11297311A - Negative electrode material for nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide high-capacity and good charge/discharge characteristics and a satisfactory cycle life in the charge/discharge at a high current density by using a complex made of silicon storing and discharging lithium ions and a metal, applying conductivity to silicon as a negative electrode active material. SOLUTION: A complex made of silicon and a conductive metal applying conductivity is used as a negative electrode active material of this battery, a metal oxide containing a transition metal for the constituting element is used as a positive electrode active material, and a nonaqueous electrolyte dissolved with a lithium compound in an organic solvent is used as an electrolyte. The silicon powder to be used may be of crystalline or amorphous from, and preferably silicon power with an average grain size of about 1-10 μm is used. Copper is desirably used for the conductive metal. The complex preferably contains the conductive metal of about 3-90 wt.%, preferably containing 5-50 wt.%. the complex is preferably manufactured through electroless plating or vacuum deposition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous secondary battery having a high capacity and excellent charge / discharge cycle characteristics, and more particularly to a negative electrode material for a non-aqueous secondary battery.

[0002]

2. Description of the Related Art In a non-aqueous secondary battery which can be expected to have high energy density, metallic lithium,
Typically, a method using an oxide of a transition metal typified by Co, Mn, and Ni as the positive electrode active material is used. However, when metallic lithium is used for the negative electrode, the metallic lithium grows in a dendritic form (dendrite) during charge and discharge, causing a short circuit inside, and the dendrite has high activity and there is a risk of ignition. is there. For this reason, fired carbonaceous materials capable of inserting and releasing lithium ions as active materials instead of metallic lithium have been put to practical use as negative electrodes. However, carbon materials have the disadvantage that the charge / discharge capacity per volume is low.

As negative electrode active materials which can be expected to have a high charge / discharge capacity per volume, 1) transition metal chalcogen compounds such as TiS ₂ and LiTiS ₂ (US Pat. No. 3,983,476);
2) a transition metal oxide having a rutile structure, for example, WO ₂ (U.S. Pat. No. 4,198,476); 3) LixFe (F
e ₂₎ spinels such as O ₄ (JP 58-2203
No. 62), 4) Lithium compound of Fe ₂ O ₃ electrochemically synthesized (US Pat. No. 4,446,447), Fe ₂ O ₃
Lithium compound (JP-A-3-112070), Nb
₂ O ₅ (JP-A-62-59412, JP-A-2-8244)
No. 7), iron _{oxide, FeO, Fe 2 O, Fe} 3 O 4, cobalt _{oxide, CoO, Co 2 O 3,} Co 3 O 4 ( JP-A-3-29
No. 1862). On the other hand, 5) Sn, Cd (Proceedings of the) which are known to form an alloy with lithium.
Electrochemical Society, 8
7-1, 1987), Al (Solid State)
Ionics, 20, 1986), Si, Pb, Bi,
Sb (Proceedings of the Ele)
crochemical Society, 87-
1,1987), compounds or alloys thereof with lithium (for example, JP-A-7-29602), and those in which a metal capable of forming an alloy with these lithiums is supported on carbon particles (JP-A-8-273702). Proposed.

[0004]

However, the above-mentioned Sn, Cd, Al, Si, Pb, Bi, Sb and their alloys with lithium have particularly high current densities (for example, 1 m
(A / cm ² or more), there is a problem that the capacity is low and the cycle life during charge / discharge is short.

Accordingly, the present invention provides 1) a negative electrode material for a non-aqueous secondary battery containing a negative electrode active material capable of reversibly inserting and releasing lithium ions and providing a high capacity; and 2) a charge / discharge at a high current density. Another object of the present invention is to provide a non-aqueous secondary battery having high capacity, good charge / discharge characteristics and cycle life.

[0006]

According to the present invention, it is possible to solve the above-mentioned problems by using a composite comprising silicon capable of inserting and releasing lithium ions and a conductive metal imparting conductivity to silicon as a negative electrode active material. It was found and completed.

[0007] The compounding of silicon and a conductive metal improves the conductivity of the negative electrode active material, facilitates the insertion and release reaction of lithium ions, improves the active material utilization rate, and improves the internal resistance of the battery. An effect such as reduction is provided, and a non-aqueous secondary battery having high capacity and excellent charge-discharge cycle characteristics can be obtained.

Further, it is desirable that the above-mentioned composite is obtained by supporting a conductive metal on silicon, or by coating silicon or a compound thereof with a conductive metal.

The silicon may be in the form of a powder or a plate.

It is desirable that the composite is obtained by reducing and precipitating a conductive metal on silicon with an aqueous solvent. By using an aqueous solvent, a conductive metal can be compounded more safely and at lower cost than when a non-aqueous solvent is used or when a dry method is used.

Further, a paste obtained by adding a binder and a solvent to the powdery silicon-containing composite and kneading the mixture is
It is preferable to form a negative electrode by coating the current collector.

Further, the above-mentioned composite containing silicon in the form of a plate comprises:
It is preferable that at least one side has a conductive metal, and a current collector is pressed against the one side to form a negative electrode.

Further, the non-aqueous secondary battery of the present invention is characterized in that a composite comprising silicon and a conductive metal imparting conductivity is used as a negative electrode active material, and a metal oxide containing a transition metal as a constituent element is used as a positive electrode active material. A lithium ion conductive non-aqueous electrolyte in which a lithium compound is dissolved in an organic solvent, or in which a lithium compound is dissolved in a polymer or an organic solvent in which a lithium compound is dissolved is held, is used as an electrolyte.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The silicon powder of the present invention may be either crystalline or amorphous, but preferably has an average particle size of about 1 to 10 μm.

Further, the conductive metal of the present invention includes copper,
And noble metals, but copper satisfying conditions such as easy reduction, high conductivity, and low cost is desirable.

In the composite of the present invention, in order to maintain a large capacity and obtain sufficient conductivity, a conductive metal is used in an amount of 3 to 9%.
0% by weight, more preferably 5 to 50% by weight.

The method for producing the composite of the present invention includes a chemical reduction method, an electrolytic plating method, and an electroless plating method capable of reducing and depositing a conductive metal on silicon or a compound thereof in an aqueous solvent. However, the electroless plating method is preferable. Another preferable method is a vacuum evaporation method.

The negative electrode active material comprising the composite obtained by the above method is vacuum-dried, and a negative electrode is prepared by the following method. When silicon or a compound thereof is powder, a binder and a solvent such as N-methyl-2-pyrrolidone are added to the vacuum-dried composite and kneaded, and the kneaded slurry is applied to a copper foil of a current collector to form a negative electrode. And When silicon or a compound thereof is plate-shaped, a negative electrode is obtained by pressing a copper foil as a current collector on the conductive metal layer side on which reduction deposition is performed. Here, instead of copper foil,
A metallurgical film in which copper is vapor-deposited on one or both surfaces of a polyester film, a polyethylene film and a polypropylene film may be used as the current collector.

As the cathode material used as the cathode active material of the present invention, any conventionally known materials can be used.
ixCoO ₂ , LixNiO ₂ , MnO ₂ , LiMnO ₂ ,
_{LixMn 2 O 4, LixMn 2-} y O 4, α-V 2 O 5, Ti
S _2, and the like.

The non-aqueous electrolyte used in the present invention is a non-aqueous electrolyte in which a lithium compound is dissolved in an organic solvent, or a polymer in which a lithium compound is dissolved or an organic solvent in which a lithium compound is dissolved is held. A polymer solid electrolyte can be used. The non-aqueous electrolyte is prepared by appropriately combining an organic solvent and an electrolyte, and any of these organic solvents and electrolytes can be used as long as they are used for this type of battery. Examples of the organic solvent include propylene carbonate, ethylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane,
1,2-diethoxyethanemethylformate, butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1-3 dioxofuran, 4-methyl-1,3
-Dioxofuran, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile,
Butyronitrile, valeronitrile, benzonitrile,
1,2-dichloroethane, 4-methyl-2-pentanone, 1,4-dioxane, anisole, diglyme, dimethylformamide, dimethylsulfoxide and the like.
One of these solvents can be used alone, or two or more can be used in combination. Examples of the electrolyte include LiClO ₄ , LiAsF ₆ , LiPF ₆ , L
iBF ₄ , LiB (C ₆ H ₅ ) ₄ , LiCl, LiBr, L
iI, LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiAlCl
_{And the} like. One of these can be used alone, or two or more can be used in combination.

The solid polymer electrolyte used in the present invention comprises:
A solution obtained by dissolving an electrolyte selected from the above electrolytes in the following polymer can be used. For example, polymers having a polyether chain such as polyethylene oxide or polypropylene oxide, polyethylene succinate, a polymer having a polyester chain such as polycaprolactam, a polymer having a polyamine chain such as polyethyleneimine, a polyalkylene sulfide Such a polymer having a polysulfide chain is exemplified. Further, as the polymer solid electrolyte used in the present invention, polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, polyethylene oxide, polyacrylonitrile, holding the non-aqueous electrolyte in a polymer such as polypropylene oxide What plasticized the said polymer can also be used.

[0022]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

Embodiment 1 FIG. 35 g of copper sulfate, 34.0 g of Rochelle salt, 3.0 g of sodium carbonate, and 7.0 g of sodium hydroxide were added to water 11, and the mixture was stirred to dissolve, and the purity was 9%.
10.0 g of a 9.9% silicon powder having an average particle diameter of 5 μm was added, and 13.0 ml of a 37% formaldehyde solution was added to reduce copper. The copper was supported on the silicon powder. 13 g of a powder were obtained. The above composite powder 10
g of polyvinylidene fluoride (PVD) as a binder
F) Add 1 g and add n-methyl-2-pyrrolidone (NMP)
Into a paste, and apply a part of the paste to copper foil.
Pressure bonding was performed at a pressure of t / cm ² . After drying, the negative electrode was punched into a predetermined size and shape. This negative electrode was combined with metallic lithium as a counter electrode, and 1 mol was added to a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio 1: 1).
A test cell was assembled using an electrolytic solution to which lithium hexafluorophosphate was added so that the concentration became 1 / l, and the current density was 2 mA.
/ Cm ² and a voltage range of 5 mV to 1500 mV. Table 1 shows the results.

Comparative Example 1 1 g of PVDF was added as a binder to 10 g of NG7 (average particle size: 7 μm) manufactured by Kansai Thermal Chemical Co., Ltd. as natural graphite powder, and NMP was added to form a paste. A part of the paste was applied to a copper foil, and then 1 t / cm ^2. Pressure. After drying, the negative electrode was punched into a certain size and shape. Except for this, all were performed under the same conditions as in Example 1. Table 1 shows the results.

Embodiment 2 FIG. 7. Lithium cobalt oxide for positive electrode
Part of a mixture consisting of 8 g, 0.6 g of acetylene black and 0.6 g of polytetrafluoroethylene resin was put into a mold on which aluminum foil was spread, and was molded under a pressure of 1 t / cm ² to have the same size and shape as the negative electrode. The positive electrode was used as the positive electrode. Except for using this positive electrode instead of metallic lithium,
The procedure was performed in the same manner as in Example 1. Table 1 shows the results.

Comparative Example 2 The same procedure as in Example 2 was carried out except that the negative electrode of Comparative Example 1 was used as the negative electrode. Table 1 shows the results.

Comparative Example 3 In Comparative Example 1, silicon powder (purity 99.9%, particle size 5 μm) instead of natural graphite powder
And a negative electrode was produced in the same manner. Table 1 shows the results.

[0028]

Table 1 Discharge capacity (mAh / g) Charge / discharge efficiency (%) Charge / discharge efficiency at 5th cycle (%) Example 1 600 83 95 Comparative Example 1 280 85 95 Example 2 600 83 95 Comparative Example 2 280 85 95 Comparative Example 3 20 20

[0029]

As described above, according to the present invention, a composite material comprising silicon capable of inserting and releasing lithium ions and a conductive metal imparting conductivity to silicon is used as a negative electrode active material. As the conductivity of the active material is improved, the insertion / release reaction of lithium ions proceeds smoothly, and effects such as improvement of the active material utilization rate and reduction of the internal resistance of the battery are brought about. A non-aqueous secondary battery having excellent characteristics can be obtained.

Claims (4)

[Claims] 1. A negative electrode material for a non-aqueous secondary battery comprising, as a negative electrode active material, a composite comprising a silicon powder capable of inserting and releasing lithium ions and a conductive metal imparting conductivity to silicon. 2. The negative electrode material for a non-aqueous secondary battery according to claim 1, wherein the composite is obtained by supporting a conductive metal on the silicon powder, or by coating the silicon powder with a conductive metal. . 3. The negative electrode material for a non-aqueous secondary battery according to claim 1, wherein the composite is obtained by reducing and depositing a conductive metal on a silicon powder with an aqueous solvent. . 4. A composite comprising silicon powder and a conductive metal imparting conductivity to silicon is used as a negative electrode active material, a metal oxide containing a transition metal as a constituent element is used as a positive electrode active material, and a lithium compound is used as an organic solvent. A non-aqueous secondary battery using, as an electrolyte, a lithium ion conductive non-aqueous electrolyte in which a lithium compound is dissolved, or a lithium compound is dissolved in a polymer, or an organic solvent in which a lithium compound is dissolved is held.