JP2002117835A - Negative electrode for lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode for a lithium ion secondary battery wherein a downsizing and light-weight of the lithium ion secondary battery used for a portable apparatus is realized and wherein a battery capacity can be made to have a high capacity. SOLUTION: This is made to be the negative electrode using a composite material containing carbon powder, tin oxide and silicon oxide, and using polyimide resin as a binder. A (110) surface crystallite size of tin oxide in this composite material is made to be 4 to 40 nm, and an amount of silicon oxide is made to be in the range of tin/silicon=1/0.1 to 1 as the molar ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative electrode for a lithium ion secondary battery of a lithium ion secondary battery mounted on, for example, a mobile phone or a personal computer.

[0002]

2. Description of the Related Art In recent years, electronic devices, particularly portable devices such as cellular phones and notebook computers, have been remarkably reduced in size and weight, and accordingly, secondary batteries for driving them have become very important components. I have. Among these secondary batteries, lithium ion secondary batteries are lightweight and have a high energy density, and are being researched and industrialized as power sources for driving these portable devices.

The negative electrode for a lithium ion secondary battery mainly uses a carbon-containing active material including graphite from the viewpoint of safety and the like. The theoretical capacity when this carbon material containing graphite is used as a negative electrode active material is 372 mAh / g. However, as described above, due to the remarkable progress of portable devices, miniaturization,
In addition to weight reduction, high-capacity batteries having a theoretical capacity exceeding 372 mAh / g have been demanded.

[0004]

In order to meet such demands, batteries having a capacity exceeding 400 mAh / g have been actively developed. As this type of battery, for example, a metal material utilizing an alloying reaction with lithium, such as tin, aluminum, cadmium, lead, or silicon, may be used. These alloying reactions involve volume expansion and contraction, so each time charge and discharge cycles are repeated,
There is a problem that the miniaturization and the adhesion between the metal and the current collector and the like are reduced, and the capacity is reduced.

[0005] In order to solve this problem, for example, Japanese Patent Application Laid-Open No. H11-288712 discloses the use of a composite oxide containing divalent tin as a center and containing at least three or more elements. It is shown that cycle deterioration can be prevented by amorphization.

Japanese Patent Application Laid-Open No. 10-308207 discloses a non-aqueous electrolyte lithium secondary battery having excellent charge / discharge cycle characteristics by using a mixture of a metal which reacts with lithium and a metal which does not react. It has been disclosed.

[0007] However, these can provide a battery having a higher capacity as compared with the case where a graphite material is used as a negative electrode active material, but it is necessary to introduce a relatively large amount of elements that do not contribute to charge and discharge in order to impart cyclability. There is. This tends to decrease the capacity in consideration of the battery capacity per unit volume, and does not satisfy the recent demand for smaller and lighter portable devices.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has been made to reduce the size and weight of a lithium ion secondary battery used in a portable device and to increase the battery capacity of a lithium ion secondary battery. An object is to provide a negative electrode for an ion secondary battery.

[0009]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have made intensive studies and found that fine tin oxide is dispersed in carbon using a solution process, and that a highly amorphous material is obtained. A composite material composed of carbon, tin oxide, and silicon oxide obtained by compounding and firing a silicon oxide (hereinafter, referred to as a C-SnO ₂ —SiO ₂ composite material).
However, it was found that the crystallite size of the tin oxide was smaller than that in the case where the silicon oxide was not combined, and the cycle stability in the charge / discharge test was excellent. Also, by including a polyimide resin as a binder in the C-SnO ₂ —SiO ₂ composite material, the binder itself has a capacity, and it has been found that a negative electrode for a lithium ion secondary battery that can have a high capacity is obtained. The present invention has been completed.

That is, the negative electrode for a lithium ion secondary battery of the present invention is characterized by using a composite material containing carbon powder, tin oxide and silicon oxide, and a binder made of a resin. Preferably, the tin oxide is SnO ₂ and the silicon oxide is SiO ₂ . Further, the (110) plane crystallite size of the tin oxide is 4 to 4.
At 40 nm, it is preferable that the amount of the silicon oxide is present in a molar ratio of tin / silicon = 1 / 0.1 to 1. Preferably, the binder contains a polyimide resin.

C-SnO ₂ -SiO used in the present invention
_{(2) The} composite material is preferably formed by a sol-gel method, which is a type of solution process. This C-Sn
The carbon constituting the O ₂ —SiO ₂ composite material is one or more of natural graphite, artificial graphite, resin charcoal, natural carbide, petroleum coke, coal coke, pitch coke, and mesocarbon microbeads. Combinations can be used.

In addition, as precursors to be SnO _{2 at} this time, in addition to inorganic salts such as SnCl ₂ , Sn ₂ P ₂ O ₇ and SnSO ₄ , tin alkoxides such as Sn (OC ₂ H ₅ ) ₄ Can be used.

Further, as a precursor for forming SiO ₂ , S
silicon alkoxide such as i (OC ₂ H ₅ ) ₄ or SiC
it is possible to use the l _4.

C-SnO ₂ -composed of the above materials
In the SiO ₂ composite, the (110) plane crystallite size of SnO ₂ is 4 to 40 nm, and the amount of SiO ₂ is expressed in a molar ratio.
Sn / Si = 1 / 0.1 to 1, preferably Sn / Si
Si exists at 1 / 0.5 to 0.7.
In addition, in order to further improve the stability during the sol-gel method, a small amount of halogen elements such as chlorine and fluorine, sulfur,
It may contain an inorganic substance such as phosphorus or an alkali metal element such as lithium. Here, when Sn / Si = 1 / 0.1, the crystallite size of SnO ₂ tends to change greatly depending on the firing temperature, and stable charge / discharge behavior cannot be expected. When Sn / Si is larger than 1/1,
This is not preferable because the cycle tends to deteriorate.

As the binder of the C-SnO ₂ —SiO ₂ composite material, polyimide, polyamide, polyamide imide or the like, which itself contributes to charge and discharge, and polyvinylidene fluoride are preferable. In addition, an aromatic polyimide, an aromatic polyamideimide, an aromatic polyamide, or the like containing an aromatic group that easily causes electron transfer can be used.

These polyimides, polyamide imides, polyamides and the like can be produced by a known method, for example,
8 "Polymer Synthesis" (published by Maruzen Co., Ltd.
992). Among them,
It is preferable to use a low-temperature polycondensation method.

In the low-temperature polycondensation method, polyimide, polyamideimide and polyamide can be synthesized by reacting tetracarboxylic dianhydride, acid chloride and diamine. Here, as the tetracarboxylic dianhydride used, pyromellitic dianhydride, 3,3 ′, 4,
4'-diphenyltetracarboxylic dianhydride, 2,
2 ', 3,3'-diphenyltetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, bis (3,4-dicarboxyphenyl) ether dianhydride, benzene-1 2,2,3,4-tetracarboxylic dianhydride, 3,4,3 ', 4'-benzophenonetetracarboxylic dianhydride, 2,3,2', 3-benzophenonetetracarboxylic dianhydride, , 3,3 ', 4'-
Benzophenonetetracarboxylic dianhydride, 1,2,2
5,6-naphthalenetetracarboxylic dianhydride, 2,
3,6,7, -naphthalenetetracarboxylic dianhydride,
1,2,4,5-naphthalene-tetracarboxylic dianhydride, 1,4,5,8-naphthalene-tetracarboxylic dianhydride, phenanthrene-1,8,9,10-tetracarboxylic dianhydride , Pyrazine-2,3,5,6-tetracarboxylic dianhydride, thiophene-2,3,4,5-tetracarboxylic dianhydride, 2,3,3 ', 4'-biphenyltetracarboxylic dianhydride Anhydride, 3,4,3 ', 4'-
Biphenyltetracarboxylic dianhydride, 2,3,2 ',
There are 3'-biphenyltetracarboxylic dianhydride and the like, and two or more kinds may be used as a mixture.

As the acid chloride, terephthalic acid chloride, isophthalic acid chloride, trimellitic anhydride monochloride and the like can be used.

Examples of the diamine compound include 3,3'-diaminodiphenylmethane, 3,3'-diaminodiphenylether, 3,3'-diaminodiphenylsulfone,
3,3'-diaminodiphenyl sulfide, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenylmethane, 3,3'-diaminobenzophenone, 4,
4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether,
There are 1,5-diaminonaphthalene and the like, and two or more kinds may be used as a mixture.

The solvent for synthesizing these is not particularly limited as long as the raw material resin and the produced polymer can be dissolved, but from the viewpoint of reactivity and a dispersion medium at the time of preparing the negative electrode, N, N-dimethylformamide, It is preferable to use N, N-dimethylacetamide and N-dimethyl-2-pyrrolidone.

Next, a method for manufacturing a negative electrode for a lithium ion secondary battery comprising a binder such as a C-SnO ₂ -SiO ₂ composite material and a polyimide resin will be described. First, a sol-gel liquid is prepared by mixing a carbon powder, a SnO ₂ precursor, and a SiO ₂ precursor in a predetermined mixture. After drying this sol-gel liquid at 80 ° C., it is baked at 500 to 1200 ° C. in a nitrogen atmosphere to form a C—SnO ₂ —SiO ₂ composite material.

Here, the compounding ratio of Sn / Si in the C—SnO ₂ —SiO ₂ composite material is, for example, when the compounding ratio of Sn / Si is the same, the SnO ₂ crystallites increase with the firing temperature. The size tends to be large, and it is necessary to set a firing temperature according to each composition. When used as an active material of a negative electrode for a lithium ion secondary battery, it is preferable that the ratio of SiO ₂ not involved in charge / discharge is relatively small and the mixing ratio of Sn / Si is 1 / 0.5 to 0.7. Preferably, the firing temperature is 600 to 800 ° C.

Further, by adding SiO ₂ having a high amorphous property, it is possible to suppress the crystal growth of SnO ₂ to some extent, so that SnO ₂ (11
The crystallite size on the 0) plane can be in the range of 4 to 40 nm.

There is no particular limitation on the mixing ratio of the carbon powder and SnO ₂ —SiO ₂ , but the cycle stability of the battery is improved by increasing the carbon ratio. However, the higher the ratio of carbon, the lower the capacity of the battery, making it difficult to satisfy the demand for higher capacity. On the other hand, when the ratio of SnO ₂ —SiO ₂ is increased, the capacity of the battery is increased, but the cycle stability is reduced. In addition, when the specific gravity is higher than carbon and the battery has a predetermined battery capacity or more, there arises a problem that the demand for reducing the size and weight of the battery cannot be satisfied. Therefore, regarding the mixing ratio of the carbon powder and SnO ₂ —SiO ₂ , the mixing ratio is appropriately determined according to the desired battery size and battery capacity.

The C-SnO ₂ -formed as described above
After pulverizing the SiO ₂ composite, mixed with a polyimide resin as a binder, and applied to a copper foil to a predetermined thickness,
A negative electrode for a lithium ion secondary battery.

[0026]

The present invention will be described below in detail with reference to examples.

Example 1 10 g of natural graphite powder was mixed with about 30 g of a sol-gel solution containing Sn and Si elements adjusted to an atomic ratio of Sn / Si = 1 / 0.5, stirred, dried at 80 ° C. The firing was performed at 600 ° C. in a nitrogen atmosphere. The weight abundance ratio of the obtained powder was C: 41%, Sn: 49%, S:
i: 10%. This powder is ground in a mortar and
After sieving so as to be not more than μm, as a result of measurement by X-ray diffraction, it was found that graphite had a (110) plane crystallite size of 14 nm.
Of tetragonal SnO ₂ was detected. This powder and the polyimide resin are mixed at a mass ratio of 90/10, and the thickness 2
0μm copper foil to a thickness of 100μm, 1
Dried at 35 ° C. Thereafter, using an ethylene carbonate / dimethyl carbonate (hereinafter, referred to as EC / DMC) electrolyte, a 0-1.5 V half-cell charge / discharge test was performed in a glove box having a dew point of -70 ° C.

Example 2 10 g of natural graphite powder was mixed with about 30 g of a sol-gel solution containing Sn and Si elements adjusted to an atomic ratio of Sn / Si = 1 / 0.7, stirred, dried at 80 ° C. The firing was performed at 600 ° C. in a nitrogen atmosphere. The weight abundance ratio of the obtained powder was C: 38%, Sn: 45%, S:
i: 18%. This powder is ground in a mortar and
After sieving so as to be not more than μm, as a result of measurement by X-ray diffraction, it was found that graphite had a (110) plane crystallite size of 7.5 n.
A peak of m tetragonal SnO ₂ was detected. This powder and a polyimide resin are mixed at a mass ratio of 90/10, and applied to a copper foil having a thickness of 20 μm so as to have a thickness of 100 μm.
Dry at 135 ° C. Then, using an EC / DMC electrolytic solution, a 0-deg.
A 1.5V half-cell charge / discharge test was performed.

Example 3 10 g of natural graphite powder was mixed with about 30 g of a sol-gel solution containing Sn and Si elements adjusted to an atomic ratio of Sn / Si = 1 / 0.5, stirred and dried at 80 ° C. The firing was performed at 600 ° C. in a nitrogen atmosphere. The weight abundance ratio of the obtained powder was C: 41%, Sn: 49%, S:
i: 10%. This powder is ground in a mortar and
After sieving so as to be not more than μm, as a result of measurement by X-ray diffraction, it was found that graphite had a (110) plane crystallite size of 14 nm.
Of tetragonal SnO ₂ was detected. This powder and polyvinylidene fluoride resin were mixed at a mass ratio of 90/10, applied to a copper foil having a thickness of 20 μm so as to have a thickness of 100 μm, and dried at 135 ° C. After that, EC / DM
Using a C electrolytic solution, a 0-1.5 V half-cell charge / discharge test was performed in a glove box having a dew point of -70 ° C.

Example 4 10 g of natural graphite powder was mixed with about 30 g of a sol-gel solution containing Sn and Si elements adjusted to an atomic ratio of Sn / Si = 1 / 0.3, stirred, dried at 80 ° C. The firing was performed at 600 ° C. in a nitrogen atmosphere. The weight abundance ratio of the obtained powder was C: 45%, Sn: 50%, S:
i: 5%. This powder is ground in a mortar and
After sieving so as to be not more than m, as a result of measurement by X-ray diffraction, a tetragonal SnO ₂ peak having a crystallite size of 39 nm in addition to graphite was detected. This powder and polyvinylidene fluoride resin were mixed at a mass ratio of 90/10, applied to a copper foil having a thickness of 20 μm so as to have a thickness of 100 μm, and dried at 135 ° C. After that, EC / DMC
Using an electrolytic solution, a 0-1.5 V half-cell charge / discharge test was performed in a glove box having a dew point of -70 ° C.

Comparative Example 1 SnO ₂ (special grade of Wako Pure Chemical Industries,
(110) plane crystallite size 42 nm) and a polyvinylidene fluoride resin in a mass ratio of 95/5,
0μm copper foil to a thickness of 100μm, 1
Dried at 35 ° C. Thereafter, using an EC / DMC electrolytic solution, a 0-1.
A 5V half-cell charge / discharge test was performed.

Comparative Example 2 10 g of natural graphite powder was mixed with about 30 g of a sol-gel solution containing Sn and Si elements adjusted to an atomic ratio Sn / Si = 1 / 0.05, stirred, dried at 80 ° C. The firing was performed at 600 ° C. in a nitrogen atmosphere. The weight ratio of the obtained powder was C: 45%, Sn: 54%,
Si: 1%. This powder is ground in a mortar and
After sieving so as to be not more than μm, it was measured by X-ray diffraction.
Of tetragonal SnO ₂ was detected. This powder and polyvinylidene fluoride resin were mixed at a mass ratio of 90/10, applied to a copper foil having a thickness of 20 μm so as to have a thickness of 100 μm, and dried at 135 ° C. After that, EC / DM
Using a C electrolytic solution, a 0-1.5 V half-cell charge / discharge test was performed in a glove box having a dew point of -70 ° C.

Comparative Example 3 10 g of natural graphite powder was mixed with about 30 g of a sol-gel solution containing Sn and Si elements adjusted to an atomic ratio Sn / Si = 1 / 1.1, stirred, dried at 80 ° C. The firing was performed at 700 ° C. in a nitrogen atmosphere. The weight ratio of the obtained powder was as follows: C: 38%, Sn: 44%, S:
i: 19%. This powder is ground in a mortar and
After sieving so as to be not more than μm, as a result of measurement by X-ray diffraction, it was found that graphite had a (110) plane crystallite size of 4.2 n.
A peak of m tetragonal SnO ₂ was detected. This powder and polyvinylidene fluoride resin were mixed at a mass ratio of 90/10, applied to a copper foil having a thickness of 20 μm so as to have a thickness of 100 μm, and dried at 135 ° C. After that, EC / D
A 0-1.5 V half-cell charge / discharge test was performed in a glove box having a dew point of -70 ° C. using an MC electrolytic solution.

Comparative Example 4 10 g of natural graphite powder was mixed with about 30 g of a sol-gel solution containing Sn and Si elements adjusted to an atomic ratio Sn / Si = 1 / 0.3, stirred, dried at 80 ° C. The firing was performed at 1300 ° C. in a nitrogen atmosphere. The weight ratio of the obtained powder was C: 45%, Sn: 50%,
Si: 5%. This powder is ground in a mortar and
After sieving so as to be not more than μm, as a result of measurement by X-ray diffraction, it was found that graphite had a (110) plane crystallite size of 48 nm.
Of tetragonal SnO ₂ was detected. This powder and the polyimide resin are mixed at a mass ratio of 90/10, and the thickness 2
0μm copper foil to a thickness of 100μm, 1
Dried at 35 ° C. Thereafter, using an EC / DMC electrolytic solution, a 0-1.
A 5V half-cell charge / discharge test was performed.

(Comparative Example 5) 10 g of natural graphite powder was mixed with about 30 g of a sol-gel solution containing Sn and Si elements whose atomic abundance ratio was adjusted to Sn / Si = 1/1, stirred, dried at 80 ° C., and nitrogen atmosphere Baking was performed at 500 ° C. below. The weight abundance ratio of the obtained powder was C: 38%, Sn: 45%, S:
i: 18%. This powder is ground in a mortar and
After sieving so as to be not more than μm, as a result of measuring by X-ray diffraction, it is found that graphite has another (110) plane crystallite size of 3.8 n.
A peak of m tetragonal SnO ₂ was detected. This powder and a polyimide resin are mixed at a mass ratio of 90/10, and applied to a copper foil having a thickness of 20 μm so as to have a thickness of 100 μm.
Dry at 135 ° C. Then, using an EC / DMC electrolytic solution, a 0-deg.
A 1.5V half-cell charge / discharge test was performed.

As described above, Examples 1 to 4 and Comparative Examples 1 to 5
Table 1 and FIG. 1 show the results of the 0-1.5 V half-cell charge / discharge test.
Are shown together.

[0037]

[Table 1]

From Table 1 and FIG. 1, it can be seen that the battery using the negative electrode material for a secondary battery according to the present embodiment has a high capacity and excellent cycle stability. In addition,
The SnO ₂ (110) plane crystallite size was calculated from the following Scherrer based on the half-width data from the X-ray diffraction measurement results.
It calculated from the formula of. D _hkL : K · λ / βcos θ where D _hkL is the crystallite size (nm) and λ is the measurement X
Line wavelength (0.15405 nm), β is the spread of the diffraction line according to the size of the crystallite (radian), θ is the Bragg angle (deg) of the diffraction line (2θ = 26.5 deg, θ = 13.2)
5 deg), and K was calculated as a constant (0.9).

This is because, by adding SiO ₂ , the (110) plane crystallite of SnO ₂ can be set in the range of 4 to 40 nm, so that it can expand even during an alloying reaction with lithium.
It is considered that the adhesion to the current collector due to the shrinkage does not easily deteriorate, so that the deterioration of the charge / discharge cycle is suppressed.

[0040]

The present invention is configured as described above.
Using a polyimide resin as a binder for a composite material containing carbon powder, tin oxide and silicon oxide, the (110) plane crystallite size of the tin oxide in this composite material is 4 to 40 nm, The amount is expressed in mol ratio,
By setting the tin / silicon = 1 / 0.1 to 1 range, by using a binder that contributes to the alloying reaction with lithium and charge / discharge, a high capacity can be realized, and the amount of tin added can be reduced. Since it can be suppressed, there is an effect that it is possible to realize a reduction in size and weight.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a lithium ion secondary battery according to the present embodiment.
It is the figure which put together the result of the 1.5V half-cell charge / discharge test.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Naoto Ota 211-2-2 Nakahime, Onohara-cho, Mitoyo-gun, Kagawa Toyo Carbon Co., Ltd. (72) Inventor Katsuhide Nagaoka 211-2-2 Nakahime, Onohara-cho, Mitoyo-gun, Kagawa Toyo Carbon F term (reference) 5H050 AA08 BA17 CB02 CB08 CB29 DA03 DA11 EA23 HA02 HA13

Claims (8)

[Claims] 1. A negative electrode for a lithium ion secondary battery, comprising: a composite material containing carbon powder, tin oxide, and silicon oxide; and a binder made of a resin. 2. The negative electrode for a lithium ion secondary battery according to claim 1, wherein the tin oxide is SnO ₂ . 3. The negative electrode for a lithium ion secondary battery according to claim 1, wherein the silicon oxide is SiO ₂ . 4. The negative electrode for a lithium ion secondary battery according to claim 1, wherein the tin oxide is SnO ₂ and the silicon oxide is SiO ₂ . 5. The negative electrode for a lithium ion secondary battery according to claim 1, wherein the (110) plane crystallite size of the tin oxide is 4 to 40 nm. 6. The lithium ion secondary battery according to claim 1, wherein the amount of the silicon oxide is in a molar ratio of tin / silicon = 1 / 0.1 to 1. For negative electrode. 7. The (110) plane crystallite size of the tin oxide is 4 to 40 nm, and the amount of the silicon oxide is mol
The negative electrode for a lithium ion secondary battery according to any one of claims 1 to 4, wherein tin / silicon is present in a ratio of 1 / 0.1 to 1 in a ratio. 8. The negative electrode for a lithium ion secondary battery according to claim 1, wherein the binder contains a polyimide resin.