JPH1092424A - Lithium secondary battery negative electrode and lithium secondary battery using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate an internal short-circuit, and maintain a function as negative electrode active material by using aluminum powder having conductive inorganic coating layers on the surfaces thereof as the negative electrode active material. SOLUTION: By forming conductive inorganic coating layers on the surfaces of aluminum powder, in a coating layer forming process, one part of or the most part of ready made aluminum oxide on the surfaces of the aluminum powder is removed, and after the formation of the coating layers, the new producing of the aluminum oxide is suppressed. Thereby, the aluminum powder maintains initial mechanical rigidity, and deals with a pulverization issue resulting from the repeated charge and discharge of a secondary battery so as to improve the same. As an aluminum simple substance, the same of purity of 99 percentage by weight or more is preferable, and the purity of 99.9 percentage by weight or more is particularly preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery using the same.

[0002]

2. Description of the Related Art Conventionally, as a negative electrode active material for a lithium secondary battery, metallic lithium and various lithium alloys are generally used. When such a lithium-based negative electrode active material is used, dendrite is charged by charging. There is a problem of causing an internal short circuit. In addition, the lithium-based negative electrode active material is used in the form of a single plate, but the charge / discharge of the secondary battery is repeated and the negative electrode active material is gradually powdered within a relatively short period of time, losing its function. There is also. On the other hand, although carbon has been used as a negative electrode active material instead of a lithium-based negative electrode active material, there is a problem that the capacity per unit volume of this negative electrode active material is not sufficient.

There is a proposal to use an aluminum-based powder as a negative electrode active material. Aluminum-based powders generally have a large capacity for inserting and extracting lithium, and therefore have a large capacity per unit volume, and since they are powders, the surface area per unit weight is several times that of lithium-based negative electrode active materials.
Since it is as large as several hundred times, the reaction amount of lithium per unit surface area becomes relatively low. As a result, there is an advantage that dendrite is hardly generated. However, in a lithium secondary battery using an aluminum-based powder negative electrode active material, the internal resistance of the battery gradually increases during use due to an increase in the amount of aluminum oxide generated over time on the surface of the aluminum-based powder, and the electromotive force decreases. There is a problem to do. Further, there is also a problem that the aluminum-based powder which has become brittle due to the generation of aluminum oxide is broken and further pulverized while the secondary battery is repeatedly charged and discharged, detaches from the negative electrode, and loses its function.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a lithium secondary battery comprising a negative electrode active material of an aluminum-based powder in which the problem of increasing the internal resistance of the lithium secondary battery and the problem of pulverization are improved. An object of the present invention is to provide a negative electrode and a lithium secondary battery using the same.

[0005]

The present invention has the following features. 1. A negative electrode for a lithium secondary battery, wherein an aluminum-based powder having a conductive inorganic coating layer on the surface is used as a negative electrode active material. 2. 2. The negative electrode for a lithium secondary battery according to the above 1, wherein the aluminum-based powder is at least one selected from the group consisting of aluminum and an aluminum alloy. 3. The constituent material of the conductive inorganic coating layer is Sn, Zn, I
3. The method according to the above 1 or 2, which is at least one selected from the group consisting of n, Pb, Mn, Mo, Co, Cu, Fe, Ni, two or more alloys thereof, Sn oxide, and In oxide. Negative electrode for lithium secondary batteries. 4. The negative electrode for a lithium secondary battery according to any one of the above 1 to 3, a positive electrode having a positive electrode active material having a potential difference of at least 1 V from the negative electrode, and a nonaqueous electrolyte or a lithium ion conductive solid electrolyte having a lithium salt. A rechargeable lithium battery. 5. 5. The lithium secondary battery according to the above item 4, wherein the positive electrode active material is a lithium-containing transition metal oxide.

[0006]

By forming a conductive inorganic coating layer on the surface of the aluminum-based powder, the above-mentioned object of the present invention can be solved for the following reasons. That is, in the process of forming the coating layer, part or most of the existing aluminum oxide on the surface of the aluminum-based powder is removed,
After the formation of the coating layer, new generation of aluminum oxide is suppressed or prevented by the coating layer. For this reason, the aluminum-based powder retains the initial mechanical robustness and improves the problem of pulverization due to repeated charging and discharging of the secondary battery.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the aluminum-based powder may be a powder of aluminum alone or an aluminum alloy. As the simple substance of aluminum, a substance having a purity of 99% by weight or more, particularly preferably 99.9% by weight or more is preferable. Examples of the aluminum alloy include an Al-M alloy. M in the Al-M alloy is Si, Zn,
One or more alloy components selected from In, Ag, Te, Mg, Pb, Bi, Sn and the like, and Al:
M (weight ratio) is 30:70 to 99: 1, particularly 50:50.
~ 80: 20. The average particle size of the aluminum-based powder is 0.1 to 50 μm, preferably 5 to 50 μm.
20 μm. At least one kind of the above-mentioned simple aluminum powder, at least one kind of aluminum alloy powder, or a mixed powder of simple aluminum and an aluminum alloy is used. In particular, a simple aluminum: aluminum alloy (weight ratio) of 1: 9 to 3: 7 is preferred.

[0008] As a constituent material of the conductive inorganic coating layer,
Conductivity generally required for a negative electrode for a lithium secondary battery, for example, various metals, alloys, metal oxides, or metals alloyed with lithium having a conductivity of at least 1 × 10 ⁴ Ωm ⁻¹ at room temperature. No. Examples of the metal to be alloyed with lithium include Sn, Zn, In, Pb, and Cu.
In addition to the action of removing and preventing the formation of aluminum oxide, they are alloyed with lithium precipitated on the surface of the aluminum-based powder during charging, and diffuse lithium into the inside of the aluminum-based powder to reduce the fineness of the powder. Also has the effect of preventing the formation. Metals that are not reactive with lithium, such as M
n, Mo, Co, Cu, Fe, Ni, and the like form a coating layer by themselves to remove aluminum oxide and prevent the formation of aluminum oxide. As the coating alloy, for example, Ag-C
u, Ag-In, Pb-Sn, Ag-Mn-Sn, etc.
Preferably, the diffusion coefficient of lithium in the coating alloy is close to or greater than the diffusion coefficient of lithium in aluminum. Since the oxides of Sn and In are conductive in themselves, they can be formed by performing an appropriate oxidation treatment after forming the layers of Sn and In.

The conductive inorganic coating layer is formed by an electroless plating method,
It can be formed by electroplating, deposition, vapor deposition or other methods. In an electroless plating method or an electroplating method, an alkaline plating solution is usually used, and aluminum oxide on the surface of the aluminum-based powder is dissolved and removed at the time of plating due to the alkalinity of the plating solution. In the deposition method and the vapor deposition method, aluminum oxide is removed by energy during deposition and vapor deposition of the conductive inorganic coating material, and the inorganic coating material is coated instead. The thickness of the conductive inorganic coating layer is preferably at least about 0.05 μm, and more preferably about 0.1 to 1 μm.

The negative electrode active material of an aluminum-based powder having a conductive inorganic coating layer on the surface is used together with a usual binder to form a negative electrode for a lithium secondary battery by a usual method. Examples of the binder include polytetrafluoroethylene, polyvinylidene fluoride, and polyethylene. Binder:
The mixing ratio with the aluminum-based powder having the conductive inorganic coating layer is 1:99 to 20:80, preferably 5:95 to 1
5:85.

[0011] The lithium secondary battery of the present invention comprises the above-described rechargeable battery.
Negative electrode for a lithium secondary battery, a positive electrode having a positive electrode active material, and
And a liquid or solid non-aqueous electrolyte. Correct
As the polar active material, the potential difference from the negative electrode is at least 1 V
, For example, V_TwoO_Five, MnO_Two, LiMn_TwoO
_Four, LiCoO_Two, LiNi_0.5Co_0.5O _Two, LiN
iO_Two, Li-Co-P-based composite oxide (LiCo_0.5P
_0.5O_Two, LiCo_0.4P_0.6O_Two, LiCo_0.6P₀.
_FourO_Two, LiCo_0.3Ni_0.3P_0.4O_Two, LiCo
_0.2Ni_0.2P_0.6O_TwoEtc.), TiS_Two, MoS_Two,
MoO_ThreePreferred are lithium-containing transition metal oxides such as
No. Among these, the electromotive force and charge / discharge voltage of secondary batteries
-Co-P-based composite oxidation that can particularly increase
Are particularly preferred.

As the non-aqueous electrolyte, an electrolyte in which salts are dissolved in an organic solvent or a solid electrolyte can be used. Salts used in the electrolyte include LiClO ₄ , LiBF ₄ , L
_{iPF 6, LiAsF 6, LiAlCl 4} , Li (CF
₃ SO ₂ ) ₂ N and the like, and one kind or a mixture of two or more kinds thereof is used. Examples of the organic solvent include ethylene carbonate, propylene carbonate, dimethyl sulfoxide, sulfolane, γ-butyrolactone,
2-dimethoxyethane, N, N-dimethylformamide, tetrahydrofuran, 1,3-dioxolan, 2-
Examples thereof include methyltetrahydrofuran and diethyl ether, and one or a mixture of two or more thereof is used. The concentration of the salt in the electrolyte is 0.1
It is used after being dissolved at a concentration of about 3 mol / liter.
Examples of the solid electrolyte include those obtained by mixing one or more of the above salts with polyethylene oxide, polyphosphazene, polyaziridine, polyethylene sulfide or a derivative thereof, or a mixture of two or more thereof. The solid electrolyte also functions as a separator between the positive and negative electrodes of the battery.

[0013]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples, and comparative examples will be shown to show the remarkable effects of the present invention.

Example 1 An aluminum powder having a purity of 99.95% by weight and an average particle diameter of 20 μm was put into a 10% by weight aqueous solution of a zinc displacing agent (DI-470 manufactured by Nippon Chemical Industry Co., Ltd.) maintained at 4 ° C.
After standing under stirring for 2 seconds, pull up, wash with pure water, 80 ℃
For 3 hours in a vacuum to obtain Zn-plated aluminum powder. The average thickness of the Zn layer of the plating powder was 1 μm when observed and measured with an electron microscope. The thus obtained negative electrode active material of the Zn-plated aluminum powder and 5 wt% N-methyl-polyvinylidene fluoride as a binder
The 2-pyrrolidone solution was mixed at a 1: 1 weight ratio. Next, this mixed solution was applied on a copper substrate having a thickness of 15 μm,
It was dried in vacuum at 120 ° C. for 3 hours to obtain a negative electrode for a lithium secondary battery comprising a copper substrate having a negative electrode active material layer having a thickness of 30 μm on one side.

Example 2 An aluminum powder having a purity of 99.95% by weight and an average particle diameter of 20 μm was replaced with Zn by the same method and under the same conditions as in Example 1, and then kept at 5 ° C. by Sn plating manufactured by Kojundo Chemical Co. The solution was poured into a 10% by weight aqueous solution of the stock solution, left standing under stirring for 120 seconds, pulled up, washed with pure water, and dried in vacuum at 80 ° C. for 3 hours to obtain Sn-plated aluminum powder. The average thickness of the Sn layer of the plating powder was 1 μm when observed and measured with an electron microscope. Using the negative electrode active material of the Sn-plated aluminum powder thus obtained, a negative electrode for a lithium secondary battery comprising a copper substrate having a 30 μm-thick negative electrode active material layer on one side was obtained in the same manner and under the same conditions as in Example 1.

Example 3 The average thickness of a Zn plating layer was obtained in the same manner and under the same conditions as in Example 1 except that an aluminum alloy powder having an average particle diameter of 17 μm having an alloy composition of Al-12% Si was used instead of the aluminum powder. An aluminum alloy powder having a thickness of 1 μm was obtained. Using the negative electrode active material of the Zn-plated aluminum alloy powder thus obtained, a thickness of 30 was obtained in the same manner and under the same conditions as in Example 1.
A negative electrode for a lithium secondary battery comprising a copper substrate having a μm negative electrode active material layer on one side was obtained.

Example 4 The average thickness of the Sn plating layer was obtained in the same manner and under the same conditions as in Example 2 except that an aluminum alloy powder having an average particle diameter of 17 μm having an alloy composition of Al-12% Si was used instead of the aluminum powder. An aluminum alloy powder having a thickness of 1 μm was obtained. Using the negative electrode active material of the Sn-plated aluminum alloy powder thus obtained, a thickness of 30 was obtained in the same manner and under the same conditions as in Example 1.
A negative electrode for a lithium secondary battery comprising a copper substrate having a μm negative electrode active material layer on one side was obtained.

Example 5 Aluminum powder having a purity of 99.95% by weight and an average particle diameter of 20 μm was maintained at 70 ° C. after Zn substitution by the same method and under the same conditions as in Example 1, and thereafter a silver electroless plating stock solution was prepared. Was left under stirring for 120 seconds, pulled up, washed with pure water, and dried in vacuum at 80 ° C. for 3 hours to obtain an Ag-plated aluminum powder. The average thickness of the Zn layer of the plating powder was 1 μm when observed and measured with an electron microscope. The thus obtained negative electrode active material of the Ag-plated aluminum powder and a 5% by weight N-methyl-2-pyrrolidone solution of polyvinylidene fluoride as a binder were mixed at a weight ratio of 1: 1. Next, this mixed solution is applied on a copper substrate having a thickness of 15 μm and dried in a vacuum at 120 ° C. for 3 hours to form a lithium secondary battery comprising a copper substrate having a negative electrode active material layer having a thickness of 30 μm on one surface. A negative electrode was obtained.

Example 6 The average thickness of the Ag plating layer was obtained in the same manner and under the same conditions as in Example 6, except that an aluminum alloy powder having an average particle diameter of 17 μm having an alloy composition of Al-12% Si was used instead of the aluminum powder. An aluminum alloy powder having a thickness of 1 μm was obtained. Using the negative electrode active material of the Zn-plated aluminum alloy powder thus obtained, a thickness of 30 was obtained by the same method and conditions as in Example 6.
A negative electrode for a lithium secondary battery comprising a copper substrate having a μm negative electrode active material layer on one side was obtained.

Comparative Example 1 The aluminum powder used in Example 1 was used as a negative electrode active material without plating, and a copper substrate having a negative electrode active material layer having a thickness of 30 μm on one side under the same method and conditions as in Example 1 , A negative electrode for a lithium secondary battery comprising:

COMPARATIVE EXAMPLE 2 The aluminum alloy powder used in Example 2 was used as a negative electrode active material without plating, and copper having a negative electrode active material layer having a thickness of 30 μm on one surface was formed in the same manner and under the same conditions as in Example 1. A negative electrode for a lithium secondary battery comprising a substrate was obtained.

Examples 7 to 12, Comparative Examples 3 and 4 LiNiO ₂ having an average particle diameter of 30 μm as a positive electrode active material,
The flaky carbon as a conductive agent and a 5% by weight N-methyl-2-pyrrolidone solution of polyvinylidene fluoride as a binder were mixed at a weight ratio of 9: 1: 9, and the obtained mixed solution was thickened. On a 25 μm aluminum substrate,
It was dried in vacuum at 120 ° C. for 3 hours to obtain a lithium battery positive electrode comprising an aluminum substrate having a positive electrode active material layer having a thickness of 80 μm on one surface. A disk having a diameter of 15 mm was obtained from the positive electrode for a lithium battery thus obtained and the negative electrode for a lithium battery of each of the above Examples and Comparative Examples, and a disk-like porous polypropylene film having a diameter of 19 mm and a thickness of 25 μm was formed between the disk-shaped electrodes. And then impregnated with an electrolyte obtained by dissolving 1 mol of LiPF ₆ per liter of a mixed solution of propylene carbonate and diethyl carbonate at a volume ratio of 1: 1 to obtain a coin-type lithium secondary battery. .

For each of the coin-type lithium secondary batteries of Examples 7 to 12 and Comparative Examples 3 and 4, the number N of charge / discharge repetitions until the discharge capacity decreased to 80% of the discharge capacity at the beginning of charge / discharge was measured. . Table 1 shows the results. The table shows that the lithium secondary battery using the negative electrode for a lithium battery of the present invention has a much longer life than the battery of the comparative example.

[0024]

[Table 1]

[0025]

By forming a conductive inorganic coating layer on the surface of the aluminum-based powder, the problem of the generation of awful aluminum oxide on the surface of the aluminum-based powder is improved. The advantages of large capacity and dendrite resistance inherent in powder are utilized. Thus, the lithium secondary battery of the present invention using the negative electrode for a lithium secondary battery comprising the negative electrode active material of the aluminum-based powder of the present invention has a long life.

Claims (5)

[Claims] 1. A negative electrode for a lithium secondary battery, wherein an aluminum-based powder having a conductive inorganic coating layer on the surface is used as a negative electrode active material. 2. The method according to claim 1, wherein the aluminum-based powder is aluminum,
At least one selected from the group consisting of aluminum alloys
The negative electrode for a lithium secondary battery according to claim 1, which is a seed. 3. The conductive inorganic coating layer is made of Sn,
Zn, In, Pb, Mn, Mo, Co, Cu, Fe, N
i, their two or more alloys, Sn oxide, and In
3. The negative electrode for a lithium secondary battery according to claim 1, wherein the negative electrode is at least one selected from the group consisting of oxides. 4. The negative electrode for a lithium secondary battery according to claim 1, wherein a potential difference between the negative electrode and the negative electrode is at least 1 V.
And a non-aqueous electrolyte or a lithium ion conductive solid electrolyte having a lithium salt. 5. The lithium secondary battery according to claim 4, wherein the positive electrode active material is a lithium-containing transition metal oxide.