JPH07122262A - Electrode and its manufacture and secondary battery using the electrode - Google Patents

Abstract

PURPOSE:To improve discharge capacity characteristic in a high output by setting a specific surface to 4m<2>/g or more of an electrode for a battery containing at least an active material. CONSTITUTION:In order to eliminate an electrode film thickness of discharge capacity of a secondary battery, a specific surface of an electrode is set to 4m<2>/g or more, preferably 5m<2>/g or more and further preferably 6m<2>/g or more. When the specific surface is decreased smaller than 4m<2>/g, an air gap in an electrode agent is decreased, to impede moving an ion in the electrode, and a diffusion controlled ion can not be eliminated. As a positive pole active material, compound oxide of Li is preferable, and LixCoO2(0<x<=1.0), LiNiO2(0< x<=1.0), LixCOyNi1-yO2 (0<x<=1.0, 0<y<=1.0), etc., are most preferable from the point of high potential, stability and long life. As a negative pole, s carbon material is preferable. As the carbon material, no particular limit is provided, but generally a burned organic object is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode, a method for manufacturing the electrode, and a secondary battery using the electrode.

[0002]

2. Description of the Related Art In recent years, with the widespread use of portable devices such as video cameras and notebook computers, demand for small and high capacity secondary batteries has increased. Most of the secondary batteries currently used are nickel-cadmium batteries using an alkaline electrolyte, but the battery voltage is low at about 1.2 V, and it is difficult to improve the energy density. Therefore, a lithium secondary battery using lithium metal for the negative electrode has been studied.

However, in a secondary battery in which lithium metal is used as the negative electrode, lithium tends to grow into dendrites due to repeated charging / discharging, resulting in short circuits and shortened life. Therefore, there has been proposed a secondary battery in which various carbonaceous materials are used for the negative electrode and used by doping and dedoping with lithium ions. Further, such various carbonaceous materials can be used as a positive electrode after being doped with anions. Secondary batteries using electrodes made by doping lithium ions or anions into the above carbonaceous materials are disclosed in JP-A-57-208079 and JP-A-58.
-93176, JP-A-58-192266, JP-A-62-90863, and JP-A-62-12.
Japanese Laid-Open Patent Publication No. 2066 and Japanese Patent Laid-Open No. 3-66856 are known.

Such carbonaceous material may be used in any form such as powder, carbon fiber or carbon fiber structure.

Further, recently, in order to meet the demand for higher energy density, a battery voltage of around 4V has appeared and has attracted attention. Higher battery voltage has been pursued by searching for and developing an active material exhibiting a high potential in the positive electrode, and inorganic compounds such as transition metal oxides and transition metal chalcogens containing alkali metals are known. Among them, Li _X C
oO ₂ (0 <x ≦ 1.0), Li _X NiO ₂ (0 <x ≦
1.0) and Li _X Co _Y Ni _1-Y O ₂ (0 <x ≦
1.0, 0 <y ≦ 1.0) and the like are considered to be the most promising in terms of high potential, stability, and long life.

[0006]

[Problems to be Solved by the Invention]
It has been found that when a powdery electrode active material is used regardless of the negative electrode, the discharge capacity decreases at a certain thickness or more, particularly at the time of high output (or high current) discharge.

[0007]

The present invention has the following constitution in order to solve the above problems.

[(1) An electrode for a battery containing at least an active material, characterized in that the specific surface area of the electrode is 4 m ² / g or more.

(2) In the method for producing a battery electrode containing at least an active material, the protrusion is pressed against the electrode so that the specific surface area of the electrode is 4 m ² / g or more. Method.

(3) A secondary battery using the electrode described in the above item 1. The electrode of the present invention is not particularly limited in what kind of battery such as a primary battery, a secondary battery and a fuel cell is used, but it is particularly preferably used as a positive electrode or a negative electrode of a secondary battery. . As a particularly preferable secondary battery, a secondary battery using a non-aqueous electrolytic solution containing an alkali metal salt as described above can be mentioned. Therefore, a lithium secondary battery will be taken as an example and described in detail below with specific examples.

The inventors of the present invention have made earnest studies on the dependence of the discharge capacity on the electrode film thickness. As a result, for example, the above-mentioned Li _X Co.
If the O ₂ of the lithium secondary battery using the positive electrode active material, when discharged at a current density of 0.1 A / cm ^2, thickness of about 2
When it becomes 0-40 μm or more, the discharge capacity starts to decrease,
The discharge capacity decreases as the film thickness increases. This film thickness dependency is strongly influenced by the current density. For example, 0.
When discharged at 02 A / cm ² , the discharge capacity did not decrease even when the film thickness was 100 μm or more. Also, 1A
The discharge capacity was 0 when the film thickness was 90 μm or more when discharged at / cm ² .

FIG. 1 shows the correlation between the electrode film thickness (μm) when discharged at 1 A / cm ² and the discharge capacity (mAh). The discharge capacity increased with an increase in the electrode film thickness up to about 40 μm, but the discharge capacity decreased sharply beyond that, and as described above, the discharge capacity was 0 when the film thickness was 90 μm or more.

In order to solve such a problem, the present inventors have
As a result of further study, it was found that the main cause of this electrode capacity dependence of the discharge capacity is that the diffusion of ions into the electrode is rate-determining. Therefore, the present inventors have begun investigations to eliminate the ion diffusion control. Here, the discharge capacity may be reduced, so that (1) the conductivity of the electrode, (2) the constituent materials of the electrode material and / or the binding force between the electrode material and the current collector is not impaired. I was careful. As a result of studying various electrode manufacturing techniques, an electrode structure effective for eliminating the dependence of the discharge capacity on the electrode film thickness was found. That is, a specific surface area 4m ² / g or more, preferably, 5 m ² / g or more, more preferably, 6 m ²
/ G or more.

FIG. 2 shows the correlation between the electrode film thickness and the specific surface area of the sample prepared in the same manner as that used in FIG. Contrasting with FIG. 1, it can be seen that a large discharge capacity is exhibited at a specific surface area of 4 m ² / g or more. If the specific surface area is less than 4 m ² / g, the voids in the electrode material will decrease, and the movement of the ions in the electrode will be impeded to a relatively large extent, making it impossible to eliminate the diffusion rate control of the ions. It is considered that the discharge capacity is reduced as a result. Here, the preferable range of the specific surface area slightly varies depending on the viscosity of the electrolytic solution, the ionic conductivity, and the like, and a particularly preferable range can be arbitrarily selected.

The specific surface area specified in the present invention is the BET specific surface area. The BET specific surface area was measured by a 1-point BET method using 2200-02 manufactured by Micromeritex Co., Ltd. in the United States. A sample with an electrode material formed on one side of the current collector,
Since it was placed in a glass cell (a glass cell is made of a large-scale custom-made product so that a large number of samples can be used) and measured, the specific surface area obtained reflects the amount of voids in the electrode material. Conceivable. Here, the surface areas of the glass cell and the one surface of the current collector were measured in advance, and were corrected by subtracting them from the sample measured values as blank values.

Effective electrode fabrication techniques include (1) mechanical perforation, (2) chemical perforation, and (3) others.
As (1), there is a method of forming holes or irregularities in the electrode by pressing a protrusion such as a sword mountain, a punch rod, an embossing roll, etc. to the electrode created by the usual method. I do not care. Rather, when the electrode material is formed on only one surface of the current collector, ion diffusion from the back surface is also useful because it can contribute to the ion mobility.
(2) is a method of forming voids by removing what is previously added to the electrode mixture or the electrode material slurry later. For example, a method of adding a water-soluble substance such as polyvinyl alcohol or lithium chloride to the electrode material slurry, and then eluting it in water to form voids, a method of adding a foaming agent and then foaming to form voids, The current collector coated with the electrode material slurry is immersed in water to remove 1,2-N-
There is a method in which a solvent such as methylpyrrolidone (hereinafter abbreviated as NMP) is replaced with water to solidify a binder such as polyvinylidene fluoride to form voids. As (3), there are a heat ray such as a laser and a perforation method using high pressure water.

The positive electrode active material preferably used in the present invention is an inorganic compound such as a transition metal oxide or a transition metal chalcogen containing an alkali metal, or a conjugate of polyacetylene, polyparaphenylene, polyphenylenevinylene, polyaniline, polypyrrole, polythiophene or the like. Examples of the positive electrode used in ordinary secondary batteries include polymer-based polymers, cross-linked polymers having disulfide bonds, and thionyl chloride. Among these, in the case of a secondary battery using a non-aqueous electrolyte containing a lithium salt, cobalt,
Manganese, molybdenum, vanadium, chromium, iron, copper,
Transition metal oxides such as titanium and transition metal chalcogens are preferably used. In particular, as mentioned above, Li _X CoO ₂
(0 <x ≦ 1.0), Li _X NiO ₂ (0 <x ≦ 1.
0) and Li _X Co _Y Ni _1-Y O ₂ (0 <x ≦ 1.
0, 0 <y ≦ 1.0) and the like are considered to be the most promising in terms of high potential, stability, and long life.

A carbonaceous material is preferably used for the negative electrode of the present invention. The carbonaceous material is not particularly limited, and a material obtained by firing an organic material is generally used. When the electron conductivity of the carbonaceous material is sufficiently high for the purpose of collecting electricity, it is not necessary to add a conductive agent. It is not necessary to add a conductive agent even when using carbon fibers, specifically, PAN-based carbon fibers obtained from polyacrylonitrile (PAN), pitch-based carbon fibers obtained from pitch of coal or petroleum, Cellulose-based carbon fibers obtained from cellulose, vapor-grown carbon fibers obtained from a gas of a low molecular weight organic substance, and the like can be mentioned. In addition, polyvinyl alcohol, lignin, polyvinyl chloride, polyamide, polyimide, phenol resin, furfuryl alcohol. A carbon fiber obtained by firing, etc. may be used. Among these carbon fibers, carbon fibers satisfying the characteristics are appropriately selected according to the characteristics of the electrode and the battery in which the carbon fibers are used. Among the above-mentioned carbon fibers, PAN-based carbon fibers, pitch-based carbon fibers, and vapor-grown carbon fibers are preferable when used in the negative electrode of a secondary battery using a non-aqueous electrolyte containing an alkali metal salt. In particular, PAN-based carbon fibers and pitch-based carbon fibers are preferable in terms of favorable doping with alkali metal ions, particularly lithium ions. Among these, "Torayca" T series or "Torayca" manufactured by Toray Industries, Inc. PAN-based carbon fibers such as "M series" and pitch-based carbon fibers obtained by firing mesophase pitch coke are more preferably used.

When the carbon fiber is used as an electrode, it may have any form, but a preferred form is to dispose it in a uniaxial direction, or to form a fabric-like or felt-like structure. Examples of the fabric-like or felt-like structure include woven fabrics, knitted fabrics, braids, laces, nets, felts, papers, non-woven fabrics, mats, and the like. Felt and the like are preferred.

The electrolytic solution of the secondary battery using the electrode of the present invention is not particularly limited, and a conventional electrolytic solution may be used, and examples thereof include an acid or alkaline aqueous solution or a non-aqueous solvent. Among these, as the electrolytic solution of the secondary battery composed of the above-mentioned non-aqueous electrolytic solution containing an alkali metal salt, propylene carbonate, ethylene carbonate, γ-butyrolactone, N-methylpyrrolidone, acetonitrile, N, N-dimethylformamide, Dimethyl sulfoxide, tetrahydrofuran, 1,3-dioxolane,
Methyl formate, sulfolane, oxazolidone, thionyl chloride, 1,2-dimethoxyethane, diethylene carbonate, derivatives and mixtures of these are preferably used. The electrolyte contained in the electrolytic solution is an alkali metal,
Particularly, lithium halides, perchlorates, thiocyanates, borofluorides, phosphorous fluorides, arsenic fluorides, aluminum fluorides, trifluoromethylsulfates and the like are preferably used.

The secondary battery using the electrode of the present invention can be used as a video camera, a personal computer, a word processor, a radio-cassette, by utilizing the features of light weight, high capacity and high energy density.
It is widely applicable to portable small electronic devices such as mobile phones.

[0022]

EXAMPLES Specific embodiments of the present invention will be described below with reference to examples, but the present invention is not limited thereto.

Example 1 Commercially available lithium carbonate (Li ₂ CO ₃ ) and basic cobalt carbonate (2CoCO ₃ .3Co (OH) ₂ ) were used in a molar ratio of L.
Weigh so that i / Co = 1/1, wet mix with a zirconia ball mill (use ethanol as the grinding solvent), then 9
LiCoO ₂ was synthesized by heat treatment at 00 ° C. for 20 hours.
This was crushed with the above ball mill to obtain LiCoO ₂ powder. Artificial graphite as a conductive agent and 10 parts by weight of polyvinylidene fluoride (hereinafter abbreviated as PVDF) as a binder were added to the powder, and the viscosity was adjusted with NMP as a solvent to form a paste. # 1000 in advance
Rubbed with emery paper, the surface of which was roughened and coated on an aluminum foil with a thickness of 20 μm, dried, roller pressed, and further heat-treated at 200 ° C. for 15 minutes to obtain a width of the electrode portion of 10 m.
A LiCoO ₂ electrode having m and a length of 20 mm was prepared. A large number of metal needles having a diameter of 100 μm attached at intervals of 200 μm were pressed against the LiCoO ₂ electrode to punch holes to form voids. When the specific surface area of this electrode was measured by the method described above, the specific surface area was 4.2.
It was m ² / g.

Next, the discharge capacity of the electrode was evaluated. The electrolyte is propylene carbonate containing 1M LiPF ₆ ,
Evaluation was carried out using a three-electrode cell in which metallic lithium foil was used for the counter electrode and the reference electrode. The current density per LiCoO ₂ is 0.
The battery was charged to 4.3 V (vs. Li ⁺ / Li) with a constant current of 05 mA / g. 3.0V (vs. Li ⁺ / L at 0.5A / g after charging)
The discharge capacity of the LiCoO ₂ electrode, which was calculated from the amount of charge discharged up to i), was 80 mAh / g.

Comparative Example 1 The same L as in Example 1 except that the electrode was not perforated.
An electrode was prepared in the same manner as in Example 1 using iCoO ₂ ,
Charge / discharge evaluation was performed. The discharge capacity at this time is 40 mAh.
/ G. The specific surface area of this electrode was also measured and found to be 3.0 m ² / g.

Example 2 A LiNiO ₂ electrode was prepared in the same manner as in Example 1 except that basic nickel carbonate (NiCO ₃ .2Ni (OH) ₂ .4H ₂ O) was used instead of basic cobalt carbonate. Then, charge and discharge evaluation was performed in the same manner as in Example 1 except that the charge potential was 4.2 V (vs. Li ⁺ / Li). The discharge capacity at this time was 100 mAh / g. Also for this electrode,
When the specific surface area was measured, it was 4.5 m ² / g.

Comparative Example 2 The same L as in Example 2 except that the electrode was not perforated.
An electrode was prepared in the same manner as in Example 2 using iNiO ₂ ,
Charge / discharge evaluation was performed. The discharge capacity at this time is 52 mAh
/ G. The specific surface area of this electrode was also measured and found to be 2.8 m ² / g.

Example 3 The electrode active material raw materials used in Examples 1 and 2 were weighed and mixed to obtain Li _1.0 (Co _0.5 Ni _0.5 ) O _{2 in} terms of oxide. In the same manner as in 2, the holes were punched and the charge / discharge was evaluated. The discharge capacity at this time is
It was 90 mAh / g. The specific surface area of this electrode was also measured and found to be 4.3 m ² / g.

Comparative Example 3 The same L as in Example 3 was used except that the electrode was not perforated.
An electrode was prepared in the same manner as in Example 3 using i _1.0 (Co _0.5 Ni _0.5 ) O ₂ , and the charge and discharge was evaluated. The discharge capacity at this time was 46 mAh / g. The specific surface area of this electrode was also measured and found to be 2.5 m ² / g.

Example 4 90 parts by weight and 10 parts by weight of commercially available pitch coke and PVDF as a binder were added, and the viscosity was adjusted with a solvent to form a paste. This is applied to a 20 μm thick copper foil whose surface has been rubbed with # 1000 emery paper beforehand, dried, roller pressed, and further heat treated at 200 ° C. for 15 minutes to obtain the width of the electrode part. 10 mm, length 20 m
m electrodes were prepared. Further, this electrode was also perforated in the same manner as in Example 1.

Next, the discharge capacity of the electrode thus manufactured was evaluated. The electrolytic solution was evaluated by a three-electrode type cell using propylene carbonate containing 1M LiPF ₆ and metallic lithium foil for the counter electrode and the reference electrode. The current density per pitch coke was a constant current of 0.05 A / g, and was 0.
It was charged to 0 V (vs. Li ⁺ / Li). 0.5A / after charging
The discharge capacity when discharged to 1.5 V (vs. Li ⁺ / Li) was 150 mAh / g. Further, the specific surface area was measured in the same manner as in Example 1 and found to be 4.5 m ² / g.

Comparative Example 4 A pitch coke electrode was produced in the same manner as in Example 4 except that the electrode was not perforated. The charge and discharge of the electrode was evaluated in the same manner as in Example 4. The discharge capacity was 80 mAh / g per weight of pitch coke. The specific surface area of this electrode was measured and found to be 3.1 m ² / g.
Met.

Example 5 A commercially available PA was added to the LiCoO ₂ positive electrode prepared in Example 1.
N-based carbon fiber ("Torayca" T-300, manufactured by Toray Industries, Inc.)
One strand (3K: 3000) was used as a negative electrode, and a secondary battery was produced by stacking the strands with a porous polypropylene film (Celguard # 2500, manufactured by Daicel Chemical Industries, Ltd.) interposed therebetween. As the electrolytic solution, propylene carbonate containing 1M lithium perchlorate was used.

Using the secondary battery thus manufactured, it was charged to 4.3 V at a constant current with a current density of 0.05 mA / g per LiCoO ₂ . 0.5A / after charging
The discharge capacity when discharged at a constant current of g is LiC of the positive electrode.
It was 82 mAh / g based on the weight of oO ₂ .

Comparative Example 5 A secondary battery was prepared in the same manner as in Example 5, except that the electrode prepared in Comparative Example 1 was used as the positive electrode. The charge / discharge evaluation of the secondary battery was performed in the same manner as in Example 4. Discharge capacity is positive electrode L
It was 38 mAh / g by weight of iCoO ₂ .

Example 6 10 parts by weight and 3 parts by weight of artificial graphite as a conductive agent and PVDF as a binder were added to the LiCoO ₂ powder prepared in Example 1, and the viscosity was adjusted by NMP to form a paste. did. Then, this is applied to an aluminum foil having a thickness of 20 μm whose surface has been rubbed with # 1000 emery paper in advance, and then immersed in water for 5 hours to replace NMP with water to solidify PVDF ( (Wet coagulation), then dry,
Roller press and the width of the electrode part is 10mm and the length is 20m.
m LiCoO ₂ electrode was prepared. For this electrode,
When the specific surface area was measured, the specific surface area was 4.6 m ² /
It was g. Next, when charge and discharge evaluation was performed in the same manner as in Example 1, the discharge capacity was 90 mAh / g.

Example 7 To the LiCoO ₂ powder prepared in Example 1, artificial graphite as a conductive agent, PVDF as a binder, and 10 parts by weight, 3 parts by weight, and 5 parts by weight of lithium chloride were added, respectively.
The viscosity was adjusted with NMP to form a paste. Then, this was applied to an aluminum foil having a thickness of 20 μm whose surface was rubbed with # 1000 emery paper in advance and then immersed in water for 5 hours to remove lithium chloride, and in Example 6. After performing the wet coagulation of the PVDF shown, the PVDF is dried and roller-pressed to form an electrode portion having a width of 10 mm and a length of 20 mm.
An iCoO ₂ electrode was produced. When the specific surface area of this electrode was measured, the specific surface area was 5.6 m ² / g. Next, when charge and discharge evaluation was performed in the same manner as in Example 1, the discharge capacity was 100 mAh / g.

[0038]

According to the present invention, it is possible to manufacture a high performance secondary battery having excellent discharge capacity characteristics, especially at high output.

[Brief description of drawings]

FIG. 1 is a diagram showing a correlation between an electrode film thickness of a LiCoO ₂ electrode and a discharge capacity (discharge current density 1 A / cm ² ).

FIG. 2 is a diagram showing a correlation between an electrode film thickness and a specific surface area of a LiCoO ₂ electrode.

Claims (12)

[Claims] 1. A battery electrode containing at least an active material, wherein the specific surface area of the electrode is 4 m ² / g or more. 2. The electrode according to claim 1, wherein the active material is a lithium composite oxide. 3. The lithium composite oxide is Li _x CoO ₂
(0 <x ≦ 1.0), Li _x NiO ₂ (0 <x ≦ 1.
0) and Li _X Co _Y Ni _1-Y O ₂ (0 <x ≦ 1.
3. The electrode according to claim 2, wherein the electrode is selected from 0, 0 <y ≦ 1.0). 4. The electrode according to claim 1, wherein the active material is a carbonaceous material. 5. A method for producing a battery electrode containing at least an active material, wherein a specific surface area of the electrode is set to 4 m ² / g or more by pressing a convex portion on the electrode. . 6. A method for producing a battery electrode containing at least an active material, wherein the substances mixed during the production of the electrode are removed after the production of the electrode so that the specific surface area of the electrode becomes 4
m ² / g or more, a method for manufacturing an electrode. 7. The method for producing an electrode according to claim 6, wherein the substance is water-soluble. 8. The method for producing an electrode according to claim 6, wherein the substance is a foaming agent. 9. A current collector is coated with a slurry comprising at least an active material, a binder and a solvent, and then immersed in water to replace the solvent with water to solidify the binder. The method for producing an electrode, wherein the specific surface area of the electrode is 4 m ² / g or more. 10. The binder is polyvinylidene fluoride,
The method for producing an electrode according to claim 9, wherein the solvent is 1,2-N-methylpyrrodoline. 11. A secondary battery using the electrode according to any one of claims 1 to 4. 12. A secondary battery, wherein the electrode according to claim 2 or 3 is used as a positive electrode, and the electrode according to claim 4 or carbon fiber is used as a negative electrode.