JPH11144715A - Manufacture of electrode for secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery having no problem in gas generation while charging, has a high utilization efficiency of an active material, and has superior charging and discharging characteristics by manufacturing an electrode having a high and even binding property between the active material and a current collector and having a sppcified filling quantity of the active material. SOLUTION: An active material mixture is provided by mixing an electrode active material and an additive of an binding agent to form a preparatory molding body 3 by integrating this active material mixture and a current collector. After compressing the preparatory molding body 3 until its porosity is 30% or less, an electrode molding body is formed by applying an isotropic pressure to the preparatory molding body 3 in an electrode molding process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an electrode used for a secondary battery, and more particularly to a method for manufacturing an electrode for a secondary battery for manufacturing an electrode formed using an active material as a main material.

[0002]

2. Description of the Related Art Generally, alkaline secondary batteries which can be charged and discharged include nickel-metal hydride batteries in which the positive electrode is a nickel hydroxide electrode and the negative electrode is a hydrogen storage alloy electrode, and nickel-hydroxide electrodes in the positive electrode and a cadmium electrode in the negative electrode. Nickel cadmium battery.

Conventionally, in a method of manufacturing an electrode of this type of secondary battery, a current collector is filled with various electrode active materials to which additives such as a conductive auxiliary agent and a binder are added. A method is used in which the preformed body formed by filling the electrode active material is pressed into contact with a mold press or roller press consisting of a fixed mold and a movable mold to produce an electrode molded body as each electrode. Have been. In the production of this electrode, when powder or fine particles are used as the electrode active material, since the active material itself is easily oxidized and easily deteriorated, the specific surface area is reduced to prevent oxidative deterioration. Is used as a granular material having a particle size distribution including those having a predetermined size or more.

[0004]

However, an additive such as a conductive auxiliary agent or a binder is added to an electrode active material comprising a granular material having a particle size distribution including a particle having a predetermined size or more. When an electrode is manufactured by press-molding a material filled in a current collector with a mold press or a roller press or the like, the electrode cannot be pressed uniformly due to unevenness due to large particles of the active material, and the electrode active material and the current collector cannot be pressed. However, there is a problem that a portion with insufficient conductive contact is formed.

[0005] When there is a portion where the conductive contact is insufficient as described above, the charging overvoltage in the vicinity thereof increases, and hydrogen gas is generated at the negative electrode and oxygen gas is generated at the positive electrode. There is a problem that the life of the sealed battery using the battery is shortened.

Japanese Patent Application Laid-Open No. 9-245779 discloses that pressing is performed by using a hydrostatic press in order to remove the influence of irregularities of the active material. When the preform is extremely high, the preform is liable to be damaged in the pressing step. Conversely, when the press pressure is low, a predetermined electrode thickness cannot be obtained and sufficient conductivity cannot be ensured. Further, in order to reduce the thickness of the electrode obtained when the pressing pressure is reduced, if the thickness of the current collector filled with the active material is previously brought close to the final thickness of the electrode, a predetermined amount of the active material cannot be obtained. Therefore, the electric capacity decreases.

Further, when the size of the electrode is increased, the electrode active material to be filled in the current collector and the amount of the additive added to the current collector are partially uneven, and the binding property between the electrode active material and the current collector is partially reduced. There is also the problem of non-uniformity.

The present invention solves the above-mentioned conventional problems, and has an electrode having a predetermined active material filling amount and a high degree of uniformity between the active material and the current collector, ie, gas generation during charging. It is an object of the present invention to provide a method for producing an electrode capable of realizing a secondary battery which does not have the above problem, has high utilization efficiency of an active material, and has excellent charge / discharge characteristics.

[0009]

According to the present invention, there is provided a method of manufacturing an electrode for a secondary battery, comprising the steps of mixing an electrode active material and an additive such as a binder to obtain an active material mixture; A preforming step of forming a preformed body by integrating the preform and a current collector; and an electrode forming step of forming an electrode molded body by pressing isotropic pressure on the preformed body. In a method of manufacturing an electrode for a secondary battery, the preformed body is formed by removing the
A compression step of compressing the compressed preformed body to the following, and subjecting the compressed preform to an electrode molding step.

[0010] By pressing the preformed body isotropically with pressure, all parts of the preformed body are pressed with a uniform pressure, and the binding between the electrode active material and the current collector is highly uniform. An electrode molded body can be obtained. Therefore, due to the strong and uniform binding between the electrode active material and the current collector, there is no problem of gas generation at the time of charging, and a secondary battery with high use efficiency of the active material and excellent charge / discharge characteristics is manufactured. It is possible to do.

In forming an electrode molded body by applying an isotropic pressure to the preformed body, it is difficult to optimize the pressing pressure, and the preformed body may be damaged, or the preformed body may have poor conductivity due to insufficient pressure contact. Although a defect that an excellent electrode molded body cannot be obtained occurs, according to the present invention, the pre-molded body has a porosity of 30%.
%, And then pressing isotropic pressure to prevent such inconvenience and to reliably obtain a high-quality molded electrode.

In the present invention, the pressing of isotropic pressure in the electrode forming step can be performed, for example, by interposing a solid elastic body as a pressure medium between the high-pressure press and the preform. By pressurizing the preform via the solid elastic body in this way, it is possible to apply pressure uniformly to each part of the preform, and to form a highly and homogeneous connection between the active material and the current collector. Can be worn.

The pressing of isotropic pressure in the electrode forming step can be performed by using a liquid substance as a pressure medium in a high-pressure vessel. In addition, pressure can be uniformly applied to each part of the preform, and the active material and the current collector can be highly and uniformly bonded.

In the present invention, a sintered nickel foam can be used as the current collector, and the thickness of the foamed nickel supplied to the preliminary molding step is 1.times. The thickness of the electrode molded body obtained in the electrode molding step. The molding conditions are adjusted so that the thickness is 5 times or more, that is, the thickness of the finally obtained electrode molded body is 1 / 1.5 or less of the thickness of the foamed nickel before being integrated with the active material mixture. It is preferable to set.

In the present invention, the electrode active material is one or two selected from the group consisting of metal hydrides, iron, zinc, cobalt, copper, cadmium, nickel hydroxide, cobalt hydroxide and manganese hydroxide. More than one species can be used.

[0016]

Embodiments of the present invention will be described below in detail.

In the present invention, first, an electrode active material and an additive such as a binder are mixed to form an active material mixture.

As the electrode active material, metal hydride, iron,
Any one of zinc, cobalt, copper, cadmium, lithium, nickel hydroxide, cobalt hydroxide, and manganese hydroxide
Species or two or more, preferably, nickel hydroxide and / or metal hydride can be used.

Such an electrode active material is used in the form of powder or fine particles. As described above, in order to prevent oxidative deterioration, for example, a material having an average particle size of about 10 to 20 μm is used in an amount of 10 to 30%. , An average particle size of about 1 to 10 μm
0 to 90%, average particle size of about 0.1 to 1 μm
The particle size distribution includes a predetermined amount of a relatively large particle size such as 10%.

Examples of the additive include a binder such as polytetrafluoroethylene (PTFE), and an average particle diameter of 0.1 to 10 μm.
m, conductive aids composed of various highly conductive granules or powders or fibrous materials such as nickel or CoO / Co granules or powders, and other thickeners such as carboxymethyl cellulose (CMC) And the like.

In order to ensure the binding between the active material and the current collector, the binder is usually mixed with the active material in an amount of 2 to 10% by weight as an active ingredient.

The conductive additive may be added to the active material, if necessary, for the purpose of improving the electrical characteristics of the obtained electrode.
0 to 20% by weight is mixed.

The binder is usually 30 to 70% by weight.
Aqueous solutions or aqueous dispersions and thickeners are usually mixed as an aqueous solution of 1 to 10% by weight with the active material and other additives, if necessary.

On the other hand, as the current collector, a nickel porous body,
Nickel fibrous, nickel foam, mesh nickel, plate nickel, expanded nickel plate, perforated nickel plate,
Good conductive granules or powders, composites of these and irons having these shapes, porous bodies of copper or the like, or those obtained by subjecting a porous plate to nickel plating can be used. As the current collector for the positive electrode, it is preferable to use foamed nickel, particularly, sintered nickel foam having a porosity of 94 to 98%. That is, conventionally, a large number of plated nickel foams in which the urethane portion is baked and removed after Ni plating on the foamed urethane has been adopted, but a sintered nickel foam having a smaller closed pore portion and a larger surface area is used as the positive electrode active material. Is suitable as a current collector because it has good adhesion and is effective in improving the active material utilization rate. As the current collector for the negative electrode, a punched metal made of iron or copper plated with nickel is preferable.

As a method of forming a preform by integrating the active material mixture and the current collector, a slurry or paste active material mixture is filled in a porous current collector and then dried. The paste-like active material mixture is sheeted and dried,
A current collector is sandwiched between the obtained dried sheets, and they are integrated by pressing. The paste-like active material mixture is applied to a current collector with a constant thickness, and dried. Such a method can be adopted.

The ratio of the active material mixture to the current collector varies depending on the type of the active material and the current collector used, the desired electrode characteristics, and the like. % Is about 200 to 400% by weight.

In the present invention, the preformed body obtained in this manner is compressed by using a mold press or the like until the porosity becomes 30% or less, preferably 10 to 20%. The pressing pressure during this compression is usually 500
２０００2000 kgf / cm ² . If the pressing pressure is higher than this, the elasticity of the electrode is lost and the electrode is easily broken.

Through the compression step, the binding between the active material and the current collector is further enhanced and uniform in the electrode forming step by pressing the isotropic pressure in the next step.

The preformed body after compression (hereinafter referred to as "compressed preformed body") is then subjected to an isotropic pressure in the electrode forming step to bond the active material mixture and the current collector under pressure. Then, an electrode molded body is obtained.

More specifically, a method in which a solid elastic body such as rubber or synthetic resin is interposed between the compression preform and the press mold to pressurize, or as shown in FIG. In a machine (CIP) 1, a compression preform 3 housed in a packaging film 2 such as a rubber sheet is hermetically housed in a high-pressure container 4, and a liquid substance such as water is filled in the high-pressure container 4 with a high-pressure generator 5. And pressurizing the isotropic pressure with a liquid material such as water as the pressure medium 6 at a predetermined pressure.

As the pressure medium, in addition to various liquids such as water, various gases and fluids such as powders and granules can be used.

In this electrode molding step, the degree of isotropic pressure applied to the preform is 500 to 3000 kgf /
cm ² . If a pressure higher than this is applied, the electrode is hardened and easily broken at the time of winding.

The method of the present invention is particularly applicable to the case where a current collector having a high porosity, for example, a porosity of 80% or more, such as sintered foamed nickel and plated foamed nickel, is used in the production of an electrode. And in this case the thickness D
_The preform obtained by filling the active material mixture into the current collector is compressed to a porosity of 30% or less, preferably 10 to 2%.
Give 0% compression preform, per isotropic pressure to the compressed preform to obtain an electrode molded product having a thickness of D ₂ and押加, D ₁ ≧ 1.5 × D _2, in particular 2.5 × D ₂ ≧ D ₁ ≧ 1.5
It is preferable to set the conditions for each step so that xD ₂ is obtained. By adopting such conditions, it is possible to obtain an electrode molded body having a predetermined active material filling amount and a higher degree of uniformity between the active material and the current collector.

[0034]

The present invention will be described more specifically below with reference to examples and comparative examples.

The raw materials used in the following examples and comparative examples are as follows.

Positive electrode active material: nickel hydroxide (particle size distribution
About 80% by weight of a powder having a particle size of 10 to 30 μm and a particle size of 10 μm
m about 20% by weight of fine particles) Negative electrode active material: hydrogen storage alloy (MmNi _3.62 Co _0.70 Mn)
_0.29 Al _0.39 ) powder (particle size distribution) 50% by weight of particles having a particle size of 30 to 60 μm, and 5% by weight of fine particles having a particle size of 30 μm or less.
0% by weight) Binder: PTFE dispersion (60% by weight PTF)
E aqueous dispersion) Thickener: CMC aqueous solution (5 wt% CMC aqueous solution) Conductive auxiliary for positive electrode: CoO.Co (particle size range 1 to 10 μm)
Anode) Conductive auxiliary for negative electrode: Ni powder (average particle size 5 μm) Positive electrode current collector: Sintered nickel foam plate
Porosity 96%, 17cm × 3.1cm, thickness 1.3m
m) Negative electrode current collector: iron punching metal (18 cm × 3.1 cm, thickness 0.08 m) with Ni plating on the surface
m) Example 1 0.8 g of CoO.Co in 7.6 g of the positive electrode active material and PTF
0.4 g of E-dispersion, 1.5 g of CMC aqueous solution and 1.5 g of distilled water were added and mixed to obtain 11.8 g of a slurry-like active material mixture. To obtain a preform.

[0037] The pre-molded body was 1100 kgf / cm ²
, And then roll-pressed and cold-pressed again to obtain a compression preformed body for a positive electrode having an porosity shown in Table 1 with an average thickness of 0.80 mm.

Separately, to 12.6 g of the negative electrode active material, 15% by weight of Ni powder, 1.0 g of PTFE dispersion, 1.3 g of CMC aqueous solution, and 2.0 g of distilled water based on the negative electrode active material
And a paste obtained by adding and mixing were formed into two sheets (18 cm × 3.1 cm) having a thickness of 0.5 mm. 1100 kgf /
After binding in cm ² , roll pressing and cold pressing again were performed to obtain a preform for negative electrode compression having an average thickness of 0.60 mm and a porosity shown in Table 1.

The obtained compression preformed body for a positive electrode and the compression preformed body for a negative electrode are each laminated two by two, and each of the laminated bodies is wrapped with a rubber sheet, and the high pressure vessel of the hydrostatic press shown in FIG. 1000kgf with water as pressure medium
CIP molding was performed by applying a hydrostatic pressure of / cm ² to obtain a positive electrode (molded body) and a negative electrode (molded body) having the thickness and porosity shown in Table 1.

The obtained nickel positive electrode was opposed to a hydrogen storage alloy negative electrode via a polyolefin separator, and a sealed cylindrical nickel-hydrogen battery having a theoretical capacity of 2200 mAh was prepared using an electrolyte consisting of 6 N KOH and 1 N LiOH. did. This was charged at 200 mA for 14 hours,
The active material utilization was determined by discharging to 0 V at 0 mA, and the results are shown in Table 1.

Example 2 A positive electrode was produced in the same manner as in Example 1 except that two compression preformed bodies for a positive electrode were laminated and a hydrostatic pressure of 3000 kgf / cm ² was applied.

The negative electrode obtained in Example 1 before applying the hydrostatic pressure was used as it was.

Using this positive electrode and negative electrode, the utilization rate of the active material was examined in the same manner as in Example 1, and the results are shown in Table 1 together with the porosity of each electrode.

Example 3 In Example 1, before filling the positive electrode current collector with the active material mixture, pressing was performed until the thickness became 0.8 mm.
Thereafter, a positive electrode was manufactured in the same manner except that the active material mixture was filled. In this case, since the thickness of the positive electrode current collector was small, only 5.2 g of the positive electrode active material could be filled.

The same negative electrode as that used in Example 1 was used.

Using the positive electrode and the negative electrode, the active material utilization was examined in the same manner as in Example 1. The results are shown in Table 1 together with the porosity of each electrode.

In this embodiment, the active material utilization is high,
Since the thickness of the positive electrode current collector before filling the active material mixture is small and the filling amount of the positive electrode active material is small, the theoretical capacity is 1500 mAh.
Met.

Comparative Example 1 A negative electrode was manufactured in the same manner as in Example 1, except that two sheets of the negative electrode compression preform were laminated and a hydrostatic pressure of 3000 kgf / cm ² was applied.

The positive electrode obtained in Example 1 before applying the hydrostatic pressure was used as it was.

Using the positive electrode and the negative electrode, the active material utilization was examined in the same manner as in Example 1. The results are shown in Table 1 together with the porosity of each electrode.

Comparative Example 2 In Example 1, the active material utilization was examined in the same manner as in Example 1 except that the positive electrode and the negative electrode obtained in Example 1 were used as they were before the application of the hydrostatic pressure. The results are shown in Table 1 together with the porosity of each electrode.

Comparative Example 3 The active material utilization was examined in the same manner as in Example 1 except that the positive electrode was further roll-pressed and used in Comparative Example 2, and the results are shown in Table 1 together with the porosity of each electrode. .

Comparative Example 4 A positive electrode and a negative electrode were produced in the same manner as in Example 1 except that the preformed body for the positive electrode was not compressed and that a hydrostatic pressure of 3000 kg / cm ² was applied. The average thickness of the negative electrode before application of hydrostatic pressure is 0.75 mm).

Using this positive electrode and negative electrode, the utilization rate of the active material was examined in the same manner as in Example 1. The results are shown in Table 1 together with the porosity of each electrode. Note that the thickness of the positive electrode and the negative electrode could not be reduced only by applying the hydrostatic pressure, and the flexibility of the electrode was reduced. Therefore, cracking of the positive electrode occurred in this battery.

[0055]

[Table 1]

[0056]

As described above in detail, according to the method for manufacturing an electrode of a secondary battery of the present invention, the active material and the current collector have a predetermined amount of active material and a high degree of uniformity. Electrode can be manufactured.

Therefore, according to the electrode manufactured by the method of the present invention, it is possible to realize a secondary battery which has no problem of gas generation at the time of filling, has high utilization efficiency of the active material, and has excellent charge / discharge characteristics. it can.

Such a method for manufacturing an electrode of a secondary battery according to the present invention is applicable to any secondary battery such as a nickel-hydrogen battery, a lead battery, a nickel-cadmium battery, a nickel-iron battery, a nickel-zinc battery, and a lithium battery. This is effective for a large secondary battery and can improve the performance of the secondary battery.

In particular, the method for manufacturing an electrode of a secondary battery according to the present invention is effective for manufacturing a positive electrode using foamed nickel as a current collector, and can realize a battery having a high positive electrode charging efficiency.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a hydrostatic press used in an electrode molding step.

[Description of Signs] 1 Hydrostatic press 2 Packaging film 3 Pre-compressed body 4 High-pressure container 5 High-pressure generator 6 Pressure medium

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tetsuo Sakai 1-38-31 Midorioka, Ikeda-shi, Osaka Pref. Inside the Osaka Institute of Technology (72) Inventor Nobuhiro Kuriyama 1--8-3 Midorioka, Ikeda-shi, Osaka No. 31 Inside the Osaka Institute of Technology (72) Inventor Sei Uehara 1-8-31 Midorioka, Ikeda-shi, Osaka Inside the Osaka Institute of Technology

Claims (5)

[Claims] 1. A mixing step of mixing an electrode active material and an additive such as a binder to obtain an active material mixture, and integrating the active material mixture and a current collector to form a preform. A method of manufacturing an electrode for a secondary battery, comprising: a preforming step; and an electrode forming step of pressing an isotropic pressure on the preformed body to form an electrode formed body. A method for producing an electrode of a secondary battery, comprising a compression step of compressing the preformed body to 30% or less, and subjecting the compressed preform to an electrode molding step. 2. The method according to claim 1, wherein the pressing of the isotropic pressure is performed by interposing a solid elastic body as a pressure medium between the high-pressure press and the preform. A method for manufacturing an electrode of a secondary battery, characterized by: 3. The method according to claim 1, wherein the pressing of the isotropic pressure is performed by using a liquid substance as a pressure medium in a high-pressure container. Method. 4. The method according to claim 1, wherein the current collector is a sintered nickel foam, and the thickness of the nickel foam supplied to the preforming step is the thickness of the electrode. A method for manufacturing an electrode for a secondary battery, wherein the thickness is 1.5 times or more the thickness of an electrode molded body obtained in a molding step. 5. The method according to claim 1, wherein the electrode active material is a metal hydride, iron, zinc, cobalt, copper, cadmium, nickel hydroxide, cobalt hydroxide and A method for producing an electrode for a secondary battery, wherein the method is one or more selected from the group consisting of manganese hydroxide.