JP3013419B2 - Electrode and method of manufacturing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electrode in an electrochemical cell and a method for producing the same.

[Prior art] Conventionally, an electrode in an electrochemical cell has powdered main components of the electrode such as an electrode active material or an electrode catalyst,
It is often manufactured by mixing or wet kneading with an organic binder such as a fluororesin and molding.

Further, as another method of manufacturing an electrode, for example, in the case of a hydrogen negative electrode having a hydrogen storage alloy as a main component of the electrode, the hydrogen storage alloy powder and a metal powder such as nickel or copper are mixed and then press-molded to manufacture. Methods are also known.

Separately from the above-described electrode manufacturing method, the surface of a negative electrode for a sealed alkaline secondary battery such as a hydrogen storage alloy negative electrode or a cadmium negative electrode or the surface of a hydrogen storage alloy powder that is a main component of the electrode is coated with carbon. There is also known a technique for promoting an oxygen gas consuming reaction by adding carbon powder into an electrode.

There has also been proposed a concept of adding a carbon powder such as expanded graphite or acetylene black as a conductive material into an electrode.

As a prior art closest to the present invention, there is a battery electrode made of a pressure-molded body of expanded graphite containing catalyst particles dispersed therein, which is one of the main components of the electrode. This electrode is manufactured by mixing catalyst particle powder, expanded graphite powder, and an organic binder such as a fluororesin, if necessary, and molding the mixture by pressure.

[Problems to be Solved by the Invention] However, the method using the organic binder has a problem that the internal resistance of the electrode increases as the content of the organic binder as an insulator increases. In this method, wet kneading is usually performed. However, depending on the type of main components of the electrode, water cannot be used in many cases, and when an organic solvent other than water is used, the organic solvent is not used. There is a problem that a process for removal of is required.
Furthermore, in the wet method, there is a problem that an electrode manufacturing process such as a kneading process, a coating or molding process, a drying process and, in some cases, a firing process is often complicated.

On the other hand, the method using metal powder is usually a dry process, but has a problem that the weight of the electrode increases. Furthermore, since the electrode has little flexibility, it is almost impossible to configure a wound power generation element,
Therefore, there is a problem that it is difficult to improve the operating current value.

Further, the method of coating the electrode surface or the surface of the powder, which is a main component of the electrode, with carbon has a problem that a coating step must be added to a normal step.

Also, the method of mixing the powder, which is the main component of the electrode, with the carbon material is uniform in the dry process when the bulk density of the powder, which is the main component of the electrode, is high or the bulk density of the carbon material is low. There is a problem that can not be. Particularly, the carbon material is a material having a very low bulk density (0.1 to 0.01) such as so-called expanded graphite obtained by treating graphite with nitric acid, sulfuric acid, or the like, and then performing a heat treatment to expand the layers of the graphite having a layered structure. When the powder which is a main component of the electrode is a material having a considerably large bulk density (1 to 5) such as a hydrogen storage alloy powder, there is a problem that mixing cannot be performed at all by a dry mixer blender.

[Means for Solving the Problems] Means of the present invention for achieving the above object will be described as follows.

The electrode according to claim (1) is characterized in that an electrode active material layer and a perforated current collector are integrally laminated and pressed between flexible graphite layers.

The method for manufacturing an electrode according to claim (2) uses a flexible graphite plate formed by pressing expanded graphite, sandwiches an electrode active material in layers between layers of the thermally flexible graphite plate, and forms the electrode active material. The present invention is characterized in that a perforated current collector is sandwiched between layers of the flexible graphite plate different from the layers of the flexible graphite plate which sandwich the substance, and these laminates are pressed and integrated.

[Function] In the electrode according to claim (1), graphite having much lower density and conductivity than metal powder such as nickel or copper is used as the electrode material holding material, so that the electrode is lightweight and has low internal resistance. It can be an electrode. In addition, since flexible graphite is used as the electrode material holding material, it can be wound, a winding-type power generating element can be formed, and the operating current can be improved. Particularly, in this electrode, a perforated current collector is used, and the perforated current collector is integrally connected to the layer of the flexible graphite plate by a lamination press using the holes, and the bonding strength between the two is reduced. Can be raised.

In the method for manufacturing an electrode according to claim (2), a flexible graphite plate formed by pressing expanded graphite by pressing graphite having much lower density and conductivity than metal powder such as nickel or copper. Since it is used in the form, it can be easily handled at the time of manufacturing the electrode. The laminate of the flexible graphite plates sandwiching the electrode active material in layers can be easily integrated by pressing. In particular, in this electrode manufacturing method, these laminates are pressed in a state where the electrode active material layer and the perforated current collector are sandwiched between different layers of the flexible graphite plate. Further, the flexible graphite can penetrate into each hole of the perforated current collector plate at the time of pressing, and the bonding strength between them can be increased. In addition, since the electrode active material layer and the perforated current collector plate are interposed between different layers of the flexible graphite plate, each of them can be securely bonded to the flexible graphite plate.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

A flexible graphite plate formed by pressing expanded graphite has a different density depending on the compression ratio. However, when a relatively low-density graphite plate is further stacked and pressed further, the density becomes higher and the unit is integrated. At this time, if the perforated current collector is sandwiched, the current collector is interposed by integrating the layers on both sides of the perforated current collector in the hole portion of the perforated current collector. Also, the bonding strength between layers can be improved.

FIG. 1 schematically shows a method for manufacturing an electrode according to the present invention utilizing the above-described properties. A long flexible graphite plate 1 manufactured by pressing expanded graphite is unwound from a flexible graphite plate roll 2 and guided to a hopper 3, and a hydrogen storage alloy is placed on the flexible graphite plate 1. A layer of the electrode active material 4 made of a powder is formed. On a flexible graphite plate 6 unwound from another flexible graphite plate roll 5, a perforated current collecting plate 8 made of nickel wire mesh unwound from a current collecting plate roll 7 is superimposed. The flexible graphite plate roll 10 unwound from the flexible graphite plate roll 9 is overlaid thereon. Thereafter, these laminates are rolled and integrated by rolling rolls 11A and 11B to form a laminate 12. Here, in order for the flexible graphite plate 6, the perforated current collector plate 8 and the flexible graphite plate 10 to be integrated into a laminate 12, the flexible graphite plate 6 and the flexible graphite plate 10 are required. Must have a low compression ratio and low density that can be further compressed. If the density of the flexible graphite plates 6 and 10 is 1.5 or less, such integration is possible. However, as described later, the flexible graphite plate 6, the perforated current collector plate 8, and the flexible Since the laminated body 12 formed by integrating the graphite plates 10 is further subjected to an integrating step by pressing thereafter, the finished density of the flexible graphite in the laminated body 12 must be 1.5 or less. Therefore, the flexible graphite plates 6, 10 must be set to have a lower density as required. If the particle size of the electrode active material 4 made of the hydrogen storage alloy powder is about 100 mesh or less and the thickness of the layer of the electrode active material 4 is about 0.3 mm, the flexible graphite plate 6 The bulk density of the exfoliated graphite plate 10 is desirably about 0.1 to 0.2, and the thickness is about 1 mm. The laminate 12 formed in this manner is stacked on the layer of the electrode active material 4 of the flexible graphite plate 1 on which the layer of the electrode active material 4 is formed and between the rolling rolls 13A and 13B. Then, they are rolled and integrated to form a laminate 14. Thereafter, the laminate 14 is guided to a second hopper 15, on which a layer of an electrode active material 16 made of a hydrogen storage alloy powder is formed. Thereafter, a flexible graphite plate 18 unwound from another flexible graphite plate roll 17 is overlaid thereon, rolled by rolling rolls 19A and 19B and integrated to form a long electrode 20. You. Here, the flexible graphite plates 1 and 18 have a bulk density of about 0.3 to 0.4 and a thickness of 1-1.
About 5 mm is desirable. In the method for manufacturing an electrode shown in FIG. 1, one layer of each of the electrode active materials 4 and 16 is formed on both sides of the perforated collector electrode 8, and in this case, the above-described bulk density and thickness If a material is used, the final long electrode 20 has a thickness of about 1 mm. If a thinner electrode is required, the thickness of the flexible graphite plates 1, 6, 10, and 18 can be reduced to about 0.5 mm. Further, when it is desired to make the layer of the electrode active material more multilayer, the bulk density at the stage before passing through the final pressing through multi-stage pressing is all 1.5 or less, preferably 1.0
Flexible graphite plates 1,6,10,1 as needed as follows:
The bulk density, thickness and press roll clearance of 8 can be selected. The long electrode 20 thus obtained is
The electrode 23 is cut into a predetermined size by a die 21 and a cutter 22.

FIG. 2 schematically shows an example of a cross section of the electrode 23 manufactured as described above. Flexible graphite layers 6A and 10A are formed on both sides of a perforated current collector plate 8 made of punched metal, and the flexible graphite layers 6A and 1A are formed in the holes 8A of the perforated current collector plate 8.
0A are interconnected and integrated. Flexible graphite layer
Electrode active material layers 4A and 16A are formed outside 6A and 10A, and flexible graphite layers 1A and 18A, and electrode active material layers 24A and 25A made of a hydrogen storage alloy powder are further formed outside. Flexible graphite layers 26A and 27A are formed on the surface. Flexible graphite layers 6A, 10A, 1A, 18A, 26A, 27A and electrode active material layers 4A, 16A, 24A,
It is integrated with 25A and the boundary is not clear. At the time of rolling, each electrode active material layer is hardened into the adjacent flexible graphite layer, so that the electrode active material layer generally has a multilayer structure, but the boundary between the layers is unclear. Further, on the surface of the electrode 23, the electrode active material particles
28 may project as shown.

All of the constituent materials of the electrode 23 manufactured in this manner are conductive materials, and have extremely low electric resistance. In addition, 20 to 30 compared to those using metal powder as a binder
% Lighter. Furthermore, since the powder of the electrode active material, which is a main component of the electrode 23, is embedded in the flexible graphite layer, it exhibits the same effect as carbon coating.

In addition, as the perforated current collector 8, a metal plate having an opening such as an expanded metal, a metal foam, or a metal fiber aggregate can be used in addition to the above-described ones.

[Effects of the Invention] As described above, according to the electrode and the method of manufacturing the same according to the present invention, the following effects can be obtained.

In the electrode according to the first aspect, graphite having much lower density and conductivity than metal powder such as nickel and copper is used as the electrode material holding material, so that the electrode is lightweight and has low internal resistance. be able to. In addition, since flexible graphite is used as the electrode material holding material, it can be wound, a winding-type power generating element can be formed, and the operating current can be improved. Further, the electrode of the present invention is a material in which all materials are conductors and has an extremely low internal resistance. Further, the electrode can be a much lighter electrode as compared with a case where metal powder is used as a binder. Moreover, the presence of the carbon material around the main constituent elements of the electrode can promote the oxygen gas absorption reaction when applied to a negative electrode for a sealed alkaline secondary battery. Particularly, in this electrode, a perforated current collector is used, and the perforated current collector is integrally connected to the layer of the flexible graphite plate by a lamination press using the holes, and the bonding strength between the two is reduced. Can be raised.

In the method for manufacturing an electrode according to claim (2), a flexible graphite plate formed by pressing expanded graphite by pressing graphite having much lower density and conductivity than metal powder such as nickel or copper. Since it is used in the form, it can be easily handled at the time of manufacturing the electrode. The laminate of the flexible graphite plates sandwiching the electrode active material in layers can be easily integrated by pressing. Further, according to the method of the present invention, it is also possible to perform a series of electrode manufacturing steps as a dry process, in which case,
For example, by setting the entire atmosphere to an inert atmosphere, deterioration can be prevented even in the case of an electrode material which is easily oxidized and deteriorated such as a hydrogen storage alloy. Further, unlike the case where the expanded graphite is mixed as a powder, the electrode can be molded even when the main components of the electrode are dense. In particular, in this electrode manufacturing method, these laminates are pressed in a state where the electrode active material layer and the perforated current collector are sandwiched between different layers of the flexible graphite plate. Can be integrated. Further, at the time of pressing, the flexible graphite penetrates into each hole of the perforated current collector plate, so that the bonding strength between them can be increased. Further, since the electrode active material layer and the perforated current collector plate are interposed between different layers of the flexible graphite plate,
Each can be reliably connected to the flexible graphite plate.

As described above, according to the present invention, by the dry process, a windable and flexible electrode having a small internal resistance can be obtained, and when applied to a sealed alkaline secondary battery, the gas absorption is low. The point that the reaction is promoted is of great industrial value.

[Brief description of the drawings]

FIG. 1 is a process diagram showing one embodiment of a method for manufacturing an electrode according to the present invention, and FIG. 2 is a longitudinal sectional view showing one embodiment of an electrode according to the present invention. 1 ... Flexible graphite plate, 2 ... Flexible graphite plate roll, 3 ...
… Hopper, 4 …… electrode active material, 4A …… electrode active material layer,
5 ... Flexible graphite plate roll, 6 ... Flexible graphite plate, 6A ...
... flexible graphite layer, 7 ... current collector plate roll, 8 ... perforated current collector plate, 8A ... hole, 9 ... flexible graphite plate roll, 10A ... flexible graphite plate, 11A, 11B …… Roll roll, 12 …… Laminate, 1
3A, 13B: rolling roll, 14: laminate, 15: hopper, 16: electrode active material, 16A: electrode active material layer, 17 ...
Flexible graphite plate roll, 18 ... Flexible graphite plate, 18A ... Flexible graphite layer, 19A, 19B ... Rolling roll, 20 ... Long electrode, 21 ... Die, 22 ... Cutter, 23 …… electrode, 24A, 25
A: Electrode active material layer, 26A, 27A: Flexible graphite layer, 28:
Electrode active material particles.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI // B32B 19/04 B32B 19/04 H01M 10/34 H01M 10/34 (56) References JP-A-61-4169 (JP, A) JP-A-63-266767 (JP, A) JP-A-63-270138 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/24 H01M 4/26 H01M 4 / 04 H01M 10/34 B32B 19/04

Claims (2)

(57) [Claims] 1. An electrode, wherein an electrode active material layer and a perforated current collector are integrally laminated and pressed between flexible graphite layers. 2. A flexible graphite plate formed by pressing expanded graphite, wherein an electrode active material is sandwiched between layers of the flexible graphite plate, and the flexible electrode plate sandwiches the electrode active material. A method for producing an electrode, comprising sandwiching a perforated current collector between layers of a flexible graphite plate different from the layers of a graphite plate, and pressing and integrating these laminates.