JP3666146B2 - Method for producing electrode of alkaline secondary battery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an electrode of an alkaline secondary battery using an active material mainly composed of nickel hydroxide.
[0002]
[Prior art]
An alkaline secondary battery (an alkaline electrolyte secondary battery) uses an electrode using an active material mainly composed of nickel hydroxide [Na (OH) ₂ ]. In such an electrode, a cobalt compound such as cobalt monoxide may be added as a conductive material in order to increase the current collecting property of the active material and improve the utilization factor.
[0003]
In a conventional electrode manufacturing method in which cobalt monoxide is added to an active material, a powder of a cobalt compound such as cobalt monoxide and water are first mixed with a powder of nickel hydroxide (particle size: 10 μm) as an active material. In addition, a conductive material (nickel), a thickener (glue), and a binder (binder) are added as necessary to produce an active material paste. And this electrode is completed by apply | coating this active material paste to the thin-plate board | substrate which is a base | substrate of an electrode, or filling and drying a three-dimensional porous substrate. The thin plate substrate is, for example, punching metal, expanded metal, metallic copper, or the like. A three-dimensional porous substrate is a porous material in which a fine conductive metal skeleton or metal fiber forms a three-dimensional network, such as foam metal (for example, nickel foam) or non-woven metal (for example, nickel fiber felt). A quality substrate. Therefore, current can be collected from the active material by putting the particles of the active material into a large number of micropores provided in the base of these electrodes. However, if only the active material is inserted, the conductivity between each active material or between this active material and the substrate is not so good, so a cobalt compound such as cobalt monoxide or metallic nickel is not used as the conductive material. Add it to collect electricity efficiently.
[0004]
For example, Japanese Patent Publication No. 5-26304 discloses that nickel hydroxide powder is mixed with 10 wt% (wt%) of cobalt monoxide powder and pulverized, and CMC (carboxymethyl cellulose) is used as a thickener. An electrode manufacturing method is described in which an aqueous material paste is added to produce an active material paste, and this active material paste is filled into a three-dimensional porous substrate.
[0005]
In Japanese Patent Publication No. 5-65988, first, nickel hydroxide powder having an average particle diameter of about 20 μm is added with 4 to 12 wt% of cobalt monoxide powder having an average particle diameter of about 0.3 to 1.0 μm. Next, cobalt monoxide particles are adhered to the surface of the nickel hydroxide particles by the charging phenomenon of the powder, and further, the cobalt monoxide particles are embedded in the surface layer of the nickel hydroxide particles by mechanical impact. An electrode manufacturing method is described in which an active material paste is produced by adding a 1% aqueous solution of CMC as a thickener, and this active material paste is filled in a three-dimensional porous substrate.
[0006]
By the way, cobalt monoxide itself has almost no conductivity. However, when an alkaline electrolyte is injected into an electrode in which cobalt monoxide is added to the active material, the cobalt monoxide [CoO] (divalent) is dissolved in the electrolyte and becomes Co (divalent) ions to form the active material. Precipitates between the particles and between the electrode substrate. The initial charge changes the cobalt hydroxide [Co (OH) ₂ ] into conductive CoOOH (trivalent) to form a conductive network between the active materials and the electrode substrate. be able to.
[0007]
Even in the above-described conventional manufacturing method, if the particle size of cobalt monoxide is sufficiently small (about 0.5 to 2.0 μm), the entire surface of the nickel hydroxide particles 1 is mixed by kneading as shown in FIG. Since the cobalt oxide particles 2 are distributed and adhered almost uniformly, by injecting an alkaline electrolyte, these cobalt monoxide particles 2 are dissolved and widely precipitated as cobalt hydroxide around the entire nickel hydroxide particles 1. Can be made. Therefore, after charging, the conductive CoOOH can reliably form a conductive network between the nickel hydroxide particles 1 and 1 and the base of the electrode.
[0008]
[Problems to be solved by the invention]
However, cobalt monoxide is very easy to aggregate, and even if it is formed to have a particle size of about 1 μm at the time of manufacture, each particle aggregates into large particles of about 10 μm during subsequent storage or transportation. Cannot be avoided. Therefore, in the above conventional manufacturing method, as shown in FIG. 4, the aggregates 3 of about 10 μm of cobalt monoxide are sparsely scattered between the nickel hydroxide particles 1 having a particle size of several tens of μm. Become. And even if it injects alkaline electrolyte in this state and performs charge, cobalt hydroxide does not precipitate on the whole circumference | surroundings of the nickel hydroxide particle 1, and electroconductive CoOOH cannot form sufficient network. In addition, since cobalt monoxide cannot be sufficiently dissolved in the electrolyte solution in the state of the aggregate 3, a lot of waste that does not contribute to conductivity increases.
[0009]
For this reason, in the conventional method for producing an electrode of an alkaline secondary battery, cobalt monoxide is kneaded with the nickel hydroxide particles 1 as the active material in the state of the aggregates 3. In addition, there is a problem that the conductivity between the electrode and the substrate of the electrode cannot be sufficiently increased, and the utilization factor of the active material is lowered. In addition, if the utilization rate of this active material is forcibly increased, a large amount of cobalt monoxide must be added, and the proportion of the active material is reduced by this amount, resulting in a decrease in battery capacity. Occurs.
[0010]
For example, in the method for producing an electrode described in Japanese Patent Publication No. 5-26304, nickel hydroxide powder and cobalt monoxide powder are mixed and pulverized. Since the aggregate 3 cannot be separated into the original fine particles, the above problem cannot be avoided. Moreover, if pulverization is performed to separate the aggregates 3 into fine particles, there arises a problem that the nickel hydroxide particles 1 as the active material are broken.
[0011]
In addition, in the electrode manufacturing method described in Japanese Patent Publication No. 5-65988, cobalt hydroxide powder having an average particle size of about 0.3 to 1.0 μm is mixed with nickel hydroxide powder. More precisely, cobalt monoxide having an average particle size of about 0.3 to 1.0 μm is manufactured and mixed, and the powder of cobalt monoxide has an average particle size of about 0.3 to 1.0 μm. It is extremely difficult to mix as it is. That is, in the laboratory, it is possible to immediately mix the manufactured cobalt monoxide powder with fine particles, but in an actual manufacturing process, storage, transportation, etc. after the production of cobalt monoxide. This process cannot be avoided, and since cobalt monoxide aggregates during this time, in practice, mixing is performed in the state of the aggregate 3 of cobalt monoxide having a larger particle size.
[0012]
Here, when the powder of cobalt monoxide was immediately mixed without agglomeration in the laboratory, when the relationship between the content of cobalt monoxide and the utilization rate of the active material was examined, this content was 2 to 3 wt. %, The utilization rate can be increased to 90% or more. However, in the manufacturing method of Japanese Patent Publication No. 5-26304, the content rate of cobalt monoxide is 10 wt%, and in the manufacturing method of Japanese Patent Publication No. 5-65988, the content rate of cobalt monoxide is 4 to 12 wt% (around 10 wt%). Is optimal). Also, in Japanese Patent Publication No. 5-65988, a document (FIG. 6 of the publication) states that the content of cobalt monoxide needs to be 4 wt% or more in order that the utilization rate of the active material exceeds 90%. Disclosure. That is, in these production methods, it is understood that cobalt monoxide is added more than necessary because aggregation of cobalt monoxide is not taken into consideration. Therefore, in these conventional manufacturing methods, a large amount of cobalt monoxide must be added in order to obtain a sufficient utilization rate of the active material, and accordingly, the content of the active material is lowered and the battery capacity is lowered accordingly. There was a problem.
[0013]
The above problem occurs not only when cobalt monoxide is used as the conductive material, but also when other cobalt compounds are used.
[0014]
The present invention has been made in view of such circumstances, and by mixing a cobalt compound with water or the like in advance and dispersing it using a ball mill or the like, the aggregate of the cobalt compound is finely mixed. It aims at providing the manufacturing method of the electrode of an alkaline secondary battery which can isolate | separate into particle | grains and can raise the utilization factor of an active material.
[0015]
[Means for Solving the Problems]
That is, in order to solve the above-mentioned problem, the invention of claim 1 mixes a cobalt compound aggregate in which fine particles are aggregated with a dispersion medium, and disperses them into particles having an average particle diameter smaller than that of the aggregate. The cobalt compound dispersion step for producing a cobalt compound paste by the step, and the cobalt compound paste produced by the cobalt compound dispersion step is mixed with an active material mainly composed of nickel hydroxide, or the active material and an additive. An active material paste generating step for generating an active material paste by the step, and an electrode forming step for forming an electrode by supporting the active material paste generated by the active material paste generating step on a substrate. To do.
[0016]
According to the means of claim 1, since the cobalt compound aggregate in which fine particles are aggregated is dispersed by the cobalt compound dispersion step, the cobalt compound aggregate is separated into the original small particle diameter cobalt. A compound paste can be produced. Therefore, when an active material mainly composed of nickel hydroxide is added to the cobalt compound paste in the active material paste production step and kneaded, the cobalt compound having a small particle size in the active material paste is spread over the entire surface of the active material having a large particle size. It can be made to adhere uniformly, whereby the utilization factor of the active material can be improved. Further, since the cobalt compound is hardly wasted, the ratio of the active material contained in the active material paste can be increased and the battery capacity can be improved.
[0017]
“Supporting” refers to an act of applying an active material paste to an electrode substrate or holding it by filling or the like.
[0018]
Further, the invention of claim 2 is characterized in that the cobalt compound dispersion step of claim 1 disperses the cobalt compound using a ball mill which is a medium type disperser or a continuous disperser.
[0019]
According to the second aspect, since the cobalt compound is dispersed by the ball mill which is a medium type dispersing machine, the aggregate of the cobalt compound can be surely separated into particles having a small particle diameter. The ball mill mentioned here includes a bead mill.
[0020]
Furthermore, the invention of claim 3 is characterized in that the cobalt compound of claim 1 or 2 is cobalt monoxide.
[0021]
According to the third aspect of the present invention, cobalt monoxide capable of generating an optimal conductive material can be used.
[0022]
In addition, as other cobalt compounds, it is possible to use cobalt hydroxide, suboxide or the like.
[0023]
Furthermore, the invention of claim 4 is characterized in that the dispersion liquid of claims 1 to 3 is water.
[0024]
According to the means of claim 4, since water is used for the dispersion liquid (dispersion medium), when drying the active material paste carried on the substrate in the electrode forming step, the water can be safely evaporated as water vapor. This water vapor treatment becomes easy. However, when water having a low viscosity is used for the dispersion as described above, it is preferable to add a thickener as an additive to the cobalt compound paste in the active material paste generation step.
[0025]
Further, in the invention of claim 5, the active material paste production step of claims 1 to 4 is performed by first adding a thickener as an additive to the cobalt compound paste and kneading, and then mainly using nickel hydroxide. It is a step of generating an active material paste by adding an active material to be kneaded and adding a binder as an additive and kneading.
[0026]
According to the means of claim 5, since a thickener is first added to the cobalt compound paste, when the dispersion liquid has a low viscosity such as water, the dispersed cobalt compound settles in the paste and the dispersion liquid Separation can be prevented. In addition, since the binder is added together with the active material, it is possible to prevent the active material paste dried in the electrode forming step from being easily peeled off due to vibration or the like. In addition, the means of claim 5 does not matter the order of addition of the active material and the binder. Moreover, in the means of claim 1, the order of addition of the active material and the additive is not limited, and these are added simultaneously, or all or part of the active material and the additive are kneaded in advance and then added together. You may make it do.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0028]
1 to 2 show an embodiment of the present invention, FIG. 1 is a process diagram showing a method for producing an electrode of an alkaline secondary battery, and FIG. 2 is the use of an active material with respect to the content of cobalt monoxide. It is a figure which shows the change of a rate.
[0029]
As shown in FIG. 1, in the method for producing an electrode of an alkaline secondary battery according to this embodiment, in the first step (cobalt compound dispersion step), cobalt monoxide powder is mixed with water, and a ball mill is used. By dispersing, a cobalt monoxide paste (cobalt compound paste) is generated (S1).
[0030]
In this embodiment, cobalt monoxide [CoO] is used as the conductive material, but cobalt compounds such as cobalt hydroxide [Co (OH) ₂ ] and suboxide can be used as well. The powder of cobalt monoxide is obtained by agglomerating fine particles of about 1 μm to an average particle size of about 8 μm. Cobalt monoxide powder that is generally available industrially becomes such an agglomerate.
[0031]
Water is used as a dispersion medium for dispersing the powder of cobalt monoxide. Therefore, only the minimum amount necessary for dispersion is used in step S1. However, instead of this water, other dispersion liquids such as organic solvents can be used. However, when using a dispersion other than water, when drying the paste in a later step, an explosion-proof facility for safely vaporizing this dispersion is provided, or the vaporized dispersion is safely treated, Or it becomes necessary to provide the equipment for collecting this. Cobalt monoxide does not dissolve in this dispersion liquid such as water or organic solvent.
[0032]
When cobalt monoxide powder and water are mixed and dispersed by a ball mill, aggregates having an average particle size of about 8 μm are separated into particles having an average particle size of about 0.5 to 2 μm. A ball mill (including a bead mill) is a medium-type disperser that stirs a large number of media such as hard spheres together with powder to disperse the powder, and a continuous disperser such as a sand grinder can also be used. As the medium, zirconia balls, zirconia beads, titania beads, alumina beads, or the like can be used. Further, the medium is not limited to a spherical shape, but may be an elliptical shape or other shapes.
[0033]
In the next step (part of the active material paste generation step), an aqueous solution in which a small amount of CMC (carboxymethyl cellulose) is dissolved in water is added to the cobalt monoxide paste generated in step S1 and kneaded. (S2).
[0034]
CMC is water-soluble, but if it is added as a powder, it will be difficult to dissolve as it becomes a lump with a powdery state remaining inside, so it is dissolved in water in advance and added as an aqueous solution. In addition, since the cobalt monoxide paste has a small water content, the cobalt monoxide paste also serves to dilute the cobalt monoxide paste by diluting with the CMC aqueous solution in order to carry it on the substrate of the electrode in a later step.
[0035]
The CMC is mainly added as a thickener (additive). That is, since cobalt monoxide is insoluble, even if water is mixed, it may settle in the paste and separate from water. Therefore, by adding a small amount of CMC, the viscosity of the paste is increased and cobalt monoxide is kept in a uniform state. However, in order to increase the proportion of the active material added in the next step in the paste as much as possible, the addition of CMC is made the minimum necessary. In addition, other thickeners may be used in place of the CMC, and there is no need to add such thickeners unless there is a risk of separation of cobalt monoxide. For example, when the dispersion is replaced with water and alcohols (organic solvents) with high viscosity such as ethylene glycol or propylene glycol are used, it is not always necessary to add a thickener. The CMC can also play a role as a binder to some extent when the paste is dried in a later step.
[0036]
Furthermore, in the next step (main part of the active material paste generation step), nickel hydroxide powder is added as an active material to the paste to which the CMC aqueous solution has been added in the above step S2 and kneaded to generate an active material paste. (S3).
[0037]
Nickel hydroxide powder having an average particle size of about several tens of μm is used. The active material only needs to be mainly composed of nickel hydroxide, and may be a material to which a small amount of cobalt, zinc, cadmium, magnesium hydroxide, or the like is added. The amount of the active material to be added is determined so that the content of cobalt monoxide with respect to the active material is 2 to 3 wt%.
[0038]
Further, in the next step (part of the active material paste generation step), a dispersion of PTFE is added to the active material paste generated in step S3 and kneaded (S4).
[0039]
A dispersion of PTFE (polytetrafluoroethylene) is a dispersion obtained by adding a small amount of water to a fine powder of PTFE. This PTFE is added as a binder (additive). That is, when the active material paste is dried in a later step, the active material is bound to the base of the electrode so that it does not easily fall off. Therefore, such a binder is also added only in a minimum amount in order to maximize the proportion of the active material in the paste. In addition, other plastics such as polyethylene, fluorinated ethylene, and fluorinated propylene copolymer can be used in place of the PTFE. If there is no risk of the active material falling off, such a binder is used. No need to add.
[0040]
In the last step (electrode formation step), the active material paste to which the PTFE dispersion has been added in the step S4 is supported on the substrate to complete the electrode (S5).
[0041]
A conductive thin plate three-dimensional porous substrate is used as the electrode substrate. The active material paste is supported by being applied to the thin plate substrate, filling the three-dimensional porous substrate, evaporating water and drying.
[0042]
With the above configuration, the aggregate of cobalt monoxide having an average particle size of about 8 μm is dispersed in the step S1 and separated into small particles having an average particle size of about 0.5 to 2 μm. When nickel hydroxide powder having a particle size of about several tens of μm is added and kneaded, the cobalt monoxide particles 2 are distributed almost uniformly over the entire surface of the nickel hydroxide particles 1 as shown in FIG. And adhere. Therefore, when the active material paste thus produced is supported on the electrode substrate and an alkaline electrolyte is injected, the cobalt monoxide particles 2 are dissolved and widely precipitated as cobalt hydroxide around the nickel hydroxide particles 1. In addition, the conductive CoOOH changed after the charging can surely form a conductive network between the nickel hydroxide particles 1 and 1 and the electrode substrate. Then, by sufficiently forming this conductive network, it is possible to increase the current collecting property of the active material carried on the substrate and improve the utilization rate.
[0043]
FIG. 2 shows an example of a change in the utilization rate of the active material when an electrode is manufactured by changing the content of cobalt monoxide in the manufacturing method of the above embodiment and the conventional manufacturing method. In the conventional manufacturing method, cobalt monoxide is sparsely dispersed as an aggregate, so that the utilization rate of the active material is lowered overall, and in order to increase the utilization rate to 90% or more, for example, 4 wt% or more of monoxide It becomes necessary to contain cobalt. Further, in order to saturate the utilization rate to the maximum value, it is necessary to add about 10 wt% or more.
[0044]
On the other hand, in the manufacturing method of this embodiment, the utilization rate can be increased to 90% or more simply by containing 2 wt% or more of cobalt monoxide, and only by containing 3 wt% or more of cobalt monoxide. The utilization factor can be almost saturated. Therefore, in the manufacturing method of this embodiment, it is appropriate to contain 2 to 3 wt% of cobalt monoxide as described above. That is, when the content of cobalt monoxide is less than 2 wt%, the utilization rate of the active material becomes too low, and when the content exceeds 3 wt%, the utilization rate does not improve, but the proportion of the active material is reduced, and the battery is wasted. This is because the capacity is reduced.
[0045]
In the above embodiment, the active material paste generation step is divided into steps S2 to S4. However, all or part of the CMC aqueous solution, the active material, and the PTFE dispersion are added simultaneously to integrate these steps. Alternatively, the order of these steps can be interchanged. Alternatively, all or part of the CMC aqueous solution, active material, and PTFE dispersion may be separately kneaded and added to the cobalt monoxide paste.
[0046]
【The invention's effect】
As is clear from the above description, according to the method for producing an electrode of an alkaline secondary battery of the present invention, only the cobalt compound is dispersed before the active material is added, so that the particles of the active material are not destroyed. Only the aggregates of cobalt compounds can be separated into particles having a small particle size. When an active material is added to the cobalt compound paste in which the cobalt compound is dispersed, the cobalt compound having a small particle size can be uniformly attached to the entire surface of the active material having a large particle size. The utilization rate can be improved. This also reduces the waste of cobalt compounds and eliminates the need to increase the content more than necessary, thus increasing the battery capacity by increasing the proportion of the active material in the active material paste carried on the substrate. You can also.
[Brief description of the drawings]
FIG. 1 is a process chart showing an embodiment of the present invention and showing a method for producing an electrode of an alkaline secondary battery.
FIG. 2, showing an embodiment of the present invention, is a diagram showing a change in utilization ratio of an active material with respect to a content ratio of cobalt monoxide.
FIG. 3 is a diagram showing a kneaded state with nickel hydroxide particles when an aggregate of cobalt monoxide is dispersed in particles having a small particle diameter.
FIG. 4 is a diagram showing a kneaded state with nickel hydroxide particles when cobalt monoxide becomes an aggregate having a large particle size.
[Explanation of symbols]
1 Nickel hydroxide particles 2 Cobalt monoxide particles 3 Aggregates

Claims (5)

A cobalt compound dispersion step for producing a cobalt compound paste by mixing an aggregate of cobalt compounds in which fine particles are aggregated with a dispersion medium and dispersing the aggregate in particles having an average particle size smaller than the aggregate;
An active material paste generating step for generating an active material paste by adding an active material mainly composed of nickel hydroxide to the cobalt compound paste generated by the cobalt compound dispersing step, or kneading the active material and an additive. When,
And an electrode forming step of forming an electrode by supporting the active material paste generated in the active material paste generating step on a substrate. A method for manufacturing an electrode of an alkaline secondary battery, comprising:   The method for producing an electrode of an alkaline secondary battery according to claim 1, wherein the cobalt compound dispersing step is to disperse the cobalt compound using a ball mill which is a medium type dispersing machine or a continuous type dispersing machine.   The method for producing an electrode of an alkaline secondary battery according to claim 1, wherein the cobalt compound is cobalt monoxide.   The method for producing an electrode for an alkaline secondary battery according to any one of claims 1 to 3, wherein the dispersion is water.   In the active material paste generating step, a cobalt compound paste is first kneaded with a thickener added as an additive, then an active material mainly composed of nickel hydroxide is added and kneaded, and the resultant is combined as an additive. The method for producing an electrode of an alkaline secondary battery according to any one of claims 1 to 4, which is a step of producing an active material paste by adding an adhesive and kneading.

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