JP2002279981A - Non-sintered nickel electrode, method of manufacturing the non-sintered nickel electrode, and sealed alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-sintered nickel electrode for alkaline secondary battery, having a performance suitable for an increase in capacity while stably assuring a proper discharge reserve, and to provide a method of manufacturing the electrode, and an alkaline secondary battery. SOLUTION: This non-sintered nickel electrode comprises a conductive non-sintered base body and electrode active material articles, filled and carried on the non-sintered base body, and the outer peripheral surface of the electrode active material particles, including oxyhydroxide, is covered with a mixture system of cobalt oxyhydroxide and cobalt oxide exceeding divalent. The method of manufacturing the electrode comprises a process of making cobalt hydroxide particles and nickel hydroxide particles coexist in alkali aqueous solution and heating the solution by radiation heat, a process of chemically oxidizing the nickel hydroxide particles having cobalt oxyhydroxide produced in the previous step and the mixture system layer of cobalt oxide exceeding divalent formed on the outer peripheral surface thereof, so as to change at least a part of the nickel hydroxide particles forming a core into nickel oxyhydroxide, and a process of filling and carrying the electrode active material particles, having the nickel oxyhydroxide as the core on the nonconductive non-sintered base body.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-sintered nickel electrode used for an alkaline secondary battery, a method for producing active material particles for a non-sintered nickel electrode, and an alkaline secondary battery.

[0002] For example, alkaline secondary batteries such as nickel hydrogen secondary batteries and nickel cadmium secondary batteries are used as power supplies for portable electronic devices, and these portable electronic devices have higher capacity or higher functionality. Accordingly, there is an increasing demand for higher capacity and longer life of power supply batteries.
When the capacity of the battery is increased, regarding the positive electrode configuration, for example, a conductive non-sintered substrate (non-sintered substrate) such as foamed nickel or punched metal, and if necessary, an electrode active material is formed into a paste Thus, a configuration of a nickel electrode that is filled and supported at a higher packing density is known.

In order to increase the capacity of the non-sintered nickel electrode, means for improving the utilization rate of the electrode active material have been studied. That is, cobalt or a cobalt compound is added to particles mainly composed of nickel hydroxide,
Means have been developed in which a cobalt compound is deposited and coated on the surface of the particle, or a cobalt compound is deposited and coated on the surface of the particle and then subjected to an oxidizing treatment with a hydrogen peroxide solution.

When the structure of the nickel positive electrode, in other words, when the electrode active material to be filled and supported contains cobalt or a cobalt compound, the utilization factor of the electrode active material is improved for the following reasons. It is explained. That is, when the nickel positive electrode having the above configuration is incorporated in an alkaline secondary battery, the cobalt species is once dissolved in the alkaline electrolyte and dispersed on the surface of the nickel hydroxide particles. -Cobalt hydroxide precipitates on the surface of the nickel hydroxide particles in a form in which the electrode active material and the electrode active material-the current collector are connected. And the precipitated cobalt hydroxide becomes cobalt oxyhydroxide,
It is considered that the conductive network of the cobalt oxyhydroxide improves the conductivity between the electrode active material and the electrode active material and between the electrode active material and the current collector, and improves the use efficiency of the electrode active material.

[0005] However, the nickel positive electrode filled and supported with an electrode active material containing cobalt or a cobalt compound has a problem that the improvement in the utilization rate is not sustained due to overdischarge. In order to solve the problem of overdischarge characteristics, it has been proposed to perform heat treatment on nickel hydroxide particles whose surface is coated with a cobalt compound in an oxygen atmosphere in which an alkali coexists. By this alkali heat treatment means, a higher-order cobalt oxide having a valence of more than 2 is formed on the surface of the nickel hydroxide particles, and together with cobalt oxyhydroxide, promotes the effect of improving conductivity and improving the overdischarge characteristics. Is being planned.

[0006]

Incidentally, in nickel-metal hydride secondary batteries and nickel-cadmium secondary batteries, the capacity of the negative electrode is usually larger than the capacity of the positive electrode. It is designed so that there is a charging part (charging reserve). In other words, at the end of charging or at the time of overcharging, oxygen gas generated from the positive electrode is absorbed by the negative electrode, thereby suppressing an increase in the internal pressure of the sealed secondary battery.
A charging reserve is provided. The charge reserve also has a function of suppressing a decrease in discharge capacity due to a decrease in the active material utilization of the negative electrode during high-rate discharge.

In the above nickel positive electrode, during charging, the cobalt oxyhydroxide generated from cobalt hydroxide on the surface of the nickel hydroxide particles is not reduced during discharging but remains as cobalt oxyhydroxide. Therefore,
The amount of electricity required for the oxidation of cobalt hydroxide to cobalt oxyhydroxide is stored in the negative electrode as a potential discharge amount (discharge reserve). On the other hand, during the first charge, oxidation of the positive electrode active material (nickel oxyhydroxide)
And the amount of electricity equal to the difference between the amount of electricity required for reduction and the amount of electricity required for reduction is stored in the negative electrode as a discharge reserve.

[0008] The discharge reserve of the negative electrode has the effect of suppressing a decrease in battery voltage due to an increase in the negative electrode potential at the end of discharge at the time of high-rate discharge. However, there is a problem that the ratio of the electrode active material that can be used is reduced. In other words, in terms of increasing the capacity of the battery, it is effective to reduce the discharge reserve, but from the viewpoint of suppressing the battery voltage drop due to the increase in the negative electrode potential, there is a conflicting problem that a discharge reserve is required. . As measures against this, various means have been proposed in Japanese Patent Publication No. 8-24041, Japanese Patent Publication No. 60-254564, and Japanese Patent Application Laid-Open No. H11-219701.

For example, focusing on the fact that the negative electrode discharge reserve is the sum of the discharge reserve generated by the positive electrode conductive agent and the discharge reserve generated by the positive electrode active material, the negative electrode discharge reserve is generated by the positive electrode active material. Attempts have been made to reduce the available discharge reserve. That is, the first active materials 60 to 9 in which nickel hydroxide particles are coated with cobalt oxyhydroxide
It has been proposed to use a mixture of 0% by weight and 40 to 10% by weight of a second active material in which nickel oxyhydroxide particles are coated with cobalt oxyhydroxide as a positive electrode active material.

[0010] However, in the case of the nickel electrode having the above-described structure, the quality and the performance vary, and there is a concern about stability or reliability. That is, a first active material in which the above-mentioned nickel hydroxide particles are coated with cobalt oxyhydroxide on a conductive non-sintered type substrate, and a second active material in which nickel oxyhydroxide particles are coated with cobalt oxyhydroxide. And
Filling and supporting as a substantially uniform mixture / dispersion system
This leads to complicated manufacturing operations. This complicated manufacturing operation leads to yield, mass productivity, low cost, etc., and there is a certain limit to the formation of a uniform mixing / dispersion system. Is done.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a non-sintered nickel for an alkaline secondary battery having a performance suitable for high capacity while ensuring a proper discharge reserve stably. An object of the present invention is to provide an electrode, a method for producing the non-sintered nickel electrode, and an alkaline secondary battery using the non-sintered nickel electrode.

[0012]

According to a first aspect of the present invention, there is provided an electroconductive non-sintered substrate, and the electrode active material particles filled and supported on the non-sintered substrate. Is a non-sintered nickel electrode characterized in that the outer peripheral surface of particles containing nickel oxyhydroxide is coated with a mixed system of cobalt oxyhydroxide and a cobalt oxide having more than two valences.

According to a second aspect of the present invention, in the non-sintered nickel electrode according to the first aspect, the electrode active material particles are subjected to heat treatment by radiant heat by allowing cobalt hydroxide particles and nickel hydroxide particles to coexist in an alkaline aqueous solution. It is characterized by being made.

According to a third aspect of the present invention, in the non-sintered nickel electrode according to the first or second aspect, the average particle diameter of the electrode active material particles is 7 to 18 μm, and the specific surface area by the BET method is 5 to ²⁰ m ^2. / G, or a cobalt hydroxide particle and a nickel hydroxide particle having a half width at 0.85 to 1.00 ° in the (101) plane in the X-ray diffraction method.

According to a fourth aspect of the present invention, there is provided a process in which cobalt hydroxide particles and nickel hydroxide particles coexist in an aqueous alkaline solution and a heat treatment by radiant heat is performed. A step of chemically oxidizing nickel hydroxide particles provided on the outer peripheral surface with a mixed layer of cobalt oxide to convert at least a part of nickel hydroxide forming a nucleus to nickel oxyhydroxide; A step of filling and supporting an electrode active material particle having a nickel-based core on a conductive non-sintered substrate,
A method for producing a non-sintered nickel electrode, comprising:

According to a fifth aspect of the present invention, in the method for producing a non-sintered nickel electrode according to the fourth aspect, the average particle diameter of the cobalt hydroxide particles and the nickel hydroxide particles is 7 to 18 μm.
It is characterized by being.

According to a sixth aspect of the present invention, in the method for manufacturing a non-sintered nickel electrode according to the fourth aspect, the specific surface area of the cobalt hydroxide particles and the nickel hydroxide particles is 5 to ²⁰ m ² / g by a BET method. It is characterized by the following.

According to a seventh aspect of the present invention, in the method for manufacturing a non-sintered nickel electrode according to the fourth aspect, the cobalt hydroxide particles and the nickel hydroxide particles have a half width at a (101) plane in an X-ray diffraction method. 0.85 to 1.00 °.

The invention according to claim 8 is a non-sintering method in which the particles containing nickel oxyhydroxide are loaded and supported with electrode active material particles whose outer peripheral surface is coated with a mixed system of cobalt oxyhydroxide and cobalt oxide having more than two valences. A positive electrode, a negative electrode disposed corresponding to the non-sintered positive electrode, a separator interposed between the non-sintered positive electrode and the negative electrode, and an alkaline electrolyte. An alkaline secondary battery characterized by the following.

In the first to seventh aspects of the present invention, the conductive non-sintered substrate forming the core is made of, for example, nickel foam,
Felt-like metal fiber-based porous material, punched metal, and the like. The electrode active material particles filled and supported on the conductive non-sintered substrate are made of nickel oxyhydroxide (NiOO).
The outer peripheral surface (surface) of the particles containing H) is coated with a mixed system of cobalt oxyhydroxide (CoOOH) and a cobalt oxide having more than two valences (for example, Co ₃ O ₄ ).

Here, the nucleus-containing particles containing nickel oxyhydroxide may be entirely formed of nickel oxyhydroxide, but may be formed of a nickel hydroxide-nickel oxyhydroxide mixed system or a hybrid system. You may. The nickel hydroxide-nickel oxyhydroxide hybrid-based particles have an average particle size of about 7 to 18 μm, and the thickness of the cobalt oxyhydroxide-containing cobalt oxide mixed system having a valence of more than 0.1 which covers the outer peripheral surface is 0.1 to 0.1 μm. It is about 0.5 μm.

In the invention of claims 1 to 7, the cobalt hydroxide (Co (OH) ₂ ) particles have an average particle size of 0.5 to 0.5.
About 2 μm, more preferably an average particle size of 0.8 to 1.2 μm
m. In addition, nickel hydroxide particles (Ni (O
H) ₂ ) has an average particle diameter of about 7 to 18 μm, more preferably about 10 to 15 μm. The mixing ratio of the cobalt hydroxide particles and the nickel hydroxide particles is about 3: 100 to 10: 100 by weight, more preferably about 5: 100 to 9: 100.

The cobalt hydroxide particles and nickel hydroxide particles used as the above-mentioned materials may be fine particles having a specific surface area of about 5 to ²⁰ m ² / g according to the BET method, or ( The half width at 101) may be about 0.85 ° to 1.00 °. That is, when the cobalt hydroxide particles and the nickel hydroxide particles are grasped by the average particle diameter, the specific surface area, the half width, or the like, if the above range is selected, the capacity and the service life can be easily increased.

In the invention according to claims 4 to 7, when depositing a mixed system of cobalt oxide having a valence of cobalt oxyhydroxide of 2 or more on the surface of the nickel hydroxide particles, the alkaline aqueous solution to be coexisted is an aqueous sodium hydroxide solution, An aqueous solution of potassium hydroxide, generally having a concentration of 1 to 14 mol /
It is about l. The radiant heat of heating the cobalt hydroxide particles and the nickel hydroxide particles in the alkaline aqueous solution is as follows:
Heating by irradiation of high frequency or electromagnetic waves. here,
By using radiant heat as the heating source, the precipitation of the mixed system of cobalt oxide having a valence of cobalt oxyhydroxide-2 above is smoothly performed, and the oxidation of nickel hydroxide by an oxidizing agent described later is easily performed. Show a tendency.

In the invention of claims 4 to 7, the mixed system layer of cobalt oxyhydroxide having a valence of more than 2 is used for chemically oxidizing nickel hydroxide particles provided on the outer peripheral surface. The oxidizing agent is, for example, hydrogen peroxide, hypochlorite, or the like. The oxidation treatment here is
Nickel oxyhydroxide is used to convert at least a portion of the nickel hydroxide particles forming the nucleus. This can be achieved by advancing chemical oxidation while stirring in an oxidizing agent aqueous solution.

In the invention according to claims 4 to 7, the means for filling and supporting the electrode active material particles having nickel oxyhydroxide-based particles as nuclei on a conductive non-sintered substrate is, for example, a conductive core such as foamed nickel. This can be achieved by applying and drying a paste containing the electrode active material on the body. That is, a general means for filling and supporting the electrode active material on the conductive non-sintered porous substrate is applied.

In the eighth aspect of the present invention, the configuration of the alkaline secondary battery is based on the general configuration of, for example, a nickel hydride secondary battery or a nickel cadmium secondary battery. A positive electrode is used. In other words, the configuration of the negative electrode, the separator, the electrolyte,
The configuration of the sealed type, the shape of the battery, and the like are general.

According to the first to third aspects of the present invention, the electrode active material filled and supported by the nickel positive electrode has at least a part of particles of nickel oxyhydroxide as a nucleus, and its surface is coated with cobalt oxyhydroxide and divalent. It is configured to be coated with a mixed system of cobalt oxides. That is, at least a portion of the nickel hydroxide constituting the nucleus of the electrode active material is previously converted to nickel oxyhydroxide, so that the discharge reserve on the negative electrode side can be reduced, and the portion can be used as a charge reserve. Therefore, damage to the negative electrode is reduced, and the life of the secondary battery and the increase in capacity are achieved.

According to the invention of claims 4 to 7, a nickel positive electrode for an alkaline secondary battery capable of reducing the discharge reserve on the negative electrode side, reducing the damage to the negative electrode, and extending the life and capacity of the secondary battery is provided. It can be provided easily and with good yield. In particular, in the inventions of claims 3 to 5, reactions such as nickel oxyhydroxide conversion and cobalt oxyhydroxide conversion proceed more smoothly, thereby improving productivity and quality.

According to the eighth aspect of the present invention, the provision of the nickel positive electrode makes it possible to provide an alkaline secondary battery having a long life and a high capacity.

[0031]

Embodiments of the present invention will be described below.

The non-sintered nickel positive electrode is, for example, a three-dimensionally porous metal substrate made of nickel fiber, positive electrode active material particles having an average particle size of about 10 μm filled and supported in the voids of the metal substrate, and It is composed of a binder resin such as polytetrafluoroethylene. Here, the positive electrode active material particles have a configuration in which nickel oxyhydroxide particles are used as a nucleus or core, and the outer peripheral surface thereof is coated with a mixed system of cobalt oxyhydroxide and a cobalt oxide having more than two valencies.

The above-mentioned positive electrode active material particles, that is, electrode active material particles having a structure in which nickel oxyhydroxide particles are used as a nucleus or core and the outer peripheral surface thereof is coated with a mixed system of cobalt oxyhydroxide and cobalt oxide having more than two valences, Can be obtained by the following means. For example, with respect to 100 parts by weight of nickel hydroxide particles having an average particle size of about 10 μm, 5 parts by weight of cobalt hydroxide having an average of about 1 μm is added and mixed, and the mixture is charged into a fluidized-bed granulator, while the mixture is infiltrated. 8N / l aqueous sodium hydroxide solution is added, and the mixture is stirred and mixed in the atmosphere.

In the process of stirring and mixing, a magnetron attached to the fluidized-bed granulator is operated to irradiate microwaves and heat at a temperature of 100 ° C. for 20 minutes.
By the above treatment, nickel hydroxide particles whose surface is coated with a mixed system of cobalt oxide having a valency of more than cobalt oxyhydroxide-2 are produced.

Next, the nickel hydroxide particles, the surface of which is coated with a mixed system of cobalt oxide having a valence of cobalt oxyhydroxide-2, are stirred while controlling the concentration of the aqueous sodium hypochlorite solution and the stirring time. . Thereafter, the mixture is filtered, washed with water, and dried, and the surface is coated with a mixed system of cobalt oxide having a valence of cobalt oxyhydroxide of at least two valences, and at least a part of nickel hydroxide constituting a core is converted to nickel oxyhydroxide. The prepared electrode active material particles are produced.
The structure and properties of the produced electrode active material particles were evaluated by SEM and EDX observation. The core particles were nickel oxyhydroxide, and the surface of the particles was cobalt oxide having a valence of more than cobalt oxyhydroxide-2. A mixed system of the products was formed uniformly.

Here, nickel hydroxide particles as a material,
And cobalt hydroxide particles, the average particle size is 7 to
About 18 μm, more preferably an average particle diameter of 10 to 15 μm
When particles having a specific surface area of about 5 to ²⁰ m ² / g by the BET method or those having a half-value width of about 0.85 ° to 1.00 ° in (101) in X-ray diffraction method are selected, Capacity and long life are promoted.

Next, an example of manufacturing a non-sintered nickel positive electrode (electrode) according to the embodiment will be described. First, nickel oxyhydroxide particles, the surface of which was coated with a mixed system 3 of cobalt oxide having a valence of cobalt oxyhydroxide-2 or more, polytetrafluoroethylene, carboxymethyl cellulose, sodium polyacrylate, and water as components. The prepared paste-like electrode active material is prepared. Next, the paste-like electrode active material is applied and filled onto a tape-like nickel fiber-based substrate prepared in advance, and then subjected to a drying treatment or a press working to obtain a non-fired nickel-metal hydride secondary battery. A molded nickel positive electrode is manufactured.

In the above-mentioned non-sintered nickel positive electrode, since the core of the electrode active material particles is partially converted to nickel oxyhydroxide in advance, it is necessary for oxidation of the positive electrode active material (nickel oxyhydroxide) in the first charge. The amount of charged electricity is not required, and as a result, the discharge reserve stored in the negative electrode is omitted.
Then, the omitted discharge reserve is used as a charge reserve for absorbing oxygen gas generated from the positive electrode at the negative electrode at the end of charging or at the time of overcharging, thereby suppressing an increase in the internal pressure of the sealed secondary battery. Contribute. Further, this charge reserve functions to suppress a decrease in discharge capacity due to a decrease in the active material utilization rate of the negative electrode during high-rate discharge (damage to the negative electrode).

Next, a non-sintered nickel positive electrode, a non-sintered hydrogen electrode (negative electrode) filled with and supporting a hydrogen storage alloy powder as an active material, and a separator made of a nonwoven fabric made of polyolefin fiber were used. The electromotive section element is manufactured. Thereafter, the electromotive section element is mounted in a battery outer can also serving as a negative electrode terminal, and an alkaline electrolyte is injected in such a manner as to impregnate the electromotive section element according to a conventional means, thereby assembling a nickel hydrogen secondary battery.

With respect to the nickel-metal hydride secondary battery, the following is used.
Charge at a constant current of 1C for 15 hours, and charge at a constant current of 1.0C.
In a charge / discharge cycle that discharges to a battery voltage of 1 V,
The pole not only exhibits high utilization efficiency of the electrode active material,
Capacitance reduction due to hydrogen electrode damage is suppressed and high performance
Has been confirmed. No such result
The tendency is that the average particle size is 7
About 18 μm, more preferably an average particle diameter of 10 to 15 μm
m, specific surface area by BET method is 5-20m ²/ G
Or half of (101) in X-ray diffraction
Nickel hydroxide particles with a value range of about 0.85 ° to 1.00 °
The same applies to the case where particles and cobalt hydroxide particles are selected.
there were.

The present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the invention. For example, the high-frequency, conductive non-sintered substrate material, or chemical oxidizing agent that becomes a radiant heat source when heat-treating cobalt species and nickel hydroxide in an alkaline aqueous solution should be replaced with other appropriate means. Can be.

[0042]

According to the first to third aspects of the present invention, at least a part of the nickel hydroxide constituting the nucleus of the electrode active material is:
With the nickel oxyhydroxide beforehand,
The discharge reserve on the negative electrode side is reduced. Further, since that amount can be used as a charge reserve, damage to the negative electrode is reduced, and a non-sintered nickel electrode capable of extending the life and increasing the capacity of the secondary battery is provided.

According to the fourth to seventh aspects of the present invention, it is possible to easily provide a nickel electrode for an alkaline secondary battery capable of achieving a longer life and a higher capacity of the secondary battery with a high yield.
In particular, according to the third to fifth aspects of the present invention, reactions such as nickel oxyhydroxide conversion and cobalt oxyhydroxide conversion proceed more smoothly, so that productivity and quality can be improved.

According to the sixth aspect of the present invention, there is provided an alkaline secondary battery having a long life and a high capacity.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G048 AA03 AB02 AB04 AB05 AC06 AD03 AE05 5H028 AA01 BB03 BB05 BB06 BB10 BB15 EE05 EE08 EE10 5H050 AA08 BA11 CA03 DA04 DA10 EA12 FA17 FA18 GA02 GA10 GA15 GA22 GA27 HA05 HA07

Claims (8)

[Claims] 1. An electroconductive non-sintered substrate, and electrode active material particles filled and supported on the non-sintered substrate, wherein the electrode active material particles have an outer peripheral surface of particles containing nickel oxyhydroxide. Is coated with a mixed system of cobalt oxyhydroxide and a cobalt oxide having more than two valences. 2. The non-electrode material according to claim 1, wherein the electrode active material particles are made by heat treatment with radiant heat in which cobalt hydroxide particles and nickel hydroxide particles coexist in an alkaline aqueous solution. Sintered nickel electrode. 3. The electrode active material particles have an average particle size of 7 to 18.
Cobalt hydroxide particles and nickel hydroxide particles having a specific surface area of 5 to ²⁰ m ² / g by the BET method or a half-width of 0.85 to 1.00 ° on the (101) plane in the X-ray diffraction method. The non-sintered nickel electrode according to claim 1, wherein the non-sintered nickel electrode is formed. 4. A step of subjecting cobalt hydroxide particles and nickel hydroxide particles to coexistence in an aqueous alkali solution and performing a heat treatment by radiant heat; and a step of producing the cobalt oxyhydroxide and the cobalt oxide having a valence of more than 2 produced by the heat treatment step. A step of chemically oxidizing the nickel hydroxide particles provided on the outer peripheral surface of the mixed system layer to form at least a part of the nickel hydroxide particles forming the nucleus into nickel oxyhydroxide; And filling and supporting the electrode active material particles forming a nucleus on a conductive non-sintered type substrate. 5. The method according to claim 4, wherein the cobalt hydroxide particles and the nickel hydroxide particles have an average particle diameter of 7 to 18 μm. 6. The cobalt hydroxide particles and the nickel hydroxide particles have a specific surface area of 5 to ²⁰ m ² / g by a BET method.
The method for producing a non-sintered nickel electrode according to claim 4, wherein 7. The non-coating material according to claim 4, wherein the cobalt hydroxide particles and the nickel hydroxide particles have a half value width of 0.85 to 1.00 ° in the (101) plane in the X-ray diffraction method. A method for producing a sintered nickel electrode. 8. A non-sintered positive electrode which is filled with and carries electrode active material particles whose outer peripheral surface containing nickel oxyhydroxide is coated with a mixed system of cobalt oxyhydroxide and a cobalt oxide having more than two valences; An alkali, comprising: a negative electrode arranged corresponding to the non-sintered positive electrode; a separator interposed between the non-sintered positive electrode and the negative electrode; and an alkaline electrolyte. Rechargeable battery.