JPH01281670A - Nickel electrode for alkaline battery - Google Patents

Abstract

PURPOSE:To shorten the forming time of a conductive network of CoOOH by using nickel hydroxide made by electrifying particles of Co or beta-Co(OH)2, causing them to adhere to the particle surface of nickel hydroxide particles and solidifying them by mechanical impact forces. CONSTITUTION:Particles of Co or beta-Co(OH)2 are uniformly distributed on the surface of nickel hydroxide (Ni(OH)2) particles. In this case, seed particles of Co or beta-Co(OH)2 are made to adhere to, enter, and not come off the surface layer of mother particles of Ni(OH)2 by electrostatic force. The seed particles made to adhere by giving them impact forces for a short period of time to the extent not to destroy the particies by means of a hybridizer are made to enter the surface layer of the mother particles. The mixture ratio of the mother particles Ni(OH)2 to the seed particles CoO or beta-Co(OH)2 is made 4-12weight% of the seed particles relative to the mother particles. This shortens the forming time of a conductive network of CoOOH.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to nickel electrodes for alkaline batteries.

Prior Art and its Problems Commonly used alkaline batteries use sintered electrodes and repeat the active material filling process many times, which is complicated and takes a long time, resulting in high costs.

Furthermore, since the porosity of the sintered substrate is practically limited to 80% or less, the packing density of the active material is low, and only electrodes with low energy density of about 400 mmh/cc can be produced.

As a proposal to improve these shortcomings, we propose a non-sintered type! ! There are poles. As described in JP-A No. 61-138458, a CoO powder that forms an active conductive network is added to a nickel hydroxide powder active material prepared from an aqueous solution of nickel sulfate and an aqueous IJ solution. It is created by adding a viscous liquid made by dissolving carboxymethyl cellulose in water and filling it in a paste state into an m-fiber substrate. This nickel electrode is considerably cheaper than the sintered type and has a high energy density of about 500mm and 4c. However, as the weight of l-tuple electronics equipment has become lighter in recent years, a high energy density of around 600" h/cc is required as a market need. In order to meet this need, the porosity of the substrate has to be limited. For this reason, it is necessary to increase the density of the nickel hydroxide powder itself.

The problem with conventional nickel hydroxide powder in densification is due to the disordered development of transition pores with a pore radius of 50 Å or more, as shown in the pore size distribution curve of nickel hydroxide powder particles in Figure 1. do.

The mechanized nickel particles are secondary particles that are a collection of fine particles.

The pores of the primary particles are micropores with a radius of 10 to 20 people,
Larger transition pores depend on the way the primary particles are backed.
That is, it depends on how primary particles grow into secondary particles. In particular, what determines the growth rate is the pH (alkali concentration) of the bath that converts nickel ions into nickel hydroxide.

With conventional methods, it is difficult to control the pH of the bath at the particle level, but a recently developed manufacturing method that uses nickel hydroxide as a raw material for bar rising treatment of iron plates can reduce the alkaline concentration of the bath to a low value. can be uniformly controlled. In this manufacturing method, nitric acid or nickel sulfate is dissolved in a weakly basic ammonia aqueous solution, and while being stabilized as a nickel ammine complex ion, nickel sulfate is hydroxylated.) An aqueous IJ solution is added, and pores are created inside the particles at an appropriate pH. In this method, nickel hydroxide is gradually deposited and grown to prevent the development of nickel hydroxide. Niacel hydroxide powder produced under appropriate conditions has particles with no development of transition pores, as shown in FIG. 1B, for example. By adding cadmium or the like in a solid solution state without changing the pore structure of this powder, a battery active material that can be used practically can be obtained.

However, an electrode made of this powder and a CoO additive
Although it has a capacity density of about 0.0121 mmh/cc, a high capacity density cannot be obtained unless the electrode is immersed in an alkaline electrolyte for one day or more. This immersion allows conductive Co to flow between the active material particles based on the reaction mechanism shown in Figure 2.
The connection is made using OOH particles, and it is desired to shorten this immersion-standing time and improve battery production efficiency.

Purpose of the Invention The present invention provides a method for using Co0OH in paste-type nickel electrodes.
The purpose of the present invention is to provide a nickel electrode with excellent production efficiency that shortens the time required to form a conductive network.

Structure of the Invention The present invention provides a paste-type nickel electrode in which a porous alkali-resistant metal fiber substrate is used as a current collector and the mechanized nickel powder is the main active material. This is a nickel electrode for alkaline batteries characterized by using nickel hydroxide in which two particles are attached by charging and fixed by mechanical impact force.

Further, the immobilized CoO or β-Co(OH)z particles are not in a solid solution state with the hydroxide elanal particles but in a free state in the above-mentioned nickel electrode for alkaline batteries.

Also, the amount of cobalt hydroxide is 4% relative to the amount of nickel hydroxide.
The above nickel electrode for alkaline batteries is in the range of ~12.

The reaction mechanism of the paste type nickel electrode is different from that of the sintered type nickel electrode. The sintered nickel electrode has a current collector made by sintering fine nickel powder, and its pore diameter is as small as 10-odd meters, so even nickel oxyhydroxide active material with low conductivity has a high active material utilization rate. can be obtained.

However, in the case of paste-type nickel electrodes, the active material, nickel hydroxide powder of several tens of pHl, must be directly filled into the current collector in the form of a paste liquid.
A large pore diameter of approximately 0μ is required. As the alternating layers of the current collector and the active material interlayer become longer, the active material utilization rate decreases significantly.

On the other hand, soluble CoO is added to the alkaline electrolyte and connected by conductive 0oOOH particles. this is,
CoO→HO002−;=β-Co(OH)2 In order to achieve uniform dispersion by the reaction, a standing period of one day or more is required.

CoO or β- is added to the surface of Nichel hydroxide particles in advance.
By uniformly dispersing the Co(OH)2 particles, the standing time is shortened. However, even if these particles are simply dispersed on the surface of the N1 (OE) 22 particles, they will easily peel off during paste liquid preparation due to poor binding properties, and uniform dispersion will be lost. CoO or β-Co(OH)2 child particles are attached to the surface by electrostatic force,
It digs into the surface layer of the base particle to prevent it from peeling off.

Figure 5 shows this modeling diagram.

Example Hereinafter, the details of the present invention will be explained using one example.

Ammonium nitrate is added to an aqueous solution of nickel nitrate and a small amount of cadmium nitrate to form an ammine complex ion of nickel and cadmium. This solution is dropped into an aqueous sodium hydroxide solution while being vigorously stirred to gradually decompose the complex ions. Hydroxide particles having an average particle diameter of about 20 pm, which are made into a solid solution of cadmium, are precipitated. As with the conventional method, when using a highly concentrated alkaline solution with a pH of 14 or higher, nickel hydroxide particles with disordered particle sizes will precipitate.
Separately precipitate at a temperature in the range of 20 to 90°C. This PH
Within this range, the higher the pH, the more porous the precipitated nickel hydroxide was. FIG. 4 shows the particle size distribution of the particles of the present invention and the particles of the conventional method. FIG. 4 shows that the particles of the present invention have a more uniform particle size than the particles of the conventional method. This result shows that the particles of the present invention do not precipitate in a disordered manner, but that the precipitation growth of the particles can be controlled.

Using the same equipment as above, the raw material was changed to cobalt sulfate salt, particle growth was stopped at about 0.3 to 1.0μ, and β-Co(O
H) Two particles were created. These particles were dehydrated in a high-temperature nitrogen atmosphere at 200 to 800°C to create CoO particles with low crystallinity.

Next, the mother particles Ni (OH) 2 and the child particles CoO or β-Co (OH) 2 were mixed using a commercially available ordered mixture dizer (0, Hoshi, Dizer).

At this time, the mixing ratio of child particles to mother particles is 4 to 12w.
%. The child particles were attached to the periphery of the mother particle using the electrostatic force of the powder charging phenomenon.

At this stage, the child particles are simply attached to the surface of the mother particle, so they are easily peeled off. In order to immobilize the attached child particles, an impact was applied for a short time (about 5 minutes) using a commercially available hyperdizer so as not to destroy the particles. As a result, the attached child particles were embedded in the surface layer of the mother particle.

A viscous aqueous solution containing 1% carboxymethyl cellulose was added to the active material powder obtained above and thoroughly kneaded to prepare a fluid paste solution. A predetermined amount of this paste liquid was filled into a sintered nickel fiber substrate with a porosity of 95≦, and after drying, a nickel electrode was obtained. Using this electrode,
The relationship between the storage conditions after injection of the alkaline electrolyte and the active material utilization rate was investigated. The nickel electrode was assembled using a cadmium electrode as a counter electrode with a 1-lipropylene nonwoven fabric separator interposed therebetween, without chemical conversion. A potassium hydroxide electrolyte having a specific gravity of 1.27 was injected into the battery to prepare a test battery. After injecting the electrolyte, the batteries were left under various conditions in order to dissolve the cobalt compound as an additive at a corrosive potential and to form connections between the nickel hydroxide powders.

FIG. 5 is a diagram examining the relationship between the standing time after electrolyte injection and the change in active material utilization rate. Here, 1 is a mixture of 000 particles using a conventional method, I is a mixture of β-Co(OH)2 particles embedded in a nickel hydroxide surface layer, and 1 Co0 particles embedded in a nickel hydroxide surface layer.

The nickel electrode of the present invention showed a high utilization rate even after being left for a short time. CoO has the highest utilization rate. Co at this
The difference in the utilization rate of O and β-co(OH)2 is due to the solubility in alkaline electrolyte, and in the case of β-(30(OH)2, it is oxidized by dissolved oxygen and becomes soluble. Poor Co0
This is because OH is formed.

Figure 6 shows the relationship between additive cutting, active material utilization rate, and energy density per plate volume.

From this result, increasing the amount of additive also improves the active material utilization rate. However, since the additive itself only contributes to conductivity and does not actually cause discharge, the best electrode plate energy density is around 10 wt%.

Effects of the Invention As described above, the present invention can provide a nickel electrode with excellent production efficiency in which the time required to form a conductive network of Co0OH in a paste-type nickel electrode is shortened, and therefore its industrial value is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a pore size distribution diagram of nickel hydroxide powder. FIG. 2 shows a modeling diagram of the conductive network formation mechanism of a cobalt compound additive in a paste-type nickel electrode. FIG. 3 models the production of particles of the invention. FIG. 4 shows the particle size distribution of the mechanized nickel powder. FIG. 5 is a diagram showing the relationship between the standing time after electrolyte injection and the active material utilization rate. FIG. 6 is a diagram showing the relationship between the amount of 000 added, the active material utilization rate, and the energy density per electrode plate volume.

Claims (4)

[Claims] (1) In a paste-type nickel electrode in which a porous alkali-resistant metal fiber substrate is used as a current collector and nickel hydroxide powder is the main active material, CoO or β-
A nickel electrode for alkaline batteries characterized by using nickel hydroxide to which Co(OH)_2 particles are attached by charging and fixed by mechanical impact force. (2) Immobilized CoO or β-Co(OH)_2
The nickel electrode for an alkaline battery according to claim 1, wherein the particles are not in a solid solution state with the nickel hydroxide particles but in a free state. (3) The amount of cobalt hydroxide is 4% compared to the amount of nickel hydroxide.
The nickel electrode for alkaline batteries according to claim 1, which has a content in the range of 12 wt%. (4) The nickel electrode for an alkaline battery according to claim 1, wherein the nickel hydroxide does not develop transition pores with a radius of 30 Å or more inside the particles and has a pore volume of 0.05 ml/g or less.