JPH0777129B2 - Nickel electrode active material and method for producing the same, nickel electrode and method for producing alkaline battery using the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to an active material for a nickel electrode, a nickel electrode, and an alkaline battery using the same.

2. Description of the Related Art Alkaline batteries generally used are referred to as "sintered batteries", in which nickel hydroxide is filled in a microporous substrate obtained by sintering nickel powder into a perforated steel plate or the like. This type of electrode is very complicated because the filling process is repeated many times, and the cost is high. Moreover, since the porosity of the substrate used is limited, the packing density of the active material is low and the energy density of the electrode is 40%.
Only about 0mAh / cc is possible.

Non-sintered electrodes have been widely developed as an attempt to improve this. For example, cobalt hydroxide-coated nickel hydroxide powder is mixed with 20% by weight of graphite powder as a conductive additive to form a sheet, which is then pressure-bonded to a nickel plate serving as a current collector to form an electrode. This conductive additive itself does not contribute to the capacity of the electrode, so the capacity density decreases,
In addition, a large amount of carbonate radicals are generated due to the decomposition of graphite. For this reason, it cannot be used in a battery with a small amount of electrolyte, such as a sealed nickel-cadmium battery. In order to overcome the above drawbacks, a paste type nickel electrode using a metal fiber substrate having a high porosity of 95% is being put to practical use. The electrode was prepared by adding nickel sulfate powder active material made from nickel sulfate aqueous solution and sodium hydroxide aqueous solution to a CoO powder forming an inter-active material conductive network, and dissolving carboxymethyl cellulose in water. It is prepared by adding a liquid and filling a fiber substrate in a paste state. This is cheaper than a sintered electrode and has an energy density of 50.
High at 0 mAh / cc.

However, as the weight of portable electronic devices has been reduced in recent years, a high energy density of about 600 mAh / cc is required as a market need. To address this,
Due to the limited porosity of the substrate, it is necessary to densify the nickel hydroxide powder itself. The high-density nickel hydroxide powder is used as a part of the raw material for the parkarizing treatment of iron plates. The production method is to dissolve nitric acid or nickel sulfate in a weakly basic aqueous ammonia solution to stabilize it as a nickel ammine complex ion, and add sodium hydroxide aqueous solution while gradually adding water so that pores do not develop inside the particles. This is to deposit nickel oxide.

This system is a high-density nickel hydroxide having high crystallinity with few grain boundaries (poor volume of pores) because it does not perform disordered precipitation unlike the conventional neutralization method.

However, due to this peculiar physical property, there are some problems in using this powder as an active material for a battery.

For example, the charge / discharge reaction of the nickel hydroxide electrode occurs due to free movement of protons in the nickel hydroxide crystal. However, due to the denseness of the crystal due to the densification of nickel hydroxide, the freedom of movement of protons in the crystal is restricted. In addition, the current density increases due to the decrease in the specific surface area, and a large amount of higher-order oxide γ-NiOOH is formed, which causes discharges such as two-stage discharge and electrode swelling and causes deterioration of life characteristics or a decrease in utilization rate. Become. The swelling mechanism associated with the formation of γ-NiOOH at the nickel electrode, which is a fatal factor of the electrode, is due to the density change from high density β-NiOOH to low density γ-NiOOH. As an effective means for preventing the formation of γ-NiOOH, the present inventor has already found that a small amount of cadmium is added as a solid solution to nickel hydroxide, but from the viewpoint of pollution, effective additives other than cadmium are desired.

OBJECT OF THE INVENTION The present invention densifies nickel hydroxide powder to a higher density, prevents the formation of γ-NiOOH with further densification by a less toxic additive, and prolongs the service life, while increasing the utilization rate of the active material. It is an object of the present invention to provide an improved active material for a nickel electrode, a nickel electrode, and an alkaline battery using the same.

The first aspect of the present invention is mainly composed of nickel hydroxide containing zinc in a solid solution state in a crystal, having an internal pore radius of 30Å or less and a total pore volume of 0.05 ml / g or less. It is an active material for nickel electrode.

A second aspect of the present invention is to use zinc hydroxide and a small amount of an aqueous solution of zinc sulfate as a starting material, and to precipitate zinc in a crystal by precipitating it in an aqueous solution controlled to PH 11 to 13 with caustic soda or potassium caustic and ammonium sulfate. A method for producing a nickel electrode active material mainly containing nickel hydroxide, which is contained in a solid solution state, has an internal pore radius of 30 Å or less, and has a total pore volume of 0.05 ml / g or less.

A third aspect of the present invention is mainly composed of a nickel hydroxide active material containing zinc in a solid solution state in a crystal, having an internal pore radius of 30Å or less and a total pore volume of 0.05 ml / g or less. Is a nickel electrode in which the alkali-resistant metal porous body is filled with the paste.

In a fourth aspect of the present invention, a cobalt compound which dissolves in an alkaline electrolyte to form a cobalt complex ion is added to the nickel hydroxide active material in an amount of 5 to 15 wt%, and the cobalt compound serves as the active material. It is a nickel electrode in a free state.

A fifth aspect of the present invention is a nickel electrode in which, in addition to zinc, a small amount of cobalt coexists in a solid solution state with the nickel hydroxide active material.

A sixth aspect of the present invention is a nickel electrode which does not contain a conductive additive and in which the conductivity between the alkali resistant metal porous body and the active material is maintained only by the cobalt compound additive.

The seventh aspect of the present invention is that the crystal contains zinc in a solid solution state, the internal pore radius is 30 Å or less, and the total pore volume is 0.05 ml.
/ g or less and a paste containing a nickel hydroxide active material as a main component to which a cobalt compound is added in a free state is prepared, and a nickel electrode filled in an alkali resistant metal porous body is prepared,
This is a method of manufacturing an alkaline battery in which the nickel electrode is assembled into a battery without chemical formation, the electrolyte solution is poured, the mixture is allowed to stand for a certain period of time, the cobalt compound is completely dissolved and reprecipitated, and then the initial charge is performed.

In the case of high-density nickel hydroxide powder with a minimum internal pore volume, a large amount of higher order oxide γ-NiOOH is generated. However, when dissimilar metal ions, especially zinc ions, are placed in the nickel hydroxide crystal, distortion occurs in the crystal, which increases the freedom of movement of protons and improves the utilization rate and γ-NiOOH.
It has been found that it has the effect of reducing the production of.

On the other hand, in the crystal outside of the nickel hydroxide to dissolve the cobalt compound additive, the current collector and between nickel hydroxide particles HCoO ₂ ^- charged after → β-Co (OH) is connected by _two reactions. Then, by β-Co (OH) ₂ → CoOOH reaction due to electrochemical oxidation called charging, it changes into cobalt oxyhydroxide with high conductivity, and the electron flow between the current collector nickel fiber and nickel hydroxide particles is changed. It has the effect of smoothing and increasing the utilization rate. This reaction mechanism is modeled and shown in FIG. As shown in the model diagram, the important point of this electrode is to dissolve the additive and connect the current collector nickel fiber and the active material.

Examples Hereinafter, details of the present invention will be described with reference to examples.

Ammonium sulfate is added to an aqueous solution of nickel sulfate with a small amount of zinc sulfate to form an ammine complex ion of nickel and zinc.

This solution is dripped into an aqueous solution of sodium hydroxide and vigorously stirred to gradually decompose complex ions to precipitate and grow nickel hydroxide particles in the form of solid solution of zinc. PH11 ~
Dilute the alkali concentration to about 13, and gradually precipitate it in the temperature range of 40-50 ° C. Depending on the pH of the precipitation solution, nickel hydroxide particles having various physical properties can be obtained.

Fig. 2 shows the relationship between the internal pore volume of the powder composed of only nickel hydroxide and the PH dependence of the γ-NiOOH production rate.

The lower the internal pore volume, the lower the PH and the more dense the powder. On the other hand, γ-NiOOH tends to be generated more easily as the pH becomes lower. The region that satisfies the two factors is the region between PH11 and 13 shown by the hatching sandwiched between the inflection points.

Fig. 3 shows the relationship between the pore volume and the specific surface area. The pore volume of nickel hydroxide changed by changing the pH of the precipitation solution, but at the same time, the specific surface area also changed. A to E are nickel hydroxide only, F is 5% zinc added in a solid solution state, and G is only nickel hydroxide by the conventional method.

The conventional method is a method in which nickel hydroxide particles are precipitated in a high-concentration alkali having a pH of 14 or higher.

In each case, the pore volume inside the particles tends to increase as the specific surface area increases. That is, there is a correlation between the specific surface area and the pore volume, and a high-density active material having a small pore volume has a small specific surface area regardless of the composition.

FIG. 4 shows a comparison of the pore size distributions of nickel hydroxide by the conventional method and the high density active material (nickel hydroxide) of the present invention calculated from the desorption side of the nitrogen adsorption isotherm.

Nickel hydroxide G prepared by the conventional method is obtained by dropping a nickel sulfate salt solution into a highly concentrated alkaline solution having a pH of 14.5 at 50 ° C.

This is present in a large amount over a wide range of specific surface area of about 65 m ² / g and pore diameter of 15 to 100 Å. Its volume is 0.15 ml / g
And the particle volume reaches 30-40% of the particle volume (0.41 ml / g), and it is a particle with considerably large voids. On the other hand, the high density nickel hydroxide (F) of the present invention has a small volume of 0.03 ml / g, which is only about 1/4 of G particles. This means that F particles are 2 more than G particles.
0-30% high density. That is, it is shown that in order for the active material particles to have a high density, the specific surface area and the pore volume should be as small as possible. These nickel hydroxide powders are dissolved in alkaline electrolyte and Co
(I) A small amount of cobalt compound, Co, which forms complex ions
Powders of O, α-Co (OH) ₂ , β-Co (OH) ₂ or cobalt acetate were mixed. Thereafter, an aqueous solution in which 1% carboxymethyl cellulose was dissolved was added to prepare a fluid paste liquid. A predetermined amount of this paste solution was filled in an alkali resistant fiber substrate having a porosity of 95%, such as a nickel fiber substrate, and dried to obtain a nickel electrode.

In order to know the utilization rate of the active material and the production rate of γ-NiOOH by charge and discharge, a cadmium electrode was assembled via a polypropylene non-woven fabric separator with this nickel electrode as a counter electrode, and a potassium hydroxide electrolytic solution having a specific gravity of 1.27 was injected. After injecting the electrolytic solution, the battery was left under various conditions in order to dissolve the cobalt compound as an additive at the corrosion potential and to connect the nickel hydroxide powders. FIG. 5 shows the relationship between the standing conditions and the active material utilization rate of a nickel hydroxide battery having a specific surface area of 65 m ² / g using CoO as an additive. The storage condition, which is an important process of forming a conductive network, shows that a high concentration electrolyte and a high temperature can obtain a high utilization rate in a short time, and that the amount of dissolved CoO is effective. Is shown. This is due to uniform dispersibility (more complete network formation) due to dissolution precipitation of the additive.

FIG. 6 shows the relationship between the type of nickel hydroxide and the utilization rate of the active material under the proper standing condition. When the active material composition is composed of only nickel hydroxide, there is a proportional relationship between the specific surface area and the active material utilization rate. This fact indicates that a high specific surface area is required to obtain a high active material utilization rate. This means that the low-density active material having a large pore volume is better than the result described above without repairing it, and ultimately the energy density of the electrode cannot be increased. However, F in which a small amount of zinc is added to the nickel hydroxide crystal shows a high utilization rate which is the same as that of the conventional powder G, although the specific surface area is small.
The energy density per unit volume of the electrode plate is
504 mAh / cc, high-density powder F is 620 mAh / cc, and high-density powder F is about 20% higher than conventional powder G. This is because the high-density powder can be filled in the same volume substrate more than the conventional powder. Since the active material utilization rate is close to the theoretical value, the pore volume of the high-density active material powder satisfying the required energy density of 600 mAh / cc must be 0.05 ml / g or less, and at the same time as the pore volume. The specific surface areas correlated with each other are 15 to 30 m ² / g. The effect of the addition of zinc is that the inlet and outlet of reactive species protons from the electrolyte are reduced due to the decrease in the specific surface area, but the nickel hydroxide crystals are distorted to smooth the proton transfer in the solid phase. It is considered as something. That is, the utilization rate means the amount of proton transfer. This is governed by two factors, the specific surface area of the particles and the diffusion rate inside the crystal (solid phase),
It is considered that when the crystals are the same, the specific surface area is dominated by the specific surface area, and when the crystals are different, the internal strain is dominated by the specific surface area. In order for the active material to react, it is necessary to smoothly move electrons from the current collector to the surface of the active material particle, and as described above, the conductive state in which the electron is in the free state (existing on the particle surface without solid solution in nickel hydroxide). A network of CoOOH particles with properties is essential. Figure 7 shows the amount of CoO added and the utilization rate of active materials.
The relationship with the energy density per electrode plate volume is shown. For CoO additives that make up this network, the active material utilization rate increases as the amount of additive increases. However, since the additive itself only contributes to conductivity and does not actually discharge, the electrode plate energy density tends to be lower than around 15%.

After charging at a high current density of 1 C, the electrode plate at the final stage of charging was examined by X-ray analysis for the correlation between the type of powder and the amount of γ-NiOOH produced. Fig. 8 shows the relationship between the amount of Zn added and the amount of γ-NiOOH produced.

It can be seen that when zinc is added in a solid solution state to nickel hydroxide crystals, the amount of γ-NiOOH produced decreases in inverse proportion to the amount added.

Fig. 9 shows γ- at the end of charging / discharging of various nickel hydroxides.
The production ratio of NiOOH is shown. The degree of the effect of suppressing the production of γ-NiOOH of zinc is also influenced by the manufacturing method of nickel hydroxide, and as shown in FIG. 9, it is different from the case of the conventional method.

Further, in the case of the conventional method, when 7% or more of zinc was added, a layer of nickel hydroxide and liberated zinc hydroxide appeared, but in the case of the present invention, it was not liberated to about 10%. It is known that the solubility of zinc in an alkaline aqueous solution depends on PH, and it is considered that it is more likely to form a solid solution in a thin alkaline aqueous solution as in the present invention. When free zinc hydroxide was present, a mixture of dissolved zinc complex ions and cobalt complex ions was precipitated during the dissolution-reprecipitation process of the cobalt oxide additive, and the conductivity was deteriorated, so that the utilization rate was lowered.

When the solid solution of zinc according to the present invention is used, it is possible to considerably discharge the γ-NiOOH, which has a poor reversibility as compared with the conventional method. This means that γ-NiOOH due to repeated charging and discharging
Can be further prevented and the life of the electrode can be extended. Thus, the effect of the solid solution additive is
It depends on the deposition conditions. However, it can be seen that, at least for the zinc of the present invention, the thin aqueous alkaline solution is superior to the conventional highly concentrated aqueous alkaline solution. In the case of high-density powder A containing no zinc, a large amount of γ-
Due to NiOOH, the discharge pressure is different from that of high-density powder F.
As shown in the figure, two-stage discharge is performed. Γ-from FIGS. 8 and 9
The effect of preventing the generation of NiOOH was recognized from the addition of 1% of zinc.
%, The γ-NiOOH disappears completely.

The effect of zinc has the same effect even when other different elements such as cobalt coexist in a solid solution state. FIG. 11 shows the relationship among the active material, the charge / discharge temperature and the active material utilization rate. In H containing both zinc and cobalt as a solid solution, an improvement in charging performance was observed at a higher temperature (about 45 ° C.) than in F containing zinc alone. Fig. 12 shows the relationship between the active material utilization rates of the additives that form the CoOOH network.

The rank of the active material utilization rate is CoO> α-Co (OH) ₂ > β-Co (OH) ₂
It is considered that the reason for becoming is due to the solubility in the electrolytic solution. That is, in the case of β-Co (OH) ₂ , it is easy to form brown poorly soluble Co (OH) _{3 which} is oxidized by dissolved oxygen after injection of the electrolytic solution, while α-Co (OH) ₂ is α. −Co (OH) ₂ → β−Co (OH)
Co (OH) ₃ is less likely to be formed because it passes through ₂ . CoO
In the case of, Co (OH) ₃ [or represented by CoHO ₂ ] is not formed at all, so it can be said that it is the most excellent additive. More specifically, from the viewpoint of the dissolution rate, it is desirable that β-Co (OH) ₂ is used as a starting material and heated and produced in a high temperature inert atmosphere at 200 to 800 ° C. to have low crystallinity.

HCoO ₂ nickel hydroxide ^- was immersed in ion, electrode powder pasted filling the formed cobalt hydroxide layer on the surface, even inferior utilization than the electrode obtained by mixing CoO powders, beta-C
It was about the electrode mixed with o (OH) ₂ powder. Further, a powder in which a conductive CoOOH layer was formed on the surface of nickel oxyhydroxide powder (specifically, after charging and discharging an electrode mixed with CoO powder, nickel fiber as a current collector was removed from the electrode). The electrode that is filled with paste again has a low utilization rate.
That is, the conductive network (Co
It is essential that OOH) be formed in the fabricated electrode. It shows that even if they are formed on the surface of the active material particles in advance, the connection between the particles becomes incomplete. Therefore, a step of dissolving and re-precipitating CoO powder after assembling the electrode as a battery is necessary.

The electrode prepared according to the present invention using the CoO additive reaches a high utilization rate close to the theoretical utilization rate by the dissolution-reprecipitation process without using a conductive additive, and thus the harmful carbonate group accompanying oxidative decomposition No formation, used for closed nickel cadmium.

In addition, although the metal fiber sintered body is shown as the substrate in the above embodiment, the substrate is not limited to these. further,
The effect of addition of zinc is similarly recognized for nickel hydroxide particles having high crystallinity, which are produced by various production methods as in the present invention.

EFFECTS OF THE INVENTION As described above, the present invention densifies nickel hydroxide powder more, prevents the formation of γ-NiOOH accompanying further densification with a less toxic additive, and prolongs the life of the active material. Since it is possible to provide an active material for a nickel electrode and a nickel electrode having an improved utilization rate and an alkaline battery using the same, the industrial value thereof is extremely large.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a model diagram of dissolution of a cobalt compound. Fig. 2 shows the precipitation solution PH, the particle internal pore volume and γ-NiOO.
It is a figure showing the correlation with the generation rate of H. FIG. 3 is a diagram showing the relationship between the specific surface area of nickel hydroxide particles and the pore volume. FIG. 4 is a diagram showing curves of pore size distributions of the conventional nickel hydroxide powder and the high-density nickel hydroxide powder of the present invention. FIG. 5 is a diagram showing the relationship between the standing condition and the active material utilization rate. FIG. 6 is a diagram showing the relationship between the type of nickel hydroxide and the active material utilization rate. FIG. 7 is a diagram showing the relationship between the amount of CoO added, the active material utilization rate, and the energy density per electrode plate volume. FIG. 8 shows the relationship between the amount of Zn added and the amount of γ-NiOOH produced. Fig. 9 shows γ at the end of charge and discharge of various nickel hydroxides.
It is a figure showing the generation ratio of -NiOOH. FIG. 10 is a diagram comparing the discharge pressure characteristics of the electrode produced in a large amount of γ-NiOOH and the electrode of the present invention. FIG. 11 is a diagram showing the relationship between the active material, the charge / discharge temperature, and the active material utilization rate. FIG. 12 is a diagram showing the relationship between various cobalt compound additives and the utilization rate of the active material.

Claims (7)

[Claims] 1. A nickel electrode active material mainly comprising nickel hydroxide, which contains zinc in a crystal in a solid solution state, has an internal pore radius of 30 Å or less, and has a total pore volume of 0.05 ml / g or less. material. 2. Zinc is dissolved in crystals by precipitating it from an aqueous solution of nickel hydroxide and a small amount of zinc sulfate aqueous solution as a starting material, and controlling the pH to 11 to 13 with caustic soda or potassium caustic and ammonium sulfate. A method for producing a nickel electrode active material mainly containing nickel hydroxide, which is contained in a state, has an internal pore radius of 30 Å or less, and has a total pore volume of 0.05 ml / g or less. 3. A paste containing a nickel hydroxide active material as a main component, which contains zinc in a solid solution state in a crystal, has an internal pore radius of 30 Å or less, and has a total pore volume of 0.05 ml / g or less. To
Nickel electrode filled in alkali resistant metal porous body. 4. A nickel compound, which is dissolved in an alkaline electrolyte to form a cobalt complex ion, is added to the nickel hydroxide active material in an amount of 5 to 15 wt%, and the cobalt compound is free from the active material. The nickel electrode according to claim 3, wherein 5. The nickel electrode according to claim 3, wherein, in addition to zinc, a small amount of cobalt coexists as a solid solution in the nickel hydroxide active material. 6. The nickel electrode according to claim 3, wherein the electroconductivity between the alkali-resistant metal porous body and the active material is maintained only by the cobalt compound additive without containing the electroconductive additive. 7. Nickel hydroxide containing zinc in a solid solution state in a crystal, having an internal pore radius of 30Å or less, a total pore volume of 0.05 ml / g or less, and a cobalt compound added in a free state. A paste containing an active material as a main component is prepared as a nickel electrode filled in an alkali-resistant metal porous body, and assembled into a battery without chemical conversion using the nickel electrode,
A method for producing an alkaline battery, in which the cobalt compound is allowed to stand for a certain period of time and then completely dissolved and reprecipitated, and then the battery is charged for the first time.