JPH02109261A - Active material for nickel electrode, nickel electrode, and alkaline battery using this electrode - Google Patents

Abstract

PURPOSE:To prevent formation of gamma-NiOOH with a less-poisonous additive by adding a specified amount of magnesium to nickel hydroxide powder active material so as to meet a specific condition in the crystal of nickel hydroxide and to increase the density of nickel hydroxide. CONSTITUTION:When high density nickel hydroxide powder whose inner pore volume is minimized is used, a large amount of gamma-NiOOH is produced. If different kind of ions, especially magnesium ions exist in the crystal of nickel hydroxide, crystal distortion arises and the formation of gamma-NiOOH is decreased. When 1-3wt.% magnesium is added to nickel hydroxide powder active material, magnesium forms solid solution in the crystal of nickel hydroxide and the growth of internal transition pores having a pore radius of 30Angstrom or less is retarded, and the total pore volume is controlled to 0.05ml/g or less. The density of nickel hydroxide powder is increased, and the formation of high density gamma- NiOOH is prevented with a less-poisonous additive.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to nickel w, an electrode active material, a nickel electrode, and an alkaline battery using the same.

Prior art and its problems - A. An alkaline battery using a Niracle electrode as a positive electrode is called a sintered battery, and is made by filling a microporous substrate made by sintering nickel powder into a perforated steel plate or the like and filling it with nickel hydroxide. be. This type of electrode requires a very complicated filling process that requires repeated filling steps, and is expensive. Moreover, since the porosity of the substrate used is limited, the packing density of the active material is low, and only electrodes with an energy density of about 40 D''h/cc can be manufactured.

In an attempt to improve this, non-sintered electrodes are being widely developed. For example, nickel hydroxide powder coated with cobalt hydroxide is mixed with 20 awt% graphite powder as a conductive additive, formed into a sheet shape, and then pressed onto a nickel plate as a current collector to form an electrode. Since this conductive additive itself does not contribute to the capacitance of the electrode, the capacitance density decreases and a large amount of carbonate radicals are generated due to the decomposition of graphite. For this reason, r/! ! It cannot be used in batteries with a small amount of electrolyte, such as closed nickel-cadmium batteries. In order to overcome the above drawbacks, a paste-type nickel electrode using a metal fiber substrate with a high porosity of 95% is being developed. The electrode is hydrated with a nickel sulfate aqueous solution) I
C00 powder, which forms a conductive network between active materials, is added to Niracle hydroxide powder active material prepared from a Jium aqueous solution, and a viscous solution of carboxymethyl hexarurose dissolved in water is added to form a paste into fibers. It is manufactured by filling a substrate. This type of electrode is cheaper than a sintered type electrode, and has a high energy density of 500'Ah/cc.

However, with the weight reduction of portable electronic devices in recent years, the market needs a high energy density of 600"h/cc. In order to meet this demand, there is a limit to the porosity of the substrate. Therefore, it is necessary to make the nickel hydroxide powder itself highly dense.High-density nickel hydroxide powder is used as part of the raw material for the parkerizing treatment of iron plates.The manufacturing method is to weaken nickel nitrate or nickel sulfate. It is dissolved in an ammonia aqueous solution containing a clay base, stabilized as a nickel ammine complex ion, and gradually precipitated as nickel hydroxide while adding an aqueous sodium hydroxide solution to prevent the development of pores inside the particles.

In this method, unlike the conventional neutralization method, disordered precipitation is not performed, so that the resulting nickel hydroxide has fewer grain boundaries and has high crystallinity (small pore volume) and high density.

However, due to its unique physical properties, there are several problems when using this powder as it is as an active material for batteries.

For example, the charge/discharge reaction of nickel hydroxide occurs due to the free movement of protons within the nickel hydroxide crystal. However, as the density of nickel hydroxide increases, the crystal becomes denser, which limits the freedom of proton movement within the crystal. Moreover, the current density increases due to the decrease in specific surface area, and a large amount of higher-order oxide γ-N100H is generated, resulting in two-stage discharge and discharge such as [Wl swelling], deterioration of life characteristics, or reduction in utilization rate. cause a phenomenon. γ− of nickel electrodes, which is a fatal factor for electrodes
NiOO1 (swelling am*ti due to formation, high density 19-N
This is due to the density change to i0OH force a density r −) JiOOH. The present inventor has already discovered the addition of a small amount of cadmium as a solid solution to nickel hydroxide as an effective means for preventing the formation of γ-Ni0OH, but from the standpoint of pollution, effective additives other than cadmium are desired.

Purpose of the Invention The present invention aims to increase the density of nickel hydroxide powder, prevent the formation of γ-NiOOH due to the increased density using less toxic additives, extend its lifespan, and increase the utilization rate of active materials. The purpose of the present invention is to provide an improved active material for a nickel electrode, a nickel electrode, and an alkaline battery using the same. The magnesium is present in solid solution in the crystals of nickel hydroxide, inhibits the development of intraparticle pores with a pore radius of 50 Å or more, and further reduces the total pore volume to 0.05"/ This is an active material for a nickel electrode, characterized in that it is controlled to 9 or less.

In addition, a porous alkali-resistant metal fiber substrate is used as a current collector,
1-5wt of magnesium in nickel hydroxide powder active material
% and the magnesium is in a solid solution state in the crystals of nickel hydroxide.It is a nickel A[pole] characterized by being filled with a paste containing a nickel WL electrode active material as a main component.

In the case of a high-density nickel hydroxide powder with a minimized internal pore volume, a large amount of higher order oxide γ-NiOOH is produced.

However, when dissimilar metal ions, especially magnesium ions, are placed in the nickel hydroxide crystal, distortion occurs in the crystal, which increases the freedom of movement of the nickel hydroxide, improving the utilization rate and reducing the formation of γ-NiOH. I found that it works.

It was generally said that the addition of magnesium would have an adverse effect on nickel, but it has become clear that an extremely high-performance electrode can be obtained by adding a trace amount of 1 to 3 wt%.

On the other hand, outside the crystal of nickel hydroxide, a cobal) compound additive is dissolved, and the current collector and the nickel hydroxide particles are bonded through a 1(CiO02-+β-Co(OH)2 reaction) and then charged. After that, β-C is produced by electrochemical oxidation called charging.

Through the (OH)2→0oOOH reaction, it changes to cobalt oxyhydroxide, which has high conductivity, smoothes the flow of electrons between the current collector nickel fibers and the nickel hydroxide particles, and has the effect of increasing the utilization rate. This reaction mechanism is modeled and shown in Figure 1. As shown in the model diagram, the important point of this electrode is to dissolve the additive and connect the current collector nickel fibers and the active material.

EXAMPLES Hereinafter, details of the present invention will be explained using examples.

Ammonium sulfate is added to an aqueous solution of nickel sulfate and a small amount of magnesium sulfate to form nickel/l' and magnesium ammine anchor ions.

This solution is dropped into an aqueous sodium hydroxide solution while being vigorously stirred to gradually decompose the complex ions and to precipitate and grow nickel hydroxide particles containing magnesium as a solid solution. At this time, the aqueous sodium hydroxide solution is made to have a low alkaline concentration of about PHII to 13, and the temperature is in the range of 40 to 50°C to gradually precipitate. Nickel hydroxide particles with various physical properties can be obtained depending on the pH of the precipitation solution.

FIG. 2 shows the relationship between the internal pore volume of a powder consisting only of nickel hydroxide and the PH survival rate of γ-NiOOH.

The internal pore volume has a low FT (fewer FT), resulting in a denser powder. On the other hand, γ-NiOOH has a low PI (poor volume) and tends to form easily.
This is a region from around PH11 to around PH13 shown by hatching between each inflection point.

FIG. 6 shows the relationship between pore volume and specific surface area.

By changing the pH of the precipitation solution, the pore volume of nickel hydroxide changed, but at the same time, the specific surface area also changed. A
-E is only nickel hydroxide, F is added in a solid solution state of 3 wt % magnesium, and G is only nickel hydroxide according to the conventional method.

Note that the conventional method is one in which nickel hydroxide particles are precipitated in a highly concentrated alkali having a pH of 14 or higher.

All of them show a tendency for the pore volume inside the particles 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 with a small pore volume has a small specific surface area regardless of whether magnesium is added or not.

FIG. 4 shows a comparison of the pore size distributions of nickel hydroxide produced by the conventional method and the magnesium-added high-density Niracle hydroxide active material produced by the present invention.

Nickel hydroxide G produced by the conventional method is obtained by dropping an aqueous nickel sulfate salt solution into a highly concentrated alkaline solution of pH-14.5 at 50° C. to precipitate it.

0 particles have a specific surface area of approximately 66 rr17g and a pore radius of 1
They exist in large numbers, ranging from 5 to 100 people. Its pore volume is o, 1b6zlyy and particle volume (0,4
It is a particle with considerably large voids, reaching 30 to 40% of the total porosity. On the other hand, the magnesium-added high-density nickel hydroxide F of the present invention has a small volume of 0.028"/9, which is only about % of 0 particles. This means that 1 particle is 20 to 30% larger than 0 particles. This means that it is highly dense.

That is, in order for the active material particles to have high density, the specific surface area and pore volume must be as small as possible. These nickel hydroxide powders contain a small amount of cobalt compound, Coo, a-Co(OH)2, which dissolves in an alkaline electrolyte to form Go(1) complex ions.
, β-Go(OH) 2 or Kobal II acetate powder were mixed. Thereafter, an aqueous solution in which 1% carboxymethyl cellulose was dissolved was added to prepare a fluid base (2). A predetermined amount of this paste liquid was filled into an alkali-resistant fiber substrate having a porosity of 95%, such as a nickel fiber substrate, and after drying, a nickel electrode was prepared.

In order to know the active material utilization rate and the production rate of γ-NiOOH due to charging and discharging, this nickel electrode was used as a positive electrode, and a cadmium electrode was assembled as a counter electrode with a polypropylene nonwoven fabric separator interposed therebetween, and a potassium hydroxide aqueous solution with a specific gravity of 1.27 was electrolyzed. Injected as a liquid. 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. Figure 5 shows a specific surface area of 66 using CtoO as an additive.
The relationship between the storage conditions and the active material utilization rate for a battery manufactured using nickel hydroxide powder of rrl/9 is shown. The leaving conditions, which are important processes for conductive network formation, are as follows:
It is shown that a high concentration electrolyte and high temperature can provide a high utilization rate in a short period of time, and that the amount of dissolved 000 is effective. This is due to the uniform dispersibility (more complete network formation) of the additives due to solution deposition.

Figure 6 shows the relationship between various types of nickel hydroxide and active material utilization under appropriate storage conditions. In A to G, the active material composition of which is 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 necessary to obtain a high active material utilization rate. Therefore, from the relationship between specific surface area and pore volume mentioned above,
In order to obtain a higher active material utilization rate, it is better to use a low-density active material with a larger pore volume, which means that it is ultimately impossible to achieve a higher energy density in the electrode. Become. Since the active material utilization rate is close to the theoretical value, the pore volume of the high-density active material powder that satisfies the required energy density of 600 n'Ah/cc is 0.05.
%, and the specific surface area, which correlates with the pore volume, is 15-30'/9.

However, F, which is made by adding a small amount of magnesium to nickel hydroxide crystals, has a small specific surface area;
It shows the same high utilization rate as conventional powder G. Compared to conventional powder, more high-density powder can be filled into the same volume of substrate, so the energy density per unit volume of the electrode plate is 504 Ah/ct for conventional powder G and 6 for high-density powder F.
The high-density powder F has a value of 20''IA, h/cc that is about 20% higher than that of the conventional powder G.

As the specific surface area decreases due to the high density of the active material, the entrance and exit for reactive species protons from the electrolyte decreases.
It is thought that the addition of magnesium creates strain in the nickel hydroxide crystal, which makes proton transfer in the solid phase smoother. In other words, the utilization rate can be said to mean the amount of proton movement. This is controlled by two factors: the specific surface area of the particles and the diffusion rate inside the crystal (solid phase).If the crystals are the same, it is controlled by the specific surface area, and if the crystals are different, it is controlled by the internal strain. It is considered that it will be done. 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 particles, and as mentioned above, the conductivity in the free state (existing on the particle surface without being dissolved in nickel hydroxide) A network of CooOH particles with properties is essential. Regarding the coo B machining that creates this network, increasing the amount of additive also increases the active material utilization rate. However, since the additive itself only contributes to conductivity and does not actually discharge,
The plate energy density shows a tendency to decrease from around 15%.

Charging at a high current density of 1C, γ at the plate in the 1* charging period
The correlation between -NiOOH yield and 11@ of the active material powder was investigated by X-ray analysis. The X-ray diffraction peaks are shown in FIG.

As shown in Figure 9, if magnesium is added as a solid solution in the crystals of nickel hydroxide, as the amount added increases, γ-
It can be seen that the amount of NiOOH produced decreases.

The effect of magnesium in suppressing the production of γ-NiOOH is also influenced by the method of producing nickel hydroxide, that is, the precipitation pH, and as shown in FIG. 10, it is different from that produced by the conventional method. In particular, in the case of the present invention, γ-NiO, which has poor reversibility, exists at the end of filling compared to the conventional method.
The feature is that 60 to 50% of OH can be discharged.

By this, γ-NiOO due to repeated charging and discharging
Accumulation of H can be further prevented, and the life of the electrode can be extended. In this way, the effect of the solid solution additive changes depending on the active material precipitation conditions. However, it can be seen that at least in the case of adding magnesium according to the present invention, precipitation in a dilute aqueous alkaline solution is better than precipitation in a conventional high concentration aqueous alkaline solution.

Figure 11 shows the relationship between the γ-NiOOH production rate and changes in electrode thickness in an overcharged state. The higher the γ-NiOOH production rate, the greater the electrode plate thickness. In order to obtain this, it is necessary to suppress the formation of γ-NiOOH, and it can be seen that addition of magnesium is very effective in this respect as well.

In addition, in the case of the conventional method, when 1 wt% or more of magnesium was added, a layer of nickel hydroxide and free magnesium hydroxide appeared, but various instrumental analyzes revealed that with the present invention, the separation does not occur up to about 3 wt%. became.

Furthermore, the addition of a large amount of magnesium increases the oxidation potential of nickel hydroxide to j!, as shown in FIG. In order to reduce the potential difference with the oxygen generation potential by shifting to 1, a competitive reaction between the oxidation reaction of nickel hydroxide and the oxygen generation reaction during charging tends to occur from the early stage of charging, and the so-called charging performance deteriorates.

Furthermore, the liberated magnesium becomes a9(OH)2 and also inhibits the charge/discharge reaction. Therefore, as shown in FIG.
The reason why the formation prevention effect appears to be large is because the active material is well charged.As evidence of this, in FIG. 16, a rapid decrease in the active material utilization rate is seen when 6 wt% or more is added.

In the case of high-density powder A that does not contain magnesium and produces a large amount of 1-Ni0OH, a two-stage discharge occurs as shown in Fig. 14, but in the case of high-density powder with magnesium addition, 1-Ni0
This does not occur because OH generation is prevented. Furthermore, it can be seen that by adding magnesium, the reduction potential of Ni0OH, which is an active material, shifts to the negative side, as in the case of charging. There have been few reports of a shift in the redox potential in the negative direction with Nickel/L/electrode additives due to negligence.
This can be said to be a major feature of magnesium addition.

Therefore, when a battery is manufactured using the magnesium-added high-density powder as a positive electrode, a battery with a high discharge voltage can be obtained.

Although detailed studies have not been conducted on this shift in redox potential, as mentioned above, the addition of magnesium causes strain in the nickel hydroxide crystal, resulting in smoother diffusion of protons within the solid phase. It is considered that.

This effect of magnesium is the same even if other different elements such as cobalt coexist in a solid solution state. 1st
Figure 5 shows the relationship among active materials, charge/discharge temperatures, and active material utilization rates.

In H, in which both magnesium and cobalt are added as a solid solution, the temperature at a higher temperature (approximately 45
An improvement in charging performance was observed at temperatures (℃). Furthermore, as shown in Figure 11, γ-NiO01 (
It was effective in preventing generation.

FIG. 16 shows the relationship between active material utilization rates for additives that form a Co0OH network.

The order of active material utilization rate is Coo>β-Co(OH)2>β
The reason why it becomes -Co(OH)2 is thought to be due to its solubility in the electrolytic solution. In the case of β-Co(OH)2, it is easily oxidized by dissolved oxygen after injection of the W and # solution, and brown, less soluble Co(OH)3 (or oxidized with C10HO2) is easily formed. On the other hand, a -CO(OH)2
In the case of (1-00(OH)2→β-00(OH)2), C1o(OH)3 is more difficult to form.

In the case of COO, it can be said to be the most excellent additive because Co(Ol()x is not formed at all.More specifically,
Melt! From the viewpoint of i\ rate, it is desirable to use β-Co(OH)2 as a starting material by heating it in an inert atmosphere at a high temperature of 200 to 800°C and have a low degree of crystallinity.

1 Filled with a paste of powder that is immersed in nickel hydroxide Ho2O3 ions and has cobalt hydroxide precipitated on the surface.
The c-electrode had a lower utilization rate than the electrode mixed with 000 powder, and was comparable to the electrode mixed with β-Co(OR)2 powder. Furthermore, conductive 0 is applied to the surface of the nickel oxyhydroxide powder.
The t-pole, which is filled with paste again with the powder that formed the oOOH layer (specifically, the nickel fiber that is the current collector is removed from the electrode after charging and discharging the electrode mixed with C00 powder), cannot be used. Bad rate.

That is, a conductive network (C
oOOl() has been created! It is essential that it be formed in the poles. In other words, this indicates that even if they are formed on the surfaces of the active material particles in advance, the connections between the particles are incomplete. Therefore, after assembling the electrode as a battery, a process of dissolving and redepositing the K coo powder is required.

Electrodes made according to the present invention using Coo additives are
Even if a conductive additive is used, a high utilization rate close to the theoretical one can be reached through the dissolution-re-precipitation process. It does not produce carbonate radicals and can be used as the positive electrode of sealed nickel-cadmium batteries.

In the above embodiments, a metal fiber sintered body is used as the substrate, but the present invention is not limited thereto. Furthermore,
In addition to the production method of the present invention, the effect of adding magnesium is also great for chive hydroxide with high crystallinity.

Effects of the Invention As described above, the present invention increases the density of nickel hydroxide powder, prevents the formation of γ-NiOO) due to the increase in density using additives with low toxicity, extends the life of the powder, and increases its activity. Since it is possible to improve the utilization rate of materials and provide a nickel 11Ei active material and a nickel electrode with a high tt level and an alkaline battery using the same, its industrial value is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a model diagram of the dissolution-precipitation mechanism of a cobalt compound. Figure 2 shows the precipitation solution PH, particle internal pore volume, and γ-N.
FIG. 3 is a diagram showing the correlation with the production rate of iOOH. FIG. 5 is a diagram showing the relationship between the specific surface area and pore volume of nickel hydroxide particles. FIG. 4 is a diagram showing pore size distribution curves of a conventional nickel hydroxide powder and a high-density nickel hydroxide powder of the present invention. FIG. 5 is a diagram showing the relationship between storage conditions and 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 X-ray diffraction peaks of various magnesium-added high-density powder active materials at the end of charging. FIG. 9 shows the relationship between the amount of magnesium added and the amount of γ-N±○○H produced. FIG. 10 is a diagram showing the production ratio of γ-NiOOH at the final stage of charging and discharging of various nickel hydroxides. FIG. 11 is a diagram showing the 7--Ni0OH production rate and electrode thickness increase rate when an electrode using an active material containing various additives is overcharged. FIG. 12 shows charging potential characteristics of various magnesium-added electrodes. FIG. 13 is a diagram showing the relationship between the amount of magnesium added and the active material utilization rate. FIG. 14 shows the discharge potential characteristics of various magnesium-added electrodes. FIG. 15 is a diagram showing the relationship among active materials, charge/discharge temperatures, and active material utilization rates. FIG. 16 is a diagram showing the relationship between various cobalt compound additives and the utilization rate of the active material.

Claims (7)

[Claims] (1) Magnesium 1 to 3 in nickel hydroxide powder active material
wt%, the magnesium is in a solid solution state in the crystal of nickel hydroxide, inhibits the development of internal transition pores with a pore radius of 30 Å or more, and further reduces the total pore volume to 0.05 m
An active material for a nickel electrode, characterized in that it is controlled to 1/g or less. (2) A porous alkali-resistant metal fiber substrate is used as a current collector, and 1 to 3 w of magnesium is added to the nickel hydroxide powder active material.
A nickel electrode characterized in that it is filled with a paste whose main component is an active material for a nickel electrode in which magnesium is added in a solid solution state in crystals of nickel hydroxide. (3) A patent claim in which an active material powder containing nickel hydroxide and a small amount of magnesium is precipitated in an aqueous solution whose pH is controlled to 11 to 13 with caustic soda or caustic potassium and ammonium sulfate, using an aqueous sulfate solution thereof as a starting material. The active material for a nickel electrode according to item 1. (4) A cobalt compound that dissolves in an alkaline electrolyte to generate cobalt complex ions is added to a nickel hydroxide active material powder containing magnesium in a solid solution state in a range of 5 to 15 wt%, and the cobalt compound powder is The nickel electrode according to claim 2, which is in a free state with the active material powder. (5) The nickel electrode according to claim 2, in which a small amount of cobalt in addition to magnesium coexists in a solid solution state. (6) The nickel electrode according to claim 2, in which the conductivity between the nickel fiber and the active material is maintained only by the cobalt compound additive without containing a conductive additive. (7) Assemble a battery using the nickel electrode described in claim 2 without chemical conversion, and leave it for at least one day after pouring the electrolyte to completely dissolve and reprecipitate the cobalt compound additive before charging it for the first time. An alkaline battery characterized by: