JPH0638336B2 - Nickel electrode for alkaline batteries - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a nickel electrode for alkaline batteries and a battery using the same.

Conventional technology and its problems The commonly used nickel electrode of an alkaline battery is called an electrode for firing, and its manufacturing method is to impregnate a nickel nitrate salt solution into a microporous substrate obtained by sintering ordinary nickel powder on a perforated steel plate or the like. Then, the step of changing to nickel hydroxide in an alkaline solution is repeated several times to fill a predetermined amount of nickel hydroxide.

However, this filling method is very complicated because the process is repeated many times, which is one of the causes for increasing the cost. Moreover, since the porosity of the substrate used is practically limited to 80% or less, the packing density of the active material is low and the energy density of the electrode is low.
The current situation is that only low products of 400 mAh / cc can be produced.

Non-sintered electrodes have been widely developed as an attempt to improve this drawback. For example, as disclosed in JP-A-56-59460, 20% by weight of graphite powder as a conductive additive is mixed with cobalt hydroxide-coated nickel hydroxide powder, and the mixture is pressed into a sheet, and then the current is collected. The nickel plate, which is the body, is pressure-bonded to both sides to form electrodes. This electrode requires a large amount of graphite, which is a conductive additive, similar to the pocket type electrode. Since the conductive additive itself does not contribute to the capacity of the electrode, the capacity density decreases, and a large amount of carbonate radicals are generated due to the decomposition of graphite, so that it is suitable for batteries with a small amount of electrolyte such as a sealed nickel-cadmium battery. It has the drawback that it cannot be used. As a method for overcoming the above-mentioned drawbacks, for example, an alternative to the above-mentioned substrate 95
%, A basted nickel electrode that can be filled in one time using a metal fiber substrate having a high porosity without repeating the step of filling the nickel hydroxide powder is being put to practical use.

The above-mentioned paste type nickel electrode is disclosed in JP-A-61-13845.
As disclosed in No. 8, CoO which forms a conductive network between active substances in a nickel hydroxide powder active material prepared from an aqueous solution of nickel nitrate and an aqueous solution of sodium hydroxide.
It is prepared by adding a powder, adding a viscous liquid in which carboxymethyl cellulose is dissolved in water, and filling a fiber substrate in a paste state. Compared with the sintered type, this nickel electrode is much cheaper and has an energy density as high as 500 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. In order to meet this need, since the porosity of the substrate is limited, it is necessary to densify the nickel hydroxide powder itself.

The high-density nickel hydroxide powder is generally used as a part of the raw material for the parkarizing treatment of the iron plate, and its manufacturing method is to dissolve nickel nitrate, nickel sulfate or nickel chloride in a weakly basic aqueous ammonia solution, It is stabilized as a complex ion, and nickel hydroxide is gradually deposited while adding an aqueous solution of sodium hydroxide so that pores do not develop inside the particles. However, 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 (H ⁺ ) in the nickel hydroxide crystal.

However, due to the denseness of the crystal accompanying the densification of nickel hydroxide, the freedom of movement of protons in the crystal is restricted,
In addition, the decrease in the specific surface area increases the current density, and a large amount of higher-order oxide γ-NiOOH, which causes discharges such as two-stage discharge and electrode swelling and deterioration of life characteristics, is generated. The swelling mechanism associated with the γ-NiOOH formation of the nickel electrode is due to the density change from high density β-NiOOH to low density γ-NiOOH, J. Appl. Electrochem., 16 , 403 (1
986) and J. Power Scurces, 12, 219 (1984).

OBJECT OF THE INVENTION The present invention densifies nickel hydroxide powder to a higher density, prevents the formation of higher-order oxide γ-NiOOH, improves the active material utilization rate, has a high energy density, and a long-life nickel electrode and the same. The present invention provides an alkaline battery using.

According to the present invention, in a paste-type nickel electrode having a porous alkali-resistant metal fiber substrate as a current collector and nickel hydroxide powder as a main component of an active material, the nickel hydroxide powder has an internal transition with a radius of 30 Å or more. A nickel electrode for an alkaline battery, which is characterized in that the development of pores is prevented and the pore volume is set to 0.05 ml / g or less.

In addition, the active material powder is obtained by precipitating nickel sulfate in an aqueous solution whose pH is controlled in the range of 11 to 13 with sodium hydroxide or potassium hydroxide and ammonium sulfate.

The nickel electrode for an alkaline battery, wherein the nickel hydroxide active material contains 2 to 7 wt% of cadmium, and cadmium is in a solid solution state in the crystals of nickel hydroxide.

In addition, the nickel electrode was built into the battery without chemical conversion,
The alkaline battery using the nickel electrode is characterized in that the electrolytic solution is left to stand for one day or more to completely dissolve and re-precipitate the cobalt compound in the electrode, and then the battery is charged for the first time.

High-density nickel hydroxide powder with a minimum internal pore volume produces a large amount of higher-order oxide γ-NiOOH, but when dissimilar metal ions, especially cadmium ions, are placed in the nickel hydroxide crystal, it forms crystals. It has the effect of causing distortion, increasing the freedom of movement of the protons and reducing the structure of the utilization rate and the production of γ-NiOOH.

On the other hand, outside the crystal of nickel hydroxide, when the cobalt compound additive is dissolved and the current collector and the nickel hydroxide particles are connected by the HCoO ₂ ⁻ → β-Co (OH) ₂ reaction and then charged, β -Co (OH) ₂ → CoOOH changes into highly conductive cobalt oxyhydroxide, smoothes the flow of electrons between the current collector nickel fibers and nickel hydroxide particles, and increases the utilization rate of the active material. There is. The modeling of this reaction mechanism is shown in FIG.

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 cadmium sulfate to form an ammine complex ion of nickel and cadmium. The 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 cadmium. As in the prior art, in a high-concentration alkaline solution having a pH of 14 or more, only nickel hydroxide particles are randomly deposited and the pore volume increases. Therefore,
The pH is set to a low alkali concentration of about 11 to 13, and the temperature is 20 to 9
Gradually precipitate in the range of 0 ° C. By varying pH and temperature, nickel hydroxide particles with various specific surface areas, pore volumes and crystallinity were obtained.

The influence on the nickel hydroxide precipitated particles was affected more by the alkali strength than the temperature. FIG. 2 is a diagram in which the internal pore volume is taken as the structural property, the production rate of γ-NiOOH is taken as the crystal structure, and the correlation with the alkaline strength (PH) of the precipitation bath is investigated. The production rate of γ-NiOOH was obtained at the final stage of charging by integrating the characteristic peaks of X-rays of β-NiOOH and γ-NiOOH, while the internal pore volume was 300 from the adsorption isotherm of nitrogen.
Å It was calculated by integrating up to the pore size. It can be seen that the most important effect of preventing the formation of γ-NiOOH is around pH = 11 or more. However, it is impossible to completely prevent it, and the limit is to reduce it to about 30%. Γ-Ni with increasing PH
OOH is reduced, but internal pore volume of the particles is increased. Therefore, it is a change point of both curves shown by hatching in FIG.
It can be seen that there is an appropriate area from around 11 to around 13 of PH. The reason why γ-NiOOH is likely to be formed in the low alkaline strength region is presumed as follows.

As is well known, it is known that nickel hydroxide, which easily produces γ-NiOOH, is α type, and β type is difficult to produce. This α type is produced with low alkaline strength and has a high alkaline strength, such as an ordinary battery electrolyte (PH = 14.3).
In the above), it is said to change to β type, but from this result it is presumed that even if it changes to β type, it has the habit of α type crystal at the time of starting. Next, the composition of the active material was changed, and the results of examining the correlation with the specific surface area are shown in FIG.

A, B, C, D, E are nickel hydroxide only, F is 5%
Is added in a solid solution state, and G is only nickel hydroxide prepared by the conventional method.

There is a correlation between the specific surface area and the pore volume, and the pore volume inside the particles tends to increase as the specific surface area increases. It can be said that a high-density active material with a small pore volume is destined to have a small specific surface area without being repaired.

According to a well-known conventional method, the nickel nitrate salt solution is heated to 90 ° C.,
The pore size distribution of about 70 m ² / g of nickel hydroxide deposited by dropping in a high-concentration alkaline solution of PH = 14.5 is shown in G of FIG. 4, and the pore size distribution of the high-density active material F is shown in FIG. No. F. The pores of the powder G deposited by the conventional method are large and disordered over a wide range with a pore radius of 15 to 100 Å, and the volume is 0.15 ml / g and the particle volume (0.41 ml / g).
Of 30 to 40%, indicating that the particles have considerably large voids. On the other hand, in the case of F particles, the volume is as small as 0.04 ml / g, which is only about 1/4 of G particles.
The results show that the F particles are 20-30% more dense than the G particles.

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.

A small amount of a cobalt compound, Co, which forms Co (II) complex ions when dissolved in an alkaline electrolyte in these nickel hydroxide powders, Co
Mix powders such as O, α-Co (OH) ₂ , β-Co (OH) ₂ or cobalt acetate, and then add a 1% aqueous solution of carboxymethyl cellulose to prepare a fluid paste solution. did. 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, dried and press-molded to obtain a nickel electrode.

In order to know the active material utilization rate and the production rate of γ-NiOOH by charge and discharge, without forming this nickel electrode, assemble via a polypropylene nonwoven fabric separator with the cadmium electrode as the counter electrode, inject the potassium hydroxide electrolyte, And After injecting the electrolytic solution, a cobalt compound as an additive was dissolved at a corrosion potential and left under various conditions in order to connect the nickel hydroxide powders. Additive CoO and specific surface area 7
FIG. 5 shows the relationship between the standing conditions and the active material utilization rate, using 0 m ² / g of nickel hydroxide. The standing condition, which is an important step of forming the conductive network, shows that the higher the concentration of the electrolytic solution and the higher the temperature, the higher the utilization factor of the active material can be obtained in a short period of time, and the amount of dissolved CoO acts effectively. It indicates that Furthermore, this cause is caused by cobalt E. P. M. A. From the photograph (Fig. 6), it is shown that the dissolution and precipitation of the additive results in uniform dispersibility (more complete network formation).

FIG. 7 shows the relationship between the type of nickel hydroxide and the utilization rate of the active material under appropriate standing conditions.

When the active material composition is composed only of nickel hydroxide, there is a proportional relationship. This fact indicates that a high specific surface area is required to obtain a high utilization ratio of the active material,
It means that a low-density active material having a large pore volume is better without being repaired. However, F in which a small amount of cadmium 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.

Table 1 On the other hand, as shown in Table 1, the energy density per unit volume of the electrode plate is 504 mAh / cc for the conventional powder G and 590 mAh / cc for the high-density powder F.
The values of cc and F are 15 to 20% higher than G.

For the above reason, the result is that the high-density powder can be filled more in the same volume substrate than the conventional powder.

The pore volume of the high-density active material powder satisfying the required energy density of about 600 mAh / cc must be 0.05 ml / g or less, and at the same time, the specific surface area correlated with the pore volume is 15 to 30 m. ² / g. The effect of adding cadmium 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 by making the nickel hydroxide crystal have strain, the proton transfer in the solid phase is smoothed. It is considered that it was compensated by this.

That is, the utilization rate of the active material means the amount of proton transfer, which 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 it is governed by the specific surface area and is governed by the internal strain when the crystals are different.

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 the free state (existing on the particle surface without solid solution in nickel hydroxide) A network of CoOOH particles with properties is essential.

Regarding the CoO additive that forms this network, Fig. 8 shows the relationship between the amount of CoO added, the active material utilization rate, and the energy density per electrode plate volume. When the amount of the CoO additive is increased, the utilization rate of the active material also increases and converges to around 100%. However, since the additive itself only contributes to conductivity and does not actually discharge, the actual electrode plate energy density is
It shows a tendency to decrease from around 15%. FIG. 9 shows a three-dimensional relationship between the active material composition and the amount of γ-NiOOH produced. Charged at a high current density of 1 C, the electrode plate at the end of charging was analyzed by X-ray analysis, and the relationship with the amount of γ-NiOOH produced by the powder type was examined. Cadmium was added to the nickel hydroxide crystal in a solid solution state. If so, γ-Ni
It can be seen that the amount of OOH produced decreases. FIG. 10 shows a comparison of the discharge pressure characteristics of the high density powder A containing no cadmium and the electrode of the high density powder F containing cadmium of the present invention. In the case of the high-density powder A that does not contain cadmium, a large amount of [gamma] -NiOOH is generated and the discharge pressure has a two-stage discharge characteristic. From Fig. 9, the effect of preventing γ-NiOOH generation is recognized from the addition of 2% of cadmium, and the complete γ-NiOOH is observed with the addition of 7%.
Disappears.

The effect of this cadmium is the same even if other different elements such as cobalt coexist in a solid solution state. A behavior similar to that of cadmium is observed in cobalt, though slightly. When the product at the end of charging is trivalent β-NiOOH, it shows theoretical capacity = 0.29Ah / g (active material amount) when it is completely reduced to divalent β-Ni (OH) ₂ by discharge. .

When the electrode shows this capacity, the active material utilization rate is 100%.
It is customary to In nickel hydroxide electrode,
It cannot be said that an electrode having a high utilization rate is an excellent electrode. For example, as described in J. Power Sources, 12, 219 (1984), an active material utilization rate of over 100% is sometimes obtained. The cause is due to the formation of tetravalent higher order oxide γ-NiOOH. γ
-NiOOH is easily generated by charging at low temperature. For example, in the case of powder G having a large specific surface area and a composition of nickel hydroxide only, which is obtained by the conventional method, as shown in FIG.
It shows a high utilization rate of 120% at 0 ° C. However, due to the large volume fluctuation and the formation of γ-NiOOH,
The electrode swells, which greatly affects the life. Therefore, the crystal form of the active material at the end of charging needs to be trivalent β-NiOOH, and in that sense, it is not preferable that the utilization rate exceeds 100%. Therefore, under any condition, γ-NiOO
It is an excellent electrode that suppresses the generation of H and maintains the utilization rate near 100%. As shown in FIG. 11, in the overdensity powder F containing 5% of cadmium in a solid solution state, around 100% is maintained even at low temperature. Regarding the high-density powder H containing 5% cadmium and 3% cobalt in a solid solution state, the high temperature performance disclosed in JP-A-59-224062 was recognized to be improved, and the capacity fluctuation was further reduced.

The results shown in FIG. 12 were obtained for the other additives described above which form the network of CoOOH. The active material utilization rate is good in the order of CoO> α-Co (OH) ₂ > β-Co (OH) ₂ . The reason for this is considered to be the solubility in the electrolytic solution. That is, in the case of β-Co (OH) ₂ , after injecting the electrolytic solution, brown Co (OH) ₃ having poor solubility which is oxidized by dissolved oxygen is easily formed, while in the case of α-Co (OH) ₂ , α-Co (OH) ₂ is used. −Co (OH) ₂ → β−
Co (OH) in order to via the ₂ Co (OH) ₃ is not easily formed. C
In the case of oO, it can be said that it is the most excellent additive because Co (OH) ₃ is not formed at all. More specifically, CoO which is desirable from the viewpoint of dissolution rate is β-Co (OH) ₂ which is heated and produced in a high temperature inert atmosphere at ₂₀₀ to 800 ° C. An electrode filled with paste containing nickel hydroxide dipped in HCoO ₂ ⁻ ions to form a cobalt hydroxide layer on the surface is Co
Inferior to the electrode mixed with O powder, β-Co (OH)
It was about an electrode in which _two powders were mixed. Further, a powder in which a conductive CoOOH layer is formed on the surface of nickel oxyhydroxide powder (specifically, an electrode in which CoO powder is mixed is charged and discharged, and then nickel fibers as a current collector are removed from the electrode). The electrode having the paste filled in) was poor in utilization. This has important implications. That is, the formation of a conductive network (CoOOH) between the active material powder and the current collector is
It is unavoidable that it is formed in the formed electrode, and even if it is formed on the surface of the active material particles in advance, its effect is low. Therefore, the nickel electrode of the present invention containing CoO powder requires the steps of assembling the battery without chemical conversion, injecting the electrolytic solution, and then leaving it to dissolve and re-precipitate the CoO powder.
Electrodes made according to the present invention with CoO additives are
Since the theoretical utilization factor of β-NiOOH is reached without using the conductive additive, the conductive additive is not required and the invention can be applied to the sealed nickel-cadmium battery. Although the metal fiber sintered body is shown as an example of the substrate, the substrate is not limited thereto.

EFFECTS OF THE INVENTION As described above, the present invention provides a nickel electrode that prevents the formation of a higher-order oxide γ-NiOOH, has an improved utilization rate of an active material, has a high energy density, and has a long life, and an alkaline battery using the same. Therefore, its industrial value is extremely high.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a model diagram of dissolution of a cobalt compound. Fig. 2 shows the precipitated PH, 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 an X-ray photograph (X-ray micro analyzer abbreviated as EPMA) as a photograph in place of a drawing, and shows a state after dissolution and precipitation of the cobalt additive. FIG. 7 is a diagram showing the relationship between the type of nickel hydroxide and the active material utilization rate. FIG. 8 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. 9 is a diagram showing the relationship between the active material composition and the amount of γ-NiOOH produced. 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 shows the relationship between the active material composition, the charge / discharge temperature, and the utilization rate of the active material. FIG. 12 shows the relationship between various cobalt compound additives and the utilization rate of the active material.

Claims (1)

[Claims] 1. A nickel hydroxide powder prepared by precipitating nickel sulphate in an aqueous solution controlled to pH 11 to 13 with caustic soda or caustic potassium and ammonium sulphate using a porous alkali resistant metal substrate as a current collector. In the paste type nickel electrode which is the main component of the material,
Nickel electrode for alkaline batteries, characterized in that the powder of nickel hydroxide prevents the development of internal transition pores having a radius of 30 Å or more, and the pore volume thereof is set to 0.05 ml / g or less.