JPH0757730A - Alkaline storage battery - Google Patents

Abstract

PURPOSE:To provide an alkaline storage battery having excellent charge and discharge efficiency by restraining swelling of an electrode at overcharge time of a cadmium unadded nickel positive electrode. CONSTITUTION:An alkaline storage battery is formed by using a nickel positive electrode obtained by adding/filling a conductive agent and a binding agent to/in an alkaline resistant metallic porous body by using nickel hydroxide powder as a main component. The alkaline storage battery is characterized in that in metal conversion, zinc of 1.0 to 2.5 weight % and cobalt of 1.5 to 5.0 weight % are contained inside of the nickel hydroxide powder together with nickel in a coprecipitation condition. An average particle diameter of nickel hydroxide may be 5 to 30mum, and tap density mad be not less than 1.8g/cm<2>, and the specific surface area is preferable to be 8 to 25m<2>/g, and a half value width of a (101) surface by an X-ray diffraction method is preferable to be not less than 0.8 deg./2theta, a thermal decomposition temperature is preferable to be not more than 270 deg.C, and a shape is perferable to be spherical.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an alkaline storage battery using a nickel positive electrode.

[0002]

2. Description of the Related Art Conventionally, as a positive electrode of an alkaline storage battery,
A sintering type positive electrode is used. This sintering type positive electrode is obtained by impregnating a nickel salt aqueous solution into holes of 10 and several μm obtained by sintering nickel powder on a core metal such as a perforated steel plate or a nickel net. Then, by subjecting this to an alkali treatment, the impregnated nickel salt is converted into nickel hydroxide to obtain a positive electrode. However, this sintered positive electrode requires a complicated operation of impregnating the active material such as impregnation of nickel salt and alkali treatment at the time of production, and in order to impregnate a predetermined amount of the active material, the above-mentioned operation is usually performed by Since it has to be repeated about 10 times, there is a problem that the manufacturing cost becomes high. Furthermore, the porosity that can maintain the mechanical strength of the nickel powder sintered body is limited to about 80%, so that there is a problem that the absolute amount of the active material to be filled is limited.

[0003]

For this reason, the nickel hydroxide powder is mixed with a conductive powder, a binder and water to form a paste, which has an average porosity of 95% or more and an average pore size of several tens. A positive electrode produced by directly filling a three-dimensional sponge-like metal porous body having a size of several 100 μm, a metal fiber mat, or the like with this is being studied. This method is generally called a non-sintering type or a paste type as opposed to a sintering type. According to the paste method, the porosity and average pore size of the metal porous body are larger than those of the sintering method, so that the active material filling process is easy and the absolute filling amount can be increased. Is very good at. However, since the pores of the metal porous body filling the paste are larger than the sintered nickel pores, the distance between the active material and the bulk of the current collector deteriorates the current collection performance, and Increasing the absolute amount of the substance itself leads to (1) decrease in conductivity, but also (2) increase in electrode swelling rate especially during overcharge, and (3) charge and discharge efficiency is included. In addition, it was inferior to the sintering type because the utilization rate of the positive electrode was lowered.

That is, the paste type is based on the advantage that the capacity is increased as compared with the sintering type.
The problems were to improve the three problems of (2) suppression of electrode swelling ratio and (3) improvement of charge / discharge efficiency.

The improvement in conductivity (1) is very important in the sense that the average charge / discharge polarization potential of the nickel electrode during charge / discharge is lowered, and (2) suppression of electrode swelling ratio and (3) charge. This is a necessary condition for improving discharge efficiency. (It is not a sufficient condition.) In order to improve the conductivity, it is general to add a cobalt compound (cobalt oxide, cobalt hydroxide, m-cobalt, etc.). However, in order to maximize the effect of adding a cobalt compound (that is, improve conductivity), not only the manufacturing method but also mixing and dispersibility, alkali electrolyte solution solubility,
It is important to suppress the factor for storage stability, and the authors have been able to address these issues in Japanese Patent Application No. 03-00.
6953, 03-006954, 03-130222,
03-130337, cobalt monoxide (CoO), dicobalt trioxide (C
focusing on the fact that it is effective to use at least one of O ₂ O ₃ ) and applying for these
I saw a tentative solution. The problem is the remaining two, (2)
Regarding the suppression of the electrode swelling rate, the problem is particularly that at the time of overcharging, and regarding (3), the charging efficiency at a high temperature is particularly a problem. Regarding the former, when overcharged, γ-nickel oxyhydroxide (γ-N) which is a high-order oxide and has a low density is used.
It is important to make as little iOOH) as possible. For the latter, increase the oxygen overvoltage of the nickel electrode at high temperature so that part of the charging electrical energy is not consumed for oxygen gas generation. is important. Regarding these (2) and (3), it is common to add a transition metal or a transition metal compound from the time of the sintering formula, and this is one guideline.

As the transition metal element to be added, generally,
Cadmium (Cd) and cobalt (Co) are widely known, and nickel hydroxide (Ni (O
H) ₂ ) A method of forming a solid solution with nickel atoms (Ni) inside the particles (= coprecipitation addition method) and Ni (OH) ₂
There are two types: a method of mixing transition metal or transition metal compound (mainly oxide or hydroxide) particles together with particles during paste kneading (= mixing and adding method).

However, recently, the awareness of the battery from the environmental aspect has increased, and even if a very small amount of cadmium contained in the nickel electrode of a nickel-hydrogen battery is attached, it is completely removed in consideration of the stricter regulation. The tendency to do so is becoming more common.

Therefore, a method of adding zinc or a zinc compound in place of cadmium is disclosed in, for example, JP-A-2-3006.
1, proposed in JP-A-3-77273. The former is
The latter is the co-precipitation addition method, which is based on the mixed addition method. Among these, the latter mixed addition method does not cause any clear difference in the electrode swelling rate of (2) above, the high temperature and low charging rate of (3) above compared to the case of no addition. Was recognized. Regarding the former coprecipitation addition method, only zinc was specified up to the addition amount, and the range was from 3 to 10 wt%, and the effect was limited to the reduction of the electrode swelling rate in (2) above. There is. That is, it does not consider the balance of optimization of coprecipitation addition amount depending on the combination of zinc and cobalt, and its particle size, tap density, specific surface area, crystal strain, and optimization of binding energy. Compared to that, the charging efficiency at high temperature and low rate is inferior by about 15 to 20%. Cadmium in the nickel electrode of alkaline batteries
The actual situation is that although a free charge has been achieved, the charging efficiency of (3) above has not been fundamentally resolved.

[0009]

According to the present invention, zinc of 1.0 to 2.5 wt% and cobalt of 1. to 2.5 wt% in terms of metal are contained in a nickel hydroxide powder used in a nickel electrode for an alkaline storage battery.
5 to 5.0 wt% together with nickel in a coprecipitated state, and the nickel hydroxide powder has an average particle size of 5 to 30.
μm, specific surface area 8 to 25 m ² / g, tap density 1.
A spherical shape of 8 g / cm ³ or more and a (101) plane peak half-value width of 0.8 ° / 2θ or more according to an X-ray powder diffraction method, T
By making the thermal decomposition temperature in G below 270 ° C, it is possible to produce a cadmium-free nickel electrode,
In particular, it is possible to provide an alkaline storage battery which is excellent not only in the above two problems, namely, in the suppression of electrode swelling during overcharge but also in charging efficiency at high temperature.

[0010]

As described above, according to the present invention, 1.
0-2.5 wt%, cobalt 1.5-5.0 wt%,
It is contained together with nickel in a coprecipitated state, and the nickel hydroxide powder has an average particle size of 5 to 30 μm and a specific surface area of 8 to
25 m ² / g spherical shape, the (101) plane peak half-value width by the X-ray powder diffraction method is 0.8% / 2θ or more, TG
By setting the thermal decomposition temperature at 270 ° C or lower,
It is possible to provide a cadmium-free nickel electrode, and in particular, it is possible to provide an alkaline storage battery which is excellent not only in suppressing electrode swelling during overcharging but also in charging efficiency at high temperatures.

The reason for doing this is as follows (a)-
They are summarized in 4 of (d).

(A) It has been recognized that when a transition metal such as zinc or cadmium is added to nickel hydroxide by coprecipitation, electrode swelling during overcharge can be suppressed as compared with the case where nothing is added. Needless to say, the degree of the effect varies depending on the type of transition metal that coprecipitates and the amount of coprecipitation. The swelling mechanism is
In general, nickel hydroxide has a layered crystal structure of cadmium iodide, and since protons and cations move in and out of this layer at each charge / discharge, it is distorted and the space between layers widens. It is said to be due. (Especially during overcharge, this is γ-nickel oxyhydroxide (γ-NiO
OH). )

In particular, the addition of an appropriate amount of transition metal by coprecipitation does not particularly hinder the diffusion of protons and causes the effect of increasing the bond strength between the layers, so that the swelling can be performed without impairing the utilization rate. It is speculated that it can be suppressed. Although it is not possible at this time to directly measure the bond strength (= bond energy) itself between the layers, the authors have found that qualitative judgment can be made by study, for example, by thermal analysis. Thermal analysis methods include, for example, thermogravimetric measurement (Thermogra
vimetry; TG) and differential thermal analysis (Differe)
ntial Thermal Analysis; DT
There is A). For example, nickel hydroxide with cadmium coprecipitation is better than nickel hydroxide without addition, which is already well known, and nickel hydroxide with zinc coprecipitation is more dependent on nickel hydroxide with cadmium coprecipitation. Although qualitative, it is recognized that the thermal decomposition temperature due to TG is high. Further, regarding cadmium and zinc, it is recognized that the higher the addition amount is, the higher the thermal decomposition temperature is up to about 10 wt% in terms of metal. This thermal decomposition temperature has an appropriate range in terms of battery characteristics. If it is too large, it will hinder proton diffusion and the utilization rate of the nickel electrode will decrease, and if it is too small, it will directly lead to an increase in electrode swelling, which is not preferable. The upper limit of the thermal decomposition temperature in TG of nickel hydroxide is about 270 ° C, and the lower limit is not clarified by the authors, but probably 2
It seems to be around 00 ° C. In the case of high density spherical nickel hydroxide to which a transition metal is coprecipitated, it is usually 27
It is common to have a TG above 0 ° C.

(B) It has been recognized that when a transition metal element such as zinc or cadmium is coprecipitated with nickel hydroxide, the oxygen overvoltage during charging increases. Oxygen overvoltage usually refers to the difference in potential between the following two reactions.

Ni (OH) ₂ + OH ⁻ → NiOOH + H ₂ O + e ⁻ (1) OH ⁻ → 1/2 H ₂ O + 1/40 ₂ ↑ + e ⁻ (2) Charge efficiency when charging at the same rate and the same depth To raise it, lower the reaction potential of the above formula (1) as much as possible, raise the reaction potential of the above formula (2) as much as possible, and use the charging electric energy as much as possible for the reaction of the formula (1). Good. That is, the oxygen overvoltage should be increased.

For example, when cobalt (Co) is co-precipitated with nickel hydroxide, the charging potential of nickel hydroxide during charging (potential when the reaction of the above formula (1) occurs)
Can be lowered compared to the case of no addition. Co-precipitation of cadmium (Cd) or zinc (Zn) can raise the oxygen generation potential (potential when the reaction of the above formula (2) is occurring) as compared with the case of no addition.

As described above, by selecting the type of transition element to be added and adjusting the reaction potentials of the above formulas (1) and (2), the oxygen overvoltage can be increased, and the charging efficiency can be increased.
It can be dramatically improved as compared with the case of no addition.

Until now, Co has been used as a paste-type nickel electrode.
One of the reasons why nickel hydroxide co-precipitated with Cd is widely used is that the oxygen overvoltage increases and the charging efficiency increases as described above.

(C) Further, in the finished nickel hydroxide, the crystal strain, the grain size, the tap density, and the surface area are important points from the viewpoint of the utilization rate (= charging / discharging efficiency). To optimize the crystal strain, particle size, tap density, and surface area of nickel hydroxide particles, lower the reaction potential of equation (1) of item (b) (the same applies to reactions in the opposite direction), and It helps to make the reaction easier. ((B) Item (2)
Is not directly related to the reaction formula of. ) Generally, the charging / discharging process in the positive electrode is a process in which protons (H ⁺ ) are diffused between the layers inside the nickel hydroxide particles, and the electrons (e ⁻ ) in which the protons enter and leave the external circuit and the nickel substrate − It can be considered as being divided into two processes of electrically neutralizing via a conductive agent.

To smooth the diffusion of protons inside the nickel hydroxide particles, the crystal strain must be increased to some extent. An X-ray powder diffraction method (X-Ray Powder Di
It is also possible depending on, for example, the peak half width of the (101) plane in the fraction method (XRD method). ((101) plane, (001) plane, (1
The idea is exactly the same even if the knowledge about the scale of crystal strain is obtained by the half width of the (00) plane. ) It can be said that the larger the peak half width is, the more the crystal is distorted. Moreover, since the binding energy (O—H, Ni—O) of nickel hydroxide is generally small in a strained crystal, it depends on the thermal analysis method typified by TG and DTA already described. Even if the binding energy is measured, the criterion for crystal strain can be obtained. However, originally, the crystal strain and the binding energy are completely different from each other as an index given to the battery characteristics of nickel hydroxide. The authors have already applied for similar patents in Japanese Patent Laid-Open Nos. 4-328255 and 4-328257.

As described above, the conductivity of the nickel electrode contributes to the latter process of neutralizing protons (H ⁺ ) and electrons (e ⁻ ). This is due to physical problems such as the mixing and dispersibility of the nickel hydroxide particles and the conductive agent particles when preparing the paste and the distance to the current collector bulk of the nickel substrate filled with them and the surface of the nickel hydroxide particles. It can be divided into chemical problems such as reaction area. Under the limitation of the substrate and the conductive agent, regarding these problems, the particle size of nickel hydroxide particles (which can be replaced by the average particle size) and the tap density and the surface area of nickel hydroxide (which can be replaced by the specific surface area) can be used. )is important. If the particle size, tap density, and surface area are not all properly controlled, the utilization factor will drop in terms of conductivity as a nickel electrode and reaction rate.

(D) The nickel hydroxide particles are preferably spherical or have a similar shape. In the first place, the crystal form of nickel hydroxide should be a hexagonal system as long as convection does not occur in the process of neutralizing the sulfuric acid complex ion of nickel with sodium hydroxide as described above. Furthermore, in this case, even if pH control and temperature control are performed, it is very difficult to eliminate the concentration gradient in the neutralization tank without causing convection when neutralizing on a large batch scale, or it is inefficient. Target. In such a state, the number of crystal nuclei of nickel hydroxide particles,
It is quite difficult to control the crystal growth, and thus to define the crystal grain size. In this case, after the crystal particles are produced, in order to adjust the particle size, there is no choice but to provide the steps of particle crushing and sieving.
This is very inefficient because it increases man-hours. If the particle size is not specified, first, the filling amount as a nickel electrode will be different, and the capacity variation between batteries will become large. Furthermore, if there is an extreme difference in particle size among the nickel electrodes in one battery, a difference in current density will occur during charging and discharging, and the degree of polarization will differ within a single nickel electrode. As a result, current concentration will occur in the portion that actually contributes to charge and discharge, which promotes cycle deterioration. Furthermore, in order to stably regulate the crystal grain size, in order to regulate the crystal nuclei and crystal growth, it is necessary to cause convection in the neutralization process from the standpoint of "gradual generation and growth". Also, when convection occurs, the particles inevitably become spherical to some extent.

From the above reasons, it is judged from the beginning that the nickel hydroxide particles are preferably spherical.

As described above, in order to suppress the swelling of the electrode and to improve the charge efficiency at the utilization rate, especially at a high temperature and a low rate, the necessary factors are attached to the nickel hydroxide particles to limit them to (a) to (d). I have detailed it. What is important is the balance of these four factors. In the following, from the viewpoint of these five factors, mainly the suppression of electrode swelling, the utilization efficiency, in particular, the charging efficiency at a high temperature and a low rate will be specifically described in Examples.

[0025]

The details of the present invention will be described below with reference to examples. (Experiment 1) Here, 2 wt% of zinc and 2 wt% of cobalt are added to nickel hydroxide in terms of metal to form a spherical shape, and X
The peak half width of the (101) plane in RD is 0.95 °
The effect of the average particle size, tap density and specific surface area on the electrode swelling rate and the nickel electrode utilization rate when the thermal decomposition temperature due to / 2θ and TG is limited to 260 ° C will be described.

First, metallic nickel (Ni), metallic zinc (Zn), and metallic cobalt (Co) are dissolved in a sulfuric acid aqueous solution to form nickel complex ions, zinc complex ions, and cobalt complex ions, and convection is caused. Then, the solution is dropped into an aqueous sodium hydroxide solution to gradually grow nickel hydroxide particles in which zinc and cobalt are solid-solved. By crystallization in a convection aqueous solution, the finished nickel hydroxide particles can be made spherical and the crystal growth itself can be moderated, so that a high density with few pores can be obtained. The size of nickel hydroxide crystal co-precipitated with zinc is the crystal nucleus of nickel hydroxide in which zinc and cobalt are solid-solved when the complex ions of nickel, zinc and cobalt in the sulfuric acid solution are neutralized with the sodium hydroxide solution. Can be increased by controlling the temperature and pH so that the component is used for crystal growth without making too much. To put it plainly, in order to make a large crystal, the temperature control is near the transition temperature (in this case, around 40 ° C),
For PH control, it is important to create a metastable region (near PH11 in this case) at a position as close to neutralization as possible by using a weak base or the like. To make small crystals, the reaction should be stopped appropriately before growing into large crystals. By doing so, it becomes possible to control the particle size of the nickel hydroxide particles while keeping the XRD, the (101) plane peak half width and the decomposition temperature of TG constant. In this way
As shown in Table 1, 2 kinds of 2 wt% zinc of A to F, 2 wt
Crystals of% cobalt co-precipitated nickel hydroxide were made. To confirm the particle size, the finished nickel hydroxide particles are subjected to particle size distribution by a known laser method, and the cumulative 50%
The value of is the average particle size, and the tap density is 2
Using a 0 cm ³ container, tapping was performed 200 times, and calculation was performed by a known method. (Equipment used: SEISH
IN TAPDENSER KYT300). The specific surface area was measured by a known nitrogen BET adsorption method. Further, any nickel hydroxide particles A to F are dissolved in hydrochloric acid and quantified by a known atomic absorption spectrometry,
It was confirmed by a known X-ray powder diffraction method that peaks of zinc and cobalt alone did not appear, and it was confirmed that it was 2 wt% zinc 2 wt% cobalt coprecipitated nickel hydroxide. at the same time,
It was confirmed that the full width at half maximum of the XRD diffraction peak on the (101) plane at that time was 0.95 ° / 2θ. It was confirmed with an electron microscope that all the nickel hydroxide particle shapes were spherical.

[0027]

[Table 1]

Accordingly, Japanese Patent Application Nos. 03-006953 and 03-006954 are applied to 100 wt% of zinc and cobalt coprecipitated nickel hydroxide powders having various average particle diameters, specific surface areas and tap densities thus obtained. Cobalt monoxide (CoO) 10 wt% shown in the above, and kneaded with a known thickener such as carboxymethyl cellulose and water to form a paste, which has a porosity of 95% and an average pore diameter of 200.
An arbitrary nickel positive electrode plate was obtained by filling a porous nickel-plated metal body of μm, drying and molding.

On the other hand, in parallel with this, commercially available Mm (Misch metal: mixture of rare earth elements), Ni, Co, M
Nm and Al are weighed so that the ratio of the elements is 4.0: 0.4: 0.3: 0.3, melted in a high-frequency melting furnace, and the melt is cooled to obtain MmNi. _4.0 Co
An alloy ingot represented by _0.4 Mn _0.3 Al _0.3 was prepared. Next, mechanically crush this ingot,
The particle size was cut to 50 μm or less to obtain a hydrogen storage alloy powder. A thickener such as carboxymethyl cellulose, water, and carbon were added to the hydrogen-absorbing alloy powder to form a paste, which was applied to a known punched metal, dried, and molded to obtain a negative electrode.

The positive and negative electrode plates thus obtained are hydrophilically treated with a polyolefin-based nonwoven fabric separator,
A nickel-hydrogen battery was produced by combining with an electrolytic solution containing potassium hydroxide as a main component, a metal battery container, a metal lid, and other parts. Then, after aging at 25 ° C. for 15 hours, the battery was charged for 15 hours with a quantity of electricity of 0.1 CmA, left for 30 minutes, and then discharged at 1.0 CmA / 1.0 V cut. (This is the first charge and discharge.). This battery is divided into two types, the first is 15C with electricity of 0.3CmA.
Charge to 0% depth, 1.0CmA / 1.0V cu
The t discharge is repeated up to 300 cycles, the nickel electrode utilization rate transition is measured, and the second is charged to a depth of 150% with an electricity amount of 0.3 CmA, 1.0 CmA / 1.0
After repeating 20 cycles of discharging to V cut,
After charging at 0 ° C. with a current of 0.1 CmA for 30 days and discharging at 25 ° C. with 1.0 CmA / 1.0 V cut, the battery was disassembled and the thickness of the nickel electrode was measured with a micrometer. The ratio with the thickness of the nickel electrode is 0 ° C,
The electrode swelling ratio was 0.1 CmA overcharge. The former is shown in FIG. 1 and the latter is shown in FIG.

From FIG. 1, it is understood that the one using B, C, D and E nickel hydroxide particles is suitable.

The main cause of the decrease in the utilization rate of F particles is
It is considered that the main reason is that the average particle size (50.0 μm) is too large and the tap density (1.3 g / cm ³ ) is too small. Regarding the specific surface area, it can be seen that the influence is small by comparing the E particles and the F particles having a relatively small difference in specific surface area. In fact, when observing the state of the electrode at the time of filling, drying, and molding the nickel paste using the nickel hydroxide particles of F into the nickel-plated metal porous body, green due to uneven filling (the color of nickel hydroxide is The difference in shade of (green) was remarkable as compared with that using B, C, D and E nickel hydroxide. The charging unevenness of the nickel hydroxide particles affects the distribution of the electrolyte solution at the electrode, so inevitably the process of activating the battery such as the above-mentioned aging and initial charging / discharging causes the conductivity due to the cobalt monoxide. This will give a difference in the degree of matrix formation. If the degree of formation of the conductive matrix in one electrode is different depending on the location, a non-uniform reaction naturally occurs, and the current concentrates on the highly conductive portion, resulting in a decrease in capacity. It will be. Further, the use of A particles is not as great as the use of F particles, but a relatively large decrease in utilization rate is observed. This is the particle size (average particle size 1.3
It is presumed that the mixing dispersibility with the above-mentioned cobalt monoxide is not sufficient due to the decrease in tap density (1.6 g / cm ³ ) due to the excessively small (μm). Further, it can be seen from FIG. 1 that the utilization of the A particles is inferior to the others, especially from the beginning of the cycle. This is due to the fact that a large amount of viscosity-stabilizing kneading liquid had to be added at the time of preparing the active material paste as the particle size decreased and the specific surface area increased. Actually, the one using A particles is 28.3 m.
Those having a large specific surface area of ² / g have been obtained.

Also in FIG. 2, the same tendency as in FIG. 1 is recognized. That is, it can be seen from FIG. 1 that the greater the decrease in the utilization rate with respect to the cycle, the greater the electrode swelling rate. This is because, as already mentioned, if the average particle size of nickel hydroxide is not within the proper range, the conductive matrix based on cobalt monoxide described above is insufficient, so current concentration occurs in the highly conductive portion. , Therefore, γ-NiOOH is formed in that part,
Further, since the electrolytic solution for discharging this γ-NiOOH is insufficient in this portion, once γ-NiOOH is generated, its generation is spurred. γ-NiOO
It is considered that H itself promotes electrode swelling due to its low conductivity and large volume as well as inferior conductivity to β-Ni (OH) ₂ and β-NiOOH. that's all,
From Table 1, FIG. 1 and FIG. 2, it can be said that those using nickel hydroxide particles of B, C, D and E are suitable.

To review the manufacturing conditions once again, Table 1
I will add a description for. The nickel hydroxide particles of A to F in Table 1 are XR, which is one measure of the crystal strain.
The full width at half maximum of the (101) plane in D is 0.95 ° /
Limited to 2θ, 2 for zinc and 2 for cobalt
2 wt% coprecipitation was added. Under this condition, it is generally relatively difficult to increase or decrease any one of the average particle size, tap density, and specific surface area.

That is, assuming that the nickel hydroxide particles are spherical and are in a region in which the influence of the volume of the internal voids can be ignored, in general, if the average particle size is small → large, the specific surface area is large. → It becomes small. This can be easily determined from the following equation.

[0036]

[Equation 1]

In fact, in Table 1, as the average particle size increases from A particles to F particles, the specific surface area decreases. Furthermore, in general, the particle size is small in a certain area →
When it becomes large, the tap density becomes small → large → small. As shown in Table 1, when the average particle size shifts from A particles to F particles, the tap density changes from 1.6 g / m ² (A particles) to 2.3 g / m ² (C particles). It can be confirmed that the maximum value of (1) is reached and the value again falls to 1.3 g / m ² (F particles). It is easy to understand that it is presumed that the tap density itself has three main balances: (a) electrostatic force of particles, (b) particle mass, and (c) particle-particle gap. That is, if the particle size is very small, (a) tends to be charged with static electricity, and (c) becomes lighter in weight, so that the particles are separated from each other by the repulsive force, so that the closest packing of particles cannot be performed. The tap density will decrease. On the contrary, if the particle size is very large, (b)
Since the mass of the particles of (a) is large, it is less likely to be affected by the electrostatic force of (a), but since the gap between the particles of (c) becomes large, the tap density will decrease even after the closest packing. That is, there is a place where the tap density takes a high value in a region where the particle size is not too small and not too large.

As described above, the three average particle diameters, tap densities, and specific surface areas have a certain degree of correlation and move in conjunction with each other to some extent, so any one of the three can be increased or decreased. It is relatively difficult to control independently and strictly. However, these three contribute to the manufacturing of the battery or the battery characteristics as independent factors, so those belonging to the above-mentioned range are preferable.

To summarize the present experiment, nickel hydroxide and zinc and cobalt are 2 wt% and 2% respectively in terms of metal.
wt% is added, the peak half width of the (101) plane in XRD is 0.95 ° / 2θ, and the thermal decomposition temperature in TG is 2
When limited to 60 ° C., the average particle size is 5 to 30 μm, the tap density is 1.8 g / m ² or more, and the specific surface area is 8 to 25 m ² / g.
In particular, Japanese Patent Application Nos. 03-006953 and 03-006954
It has a good compatibility with cobalt monoxide as shown in the above, the conventional kneading liquid does not require much, the uniform filling property is high, and the utilization rate is sufficient.

(Experiment 2) In Experiment 1, 2 wt% zinc, 2 wt% cobalt, and nickel were co-precipitated, and the XRD
Half width of (101) plane at 0.95 ° / 2θ, T
When nickel hydroxide having a thermal decomposition temperature of 260 ° C. of G is used, the average particle size is 5 to 50 μm, the tap density is 1.8 g / cm ³ or more, and the specific surface area is 8 to 25 m ² /
I said that what is g is good.

In this experiment, the definition of the addition amount of the transition metal element will be described. Since it is difficult to mention all the combinations, the cobalt coprecipitation amount was set to 0, 0.5, 1,
Zinc coprecipitation amount of 0, 0.5, 1, 1.5, 3, 5, 8, 10 wt% of 8 types of 1.5, 3, 5, 8 wt% of 8 types
A total of 56 types of nickel hydroxide particles produced from the combinations are prepared, and the evaluation results of the charging efficiency and the swelling ratio of the overcharged electrode when the particles are used will be described. The 56 types of nickel hydroxide particles differ only in the amount of cobalt and zinc coprecipitated, and the shape of the particles is spherical, the size is 10 μm in average particle diameter, and the tap density is 2.2 g / cm 2.
^{3. The} specific surface area was 18.0 m ² / g, and the method was the same as Experiment 1 from the method of making the nickel hydroxide particles to the battery component parts, assembling method, and initial charging method.

After that, charging to a depth of 150% with a current of 0.3 CmA and discharging to 1.0 CmA / 1.0 V cut was repeated 20 cycles at 20 ° C. or lower to stabilize the discharge capacity, and then this was carried out. Divide into two, the first is Experiment 1
Similar to the above, the second swelling rate was evaluated using the second method.
It is charged to a depth of 150% at a current of 0.1 CmA at 0 ° C. and discharged at 1.0 CmA / 1.0 V cut at 20 ° C., and the discharge capacity is 0.1 CmA at 20 ° C., 15
As a reference value of the amount of charge at 0% charge, after that, charge at a current of 0.1 CmA to a depth of 150% at 45 ° C.
A discharge of 1.0 CmA / 1.0 V cut was performed at a temperature of 0 ° C., and the ratio of the discharge capacity to the charge amount reference value was used as the evaluation of the charge effect.

The results of charging efficiency are shown in FIG. 3, and the results of overcharge electrode swelling ratio are shown in FIG. As a comparative example, 5 wt% zinc, which is a conventional cadmium-free type, 1 wt
% Cobalt co-precipitated nickel hydroxide is used as shown by a solid line in the figure.

First, the charging efficiency at 45 ° C. will be described. From FIG. 3, generally, in any case, as the amount of zinc co-precipitated increases, the charging efficiency increases to 1.0 to 1.5.
2.5wt with a critical point around wt%
It is observed that saturation has been reached above%. Especially, the charging efficiency is 0 to 1.0 wt.
%, And cobalt is clearly divided into 1.5 to 8.0 wt% groups. This means that in the case of coprecipitation addition based on the combination of cobalt and zinc, the critical point of cobalt coprecipitation amount with respect to charging efficiency is 1.5 wt%.
It means that it is in the vicinity. That is, to put it plainly, 1 wt% of cobalt coprecipitation addition is not sufficient, and at least 5 wt%
It can be said that it is inefficient to improve the charging efficiency in the range exceeding%. That is, adding a transition metal element other than nickel to the nickel hydroxide particles tends to reduce the purity of nickel hydroxide and impair the capacity.
Based on the idea that it is important to suppress the amount of coprecipitation added as much as possible.

After all, conventional zinc 5 wt% and cobalt 1 w
In the region where the charging efficiency (65%) when using t% coprecipitation type nickel hydroxide is balanced with nickel hydroxide purity, the coprecipitation amount of cobalt is 1.5 to 5.
It can be said that 0 wt% and the coprecipitation amount of zinc are 1.0 to 2.5 wt%.

Next, the swelling ratio of the overcharge electrode will be described. As generally shown in FIG. 4, in any case, as the amount of zinc coprecipitated increased, the electrode swelling rate decreased to 1.0 to 2.5 w.
It is recognized that the critical point is taken at t% and the saturation is reached in the area exceeding 5 wt%. And the tendency is divided into two in the combination of the cobalt coprecipitation amount like the above charging efficiency. That is, cobalt 1.5-8.0w than the group of cobalt 0-1.0wt%
In the t% group, the electrode swelling rate was large when the coprecipitation addition amount due to the combination with zinc was less than 0.5 wt%, but the reduction rate was large, and conversely when the coprecipitation addition amount was 0.5 wt% or more, the electrode swelling rate was low. I know that there is. This is because the functions of cobalt and zinc are different, and cobalt is effective in facilitating the charging reaction of nickel hydroxide (compared to zinc) (the reaction of the "action" (b) item (1) equation). , Zinc seems to be effective in suppressing electrode swelling (compared to cobalt). That is, in the case where the required amount of cobalt that facilitates the charging reaction is added in the region where the amount of zinc coprecipitated, which has the effect of suppressing the electrode swelling ratio, is small (in this case, 1.5
〜8.0wt%), it falls into overcharge and produces a large amount of γ-NiOOH, which is a low-density, high-order oxide. As a result, electrode swelling occurs. The electrode swelling is suppressed together with the increase in the amount of cobalt, and the addition of cobalt coprecipitation (1.5 to 8.0 wt%) contributes to uniformly react the entire nickel hydroxide particles, so that the amount of cobalt coprecipitation is small. It is considered that the electrode swelling rate becomes smaller than (0 to 1.0 wt%).

As is well known, it is preferable to suppress the electrode swelling rate as much as possible, which contributes to the improvement of cycle characteristics. The guideline is, for example, (Experiment 1)
From the above, it can be said that it is about 130% or less (when E particles are used) or less. Judging from this, the zinc coprecipitation amount is 1.0 wt% or more and the cobalt content is 1.5 in FIG.
It is expected that good cycle characteristics such as B, C, D and E in FIG. 1 can be obtained in any combination as long as the content is at least wt%.

On the other hand, as described above, the larger the amount of the coprecipitating additive element is, the more the electrode swelling rate can be suppressed, but it is not preferable to add more than necessary because the purity of nickel hydroxide is impaired. That is, considering the balance with the nickel hydroxide purity while suppressing the electrode swelling ratio to 130% or less, the cobalt coprecipitation amount is 1.5 to 5.0 wt% including the result of FIG. 3 (charging efficiency). , Zinc coprecipitation amount is 1.0 to 2.5
It can be said that wt% is the proper range. In fact, a stable cycle trend such as B, C, D and E particles shown in FIG. 1 was obtained in the shaded area.

In any of the above, the appropriate ranges of charging efficiency and electrode swelling ratio are 1.0 to 2.5 in terms of zinc coprecipitation amount, in view of the balance with the purity of nickel hydroxide in the nickel hydroxide particles.
It can be said that the region where the combination of the wt% and the cobalt coprecipitation amount is 1.5 to 5.0 wt% is appropriate.

In the above, the shape of the nickel hydroxide particles is spherical,
Average particle size 10 μm, tap density 2.2 g / cm ³ , specific surface area 18 m ² / g, XRD, peak half width of (101) plane 0.95 ° / 2θ, thermal decomposition temperature in TG 260
As mentioned above, the average particle size is limited to 5 ° C.
30 μm, tap density of 1.8 g / cm ² or more, specific surface area of 8 to 25 m ² / g, peak half width of (101) plane in XRD is 0.8 ° / 2θ or more, thermal decomposition temperature in TG The same tendency was obtained even when the temperature was 270 ° C. or lower.
That is, the proper range is a zinc coprecipitation amount of 1.0 to 2.5 wt% and a cobalt coprecipitation amount of 1.5 to 5.0 wt%.

(Experiment 3) Here, 2 wt% of zinc and 2 wt% of cobalt in terms of metal were added to nickel hydroxide particles to form a spherical shape, the average particle diameter of which was 10 μm, and the tap density was 2.2 g / cm ^3. The influence of the peak half-value width on the (101) plane of XRD and the thermal decomposition temperature of nickel hydroxide in TGA on the cycle characteristics when the specific surface area is limited to 18 m ² / g will be described.

The method for producing nickel hydroxide particles is basically the same as that described in (Experiment 1), but here, the XRD (101) plane peak half width and TGA are used.
In order to intentionally change the thermal decomposition temperature of the salt, when neutralizing the acid in the complex ion state with a base to form a salt, the pH, complex ion concentration and neutralization bath temperature are controlled to crystallize. The growth rate was changed variously. In addition, the XRD measuring device,
Shimadzu Corporation XD-3A type (XR tube is CuK
α) was used, and SSC-5200, TG, and DTA-320 manufactured by Seiko Instruments Inc. were used as the TGA measuring device.

In this way, in XRD (1
01) plane equivalent 38.7 ° Peak full width at half maximum is 0.4,
0.6, 0.8, 1.0 ° nickel hydroxide particles G,
Nickel hydroxide particles K, L, M and N having thermal decomposition temperatures of Ni (OH) ₂ → NiO in H, I, J and TG of 260, 270, 280 and 290 ° C. were obtained. An example of the XRD chart is shown in FIG. 5 and an example of the TGA chart is shown in FIG.

Further, these G, H, I, J, K, L,
Except that M and N nickel hydroxide particles were used, the same procedure as Experiment 1 described above was performed from the battery constituent parts to the assembling method, initial charging method, and cycle evaluation.

The results of the cycle evaluation of nickel hydroxide particles G, H, I and J are shown in FIG. 7, and the results of the cycle evaluation of nickel hydroxide particles K, L, M and N are shown in FIG.

From FIG. 7, the full width at half maximum of the (101) plane in the XRD of nickel hydroxide is 0.8 ° or more (I, J
Particles) are good with little deterioration in the utilization rate of nickel hydroxide with respect to the cycle, and from FIG. 8, those having a thermal decomposition temperature of 270 ° C. or lower (using K and L particles) are hydroxylated with respect to the cycle. It can be seen that there is little deterioration in the nickel utilization rate, which is good. This is considered to be linked to the degree of proton diffusion in the nickel hydroxide particles as described above. The half-value width according to XRD relates to the crystal strain of nickel hydroxide, and the thermal decomposition temperature according to TG relates to the binding energy. It is presumed that proton diffusion does not occur smoothly unless the energy is reduced to some extent. If the proton diffusion does not occur smoothly, the utilization rate is low from the beginning, and this phenomenon is somewhat alleviated as the cycle progresses, and the utilization rate slightly increases, but the polarization tends to increase, so it is easy to cause partial overcharge phenomenon. , Cycle deterioration occurs relatively early. One of the factors contributing to the cycle deterioration speed is the balance between the smoothness of proton diffusion and the durability of nickel hydroxide to swelling and shrinking associated with charging and discharging.

As described above, 2 wt% of zinc and 2 wt% of cobalt are added to the nickel hydroxide particles to form a spherical shape, the average particle diameter of which is 10 μm, and the tap density is 2.2 g /
cm ³ and specific surface area of 18 m ² / g, XR
Half-value width of (101) plane depending on D is 0.8 ° or more, TGA
It was found that those having a thermal decomposition temperature of 270 ° C. or less had excellent utilization and cycle characteristics. Also, an average particle size of 5
A similar tendency was obtained even for those having a thickness of 30 μm, a tap density of 1.8 g / cm ³ or more and a specific surface area of 8 to 25 m ² / g. That is, the full width at half maximum of the (101) plane according to XRD is 0.8.
It is appropriate that the thermal decomposition temperature according to TGA is 270 ° C. or less and 270 ° C. or less. Further, although the embodiments of the present invention have been described by taking the nickel-hydrogen battery as an example, the present invention is not necessarily limited to this, and basically any alkaline storage battery using nickel hydroxide for the positive electrode is similar. The result is obtained.

[0058]

As described above, according to the present invention, 1.0 to 2.5 wt% of zinc and 1.5 to 5.0 wt% of cobalt are contained in the nickel hydroxide powder used in the nickel electrode for alkaline storage batteries.
% Nickel and co-precipitated and its average particle size is 5
~ 30 μm, tap density 1.8 or more, specific surface area 8 ~
25 m ² / g, peak full width at half maximum of (101) plane in XRD is 0.8 ° or more, thermal decomposition temperature in TG is 270
By making the temperature below ℃ and spherical, it is possible to provide an alkaline storage battery which is cadmium-free and which is excellent in charge / discharge efficiency and suppression of electrode swelling during overcharge, which is a conventional weak point. Therefore, its industrial value is extremely large.

[Brief description of drawings]

FIG. 1 is a cycle characteristic diagram of the utilization rate of a positive electrode active material of a nickel hydrogen battery using nickel hydroxide A to F.

FIG. 2 is a swelling ratio of the thickness of a nickel positive electrode of a nickel hydrogen battery using nickel hydroxide A to F.

FIG. 3 is a charging efficiency characteristic diagram according to the amount of zinc coprecipitated in each amount of cobalt coprecipitated.

FIG. 4 is a swelling ratio of the thickness of a nickel positive electrode depending on the amount of zinc coprecipitated in each amount of cobalt coprecipitated.

FIG. 5 is an XRD chart.

FIG. 6 is a TGA chart diagram.

FIG. 7 is a cycle characteristic diagram of utilization rates of nickel hydroxides G to J by half width.

FIG. 8 is a cycle characteristic diagram of utilization rates of nickel hydroxide K to N according to thermal decomposition temperatures.

Claims (6)

[Claims] 1. An alkaline storage battery using a nickel positive electrode comprising an alkali-resistant metal porous body mainly composed of nickel hydroxide powder, and a conductive agent and a binder added thereto. Zinc is 1.0 in terms of metal
The alkaline storage battery is characterized in that the co-precipitation state contains cobalt in an amount of 2.5% by weight to 2.5% by weight. 2. The nickel hydroxide powder has an average particle size of 5
The alkaline storage battery according to claim 1, wherein the alkaline storage battery has a tap density of ˜30 μm and a tap density of 1.8 g / cm ³ or more. 3. The specific surface area of the nickel hydroxide powder is 8
It is -25 m < ² > / g, The alkaline storage battery of Claim 1 or 2 characterized by the above-mentioned. 4. The half width of the (101) plane peak by the X-ray powder diffraction method of the nickel hydroxide powder is 0.8 ° / 2θ or more, wherein the nickel hydroxide powder has a peak half width of 0.8 ° / 2θ or more. Alkaline storage battery. 5. The thermogravimetric thermolysis (Ni (OH) ₂ → NiO + H ₂ O) temperature of the nickel hydroxide powder is 27.
It is 0 degreeC or less, Claim 1, 2, 3, 4 characterized by the above-mentioned.
The alkaline storage battery described. 6. The alkaline storage battery according to claim 1, wherein the nickel hydroxide powder has a spherical shape.