JP2002304992A - Nickel hydroxide powder for alkaline secondary battery and its evaluation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide nickel hydroxide powder suitable for a positive electrode active material in order to improve an output characteristic and a high- temperature characteristic of an alkaline secondary battery and to provide a method for evaluating the nickel hydroxide powder with a simple means. SOLUTION: This nickel hydroxide powder has an average fine hole diameter of 5.50 nm or less, a fine hole volume of 0.03 ml/g or less and a specific surface area of 12 m<2> /g or less. In the cross-sectional structure of each particle 1 thereof, crystal grains having two or more of a ratio a/b of the long side (a) to the short side b thereof occupies 50% or more, and crystal grains each having the long side (a) thereof >=1/2 of the radius R of the particle are present or the compression strength of the particle 1 is 40 MPa or above. The cross-sectional structure of the particles 1 is evaluated by electron microscope observation by making a sample with ruptured surfaces of the particles 1 exposed by embedding the nickel hydroxide powder with a resin and by rupturing it after cooling it below the embrittling temperature of the resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nickel hydroxide powder suitable as a positive electrode active material for a non-sintered alkaline secondary battery and a method for evaluating the nickel hydroxide powder.

[0002]

2. Description of the Related Art As portable electronic devices have become smaller and lighter, batteries having a high power density have been required. Accordingly, the energy density of the secondary battery has been improving year by year, and at present, the capacity energy density has reached about 350 Wh / l.

[0003] In recent years, with the advancement of multifunctional and high-performance devices, demands for battery performance are increasing, and high-performance in a high-temperature state resulting from heat generation of the devices, or use under high loads. There is a demand for further improvement in high-temperature characteristics and output characteristics, such as higher output and longer life.

For example, as in the EU, there is a movement to restrict the use of nickel-cadmium secondary batteries in consideration of the environment (“Rare Metal News”, March 16, 1998). For this reason, development of a battery having excellent output characteristics in place of a nickel-cadmium secondary battery is urgently required. As a substitute for an inexpensive nickel-cadmium secondary battery, a nickel-metal hydride secondary battery is considered to be promising in terms of cost, and improvement of its output characteristics and high-temperature characteristics is particularly desired.

[0005] The improvement of the output characteristics of a nickel-metal hydride secondary battery is described, for example, in US Pat.
Addition of boron according to JP-A-320738,
No. 74513 proposes addition of CaF _{2 or} the like, but has not been put to practical use. In addition, improvement of the electrode structure and modification by coating have been studied,
It is not desirable because it causes an increase in cost. Under such circumstances, improvement of the nickel hydroxide powder itself, which is a positive electrode active material, is desired.

In order to improve the high-temperature characteristics of nickel-metal hydride batteries, a means of adding / dissolving a Co compound is currently employed, but many proposals have been made to further improve the charging efficiency at high temperatures. ing. For example, Japanese Patent Application Laid-Open
Japanese Patent No. 182663 describes a method for improving the solution by solid solution of zinc, magnesium, cadmium, barium and the like. JP-A-7-37586 proposes nickel hydroxide having a plate-like single crystal, a major axis of 0.005 to 1 μm, and a thickness (C axis) of 0.001 to 0.1 μm. I have. However, these methods have a problem that a decrease in the capacity of the active material itself due to the solid solution element or a decrease in the battery capacity due to a decrease in the powder density occur simultaneously.

On the other hand, nickel hydroxide powder used as a raw material for a positive electrode active material of a secondary battery is also evaluated mainly by a method of evaluating the external physical properties of the powder, such as measurement of tap density, bulk density, and particle size distribution. The method of evaluating the internal structure of the powder was not used as a judgment index of battery characteristics when used as a positive electrode active material.

In general, the most widely used method for evaluating the internal structure of various powders is to embed the powder particles in a resin, then polish the cross section, and observe the exposed polished surface using a microscope. ing. Also, a method of cutting a cross section of a resin-embedded powder by a supermicrotome method has been established as a sample pretreatment technique. However, in these methods, since the observation surface of the sample is finished very smoothly, there is a problem in that it is not possible to observe information on irregularities caused by the internal structure of the target powder, that is, information on the shape of crystal grains and the like. Was.

As a method of solving such a problem and observing and evaluating the internal structure of the powder, in the case of a metal powder such as copper or stainless steel, the cross section of the resin-embedded powder is etched to make it easier to observe the grain boundaries. The method is adopted.
However, in the case of nickel hydroxide powder, the optimum etching solution has not been clarified, and it has been difficult to easily observe the internal structure. The X-ray diffraction method for slightly evaluating the crystallinity was used to merely estimate the internal structure in the order of several to 10 μm from the measurement result of the obtained single crystal order.

[0010]

SUMMARY OF THE INVENTION In view of the above-mentioned circumstances, the present invention aims at improving the output characteristics and the high-temperature characteristics of a non-sintered alkaline secondary battery, and therefore, it is preferable to use a suitable hydroxide as a positive electrode active material. A primary object is to provide a nickel powder.

The present invention also evaluates the internal structure and physical properties of the nickel hydroxide powder by simple means to evaluate a nickel hydroxide powder suitable as a positive electrode active material for a non-sintered alkaline secondary battery. A second object is to provide a method.

[0012]

In order to achieve the first object, the nickel hydroxide powder for an alkaline secondary battery provided by the present invention has an average pore diameter of 5.50 nm or less and a pore volume of 0.03 ml. / G or less, and a specific surface area of 12 m ² /
g or less, and in the cross-sectional structure of the powder particle, the crystal grains in which the ratio of the long side a to the short side b is 2 or more occupy 50% or more, and the long side a of the crystal grain is 1 / radius R
It is characterized in that there are two or more crystal grains.

Secondly, the nickel hydroxide powder for an alkaline secondary battery provided by the present invention has an average pore diameter of 5.5.
0 nm or less, a pore volume of 0.03 ml / g or less, a specific surface area of 12 m ² / g or less, and a compressive strength of powder particles of 40 MPa or less.

In order to achieve the second object, the first aspect of the nickel hydroxide powder for an alkaline secondary battery provided by the present invention is provided.
The evaluation method is that after embedding nickel hydroxide powder in resin,
By cooling to below the embrittlement temperature of the resin and fracturing, a sample was prepared in which the fracture surface of the nickel hydroxide particles was exposed, and this was observed by observing the fracture surface of the nickel hydroxide particles in this sample. It is characterized in that an evaluation as a positive electrode active material is performed based on the internal structure.

In a second method for evaluating nickel hydroxide powder for an alkaline secondary battery according to the present invention, the compression strength of particles of nickel hydroxide powder is measured, and the evaluation as a positive electrode active material is made based on the obtained compression strength. It is characterized by performing.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted various studies and studies on nickel hydroxide powder, which is a positive electrode active material of an alkaline secondary battery, and found that the internal structure of nickel hydroxide particles or nickel hydroxide particles The present inventors have found that there is a close correlation between the compressive strength and the output characteristics and high-temperature characteristics of the alkaline secondary battery, and have reached the present invention.

The nickel hydroxide powder for an alkaline secondary battery composed of spherical particles has a structure extending radially from the center. This is considered to be because fine primary particles condense during powder synthesis to grow the particles and form a texture radially. When this radial structure develops, the crystallinity of the particles tends to develop particularly in the (001) plane, and accordingly, it has been found that the nickel hydroxide particles improve the reactivity as an electrode active material.

Regarding the internal structure of the nickel hydroxide powder, when observing the cross-sectional structure of the powder particles, the ratio of the long side a to the short side b of the crystal grain is 2 or more, that is, a / b ≧ 2. The crystal grains occupy 50% or more, and the long side a of the crystal grains is 以上 or more of the radius R of the nickel hydroxide particles, that is, a ≧ R
It is necessary that crystal grains having a relationship of / 2 exist. In particular, 50% of the crystal grains have a relationship of a ≧ R / 2.
It is preferable that these exist.

In order to examine the crystal grains in the internal structure of the nickel hydroxide particles, the cross section of the particles is observed with an observation instrument such as an SEM. For example, as described later, after embedding a large number of nickel hydroxide powders in a resin and cooling them to a temperature lower than the embrittlement temperature of the resin and breaking the resin, the fracture surface of the obtained sample has broken nickel hydroxide particles. Since the cross section is exposed, the internal tissue can be directly observed as it is.

In the nickel hydroxide powder having such a developed radial internal structure, (001)
Since the crystallite diameter of the surface is large, the compressive strength of the particles is 40
It was also found that the pressure was below MPa. Note that the compression strength St is
Hiramatsu et al.'S formula shown in the following formula 1
Vol. 932, December 1965, 1024-1
030).

[0021]

## EQU1 ## St = 2.8P / πd²  (D: particle diameter, P: load applied to particles)

The change in the internal structure of the powder particles also affects the characteristics of the aggregated nickel hydroxide powder. That is, the average pore diameter, the pore volume, and the specific surface area of the nickel hydroxide powder tended to decrease with the development of the radial structure. Specifically, the average pore diameter is 5.50 nm or less, and the pore volume is 0.5 mm.
03 ml / g or less, and a specific surface area of 12 m ² / g
g or less, and if any of these values is exceeded, the output characteristics of the battery deteriorate. Preferably, the average pore size is 5.00 nm or less and the pore volume is 0.02.
ml or less, and the specific surface area is 10 m ² / g or less.

Therefore, by using the nickel hydroxide powder having the internal structure in which the radial structure is developed as the positive electrode active material, the output characteristics and the high temperature characteristics of the alkaline secondary battery can be improved. The nickel hydroxide powder desirably contains at least one element selected from the group consisting of cobalt, manganese, and Group 2 elements of the periodic table.

Next, a method for evaluating a nickel hydroxide powder suitable as a positive electrode active material for an alkaline secondary battery, that is, capable of improving the output characteristics and high-temperature characteristics of the battery will be described.

The first of the nickel hydroxide powders in the present invention
Is a method of observing the fracture surface of the particles using an electron microscope or the like. That is, in this first evaluation method,
After embedding a large number of nickel hydroxide powders in a resin, the sample is cooled by using liquid nitrogen or the like to a temperature lower than the embrittlement temperature of the resin and broken to prepare an observation sample. Since the fracture surface of each nickel hydroxide particle is exposed in the fracture surface of the obtained sample, the internal structure of the fracture surface of the particle can be directly observed with a scanning electron microscope or the like.

The feature of the first evaluation method is that the resin in which the nickel hydroxide powder is embedded is cooled to a temperature lower than the embrittlement temperature and broken. When the resin is broken at room temperature, the resin particles are broken in a stretched manner due to the ductility of the resin itself, so that the embedded powder particles themselves are not broken. Therefore, in the present invention, in order to eliminate ductility of the resin as much as possible, the resin is broken after cooling to a temperature lower than the embrittlement temperature of the resin, whereby the internal powder particles can be broken together with the resin. As a means for cooling the resin to the embrittlement temperature or lower, in addition to liquid nitrogen, for example, a cryogen such as a mixed solution of liquid nitrogen or dry ice and an alcohol such as ethanol or methanol, a refrigerator, or the like can be used.

Specifically, for example, a commercially available cold resin is used as the embedding resin, and after about 1 g of nickel hydroxide powder is dispersed, the resin is allowed to stand at room temperature and solidified. In order to easily break the solidified powder-containing resin, it was cut about 1-2 mm upward from the bottom at the time of solidification, and a cut was made in a part of the cut disk-shaped sample. Let cool for 1-2 minutes. Then, it is taken out of liquid nitrogen and broken immediately. As a final treatment, the fracture surface is subjected to a normal conductive treatment (carbon vacuum evaporation or platinum-palladium alloy sputter coating) to obtain an observation sample for a scanning electron microscope.

Therefore, according to this method, complicated pretreatment is not required in the preparation of a conventional sample for an electron microscope, and the preparation of the sample can be reliably performed by a simple breaking operation. Moreover, since the internal structure of the nickel hydroxide particles is exposed on the fracture surface of the sample, observation with an electron microscope is possible as it is, and the internal structure of the nickel hydroxide powder can be observed and evaluated.

In particular, when evaluating the nickel hydroxide powder based on the internal structure, it is preferable to determine a numerical evaluation index so that the difference in the internal structure between the samples can be compared. Specifically, the fracture surface of the sample prepared as described above was observed, and the ratio of the long side to the short side of the crystal grains present in the nickel hydroxide particles, and the length of the crystal grains with respect to the radius of the nickel hydroxide particles The crystal grains are classified according to the classification, and the evaluation index of the internal structure of the nickel hydroxide powder is determined based on the degree of mixture of the crystal grains of each classification.

As a preferred specific example of the evaluation index, for example, as shown in FIG. 1, crystal grains 2a, 2b present on the fracture surface of nickel hydroxide particles 1 observed by an electron microscope,
A case where the internal texture index is determined based on the shape and size of 2c will be described. That is, each crystal grain 2a, 2b, 2c
Is measured, and the crystal grain 2a whose long side a is equal to or more than １ ／ of the radius R of the nickel hydroxide particle 1 is columnar (a
.Gtoreq.R / 2), the crystal grains 2c having a ratio of the long side a to the short side b of the crystal grains less than twice are granulated (a / b <2), and the crystal grains 2b having a size between the two are rod-shaped. Classify as The observation conditions with an electron microscope may be any conditions, and are preferably conditions under which the shape of crystal grains existing on the fractured surface can be most clearly observed.

Each of the crystal grains 2a, 2b,
Based on the ratio of 2c present in the fractured surface (mixture degree),
As shown in Table 1 below, the internal structure index quantified is determined depending on whether it is mainly composed of columns or mainly granular.

[0032]

[Table 1]

This internal texture index has a good correlation with the crystallinity data measured by X-ray analysis. Therefore, by using this internal structure index, the internal structure and the crystallinity of the nickel hydroxide powder can be easily and accurately evaluated only by observation with a scanning electron microscope without measuring X-ray diffraction.

The second aspect of the nickel hydroxide powder of the present invention
Is a method of measuring the compressive strength of the particles of the nickel hydroxide powder. The compressive strength of the nickel hydroxide particles varies greatly depending on the state of the internal structure. In the case of a structure parallel to the applied load direction, the structure is easily broken.
This results in a correlation between the radial tissue morphology and the compressive strength, and the particles easily break as the tissue develops.

By utilizing these characteristics, the internal structure of the nickel hydroxide powder can be evaluated based on the compressive strength, and further, the battery characteristics can be predicted. That is, if the correlation between the internal structure of the nickel hydroxide particles or the characteristics of the battery using the powder and the compressive strength of the nickel hydroxide particles is determined in advance, the particle size of the nickel hydroxide powder to be evaluated can be improved. It is possible to evaluate the nickel hydroxide powder from the correlation obtained in advance simply by measuring the compressive strength of the powder.

The compressive strength of the nickel hydroxide powder particles is measured using an apparatus having a powder probe because the particle size is very fine, 10 to 20 μm. The particles to be measured are arbitrarily selected, a load is continuously applied until the particles are crushed, and the force (load) applied when the particles are broken is measured. In order to improve the accuracy, it is desirable to measure as many particles as possible to obtain an average value. However, if the strength is obtained for about 10 arbitrary particles and the average value is taken as the compressive strength, the present invention provides Is sufficient for the evaluation.

[0037]

EXAMPLES [Production of Nickel Hydroxide Powder] High bulk density nickel hydroxide, which is a positive electrode active material, is disclosed in, for example,
It can be produced by the method described in JP-A-017429. That is, an aqueous solution containing nickel, an alkali hydroxide, and an aqueous ammonium solution are simultaneously and continuously supplied to a reaction tank equipped with a stirrer, and the concentration of nickel ions in the reaction solution is 5 to 50 mg / l and the concentration of ammonia is 6 to 6. ~ 16g / l,
This is a method in which the reaction temperature is 40 to 70 ° C., the discharge head of the stirring blade of the stirrer is 14 to 70 m ² / sec ² , and the residence time of the generated nickel hydroxide in the reaction tank is 6 hours or more.

By changing the manufacturing conditions by this method, six types of nickel hydroxide powders A to F serving as samples are obtained.
Was manufactured. The nickel hydroxide powder of all the samples had the same composition (Ni: 57 wt%, Co: 1.0 wt%, Zn:
4.0 wt%). The three types of nickel hydroxide powders D to F of the present invention have a variation range of the nickel concentration in the reaction solution of ± 2 mg / l or less, a variation range of the ammonia concentration of ± 1 g / l or less, ± 1 ° C fluctuation range of reaction temperature
It can be manufactured by operating stably for one week or more while keeping the temperature below.

For each of the obtained nickel hydroxide powders of Samples A to F, together with the crystallite diameter of the (001) plane actually measured by X-ray diffraction, the specific surface area determined by the BET one-point method,
The average pore diameter and the pore volume obtained from the pore diameter distribution measurement are shown in Table 2 below.

[Observation of Structure of Powder Cross Section] Observation samples for a scanning electron microscope for observing the internal structure of the obtained nickel hydroxide powders A to F were prepared. That is, the nickel hydroxide powder of each sample was dispersed in a resin, allowed to stand at room temperature and solidified, and then cut about 1.5 mm above the bottom. Cut a part of this disk-shaped sample,
After being immersed in liquid nitrogen for 1 to 2 minutes and cooled, it was taken out of liquid nitrogen and immediately broken. A normal conductive treatment was applied to the fractured surface to obtain a sample for observation with a scanning electron microscope.

Next, with respect to each of the obtained observation samples, the fracture surface subjected to the conductive treatment was observed with a scanning electron microscope. In sample A having a small crystallite diameter, the shape of most of the crystal grains observed in the fracture surface was granular, whereas in sample F having a large crystallite diameter, the shape of most of the crystal grains was columnar. . Other samples were observed in the same manner, and the internal structure index was determined in accordance with Table 1 which defines the relationship between the degree of mixture of crystal grains and the internal structure index. The results are shown in Table 2 below.

FIG. 2 shows the correlation between the crystallite diameter of the (001) plane of nickel hydroxide particles actually measured by X-ray diffraction and the internal structure index determined as described above. As the crystallite diameter increases, a positive correlation in which the internal texture index increases is observed, and the correlation coefficient is 0.9 or more, which is a good correlation. In addition, it is clear that only the growth of a single crystal can be quantified by the crystallite diameter by X-ray diffraction, but the growth of grains on the order of microns or more can be evaluated by the internal texture index in addition to data on the improvement of crystallinity. .

[Measurement of Compressive Strength] Next, for nickel hydroxide powders A to F, a micro compression tester MC of Shimadzu Corporation was used.
The compressive strength was measured using TM-200. That is, a test load was set to 50 mN, a load speed was set to 19.34 mN / sec, and measurement was performed for 10 arbitrary particles using a flat type indenter having a diameter of 50 μm, and the average value was defined as the compressive strength. The results obtained are shown in Table 2 below.

[0044]

[Table 2]

The (001) of each nickel hydroxide powder was
FIG. 3 shows the relationship between the crystallite diameter of the plane and the compressive strength, and FIG. 4 shows the relationship between the internal structure index and the compressive strength. It can be seen that the correlation between the compressive strength, the crystallite diameter and the internal structure index all show very good linearity. From this, by measuring the compressive strength of the nickel hydroxide particles, it is possible to obtain information on the internal structure, and the evaluation of the nickel hydroxide powder can be performed without performing X-ray removal measurement or electron microscope observation. It turns out that it is possible.

[Preparation of Battery] Using the nickel hydroxide powders of Samples A to F, a positive electrode was prepared as follows.
That is, cobalt hydroxide powder (manufactured by Ise Chemical Co., Ltd.) is added to nickel hydroxide powder so that the amount of Co in the positive electrode becomes 8 wt%, and HPC (hydroxypropyl cellulose 1000, viscosity 4000 c) is added so that the binder amount becomes 2 wt%.
P; Wako Pure Chemical Industries, first grade reagent) aqueous solution is added, paste is formed using a non-babbling kneader (manufactured by Nippon Seiko), filled into foamed nickel ("Celmet" manufactured by Sumitomo Electric; porosity 97%), and dried. After that, isostatic pressing was performed at a pressure of ² ton / cm ² .

Along with the positive electrode thus prepared, a cadmium electrode was used as a negative electrode, a sulfonated polyolefin insulative cloth was used as a separator, and 7.2 mol / mol of electrolyte was used.
Using 1 l of aqueous potassium hydroxide solution, an alkaline secondary battery was produced.

[Evaluation of Batteries] Batteries (test cells) prepared for each of the nickel hydroxide powders of Samples A to F above were kept in a thermostat to keep the temperature constant (20 ° C.) and charged at 0.1.
C was performed up to 150% of the theoretical capacity (289 mAh / g), and discharge was performed up to 1.0V at 0.2C, 1C and 3C. At this time, the utilization is expressed as a percentage of the discharge capacity with respect to the theoretical capacity. Furthermore, as high temperature characteristics, 50 ° C
In the same manner, charging at 0.1 C and discharging at 0.2 C were performed, the utilization at that time was obtained, and the ratio (%) to the utilization at 20 ° C./0.2 C was calculated. . The results obtained are summarized in Table 3 below.

[0049]

[Table 3]

From the above results, it can be concluded that the structure inside the particles develops, and therefore, the higher the internal structure index or the smaller the compressive strength of the particles, the higher the utilization factor and the less the deterioration during high-rate discharge. it is obvious. Regarding the high-temperature properties, the ratio of the utilization rate at 50 ° C. as compared with the utilization rate at 20 ° C. is higher as the internal structure index is higher or the compressive strength is lower, and the decrease in the utilization rate at high temperatures is lower. It turns out that it is suppressed.

The present invention is not limited to the nickel hydroxide powder having the composition shown in the examples. The high-temperature characteristics can be improved by increasing the amount of nickel hydroxide powder in the solid solution of cobalt, and can also be improved by coating with cobalt hydroxide. The present invention can be applied to nickel oxide powder, and a similar effect can be obtained.

[0052]

According to the present invention, it is possible to provide nickel hydroxide which is suitable as a positive electrode active material of an alkaline secondary battery. By using this nickel hydroxide powder, excellent output characteristics and high temperature characteristics are obtained. An alkaline secondary battery can be manufactured. In addition, nickel hydroxide powder suitable as a positive electrode active material for an alkaline secondary battery can be easily and reliably selected and controlled by evaluation of the internal structure of the powder particles or evaluation based on the compressive strength of the particles.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing crystal grains present in a fracture surface of nickel hydroxide particles observed by an electron microscope.

FIG. 2 is a graph showing the relationship between the (001) crystal grain size of nickel hydroxide particles and the internal texture index.

FIG. 3 is a graph showing the relationship between the (001) crystal grain size of nickel hydroxide particles and compressive strength.

FIG. 4 is a graph showing the relationship between the internal structure index of nickel hydroxide particles and compressive strength.

[Description of Signs] 1 Nickel hydroxide particles 2a, 2b, 2c Crystal grains

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G048 AA02 AB02 AC06 AD03 AD06 AE05 5H050 AA05 BA11 CA03 CA04 CB16 FA17 GA02 GA05 GA28 HA00 HA05 HA06 HA07

Claims (6)

[Claims] 1. An average pore size of 5.50 nm or less, a pore volume of 0.03 ml / g or less, and a specific surface area of 12 m ² / g.
g or less, and in the cross-sectional structure of the powder particle, the crystal grains in which the ratio of the long side a to the short side b is 2 or more occupy 50% or more, and the long side a of the crystal grain is 1 / radius R
A nickel hydroxide powder for an alkaline secondary battery, wherein two or more crystal grains are present. 2. The water for an alkaline secondary battery according to claim 1, wherein 50% or more of the crystal grains whose long side a of the crystal grains is at least の of the radius R of the particles are present. Nickel oxide powder. 3. An average pore diameter of 5.50 nm or less, a pore volume of 0.03 ml / g or less, and a specific surface area of 12 m ² / g.
g or less, and the compressive strength of the powder particles is 40 MPa or less, the nickel hydroxide powder for an alkaline secondary battery. 4. After embedding the nickel hydroxide powder in a resin,
By cooling to below the embrittlement temperature of the resin and fracturing, a sample was prepared in which the fracture surface of the nickel hydroxide particles was exposed, and this was observed by observing the fracture surface of the nickel hydroxide particles in this sample. A method for evaluating a nickel hydroxide powder for an alkaline secondary battery, wherein the evaluation as a positive electrode active material is performed based on the internal structure. 5. The long side a and the short side b of the crystal grain in the fracture surface of the nickel hydroxide particle and the radius R of the grain are determined, the ratio of the long side a to the short side b of the crystal grain, and the long side of the crystal grain. Classifying the crystal grains according to the ratio of a to the radius R of the particles, determining an evaluation index of the internal structure of the nickel hydroxide powder based on the degree of mixture of the crystal grains of each classification, and performing evaluation based on the evaluation index The method for evaluating a nickel hydroxide powder for an alkaline secondary battery according to claim 4, characterized in that: 6. A method for evaluating a nickel hydroxide powder for an alkaline secondary battery, comprising measuring the compressive strength of particles of the nickel hydroxide powder, and performing an evaluation as a positive electrode active material based on the obtained compressive strength. .