JPH1074513A - Nickel hydroxide active material and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce drop in potential in high rate discharge and enhance charging efficiency at high temperature by containing powdery CaF 2 or calcium compound on the inside of nickel hydroxide particles so as to localize in the central part. SOLUTION: CaF2 or calcium compound particles are used as a nucleus, and a nickel hydroxide is crystallized and grown on the surfaces of the nucleus particles. Particle structure constituted by covering powdery CaF2 or calcium compound with nickel hydroxide is easily obtained without forming the calcium compound forming a resistance layer on the interface between a substrate and the nickel hydroxide. As a result, a nickel hydroxide active material containing the CaF2 or the calcium compound on the inside of nickel hydroxide particles so as to localize in the central part is obtained, the utilization factor is enhanced at the wide temperature range, and drop in potential at high rate discharge is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel hydroxide active material and a method for producing the same, and more particularly to an improvement in charging efficiency of a nickel hydroxide active material used for a nickel positive electrode for a secondary battery at a high temperature, and a discharge potential at a high rate. A nickel hydroxide active material having improved and improved electrode swelling suppression during overcharge and a method for advantageously producing the same are proposed.

[0002]

2. Description of the Related Art Nickel hydroxide is an industrial product used for various applications. Particularly, for a non-sintered nickel positive electrode for an alkaline battery, the particle shape is spherical and its particle size is large. What has a narrow distribution is required. This is achieved by using such nickel hydroxide particles.
When the nickel positive electrode is filled into a carrier or the like as an active material, the particles do not fall off from the fine pores of the carrier and can be densely packed. In the case of using, the paste property such as fluidity is stabilized, so that the filling property and the filling rate are improved. Therefore, in each case, the utilization rate of the active material is improved, and an electrode having excellent performance can be obtained. However, nickel hydroxide produced by the conventional method has a drawback that the charging efficiency at a high temperature is reduced and the utilization rate is reduced.

[0003] Therefore, among such prior arts, as a method of improving the high-temperature charging efficiency, C with a large oxygen overvoltage is used.
There has been proposed a method of mixing and adding the compound a at the time of preparing a paste (Japanese Patent Application Laid-Open No. 5-101825) and a method of coating and adding to the surface of nickel hydroxide particles (Japanese Patent Application Laid-Open No. 7-272722). Further, as a method of suppressing electrode swelling during overcharge, there has been proposed a method of suppressing the generation of γ-NiOOH by forming a solid solution of Zn and Co (Japanese Patent Laid-Open No. 7-77129).

[0004]

The technique of adding calcium to the nickel hydroxide active material employed in the conventional method certainly increases the oxygen overvoltage of the nickel hydroxide active material,
It has the effect of improving high temperature characteristics. Further, by forming a solid solution of Zn and Co, there is an effect of suppressing generation of γ-NiOOH and preventing electrode swelling.

However, in the proposals disclosed in JP-A-5-101825 and JP-A-7-2727227, the added Ca compound intervenes between the current collector Ni substrate and the nickel hydroxide to form a resistance layer. , There is a problem that the discharge potential decreases in the high-rate discharge and the utilization rate decreases.

Further, in the proposal of the above-mentioned Japanese Patent Application Laid-Open No. 7-77129, a method in which Zn and Co metal elements are precipitated and formed into a solid solution in nickel hydroxide particles at the same time as the so-called coprecipitation addition is used. Although a method of containing the particles in nickel hydroxide particles is employed, a large amount of Zn and Co is required to exhibit the effect. For this reason, Z
n and Co act as impurities. This reduces the discharge capacity per unit weight of the filling.

Accordingly, the present invention has developed a method for producing a nickel hydroxide active material capable of improving the charging efficiency at a high temperature without lowering the potential at a high rate. It is an object of the present invention to provide a nickel hydroxide active material with further improved swelling suppression.

[0008]

Means for Solving the Problems The inventors of the present invention have made intensive studies for realizing the above-mentioned object, and as a result, have completed the present invention having the following constitution as a summary. That is, the nickel hydroxide active material of the present invention contains granular CaF ₂ or Ca
It is characterized in that the compound is contained in a state of being localized from the central portion inside the nickel hydroxide particles. In another aspect, the nickel hydroxide active material of the present invention comprises a plurality of particulate CaF ₂ or Ca inside the nickel hydroxide particles.
A compound is characterized in that the CaF ₂ or Ca compound is contained in a state of being localized from the central portion inside the nickel hydroxide particles. Here, the CaF ₂ or Ca compound preferably has an average particle diameter of 0.1 to 5 μm and an addition amount of 0.5 to 3% by weight based on nickel hydroxide. In addition, Mg and / or Fe is preferably contained in the nickel hydroxide in an amount of preferably 0.1 to 3.0 wt%.
It is preferably added in a solid solution state of 0.01 to 0.5 wt%. Further, it is preferable that the amount of the CaF ₂ or Ca compound, Mg and / or Fe added to nickel hydroxide is 4 wt% or less. As a method for advantageously producing such a nickel hydroxide active material, the present invention provides a nickel salt aqueous solution, an ammonium ion supplier and a hydroxide solution in an aqueous solution in which granular CaF ₂ or a Ca compound is previously suspended. An alkaline aqueous solution is added under stirring conditions, and with the particles of CaF ₂ or Ca compound as nuclei, nickel hydroxide is crystallized and grown on the particle surface, whereby granular CaF ₂ or Ca compound is obtained.
The present invention proposes a method for producing a nickel hydroxide active material, characterized in that the nickel hydroxide active material is contained in a state localized from the central portion inside the grown nickel hydroxide particles. The nickel salt aqueous solution contains one of magnesium ions and iron ions.
Alternatively, it is preferable to add a mixed aqueous solution containing both of them. Furthermore, in adopting such a method,
The CaF ₂ or Ca compound has an average particle size of
0.1-5 μm, the amount of addition is based on nickel hydroxide
It is preferably 0.5 wt%.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing a nickel hydroxide active material according to the present invention is characterized in that particles of CaF ₂ or a Ca compound are used as nuclei, and nickel hydroxide is crystallized and grown on the surfaces of the core particles. There is. According to such a method of the present invention, Ca serving as a resistance layer is provided at the interface between the substrate and nickel hydroxide.
It is easy to form granular CaF ₂ without forming a compound.
Alternatively, a particle structure in which a Ca compound is included in nickel hydroxide can be used, so that CaF ₂ or Ca
It is possible to obtain a nickel hydroxide active material containing the compound in a state where the compound is localized at a central portion inside the nickel hydroxide particles. Therefore, according to the present invention, the utilization factor is further improved over a wide temperature range as compared with the prior art,
It is possible to provide a nickel hydroxide active material with a small decrease in potential in high-rate discharge.

In the present invention, as the core particles for crystallizing nickel hydroxide, CaF ₂ or Ca (O
H) Ca compounds such as ₂ and CaSO ₄ are used. The reason for this is that the CaF ₂ or Ca compound does not dissolve and precipitate in the nickel salt aqueous solution to form the Ni—Ca compound. Therefore, in the present invention, such CaF ₂
Or, among Ca compounds, particularly insoluble CaF ₂ is most preferable.

In the present invention, the CaF ₂ or Ca compound preferably has a particle size of 0.1 to 5 μm. The reason for this is that below 0.1 μm, CaF
_{This is because the 2} or Ca compound aggregates and it is difficult to uniformly incorporate the compound in the nickel hydroxide.
When m exceeds m, it is difficult to incorporate the particles in the nickel hydroxide particles, and it is difficult for the nickel hydroxide to be densified.

Further, in the present invention, C added as a nucleus
amount of aF ₂ or Ca compound is preferably a 0.5 wt% to 3 wt% relative to the nickel hydroxide powder weight.
The reason is that if the added amount is small, sufficient effect cannot be obtained,
This is because if the amount is too large, the energy density is reduced.

In the present invention, the nickel hydroxide active material preferably has a spherical shape. The reason is that when a spherical nickel hydroxide active material is used, the filling property and the filling rate are improved, and as a result, the utilization rate as the active material is improved.

In the method of the present invention, an aqueous solution of various water-soluble nickel salts such as nickel nitrate, nickel sulfate and nickel chloride can be used as the nickel salt aqueous solution. The concentration of this nickel salt aqueous solution is usually 0.5 to
It is appropriate to use about 3 mol / l.

As the aqueous alkali hydroxide solution, sodium hydroxide, potassium hydroxide or the like can be used. This aqueous alkali hydroxide solution is usually preferably used as an aqueous solution of about 4 to 8 mol / l.

As the ammonium ion supplier, aqueous ammonia, ammonia gas, or an aqueous solution of an ammonium salt such as ammonium nitrate can be used. In the case of aqueous ammonia, it is appropriate to use one having a concentration of about 28% by weight. In the case of an aqueous solution of an ammonium salt, it is usually appropriate to use a solution having a concentration of about 16 mol / l.

The method of supplying the reaction system is carried out with sufficient stirring, and the rate of addition depends on the capacity of the reaction vessel,
The residence time in the reaction system is usually 8
It is good to adjust appropriately so that it may be up to 30 hours.

The temperature of the reaction system at this time is 40 to 50 ° C.
Is kept constant. Usually, it is preferable to maintain the temperature at a predetermined value of about ± 2 ° C. Similarly, the pH of the reaction system is 11-12
Is kept constant. Normally, it is preferable to maintain the value at about ± 0.1.

[0019]

【Example】

Example 1 35 g of calcium fluoride powder having an average particle size of 2.2 μm was dispersed in water and stirred in a 2 liter reaction layer, and then a nickel sulfate aqueous solution adjusted to a predetermined concentration was mixed with 28% by weight. Of ammonia water and a 6 mol / l aqueous solution of sodium hydroxide were supplied at a constant rate to carry out a reaction at a constant pH, and nickel hydroxide was crystallized and grown using calcium fluoride as a seed crystal. The reaction was stopped 10 hours after the start of the reaction, and the obtained nickel hydroxide active material was washed and dried to obtain a sample A. An active material was produced in the same manner as described above except that a mixed solution of an aqueous solution of magnesium sulfate and an aqueous solution of iron sulfate was added to the aqueous solution of nickel sulfate to obtain a sample B.

The obtained nickel hydroxide active material (sample A)
Had an average particle size of 7 μm and a tap density of 2.0 g / ml. The nickel hydroxide active material contained 1.6% by weight of calcium fluoride with respect to the nickel hydroxide in the active material. The cross section of the particles was subjected to line analysis by EDS, and as shown in FIG. As described above, Ni was present in a form including CaF ₂ particles, and it was confirmed that a plurality of calcium fluoride particles were incorporated into the nickel hydroxide particles. The nickel hydroxide active material of the sample B had a solid solution state of 1 wt% of magnesium and 0.1 wt% of iron.

This nickel hydroxide active material (samples A and B)
5% by weight of water and CoO to make paste, porosity 95%
And dried at 100 ° C. for 1 hour and then pressed to obtain a nickel positive electrode. A battery was assembled using the obtained nickel positive electrode as a negative electrode of an MH alloy as a counter electrode, and the positive electrode utilization rate (active material utilization rate) at 0.2 C, 3 C and 45 ° C. discharge and the discharge position at 3 C discharge were measured. Table 1 shows the results.

Comparative Example As a comparative example, a nickel hydroxide active material without any additive such as calcium (sample C), a nickel hydroxide active material comprising 1 part by weight of Mg and 0.1 part by weight of Fe without addition of Ca (Sample D) Without adding Ca, 1.6 parts by weight of nickel hydroxide consisting of 1 part by weight of Mg and 0.1 part by weight of Fe
Nickel hydroxide active material (Sample E) mixed with CaF ₂ powder of 1 wt% and 1.6 wt% of Ca (O
H) A nickel hydroxide active material (sample F) on which ₂ was precipitated was prepared, CoO and water were added to each nickel hydroxide active material, a positive electrode was prepared in the same manner as in the above example, and a battery was assembled. The positive electrode utilization rate (active material utilization rate) of the battery at 25 ° C / 0.2C, 25 ° C / 3C, 45 ° C / 0.2C charge / discharge and the discharge position at 3C discharge were measured. The results are shown in Table 1. The utilization rate was defined by the following equation.

[0023]

[Table 1]

As is clear from the results shown in Table 1, the samples (B and C) containing no calcium compound have a low positive electrode utilization at high temperatures. Sample C containing magnesium and iron
The discharge potential was improved by 30 mV or more as compared with the sample B without addition.

In particular, as apparent from the results shown in Table 1, Samples A and B in which calcium fluoride was added and contained in nickel hydroxide particles and Sample E in which calcium fluoride was simply added to nickel hydroxide and mixed. In comparison with Sample F in which calcium hydroxide was precipitated on the particle surface, A and B according to the present invention obtained higher discharge potential and higher utilization at a high rate. This indicates that the presence of the Ca compound on the surface of the nickel hydroxide particles causes a decrease in the discharge potential at a high rate, and that calcium fluoride is incorporated inside the nickel hydroxide particles. Thus, the discharge potential at a high rate can be improved while maintaining a high utilization rate at a high temperature.

Next, in the examples, in order to examine the optimum amounts of calcium fluoride and solid solution magnesium and iron present in the nickel hydroxide, a nickel hydroxide active material (sample G ~ L), and
CoO and water were added to each nickel hydroxide active material to form a positive electrode in the same manner as in the above example, and batteries were assembled. Each battery was charged and discharged at 25 ° C / 0.2C, 25 ° C / 3C, 45 ° C / 0.2C. The positive electrode utilization rate (active material utilization rate) and the discharge potential in 3C discharge were measured. Table 2 shows the results.

[0027]

[Table 2]

As is clear from the results shown in Table 2,
The utilization rate of the positive electrode of the nickel hydroxide active material increases with the content of calcium fluoride as a seed crystal up to 2% by weight, and decreases when the content exceeds 2% by weight. Similarly, the utilization rate of the positive electrode of the nickel hydroxide active material increases with the content of magnesium dissolved in nickel hydroxide up to 1 wt%, and decreases when the content exceeds 2 wt%. Further, as the content of iron dissolved in nickel hydroxide is smaller, the utilization rate of the positive electrode is improved. If the amount of calcium fluoride and solid solution magnesium and iron added as seed crystals of nickel hydroxide is too large, the proportion of nickel hydroxide in the positive electrode active material will decrease, and the capacity density of the positive electrode will decrease .

As is clear from the results shown in Table 2, the discharge potential of the nickel hydroxide active material at a high rate increases in proportion to the amount of magnesium and iron contained.

Next, to see the effect of suppressing electrode swelling, Zn
Sample M and Sample B in which 4.7 wt% and Co 0.7 wt% are dissolved.
~ L, and the nickel hydroxide active material is C
A positive electrode was prepared in the same manner as in the above example by adding oO and water, and a battery was assembled. The thickness of the electrode before the test and the thickness of the electrode after the 400% overcharge test were measured. It was calculated from the formula. Table 3 shows the results.

[0031]

[Table 3]

As is evident from the results shown in Table 3, the electrode expansion coefficients of the sample C without the additive and the sample D without the Ca were significantly higher than those of the samples (B, G to L) of the present invention. It was big. In addition, the electrode swelling suppressing effect was improved with an increase in the amount of added magnesium and iron. In addition, the sample prepared according to the present invention can suppress swelling of the electrode with a small amount of addition as compared with the sample M in which Zn and Co are dissolved.

[0033]

As described above, according to the method of the present invention, a granular CaF ₂ or Ca compound can be easily hydroxylated without forming a Ca compound serving as a resistance layer at the interface between the substrate and nickel hydroxide. It is possible to obtain a nickel hydroxide-containing active material containing CaF ₂ or a Ca compound in a localized state from the central portion inside the nickel hydroxide particles. As a result, it is possible to provide a nickel hydroxide active material with a further improved utilization factor over a wide temperature range as compared with the prior art, and with a small decrease in potential at high-rate discharge. Further, Mg and Fe are each 0.1 to 3.0 in the nickel hydroxide.
High energy density nickel hydroxide with improved discharge potential at high rates and reduced electrode swelling with less additive than conventional technology by being added in a solid solution state of wt% and 0.01-0.5 wt% can do.

[Brief description of the drawings]

FIG. 1 is a micrograph showing the particle structure of a nickel hydroxide active material according to the present invention, wherein (a) shows the results of a line analysis of nickel and (b) shows the results of a line analysis of calcium.

Continued on the front page (72) Koichi Kobe, Inventor 8-4 Koamicho, Nihonbashi, Chuo-ku, Tokyo Inside Japan Heavy Chemical Industry Co., Ltd.

Claims (8)

[Claims] 1. A nickel hydroxide active material characterized in that it contains granular CaF ₂ or a Ca compound in a localized state from the central portion inside the nickel hydroxide particles. 2. A plurality of particulate CaF ₂ or Ca compounds are contained inside the nickel hydroxide particles, and the CaF ₂ or Ca compounds are contained in a state localized at a central portion inside the nickel hydroxide particles. A nickel hydroxide active material, characterized in that: 3. The nickel hydroxide according to claim 1, wherein the CaF ₂ or Ca compound has an average particle size of 0.1 to 5 μm, and an amount of the CaF ₂ or Ca compound is 0.5 to 3 wt% based on the nickel hydroxide. Active material. 4. The nickel hydroxide contains 0.1 to 3.0 wt% and 0.01 to 0.5 wt% of Mg and / or Fe, respectively.
The solid solution is added in a state of claim 1.
3. The nickel hydroxide active material according to any one of 3. 5. The nickel hydroxide active material according to claim 1, wherein the amount of the CaF ₂ or Ca compound, Mg and / or Fe added to nickel hydroxide is 4 wt% or less. 6. An aqueous nickel salt solution, an ammonium ion donor and an aqueous alkali hydroxide solution are added to an aqueous solution in which granular CaF ₂ or a Ca compound is suspended in advance, and the CaF ₂ or Ca compound particles are added. Nuclei are used to crystallize and grow nickel hydroxide on the surface of the particles, so that granular CaF ₂ or a Ca compound is contained in a state localized from the central portion inside the grown nickel hydroxide particles. A method for producing a nickel hydroxide active material, comprising: 7. The method for producing a nickel hydroxide active material according to claim 6, wherein an aqueous solution containing one or both of magnesium ions and iron ions is added to the aqueous nickel salt solution. 8. The nickel hydroxide active material according to claim 6, wherein the CaF ₂ or Ca compound has an average particle size of 0.1 to 5 μm, and an amount of the CaF ₂ or Ca compound is 0.5 to 3% by weight based on the nickel hydroxide. .