JPH11185747A - Positive electrode material for alkaline storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the utilization ratio to be a maximum level without changing concentration of aluminum by controlling the crystallization determined from an X-ray diffraction pattern, as an aluminum contained nickel hydroxide to be used as a positive electrode material. SOLUTION: An αtype Al substituted Ni(OH)2 represented by a structural formula: (Alx Ni1-x )(OH)2 Y, where 0.15<x<0.3, Y is negative ion, is used as a positive electrode material. Ion sulfate, ion nitrate or ion carbonate is preferably used as the negative ion of Y. The half-value width of (003) peak of the Al substituted α-nickel hydroxide, in an X-ray diffraction pattern may be arbitral. However, it is desirable to be less than 8.2 Å. The crystallization of Al substituted α-nickel hydroxide is improved according to the largeness of the alkali-metal ratio. The crystallization is also improved according to the length of aging time and the highness of temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a cathode material for an alkaline storage battery and an alkaline storage battery using the cathode material.

[0002]

2. Description of the Related Art A nickel hydroxide positive electrode commonly used in alkaline storage batteries such as nickel-cadmium storage batteries and nickel-metal hydride storage batteries is required to have a high energy density. In the course of the increase, the paste type capable of increasing the capacity density has been mainly used instead of the conventional sintered type. The paste-type nickel positive electrode is obtained by filling a nickel foam powder or a nickel fiber substrate having a high porosity of about 95% with a nickel compound powder and a cobalt compound powder and press-forming. Such a foamed nickel substrate is obtained by plating nickel on a foamed plastic such as urethane and then heating it to thermally decompose the foamed plastic to obtain a foamed metal.

The reaction during charging and discharging of nickel hydroxide, which is a positive electrode material for an alkaline storage battery, is generally carried out by β-Ni (O
It utilizes the reaction between H) ₂ and β-NiOOH, which is a one-electron reaction, but the most stable and widely used.

[0004] This is called β-Ni (OH) ₂ and γ-NiOOH.
If a multi-electron reaction is obtained by utilizing the reaction between
There is an advantage that capacity is increased. However, β-Ni
There is a problem that the volume change during charging and discharging is large due to the difference in lattice constant between (OH) ₂ and γ-NiOOH.

On the other hand, α-Ni (OH) ₂ and γ-NiOOH
Is advantageous in that the capacity is increased because this is also a multi-electron reaction, and α-Ni (O
H) ₂ and γ-NiOOH have a small difference in lattice constant, so that the change in volume during charging and discharging is small, which is preferable.

However, α-Ni (OH) ₂ is unstable in an alkaline solution and easily changes to β-Ni (OH) ₂ . . FIG. 1 shows an X-ray diffraction diagram of a typical α-Ni (OH) ₂ and the surface index of the peak.

As an attempt to stabilize such α-Ni (OH) ₂ , there is a report that part of Ni is replaced with Al, Fe, Cr or the like. There is a report on the correlation of the discharge potential (JP-A-49-109842). However, even in this publication, there is no report on the correlation between the crystallinity of nickel hydroxide and the battery characteristics at the same Al concentration.

Accordingly, an object of the present invention is to provide a positive electrode material for an alkaline storage battery with an improved utilization factor and an alkaline storage battery using the positive electrode material.

[0009]

Means for Solving the Problems As a result of intensive studies, the present inventors have controlled the crystallinity determined from the X-ray diffraction diagram of aluminum-containing nickel hydroxide used as a cathode material for alkaline storage batteries. By doing so, it was found that the maximum utilization rate can be obtained without changing the aluminum concentration.

The present invention has been made based on the above findings, and has the following composition formula (Al _x Ni _{1 -x} ) (OH) ₂ Y (where 0.15 <x <0.3, Y is an anion) ) represented by α-type Al-substituted Ni (OH) a _2, full width at half maximum of the peak of the X-ray diffraction diagram (003) is 1.5deg
A positive electrode material for an alkaline storage battery, wherein

Further, the present invention provides an alkaline storage battery using the above-mentioned positive electrode material.

[0012]

By appropriately setting the synthesis conditions, the crystallinity can be improved even at the same Al concentration so that the full width at half maximum of the (003) peak in the X-ray diffraction diagram is less than 1.5 deg. It has been experimentally found that (1) the spacing between the c-plane (001) planes is reduced; (2) the a-axis directions of the respective c-plane layers are aligned; The increase in capacity can be considered in relation to these events as follows.

[0013] While the present as bivalent Ni is in a hydroxide, it is considered that Al is incorporated by trivalent, because of its charge compensation, NO ₃ between the layers of c-plane ^-, C
O ₃ ^{2 -} such anions are incorporated. But in reality,
Since there are many OH defects, anions are similarly taken in between layers for charge compensation by that amount, and it is considered that a larger amount of anions is present than necessary for charge compensation of Al. It is considered that the reason why the spacing between the c-planes is reduced when the crystallinity is improved by changing the synthesis conditions is that the OH deficiency is reduced and the anions that compensated for this are reduced and the amount required for Al charge compensation is approached. . Since the anions between the layers are likely to hinder the entry and exit of H ⁺ during charging and discharging, it is considered that if the number of ions decreases, the utilization rate of the battery increases.

The anions and H ₂ O between the layers are considered to be hydrogen-bonded to the OH groups in the c-plane layer. However, if the a-axis direction of each layer becomes uniform, the distribution of hydrogen bonds between the layers becomes regular. Occur, making it difficult to prevent the movement of H ⁺ during charge and discharge.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The nickel hydroxide used as the positive electrode material for an alkaline storage battery of the present invention has the following composition formula (Al _x Ni _{1 -x} ) (OH) ₂ Y (0.15 <x <0.3, Y is an anion) Is an α-type Al-substituted Ni (OH) ₂ represented by Here, when x is 0.15 or less, the α phase of nickel hydroxide is not stable. When x is 0.3 or more, the capacity decrease due to the decrease in nickel directly involved in charge / discharge exceeds the capacity increase due to the addition of aluminum. I will. Y represents an anion, such as a sulfate ion, a nitrate ion, and a carbonate ion.

Further, the full width at half maximum of the (003) peak in the X-ray diffraction of the above nickel hydroxide needs to be less than 1.5 deg, and preferably less than 0.5 deg. The full width at half maximum of the peak of (003) is 1.5 deg.
With the above, a sufficient utilization rate cannot be obtained.

Further, the d value of the (003) peak in the X-ray diffraction pattern of the nickel hydroxide is not particularly limited, and is arbitrary, but preferably less than 8.2 °.

The above-mentioned aluminum-substituted α-nickel hydroxide is produced by the following method. First, an aqueous metal salt solution and an aqueous alkali solution as a raw material for producing nickel hydroxide include aluminum sulfate, aluminum nitrate, nickel sulfate, nickel nitrate, potassium hydroxide, sodium hydroxide, and lithium hydroxide.
Aluminum chloride, nickel chloride, ammonia and the like can also be used. Among them, the crystallinity of aluminum-substituted α-nickel hydroxide obtained from a combination of nitrate and lithium hydroxide is the best under the same synthesis conditions.

An aqueous solution of a metal salt and an aqueous solution of an alkali having a predetermined ratio of aluminum / nickel within the above range are mixed. At the time of mixing, a static mixer may be used to keep the alkali / metal ratio constant and to make the reaction uniform. Thereafter, aging, washing, filtration and drying are performed to obtain aluminum-substituted α-nickel hydroxide.

Here, (1) As the alkali / metal ratio increases, the crystallinity of the obtained aluminum-substituted α-nickel hydroxide improves. (2) The longer and higher the aging time and temperature, the better the crystallinity of the aluminum-substituted α-nickel hydroxide. However, since the process of improving the crystallinity of the α phase is also a competitive reaction with the α → β transition reaction,
In order to obtain a highly crystalline α phase without causing a transition, the above (1)
And the range of (2) is limited, and it depends on the Al concentration.

That is, when the Al concentration is high, the alkali /
Even under the condition of metal ≧ 2 (equivalent or more), the α phase is maintained and crystallization proceeds. Also, if the Al concentration is low, β-formation occurs even at room temperature aging at an equivalent amount, so it is necessary to set alkali / metal <2.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments and the like.

Test Example 1 The discharge potential was evaluated by changing only the concentration of Al substituted in α-Ni (OH) ₂ . The result is shown in FIG. In addition, the utilization rate was evaluated. The result is shown in FIG. As is apparent from FIGS.
It can be seen that up to 25%, the discharge intermediate potential and the utilization rate increase as the concentration increases.

Here, the utilization factor is obtained by dividing the discharge capacity per unit weight of the positive electrode material by the discharge capacity per unit weight obtained when Ni contained in the material is completely oxidized from divalent to trivalent. Value. The discharge intermediate potential indicates a potential at a half point of the capacity in the third cycle.

Test Example 2 FIG. 4 shows the distribution of phases obtained when the aging temperature and the alkali / metal ratio were changed in the synthesis of Al-substituted Ni (OH) ₂ . In FIG. 4, (a) shows an aluminum content of 20 mol% (x = 0.
2) and (b) show an aluminum content of 10 mol% (x =
0.1) and (c) are aluminum content of 5 mol% (x =
0.05). In addition, ● represents an α-phase single phase, and ○ represents a β-phase single phase or an α + β mixed phase. From FIG. 4, it can be seen that, when Al is 10 mol% and 5 mol%, the β phase is already generated under the equivalent conditions, so that the α phase is unstable.

Example 1 Ni with a concentration of 1.5 mol / l
SO ₄ or Ni (NO ₃ ) ₂ + Al ₂ (SO ₄ ) ₃ or Al
(NO ₃ ) ₃ (however, Ni: Al = 8: 2) mixed solution 1
One liter was mixed with one liter of a solution of NaOH, LiOH or NH ₃ using a static mixer.

The alkali / metal ratio was 1 to 3, the autoclave was used for aging, and the temperature was appropriately set so that the α phase was formed at a temperature of 30 to 150 ° C. The aging time is 16 hours. The obtained precipitate was washed with pure water, filtered, and air-dried at 50 ° C. This powder was pulverized by an appropriate means, and X-ray diffraction was measured. FIG. 5 shows X-ray diffraction patterns of four representative samples.
Table 1 shows the synthesis conditions for (a)-(b) and FIGS. 6 (a)-(b). 5 (a) is the compound of Table 1 (a), FIG. 5 (b) is the compound of Table 1 (b), FIG. 6 (a) is the compound of Table 1 (c), and FIG. FIG. 2 is an X-ray diffraction diagram of the compound of Table 1 (d).

[0028]

[Table 1]

In the battery test, these nickel hydroxides were used as a cathode material (cathode active material), and the cathode material: Co (O
H) A structure was prepared in which 0.1 g of a positive electrode mixture mixed so as to have a weight ratio of 2: 2: 3: 1 with a ₂ : Co: PTFE binder was weighed and sandwiched between nickel foam and a nickel mesh. A nickel mesh was used for the counter electrode. The electrolyte was 7 NKOH containing 0.1 N LiOH. Both charging and discharging were performed at 0.2 C, charging was performed for 7.5 hours, and discharge cutoff potential was set at 0.1 V with respect to the Hg / HgO reference electrode.

As a result, a standard sample (containing Co and Zn and having a Ni content of 55.8) subjected to a battery test under the same conditions was used.
%) Was 140%.

FIG. 7 shows the utilization factor of the (003) peak in the X-ray diffraction diagram with respect to the full width at half maximum, and FIG. 8 shows the discharge intermediate potential with respect to the d value of the (003) peak in the X-ray diffraction diagram. From Example 1, even with the same Al concentration, if the crystallinity is improved, the utilization factor for Ni is also increased.
It turns out that a multi-electron reaction is occurring. It can also be seen that, even at the same Al concentration, the discharge potential increases when the c-plane spacing decreases. The discharge capacity per unit weight also increases as the crystallinity improves, but the best one is 110% of the standard sample.

FIG. 9 shows a charge / discharge diagram of the sample and the standard sample shown in Table 1 (d). In the sample of Table 1 (d), it can be seen that the charged portion of Ni and the oxygen generating portion are clearly separated. This eliminates the necessity of overcharging, which is conventionally indispensable for the positive electrode of an alkaline storage battery, and can be expected to improve charging efficiency.

Comparative Example 1 Ni having a concentration of 1.5 mol / l
SO ₄ + Al ₂ (SO ₄ ) ₃ mixed solution (Ni / Al = 8 /
2) 1 liter was mixed with 1 liter of a NaOH solution prepared so that alkali / metal = 4.36 using a static mixer, and aged at 100 ° C. in an autoclave. Example 1
A battery test was performed in the same manner as described above. FIG. 10 shows an X-ray diffraction diagram of this aluminum-containing nickel hydroxide.

FIG. 10 shows that this sample is not a single α-phase but a β-phase. Α of this sample
Focusing on the phase peaks, the crystallinity is better than the sample of FIG. 5 (b), and although it is close to FIG. 6 (a), the utilization is 141%, which is 21% lower than the sample of FIG. 5 (b). Was. Also, the discharge potential is lower than that of the sample of FIG. This can be explained by considering that the α phase having better crystallinity has a higher discharge potential and a higher utilization factor than the β phase. Thus, α- (Al, Ni, (OH) ₂
Ni) (OH) ₂ has a higher discharge potential and a higher utilization factor.

[0035]

As described above, the utilization factor can be improved by the positive electrode material for an alkaline storage battery of the present invention.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of a typical α-Ni (OH) ₂ .

FIG. 2 is a graph showing a relationship between an Al concentration and a discharge intermediate potential in Test Example 1.

FIG. 3 is a graph showing the relationship between Al concentration and utilization in Test Example 1.

FIG. 4 is a graph showing phases obtained when the aging temperature and the alkali / metal are changed in the synthesis of (Al _x Ni _1-x ) (OH) ₂ .

FIG. 5 is an X-ray diffraction diagram of a representative example of a sample obtained in Example 1.

FIG. 6 is an X-ray diffraction diagram of a representative example of a sample obtained in Example 1.

FIG. 7 is a graph showing a utilization rate with respect to a full width at half maximum of a peak of (003) in Example 1.

FIG. 8 is a graph showing the discharge intermediate potential with respect to the d value of the peak of (003) in Example 1.

FIG. 9 is a charge / discharge diagram of a sample (d) and a standard sample shown in Table 1.

FIG. 10 is a graph showing X of the sample obtained in Comparative Example 1.
Line diffraction diagram.

Claims (5)

[Claims] An α-type Al-substituted Ni (α) represented by the following composition formula (Al _x Ni _1-x ) (OH) ₂ Y (where 0.15 <x <0.3, Y is an anion) OH) ₂ and the full width at half maximum of the (003) peak in the X-ray diffraction pattern is 1.5 deg.
A positive electrode material for an alkaline storage battery, wherein 2. The positive electrode material for an alkaline storage battery according to claim 1, wherein the full width at half maximum of the (003) peak in the X-ray diffraction pattern is less than 0.5 deg. 3. The positive electrode material for an alkaline storage battery according to claim 1, wherein the d value of the peak of (003) in the X-ray diffraction diagram is less than 8.2 °. 4. The positive electrode material for an alkaline storage battery according to claim 1, wherein the d value of the peak of (003) in the X-ray diffraction pattern is 8.2 ° or more. 5. An alkaline storage battery using the positive electrode material according to claim 1.