JP3518259B2 - Nickel-hydrogen storage battery and method for producing positive electrode active material thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel-hydrogen storage battery, in which a positive electrode active material is improved to improve its capacity density and the characteristics of the positive electrode.

[0002]

2. Description of the Related Art In recent years, alkaline storage batteries have been required to have a higher capacity with the spread of portable devices. In particular, a nickel-hydrogen storage battery is a battery having a positive electrode made of an active material mainly containing nickel hydroxide and a negative electrode mainly made of a hydrogen storage alloy, and has rapidly spread as a high-capacity and highly reliable battery. .

Positive electrodes for alkaline storage batteries are roughly classified into a sintered type and a non-sintered type. The sintered positive electrode is obtained by impregnating a porous nickel sintered substrate having a porosity of about 80% obtained by sintering nickel powder with a nickel salt solution such as a nickel nitrate aqueous solution, and then immersing it in an alkaline aqueous solution. It is manufactured by producing a nickel hydroxide active material in a porous nickel sintered substrate. Since it is difficult to increase the porosity of the substrate in this electrode any more, the amount of the active material to be filled cannot be increased, and there is a limit to increase the capacity.

A non-sintered positive electrode is disclosed, for example, in JP-A-60-4.
The three-dimensionally continuous sponge-like porous body made of nickel metal and having a porosity of 95% or more, as disclosed in Japanese Patent No. 0667, is filled with nickel hydroxide as an active material. It is currently widely used as a positive electrode for high capacity alkaline storage batteries.

In this non-sintered positive electrode, it has been proposed to fill the pores of the sponge-like nickel porous body with spherical nickel hydroxide in order to increase the capacity. This is because the sponge-like nickel porous body has a pore size of 20
0 to 500 μm, and the pores have a particle size of several μm
It is filled with spherical nickel hydroxide having a diameter of several tens of μm. In this structure, since the nickel hydroxide in the vicinity of the skeleton of the nickel porous body maintains conductivity, the charge / discharge reaction proceeds smoothly, but the reaction of nickel hydroxide separated from the skeleton does not proceed sufficiently.

Therefore, in the non-sintered positive electrode, in order to improve the utilization rate of the filled nickel hydroxide, a conductive agent is used in addition to the active material, nickel hydroxide, to form spherical nickel hydroxide particles. The electrically connecting portions are electrically connected to each other to form a conductive network. As the conductive agent, a cobalt compound such as cobalt hydroxide or cobalt monoxide, metallic cobalt, metallic nickel, or the like is used. As a result, in the non-sintered positive electrode, it is possible to maintain the conductivity even when the active material is densely packed, and it is possible to increase the capacity.

[0007]

However, the spherical nickel hydroxide used as the active material of the non-sintered positive electrode is activated nickel hydroxide (β-Ni (O
H) ₂ ) and the average valence of nickel is 2.
It is bivalent. This active material becomes β-type nickel oxyhydroxide (β-NiOOH) in a charged state, and it is said that the average valence of nickel is around 3.2.

Therefore, in charge and discharge, the utilization rate becomes 100% in almost one electron reaction. (The utilization rate is a percentage of the value obtained by dividing the capacity actually measured by the theoretical unit weight of 289 mAh / g assuming a one-electron reaction.) As a result, when this active material is used, the capacity density of the positive electrode is about 650 mAh / cc. become.

It has also been confirmed that, when a nickel-hydrogen storage battery is continuously overcharged with a small current at a low temperature, the nickel valence of the positive electrode becomes higher and the valence rises to 3.67. ing.

However, the average valence of nickel is 3.5
Nickel hydroxide is gamma type oxyhydroxide nickel over
(Γ-NiOOH). γ-NiOOH is Cu
Diffraction angle 2θ in X-ray diffraction using Kα as a radiation source is 12 degrees
There is also a diffraction peak of the (003) plane at (λ = 1.5405)
It is a material that has a nickel-nickel metal surface between layers.
, Anions, water, etc. are inserted, β-NiOOH
(Density 4.68 g / cm ³), The crystal expands more easily than
Yes.

Γ-NiOOH (density 3.79 g / c
m³) Is α-3Ni (OH) when discharged.₂・ 2H₂O
(Density 2.82 g / cm³)become. In addition,
γ-NiOOH has a nickel valence of 3 or more.
Composition formula is NiOOH_1-XIt is represented by. X here is 0
It takes a value larger than 1 and smaller than 1. That is, proton
(H ⁺) Will be missing. Then bond with nickel
Oxygen is δ^-Take on.

Due to this Coulomb force with δ ⁻ , cations such as K ⁺ are taken in between the layers of the nickel-nickel metal surface. Anions also have a crystal structure incorporated between the layers of the nickel-nickel metal surface in order to cancel the excess charges of monovalent K ⁺ and δ ⁻ and maintain charge neutrality.

When this γ-NiOOH is electrochemically discharged, cations and anions taken in between the layers of the nickel-nickel metal surface are released into the electrolytic solution and α-3Ni.
It is considered to be (OH) ₂ .2H ₂ O. However, γ-Ni having cations and anions incorporated between layers is used.
When OOH is discharged, protons (H ⁺ ) diffuse into the crystal and combine with oxygen. Since the oxygen takes on δ ⁻ , the cations taken in between the crystal layers lose the stability between the crystal layers due to the Coulomb force and should diffuse and be released into the electrolytic solution. ^It is considered to be slower than that of ⁺ ), and cations and anions remain between layers even in the discharged state.

Therefore, in a sealed nickel-hydrogen storage battery or the like, the electrolyte is diluted and the battery characteristics are deteriorated. In addition, γ-NiOOH and _{α-3Ni (OH) 2 ·} 2
In the charging reaction of H ₂ O, the density of the active material changes greatly, and the active material repeatedly expands. The α-3Ni (O generated here
It has been confirmed that H) ₂ .2H ₂ O chemically slowly changes the crystal structure to active nickel hydroxide (β-Ni (OH) ₂ ).

Therefore, spherical nickel hydroxide has a spherical shape that collapses, or γ-NiOOH in a charged state accumulates without discharging, and the positive electrode swells and absorbs the electrolytic solution in the battery.

As a result, the amount of the electrolytic solution held by the separator is reduced and the separator is drained, and the internal resistance of the battery is increased to make discharge impossible. This phenomenon has been known for a long time even when a sintered positive electrode is used, and particularly in a sealed battery, deterioration of battery characteristics occurs due to swelling of the positive electrode.

Therefore, in order to utilize high-order nickel hydroxide, γ-NiOOH, which is excellent in reversibility at room temperature, is used.
Needs to be generated. Also, in the discharge process, α-3Ni
It is necessary to discharge to active nickel hydroxide (β-Ni (OH) ₂ ) without passing through (OH) ₂ .2H ₂ O. Furthermore, it is necessary to minimize the amount of cations taken up by the electrolytic solution in the sealed battery in the charged state.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a nickel-hydrogen storage battery in which the positive electrode active material is improved to improve its capacity density and the characteristics of the positive electrode.

[0019]

In order to achieve the above object, the present invention provides a positive electrode using nickel hydroxide as an active material,
A negative electrode mainly composed of a hydrogen storage alloy, an alkaline electrolyte,
A battery comprising a separator, wherein nickel hydroxide is a solid solution of at least one transition metal and at least one alkali metal in an amount smaller than the transition metal. The amount of solid solution is 2 to 12% by weight with respect to the amount of nickel hydroxide converted to metallic nickel.
In the nickel-hydrogen storage battery, the solid solution amount of the alkali metal is 10 to 70 atom% with respect to that of the transition metal.

Further, in the method for producing nickel hydroxide which is the positive electrode active material, nickel hydroxide is prepared by reacting the nickel compound obtained in the first step with alkali in the first step of solid-dissolving the transition metal in the nickel compound. The second step of obtaining, the third step of oxidizing the transition metal in the nickel hydroxide obtained in the second step, and the stirring and heat treatment of the nickel hydroxide obtained in the third step in an alkaline solution And a fourth step of solid-dissolving an alkali metal in nickel hydroxide.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention is a battery comprising a positive electrode using nickel hydroxide as an active material, a negative electrode mainly containing a hydrogen storage alloy, an alkaline electrolyte, and a separator. And the nickel hydroxide is M
At least one kind of transition metal of n, Fe, Cr and Co and at least one kind of alkali metal are dissolved in a smaller amount than the transition metal, and the solid solution amount of the transition metal is The amount of nickel hydroxide is 2 to 12% by weight based on the metallic nickel equivalent, and the amount of the solid solution of the alkali metal is 10 to 70 relative to that of the transition metal.
It is expressed in atomic%.

The solid solution referred to herein has a structure in which a transition metal is crystallographically substituted with a nickel atom of nickel hydroxide to form a solid solution.

This nickel hydroxide is considered to be free from cations and anions because the valence of nickel is always 3 or more in the potential range of the positive electrode in the charge / discharge state of the nickel-hydrogen storage battery, and it is considered that cations and anions are not involved. Dilution does not occur either.
Further, nickel hydroxide traps cations in the vicinity of the transition metal and causes strain in the crystal. Therefore, at room temperature, γ-NiOOH is charged and (β-NiOOH is discharged at normal temperature.
(OH) ₂ ) and the reaction of γ-β can occur reversibly, and a nickel-hydrogen storage battery with high energy density can be provided.

The invention according to claim 4 is a nickel compound containing at least one of Mn, Fe, Cr and Co.
A first step of forming a solid solution of a transition metal of the same class , a second step of reacting the nickel compound obtained in the first step with an alkali to obtain nickel hydroxide, and a nickel hydroxide obtained in the second step a third step of oxidizing the transition metal, a third
The method for producing a positive electrode active material for an alkaline storage battery, comprising the fourth step of stirring and heating the nickel hydroxide obtained in the step of 1) in an alkaline solution to form a solid solution of the alkali metal in the nickel hydroxide. .

Nickel hydroxide in which a transition metal is solid-dissolved is subjected to heat treatment in an oxygen atmosphere or heat treatment with an aqueous solution containing an oxidant to preferentially oxidize the transition metal without oxidizing nickel. You can

In the nickel hydroxide obtained by oxidizing the transition metal, the valence of nickel is divalent, and the oxidation number of the transition metal is trivalent or higher. In other words, focusing only on the transition metal, it is represented as MeOOH _1-X (Me is a transition metal, X is a value larger than 0 and smaller than 1), and oxygen bound to the transition metal Me has a proton (H ⁺ ) deficient state. next to δ ^- take on. Next, it is possible to stir the nickel hydroxide in an aqueous solution of alkali hydroxide so that the positively charged cations can be stably coordinated in the vicinity of δ ⁻ -bearing oxygen. At this time, since the valence of the cation is monovalent, surplus δ ⁺ is generated. Anions also enter at the same time to compensate for this charge.

As a result, the transition metal is solid-dissolved in nickel hydroxide, and the nickel hydroxide is oxidized and subjected to stirring treatment in an aqueous alkali hydroxide solution, whereby the transition metal of the transition metal dissolved in nickel hydroxide is dissolved. An active material in which an alkali cation is selectively solid-dissolved in the vicinity can be obtained.

[0028]

EXAMPLES Specific examples of the examples of the present invention will be shown below.

A solution of Mn in nickel hydroxide, which is a positive electrode active material, was prepared by the following method.

As raw material liquids, nickel sulfate aqueous solution and manganese sulfate were adjusted so that the amount of Mn was 5% by weight with respect to metallic Ni. The raw material liquid was charged into a reaction vessel capable of being kept substantially sealed, and a portion for introducing and exhausting an inert gas was provided, and the reaction was performed while supplying the inert gas to the reaction system.

As the reaction liquid, a raw material liquid, an aqueous solution of sodium hydroxide and aqueous ammonia having a concentration ratio of 1: 2.3: 2 were prepared. This reaction liquid was dropped into the reaction container. At this time, the reaction temperature was 40 ° C. The pH at this time is 12
Kept at.

The precipitate obtained by this reaction is washed with water and dried,
There was obtained nickel hydroxide powder in which 5% by weight of Mn was formed as a solid solution based on the metal nickel equivalent.

This nickel hydroxide powder is usually used in the range of 80-12.
It is heat-treated at 0 ° C. for 1 to 30 hours, but here, it is heat-treated at 100 ° C. for 24 hours to selectively oxidize Mn, and the nickel hydroxide powder is usually added to an aqueous solution of lithium hydroxide 10 mol / l for 30 to 100 hours. The mixture is heated and stirred at 1 ° C. for 1 to 30 hours, but here, the mixture is heated and stirred at 80 ° C. for 10 hours to dissolve Li in the nickel hydroxide powder.

To 100 parts by weight of this nickel hydroxide powder,
0.5 parts by weight of polytetrafluoroethylene as a binder, 10 parts by weight of cobalt hydroxide as a conductive agent, and an appropriate amount of water as a dispersion medium were added to form a paste, which was formed into a pore portion of a sponge-like nickel porous body. Then, the positive electrode plate 1 was manufactured by rolling it in a roll press and rolling it. The positive electrode plate 1 has dimensions of width 35 mm, length 120 mm, and thickness 0.7.
It was 8 mm. The theoretical capacity of this positive electrode (calculated as 289 mAh / g assuming that nickel hydroxide is a one-electron reaction) was 1600 mAh.

As the negative electrode plate 2, 100 parts by weight of AB ₅ type hydrogen storage alloy powder, 1 part by weight of carbon powder, 1 part by weight of polytetrafluoroethylene and 1 part by weight of water were added to form a paste, which was punched. It was applied to metal, dried, and then rolled. The dimensions of the negative electrode plate 2 were 35 mm in width, 145 mm in length, and 0.39 mm in thickness. The theoretical capacity of this negative electrode (the quantity of electricity per unit weight of the hydrogen storage alloy is 280
(calculated as mAh / g) was 2900 mAh.

The positive electrode plate 1 and the negative electrode plate 2 produced above,
A polypropylene non-woven fabric separator 3 is placed between the two, and the whole is spirally wound to form an electrode plate group, which is inserted into a battery case 4 and an aqueous solution of potassium hydroxide 10 mol / l is used as an alkaline electrolyte. After injecting a predetermined amount, a nickel-hydrogen storage battery A having a size of 4/5 A and a nominal capacity of 1600 mAh was constructed by sealing with a sealing plate 5 also serving as a positive electrode terminal. A configuration diagram of the battery A is shown in FIG.

Further, in the positive electrode plate 1 produced above,
A battery having the same configuration as the above except that nickel hydroxide in which neither Mn nor Li was solid-solved was used was designated as Battery B of Comparative Example.

Each of the batteries A and B was set to 1 at 160 mA.
After charging for 5 hours and leaving for 1 hour, a charging / discharging cycle of discharging at 320 mA until the terminal voltage reaches 1 V was performed twice.

Further, after aging by leaving it in an atmosphere of a temperature of 45 ° C. for 3 days, it is subjected to 1-amount in an atmosphere of a temperature of 20 ° C.
After charging for 18 hours with a current of 60 mA and leaving it for 1 hour,
The battery was discharged at 320 mA until the terminal voltage reached 1 V. Utilization rate of positive electrode active material obtained from discharge capacity at this time (percentage when actual discharge capacity / positive electrode theoretical capacity is 289 mAh)
The battery A was 112% and the battery B was 98%.

For confirmation, the batteries A and B in the charged state were disassembled, the positive electrode plate was taken out, and analyzed by X-ray diffraction using CuKα of the active material as a radiation source (wavelength λ is 1.5405). . As a result of obtaining the diffraction angle 2θ by this analysis, the positive electrode plate of the battery A is due to γ-NiOOH (00
3) The diffraction peak of the plane was observed near 2θ = 12 degrees, and β
-The diffraction peak of the (001) plane due to NiOOH is also 2
Observed around θ = 20 degrees, γ-NiOO in the charged state
It was confirmed to be a mixed phase of H and β-NiOOH.
In the discharged state, activated nickel hydroxide (β-Ni (O
Only the diffraction peak of H) ₂ ) could be confirmed. Further, in this nickel hydroxide powder, 50 atomic% of Li was solid-solved with respect to the solid solution amount of Mn. On the other hand, in the positive electrode plate of the battery B, the same diffraction peak as that of the battery A could not be confirmed.

From the above, in the battery B of the comparative example, the positive electrode active material becomes β-NiOOH in the charged state, and the average valence of nickel is 3.2, so that the utilization rate of the positive electrode active material is high. Is 98%.

In the battery A of the example, 5% by weight of Mn was dissolved in nickel hydroxide as the positive electrode active material with respect to the amount of metallic nickel converted.
Is a solid solution of 50 atomic%, it becomes a higher-order nickel oxidation state in the charged state, and the average valence increases to 3.5 valence, so the number of reaction electrons increases compared to the comparative example, and the capacity of nickel hydroxide itself The density is improved. Therefore, the utilization rate of the positive electrode active material was 112%, which was 14% higher than that of the comparative example.
Further, since Li is solid-dissolved in the positive electrode active material, the electrolyte is not diluted. In addition, since α-3Ni (OH) ₂ .2H ₂ O is not generated even in a discharged state, the capacity density can be improved and the nickel-hydrogen storage battery has excellent charge / discharge cycle characteristics.

In the examples of the present invention, nickel hydroxide, which is the positive electrode active material, contains 5% by weight of Mn based on the amount of metallic nickel converted, and 50 atomic% of Mn with respect to Li.
Was used as a solid solution, but the solid solution amount of Mn is 2 to 10
The solid solution amount of wt% and Li is 10 with respect to the solid solution amount of Mn.
In the range of up to 70 atomic%, almost the same effect as the embodiment can be obtained. The most preferable range of the solid solution amount of Li was 20 to 60 atom% with respect to the solid solution amount of Mn.

In the examples, Mn was used as the transition metal and Li was used as the alkali metal as the solid solution metal in the nickel hydroxide as the positive electrode active material.
Even if at least one of e, Cr, and Co and at least one of Na, K, Rb, and Cs are used as the alkali metal, substantially the same effect as the embodiment can be obtained.

The method for producing the positive electrode active material of the embodiment is as follows:
The nickel hydroxide powder having a transition metal dissolved therein is heat-treated in the presence of oxygen at 100 ° C. for 24 hours to selectively oxidize the transition metal dissolved in nickel hydroxide, and the nickel hydroxide powder is heated at 80 ° C. 10 in aqueous lithium hydroxide
The method of dissolving Li, which is an alkali metal, in nickel hydroxide powder by heating and stirring for a time was shown. Nickel hydroxide powder in which a transition metal was solid-dissolved was used with an oxidizing agent such as hydrogen peroxide solution. The alkali metal Li can be solid-dissolved in the nickel hydroxide powder by chemically oxidizing the transition metal solid-dissolved in the nickel hydroxide powder and using the subsequent steps in the same manner as in the example.

As the above-mentioned manufacturing method, nickel hydroxide powder in which a transition metal is solid-dissolved is oxidized, and Li, which is an alkali metal, is converted into nickel hydroxide powder by using an aqueous solution of lithium hydroxide which is an aqueous solution of alkali salt. I made it a solid solution,
Even if an aqueous solution of at least one of lithium hydroxide, sodium hydroxide, potassium hydroxide, rubidium hydroxide and cesium hydroxide is used as the alkaline salt aqueous solution, alkali metals such as Li, Na, K, Rb and C are used.
At least one of s can be solid-dissolved in the nickel hydroxide powder.

[0047]

As described above, in the nickel-hydrogen storage battery of the present invention, the nickel hydroxide which is the active material of the positive electrode is M
at least one transition metal of at least one transition metal of n, Fe, Cr and Co and at least one transition metal of an alkali metal in a smaller amount than the transition metal. , The solid solution amount of this transition metal is 2 to 10% by weight based on the nickel equivalent of nickel hydroxide.
Since the solid solution amount of the alkali metal is 10 to 70 atom% with respect to that of the transition metal, nickel hydroxide becomes a mixture of γ-NiOOH and β-NiOOH in the charged state, and the average value of nickel is Since the number is 3.5 and a higher valence, the number of reaction electrons is increased and the capacity density of the active material is improved. Further, since nickel hydroxide is a solid solution of alkali metal, the electrolyte is not diluted in the sealed battery, and the charge / discharge cycle characteristics of the battery can be improved.

[0048]

[Brief description of drawings]

FIG. 1 is a configuration diagram of a nickel-hydrogen storage battery according to an embodiment of the present invention.

[Explanation of symbols] 1 Positive plate 2 Negative electrode plate 3 separator 4 battery case 5 Seal plate

   ─────────────────────────────────────────────────── ─── Continued front page       (56) References JP-A-57-126074 (JP, A)                 International Publication 97/019478 (WO, A1)

Claims (7)

(57) [Claims] 1. A battery comprising a positive electrode having nickel hydroxide as an active material, a negative electrode mainly having a hydrogen storage alloy, an alkaline electrolyte and a separator, wherein the nickel hydroxide is Mn, Fe, At least one of Cr and Co
It is a solid solution of several kinds of transition metals and is less than that.
A small amount of Li, Na, K, Rb and Cs with no amount
At least one type of alkali metal is in solid solution
Ri, solid solution amount of the transition metal is from 2 to 10 wt% relative to the amount obtained by converting the nickel hydroxide to the metallic nickel,
Solid solution amount of the alkali metal Ri 10-70 atomic% der to that of the transition metal, the transition metal is oxidized
It is nickel - hydrogen storage battery. 2. A battery comprising a positive electrode containing nickel hydroxide as an active material, a negative electrode mainly containing a hydrogen storage alloy, an alkaline electrolyte and a separator, wherein the nickel hydroxide is Mn and Mn. Li is dissolved in a smaller amount than
The solid solution amount of Mn is nickel hydroxide and gold.
3 to 8% by weight based on the amount converted to group nickel,
The solid solution amount of Li is 20 to 60 with respect to that of Mn.
Nickel-hydrogen storage battery , wherein the transition metal is atomic% and the transition metal is oxidized . 3. A nickel compound containing Mn, Fe, Cr and
A first step of forming a solid solution with at least one transition metal of Co , a second step of reacting the nickel compound obtained in the first step with an alkali to obtain nickel hydroxide, and a second step a third step of oxidizing the transition metal of nickel hydroxide, which is, to a solid solution of an alkali metal to a stirred heated to nickel hydroxide obtained nickel hydroxide in the alkaline solution in the third step A method for producing a positive electrode active material for an alkaline storage battery, which comprises the fourth step. 4. A nickel compound containing 2 to 12% by weight of Mn and F based on the amount of nickel metal converted to the nickel compound.
a first step of forming a solid solution with at least one transition metal of e, Cr and Co, and a second step of reacting the nickel compound obtained in the first step with an alkali to obtain nickel hydroxide the nickel hydroxide obtained in the second step was 30 hours of heat treatment at a temperature of 80 to 120 ° C. in an air or oxygen atmosphere, a third step of oxidizing the transition metal hydroxide in the nickel A method for producing a positive electrode active material for an alkaline storage battery, which comprises a fourth step of stirring and heating the nickel hydroxide obtained in the third step in an alkali solution to form a solid solution of an alkali metal in the nickel hydroxide. 5. The alkaline salt aqueous solution is LiOH, NaO.
The method for producing a positive electrode active material for an alkaline storage battery according to claim 4, which is an aqueous solution containing at least one of H, KOH, RbOH and CsOH. 6. A nickel compound containing 2 to 12% by weight of Mn, F based on the nickel equivalent of the nickel compound.
a first step of forming a solid solution with at least one transition metal of e, Cr and Co, and a second step of reacting the nickel compound obtained in the first step with an alkali to obtain nickel hydroxide the nickel hydroxide obtained in the second step was 30 hours of heat treatment at a temperature of 80 to 120 ° C. in an aqueous solution containing an oxidizing agent, a third oxidizing the transition metal hydroxide in the nickel
And a step of stirring the nickel hydroxide obtained in the third step in an aqueous solution containing an oxidizing agent at a temperature of 80 to 120 ° C. for 1 to 30 hours to form an alkali metal solid solution in nickel hydroxide. A method for producing a positive electrode active material for an alkaline storage battery, which comprises the step of. 7. The alkaline salt aqueous solution is LiOH, NaO.
The method for producing a positive electrode active material for an alkaline storage battery according to claim 6, which is an aqueous solution containing at least one of H, KOH, RbOH and CsOH.