JP3953550B2 - Positive electrode active material for alkaline storage battery, method for producing the same, and positive electrode for alkaline storage battery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a positive electrode active material used for alkaline storage batteries such as a nickel metal hydride battery, a nickel cadmium battery, and a nickel zinc battery, a manufacturing method thereof, and a positive electrode using the positive electrode active material.
[0002]
[Prior art and its problems]
As a technology for increasing the energy density of nickel metal hydride batteries and nickel cadmium batteries, in recent years, a paste-type (non-sintered) electrode has been used instead of a conventional sintered electrode for a nickel electrode that is a positive electrode. It is. The paste type nickel electrode uses a highly porous material of 95% or more as an electrode substrate, so it can be filled with nickel hydroxide as an active material in a larger amount than the conventional electrode, and as a result, high capacity and high energy density are possible. It is what.
[0003]
However, in a paste-type nickel electrode, simply filling nickel hydroxide particles as an active material has an active material utilization rate of only about 60%, which is not practical. Therefore, in order to increase the active material utilization rate, various conductive additives such as nickel powder, graphite powder, and cobalt compounds are added, and among these, addition of cobalt oxide is most effective. It is said.
[0004]
However, it is known that not all cobalt oxides are effective as additives for increasing the active material utilization rate, and the effect is greatly influenced by the crystal structure of the cobalt oxide. For example, Co ₃ O ₄ has no effect, but Co (OH) ₂ , CoO, and other alkali-soluble cobalt oxides have an effect.
[0005]
The action mechanism of such effective cobalt oxide is as follows. That is, a cobalt oxide is dissolved in an alkaline aqueous solution to form a divalent cobalt complex ion, and this complex ion is precipitated as cobalt hydroxide on the surface of nickel hydroxide particles or a current collector. Is changed to conductive cobalt oxyhydroxide (CoOOH) in the initial charging process, thereby forming a conductive network connecting active material particles and current collectors, thereby enabling a high active material utilization rate. . As can be seen from this, in order to obtain a high active material utilization rate, the dissolution and precipitation process of cobalt oxide in an alkaline aqueous solution is important, and a sufficient conductive network must be formed.
[0006]
Conventionally, in order to sufficiently form a conductive network, an alkaline electrolyte is poured into a battery using a paste-type nickel electrode, sealed, and left for a long time, during which cobalt additive is dissolved and dispersed. Thus, a cobalt hydroxide layer is uniformly formed on the entire active material surface. However, since the leaving time is long, there is a problem that a post-assembly process such as a chemical conversion process cannot be smoothly advanced.
[0007]
Thus, in order to shorten the standing time, for example, Japanese Patent Application Laid-Open No. 62-234867 proposes to produce active material particles in which the surface of nickel hydroxide particles is coated with a cobalt hydroxide layer. Furthermore, the solubility in an alkaline electrolyte is increased by changing the crystal structure of the cobalt hydroxide to be coated. For example, the melting process is promoted by changing the crystal structure of cobalt hydroxide from an ordinary β type (interlayer: 4.65 Å) to an α type (interlayer: ˜8 Å).
[0008]
By the way, in a high concentration alkaline electrolyte, β-type cobalt hydroxide is stable and its dissolution rate is slow. In contrast, α-type cobalt hydroxide is unstable and changes to stable β-type cobalt hydroxide through cobalt complex ions. Therefore, α-type cobalt oxide is desirable for forming a strong conductive network. However, it is very difficult to synthesize pure α-type cobalt hydroxide, and cobalt hydroxide powder generally referred to as α-type is disclosed in, for example, an X-ray diffraction diagram of Japanese Patent Application Laid-Open No. 62-234867. As shown, the β-type and the α-type coexist, and the original characteristics have not yet been sufficiently extracted. This point remains as a problem to be further improved.
[0009]
On the other hand, in order to improve the charging efficiency of the nickel electrode, in addition to the purpose of imparting conductivity as described above, a rare earth element or an oxide of a group 2 element is added to the additive in combination. It is. These compounds are known to have an action of making the oxygen generation potential of the nickel electrode noble and increasing the oxygen overvoltage to improve the charging efficiency at high temperatures.
[0010]
However, adding a plurality of additives for different purposes to the nickel hydroxide particles as the main active material makes it difficult to uniformly fill the active material into the electrode substrate, or There was a problem that the production rate and quality could not be stably produced by reducing the utilization rate.
[0011]
The present invention has been made in view of the above problems and the like, and by setting the composition and crystal structure of a cobalt compound to be coated on the nickel hydroxide particle surface to a predetermined one, the formation of a conductive network is achieved. Providing a positive electrode active material for an alkaline storage battery that can be made easy, providing a method for producing such an active material, and providing a positive electrode for an alkaline storage battery using such an active material, Objective.
[0012]
[Means for Solving the Problems]
The positive electrode active material for alkaline storage battery of the present invention, the production method thereof, and the positive electrode for alkaline storage battery are as follows. However, in all the chemical composition formulas, A is Zn (zinc), E is Al (aluminum) or Yb (ytterbium) , B and D are sulfate ion, nitrate ion, carbonate ion, borate ion , And phosphate ions, x is 0.05 to 0.5, y is {(valence of element E) −2} × x ÷ (valence of ion D), z is 0 to 0.5, w is {(valence of the element a) -2} × z ÷ (valence of ion B) Ru der.
[0013]
[0014]
[0015]
The positive electrode active material for an alkaline storage battery according to claim 1, wherein the chemical composition _{Ni 1-z A z (OH} ) surface of the particles of the nickel hydroxide is ₂ B _w, the chemical composition _{Co 1-x} E x OOH A layer made of cobalt oxide is formed.
[0016]
In the first aspect of the present invention, since a layer consisting of cobalt oxide on the surface of the particles of the nickel hydroxide is formed, the formation of conductive network is facilitated, it is shortened standing time after battery assembly . In addition, since cobalt oxide is excellent in conductivity, the conductive network becomes highly efficient and the active material utilization rate is improved. Moreover, since element E is doped in the cobalt oxide, the oxidative decomposition reaction of the alkaline electrolyte is suppressed, and the charging efficiency at a high temperature when the electrode is used is improved.
[0017]
The positive electrode active material for an alkaline storage battery according to claim 2, wherein, in addition to the configuration of claim 1 Symbol placement, the ratio of cobalt oxide against the nickel hydroxide is 3 to 15 wt%.
[0018]
In the invention of claim 2 , satisfactory active material utilization and battery capacity can be obtained. This is because if the amount is less than 3% by weight, sufficient conductivity due to the conductive network is not ensured, and the utilization factor of the active material is reduced. If the amount exceeds 15% by weight, the amount of nickel hydroxide as the active material This is because the battery capacity is reduced.
[0019]
The positive electrode active material for an alkaline storage battery according to claim 3 is the composition according to claim 1 , wherein the cobalt oxide having a chemical composition of Co _1-x E _x OOH has a chemical composition of Co _1-x E _x (OH). cobalt hydroxide is ₂ D _y is obtained by chemical oxidation.
[0020]
In invention of Claim 3 , after obtaining a cobalt hydroxide, a cobalt oxide is obtained easily.
[0021]
[0022]
The method for producing a positive electrode active material for an alkaline storage battery according to claim 4, wherein the chemical composition is put particles nickel hydroxide is _{Ni 1-z A z (OH} ) 2 B w in the reaction vessel, cobalt and an anion D An aqueous solution containing a salt consisting of and a salt consisting of element E and anion D is dropped into an aqueous solution containing ammonia or an ammonium ion supplier and an alkali metal hydroxide while controlling the pH to 8-13, Cobalt hydroxide having a chemical composition of Co _1-x E _x ( OH ) ₂ D _y is deposited on the surface of nickel hydroxide particles , and then the cobalt hydroxide is chemically oxidized to have a chemical composition of Co It is characterized by being a cobalt oxide which is _1-x E _x OOH.
[0023]
As the oxidizing agent used for the chemical oxidation treatment, hydrogen peroxide, potassium persulfate, hypochlorite, or the like is used.
[0024]
In the invention of claim 4, wherein, for ammonia or ammonium ion donor are present, cobalt hydroxide single crystal structure is stably generated.
[0025]
In the invention according to claim 4 , a cobalt oxide can be easily obtained.
[0026]
[0027]
[0028]
For an alkaline storage battery positive electrode according to claim 5, there is provided a paste type electrode, the chemical composition is _{Ni 1-z A z (OH} ) 2 the surface of the particles of the nickel hydroxide is B _w, the chemical composition Co ₁ nickel active material layer consisting of cobalt oxide is _{-x E} x _OOH is formed, is characterized in that it is constituted by filling the porous substrate.
[0029]
In the invention described in claim 5 , since a strong and highly efficient conductive network is formed, further high capacity and high energy density are possible.
[0030]
As the porous substrate of claim 5 , a perforated steel plate, a metal mesh, a foamed metal porous body, a fibrous metal porous body, or the like is used.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
The basic embodiment of the present invention will be described below, but the present invention is not limited to this.
[0032]
[Preparation of nickel active material particles]
(1) Preparation of nickel hydroxide particles:
After ammonium sulfate is added to an aqueous solution in which nickel sulfate and zinc sulfate are dissolved at a predetermined ratio to form an ammine metal complex, the aqueous sodium hydroxide solution is added dropwise while vigorously stirring and controlling to pH 10-13, Spherical nickel hydroxide particles having a solid solution of 5 mol% were obtained. Its chemical composition was Ni _0.95 Zn _0.05 (OH) ₂ .
[0033]
(2) Preparation of nickel hydroxide particles coated with cobalt hydroxide:
The nickel hydroxide particles obtained in (1) are put into an aqueous solution controlled to pH 8 to 13 with ammonium sulfate and an aqueous sodium hydroxide solution, and an aqueous solution in which cobalt sulfate and aluminum sulfate are mixed at a predetermined ratio. And an aqueous sodium hydroxide solution were added dropwise while stirring and controlling the pH to 8-13. At this time, it is preferable to hold at a predetermined pH for 10 minutes to 2 hours.
[0034]
Then, filtration, washing with water, and vacuum drying were performed to obtain nickel hydroxide particles coated with cobalt hydroxide (hereinafter referred to as nickel active material a particles).
[0035]
The amount of aluminum in the cobalt hydroxide was set by adjusting the ratio of nickel salt (nickel sulfate) and aluminum salt (aluminum sulfate) dissolved in the aqueous solution. The coating amount of cobalt hydroxide was 5% by weight, and the chemical composition of cobalt hydroxide was Co _0.8 Al _0.2 (OH) ₂ (SO ₄ ) _0.1 . As shown in the X-ray diffraction diagram of FIG. 1, this cobalt hydroxide has a pure α-type structure, and the dissolution rate in an alkaline electrolyte (6M-KOH aqueous solution) is the conventional β-type / α. A large value was shown in comparison with the type Co (OH) ₂ .
[0036]
(3) Preparation of nickel hydroxide particles coated with cobalt oxide:
The nickel active material a particles obtained in (2) are chemically oxidized with a hypochlorous acid aqueous solution, and the coated cobalt hydroxide is converted to Co _0.8 Al _0.2 which is a higher-order cobalt oxide. Converted to OOH. That is, nickel hydroxide particles coated with cobalt oxide (hereinafter referred to as nickel active material b particles) were obtained. The conductivity of the nickel active material b particles was higher than that of nickel oxyhydroxide.
[0037]
[Preparation of paste type positive electrode]
(1) Preparation of positive electrode using nickel active material a particles:
20 parts by weight of an aqueous solution in which a thickener such as carboxymethyl cellulose is dissolved is added to 80 parts by weight of the nickel active material a particles, kneaded to form a paste, filled into a 95% nickel porous substrate, pressed after drying Thus, a positive electrode (hereinafter referred to as positive electrode a) was produced.
[0038]
(2) Fabrication of positive electrode using nickel active material b particles:
A nickel active material b particle was used in place of the nickel active material a particle, and a positive electrode (hereinafter referred to as positive electrode b) was produced in the same manner as (1).
[0039]
[Solubility of cobalt in alkaline electrolyte]
About the nickel active material a particle | grains, the solubility of cobalt in alkaline electrolyte was investigated. FIG. 2 shows the relationship between the cobalt / aluminum molar ratio in the cobalt hydroxide and the relative value of the amount of cobalt dissolved after being left in the KOH electrolyte for a certain period of time. The dissolution rate increased with an increase in the doping amount of the different element (here, aluminum), reached a maximum at a molar ratio of 0.3, and maintained a high value even at 0.5. On the other hand, an increase in the amount of doping causes a decrease in the amount of cobalt necessary for forming the conductive network. Therefore, the molar ratio of the doping amounts of the different elements is preferably 0.05 to 0.5.
[0040]
[Active material utilization rate]
About the nickel active material a particle | grain, the relationship between the coating amount of a cobalt hydroxide and an active material utilization factor was investigated. FIG. 3 shows the result. As can be seen from FIG. 3, when the coating amount is 3% by weight or more, a high active material utilization rate of 95% or more is obtained. On the other hand, from a practical standpoint, setting the coating amount to a value exceeding 15% by weight is not preferable because the battery capacity is reduced. Therefore, the coating amount is preferably 3 to 15% by weight.
[0041]
[Relationship between immersion time in alkaline electrolyte and utilization rate of active material]
(1) For the positive electrode a, the relationship between the immersion time in the alkaline electrolyte and the active material utilization rate was examined. On the other hand, a positive electrode (referred to as comparative electrode 1) using nickel hydroxide particles coated with β-type cobalt hydroxide as an active material, and a positive electrode using nickel hydroxide particles mixed with cobalt monoxide powder as an active material. It investigated similarly about (referred to as the comparative electrode 2).
[0042]
FIG. 4 shows the result. In the positive electrode a, unlike the conventional electrodes which are the comparative electrodes 1 and 2, a high active material utilization rate was obtained even when the immersion time in the alkaline electrolyte was short.
[0043]
In this way, in the positive electrode a, the cobalt hydroxide of the nickel active material a particles is doped with a different element, so that the cobalt hydroxide can have an α-type structure and dissolved in an alkaline electrolyte. Improves. As a result, the leaving time after battery assembly is greatly shortened compared to the conventional case.
[0044]
(2) Similarly, for the positive electrode b, the relationship between the immersion time in the alkaline electrolyte and the active material utilization rate was examined. Material utilization rate was obtained.
[0045]
[Charging efficiency at high temperature]
A positive electrode c in which aluminum of cobalt hydroxide of nickel active material a particles was replaced with ytterbium was produced, and charging efficiency at a high temperature of 40 ° C. was examined. That is, the nickel active material particles, chemical composition _Ni 0.95 _{Zn 0.05} (OH) ₂ particle surfaces of the nickel hydroxide is the chemical composition _{Co 0.8 Yb 0.2 (OH) 2} ( SO ₄ ) _0.1 is coated with cobalt hydroxide, and the coating amount is 5% by weight.
[0046]
On the other hand, the positive electrode (referred to as the comparative electrode 3) using nickel hydroxide particles mixed with the comparative electrode 2 and ytterbium oxide powder as an active material was also examined in the same manner. In addition, it is known that ytterbium oxide has the effect | action which improves the charging efficiency of a nickel electrode.
[0047]
FIG. 5 shows the result. As can be seen from FIG. 5, the positive electrode c is excellent in charging efficiency at a high temperature as in the comparative electrode 3.
[0048]
【The invention's effect】
[0049]
[0050]
( 1 ) According to the positive electrode active material for an alkaline storage battery according to claim 1 , since the layer made of cobalt oxide is formed on the surface of the nickel hydroxide particles, the formation of the conductive network is facilitated. Therefore, the time for which the battery is left after the battery assembly can be shortened, and the battery manufacturing process can be shortened.
[0051]
And since cobalt oxide is excellent in electroconductivity, a conductive network can be made highly efficient and an active material utilization factor can be improved.
[0052]
Moreover, since the element E is doped in the cobalt oxide, the oxidative decomposition reaction of the alkaline electrolyte can be suppressed, and the charging efficiency at a high temperature when the electrode is used can be improved.
[0053]
( 2 ) According to the positive electrode active material for an alkaline storage battery according to claim 2 , a satisfactory active material utilization rate and battery capacity can be obtained.
[0054]
( 3 ) According to the positive electrode active material for an alkaline storage battery of claim 3 , the cobalt oxide can be easily obtained after obtaining the cobalt hydroxide.
[0055]
[0056]
( 4 ) According to the method for producing a positive electrode active material for an alkaline storage battery according to claim 4 , since the ammonia or ammonium ion supplier is present, it is possible to stably produce cobalt hydroxide having a single crystal structure, Therefore, cobalt oxide can also be generated stably. In addition, the cobalt oxide is easy because it can be obtained simply by chemically oxidizing the cobalt hydroxide. Therefore, the active material according to claim 1 can be obtained reliably and easily.
[0057]
[0058]
( 5 ) According to the positive electrode for an alkaline storage battery according to claim 5 , further higher capacity and higher energy density can be realized.
[Brief description of the drawings]
FIG. 1 is an X-ray diffraction pattern of a cobalt hydroxide produced in an embodiment of the present invention.
FIG. 2 shows the relationship between the amount of different elements in cobalt hydroxide and the solubility of cobalt in alkaline electrolyte with respect to nickel hydroxide particles coated with cobalt hydroxide produced in an embodiment of the present invention. It is a figure which shows a relationship.
FIG. 3 is a diagram showing the relationship between the coating amount of cobalt hydroxide and the active material utilization rate for nickel hydroxide particles coated with cobalt hydroxide produced in an embodiment of the present invention.
FIG. 4 shows the relationship between the immersion time in an alkaline electrolyte and the active material utilization rate for a positive electrode formed using nickel hydroxide particles coated with cobalt hydroxide produced in an embodiment of the present invention. FIG.
FIG. 5 is a diagram showing charging efficiency at a high temperature with respect to a positive electrode configured using nickel hydroxide particles coated with cobalt hydroxide of another example manufactured in an embodiment of the present invention.

Claims (5)

The surfaces of the particles of the nickel hydroxide is a chemical composition _{Ni 1-z A z (OH} ) 2 B w, a layer consisting of cobalt oxide is formed chemical composition is _{Co 1-x} E _x OOH A positive electrode active material for an alkaline storage battery. In the above chemical composition formula, A is Zn, E is Al or Yb , B is any one of sulfate ion, nitrate ion, carbonate ion, borate ion, and phosphate ion, and x is 0.05 to 0.5, z is 0 to 0.5, and w is {(valence of element A) −2} × z ÷ (valence of ion B).   The positive electrode active material for an alkaline storage battery according to claim 1, wherein the ratio of cobalt oxide to nickel hydroxide is 3 to 15% by weight. The cobalt oxide having a chemical composition of Co _1-x E _x OOH is obtained by chemically oxidizing a cobalt hydroxide having a chemical composition of Co _1-x E _x (OH) ₂ D _y Item 6. The positive electrode active material for an alkaline storage battery according to Item 1. In the above chemical composition formula, D is any one of sulfate ion, nitrate ion, carbonate ion, borate ion, and phosphate ion, and y is {(valence of element E) −2} × x ÷. (Valence of ion D). Chemical composition put particles nickel hydroxide is _{Ni 1-z A z (OH} ) 2 B w in the reaction vessel, a salt of cobalt and an anion D consisting of salt and elemental E and anion D The aqueous solution containing the solution is dropped into an aqueous solution containing ammonia or an ammonium ion supplier and an alkali metal hydroxide while controlling the pH to 8 to 13, and the chemical composition is Co _{1-x on} the particle surface of the nickel hydroxide. Cobalt hydroxide which is E _x (OH) ₂ D _y is precipitated, and then the cobalt hydroxide is chemically oxidized to form cobalt oxide whose chemical composition is Co _1-x E _x OOH. The manufacturing method of the positive electrode active material for alkaline storage batteries. However, in the above chemical composition formula, A is Zn, E is Al or Yb , B and D are any of sulfate ion, nitrate ion, carbonate ion, borate ion, and phosphate ion, x is 0.05 to 0.5, y is {(valence of element E) −2} × x ÷ (valence of ion D), z is 0 to 0.5, and w is {(Valence of element A) −2} × z ÷ (valence of ion B). From a cobalt oxide having a chemical composition of Co _1-x E _x OOH on a surface of a nickel hydroxide particle having a chemical composition of Ni _1-z A _z (OH) ₂ B _w A positive electrode for an alkaline storage battery, characterized in that a nickel active material in which a layer to be formed is filled in a porous substrate. In the above chemical composition formula, A is Zn, E is Al or Yb , B is any one of sulfate ion, nitrate ion, carbonate ion, borate ion, and phosphate ion, and x is 0.05 to 0.5, z is 0 to 0.5, and w is {(valence of element A) −2} × z ÷ (valence of ion B).

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