JPH0982323A - Nickel hydroxide for battery and alkaline battery using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the high rate charge/discharge capability and the utilization factor of an active material by previously treating the surface of nickel hydroxide, covering the surface with a stable metal in an alkaline aqueous solution, and giving conductivity and activity to the nickel hydroxide. SOLUTION: Deposited metal is attached to the surface of powdery nickel hydroxide 3 with adequate gaps produced. Conductive powder 2 such as nickel powder for giving conductivity when the nickel hydroxide is used as an active material fills gaps between nickel hydroxide particles covered with deposited metal to give conductivity. The deposited metal attached to the surface effectively supplies electricity to the surface of the nickel hydroxide 3. By selecting the kind of metal, electrochemical characteristics can be given to the surface of the nickel hydroxide. When the surface of the nickel hydroxide is activated, then the nickel hydroxide is immersed in an electroless plating solution containing a metal salt having catalytic action, the surface of the nickel hydroxide particle is covered with deposited metal having catalytic action.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an improvement in nickel hydroxide used as a positive electrode active material of an alkaline battery, an alkaline battery using the same, and a method for producing improved nickel hydroxide.

[0002]

2. Description of the Related Art Conventionally, nickel hydroxide has been used as a positive electrode active material for alkaline secondary batteries. There are two types of positive electrode production, one of which is called the sintering method. After immersing the sintered metal substrate in the nickel salt aqueous solution,
Further, the operation of immersing in an alkaline aqueous solution is repeated to deposit nickel hydroxide on the substrate. The other is a method called a paste method, in which a paste made by mixing granular nickel hydroxide having a diameter of several to several tens of microns, an electronically conductive powder, a binder, etc., and having a pore diameter of several tens to several hundreds. This is a method of compressively filling a porous conductive substrate made of micron nickel or the like. Although each has its own characteristics, the latter has the advantage that the electric capacity of the battery is large because it can store a larger amount of nickel hydroxide.

When making a paste in which the above nickel hydroxide is kneaded, since nickel hydroxide is not an electronic conductor by nature, the inside of the paste mixed with a binder mainly composed of a polymer, which is an electrical insulator, is used. , Electricity does not conduct. For this reason, in a porous substrate having a sparse conductive network, it is difficult for electricity to flow from the substrate to the surface of the active material during charge / discharge, and the current collecting ability is poor. As it is, nickel hydroxide does not act as an active material. In order to solve this problem, a method is adopted in which a conductive powder of carbon, nickel metal, cobalt oxide or the like is mixed in the paste in an amount of about 10% to impart electric conductivity to the paste. In this case, inside the binder, electricity flows by electron conduction due to the contact between the conductive powders. At the same time, since the conductive fine powder is also in contact with nickel hydroxide particles, electrons are carried from the substrate to nickel hydroxide and an electrolytic reaction occurs on the surface of nickel hydroxide, and at the same time, hydroxide is generated by ionic conduction. Electricity is carried inside the nickel, and the entire nickel hydroxide acts as an active material. A partial cross section of the positive electrode in which granular nickel hydroxide, conductive powder and the like are filled between the porous conductive substrates is illustratively shown in FIG.

By the way, in recent years, in order to further improve the electric capacity of a battery, a paste is made by using fine particles of nickel hydroxide particles that are spherically shaped, and the paste is made even more dense inside the holes of the conductive porous substrate. A method of stuffing nickel hydroxide particles into is developed and actually used. This method increased the electric capacity of the battery by several tens of percent.
However, since nickel hydroxide is almost spherical, the surface area is relatively small, the contact with the conductive fine powder mixed in the paste is also small, and the electrochemical reaction activity of the surface of the nickel hydroxide particles is small. Therefore, there is a tendency that the entire nickel hydroxide cannot be fully utilized as an active material. For this reason, even if the electric capacity of the battery is improved, the high-current charge / discharge property of the battery and the utilization rate of the active material are likely to be sacrificed.

[0005]

SUMMARY OF THE INVENTION In order to remedy the above-mentioned drawbacks, the present invention enhances the activity of the surface of spherical nickel hydroxide, which is an active material, so that the surface can be effectively supplied with electricity, and An alkaline battery using the same is provided.

[0006]

Means for Solving the Problems The method of the present invention for achieving the above object is to pretreat the surface of nickel hydroxide and deposit a stable metal in an alkaline aqueous solution on the surface of spherical nickel hydroxide. Thus, it imparts conductivity and activity. By doing so, if the nickel hydroxide particles are in contact with each other, a current flows from or to the substrate, and the nickel hydroxide efficiently reacts with charging and discharging, and sufficiently functions as an active material. It becomes possible. Therefore, in the conventional method, it is possible to drastically reduce the amount of conductive powder such as carbon, nickel and cobalt oxide added to impart conductivity to the paste, or to eliminate it altogether. Since that portion can be replaced with nickel hydroxide, more nickel hydroxide can be filled in the substrate space, and the battery capacity can be increased.

Further, in the conventional method, the drawback that sufficient and uniform electrical contact cannot be established between the nickel hydroxide particles and the conductive powder is improved, and the reaction uniformly occurs on the entire surface of the nickel hydroxide. Therefore, the high current charge / discharge property is also improved.
Further, even after repeated charge and discharge, the electrical contact with the surface of nickel hydroxide does not loosen, the charge and discharge of nickel hydroxide as the positive electrode active material is facilitated, and the utilization rate of the positive electrode active material is kept high. There is also an effect. Further, if a metal having a catalytic action that promotes an electrochemical reaction is selected as the metal to be deposited, the reaction is promoted and the high current charge / discharge property is similarly improved. Nickel hydroxide used as a battery active material is not used in a pure form in many cases, and water such as zinc or cobalt is used for the purpose of preventing the volume change during charge / discharge and improving the utilization rate. Although modification such as mixing oxides or oxides has been made, the present invention is not limited to pure nickel hydroxide, but nickel hydroxide to which these modifications have been added,
It can be applied without any problems. In the following description, these are collectively referred to as nickel hydroxide. Further, nickel hydroxide generally used in batteries is a granular body having a diameter of several to several tens of microns, and these are collectively referred to as granular nickel hydroxide. In the present invention, the so-called electroless plating method is applied to the method used for depositing a metal on the surface of nickel hydroxide. As the electroless plating method used in this method, a commonly used method can be used, and there are an acidic solution and an alkaline solution,
In the case of this method, since the object to be plated is a hydroxide,
It is more preferable to use an alkaline liquid, but an acidic liquid that is weakly acidic can be sufficiently used.

The metal stable in alkaline aqueous solution is selected from the group consisting of copper, nickel, cobalt, silver, gold and mixtures thereof, or the group consisting of platinum group metals and oxides thereof. Nickel, cobalt, copper,
When gold is deposited, it is necessary to apply a so-called activation treatment, which is used for electroless plating on an insulator, to the surface of the granular nickel hydroxide. In the usual activation treatment, granular nickel hydroxide is stirred and dipped in an aqueous solution of stannous salt, filtered, dried and then dipped in an aqueous solution of palladium salt, and the fine particles of palladium are reduced by the reducing power of stannous ion. A method is used in which a very small amount is attached to the surface of the nickel hydroxide particles and an activation treatment is performed. The stannous salt and the palladium salt cannot be completely dissolved unless they are acidic aqueous solutions,
The pH is kept as high as possible and the immersion time is shortened to prevent the nickel hydroxide from dissolving as much as possible.

In this way, the surface-activated granular nickel hydroxide is immersed in an electroless plating solution to deposit a metal on the surface. As the electroless plating solution used, a solution having a commonly used composition can be used. Since the treatment time is short, an acidic composition can be used, but an alkaline composition is more preferable. As the reducing agent, sodium hypophosphite, hydrazine, boron hydride compound, formaldehyde and the like are used. In this case, since the activated nickel hydroxide surface is very active, when immersed in an electroless plating solution containing all the reagents constituting the composition, a rapid reaction occurs depending on the concentration and the deposited metal becomes nonuniform. Sometimes it becomes. In that case, a method of preparing an aqueous solution containing no reducing agent, maintaining it at a set temperature, adding granular nickel hydroxide therein, stirring and dispersing, and then gradually adding an aqueous solution containing a reducing agent. By taking the above, the metal can be uniformly deposited on the surface. Since the amount and speed of the metal to be precipitated can be adjusted by the addition amount and speed of the aqueous solution containing the reducing agent, the reaction can be stopped in a desired state.
When precipitating silver, even if the surface of the nickel hydroxide particles is not pretreated in advance, granular nickel hydroxide should be added to the aqueous solution of silver salt and stirred while adding the aqueous solution containing the reducing agent. This makes it possible to deposit silver on the surface of the particles. As the silver salt, nitrate is usually used. Further, as the reducing agent, an aqueous formaldehyde solution is usually used, but the reducing agent is not limited thereto.

Only when nickel metal is deposited on the surface of nickel hydroxide particles, in an aqueous solution having a composition obtained by removing a nickel compound from an ordinary electroless plating solution for nickel,
The surface of the granular nickel hydroxide is reduced by simply adding the activated granular nickel hydroxide and stirring,
Since it changes into nickel metal, the surface of the granular nickel hydroxide can be covered with nickel fine particles. As described above, in electroless plating performed in an aqueous solution, an extremely small amount of oxides or hydroxides are partially mixed in the deposited metal due to the influence of air, hydroxyl groups, etc. existing in the aqueous solution. In some cases, these impurities do not hinder the present invention.

Generally, when a plating object is metal-coated with a plating method, deposits are scattered and deposited on the surface, and the surface of the plating object is exposed at an early stage. However, in the present invention, the reaction represented by the following reaction formula (1) must occur on the surface of nickel hydroxide. Therefore, it is necessary to bring in and out water, hydroxyl groups and the outside. For this reason, it is not desirable that the surface of nickel hydroxide is completely covered by the plated product, since this leads to a decrease in activity. It is preferable that the surface of nickel hydroxide is partially or slightly exposed.

[0012] This situation can be judged to some extent by observing the color of the surface of the nickel hydroxide particles during plating. That is, as the plating proceeds, the surface of the nickel hydroxide, which has been green, is discolored to a metallic color or black.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 is an explanatory view of a partial cross section of a positive electrode in which these partially metallized granular nickel hydroxide and conductive powder are filled between porous conductive substrates. The deposited metal adheres to the surface of nickel hydroxide with an appropriate gap. When used as an actual active substance, conductive powder such as nickel, cobalt oxide, etc. added to impart conductivity should be filled with nickel hydroxide particles coated with a deposited metal so as to have conductivity. However, the deposited metal adhering to the surface efficiently supplies electricity to the surface of the granular nickel hydroxide. When a large amount of deposited metal adheres, as shown in Fig. 3,
Even if no conductive additive is added, the whole surface of the nickel hydroxide coated with metal works sufficiently as a conductor.

Further, by selecting the kind of the coating metal, it can be used for imparting electrochemical activity to the surface of the nickel hydroxide particles. In this case, first, the surface of nickel hydroxide is activated by the above-mentioned method, and then the reaction formula (1) is immersed in an electroless plating solution containing a metal salt having a catalytic action to remove water. The surface of the nickel oxide particles can be coated with a deposit having a catalytic action. As the metal element used for this purpose, a platinum group metal such as platinum, palladium, iridium or a mixture thereof is effective, and these elements have an effect of promoting the reaction represented by the above reaction formula (1). is there.
However, when the platinum group element is reduced from an electroless plating solution containing these metal ions to form a coating deposit, it may not be completely reduced but may partially contain an oxide. Also does not change the catalytic action for promoting the above reaction formula (1) and has conductivity.

By such treatment, the electron transfer reaction on the surface of nickel hydroxide easily occurs, and the performance of nickel hydroxide as an active material is improved. For this purpose, the metal or /
In general, the amount of the metal oxide and the amount of the metal oxide may be small as compared with the case of coating the above-mentioned metal that imparts only conductivity. Next, the present invention will be described in detail with reference to examples.

[0016]

Example 1 2.5 g of stannous chloride was added to 250 ml of water with stirring, 2.5 ml of 35% hydrochloric acid was added, and dissolved by stirring at 40 ° C. 51 g of granular nickel hydroxide used for the positive electrode active material of the alkaline battery was put in the solution, stirred for 10 minutes, suction filtered, washed, dried in a dryer at 60 ° C., and chlorinated. A granular stannous treated nickel hydroxide (1) is prepared.
0.1 g of palladium chloride is added to 250 ml of water, 0.75 ml of 35% hydrochloric acid is added with stirring, and the mixture is dissolved with stirring at 40 ° C. for about 3 hours to obtain a yellow aqueous solution. The total amount of granular nickel hydroxide (1) prepared above was added to this solution, stirred for 10 minutes, and then suction filtered,
After washing, it was dried in a dryer at 60 ° C. to obtain 50.5 g of activated nickel (2) hydroxide granules.

Nickel electroless plating solution was prepared by dissolving 5 g of nickel sulfate hexahydrate, 15 g of sodium citrate, 2.5 g of sodium hydroxide and 7.5 g of sodium hypophosphite in 500 ml of water. Prepare (3). The solution was heated to 50 ° C., 50 g of the activated nickel hydroxide (2) prepared previously was added to the solution, and the mixture was stirred and reacted for 40 minutes, followed by suction filtration. After washing, it was thoroughly dried in a dryer at 60 ° C. The obtained granular nickel hydroxide had a black color. As a result of a scanning microscope and EPMA analysis, it was observed that nickel fine particles having a diameter of 0.1 to 0.5 μm were uniformly attached to the surface of the nickel hydroxide particles (Sample 1).

[0018]

[Example 2] Nickel electroless plating solution (3) of Example 1
Instead of, an aqueous solution having the following composition was prepared. Water 500 ml Nickel chloride hexahydrate 5 g Sodium citrate 25 g Hydrazine 15 g Activated in the same manner as in Example 1 while keeping the plating solution at 95 ° C. 50 g of granular nickel hydroxide (2) The mixture was put in and reacted for 1 hour, filtered, washed and dried, and then almost Example 1
A sample similar to that was obtained (Sample 2).

[0019]

[Example 3] Nickel electroless plating solution (3) of Example 1
Instead of, an aqueous solution having the following composition was prepared. Water 500 ml Nickel chloride hexahydrate 7.5 g Sodium hydroxide 15 g Ethylenediamine 25 g Sodium fluff 1.25 g Sodium borohydride 0.5 g While maintaining the temperature at 90 ° C. In the same manner, 50 g of activated granular nickel hydroxide (2) was added and reacted for 1 hour, followed by filtration, washing and drying, and a product similar to that of Example 1 was obtained (Sample 3).

[0020]

[Example 4] Electroless nickel plating solution (3) of Example 1
Instead of, an aqueous solution having the following composition was prepared. Water 500 ml Cobalt chloride hexahydrate 7.5 g Sodium citrate 17.5 g Ammonium chloride 25 g Adjust the pH to 9-10 with ammonia and keep at 80 ° C. and prepare in the same manner as in Example 1. The activated nickel hydroxide (2) (50 g) was added, and an aqueous solution prepared by dissolving 10 g of sodium hypophosphite in 100 ml of the solution was gradually added with stirring and then reacted for 1 hour. Then, it was suction filtered, washed, and dried. The obtained granular nickel hydroxide had a black color. As a result of scanning microscope and EPMA analysis, the surface of the nickel hydroxide particles was
It was observed that fine particles mainly composed of cobalt metal were uniformly attached (Sample 4).

[0021]

[Embodiment 5] Electroless nickel plating solution (3) in Embodiment 1
Instead of, an aqueous solution having the following composition was prepared. Water 500 ml Cobalt chloride hexahydrate 5 g Nickel chloride hexahydrate 5 g Rochelle salt 20 g Ammonium chloride 20 g An aqueous solution was kept at 90 ° C., and an activation treatment prepared in the same manner as in Example 1 was carried out. 50 g of granular nickel hydroxide containing 4.5% zinc compound was added, and an aqueous solution in which 125 g of sodium hypophosphite was dissolved in 125 ml was gradually added with stirring, followed by stirring for 1 hour. After that, it was filtered, washed and dried. The obtained nickel hydroxide was black, and as a result of observing with a scanning electron microscope, fine particles were uniformly attached to the surface. As a result of analysis by EPMA, these fine particles were a mixture of nickel and cobalt. There was (Sample 5).

[0022]

Example 6 Electroless nickel plating solution (3) of Example 1
Instead of, an aqueous solution having the following composition was prepared. Water 1 liter Copper sulphate pentahydrate 10 g Roussel salt 25 g Sodium hydroxide 6 g In this, 10 ml of about 38% formalin solution was dissolved with stirring and kept at 30 ° C. Similarly, 50 g of activated granular nickel hydroxide (2) prepared in the same manner was added, reacted for 1 hour while stirring, suction filtered, washed, and then sufficiently dried in a dryer at 60 ° C. Dried. The obtained granular nickel hydroxide had a blackish brown color. As a result of scanning microscope and EPMA analysis, it was observed that fine copper powder was uniformly attached to the surface of the nickel hydroxide particles (Sample 6).

[0023]

[Example 7] Electroless nickel plating solution (3) of Example 1
Instead of, an aqueous solution having the following composition was prepared. Water 200 ml Palladium chloride 0.4 g Hydrochloric acid (35%) 2 ml After stirring and dissolving, 50 g of activated nickel hydroxide nickel (2) prepared in the same manner as in Example 1 was added and stirred. 1% solution of sodium hypophosphite 200
After adding milliliter, the reaction was carried out at 30 ° C. for 1 hour. The granular nickel hydroxide obtained after suction filtration, washing and drying was black. As a result of the EPMA analysis, the adhesion of palladium on the surface could be detected, but it could not be discriminated by a scanning electron microscope (Sample 7).

[0024]

[Embodiment 8] Electroless nickel plating solution (3) of Embodiment 1
Instead of, an aqueous solution having the following composition was prepared. Water 250 ml Sodium hypophosphite 2.5 g Agitated and dissolved aqueous solution was heated to 50 ° C., and 50 g of activated nickel hydroxide (2) prepared in the same manner as in Example 1 was added. Stir and react for 2 hours.
The surface color of the granular nickel hydroxide particles gradually turns black. After the reaction, suction filtration, washing and drying were performed, and then EPMA analysis was performed to confirm the precipitation of nickel (Sample 8).

[0025]

[Example 9] Electroless nickel plating solution (3) of Example 1
Instead of, an aqueous solution having the following composition was prepared. Water 500 ml Silver nitrate 5 g Ammonia water (28%) 15 ml Dissolved, granular nickel hydroxide 50 g was added and stirred, and formalin (about 38%) 5 ml was dissolved in water 100 ml 10 ml was gradually added and reacted at room temperature for 30 minutes. The surface color of the granular nickel hydroxide particles gradually changed to gray. After the reaction, after suction filtration, washing and drying, the surface was observed with a scanning electron microscope and EPMA. As a result, deposition of silver particles of 0.5 to 1 micron was observed, which was considerably larger than when other metals were deposited. (Sample 9).

An evaluation test was conducted using a representative sample. 1. Conductivity evaluation Sample untreated granular nickel hydroxide for comparison, 5 grams of granular nickel hydroxide of Samples 1, 6, 7 and 9 selected as representatives, to each 5 grams of nickel powder and a 60% Teflon aqueous emulsion 0 0.1 g was added, and the mixture was sufficiently kneaded in a mortar, dried, pulverized, put into a mold having a diameter of 15 mm, and compressed at a pressure of 1500 kg / cm ² to obtain pellets. On both sides of this pellet, a copper plate with a lead wire having a diameter of 17 mm was pressure-bonded from both sides as shown in FIG. 4 and pressure-bonded, and the resistance between both lead wires was measured. The pressure was applied from both sides, the resistance R was measured when the resistance became constant, the thickness L of the pellet was measured with a micrometer, and the specific resistance ρ was calculated by the following formula to obtain the results shown in Table 1. It was

Ρ = (R × 1.52 × 3.14) / (L × 4)

[0028]

[Table 1] In Sample 1, the same conductivity can be obtained by adding about 50% of nickel powder compared to the untreated product, and in Samples 6 and 9, without addition of nickel powder,
A sufficiently high conductivity was obtained. Sample 7 is a sample in which a very small amount of platinum group metal is attached for the purpose of imparting catalytic properties to the surface of the granular nickel, and the conductivity itself is not significantly improved.

2. Battery evaluation Make the combination of nickel hydroxide and nickel powder as shown in Table 2,
To 100 parts by weight of each blended product, 2 parts by weight of 60% aqueous Teflon emulsion and 30 parts by weight of water were added and kneaded.
After adjusting to a paste, this paste has an average pore size of 200μ
m, a sponge-like nickel porous plate having a porosity of 95% and a thickness of 1.6 mm, dried, and compressed to a thickness of 0.56 mm,
After further drying, the lead was welded to obtain a positive electrode.

[0030]

[Table 2] The positive electrode of the paste type nickel electrode and the negative electrode manufactured by using the hydrogen storage alloy were wound together with a nylon separator into a battery can to make an AA size battery, and the charge and discharge characteristics were measured. , As shown in FIG. Table 3 shows the results of calculating the utilization rate of the positive electrode active material at the time of discharge after repeated charge and discharge for each prototype.

[0031]

[Table 3] From the measurement of the discharge capacity, the discharge capacities of the prototype 2 and the prototype 4 are increased by 8 to 14% as compared with the prototype 1 at both 0.2 CmA and 3 CmA. Further, the voltage during discharge shows higher values for the prototypes 2, 3 and 4 than the prototype 1 for 0.2 and 3 CmA, respectively, indicating that the reaction of the positive electrode active material is promoted. Recognize. Especially, the prototype 3 shows a high value, which shows that the surface is activated by the catalyst.

[0032]

INDUSTRIAL APPLICABILITY According to the present invention, by coating the surface of granular nickel hydroxide used as the active material of the positive electrode of an alkaline battery with a metal stable in an alkaline aqueous solution and / or a partially oxidized metal, granular water can be obtained. It is possible to impart conductivity to nickel oxide itself and reduce the amount of conductive additive added for imparting other conductivity, and to uniformly charge the surface to increase charge / discharge characteristics and utilization rate. It makes it possible. Further, by coating the surface with a metal having a catalytic effect for promoting the reaction or / and a partially oxidized metal, the activity of the battery can be enhanced and the high load charge / discharge performance can be enhanced.

[Brief description of drawings]

FIG. 1 is an explanatory view of a partial cross section of a conventional positive electrode in which granular nickel hydroxide, conductive powder and the like are filled between porous conductive substrates.

FIG. 2 is an explanatory view of a partial cross-section of a positive electrode in which a partially metal-coated granular nickel hydroxide and a smaller amount of conductive powder than those in a conventional positive electrode are filled between porous conductive substrates. is there.

FIG. 3 is an explanatory view of a partial cross section of a positive electrode in which granular nickel hydroxide substantially entirely covered with metal is filled between porous conductive substrates without addition of conductive powder or the like.

FIG. 4 is an explanatory diagram of a resistance measuring device for sample pellets.

FIG. 5 is a result of measuring discharge characteristics by making an AA size battery by winding a positive electrode of a paste type nickel electrode and a negative electrode made of a hydrogen storage alloy together with a nylon separator into a battery can. .

FIG. 6 is a result of measuring charging characteristics of the battery used in FIG.

[Explanation of symbols]

 1: Porous conductive substrate 2: Conductive powder 3: Granular nickel hydroxide 4: Sample pellet 5: Copper plate 6: Insulating plate 7: Resistance measuring instrument

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication C23C 18/36 C23C 18/36

Claims (5)

[Claims] 1. Nickel hydroxide used as a positive electrode active material of an alkaline battery, the surface of which is coated with a metal stable in an alkaline aqueous solution. 2. An alkaline battery in which the nickel hydroxide of claim 1 is filled in the holes of a conductive porous substrate. 3. A metal which is stable in an alkaline aqueous solution,
The nickel hydroxide of claim 1 selected from the group consisting of copper, nickel, cobalt, silver, gold and mixtures thereof. 4. The nickel hydroxide according to claim 1, wherein the metal stable in an alkaline aqueous solution is selected from the group consisting of platinum group metals and oxides thereof. 5. The hydroxide according to claim 1, wherein a metal stable in an alkaline aqueous solution is deposited and coated on the surface of nickel hydroxide used as a positive electrode material of an alkaline battery by using an electroless plating method. Method for producing nickel.