JP2006286345A - Surface finishing method of hydrogen storage alloy, surface-finished hydrogen storage alloy, and nickel-hydrogen secondary battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface finishing method of a hydrogen storage alloy, a surface-finished hydrogen storage alloy, and a nickel-hydrogen secondary battery using this alloy. <P>SOLUTION: The surface finishing method of the hydrogen storage alloy particle is characterized by improvement of the electrochemical performance, especially the initial cycle activity and high rate of discharging characteristics, as well as enhancement of the cycle life performance through formation of the durable nickel-coating film on a surface of the hydrogen storage alloy particle and control of its coating amount within the specified range. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a nickel-hydrogen secondary battery using a hydrogen storage alloy as a negative electrode, nickel hydroxide as a positive electrode, and a high-concentration alkaline aqueous solution as an electrolyte. Furthermore, the present invention relates to a surface treatment method for improving the electrochemical characteristics of a hydrogen storage alloy, which is a negative electrode active material, in particular, the activity at the beginning of the cycle and the high rate discharge characteristics and at the same time improving the cycle life characteristics.

  Nickel-cadmium secondary battery, which is a type of alkaline storage battery that has been used in the past, uses cadmium for the negative electrode, nickel hydroxide for the positive electrode, and high-concentration alkaline aqueous solution for the electrolyte, and is low in cost and highly durable In addition, since it can easily discharge a large current, it is useful as a power source in applications requiring power, such as electric tools and cordless vacuum cleaners. However, since cadmium, which is a harmful substance, is used, its use is gradually being restricted.

  On the other hand, the nickel-hydrogen secondary battery put into practical use in 1990 as a new type of alkaline storage battery has the same configuration as the nickel-cadmium battery except that a hydrogen storage alloy electrode is used for the negative electrode. Are also the same, have a higher capacity than nickel-cadmium secondary batteries, and do not use materials with high environmental impact. In recent years, it has rapidly become widespread as a power source for still cameras, and recently as a large battery for hybrid vehicles and electric vehicles.

By the way, hydrogen storage alloys are susceptible to surface oxidation due to the action of oxygen in the air. In particular, commercially available hydrogen storage alloy powders have a process of crushing the alloy lump, and the surface is oxidized during storage to form an oxide film with low conductivity. Is low.
Therefore, a nickel-hydrogen secondary battery manufactured using such a hydrogen storage alloy powder has a problem that it must be activated by repeating charging and discharging several times in advance. In addition, when a hydrogen storage alloy with low conductivity is used, the contact resistance between the alloys inside the electrode increases, and the current generated during discharge cannot be collected with high efficiency. Therefore, it is regarded as a drawback of the nickel-hydrogen secondary battery that the alloy utilization rate is lowered particularly during high rate discharge.

  Furthermore, it is assumed that devices such as electric tools can be used in various environments. For example, durability at high temperatures is also required for batteries. However, since the hydrogen storage alloy, which is the negative electrode active material, is fragile, the nickel-hydrogen secondary battery has a problem in durability, such as the elution of the alloy constituent material into the electrolyte solution becomes remarkable particularly at high temperatures. ing. Therefore, in applications where power is required and durability is required, such as electric tools and cordless vacuum cleaners, the current situation is that nickel-cadmium secondary batteries with a high environmental load must still be used.

  As a method for solving these problems, a so-called microencapsulated hydrogen in which the surface of a hydrogen storage alloy particle is coated with a conductive nickel or copper thin film by a self-catalytic wet electroless plating method using a reducing agent. A method using an occlusion alloy has been proposed (Patent Document 1, Patent Document 2, and Patent Document 3), but the effect is not sufficient and has not been put into practical use.

In particular, Patent Literature 2 and Patent Literature 3 disclose hydrogen storage alloy particles coated with pure nickel plating. In the hydrogen storage alloy particles disclosed in Patent Document 2, the coating thickness of nickel plating is 0.5 to 2 μm, and if it is thinner than 0.5 μm, the effect is small in terms of improving conductivity, and a uniform plating film is formed. As a result, the alloy powder falls off and peels off, and if it is thicker than 2 μm, it does not form a uniform coating film, and agglomeration of excess nickel or nickel alloy particles is observed, and the overall hydrogen storage capacity is low. It is supposed to deteriorate. This patent application presupposes a uniform plating film. Patent Document 3 does not mention the difference due to the plating thickness, but only mentions that the plating deposition rate is 0.7 μm / h or less. This patent application uses a special titanium-nickel alloy (not put into practical use), and its main purpose is to improve the conductivity and durability. In addition, the film thickness of the plating in these patent applications is not directly measured from the plating on the alloy particles, but is estimated from the plating performed on the flat plate.
Further, in the techniques disclosed in these patent applications, in order to activate the hydrogen storage alloy, it is essential to hydrogenate the hydrogen storage alloy in advance (physically storing and releasing hydrogen), It is mentioned that if such activation is not performed, the performance is degraded.

JP-A 61-64069 JP-A-61-163569 JP 2003-309327 A

  Thus, in the nickel-hydrogen secondary battery, the surface treatment method of the hydrogen storage alloy capable of improving the electrochemical characteristics and at the same time improving the durability has not been found so far. It is. The present invention is to solve this problem, and in a hydrogen storage alloy which is a negative electrode active material of a nickel-hydrogen secondary battery, its electrochemical characteristics, particularly initial activity and high rate discharge characteristics are improved. A surface treatment method capable of simultaneously obtaining durability and a nickel-hydrogen secondary battery using the same are provided.

In order to solve this problem, the inventors have conducted intensive studies, and as a result, by using an electroless pure nickel plating method and controlling the deposition amount of the plating coating film within a specific range, the electrochemical properties of the hydrogen storage alloy particles are reduced. It has been found that it is possible to improve the durability while improving the characteristics.
In other words, the elution of constituent components from the hydrogen storage alloy is suppressed by the action of the coating film by pure nickel plating, so that the cycle life characteristics are improved, and at the same time, the conductivity is improved by the action of the pure nickel coating film. Moreover, since the amount of the coating film is strictly controlled so as not to prevent the permeation of hydrogen, the electrochemical characteristics are also improved.

Accordingly, the subject of the present invention is a surface treatment of hydrogen storage alloy particles, characterized in that a durable nickel coating film is formed on the surface of the hydrogen storage alloy particles and the coating amount is controlled within a specific range. Is in the way.
According to a preferred embodiment, the durable nickel coating is formed by electroless nickel plating. The electroless nickel plating method is characterized by electroless nickel plating not containing phosphorus and boron.

  According to a further preferred embodiment of the present invention, the electroless nickel plating method is an electroless nickel plating method using trivalent titanium ions as a reducing agent. More preferably, the electroless nickel plating method using trivalent titanium ions as a reducing agent is a plating method in combination with electrolytic reduction regeneration of a plating bath.

  In particular, the specific subject matter of the present invention is characterized in that the formed durable nickel coating film is formed in an amount of 0.005 g to 0.02 g in terms of nickel per 1 g of hydrogen storage alloy powder. A surface treatment method for hydrogen storage alloy particles.

  Another subject of the present invention resides in hydrogen storage alloy particles subjected to the surface treatment method described above.

  Still another subject matter of the present invention resides in a secondary battery using the hydrogen storage alloy particles subjected to the surface treatment and a nickel-hydrogen secondary battery using such hydrogen storage alloy particles.

  According to the present invention, a durable nickel coating film is formed on the surface of the hydrogen storage alloy particles, so that the electrochemical characteristics of the hydrogen storage alloy, which is the negative electrode active material of the nickel-hydrogen secondary battery, particularly the activity at the beginning of the cycle. As a result, the high-rate discharge characteristic is improved and the cycle life characteristic is improved.

  According to the surface treatment method of the present invention, the durable nickel coating film can be formed directly on the surface of the hydrogen storage alloy particles under a mild condition by a simple process. In addition, since the coated hydrogen storage alloy particles are imparted with conductivity by the nickel coating film on the surface thereof, the nickel-hydrogen secondary battery using the coated hydrogen storage alloy particles as a negative electrode has battery performance, particularly high activity and high initial cycle performance. The rate discharge characteristics can be improved. Further, such a nickel coating film has alkali resistance, and therefore has an action of suppressing elution of constituent components from the hydrogen storage alloy. Therefore, cycle life characteristics can be improved.

The hydrogen storage alloy particles to be surface-treated in the present invention are not particularly limited, and the alloy itself can be appropriately selected from known ones used for negative electrodes of nickel-hydrogen secondary batteries. Specifically, for example, misch metal (Mm) made of a mixture of rare earth elements such as La and Ce and AB ₅ type mainly containing Ni, Mn, Co, Al, etc., and Ni, Mg, Ti, etc. as main ingredients. The AB ₂ type is preferable as the alloy, but the AB ₅ type is preferable from the viewpoint of obtaining cycle life characteristics. The size of the particles is not particularly limited, but the average particle diameter is about 1 to 125 μm, preferably about 1 to 50 μm, from the viewpoint of processability when processing into an electrode and battery performance when an electrode is formed. Things are good.
According to the method of the present invention, it is possible to perform direct plating without performing treatment such as hydrogenation on commercially available alloy particles. Thereby, there exists the characteristic which can simplify a manufacturing process.

The method of nickel plating on the surface of the hydrogen storage alloy is roughly divided into electroplating and electroless plating. As mentioned above, since the particle size of the hydrogen storage alloy is small, it is more practical to perform electroless plating in terms of the plating equipment. Is. The electroless nickel plating that has been used industrially so far mainly uses sodium hypophosphite or sodium borohydride as a reducing agent. However, in the case of these electroless nickel platings, phosphorus and boron are incorporated in a large amount of several percent to several tens of percent into the nickel plating coating film, and these are the electrical, mechanical or chemical characteristics of the nickel plating coating film. Affects. Although the reason is not clarified, if the surface of the hydrogen storage alloy is coated with such nickel plating containing phosphorus or boron and used as the negative electrode of a nickel-hydrogen secondary battery, the durability of the battery is low. It is also known that Also, the plating rate is relatively fast, and it is very difficult to control the deposition amount of the plating film within a specific range, which is the subject of the present invention.
On the other hand, in the present invention, the above problem was solved by using a plating solution containing trivalent titanium ions as a reducing agent. That is, in this plating process, pure nickel plating containing no phosphorus or boron is deposited, so that phosphorus or boron does not adversely affect the characteristics of the coating film. Also, since the deposition rate of plating is relatively slow, the amount of plating coating film does not hinder the permeation of hydrogen, that is, it is possible to strictly control the film thickness so that the plating coating film is very thin. is there.

  In general, for catalyst application, which is a pretreatment for electroless plating on non-metal or non-catalytic (or low) metal, after adding sensitivity with a solution containing tin, catalytic activity is achieved with a solution containing palladium. Is used. Also, a method of treating with a solution in which palladium and tin are made into one solution is widely performed. As for the electroless nickel plating on the hydrogen storage alloy in the present invention, the plating proceeds more smoothly when the pretreatment of these platings is performed. The pretreatment method is not particularly limited, and a normal pretreatment method may be adopted. For example, in order to efficiently apply the catalyst in the next step, after the object to be plated is treated with a surface conditioner comprising a surfactant as a main component, the object to be plated is applied to a catalyst solution containing palladium and tin as one solution. By adding the catalyst, the catalyst is applied. At this time, in addition to palladium serving as a catalyst, tin is also partially adsorbed on the object to be plated, but this tin needs to be removed because it adversely affects the adhesion of the plating film. Then, after processing with an accelerator liquid and removing this tin, a to-be-plated object is thrown into the electroless nickel plating liquid which uses a trivalent titanium ion as a reducing agent, and nickel plating is performed.

  The bath temperature of nickel plating using trivalent titanium ions as a reducing agent is preferably 20 to 90 ° C, more preferably 20 to 70 ° C. If it is less than 20 ° C., the nickel plating speed is very slow and the working efficiency is deteriorated, and if it is 90 ° C. or more, the plating bath becomes unstable and easily decomposes. The pH of the plating bath is preferably 4 to 11, and more preferably 5 to 10. When the pH is less than 4, nickel plating does not precipitate. When the pH is 11 or more, the plating bath is easily decomposed.

The concentration of trivalent titanium ions as a reducing agent is preferably about 0.001 to 0.1 mol / liter, and more preferably about 0.005 to 0.05 mol / liter. Examples of complexing agents and stabilizers for stably presenting titanium ions and nickel ions in the plating solution include carboxylic acids such as ethylenediamine, citric acid, nitrilotriacetic acid, and ethylenediaminetetraacetic acid, and sodium salts and potassium thereof. Derivatives such as salts and ammonium salts may be mentioned, and these may be used alone or in combination of two or more. Furthermore, a stabilizer for stabilizing nickel ions may be added, metal ions such as lead (for example, Pb, Sn, As, Tl, Mo, In, Ga, Cu, etc.), iodides such as KIO ₃ , or One type or a combination of two or more types of sulfur-containing compounds such as thiourea and thiodiglycol can be used.
The concentration of these complexing agent and stabilizer may be appropriately set according to the concentration of titanium ions and nickel ions contained in the plating solution, but is usually about 0.001 to 2 mol / liter, particularly 0. It is preferably about 0.01 to 1 mol / liter. Further, in the plating solution, a pH buffering agent such as boric acid may be added in order to adjust the pH to the above-mentioned preferred range, and the concentration is about 0.001 to 0.2 mol / liter. Is preferred. If it is less than 0.001 mol / liter, the effect of stabilizing the pH of the liquid is not sufficient. Conversely, if it exceeds 0.2 mol / liter, the pH buffering agent will precipitate when the liquid temperature falls below room temperature. Then, it may be difficult to regenerate and activate the liquid.

  Pure nickel plating using trivalent titanium ions as a reducing agent may be performed in the same manner as a normal electroless plating method. That is, while maintaining the plating solution at a constant temperature and a constant pH within the above-mentioned range, a hydrogen storage alloy that is an object to be plated that has been appropriately pretreated is put into the plating solution and stirred. Nickel ions are reduced and deposited on the surface to obtain a plating coating film.

  In the case of electroless nickel plating using trivalent titanium ions as a reducing agent in the present invention, the trivalent titanium ions spent for the reduction of nickel ions become tetravalent titanium ions. This reaction has a very high reversibility due to a simple mechanism in which only one electron is taken away. In other words, the tetravalent titanium ions that have been consumed for the reduction of nickel ions and are oxidized are reduced electrochemically to return them to trivalent titanium ions. From such a point of view, the plating solution containing tetravalent titanium ions, which increase with the progress of nickel plating, is transferred to an electrolytic bath provided separately from the plating bath, where it is reduced by electrolysis, thereby trivalent titanium ions. It is preferable to perform the process of returning to. By such a process, it is possible to recycle the reducing agent, that is, to activate the plating solution. Once the plating solution is built, it is theoretically unnecessary to add the reducing agent. Recently, the disposal of plating solutions has become very problematic from the viewpoint of environmental problems, and it is important to develop environmentally friendly plating solutions and plating solution recycling systems. By using this plating solution activation process, it is possible to significantly reduce the plating solution waste solution after use. In addition, the activation of the plating solution can be performed at an arbitrary point in the plating process. For example, by performing it in parallel with the plating process, the plating solution can be used continuously over a long period of time. This is also a very effective process.

The weight ratio of the nickel coating film formed on the surface of the coated particles, that is, the amount of precipitation of the nickel coating film per gram of the coated hydrogen storage alloy particles is determined by dissolving the coated hydrogen storage alloy particles in dilute nitric acid. The amount was calculated as a nickel equivalent by quantifying the amount by atomic absorption spectrometry. As a measuring apparatus, “polarized Zeeman atomic absorption photometer Z-5710” (manufactured by Hitachi High-Technologies Corporation) was used. Further, the plating state on the surface of the coated hydrogen storage alloy particles was observed using a “field emission scanning electron microscope S-800” (manufactured by Hitachi, Ltd.).
According to the surface treatment method of the present invention, the coating amount is preferably 0.005 g to 0.02 g per 1 g of the hydrogen storage alloy powder. If the coating amount is less than 0.005 g, a sufficient effect cannot be obtained, and if it exceeds 0.02 g, hydrogen permeation is inhibited and electrochemical characteristics are impaired. Further, the alloy surface need not be uniformly coated, and there may be a coated portion and a non-coated portion.
In the present invention, the surface treatment alloy is dissolved in an acid, and the amount of coating can be accurately quantified by using atomic absorption spectroscopy. By adjusting the plating treatment conditions using this method, the plating coating state and battery performance can be managed.

  Next, the negative electrode for a nickel-hydrogen secondary battery according to the present invention will be described. The negative electrode uses the coated hydrogen storage alloy particles according to the present invention as an active material, and can be prepared by various known means. Specifically, the coated hydrogen storage alloy particles and a known binder are mixed and applied to a two-dimensional substrate such as a three-dimensional porous substrate such as a foamed nickel substrate or a punching metal substrate. It can be obtained by pressure molding after drying. The binder is not particularly limited, and examples thereof include polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, polyethylene oxide, and polytetrafluoroethylene, and these can be used alone or in combination of two or more. The binder may be used in an amount of about 0.1 to 20% by weight (solid content) with respect to the coated hydrogen storage alloy particles. Moreover, you may use 0.1-10 weight% of conductive support agents, such as Ni, Co, Cu powder | flour, acetylene black, carbon black, and yttrium oxide, with respect to this covering hydrogen storage alloy particle for a negative electrode.

  Finally, the nickel-hydrogen secondary battery according to the present invention will be described. The battery uses the negative electrode, a known positive electrode such as a sintered nickel hydroxide electrode, a known separator such as a polypropylene or acrylic nonwoven fabric, a known alkaline electrolyte, and a known storage container. And assembled into a battery.

  EXAMPLES Hereinafter, although an Example further demonstrates this invention in full detail, this invention does not receive any restriction | limiting by this, In the range which does not change the summary, it shall change suitably. In the following text, “%” means “% by weight” and “parts” means “parts by weight” unless otherwise specified.

Example 1
As the hydrogen storage alloy powder, an AB ₅ type (average particle diameter of 35 μm) generally used for nickel-hydrogen secondary batteries was used.
Prior to pure nickel plating, the hydrogen storage alloy was subjected to surface adjustment, catalysis and accelerator treatment in accordance with a conventional method. That is, first, 20 g of a hydrogen storage alloy was put into 1 L of a surface conditioner (Daiwa Kasei, Dine Cleaner PB-810), and stirred at 60 ° C. for 3 minutes. Next, it was put into 1 L of a general palladium-tin colloid catalyst solution for electroless plating and stirred at 25 ° C. for 3 minutes. Furthermore, it was put into 1 L of accelerator liquid (2% sulfuric acid), and stirred at 25 ° C. for 3 minutes. After the plating pretreatment process as described above, 1 L of electroless pure nickel plating solution (Daiwa Kasei, Dyne Nickel SD) using trivalent titanium ions as a reducing agent is adjusted to 50 ° C. and pH 8.5, The pretreated hydrogen storage alloy powder was added, and plating was performed for 90 minutes with stirring. After the completion of plating, washing with water and vacuum drying were performed to prepare a pure nickel-coated sample. During the plating period, the plating solution was continuously flowed into the cathode chamber partitioned by the ion exchange membrane, and plating was performed while electrolytic regeneration of trivalent titanium ions was performed.
The amount of nickel coating film deposited on the surface of the hydrogen storage alloy that has been subjected to electroless pure nickel plating is determined by weighing a predetermined amount of the hydrogen storage alloy powder before and after plating and completely dissolving it in dilute sulfuric acid. Was calculated by measuring and quantifying by an atomic absorption method.
The SEM image (50,000 times) of the surface of the electroless pure nickel-plated hydrogen storage alloy obtained in Example 1 is shown in FIG.

Example 2
Except that the plating time in electroless pure nickel plating was 60 minutes, the same treatment as in Example 1 was performed to prepare a pure nickel-coated sample.
FIG. 2 shows an SEM image (50,000 times) of the surface of the hydrogen storage alloy obtained in Example 2 and treated with electroless pure nickel plating.

Comparative Example 1
A pure nickel-coated sample was prepared in the same manner as in Example 1 except that the plating time in electroless pure nickel plating was 300 minutes.
FIG. 3 shows an SEM image (50,000 times) of the surface of the hydrogen storage alloy obtained by Comparative Example 1 and treated with electroless pure nickel plating.

Comparative Example 2
Moreover, the hydrogen storage alloy powder which has not performed the plating process was prepared for the comparison. FIG. 4 shows an SEM image (50,000 times) of the surface of the hydrogen storage alloy particles.

Production of Electrode A predetermined amount of the hydrogen storage alloy powder subjected to the electroless pure nickel plating treatment (Example 1, Example 2 and Comparative Example 1) was weighed and mixed with a 2% aqueous polyvinyl alcohol solution to obtain a hydrogen storage alloy 98. Part and 2 parts of polyvinyl alcohol solid content were prepared. This was applied to a foamed nickel substrate (nickel weight 575 g / m ³ , 2 × 4 cm) and dried under reduced pressure. Next, this substrate was pressed, and a nickel ribbon as a lead wire was electrically welded to produce a hydrogen storage alloy negative electrode. Moreover, the electrode was similarly produced using the hydrogen storage alloy powder (comparative example 2) which has not been plated.

A nickel-hydrogen secondary battery open model cell was assembled. One negative electrode of the hydrogen storage alloy was sandwiched between two electrodes of a sintered nickel hydroxide electrode as a positive electrode and an acrylic non-woven fabric as a separator.
Further, these three electrode plates were sandwiched between two acrylic plates and fixed with bolts to assemble a negative electrode-regulated nickel-hydrogen secondary battery model cell. Using the prepared model cell, a nickel-hydrogen secondary battery open model cell was assembled using a 6M aqueous potassium hydroxide solution as an electrolyte.

Constant current charge / discharge test A constant current charge / discharge test device was connected to this open model cell, charged at a current density of 200 mA / g for 2 hours, rested for 10 minutes, and then the potential difference between positive and negative electrodes became 0.9 V at 200 mA / g. A charge / discharge cycle test was conducted in which the battery was discharged until the end of the discharge and rested for 10 minutes. This charge / discharge cycle test was repeated 20 cycles, and the discharge capacity of the 20th cycle was regarded as the discharge capacity of the hydrogen storage alloy. In addition, this charging / discharging cycle test was implemented on 30 degreeC conditions in the thermostat. The obtained results are shown in Table 1.

High-rate discharge characteristic test After the charge / discharge cycle test, a high-rate discharge characteristic test was continuously performed.
That is, the battery was charged at 200 mA / g for 2 hours, rested for 10 minutes, and then discharged as a first discharge at 1000 mA / g until the potential difference between the positive and negative electrodes became 0.9V. Next, after a 10-minute pause, discharging was performed at 40 mA / g until the potential difference between the positive and negative electrodes became 0.9 V as a second discharge. The high rate discharge characteristics were calculated by the following equation, assuming that the _first discharge capacity is C ₁ and the second discharge capacity is C ₂ .
High rate discharge characteristics (%) = C ₁ / (C ₁ + C ₂ ) × 100
The obtained results are shown in Table 1. In addition, FIG. 5 shows discharge curves for Example 1 and Comparative Example 2 when discharged at current densities of 200 mA / g and 1000 mA / g.

Evaluation of durability Next, the nickel-hydrogen secondary battery open model cell was placed in a thermo-hygrostat set to 45 ° C. and humidity 80% RH, charged at a current density of 200 mA / g for 2 hours, and then 10 minutes. After the rest, a charge / discharge cycle life test was conducted in which the battery was discharged at 200 mA / g until the potential difference between the positive and negative electrodes became 0.9 V, and rested for 10 minutes after the end of the discharge. This test was repeated 200 cycles, the discharge capacity after 200 cycles was measured, and the durability was evaluated by comparing the charge / discharge capacity retention rate. The obtained results are shown in Table 1.

From Table 1, it can be seen that in Example 1 subjected to the electroless pure nickel plating treatment, the discharge capacity was greatly improved as compared with the hydrogen storage alloy not subjected to the plating treatment, and the high rate discharge characteristics were also improved. Recognize. In Example 2 where the coating amount was reduced, the discharge capacity and the capacity retention after 200 cycles at 45 ° C. were slightly lower than in Example 1, but it was found that the high rate discharge characteristics were improved. In Comparative Example 1 in which the precipitation amount was increased, the capacity retention after 200 cycles at 45 ° C. was improved, but the discharge capacity and the high rate discharge characteristics were decreased. From this, it can be said that by controlling the coating amount of the plating film, it is possible to perform surface treatment that achieves both battery performance and durability, and it can be said that the effect of the present invention has been demonstrated.
When the discharge curves of FIG. 5 are compared, the battery produced using Example 1 subjected to the electroless pure nickel plating treatment was more discharged than the battery produced using the hydrogen storage alloy not subjected to the plating treatment. The voltage is high. In particular, the effect appears remarkably at the time of high rate discharge of 1000 mA / g. This means that even in a power application that requires a large current, it is possible to efficiently take a current while maintaining a high voltage, and it can be said that the effect of the present invention appears.

    The nickel-hydrogen secondary battery produced according to the present invention has a high discharge capacity and good high rate discharge characteristics, and its effect is remarkable at the time of power use requiring a large current, especially at a high rate discharge of 1000 mA / g level. Therefore, it can be used not only for normal applications of nickel-hydrogen secondary batteries, but also for applications that require power and require durability, such as electric tools and cordless vacuum cleaners. .

2 is an SEM image (50,000 times) of the surface of an electroless pure nickel-plated hydrogen storage alloy obtained in Example 1. FIG. The SEM image (50,000 times) of the electroless pure nickel plating process hydrogen storage alloy surface obtained in Example 2. FIG. 2 is an SEM image (50,000 times) of the surface of an electroless pure nickel-plated hydrogen storage alloy obtained in Comparative Example 1. FIG. It is a SEM image (50,000 times) of the hydrogen storage alloy surface which has not performed plating processing. It is a discharge curve in Example 1 and Comparative Example 2.

Claims (9)

  A surface treatment method for hydrogen storage alloy particles, comprising forming a durable nickel coating film on the surface of the hydrogen storage alloy particles, and controlling the coating amount within a specific range.   2. The surface treatment method for hydrogen storage alloy particles according to claim 1, wherein the durable nickel coating film is formed by an electroless nickel plating method.   The surface treatment method for hydrogen storage alloy particles according to claim 1 or 2, wherein the electroless nickel plating method is electroless nickel plating not containing phosphorus and boron.   The surface treatment method for hydrogen storage alloy particles according to claim 1, wherein the electroless nickel plating method is an electroless nickel plating method using trivalent titanium ions as a reducing agent.   The surface treatment method for hydrogen storage alloy particles according to any one of claims 1 to 4, wherein the electroless nickel plating method using trivalent titanium ions as a reducing agent is a plating method in which electrolytic reduction regeneration of a plating bath is used in combination. .   6. The hydrogen storage film according to claim 1, wherein the formed durable nickel coating film is formed in an amount of 0.005 g to 0.02 g in terms of nickel per 1 g of hydrogen storage alloy powder. A method for surface treatment of alloy particles.   The hydrogen storage alloy particle by which the surface treatment method in any one of Claims 1-6 is given.   A secondary battery using the hydrogen storage alloy particles according to claim 7. A nickel-hydrogen secondary battery using the hydrogen storage alloy particles according to claim 8.