JP2000090918A - Hydrogen storage electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the corrosion resistance while providing the water repellency in a surface of an electrode, and accelerate the initial activation by forming a metal plating coat including the fine grains of the thermoplastic resin in a surface of the electrode. SOLUTION: A pressurized compact of the hydrogen storage alloy grains 2 is integrally connected onto a collector metal 1, and this electrode is plated in the plating liquid so as to form a plating coat 3. Quantity of the plating coat 3 is set at 20 wt.% or less in relation to the quantity of the hydrogen storage alloy, and the plating coat is selected from among Ni, Cu, Co, Ni-P, Ni-B, Co-P, Co-B, and the thermoplastic resin fine grains selected from among polytetrafluoroethylene, polyethylene, an ABS resin, polyamide and polysulfone is contained. Depth (a) of the plating between the alloy grains of the electrode is set at 100 μm or less, and plating thickness (b) coating each alloy grains of an electrode surface layer is set at 1-10 μm. Rise of the internal pressure is thereby restricted, and a battery having a long lifetime is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a hydrogen storage electrode using a hydrogen storage alloy.

[0002]

2. Description of the Related Art In recent years, nickel-hydride batteries using a hydrogen storage alloy as a negative electrode material have been used as various types of power sources from small portable devices such as mobile phones and notebook computers to electric vehicles. Conventionally, the life of alkaline storage batteries such as nickel-hydride batteries has been caused by separator dryout due to electrode swelling of the positive electrode. However, electrode swelling has been suppressed by improving the positive electrode active material. On the other hand, in the negative electrode, the hydrogen storage alloy is a rare earth metal or A
There is a problem in that it is deteriorated by corrosion due to elution of l, Mn and the like and oxidation by oxygen generated from the positive electrode. As a result, the discharge capacity is reduced and hydrogen gas is easily generated, and the oxygen gas generated from the positive electrode cannot be absorbed efficiently, so that the internal pressure of the battery increases, and the safety valve operates to cause separator dryout, leading to cycle life. That is, as the improvement of the positive electrode active material progresses, the cause of the life degradation shifts from the positive electrode to the negative electrode.

[0003] In order to improve the life characteristics of a battery, it is necessary to suppress an increase in the internal pressure of the battery. For that purpose, a hydrogen storage alloy for a negative electrode having good gas absorption and excellent corrosion resistance has been desired. To suppress the rise in internal pressure, a method of applying a water repellent to the electrode surface to form a three-phase interface to promote gas absorption, and to improve corrosion resistance, control of the composition and structure of the alloy, etc. are carried out. Had been On the other hand, the initial activation of the negative electrode is important to maintain the capacity balance between the precisely designed positive and negative electrodes. Normally, the negative electrode capacity is 1.
It is estimated to be approximately 4 to 1.8 times larger, and the balance is maintained as a charge reserve and a discharge reserve. This is designed to withstand overcharging and overdischarging, but if it breaks down, oxygen gas or hydrogen gas is generated at the end of charging or at the end of discharging, causing an increase in battery internal pressure. That is, it can be said that the early activation characteristic of the negative electrode is also one of the important characteristics for suppressing the internal pressure rise. Conventionally, for early activation, methods such as surface treatment such as acid treatment and alkali treatment, and mixing of a conductive agent have been performed.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a hydrogen storage electrode having a water repellent surface, excellent corrosion resistance, and quick initial activation. It is.

[0005]

The hydrogen storage electrode of the present invention is an electrode using a hydrogen storage alloy capable of storing and releasing hydrogen reversibly, and is a metal plating film containing fine particles of a thermoplastic resin on the surface of the electrode. It is characterized by having. Here, the metal plating film is preferably a porous film that allows diffusion of hydrogen. Further, the amount of the metal plating film is preferably 20% by weight or less based on the amount of the hydrogen storage alloy.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The hydrogen storage electrode of the present invention is a hydrogen storage electrode such as an electrode obtained by pressing a hydrogen storage alloy powder into a current collector or an electrode having a porous support filled with the hydrogen storage alloy powder. It can be produced by forming a metal plating film containing fine particles of a thermoplastic resin on the surface of the main body. In the hydrogen storage electrode according to the present invention, the electrode surface is coated with a metal plating film, and a conductive network is formed by the plating film, so that the contact resistance between the hydrogen storage alloy particles is reduced. Therefore, the reaction efficiency is improved, and early activation is possible. In addition, the plating film reduces the area where the hydrogen storage alloy particles are in direct contact with the electrolytic solution, and further reduces the solid-liquid interface due to the water repellency of the thermoplastic resin particles included in the plating film.
These improve the corrosion resistance of the electrode. As described above, the hydrogen storage electrode of the present invention has a quick initial activation, is excellent in corrosion resistance, and has water repellency by using a water repellent resin included in the plating film. Lifetime batteries can be provided.

[0007] The metals of the plating film formed on the electrode surface include Ni, Cu, Co, Ni-P, Ni-B and Co-.
A material selected from the group consisting of P and Co-B is preferable. When the plating amount is large, the energy density per unit weight of the electrode is reduced. Therefore, it is preferable to reduce the plating amount as much as possible and to form a good conductive network. FIG. 1 schematically shows the configuration of a hydrogen storage electrode according to the present invention. 1 represents a collector metal. A pressure-formed body of the hydrogen storage alloy particles 2 is integrally bonded to the current collector. The coating 3 is formed by plating this electrode in a plating solution. Here, a represents the plating depth of the electrode plated on the alloy so as to penetrate between the alloy particles of the electrode, and b represents the plating thickness of the individual alloy particles on the electrode surface layer. The upper limit of the amount of the plating film is 20% by weight of the hydrogen storage alloy, the plating depth represented by a is preferably 100 μm or less, the plating thickness represented by b is preferably 1 to 10 μm, and the plating amount is 0.1 to 4% by weight, and the plating depth is more preferably 10 μm or less. The plastic resin to be included in the metal plating film is polytetrafluoroethylene, polyethylene, AB
Those selected from the group consisting of S resin, polyamide, polysulfone, AS resin, polystyrene, vinyldene chloride resin, polyphenylene ether, methylpentene resin, and methacrylic acid resin are preferable. Among them, polytetrafluoroethylene is most preferable from the viewpoint of water repellency.

[0008]

The present invention will be described below in detail with reference to examples. Example 1 First, a predetermined amount of each metal was weighed so as to have a composition of MmNi _3.6 Co _0.75 Mn _0.35 Al _0.3 (Mm means a misch metal which is a mixture of rare earth elements), and high frequency induction melting was performed under an inert atmosphere. Make alloy ingot in furnace
Heat treatment was performed at 00 ° C. to obtain an alloy sample. This alloy ingot was mechanically pulverized to a particle size of 75 μm or less to obtain a hydrogen storage alloy powder sample. The alloy powder sample may be one prepared by a quenching method such as a single roll method or a gas atomizing method. A thickener was added to the alloy powder sample to form a paste, which was filled in a three-dimensional nickel foam substrate, dried and pressed. This electrode is made of polytetrafluoroethylene (PTF
Composite plating was performed in the following nickel plating solution containing particles having an average particle size of about 5 μm (represented by E) (molecular weight: about 7,500 to 10,500).

Ni (NH ₂ SO ₃ ) ₂ .4H ₂ O 350 (g / l) NiCl ₂ .6H ₂ O 45 (g / l) H ₃ BO ₃ 40 (g / l) Surfactant 1.0 (g / l) g / l) PTFE 100 (g / l) pH 4.0 Cathode current density 10 A / dm ² Temperature 50 ° C. Anode Ni plate Stirring Circulation Plating amount Equivalent to 2 wt% of hydrogen storage alloy

[0010] A desired amount of Ni was plated on the electrode surface, washed with water and dried to obtain an electrode sample. This electrode is referred to as electrode A. The electrode of the present invention can be produced by electroless plating in addition to the electrolytic plating as described above. Further, a thickener was added to the alloy powder sample to form a paste, and an SBR binder was mixed, applied to a punched metal substrate, dried and pressed. This electrode was composite-plated under the same plating conditions as electrode A to obtain an electrode sample. This electrode is referred to as electrode B. Next, paste-type electrodes were prepared in the same manner as the electrodes A and B, and these electrodes were made of PTFE.
Nickel plating was performed under the same conditions as for the electrode A except that a plating solution containing no Ni was used. The electrodes thus obtained are referred to as a comparative electrode C and a comparative electrode D, respectively. further,
Paste electrodes are prepared in the same manner as the electrodes A and B, and these electrodes are used as comparative electrodes E and F, respectively, without plating.

The thus prepared electrode was immersed in a 6 mol / l aqueous solution of potassium hydroxide together with a nickel hydroxide electrode of a counter electrode to prepare an open-type battery. And
At an ambient temperature of 20 ° C., the battery is charged 150% at 0.1 C.
A charge / discharge test was performed at 0.2 C to discharge to -0.6 V based on a mercury oxide electrode. FIG. 2 shows the test results at the beginning of charging and discharging. As is clear from FIG. 2, the comparative electrode E and the comparative electrode F, which have not been plated, have a slow initial activation, require 10 cycles or more to reach the maximum capacity, and have a small maximum capacity. On the other hand, the electrode A, the electrode B, the comparative electrode C, and the comparative electrode D of the present invention, which have been subjected to the plating process, have a high initial capacity and reach the maximum capacity in the second cycle, and have a large maximum capacity. The reason why the plating electrode can be activated early is that the electrode surface is covered with a plating layer to form a conductive network, and as a result, the contact resistance between the alloy particles is reduced and the reaction efficiency is increased.

Next, the battery is charged 150% at 1.0 C,
A charge / discharge cycle of discharging at -C to -0.6 V with respect to a mercury oxide electrode was repeated, and a life test was conducted to examine a change in discharge capacity.
The result is shown in FIG. As is apparent from FIG. 3, the cycle life of the electrodes A and B of the present invention was increased by about 30% as compared with the comparative electrodes C and D. To examine the relationship between cycle life and corrosion resistance, each electrode was
In 100 ml of 6 mol / l aqueous potassium hydroxide solution at
After immersion for days, the concentrations of the leached cobalt, aluminum and manganese ions were measured. FIG. 4 shows the results. As is clear from FIG. 4, the ions eluted from the electrodes A and B of the present invention are smaller than those of the comparative electrode,
It can be seen that the corrosion resistance is excellent. Nickel plating reduces the area of direct contact between the interface between the hydrogen storage alloy and the electrolyte, and the PTFE contained in the plating film
It is considered that the fact that the solid-liquid interface was further reduced due to the water repellent effect was due to the improvement in corrosion resistance.

Next, an AA size sealed battery having a nominal capacity of 1300 mAh was manufactured using each of the electrodes A, B, C, D, E and F and a paste-type nickel hydroxide electrode. Battery A, Battery B, respectively
It is assumed that battery C, battery D, battery E, and battery F. After activating these batteries, at ambient temperature 20 ° C., 1.0
The battery was charged 200% with C, and the change in the internal pressure of the battery with the amount of charge was measured. The result is shown in FIG. As is clear from FIG. 5, only the battery A and the battery B of the present invention exhibited low internal pressure characteristics. PTF contained in the composite plating on the electrode surface
This is because a three-phase interface is formed due to the water-repellent effect of E, and the efficiency of absorbing oxygen gas generated from the positive electrode during overcharge is increased. The formation of such a three-phase interface not only absorbs oxygen gas but also promotes an absorption reaction by a solid-gas reaction of hydrogen gas accumulated inside the battery, so that a significant increase in internal pressure can be suppressed. Next, for each of the batteries A to F, the ambient temperature 2
At 0 ° C., a cycle life test was conducted in which the battery was charged at 1.0 C at 120% and discharged at 1.0 C to 1.0 V. FIG. 6 shows the result. The life test conditions are generally such that the cycle life is caused by the internal pressure reaching the safety valve operating pressure, the gas inside the battery and the vaporized electrolyte leaking out, and the internal resistance of the battery increases due to the exhaustion of the electrolyte. In the battery of the present invention, the negative electrode forms a three-phase interface to promote oxygen gas absorption, and also has the corrosion resistance of the hydrogen storage alloy, so that the internal pressure rise can be largely suppressed.

[0014]

As described above, the hydrogen storage electrode of the present invention is
Since the surface has both water repellency, excellent corrosion resistance, and quick initial activation, a rise in internal pressure can be suppressed, and a long-life battery can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a configuration example of an electrode according to the present invention.

FIG. 2 is a diagram showing the relationship between the discharge capacity of various electrodes at the initial stage of charge and discharge and the number of cycles in an example of the present invention.

FIG. 3 is a diagram showing the results of a life test of various electrodes.

FIG. 4 is a diagram comparing the results of quantitative analysis of ions eluted when various electrodes are immersed in a high-temperature alkali.

FIG. 5 is a diagram showing a relationship between a charging time of a battery using various electrodes and an internal pressure.

FIG. 6 is a view showing a result of a life test of the battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Current collector 2 Hydrogen storage alloy particle 3 Plating film a Plating depth b Plating thickness

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H003 AA04 BB02 BB32 BB34 BC01 BC04 BC05 BD02 BD04 5H016 AA01 BB08 CC03 CC04 EE01 EE09 HH01 HH13

Claims (5)

[Claims] 1. An electrode using a hydrogen storage alloy capable of reversibly storing and releasing hydrogen, wherein the electrode has a metal plating film containing fine particles of a thermoplastic resin on the surface of the electrode. 2. The hydrogen storage electrode according to claim 1, wherein the metal plating film is a porous film that allows diffusion of hydrogen. 3. The hydrogen storage electrode according to claim 1, wherein the amount of the metal plating film is 20% by weight or less of the amount of the hydrogen storage alloy, and the plating depth from the electrode surface is 100 μm or less. 4. The method according to claim 1, wherein the metal plating film is Ni, Cu, C
The hydrogen storage electrode according to claim 1, wherein the hydrogen storage electrode is selected from the group consisting of o, Ni-P, Ni-B, Co-P, and Co-B. 5. The plastic resin is selected from the group consisting of polytetrafluoroethylene, polyethylene, ABS resin, polyamide, polysulfone, AS resin, polystyrene, vinyldene chloride resin, polyphenylene ether, methylpentene resin, and methacrylic acid resin. The hydrogen storage electrode according to claim 1, wherein