JP3472489B2 - Hydrogen storage electrode and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a hydrogen storage electrode using a hydrogen storage alloy and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, nickel-hydride batteries using a hydrogen-absorbing alloy as a negative electrode material have been used as a power source for various models from small portable devices such as mobile phones and notebook computers to electric vehicles. Conventionally, the life of alkaline storage batteries including nickel-hydride batteries has been caused by separator dryout due to electrode swelling of the positive electrode, but electrode swelling has been suppressed by the improvement of the positive electrode active material. On the other hand, in the negative electrode, the hydrogen storage alloy is rare earth metal or A
There is a problem that it is deteriorated due to corrosion due to elution of l, Mn, etc. and oxidation due to 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 efficiently absorbed, so that the internal pressure of the battery rises and the separator dryout occurs due to the operation of the safety valve to reach the cycle life. That is, as the improvement of the positive electrode active material progresses, the cause of the deterioration of life has shifted from the positive electrode to the negative electrode.

In order to improve the life characteristics of a battery, it is necessary to suppress an increase in the internal pressure of the battery, and for that purpose, a hydrogen storage alloy for a negative electrode having good gas absorption and excellent corrosion resistance is desired. In order to suppress the increase in internal pressure, a method of applying a water repellent agent to the surface of the electrode to form a three-phase interface to promote gas absorption, and to improve corrosion resistance, control of the alloy composition and structure has been performed. On the other hand, the electrode manufacturing method is a process in which an alloy, a thickener, a binder, etc. are mixed to prepare a paste, which is applied to a punching metal substrate, dried, and pressed to obtain a paste. This is a rather complicated manufacturing method when the agent coating step is also added.

[0004]

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a hydrogen storage electrode having excellent gas absorption performance and a small increase in internal pressure. The present invention also aims to provide a simplified method of manufacturing such a hydrogen storage electrode.

[0005]

The hydrogen storage electrode of the present invention is an electrode using a hydrogen storage alloy capable of reversibly storing and releasing hydrogen, wherein the main electrode constituent material is hydrogen storage alloy particles and a surface A flat metal collector having a metal plating coating containing fine particles of a thermoplastic resin, wherein at least a part of the hydrogen storage alloy particles has a metal plating coating containing fine particles of a thermoplastic resin on the surface. The hydrogen absorption
The alloy particles are dry, and by roller press,
Crimp the metal current collector, characterized that you have been pressure-formed. Further, the plating film of the hydrogen storage alloy particles is preferably a porous film which allows diffusion of hydrogen.

According to the present invention, a metal-plated film having at least a part thereof containing fine particles of a thermoplastic resin is provided on a flat metal current collector having a metal-plated film containing fine particles of a thermoplastic resin on its surface. Dry the hydrogen storage alloy particles
A method for manufacturing a hydrogen storage electrode, characterized in that pressure bonding is performed by a method and by a roller press .

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The hydrogen storage electrode of the present invention is obtained by press-molding hydrogen storage alloy particles on one or both sides of a metal current collector having a metal plating coating containing fine particles of a thermoplastic resin on the surface. It can be manufactured. This pressure molding is preferably performed at a temperature not lower than the glass transition temperature or melting point of the thermoplastic resin and lower than the thermal decomposition temperature. The electrode produced by this method has an adhesion effect between the current collector and the alloy particles or further between the alloy particles due to the anchor effect of the unevenness of the metal plating film on the surface of the metal current collector or the unevenness of the metal plating film on the surface of the alloy particles. Improves the adhesion. Further, when pressure molding is performed under a specific temperature as described above, the resin particles contained in the metal plating film flow and act as a binder in a wide range, so that the drop of alloy particles from the current collector is further reduced. be able to. According to the present invention, the hydrogen-absorbing alloy particles can be pressure-bonded to a long strip-shaped metal current collector continuously by a dry method with a roller press. Therefore, electrodes with stable quality can be mass-produced.

In the present invention, the metal current collector preferably contains at least one of Fe, Ni, and Cu and has a flat plate shape. It is also possible to use punching metal. As the metal of the plating film formed on the surface of the metal current collector, Ni, Cu, Ni-P,
And a material selected from the group consisting of Ni-B is preferable. The thickness of the plating film is preferably 1 to 10 μm. On the other hand, as the metal of the plating film formed on the surface of the hydrogen storage alloy particles, Ni, Cu, Co, Ni-P, Ni-B,
A material selected from the group consisting of Co-P and Co-B is preferable. The alloy particles have an average particle size of 10 to 100 μm, and the coating film plated on the surface has a thickness of 0.01 to 100 μm.
It is preferably 50 μm and corresponds to 0.1 to 4% by weight of the alloy.
Metals such as nickel plated on the alloy particles hardly absorb hydrogen, so if a large amount of metal is plated,
The energy density per unit weight of the electrode is reduced. Therefore, it is desired to reduce the plating amount as much as possible.
However, it is possible to maintain an apparent energy density per unit weight by mixing hydrogen storage alloy particles with plating of more than 4% by weight with hydrogen storage alloy particles without plating. is there. The condition is that the electroconductivity and the binding property are not deteriorated even when the hydrogen storage alloy particles which are not plated are mixed. The upper limit of the plating amount that does not reduce the conductivity and the binding property is equivalent to 20% by weight of the entire hydrogen storage alloy particles. When both the metal current collector and the alloy particles are metal-plated, it is preferable to form the plating film with the same material for plating the metal current collector.

The plastic resin contained in the plating film of the metal current collector is polytetrafluoroethylene, polyethylene, ABS resin, polyamide, polysulfone,
A resin selected from the group consisting of AS resin, polystyrene, vinylidene chloride resin, polyphenylene ether, methylpentene resin, and methacrylic acid resin is preferable. As the plastic resin included in the plating film of the hydrogen storage alloy particles, the same ones as described above are used. When a plating film is formed on both the current collector and the alloy particles, the resin particles contained therein are preferably made of the same material. The average particle size of the resin particles used here is 1 to 5
μm is preferred. The amount of the resin particles contained in the plated coating of the alloy particles corresponds to 1 to 10% by weight of the alloy, and the amount of the resin particles contained in the plated coating of the current collector is 0.1 to 5 per unit area. 0.0 g / m ² is preferable.

[0010]

EXAMPLES The present invention will be described below with reference to examples. Example 1 First, an iron plate having a thickness of 0.06 mm is pretreated by degreasing, activating, washing with water, etc., and then polytetrafluoroethylene (hereinafter referred to as PTFE) (molecular weight of about 7500 to 10500).
A plating treatment was performed in the following nickel plating solution containing particles having an average particle diameter of 5 μm, washed with water and dried to obtain a current collector base sample. This is the base A.

[0011] Electroless nickel plating (sulfamate _{bath) 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) PTFE particles 100 (g / l) pH 4.0 Cathode current density 10 A / dm ² Temperature 50 ° C. Anode Ni plate stirring Circulation plating time 15 minutes Film thickness 5 μm

Next, the same iron plate material was used to carry out the same pretreatment, followed by ordinary nickel plating in a nickel plating solution containing no PTFE particles, followed by washing with water and drying. This is the base B. In addition, a steel plate having a thickness of 0.06 mm has a diameter of 1.
A punching metal in which holes of 5 mm and a pitch of 2.0 mm were regularly formed was plated in the same manner as the substrate B. This is referred to as base C.

On the other hand, MmNi _3.6 Co _0.75 Mn _0.35 Al
_A predetermined amount of each metal is weighed so as to have a composition of _0.3 (Mm means Misch metal which is a mixture of rare earth elements), an alloy ingot is produced in a high frequency induction melting furnace in an inert atmosphere, and heat treated at 1000 ° C. Then, an alloy sample was obtained.
This alloy ingot was mechanically crushed to have a particle size of 75 μm or less to obtain a hydrogen storage alloy powder sample. Alternatively, the alloy powder sample may be prepared by a quenching method such as a single roll method or a gas atomizing method.

This alloy powder sample was pretreated by degreasing, activating, washing with water, etc., and then the amount of plating was equivalent to 2% by weight of the alloy by a barrel plating apparatus using a nickel plating solution containing PTFE particles similar to the above. Electroplating was performed so that This barrel plating device is described in detail in JP-A-9-106817. The alloy sample having the composite plating film thus obtained is called alloy A. FIG. 1 shows a SEM image of the particle surface of alloy A. From FIG. 1, it was found that on the surface of the alloy particles, plated metal nickel particles and holes in which the PTFE particles were supposed to exist were observed, and many irregularities were formed. S
During processing of the sample for taking an EM image, shedding of the PTFE particles contained in the metal plating coating was observed. A similar state including many irregularities was also observed on the surface of the current collector substrate A. Further, an alloy sample which is not plated is referred to as Comparative Alloy B.

The alloy A is evenly placed on one surface of the base A and pressure-bonded by a roller press, and the same amount of the alloy is pressure-bonded on the other surface in the same manner to a thickness of about 0.4 m.
m hydrogen storage electrode was produced. The electrode thus obtained is called electrode A. Next, electrodes were prepared by the same method using the base B and the base C, and the reference electrode B and the reference electrode C were prepared.
And Further, a thickening agent and a binder were added to Comparative Alloy B to form a paste, which was coated on each of Substrate A, Substrate B and Substrate C, dried and pressed to produce a hydrogen storage electrode. The electrodes thus obtained are referred to as a comparison electrode D, a comparison electrode E, and a comparison electrode F, respectively.

The electrode prepared as described above was dipped in a 6 mol / L potassium hydroxide aqueous solution together with the nickel hydroxide electrode of the opposite electrode to prepare an open type battery. And
At an ambient temperature of 20 ° C., a charge / discharge test was performed in which the battery was charged at 0.1 C (30 mA / g) at 150% and discharged at 0.2 C (60 mA / g) to −0.6 V based on the mercury oxide electrode standard. The result is shown in FIG. As is clear from FIG.
Only the electrode A and the comparative electrode F according to the present invention showed stable discharge capacity. This is related to the adhesion between the alloy and the substrate. Since the electrode A has many irregularities on the surfaces of both the alloy and the substrate, as shown in the schematic view of FIG. 3, just by pressing, the adhesion effect increases due to the anchor effect of both. In FIG. 3, 1 represents a hydrogen storage alloy particle. Particle 1 is
It has a nickel plated coating 2 containing PTFE particles 3. On the other hand, the metal current collector 4 has a nickel-plated coating 5 containing PTFE particles 6 on its surface. In addition, in the electrode A, the composite-plated PTFE particles are melted by pressing heat and act as a binder. On the other hand, since the reference electrode F has a hole in the base,
Since the alloys on the front and back of the base are bound via a binder, the adhesion is high. The other electrodes had poor adhesion between the alloy and the substrate, so the alloy was peeled or dropped from the substrate, and the discharge capacity decreased.

Next, the electrode A and the reference electrodes B to F are used.
And a nominal capacity of 1 using a paste type nickel hydroxide electrode
An AA size sealed battery of 300 mAh was produced. These are referred to as Battery A and Comparative Batteries B to F according to the present invention, respectively. After activating these batteries, at ambient temperature of 20 ° C., charge them 150% at 0.1 C (130 mA), and
Charging / discharging in which the terminal voltage was lowered to 1.0 V at C (260 mA) was repeated 10 cycles. Then, at an ambient temperature of 20 ° C., an internal pressure sensor was attached to the battery and charged to 200% at 1.0 C (1300 mA),
Charging / discharging was repeated at 2 C (260 mA) until the terminal voltage dropped to 1.0 V, and a battery internal pressure measurement test was performed. FIG. 4 shows the measurement results of the battery internal pressure at the end of charging after the 11th cycle. As is clear from FIG. 4, only the electrode A of the present invention stably showed a low internal pressure. Alloy A
The electrode A, the comparative electrode B, and the comparative electrode C, each of which had a low internal pressure, initially showed low internal pressures, but the internal pressures of the electrodes other than the electrode A increased as the charge / discharge cycle progressed. This is because the peeling of the alloy from the substrate locally increased the current density and the gas generation became remarkable. Further, the comparative electrodes D to F containing no PTFE particles have a low water-repellent effect, and thus have a high internal pressure from the initial stage.

Example 2 An alloy powder sample was prepared in the same manner as in Comparative Alloy B above,
After sieving into 38 μm or more and less than 38 μm, and degreasing and activating treatment using an alloy of 38 μm or more, the plating amount in the nickel plating solution containing PTFE particles is 5% by weight, 10% by weight of the alloy, and 20% by weight. Wt% and 30
Electroplating was performed so as to be equivalent to wt%, washed with water and dried. Alloy powder samples having these composite plating films are designated as alloy G, alloy H, alloy I and comparative alloy J. Electrodes are produced using these alloys in the same manner as the electrode A, and are used as the electrode G, the electrode H, the electrode I, and the reference electrode J. Using these electrodes, an open-type battery was prepared using the nickel hydroxide electrode as a counter electrode in the same manner as in Example 1, and a charge / discharge test was conducted. The result is shown in FIG. As is clear from FIG.
The larger the amount of plating, the smaller the discharge capacity per weight.

Here, the plating amount is 10% by weight, 20% by weight
And an alloy of 30% by weight were mixed so that the above alloy powder sample of 38 μm or less was apparently plated at an amount of 5% by weight, and an electrode was prepared in the same manner as the electrode A. Electrode K, electrode L, reference electrode Let M. Using these electrodes, an open-type battery was prepared using the nickel hydroxide electrode as a counter electrode in the same manner as in Example 1, and a charge / discharge test was conducted. The result is shown in FIG. As apparent from FIG. 6, the discharge capacity was the same because the apparent plating amount was set to 5% by weight in all cases. However, the larger the substantial amount of plating, the greater the amount of the alloy powder sample without plating mixed, resulting in a decrease in the adhesion between particles and a decrease in the discharge capacity with the progress of charge / discharge cycles.

Next, using the above electrodes, a nominal 1300 mA
The sealed battery of h is manufactured and used as battery K, battery L and comparative battery M. FIG. 7 shows the results of an internal pressure measurement test similar to that of Example 1 using these batteries. As is clear from FIG. 7, it was only the battery K and the electrode L according to the present invention that the internal pressure was low and stable even in the internal pressure measurement test.

[0021]

As described above, the hydrogen storage electrode of the present invention can suppress an increase in internal pressure when it is used as a sealed battery. In addition, it is possible to provide an electrode that can be manufactured by a simple method that does not require a thickening agent, a binder, a drying step, and a water repellent application step, and at the same time, it is possible to use a substrate that does not require holes, thereby reducing costs. An extremely excellent effect can be obtained.

[Brief description of drawings]

FIG. 1 is an electron micrograph showing the structure of alloy particles in an example of the present invention.

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

FIG. 3 is a schematic view of details of electrodes in an example of the present invention.

FIG. 4 is a diagram showing the relationship between the internal pressure and the cycle number of a battery using various electrodes in an example of the present invention.

FIG. 5 is a diagram showing a relationship between a discharge capacity and a cycle number of a battery using various electrodes according to an example of the present invention.

FIG. 6 is a diagram showing a relationship between a discharge capacity and a cycle number of a battery using various electrodes according to an example of the present invention.

FIG. 7 is a diagram showing a relationship between a charge amount and a battery internal pressure of a battery using various electrodes in an example of the present invention.

[Explanation of symbols]

1 Hydrogen storage alloy particles 2, 5 plating film 3,6 PTFE particles 4 Current collector

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ identification code FI H01M 4/66 H01M 4/66 A 4/70 4/70 A (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 4/14-4/84

Claims (11)

(57) [Claims] 1. An electrode using a hydrogen storage alloy capable of reversibly storing and releasing hydrogen, wherein the main electrode constituent material is a hydrogen storage alloy particle, and a metal plating film containing fine particles of a thermoplastic resin on the surface. It consists of a plate-like metal current collector having, at least a portion of the hydrogen-absorbing alloy particles have a metal plating film that includes fine particles of a thermoplastic resin on the surface, said hydrogen storage alloy particles, a dry, And roller press
A hydrogen storage electrode, which is pressure-molded by pressure bonding to the metal current collector . 2. The hydrogen storage electrode according to claim 1, wherein the metal plating film of the hydrogen storage alloy particles is a porous film which allows diffusion of hydrogen. 3. The hydrogen storage electrode according to claim 1, wherein the metal plating film of the hydrogen storage alloy particles is 20% by weight or less based on the weight of the hydrogen storage alloy. 4. The metal plating film of the hydrogen storage alloy particles is Ni, Cu, Co, Ni-P, Ni-B, Co-P,
The hydrogen storage electrode according to claim 1, which is selected from the group consisting of Co-B and Co-B. 5. The metal plating film of the metal current collector is N
The hydrogen storage electrode according to claim 1, which is selected from the group consisting of i, Cu, Ni-P, and Ni-B. 6. The metal plating film of the hydrogen storage alloy particles and the metal plating film of the metal current collector are Ni, Cu,
The hydrogen storage electrode according to claim 1, which is the same material selected from the group consisting of Ni-P and Ni-B. 7. The thermoplastic resin contained in the metal plating film of the hydrogen storage alloy particles is polytetrafluoroethylene, polyethylene, ABS resin, polyamide, polysulfone, AS resin, polystyrene, vinylidene chloride resin, polyphenylene ether, methyl. The hydrogen storage electrode according to claim 1, which is one or more selected from the group consisting of a pentene resin and a methacrylic acid resin. 8. The thermoplastic resin contained in the metal plating film of the metal current collector is polytetrafluoroethylene, polyethylene, ABS resin, polyamide, polysulfone, AS resin, polystyrene, vinylidene chloride resin, polyphenylene ether, methyl. The hydrogen storage electrode according to claim 1, which is one or more selected from the group consisting of a pentene resin and a methacrylic acid resin. 9. The thermoplastic resin included in the metal plating film of the hydrogen storage alloy particles and the thermoplastic resin included in the metal plating film of the metal current collector are polytetrafluoroethylene, polyethylene, ABS resin, polyamide,
The hydrogen storage electrode according to claim 1, which is one or more same materials selected from the group consisting of polysulfone, AS resin, polystyrene, vinylidene chloride resin, polyphenylene ether, methylpentene resin, and methacrylic acid resin. 10. The metal current collector is at least Fe, N
The hydrogen storage electrode according to claim 1, comprising at least one selected from the group consisting of i and Cu. 11. A hydrogen plate having a metal-plated coating, the surface of which has a metal-plated coating containing fine particles of a thermoplastic resin, at least a portion of which has a metal-plated coating containing fine particles of a thermoplastic resin. The occlusion alloy particles are dry type,
A method for producing a hydrogen storage electrode , which comprises pressing with a roller press .