JP3469754B2 - Hydrogen storage alloy electrode - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage alloy used as a negative electrode of an alkaline secondary battery such as a nickel-hydrogen storage battery, and more particularly to improvement of characteristics of particle surface of carbon powder used as a conductive material. Is.

[0002]

2. Description of the Related Art Conventionally, nickel-cadmium storage batteries and lead storage batteries have been widely used as secondary batteries. In recent years, in particular, with the development of small information devices such as mobile phones and notebook computers, the energy density has been There is a demand for the development of a large and clean secondary battery. Therefore, attention has been paid to a sealed nickel-hydrogen storage battery in which an electrode made of a hydrogen storage alloy that does not contain harmful substances such as cadmium and lead is used as a negative electrode.

A nickel-hydrogen storage battery is provided with a negative electrode made of a hydrogen storage alloy, a nickel positive electrode, an alkaline electrolyte, a separator and the like. The hydrogen storage alloy electrode serving as a negative electrode is a hydrogen storage alloy powder obtained by crushing a hydrogen storage alloy lump. It is manufactured by adding a conductive material and a binder to and molding it into an electrode shape.

In a nickel-hydrogen storage battery using a hydrogen storage alloy as a negative electrode, the surface of the hydrogen storage alloy comes into contact with an alkaline electrolyte, so that a vapor phase reaction and an electrochemical reaction simultaneously proceed on the alloy surface. That is, in the relationship between hydrogen pressure and temperature, hydrogen is stored in the hydrogen storage alloy or released from the hydrogen storage alloy (gas phase reaction). On the other hand, regarding the relationship between voltage and current, hydrogen generated by electrolysis of water is occluded in the hydrogen storage alloy by voltage application (charging), and hydrogen is oxidized to water by current extraction (discharging) ( Electrochemical reaction).

[0005]

However, in the nickel-hydrogen storage battery, when the electric conductivity of the hydrogen storage alloy electrode is insufficient, the movement of electrons is delayed and the inside of the electrode is saturated with electrons. At this time, gaseous oxygen is generated on the surface of the nickel electrode that is the positive electrode, and gaseous hydrogen is generated on the surface of the hydrogen storage alloy electrode that is the negative electrode, and the internal pressure of the battery rises. In a sealed nickel-hydrogen storage battery, an excessive rise in the internal pressure of the battery has a problem such as a decrease in charge / discharge capacity due to the diffusion of the electrolytic solution to the outside. Furthermore, when water is generated by the recombination of these hydrogen atoms and oxygen atoms, the internal pressure of the battery drops, but the electric energy is dissipated as heat energy, and the discharge capacity and the high-voltage discharge characteristics deteriorate.

In a nickel-hydrogen storage battery that is currently generally used, gas is generated by mixing a hydrogen storage alloy with a conductive agent such as metal powder or carbon powder to improve the conductivity of the hydrogen storage alloy electrode. While suppressing the increase in the internal pressure of the battery during charging, the sufficient effect cannot be obtained, and it is desired to further improve the electric conduction characteristics of the electrode.

An object of the present invention is to provide a hydrogen storage alloy electrode containing carbon powder as a conductive agent, by further improving the electrical conductivity of the carbon powder, it is possible to obtain excellent battery characteristics such as battery internal pressure characteristics and high rate discharge characteristics. Another object is to provide a hydrogen storage alloy electrode.

[0008]

A hydrogen storage alloy electrode according to the present invention is a hydrogen storage alloy electrode containing a mixture of a hydrogen storage alloy powder B and a conductive material powder A as a main material. The powder A is a metal-coated carbon powder in which at least a part of the surface of the carbon particles (22) is covered with the metal coating (23).

In order to efficiently perform the gas phase reaction and the electrochemical reaction in the hydrogen storage alloy, the three-phase interface of gas phase (oxygen, hydrogen) -solid phase (hydrogen storage alloy) -liquid phase (electrolyte) is set. It is necessary to form an electrically conductive state. Carbon powder as a conductive agent has an affinity for gaseous hydrogen and gaseous oxygen, supply of gas to the reaction system,
That is, it has the effect of promoting the interaction between the gas phase and the solid phase.
In the hydrogen storage alloy electrode according to the present invention, the metal-coated carbon powder A in which the metal coating film (23) made of a highly conductive metal is formed on the surface of the carbon particle (22) is used as a conductive material. The metal-coated carbon powder A maintains the function of the above-mentioned carbon powder, and due to the good electric conductivity of the metal coating the surface thereof, the particles of the hydrogen storage alloy powder B (24) and the particles of the metal-coated carbon powder A ( 21) And, it becomes possible to promote the transfer of electrons between the three members of the current collector. As a result, the electrical contact between the particles or between the current collector and the particles in contact with the current collector is improved, the high-rate discharge characteristics are improved, and the hydrogen storage alloy powder contains hydrogen. Promotes the absorption of atoms,
The rise in battery internal pressure is suppressed.

Specifically, the metal elements are Ti, V,
It is one or more transition metals selected from Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, Sb, and Al. Further, the carbon powder is 1 selected from graphite and carbon black.
It consists of more than one kind of carbon powder.

In the specific constitution, it is desirable to use a material having good conductivity as the conductive agent, and it is preferable to use at least one selected from graphite and carbon black as the carbon powder as the base material. , Particles of said carbon powder (22)
The metal elements that cover the surface of Ti, V, Cr, Mn,
It is preferable to use at least one transition metal selected from Fe, Co, Ni, Cu, Zn, Sn, Sb, and Al.

More specifically, the metal-coated carbon powder A
Has a particle size of 1 to 30 μm. In addition, the metal coating (2
The specific surface area of 3) is 0.3 to 0.6 m ² / g per unit weight of the particles (22) of the carbon powder.

As described above, the conductivity of the hydrogen storage alloy electrode according to the present invention is improved by forming the metal coating (23) on the surface of the particles (22) of the carbon powder. It is more desirable for improving the conductivity of the hydrogen storage alloy electrode that the particles are in close contact with each other and have a high packing rate. By reducing the particle size of the metal-coated carbon powder A, the filling rate of the electrode mixture can be increased.
The particle diameter of is preferably 1 μm to 30 μm.
The particle size of the hydrogen-absorbing alloy powder B is preferably 10 μm or more with respect to the optimum particle size of the metal-coated carbon powder A, and the size relationship between the two particles does not matter. Further, if the metal coating (23) is too thick, or if the coating area of the metal coating (23) with respect to the particles (22) of the carbon powder is too wide, the good gas affinity originally possessed by the carbon powder is suppressed. However, the effect of improving the battery characteristics cannot be obtained. Therefore, in order to balance the gas affinity of the carbon powder and the good electrical conductivity of the metal coating (23), the specific surface area of the metal coating (23) to the particles (22) of the carbon powder is 0. 3m ² / g~
It is preferably 0.6 m ² / g.

[0014]

EFFECTS OF THE INVENTION According to the hydrogen storage alloy electrode of the present invention, the carbon powder, which is a conductive agent, is partially covered with a transition metal having a high electric conductivity to maintain a good gas affinity of the carbon powder. The particles of the hydrogen storage alloy powder B (2
4), the electrical connection between the metal-coated carbon powder A particles (21) and the current collector is enhanced. Therefore, the battery internal pressure characteristics and high-pressure discharge characteristics of the alkaline secondary battery using the hydrogen storage alloy electrode according to the present invention are improved, and an alkaline secondary battery having excellent battery characteristics can be obtained.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION As shown in FIG. 1, an active material layer (2) of a hydrogen storage alloy electrode according to the present invention comprises a hydrogen storage alloy powder B.
The particles (21) of the metal-coated carbon powder A are present between the particles (24). The particles (21) of the metal-coated carbon powder A are composed of carbon powder particles (22) and a metal coating (23) for coating the surface thereof. However, in order not to impair the gas affinity of the carbon powder, all the particles of the metal-coated carbon powder A (21) present in the hydrogen-absorbing alloy electrode mixture should be the particles of the carbon powder.
The metal coating (23) should not be formed so as to cover the entire surface of (22). Hereinafter, embodiments of the hydrogen storage alloy electrode of the nickel-hydrogen storage battery in which the present invention is to be implemented will be specifically described.

[0016]

Example 1 (Preparation of hydrogen storage alloy) Misch metal (hereinafter referred to as Mm) which is a mixture of rare earth elements, and purity 99.9% respectively
Ni, Co, Al, and Mn, which are simple metals, are mixed at a predetermined molar ratio, and are melted in an arc melting furnace in an argon atmosphere, and then they are naturally cooled to have a composition formula MmNi having a CaCu ₅ type crystal structure. A hydrogen storage alloy represented by _3.6 Co _0.6 Al _0.2 Mn _0.6 was prepared. The hydrogen storage alloy ingot was mechanically crushed in air to obtain a hydrogen storage alloy powder having an average particle size of 30 μm.

(Surface coating treatment of carbon black by chemical plating) Co, Cu, Ni, Cr, Zn, or Sn chloride of 0.5 mol / l and sodium hypophosphite of 1.0, respectively.
Carbon black having a particle size of 1.0 μm was dipped in 6 kinds of plating baths in which mol / l and sodium citrate were dissolved so as to be 0.5 mol / l for 2 hours, washed and dried to obtain 6
A seed metal-coated carbon powder was obtained.

(Production of Electrode) The hydrogen-absorbing alloy powder as an active material, the six kinds of metal-coated carbon powder as a conductive agent, and an aqueous solution containing 0.5% by weight of polyethylene oxide as a binder were mixed, Six pastes were prepared.
These 6 kinds of pastes were applied on both surfaces of a core body made of punched metal plated with nickel, dried at room temperature, and then cut into a predetermined size to prepare 6 kinds of negative electrodes. A conventionally known sintered nickel electrode was used as the positive electrode.

(Preparation of nickel-hydrogen storage battery) Using the above positive electrode and six kinds of negative electrodes, the theoretical capacity of the positive electrode capacity regulation 1
Six types of sealed nickel-hydrogen storage batteries A1 to A6 having 000 mAh were produced. As shown in FIG. 2, the nickel-hydrogen storage battery A1 (1) manufactured by using the hydrogen storage alloy electrode according to the present invention has a positive electrode (11), a negative electrode (12) and a separator (1).
3), positive electrode lead (14), negative electrode lead (15), positive electrode external terminal (1
6), a negative electrode can (17), a sealing lid (18) and the like. The positive electrode (11) and the negative electrode (12) are housed in the negative electrode can (17) in a state of being spirally wound via the separator (13), and the positive electrode (11) is connected via the positive electrode lead (14). To the lid (18),
The negative electrode (12) is connected to the negative electrode can (17) via the negative electrode lead (15). An insulating packing (20) is attached to the joint between the negative electrode can (17) and the sealing lid (18) to seal the battery A1 (1). A coil spring (19) is provided between the positive electrode external terminal (16) and the sealing lid (18), and can be compressed when the internal pressure of the battery rises abnormally to release the gas inside the battery to the atmosphere. It has become like.

(Battery Characteristic Experiment) The six kinds of nickel-hydrogen storage batteries A1 to A6 for carrying out the present invention were charged and discharged twice at 100 mA in order to meet the conditions. In order to study the high rate discharge characteristics, after the above charge / discharge reaction, charging was performed at 100 mA for 16 hours, and the discharge capacity when discharging at 4000 mA was measured. Also, as with the measurement of the discharge capacity, after carrying out the charge / discharge reaction twice at 100 mA,
Charged at 100mA for 16 hours, then at 1000mA for 8 hours
The battery internal pressure at the time of charging for 0 minutes was also measured.

Example 2 Small metal pieces of Ti, V, Mn, Fe, Sb or Al were placed in a container together with carbon black powder. In each of the 6 types of containers, a high vacuum of 10 × 10 ⁻³ mmHg or less is set,
The tungsten filament was electrically heated to melt and evaporate the metal pieces. The vapor was deposited as a thin film on the surface of carbon black particles to obtain 6 kinds of metal-coated carbon black. As described above, except that the surface coating treatment of carbon black is performed by the vapor deposition method,
Six types of nickel-hydrogen storage batteries A7 to A12 for carrying out the present invention were prepared in the same manner as in Example 1, and a battery characteristic test was conducted.

Example 3 (Preparation of nickel-hydrogen storage battery) As shown in Table 3, the average particle size is 0.5 to 42 μm and the specific surface area is 0.62 to 0.29.
Eight types of cobalt-coated carbon black treated by the above chemical plating method were obtained by using m ² / g of eight types of carbon black and cobalt chloride. Nickel-hydrogen storage batteries B1 to B8 for carrying out the present invention were produced in the same manner as in Example 1 except that these eight types of cobalt-coated carbon black were used.

(Battery Characteristic Experiment) Eight kinds of nickel-hydrogen storage batteries B1 to B8 for carrying out the present invention were charged and discharged twice at 100 mA in order to make the conditions uniform. In order to study the high rate discharge characteristics, after the above charge / discharge reaction, charging was performed at 100 mA for 16 hours, and the discharge capacity when discharging at 3000 mA was measured. Also, as with the measurement of the discharge capacity, after carrying out the charge / discharge reaction twice at 100 mA,
Charged at 100mA for 16 hours, then at 1500mA for 6 hours
The battery internal pressure at the time of charging for 0 minutes was also measured.

Comparative Example A conventional nickel-hydrogen storage battery C1 was prepared in the same manner as in Example 1 except that the carbon black powder was not subjected to a metal coating treatment, and a battery characteristic test was conducted.

The results of the battery characteristic tests of Examples 1 to 3 and Comparative Example are shown in Tables 1 to 3 below.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

[Table 3]

As shown in Tables 1 and 2, in the nickel-hydrogen storage batteries A1 to A12 in which the present invention is to be carried out, the discharge capacity is remarkably increased and the high rate is high as compared with the conventional nickel-hydrogen storage battery C1. The discharge characteristics are improved. Also, the battery internal pressure during the charging reaction is the same as the conventional nickel-hydrogen storage battery C1.
It is suppressed to be low as compared with, and it is clear that the electrical conductivity of the hydrogen storage alloy electrode was improved by coating the carbon powder particles with the metal.

Further, in Table 3, taking a carbon black coated with cobalt as an example, the optimum range of the particle size of the carbon powder to be added to the mixture of the hydrogen storage alloy electrode according to the present invention and the amount of surface coating with the transition metal is shown. The examination result about is shown.
The nickel-hydrogen storage batteries B1 to B6 using carbon black having a cobalt coating as the conductive material of the negative electrode are
Compared to the conventional nickel-hydrogen storage battery C1, it has excellent high-rate discharge characteristics and battery internal pressure characteristics. Especially nickel
Those effects are remarkable in the hydrogen storage batteries B2 to B4, and the particle diameter of the metal-coated carbon powder used in the hydrogen storage alloy electrode according to the present invention is preferably 1 μm to 30 μm,
In addition, the specific surface area of the metal-coated carbon powder particles is 0.3.
m ² /g~0.6m ² / g It is preferred revealed.

The configuration of each part of the present invention is not limited to the above embodiment, and various modifications can be made within the technical scope described in the claims. For example, in addition to using a hydrogen storage alloy having a CaCu ₅ type crystal structure, C14 type or C type
Using a hydrogen storage alloy having a 15-type Laves phase structure,
It is also possible to produce the hydrogen storage alloy electrode according to the present invention.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view schematically showing an active material layer of a hydrogen storage alloy electrode according to the present invention.

FIG. 2 is a sectional view of a nickel-hydrogen storage battery in which the present invention is to be implemented.

[Explanation of symbols]

A metal-coated carbon powder B Hydrogen storage alloy powder (1) Nickel / hydrogen storage battery A1 (11) Positive electrode (12) Negative electrode (13) Separator (2) Active material layer (21) Particles of metal-coated carbon powder A (22) Carbon powder particles (23) Metal coating (24) Particles of hydrogen storage alloy powder B

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Yohei Hirota 2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture Sanyo Electric Co., Ltd. (72) Mamoru Kimoto 2-5 Keihan Hondori, Moriguchi City, Osaka Prefecture No. 5 Sanyo Electric Co., Ltd. (72) Inventor Shin Fujitani 2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture Sanyo Electric Co., Ltd. (72) Koji Nishio 2-5 Keihan Hondori, Moriguchi City, Osaka Prefecture No. 5 within Sanyo Electric Co., Ltd. (56) Reference JP-A-3-252056 (JP, A) JP-A-4-269454 (JP, A) JP-A-4-160763 (JP, A) (58) Survey Areas (Int.Cl. ⁷ , DB name) H01M 4/00-4/62

Claims (5)

(57) [Claims] 1. A hydrogen storage alloy electrode comprising a mixture of a hydrogen storage alloy powder B and a conductive material powder A as a main material, wherein the conductive material powder A is at least one of the surfaces of carbon particles (22). A hydrogen storage alloy electrode, which is a metal-coated carbon powder in which a metal coating (23) is formed so as to cover a partial region. 2. The metal element forming the metal coating (23) is Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, S.
The hydrogen storage alloy electrode according to claim 1, which is one or more kinds of transition metals selected from n, Sb, and Al. 3. The carbon powder comprises at least one carbon powder selected from graphite and carbon black.
Alternatively, the hydrogen storage alloy electrode according to claim 2. 4. The particle diameter of the metal-coated carbon powder A is 1
The hydrogen storage alloy electrode according to any one of claims 1 to 3, having a thickness of -30 μm. 5. The specific surface area of the metal coating (23) is 0.3 to 0.6 m ² per unit weight of the particles (22) of the carbon powder.
/ G, The hydrogen storage alloy electrode according to any one of claims 1 to 4.