JP3365642B2 - Anode body of nickel-hydride battery - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative electrode body for a nickel-hydride battery having a high weight energy density, which is obtained by supporting a negative electrode active material on a porous carbon molding.

[0002]

2. Description of the Related Art In recent years, the emergence of secondary batteries with high energy density and long service life is expected, and various types of high-performance batteries have been the subject of research and development. Of these, nickel
For hydrogenated batteries, the development of hydrogen storage alloys, which serve as the negative electrode active material, has progressed, so research into practical applications is particularly active as promising candidates for power supplies for portable devices and electric vehicles, batteries for power storage, etc. It is done in.

In a nickel-hydrogen secondary battery, usually, a fine powdery hydrogen storage alloy is supported on a metal mesh together with a conductive material such as copper powder to form a negative electrode, and a conductive metal mesh is used as a supporting metal mesh. Nickel is widely used from the viewpoint of its chemical stability and chemical stability. However, since nickel is a heavy metal, the weight energy density is increased even if it is used as a carrier.

[0004]

In order to put the secondary battery into practical use as a power source for portable devices and electric vehicles, downsizing and weight saving are extremely important problems to be solved. For example, a nickel-hydrogen battery currently on the market or under development has a weight energy density of 50 to 60 Wh / kg. Therefore, if a battery of 20 KWh level, which is considered to be necessary for electric vehicles, is manufactured, the battery weight will exceed 300 kg. Becomes difficult.

The inventors of the present invention have conducted multifaceted research on a lightweight support material which replaces conventional nickel. As a result, a porous carbon molded body having a specific property, which has not been noticed until now, has been used as a negative electrode support material. Then, it was confirmed that the weight energy density can be significantly improved without impairing the battery characteristics.

The present invention was developed on the basis of the above findings, and an object thereof is to provide a negative electrode body for a nickel-hydride battery which can reduce the weight of the battery and increase the weight energy density. .

[0007]

[Means for Solving the Problems] A negative electrode body of a nickel-hydride battery according to the present invention for achieving the above object is
A porous carbon molded body having a bulk density of 1.0 g / cc or less and a porosity measured by a mercury porosimetry method of 35% or more,
A structural feature is that a hydrogen storage alloy that is a negative electrode active material is supported.

In the present invention, the porous carbon molded body serving as the carrier for the hydrogen storage alloy is not limited by the raw material and the manufacturing method, and carbon bodies having various porous structures can be used. For example, coke powder of uniform particle size is kneaded with a carbonaceous binder such as tar pitch, crushed, molded, and calcined to obtain a carbon molded product of a coke raw material, a resin foam such as polyurethane foam, and a phenolic compound. A carbon molded product made of glassy carbon obtained by impregnating and curing a carbonized furan-based curable thermosetting resin liquid and then firing and carbonizing it, as well as a carbonized thermosetting resin liquid for a mixed molded product of carbon fiber and pulp. Examples thereof include those impregnated with and calcined and carbonized, and those obtained by molding vegetable powder such as sawdust with pitch or a thermosetting resin and calcined and carbonized.

However, as the porous carbon molded body to which the present invention is applied, those having a bulk density of 1.0 g / cc or less as a texture property and a porosity of 35% or more measured by a mercury penetration method are selectively used. Doing is an important requirement. When the bulk density of the used porous carbon molded product exceeds 1.0 g / cc and the porosity is less than 35%, not only the weight energy density declines but also the hydrogen transfer does not proceed smoothly and the discharge capacity remarkably decreases. To do. In addition to this porous texture property, when a porous carbon molded body having a layer surface distance d (002) determined by X-ray diffraction in the range of 0.345 to 0.285 nm is used, the hydrogen overvoltage becomes large and the electrolytic solution in the charging process becomes large. Since it becomes possible to effectively suppress the hydrogen generation reaction based on the decomposition of, the present invention can be further adapted to the object of the present invention. Such crystallinity is an index showing that the porous carbon molded body has an appropriate carbonization degree, and can be adjusted by controlling the raw material selection and the firing carbonization temperature during production.

As the hydrogen storage alloy of the negative electrode active material supported on the above-mentioned porous carbon compact, there are commonly used alloys such as ternary, quaternary and quaternary alloys of misch metal mainly composed of La. Used. The negative electrode body is formed into a paste form by adding an electrically conductive material powder such as Ni or Cu to the finely pulverized hydrogen storage alloy powder, and adding an aqueous solution containing various binders such as polyvinyl alcohol or PTFE, It is manufactured by filling a porous carbon molded body with this and drying and curing.

[0011]

The carbon compact has a low specific gravity as a material and is extremely chemically stable, and the properties of its porous structure can be adjusted to a desired range relatively easily by setting the production conditions.
In the present invention, among them, a porous carbon molded body having a texture property of a bulk density of 1.0 g / cc or less and a porosity of 35% or more by a mercury intrusion method is used as a negative electrode active material carrier, and thus is excellent. Further, the weight energy density can be significantly improved while maintaining the discharge capacity. That is,
The porous carbon compact of the present invention has a specific gravity of 1/4 or less of the material itself as compared with the conventional nickel mesh support, and the weight energy density increases according to the weight reduction.

Further, when the layer surface distance d (002) determined by X-ray diffraction of the porous carbon compact is in the range of 0.345 to 0.385 nm, the hydrogen overvoltage is maintained at a level of 0.05 V or more and overcharged. Generation of hydrogen is suppressed and, at the same time, sufficient conductivity is imparted, so that more excellent battery performance is exhibited.

[0013]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples.

Examples 1 to 3 and Comparative Examples 1 to 3 (1) Preparation of Negative Electrode Body As the negative electrode support, the porous carbon compact and nickel porous body having the texture shown in Table 1 were used.

[0015]

[Table 1]

[0016] as the negative electrode active material, Mm -Ni _3.55 -Co
_0.76 -Mn _0.4 -Al _0.3 (Mm: misch metal) A hydrogen storage alloy with a composition of finely pulverized to a particle size of 100 mesh or less was mixed with 30% by weight of Cu powder, and then 3% by weight of the alloy component was used. % Of polyvinyl alcohol to form a paste, which was filled in each of the negative electrode supporting bodies. Then, it was dried and cured to obtain a negative electrode body of a nickel-hydrogen battery.

(2) Performance evaluation of negative electrode body A constant current charge / discharge test (50 mA / g) was conducted using 6N-KOH as an electrolyte and a Pt electrode as a counter electrode, and the discharge capacity at the 10th cycle (total weight of the negative electrode body) Was calculated) to evaluate the unipolar performance. The results are shown in Table 2.

[0018]

[Table 2]

From the results shown in Table 2, all of the negative electrode bodies of Examples satisfying the requirements of the present invention were lightweight and showed excellent discharge capacity. On the other hand, even in the case of the same kind of porous carbon molded article, the porosity was less than 35% in Comparative Example 2 and the bulk density was 1.0 g.
In Comparative Example 3 exceeding / cc, the discharge capacity was reduced, and Comparative Example 3 using a nickel porous body having a bulk density of 1.88 g / cc as the negative electrode body also showed a low discharge capacity.

Examples 4 to 7 Four kinds of glassy carbon molded products having the same porous texture properties as those of Example 1 and the crystal properties as shown in Table 3 are important characteristics as a negative electrode carrier. The resistivity and hydrogen overvoltage were measured. For the measurement, a voltage drop method was used for the specific resistance, and a potential scanning method (scanning speed 50 mV / sec.) In the direction of the cathode in a 6N-KOH aqueous solution was used for the hydrogen overvoltage. The results are also shown in Table 3 in comparison with the crystal properties of the porous glassy carbon molded body as a sample.

[0021]

[Table 3]

From the results shown in Table 3, when a porous carbon molded body having a crystallographic property in which the inter-layer surface distance d (002) is in the range of 0.345 to 0.385 nm is used, it is particularly suitable as a negative electrode body of a nickel-hydride battery. It was confirmed that a secondary battery that exhibits conductivity and high hydrogen overvoltage and is resistant to overvoltage can be obtained.

[0023]

As described above, according to the present invention, by using a porous carbon molding having a specific property as a support for the negative electrode active material, the weight of the battery is reduced, and high-performance nickel with high weight energy density is used. A negative electrode body of a hydride battery can be provided. Therefore, it can be expected to be extremely useful as a secondary battery member intended as a power source for portable devices and electric vehicles.

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Claims (2)

(57) [Claims] 1. A hydrogen-absorbing alloy, which is a negative electrode active material, is supported on a porous carbon compact having a texture density of 1.0 g / cc or less and a porosity of 35% or more as measured by mercury porosimetry. A negative electrode body for a nickel-hydride battery, comprising: 2. A layer surface distance d obtained by X-ray diffraction.
A negative electrode body for a nickel-hydride battery, wherein the porous carbon compact according to claim 1 having (002) in the range of 0.345 to 0.385 nm carries a hydrogen storage alloy as a negative electrode active material.