JPH07230807A - Manufacture of metal oxide-hydrogen secondary battery - Google Patents

Abstract

PURPOSE:To provide a manufacturing method for a metal oxide-hydrogen secondary battery in which restriction of pulverization by progress of charge/ discharge cycles of a negative electrode can be achieved. CONSTITUTION:A process of heat-treating rare earth-based hydrogen storage alloy in an inactive gas atmosphere of 950-1100 deg.C, and then forcedly cooling it at least to 400 deg.C is provided. In addition, a process of crushing this rare earth-based hydrogen storage alloy, and forming a negative electrode including this powder, and a process of forming a group of electrodes by providing a separator between the negative electrode and a positive electrode including metal oxide, and containing the electrode group in a container with alkaline electrolyte are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a metal oxide / hydrogen secondary battery using a metal oxide as a positive electrode active material and hydrogen as a negative electrode active material, and particularly a metal oxide having an improved method for producing a negative electrode. -It relates to a method for manufacturing a hydrogen secondary battery.

[0002]

2. Description of the Related Art At present, a metal oxide / hydrogen secondary battery of a type in which a hydrogen negative electrode is composed of a hydrogen storage alloy is drawing attention. The reason is that this battery system originally has a high energy-density and thus is advantageous in volumetric efficiency.
Moreover, it is possible to operate safely and is excellent in terms of characteristics and reliability. The secondary battery is manufactured by the following method. First, a rare earth-based hydrogen storage alloy is pulverized to prepare a paste containing the obtained powder, and the paste is filled in a conductive core body such as a reticulated sintered metal fiber to prepare a negative electrode. An electrode group is prepared by interposing a separator made of a synthetic resin fiber non-woven fabric between the negative electrode and a positive electrode containing a metal oxide such as nickel hydroxide. The secondary battery is manufactured by accommodating the electrode group together with an alkaline electrolyte in a container.

LaNi ₅ has been frequently used as the rare earth hydrogen storage alloy. Also, La, C
An alloy of Misch metal (hereinafter referred to as Mm), which is a mixture of lanthanum-based elements such as e, Pr, Nd, and Sm, and Ni, that is, MmNi ₅ is also widely used. MmN
Since i ₅ uses Mm as a rare earth component, it is cheaper and more practical than LaNi ₅ which uses only expensive La element as a rare earth component.

Regarding LaNi ₅ and MmNi ₅ , a part of Ni is Al, Mn, Fe, Co, Ti, C.
A multi-element system in which elements such as u, Zn, Zr, Cr, V and B are substituted is also used.

However, in such a metal oxide / hydrogen secondary battery, the powder of the rare earth-based hydrogen storage alloy having the above-mentioned composition is pulverized by hydrogenation as the charge / discharge cycle progresses. As a result, the negative electrode is deteriorated, so that there is a problem that the charge / discharge cycle life is shortened. Further, since the degree of pulverization of the rare earth-based hydrogen storage alloy powder varies depending on the alloy lot, there is a problem that the charge / discharge cycle life of the secondary battery varies. This difference in the degree of pulverization is due to impurities contained in the hydrogen storage alloy, variations in the homogeneity of the alloy due to changes in the alloy manufacturing conditions, or the composition of the alloy due to changes in the yield of each alloy component during alloy production. This may be due to the variation in the ratio, but it is not clear at this stage.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the conventional problems, and provides a metal oxide / hydrogen secondary battery capable of suppressing the pulverization accompanying the progress of the charge / discharge cycle of the negative electrode. It is intended to provide a manufacturing method.

[0007]

According to the present invention, there is provided a step of heat-treating a rare earth hydrogen storage alloy in an inert gas atmosphere at 950 ° C to 1100 ° C, and then forcibly cooling it to at least 400 ° C, and the rare earth hydrogen storage alloy. A step of crushing an occlusion alloy and producing a negative electrode containing this powder, and an electrode group is produced by interposing a separator between the negative electrode and a positive electrode containing a metal oxide, and the electrode group together with an alkaline electrolyte. A method of manufacturing a metal oxide / hydrogen secondary battery, comprising the step of housing in a container.

The rare earth-based hydrogen storage alloy has the general formula LmAx (where Lm is at least one selected from rare earth elements including La, and A is Ni, Co, M).
The composition having a composition represented by at least one element selected from n, Al, B, Cu, Zr and V, and x is 4.8 to 5.5) has excellent hydrogen storage capacity. Preferred for.

The heat treatment of the rare earth-based hydrogen storage alloy is preferably performed in an argon gas atmosphere. The temperature of the heat treatment of the rare earth-based hydrogen storage alloy is limited to the above range for the following reason. The temperature is 950
When the temperature is lower than 0 ° C., it becomes difficult to reduce the segregation of alloy components generated during the production of the rare earth-based hydrogen storage alloy and improve the homogeneity of the rare earth-based hydrogen storage alloy. On the other hand, when the temperature exceeds 1100 ° C., the rare earth-based hydrogen storage alloy melts.

The rare earth-based hydrogen storage alloy which has been heat-treated under the above conditions has a temperature of 40 when it is naturally cooled.
Since segregation of alloy components may occur again in the temperature range of 0 ° C, forced cooling must be performed until the temperature reaches at least 400 ° C. The average cooling rate when forcibly cooling the rare earth-based hydrogen storage alloy is preferably 40 ° C./hr or more. More preferable average cooling rate is 60 ° C /
It is in the range of hr or more.

Examples of the pulverization method of the rare earth hydrogen storage alloy include mechanical pulverization, hydrogenation pulverization, spray pulverization and the like. Among them, the mechanical pulverization is preferable because the equipment is simple, the pulverization work is easy, and the safety is high.

The particle size of the rare earth hydrogen storage alloy powder is
It is desirable to set it in the range of 20 μm to 70 μm. The negative electrode is obtained by subjecting the rare earth-based hydrogen storage alloy to heat treatment and cooling under the conditions described above, crushing the alloy by the method described above, and adding a polymer binder and a conductive powder to the obtained powder. It is manufactured by kneading in the presence of water to prepare a paste, and filling the paste into the conductive core.

Examples of the polymer binder include sodium polyacrylate and polytetrafluoroethylene (P
TFE), carboxymethyl cellulose and salts thereof (C
MC) and the like. The blending ratio of the polymer binder is preferably in the range of 0.5 to 5 parts by weight with respect to 100 parts by weight of the rare earth-based hydrogen storage alloy powder.

Examples of the conductive powder include carbon black and graphite. The blending ratio of the conductive powder is preferably 4 parts by weight or less with respect to 100 parts by weight of the hydrogen storage alloy powder.

Examples of the conductive core include a two-dimensional structure such as punched metal, expanded metal, and wire mesh, and a three-dimensional structure such as foam metal and reticulated sintered metal fiber.

For the positive electrode, a paste containing cobalt oxide, a polymer binder, etc. in addition to a metal oxide such as nickel hydroxide, for example, a sintered fiber substrate, foam metal,
It is manufactured by filling a conductive core body such as a non-woven fabric plated substrate or a punched metal substrate. Examples of the polymer binder include those similar to the polymer binder in the negative electrode. Examples of the alkaline electrolyte include 25 to 31 wt% potassium hydroxide aqueous solution to which 15 to 50 g / l of lithium hydroxide is added.

[0017]

The present inventors have found that the rare earth-based hydrogen storage alloy is 950
The alloy of the rare earth-based hydrogen storage alloy is reduced by segregating alloy components in the rare earth-based hydrogen storage alloy by heat-treating in an inert gas atmosphere of ℃ to 1100 ℃, and then forcibly cooling to at least 400 ℃. It has been found that since the homogeneity of the components can be improved, the charge / discharge cycle life of the metal oxide / hydrogen secondary battery including the negative electrode can be improved.

This is because the rare earth-based hydrogen storage alloy of the negative electrode manufactured by the conventional method crushes due to segregation of the alloy components when it occludes hydrogen as the charging / discharging cycle progresses. , The rare earth-based hydrogen storage alloy having improved homogeneity of the alloy components by the above-described method has less segregation of the alloy components, and thus is difficult to be crushed when hydrogen is occluded, and atomized with the progress of charge / discharge cycles of the negative electrode It is thought that this is because the above can be suppressed.

[0019]

EXAMPLES Examples of the present invention will be described in detail below. Examples 1 to 5 First, the rare earth element Lm having a purity of 99.9% (Lm is La
45.1%, Ce 4.6%, Pr 12.1%, N
d is 37.0% and other rare earth elements are 1.1%), Ni, Co, Mn, and Al are constituent components, and the composition is LmNi _4.0 Co _0.4 Mn by high frequency melting.
A rare earth hydrogen storage alloy ingot represented by _0.3 Al _0.3 was produced.

Next, the rare earth hydrogen storage alloy ingot is placed in a furnace and heat-treated in an argon gas atmosphere at 1000 ° C. for 5 hours, and then the argon gas in the furnace is circulated to 150 ° C. up to 400 ° C. / H
r, 100 ° C / hr, 80 ° C / hr, 60 ° C / hr, 4
It cooled at the average cooling rate of 0 degreeC / hr, and also cooled to room temperature on the same conditions. Subsequently, each rare earth-based hydrogen storage alloy ingot was mechanically crushed to obtain a rare earth-based hydrogen storage alloy powder having an average particle size of 30 to 40 μm.

Next, polytetrafluoroethylene, sodium polyacrylate and sodium carboxymethyl cellulose as a polymer binder are used in combination with the powder of each of the rare earth hydrogen storage alloys, and carbon black and water as conductive powder and water are used. And were added and kneaded to prepare a paste. Subsequently, each paste was applied to a punched metal that is a conductive core, dried, pressed, and then cut to prepare a negative electrode.

On the other hand, a paste containing nickel hydroxide and cobalt oxide was prepared. This paste was filled into a nickel sintered fiber substrate, further dried, and then pressed all over,
A non-sintered nickel positive electrode was produced by cutting.

A test cell having a capacity of 1000 mAh shown in FIG. 1 was assembled using each of the obtained negative electrodes and the non-sintered nickel positive electrode. That is, the negative electrode 1 is spirally wound with the separator 3 interposed between the negative electrode 1 and the positive electrode 2, and is housed in the AA size cylindrical container 4. The negative electrode 1 is arranged on the outermost periphery of the prepared electrode group and is in electrical contact with the container 4. An alkaline electrolyte composed of 7N potassium hydroxide and 1N lithium hydroxide is contained in the container 4. A circular sealing plate 6 having a hole 5 in the center is arranged in the upper opening of the container 4. The ring-shaped insulating gasket 7 is arranged between the peripheral edge of the sealing plate 6 and the inner surface of the upper opening of the container 4, and the sealing plate is attached to the container 4 by caulking to reduce the diameter of the upper opening inward. 6 is airtightly fixed via the gasket 7. The positive electrode terminal 8 having a collar portion has the lower surface of the collar portion welded to the sealing plate 6 via a ring-shaped spacer 9. The positive electrode lead 10 has one end connected to the positive electrode 2 and the other end connected to the positive electrode terminal 8. Comparative Example 1 The test cell shown in FIG. 1 described above was assembled in the same configuration as in Examples 1 to 5 except that the negative electrode shown below was used.

Rare earth hydrogen storage alloy ingots having the same composition as in Examples 1 to 5 were mechanically crushed to have an average particle size of 3
A rare earth hydrogen storage alloy powder having a size of 0 to 40 μm was obtained. A polymer binder and a conductive powder similar to those in Examples 1 to 5 were added to this powder to produce a negative electrode by the same method as in Examples 1 to 5. Reference Example 1 The test cell shown in FIG. 1 was assembled in the same configuration as in Examples 1 to 5 except that the negative electrode shown below was used.

A rare earth-based hydrogen storage alloy ingot having the same composition as in Examples 1 to 5 was placed in a furnace at 1000 ° C.
Heat treatment is performed for 5 hours in the argon gas atmosphere of
It was left in the furnace until it reached room temperature. The alloy ingot was mechanically pulverized, and the obtained rare earth-based hydrogen storage alloy powder having an average particle size of 30 to 40 μm was added with the same polymeric binder and conductive powder as in Examples 1 to 5 to obtain Example 1 A negative electrode was produced by the same method as described in Nos. 5 to 5.

Ten test cells of each of the obtained Examples 1 to 5 and Comparative Example 1 and Reference Example 1 were prepared and charged at 1000 mAh for 90 minutes, and the final voltage was set to 1V. The charge / discharge cycle of discharging at 1000 mAh was repeated, the number of cycles required until the capacity became 1/2 of the initial charge / discharge cycle was measured, the average number of cycles was determined, and the results are shown in Table 1 below.

[0027]

[Table 1]

As is apparent from Table 1, after heat treatment was performed in an argon gas atmosphere at 1000 ° C., 40 ° C./hr.
It can be seen that the test cells of Examples 1 to 5 provided with the negative electrode containing the powder of the rare earth-based hydrogen storage alloy that was forcibly cooled at the above average cooling rate had a long charge / discharge cycle life. On the other hand, the test cell of Comparative Example 1 provided with the negative electrode containing the powder of the rare earth-based hydrogen storage alloy that was not heat-treated and the heat-treated test cell of the rare earth-based hydrogen storage alloy that was cooled by natural cooling. It can be seen that the test cell of Reference Example 1 including the negative electrode containing the powder and the test cells of Examples 1 to 5 have shorter charge / discharge cycle life.

[0029]

As described in detail above, according to the method for producing a metal oxide / hydrogen secondary battery of the present invention, it is possible to suppress pulverization accompanying the progress of charge / discharge cycles of the negative electrode, and
It has a remarkable effect that the charge / discharge cycle life of the hydrogen secondary battery can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a test cell used in an example of the present invention.

[Explanation of symbols]

1 ... Negative electrode, 2 ... Positive electrode, 3 ... Separator, 4 ... Cylindrical container with a bottom.

Claims (1)

[Claims] 1. A rare earth hydrogen storage alloy is used at 950 ° C. to 11 ° C.
Heat treatment in an inert gas atmosphere at 00 ° C., then forced cooling to at least 400 ° C., crushing the rare earth-based hydrogen storage alloy to produce a negative electrode containing this powder, the negative electrode and metal oxidation A metal oxide / hydrogen secondary, comprising a step of forming an electrode group by interposing a separator between the positive electrode containing a substance and a positive electrode, and storing the electrode group together with an alkaline electrolyte in a container. Battery manufacturing method.