JPH0773879A - Metal oxide-hydrogen secondary battery - Google Patents

Abstract

PURPOSE:To lengthen the cycle life of a battery and to decrease the dispersion of the cycle life. CONSTITUTION:A rare earth hydrogen storage allay used in a negative electrode has 1. a hydrogen storage amount as determined by pressure-component constant temperature line at 60+ or -5 deg.C based on JIS H7201 of 0.76 or more, 2. an equilibrium hydrogen pressure of 0.8-2.0atm, and 3. a BET specific surface area after crushed once under a condition of a gage pressure of 5-10atm at 2-30 deg.C of 0.04-0.11m<2>/g.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal oxide / hydrogen secondary battery using a metal oxide as a positive electrode active material and hydrogen as a negative electrode active material.

[0002]

2. Description of the Related Art At present, metal oxide / hydrogen secondary batteries of the type in which the negative electrode is composed of a hydrogen storage alloy are drawing attention. The reason is that this battery system originally has a high energy density, is advantageous in volumetric efficiency, can be operated safely, and is excellent in characteristics and reliability. .

As a hydrogen storage alloy used for the negative electrode material of this type of battery, LaNi ₅ has been frequently used. Such a hydrogen storage alloy containing only La element as a rare earth component is excellent as a battery negative electrode material, but it is not practical because La is expensive. Therefore, an alloy of Misch metal (hereinafter referred to as Mm), which is a mixture of lanthanum elements such as La, Ce, Pr, Nd, and Sm, and Ni, that is, MmNi ₅ is also widely used.

Regarding LaNi ₅ and MmNi ₅ , a part of Ni is Al, Mn, Fe, Co, Ti, C.
A multi-element system in which an element such as u, Zn, Zr, Cr, V or B is substituted is also used. As such a hydrogen storage alloy, an alloy ingot is manufactured by a method such as high frequency melting of the constituents, and powdered by a method such as mechanical crushing.

However, the conventional metal oxide / hydrogen secondary battery has a problem that the charge / discharge cycle life is short and varies. The direct cause of shortening the charge / discharge cycle life is that as the charge / discharge cycle progresses, the hydrogen storage alloy is hydro-pulverized and pulverized, and the deterioration of the negative electrode material progresses. The variation in cycle life is due to the fact that the progress of pulverization of the hydrogen storage alloy differs depending on the alloy lot. The differences in the progress of this pulverization phenomenon are considered to be the effects of impurities in the hydrogen storage alloy and variations in alloy homogeneity due to changes in alloy production conditions.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a metal oxide / hydrogen secondary battery having a long charge / discharge cycle life and a small variation thereof in order to solve the above problems.

[0007]

The present invention is directed to a positive electrode, an alkaline electrolyte, and a general formula LmA _x (wherein Lm is one or more elements selected from rare earth elements containing La, and A is Ni, Co, Mn and Al, or N
In addition to i, Co, Mn and Al, it contains an element selected from the group consisting of B, Cu, Zn and V, and x is 5.1 to 5.
In a metal oxide / hydrogen secondary battery including a negative electrode containing a rare earth-based hydrogen storage alloy as a main material, the rare earth-based hydrogen storage alloy is (1) equilibrium hydrogen pressure (H / The discharge pressure of M = 0.4, where
H is the number of hydrogen atoms occluded, and M is the number of metal atoms represented by LmA _x ) 0.8 to 2.0
atm; (2) According to JIS H7201, the hydrogen storage amount (the above H / M value at 10 atm) by pressure-composition isotherm (hereinafter referred to as "PCT line") at 60 ± 5 ° C is 0.76.
And; (3) The specific surface area by the BET method after hydro-grinding once under the conditions of a temperature of 2 to 30 ° C. and a gauge pressure of 5 to 10 atm is 0.04 to 0.11 m ² / g. And a metal oxide / hydrogen secondary battery.

Rare earth type hydrogen storage alloys have the general formula LmA _x
(In the formula, Lm is at least one or two or more rare earth elements containing La, and A is Ni, Co, Mn, Al,
It is at least one element selected from the group consisting of B, Cu, Zr, and V, and x has a composition represented by 5.1 to 5.4) from the hydrogen storage capacity. For example, LmNi _a Co _b Mn _c Al _d (here, 3.9
0 ≦ a ≦ 4.50, 0.38 ≦ b ≦ 0.50, 0.28
≤ c ≤ 0.50, 0.28 ≤ d ≤ 0.50, 5.1 ≤ a
+ B + c + d ≦ 5.4) is used.

The specific surface area by the BET method of the alloy powder of the present invention hydrogenated and pulverized under specific conditions correlates with the charge / discharge cycle life of the battery. The smaller the specific surface area, the longer the cycle life. Further, the larger the hydrogen storage amount and the lower the equilibrium hydrogen pressure, the better the PCT characteristics, and in the opposite case, the electrode capacity decreases and the battery internal pressure increases.
The larger the value of x in the general formula LmAx is, the smaller the specific surface area by the BET method is, and accordingly the hydrogen storage amount is decreased and the equilibrium hydrogen pressure is increased. As described above, the specific surface area, the hydrogen storage amount, the equilibrium hydrogen pressure, and the value of _x in the general formula LmA _x are mutually related properties.

Then, the optimum range of the above-mentioned characteristics was examined, and it was found that 5.1 ≦ x ≦ 5.4 and the hydrogen storage amount was 0.76.
As described above, the equilibrium hydrogen pressure is 0.8 to 2.0 atm and the specific surface area is 0.1.
It was found to be 040 to 0.11 m ² / g. The conditions for the hydrogenation and pulverization in the previous stage of the measurement of the specific surface area are a temperature of 2 to 30 ° C., a pressure of 5 to 10 atm (gauge pressure), and one pulverization. The reason is as follows.

In the hydrogen storage alloy, when hydrogenated, hydrogen atoms enter the crystal lattice and the lattice swells, so that internal stress causes fracture and hydrogenation and pulverization. At this time, the specific surface area of the powder of the hydrogen storage alloy is determined by the properties such as the fine structure of the alloy, and the temperature and the hydrogen pressure which are the conditions for the hydrocracking. Generally, when hydrogenation and pulverization is repeated, the hydrogen storage alloy becomes finer and the specific surface area gradually increases, so the specific surface area is also affected by the number of times of hydrogen pulverization.

The present inventors have found that the hydrogen storage alloy has a temperature of 2-3.
The specific surface area of the alloy powder obtained by hydrocracking once at 0 ° C., for example 10 ° C., and hydrogen pressure of 5-10 atm, for example 10 atm, correlates with the charge / discharge cycle life of the battery. I found that there is a property. That is, when a hydrogen storage alloy satisfying the above requirements is pulverized by a method such as mechanical pulverization, and the obtained powder of the alloy is used as a negative electrode material,
It is possible to obtain a battery having a long charge / discharge cycle life.

In order to obtain the powder of such a hydrogen storage alloy, any method such as mechanical pulverization, hydrogenation pulverization and spray pulverization can be used. In actual production, mechanical crushing is preferable because the equipment is simple and the work is easy, and safety is ensured. In particular, stable particle size can be obtained,
From the viewpoint of cost, it is desirable to use those crushed by an impact crusher. As the impact type crusher, for example, a hammer mill or the like can be used. If the specific surface area under the above-mentioned conditions is within the range of the present invention, the particle size of the hydrogen storage alloy actually used for producing the negative electrode material is arbitrary, and for example, the average particle size is in the range of 20 to 70 μm.

The negative electrode used in the present invention is produced by using a mixture prepared by mixing the above hydrogen storage alloy powder, preferably a polymer binder, and, if necessary, a conductive powder. . That is, the negative electrode has a structure in which such a mixture is coated on and fixed to a conductive core that is a current collector.

Examples of the polymer binder include sodium polyacrylate and polytetrafluoroethylene (PTF).
E), carboxymethyl cellulose and salts thereof (CM
C) and the like can be mentioned, and these may be used in combination. 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 hydrogen storage alloy powder. Examples of the conductive powder blended in the mixture 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.

The conductive core which is the above current collector is
For example, one having a two-dimensional structure such as punched metal, expanded metal, and wire mesh, and one having a three-dimensional structure such as foam metal and reticulated sintered metal fiber can be mentioned.

As the positive electrode of the present invention, a metal oxide electrode such as a non-sintered nickel oxide electrode is used. That is, it is manufactured by a method of filling a paste containing a polymer binder and the like in addition to nickel hydroxide into, for example, a sintered fiber substrate, a foam metal, a non-woven fabric plated substrate or a punched metal substrate. Examples of the polymer binder include the same as the polymer binder for the negative electrode. Examples of the alkaline electrolyte used in the present invention include 25 to 31 wt% potassium hydroxide aqueous solution to which 15 to 50 g / liter of lithium hydroxide is added.

[0018]

The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In addition,% of composition is% by weight
Means

Examples 1 to 3 (1) Preparation of sample Rare earth element Lm with purity 99.9% (La 45.1%, C
e 4.6%, Pr 12.1%, Nd 37.0%, other rare earth elements 1.2%), Ni, Co, Mn and Al as constituent components, and alloys having the compositions shown in Table 1 were obtained by high frequency melting. . Regarding these three types of alloys, JIS H 7
Pressure-composition isotherm is measured at 60 ° C according to 201, hydrogen storage capacity (H / M at 10 atm) and equilibrium hydrogen pressure (H / M).
= 0.4). Further, hydrogenation and pulverization were performed once under the conditions of 10 ° C. and 10 atm of hydrogen pressure, and the specific surface area was measured by the BET method. The results are shown in Table 1. Next, the same ingots as those evaluated were mechanically pulverized to obtain respective hydrogen storage alloy powders having an average particle diameter of 30 to 40 μm.

(2) Preparation of Negative Electrode and Positive Electrode Polytetrafluoroethylene, sodium polyacrylate and carboxymethylcellulose sodium salt are used in combination with each of these hydrogen storage alloy powders, and carbon black and water are used as conductive agents. A paste was prepared by adding and mixing. This paste was applied to a punched metal, dried, pressed, and cut to produce a negative electrode. On the other hand, a paste containing nickel hydroxide and cobalt oxide was prepared, this was filled in a nickel sintered fiber substrate, and a non-sintered nickel oxide positive electrode was produced through a drying, pressing and cutting process.

(3) Assembly of test battery Next, as shown in FIG. 1, three kinds of hydrogen storage alloy negative electrodes 1 produced by the above-mentioned method are put together with the non-sintered nickel oxide positive electrode 2 through a separator 3. And each was wound and inserted into the AA size battery can 4. Furthermore, after pouring an electrolytic solution, which is a mixture of 7N potassium hydroxide aqueous solution and 1N lithium hydroxide aqueous solution, the battery can is sealed and three kinds of nickel hydrogen having a capacity of 1,000mAh are filled. A secondary battery was produced. In this test battery, a positive electrode lead 5 derived from the non-sintered nickel oxide positive electrode 2 is welded to a positive electrode terminal 6, and a flange portion on an upper side of the positive electrode terminal 6 is a ring-shaped space on a sealing plate 7. It is welded through the chamber 8 and is hermetically fixed to the opening of the battery can 4 by hermetically fixing the peripheral portion of the sealing plate 7 through the insulating gasket 9.

(4) Charge / Discharge Cycle Test Each of these test batteries was subjected to a charge / discharge cycle test. Table 1 shows the number of cycles required until the battery capacity became 1/2 of the initial capacity after repeating charging and discharging under the conditions of charging at 1000 mA for 90 minutes and discharging at 1000 mA and the final voltage of 1V. Note that this cycle number is for battery 1
It is an average value of 0 pieces.

Comparative Examples 1 and 2 The same rare earth elements Lm, Ni, as used in Examples 1 to 3,
(1) Preparation of a sample, (2) Preparation of a negative electrode and a positive electrode, (3) Test similar to Example 1 except having used the alloy which has Co, Mn, and Al as a structural component and which has the composition shown in Table 1. The battery was assembled and (4) charge / discharge cycle test was performed. The results are also shown in Table 1.

[0024]

[Table 1]

[0025]

EFFECTS OF THE INVENTION According to the present invention, by using a powder obtained by crushing a hydrogen storage alloy having the above requirements as a negative electrode, it is possible to prevent pulverization during charge / discharge cycles of a battery and improve the cycle life of the battery. With this, it is possible to prevent variations in cycle life. The metal oxide / hydrogen secondary battery of the present invention is used as a power source for a device requiring a large current such as a personal computer, a headphone stereo, and an 8 mm video, and replaces the conventional nickel-cadmium battery.

[Brief description of drawings]

FIG. 1 is a sectional view of a test battery assembled in an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Hydrogen storage alloy negative electrode 2 ... Non-sintered nickel oxide positive electrode 3 ... Separator 4 ... Battery can 5 ... Positive electrode lead 6 ... Positive electrode terminal 7 ... Sealing plate 8 ... Spacer 9 ... Insulation gasket

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Nobuaki Chiba 3-4-10 Minami-Shinagawa, Shinagawa-ku, Tokyo Toshiba Battery Co., Ltd. (72) Inventor Kazuta Takeno 3-4-10 Minami-Shinagawa, Shinagawa-ku, Tokyo No. within Toshiba Battery Co., Ltd.

Claims (1)

[Claims] 1. A positive electrode, an alkaline electrolyte, and a general formula Lm.
A _x (In the formula, Lm is one or more elements selected from rare earth elements including La, and A is Ni, Co, Mn.
And Al, or contains an element selected from the group consisting of B, Cu, Zn, and V in addition to Ni, Co, Mn, and Al, and x is 5.1 to 5.4). In a metal oxide / hydrogen secondary battery including a negative electrode whose main component is a rare earth-based hydrogen storage alloy, the rare earth-based hydrogen storage alloy is (1) equilibrium hydrogen pressure (release of H / M = 0.4). Pressure, where
H is the number of hydrogen atoms occluded, and M is the number of metal atoms represented by LmA _x ) 0.8 to 2.0
atm; (2) Pressure at 60 ± 5 ° C. according to JIS H7201-hydrogen storage amount by the composition isotherm (H / M value at 10 atm) is 0.76 or more; and (3) Temperature 2 to 30 ° C. and gauge pressure A metal oxide / hydrogen secondary battery having a specific surface area of 0.04 to 0.11 m ² / g according to the BET method after hydro-pulverization once under a condition of 5 to 10 atm.