JP3504350B2 - Manufacturing method of alkaline secondary battery - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an alkaline secondary battery, and more particularly to a method for manufacturing an alkaline secondary battery having an improved thickness control step for producing a negative electrode. It is. 2. Description of the Related Art A demand for a nickel-hydrogen secondary battery, which is an example of an alkaline secondary battery, has been greatly increased because it is highly reliable and can be discharged at a large current value. The nickel-metal hydride secondary battery, by interposing a separator made of synthetic resin fiber between a positive electrode containing nickel hydroxide as an active material and a negative electrode containing a hydrogen storage alloy as an active material, by winding these It has a structure in which the produced electrode group is housed in a container together with an alkaline electrolyte. The negative electrode,
Prepare a paste consisting of the hydrogen storage alloy powder, conductive material powder, binder and water, fill the paste into a conductive substrate such as a porous metal plate or a foamed metal, and after drying this, press It is manufactured by adjusting the thickness. The negative electrode has a function as a recombination catalyst for absorbing the oxygen gas generated from the positive electrode at the time of overcharging, since the hydrogen storage alloy is a hydrogen storage body, and thus performs an internal reaction during overcharge in addition to performing an electrode reaction. It is a very excellent electrode that can prevent the rise. [0003] Conventionally, as the hydrogen storage alloy, L
aNi ₅ or MmNi ₅ (Mm is La, Ce, Pr,
Nd, Sm, etc. means a misch metal which is a mixture of lanthanum-based elements).
e, Co, Ti, Cu, Zn, Zr, Cr, V, and a multi-element system substituted with elements such as B are used.
Above all, a hydrogen storage alloy using Mm as a rare earth component is inexpensive and practical as compared with an alloy using only expensive lanthanum element as a rare earth component. [0004] After the secondary battery is assembled in the above-described structure, an activation step of charging and discharging the battery to increase the initial capacity and the average operating voltage is performed. However, the secondary battery provided with the negative electrode manufactured by the above-described method using the hydrogen storage alloy having such a composition has a problem that the initial capacity and the number of charge / discharge cycles required until the average operating voltage rises vary. was there. When the number of cycles required until the initial capacity and the average operating voltage of the secondary battery rise, the time required for the activation process increases, and thus the production efficiency of the secondary battery decreases. SUMMARY OF THE INVENTION The present invention has been made to solve the conventional problems, and reduces the number of charge / discharge cycles required to raise the initial capacity and the average operating voltage in the activation step. It is an object of the present invention to provide an improved alkaline secondary battery. According to the present invention, there is provided an alkaline secondary battery according to the present invention.
A method of manufacturing a secondary battery includes a step of preparing a paste containing a hydrogen storage alloy powder containing a rare earth element , nickel and cobalt as a negative electrode active material, and filling the paste into a conductive substrate; and before There and drying the conductive substrate filled, a conductive substrate on which the paste is filled
The saturation magnetization due to the ferromagnetic component of the hydrogen storage alloy powder
As 0.01 emu / g to 0.04 emu / g increase
A negative electrode by a method comprising the steps of:
It is characterized by the following. Hereinafter, an alkaline secondary battery manufactured by the method of the present invention will be described with reference to a nickel hydrogen secondary battery shown in FIG. 1 as an example. The positive electrode 1 has a separator 3 between the negative electrode 2
Is wound in a spiral shape and is stored in a cylindrical container 4 having a bottom. The negative electrode 2 is arranged at the outermost periphery of the manufactured electrode group and is in electrical contact with the container 4. The alkaline electrolyte is contained in the container 4. A circular sealing plate 6 having a hole 5 in the center is
Is arranged in the upper opening. The ring-shaped insulating gasket 7 is disposed 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 formed on the container 4 by caulking to reduce the diameter of the upper opening inward. 6 is hermetically fixed via the gasket 7. One end of the positive electrode lead 8 is connected to the positive electrode 1, and the other end is connected to the lower surface of the sealing plate 6. The positive electrode terminal 9 having a hat shape is
It is mounted on the sealing plate 6 so as to cover the hole 5. A rubber safety valve 10 is disposed in a space surrounded by the sealing plate 6 and the positive electrode terminal 9 so as to close the hole 5. The negative electrode 2 comprises a hydrogen storage alloy powder containing a rare earth element, nickel and cobalt, and a conductive agent, a binder,
The paste is prepared by adding water and kneading them to prepare a paste, filling the paste into a conductive substrate, drying the paste, and adjusting the thickness with a press. The thickness is controlled such that the saturation magnetization of the ferromagnetic component generated by oxidizing the newly exposed surface of the hydrogen storage alloy powder by pulverization is 0.0
It is performed so as to be 1 emu / g or more. The thickness adjustment is performed so that the saturation magnetization of the ferromagnetic component generated by oxidizing the newly exposed surface of the hydrogen-absorbing alloy powder is crushed for the following reason. It is. When the thickness adjustment is performed so that the saturation magnetization of the ferromagnetic component is less than 0.01 emu / g, the secondary battery including such a negative electrode can be used until the initial capacity and the average operating voltage rise in the activation step. , The number of charge / discharge cycles required increases. When the thickness is adjusted so that the saturation magnetization of the ferromagnetic component exceeds 0.04 emu / g, the hydrogen storage alloy powder of such a negative electrode may have an excessively large amount of reaction with the alkaline electrolyte. Therefore, the electrolyte may be depleted as the charge / discharge cycle of the secondary battery including the negative electrode progresses, and the discharge capacity may decrease. Therefore, a preferable upper limit of the saturation magnetization of the ferromagnetic component is 0.04 emu / g, and a more preferable upper limit is 0.03 emu / g. The saturation magnetization of the ferromagnetic component varies depending on the thickness of the paste filled in the conductive substrate and the number of presses. The conditions of the paste filling thickness and the number of times of pressing for performing the thickness adjustment so that the saturation magnetization of the ferromagnetic component satisfies the above range are obtained as follows. A paste-filled substrate having a paste thickness continuously changed is prepared, dried, and then pressed to a predetermined thickness. For each of the produced negative electrodes, the saturation magnetization of the ferromagnetic component generated by oxidizing the newly exposed surface of the hydrogen storage alloy powder in the thickness adjusting step is determined.
From these results, the conditions for the paste filling thickness and the number of presses are determined. Further, since the saturation magnetization of the ferromagnetic component varies depending on the hardness and particle size of the hydrogen storage alloy powder, the conditions of the paste filling thickness and the number of times of pressing differ depending on the type of the hydrogen storage alloy. The hydrogen storage alloy powder is formed from a rare earth element, nickel and cobalt, or is mixed with a rare earth element, nickel and cobalt, for example, Al, Mn, Ti,
It may be formed from one or more elements selected from Cu, Zn, Zr, Cr, and B. As the rare earth element,
For example, La, Ce, Pr, Nd, Sm and the like can be mentioned. In particular, Mm (Mm is La, Ce, Pr, Nd
Is a misch metal containing 99% by weight or more in total) of 31% to 35% by weight, a nickel content of 40% to 60% by weight, and a cobalt content of 4% by weight or less. 15% by weight, manganese content is 4% by weight
It is more preferable to use a hydrogen storage alloy having an aluminum content of 1 to 12% by weight and an aluminum content of 1 to 3% by weight.
This is due to the following reasons. (1) Mm When the content of Mm is less than 31% by weight, the hydrogen storage capacity of the hydrogen storage alloy may decrease. On the other hand, if the content of Mm exceeds 35% by weight, the cycle life of a secondary battery including the negative electrode containing the hydrogen storage alloy may be reduced. (2) Nickel If the nickel content is less than 40% by weight, the number of charge / discharge cycles required for the initial capacity and the average operating voltage of the secondary battery to rise in the activation step may increase. . On the other hand, the content of nickel is 60% by weight.
Exceeds, the hydrogen equilibrium pressure of the hydrogen storage alloy increases,
It may be difficult to use the alloy as a negative electrode active material. (3) Cobalt If the content of cobalt is less than 4% by weight, the number of charge / discharge cycles required until the initial capacity and the average operating voltage of the secondary battery rise in the activation step may be increased. . On the other hand, when the content of cobalt exceeds 15% by weight, the capacity of the negative electrode may be reduced. (4) Manganese When the manganese content is less than 4% by weight, the hydrogen equilibrium pressure of the hydrogen storage alloy increases, which may make it difficult to use the alloy as a negative electrode active material. on the other hand,
If the manganese content exceeds 12% by weight, the reactivity of the hydrogen storage alloy with an alkaline electrolyte may increase, and the cycle life of a secondary battery including a negative electrode including the hydrogen storage alloy may be reduced. is there. (5) Aluminum When the content of aluminum is less than 1% by weight, the corrosion resistance of the negative electrode containing the hydrogen storage alloy to an alkaline electrolyte may decrease. On the other hand, when the content of the aluminum exceeds 3% by weight, the hydrogen storage amount of the hydrogen storage alloy may decrease. Examples of the conductive powder include carbon black. Examples of the polymer binder include polytetrafluoroethylene, carboxymethylcellulose, methylcellulose, sodium polyacrylate, and polyvinyl alcohol. Examples of the conductive substrate include a two-dimensional substrate such as a punched metal, an expanded metal, a perforated rigid plate, and a nickel net; a felt-like porous metal;
Examples include a three-dimensional substrate such as a sponge-like porous metal body. The positive electrode 1 is prepared by preparing a paste containing a metal oxide powder, a conductive agent, a polymer binder, and water, filling the paste into an alkali-resistant metal porous body, and drying the paste. It is manufactured by pressing and then cutting to a desired size. Examples of the metal oxide include nickel hydroxide. Examples of the conductive agent include cobalt compounds such as cobalt monoxide, dicobalt trioxide, and cobalt hydroxide. Examples of the polymer binder include those similar to the polymer binder used for the negative electrode. Examples of the alkali-resistant porous metal include those having a sponge-like, fibrous, or felt-like porous structure made of a metal such as nickel or stainless steel, or a resin plated with nickel. Examples of the separator 3 include a nonwoven fabric made of a polyolefin fiber such as a polyethylene fiber or a polypropylene fiber and a hydrophilic functional group added to the nonwoven fabric, and a nonwoven fabric made of a polyamide fiber. Examples of the alkaline electrolyte include a potassium hydroxide solution, a mixed solution of sodium hydroxide and lithium hydroxide, a mixed solution of potassium hydroxide and lithium hydroxide,
A mixed solution of potassium hydroxide, lithium hydroxide and sodium hydroxide or the like can be used. The present inventors have conducted intensive studies and found that the initial capacity and the average operating voltage of an alkaline secondary battery provided with a negative electrode containing a hydrogen storage alloy powder containing a rare earth element, nickel and cobalt are increased. The number of charge / discharge cycles required
The inventors have found that there is a correlation with the step of adjusting the thickness of the negative electrode, and have reached the present invention. According to the method of manufacturing an alkaline secondary battery of the present invention, a step of preparing a paste containing the hydrogen storage alloy powder as a negative electrode active material and filling the paste into a conductive substrate; Drying the conductive substrate and adjusting the thickness of the conductive substrate filled with the paste, and adjusting the thickness of the ferromagnetic component generated by oxidizing the newly exposed surface when the hydrogen storage alloy powder is pulverized. By providing a step of manufacturing the negative electrode by performing the operation so that the saturation magnetization is 0.01 emu / g or more, the number of charge / discharge cycles required for activating the secondary battery can be reduced. The hydrogen storage alloy powder containing a rare earth element, nickel, and cobalt is immediately oxidized in air or in an atmosphere containing oxygen to cause surface segregation. As a result, an oxide film containing a rare earth element oxide on the surface of the hydrogen storage alloy powder and a transition metal layer containing nickel and cobalt and containing nickel as a main component are formed at appropriate thicknesses inside the film. Is done. The transition metal layer has a recombination catalytic ability that promotes the storage and release of hydrogen and promotes absorption of oxygen gas generated from the positive electrode during overcharge. On the other hand, in the drying step, the conductive substrate filled with the paste is heated to evaporate the water in the paste. In this step, the hydrogen storage alloy powder is oxidized, and at this time, the degree of oxidation increases due to the presence of heat and moisture in the paste. As a result, the oxide film and the transition metal layer formed on the surface of the hydrogen storage alloy powder become too thick, so that the hydrogen storage alloy powder hardly stores hydrogen, and the recombination catalytic ability of the oxygen gas is inferior. . When the thickness of the conductive substrate filled with the paste is adjusted after the drying step, the hydrogen storage alloy powder is pulverized, and the surface is newly exposed and oxidized. Since this oxidation is performed in the absence of heat and moisture, the oxide film and the transition metal layer having an appropriate thickness are formed on the newly exposed surface. Nickel and cobalt contained in the transition metal layer exhibit ferromagnetism. As a result, after the drying step, the thickness is adjusted such that the saturation magnetization of the ferromagnetic component generated by oxidizing the newly exposed surface of the hydrogen storage alloy powder is reduced to less than 0.01 emu / g. Since the hydrogen storage alloy powder of the negative electrode produced by such a method has a small effective transition metal layer,
The hydrogen storage / release capability and the recombination catalytic capability are low. For this reason, in the secondary battery provided with the negative electrode, in the activation step, the hydrogen storage alloy powder is pulverized to improve the hydrogen storage / release capability and the recombination catalyst capability, and thus perform extra charge / discharge. Activation, and takes a long time to activate. Therefore, after the drying step, the thickness of the ferromagnetic component generated by oxidizing the newly exposed surface of the hydrogen storage alloy powder after the hydrogen storage alloy powder is pulverized is adjusted to 0.01 em.
By performing so as to be not less than u / g, the hydrogen storage alloy powder of the negative electrode produced by such a method has a sufficient effective transition metal layer before the activation, and has the hydrogen storage / release capability and the rechargeability. Since the combined catalytic activity is high, the initial capacity and the average operating voltage of the secondary battery can be increased in a small number of cycles in the activation step, and the production efficiency can be improved. Embodiments of the present invention will be described below in detail with reference to the drawings. Examples 1-8 First, hydrogen whose composition is represented by the formula Mm (Mm is La, Ce, Pr, means a misch metal containing 99 wt% or more in total content of _{Nd) Ni 4.0 Co 0.4 Mn 0.3} Al 0.3 Storage alloy (Mm content is 33% by weight, nickel content is 55% by weight, total content of cobalt is 5.5% by weight, manganese content is 4% by weight, aluminum content is 2% by weight %) Has an average particle size (weight average) of about 2
It was pulverized to 5 μm and about 40 μm. 1 part by weight of polytetrafluoroethylene, 1 part by weight of carbon black, 0.5 part by weight of sodium polyacrylate, 0.2 part by weight of carboxymethylcellulose, and 0.2 part by weight of water were added to 100 parts by weight of powder having each average particle diameter. 60 parts by weight were added and stirred to prepare a paste. The paste was applied to a punched metal having a thickness of 0.08 mm as a conductive substrate so that the paste had a thickness of 1.4 to 1.7 mm. This was dried in an air-circulating drying oven at 80 ° C. for 1 hour. Here, a part of the paste filled in the substrate was peeled off, and the saturation magnetization of the ferromagnetic component of the hydrogen storage alloy powder contained in the paste was measured. The result is shown in Table 1 below. The dried paste-filled substrate was pressed to adjust the thickness to a thickness of 0.34 mm to 0.36 mm to produce a negative electrode having a capacity of 1800 mAh. Here, a part of the paste filled in the substrate was peeled off, and the saturation magnetization of the ferromagnetic component of the hydrogen storage alloy powder contained in the paste was measured. From the difference between the result and the saturation magnetization after drying, the saturation magnetization of the ferromagnetic component generated by oxidizing the newly exposed surface of the hydrogen-absorbing alloy powder in the thickness control step was determined. The results are shown in Table 1 below. To a mixed powder consisting of 90 parts by weight of nickel hydroxide powder and 10 parts by weight of cobalt oxide powder, 3 parts by weight of carboxymethyl cellulose and 5 parts by weight of polytetrafluoroethylene were added to the nickel hydroxide powder. Further, a paste was prepared by adding 45 parts by weight of pure water thereto and kneading them. After filling this paste into a sintered fiber substrate, the paste was further applied to both surfaces thereof, dried, and rolled by a roller press to produce a paste-type nickel positive electrode having a capacity of 1200 mAh. Next, a separator made of a nonwoven fabric made of polyamide having a thickness of 0.20 mm was interposed between each of the negative electrode and the positive electrode, and spirally wound to form an electrode group. These electrode groups were housed in a container together with an alkaline electrolyte composed of 7N potassium hydroxide and 1N lithium hydroxide to have the structure shown in FIG. 1 described above and a capacity of 1200 m
An AA size nickel-metal hydride secondary battery of Ah was assembled. Comparative Examples 1 to 5 A paste having the same composition as in Examples 1 to 8 was applied to a punched metal having a thickness of 0.08 mm and a paste thickness of 1.3 to
It was applied so as to have a thickness of 1.5 mm, and dried in an air-circulating drying oven at 80 ° C. for 1 hour. The dried and dried paste-filled substrate is pressed into a 0.34 mm to 0.
The capacity is 1800m by adjusting the thickness to 36mm
A negative electrode of Ah was produced. An electrode group was prepared by interposing a separator similar to those in Examples 1 to 8 between the negative electrode and the positive electrode similar to Examples 1 to 8, and these electrode groups were used in Examples 1 to 8. An AA-size nickel-metal hydride secondary battery having a capacity of 1200 mAh and having the structure shown in FIG. With respect to the negative electrodes of the secondary batteries of Comparative Examples 1 to 5,
The saturation magnetization of the ferromagnetic component of the hydrogen-absorbing alloy powder after the completion of drying and the thickness adjustment of the paste-filled substrate was measured in the same manner as in Examples 1 to 8, and the difference between these ferromagnetic saturation magnetizations was determined. In the thickness control step, the saturation magnetization of the ferromagnetic component generated by oxidizing the newly exposed surface of the hydrogen-absorbing alloy powder was pulverized. The results are shown in Table 1 below. The content of the hydrogen storage alloy (Mm EXAMPLE 9-13 composition represented by MmNi _3.0 Co _1.0 Mn _0.7 Al _0.3 33 wt%, the nickel content is 41 wt%, the total content of cobalt 14
%, The manganese content is 10% by weight, and the aluminum content is 2% by weight).
A paste similar to 8 was prepared. The above paste is applied to a punched metal having a thickness of 0.08 mm and the paste thickness is 1.7.
It was applied so as to have a thickness of ２．０2.0 mm, and was dried for 1 hour in an air circulation type drying oven at 80 ° C. The dried paste-filled substrate is pressed to 0.34 mm
By adjusting the thickness to 0.36 mm, the capacity becomes 180
A negative electrode of 0 mAh was produced. An electrode group was prepared by interposing a separator similar to those in Examples 1 to 8 between the negative electrode and the positive electrode similar to Examples 1 to 8, and these electrode groups were formed in Examples 1 to 8. An AA-size nickel-metal hydride secondary battery having a capacity of 1200 mAh and having the structure shown in FIG. With respect to the secondary batteries of Examples 9 to 13, the saturation of the ferromagnetic component of the hydrogen storage alloy powder after the completion of drying and the thickness adjustment of the substrate filled with the paste was performed in the same manner as in Examples 1 to 8. The magnetization amount was measured, and the saturation magnetization amount of the ferromagnetic component generated by oxidizing the newly exposed surface of the hydrogen storage alloy powder in the thickness adjusting step was determined from the difference between these ferromagnetic saturation magnetization amounts. The results are shown in Table 2 below. Comparative Examples 6 and 7 Examples 9 to 13 for punched metal having a thickness of 0.08 mm
A paste having a composition similar to that of
It was applied so as to have a thickness of 1.8 mm to 1.8 mm, and was dried in an air circulation type drying oven at 80 ° C. for 1 hour. The dried paste-filled substrate is pressed to 0.34 mm
By adjusting the thickness to 0.36 mm, the capacity becomes 18
A negative electrode of 00 mAh was produced. An electrode group was prepared by interposing a separator similar to those in Examples 1 to 8 between the negative electrode and the positive electrode similar to Examples 1 to 8, and these electrode groups were used in Examples 1 to 8. An AA-size nickel-metal hydride secondary battery having a capacity of 1200 mAh and having the structure shown in FIG. With respect to the negative electrodes of the secondary batteries of Comparative Examples 6 and 7,
The saturation magnetization of the ferromagnetic component of the hydrogen-absorbing alloy powder after the completion of drying and the thickness adjustment of the paste-filled substrate was measured in the same manner as in Examples 1 to 8, and the difference between these ferromagnetic saturation magnetizations was determined. In the thickness control step, the saturation magnetization of the ferromagnetic component generated by oxidizing the newly exposed surface of the hydrogen-absorbing alloy powder was pulverized. The results are shown in Table 2 below. The obtained Examples 1 to 13 and Comparative Examples 1 to 7
About 1 day at room temperature,
Charge for 15 hours with A current, 1V with 1200mA current
Until discharge. Thereafter, the battery was charged with a current of 1200 mA for 72 minutes, and then repeatedly charged and discharged with a current of 1200 mA to 1 V.
The number of cycles required to reach 1.20 V and the number of cycles required to reduce the battery capacity to 1000 mAh were measured, and the results are also shown in Tables 1 and 2 below. [Table 1] [Table 2] As can be seen from Tables 1 and 2, the thickness of the ferromagnetic component generated by oxidizing the newly exposed surface of the hydrogen storage alloy powder when the hydrogen storage alloy powder is pulverized is adjusted to 0.07.
In the secondary batteries of Examples 1 to 13 performed so as to be 1 emu / g or more, the number of charge / discharge cycles required for the average operating voltage to rise to 1.19 V and 1.20 V is small, and the charge / discharge cycle life is short. It turns out that it is long. In contrast, Comparative Examples 1 to 7 in which the thickness was controlled such that the saturation magnetization of the ferromagnetic component generated by oxidizing the newly exposed surface of the hydrogen-absorbing alloy powder after the pulverization of the hydrogen-absorbing alloy powder was less than 0.01 emu / g.
It can be seen that the secondary battery has a long cycle life, but requires a large number of cycles for the average operating voltage to rise to 1.19 V and 1.20 V. As described in detail above, according to the method for manufacturing an alkaline secondary battery of the present invention, the secondary battery has a long cycle life and reduces the number of charge / discharge cycles required for activation. And the production efficiency can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing a nickel-metal hydride secondary battery as an example of an alkaline secondary battery manufactured by the method of the present invention. [Description of Signs] 1 ... negative electrode, 2 ... positive electrode, 3 ... separator, 4 ... container, 6 ...
Sealing plate.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-137361 (JP, A) JP-A-6-290777 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/24 H01M 10/28

Claims (1)

(57) Claims 1. A step of preparing a paste containing a hydrogen storage alloy powder containing a rare earth element , nickel and cobalt as a negative electrode active material, and filling the paste into a conductive substrate; Drying the conductive substrate filled with the paste; and bonding the conductive substrate filled with the paste with the hydrogen absorbing compound.
The saturation magnetization due to the ferromagnetic component of the gold powder is 0.01 emu
/ G to 0.04 emu / g. A method for producing an alkaline secondary battery, comprising: preparing a negative electrode by a method comprising :