JPH0935718A - Alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the increase of an internal pressure at the time of overcharge and overdischarge by using polytetrafluoroethylene with specified molecular weight for the binding agent of the negative electrode of an alkaline secondary battery and specifying the specific surface area of the conductive agent of the negative electrode. SOLUTION: In an alkaline secondary battery comprising a positive electrode 2, a negative electrode 4, a separator 3 installed between the positive electrode 2 and the negative electrode 4 and an alkaline electrolytic solution, a material containing the polytetrafluoroethylene having average molecular weight of 20×10<4> to 100×10<4> , the polytetrafluoroethylene having average molecular weight of 200×10<4> to 1000×10<4> and the other polymer is used for the binding agent of the negative electrode. For a conductive material of the negative electrode, a material containing as a main body a carbon black having a specific surface area of not less than 700m<2> /g is used. It is preferable that the polytetrafluoroethylene having average molecular weight of 20×10<4> to 200×10<4> of approximately 0.1 to 2.1 parts by weight is added to a hydrogen storage alloy powder of 100 parts by weight, and also it is preferable that the polytetrafluoroethylene having average molecular weight of 200×10<4> to 1000×10<4> of approximately 0.9 to 2.0 parts by weight is added thereto.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkaline secondary battery provided with a paste type hydrogen storage alloy negative electrode having an improved binder and conductive agent.

[0002]

2. Description of the Related Art A nickel-hydrogen secondary battery, which is an example of an alkaline secondary battery, is manufactured by interposing a separator between a positive electrode containing nickel hydroxide as an active material and a negative electrode containing hydrogen storage alloy powder. The electrode group is housed in a container together with the alkaline electrolyte. In the secondary battery,
The capacity of the negative electrode is made larger than that of the positive electrode. When the secondary battery is overcharged, charging of the positive electrode ends first,
Oxygen gas is generated from the positive electrode. Therefore, the boundary surface between the portion where the alkaline electrolyte layer is formed and the portion where the alkaline electrolyte layer is not formed on the surface of the hydrogen storage alloy powder of the negative electrode, that is, the three phases of gas phase, liquid phase and solid phase By reducing the oxygen gas to water at the interface, an increase in internal pressure during overcharge is prevented. On the other hand, when the secondary battery is over-discharged, hydrogen gas is generated from the positive electrode whose discharge is completed first. By oxidizing this hydrogen gas at the three-phase interface of the negative electrode and converting it into water, an increase in internal pressure during overdischarge is prevented.

By the way, for the negative electrode, for example, a water-absorbing polymer binder such as polyacrylate and polytetrafluoroethylene and a conductive agent are added to hydrogen-absorbing alloy powder, and the mixture is kneaded in the presence of water. After the paste is prepared by applying the paste to a conductive substrate such as punched metal, the paste is dried and rolled. Since such a negative electrode contains a water-soluble polymer binder, the alkaline electrolyte easily penetrates. Therefore, since the entire surface of the hydrogen storage alloy powder of the negative electrode is covered with the alkaline electrolyte layer, there is no three-phase interface, and the secondary battery including the negative electrode has a problem that the internal pressure increases during overcharge and overdischarge. was there.

From the above, attention is paid to the fact that the polytetrafluoroethylene added to the negative electrode for ensuring the strength has high water repellency, and the amount of polytetrafluoroethylene in the paste is increased. Alternatively, the water repellency is improved and the three-phase interface is increased by applying a suspension of polytetrafluoroethylene to the surface of the negative electrode.

However, if the amount of polytetrafluoroethylene in the negative electrode is increased, the fluidity and adhesiveness of the paste will be significantly reduced, and the applicability of the paste to the conductive substrate will be significantly impaired.

On the other hand, when polytetrafluoroethylene is coated on the surface to form a negative electrode, it is difficult to improve the water repellency inside the negative electrode. It was difficult to sufficiently suppress the rise in internal pressure. Furthermore, since the water repellent treatment process is increased,
There is a problem that the manufacturing work of the secondary battery becomes complicated.

Incidentally, acetylene black, metal powder and the like have been conventionally known as the conductive agent for the negative electrode. However, since the amount of insulating polytetrafluoroethylene is increased in the negative electrode to which the water repellency is imparted by the method as described above, the conduction between the hydrogen storage alloy powders is sufficiently improved by such a conductive agent. It was difficult to do. As a result, the negative electrode has a large electric resistance, so that the large-current discharge characteristic of the secondary battery including the negative electrode deteriorates. Further, a method of improving conduction between alloy powders by coating the surface of the hydrogen storage alloy powder with a metal film instead of adding such a conductive agent to the paste is known, but the manufacturing process of the negative electrode is complicated. Therefore, there is a problem that the manufacturing cost rises.

[0008]

The object of the present invention is to improve the charge / discharge characteristics at a large current by improving the binder and the conductive agent, and suppress the rise of the internal pressure during overcharge and overdischarge. And to provide an alkaline secondary battery in which a negative electrode can be produced by a simple method.

[0009]

The alkaline secondary battery of the present invention comprises a positive electrode, a negative electrode comprising a conductive substrate filled with a paste containing a hydrogen storage alloy, a binder and a conductive agent, the positive electrode and the In an alkaline secondary battery including a separator interposed between a negative electrode and an alkaline electrolyte, the binder of the negative electrode has an average molecular weight of polytetrafluoroethylene of 200,000 to 1,000,000 and an average molecular weight of 2 million to 1
The electroconductive agent of the negative electrode contains carbon black having a specific surface area of 700 m ² / g or more as a main component and contains 10 million polytetrafluoroethylene.

An example of the alkaline secondary battery (cylindrical alkaline secondary battery) according to the present invention will be described below with reference to FIG. As shown in FIG. 1, a positive electrode 2, a separator 3, and a paste-type negative electrode 4 are placed in a bottomed cylindrical container 1 that also serves as a negative electrode terminal.
An electrode group 5 manufactured by stacking and winding in a spiral shape is housed. The negative electrode 4 is arranged at the outermost periphery of the electrode group 5 and is in electrical contact with the container 1. The alkaline electrolyte is contained in the container 1. A circular sealing plate 7 having a hole 6 in the center is arranged in the upper opening of the container 1. The ring-shaped insulating gasket 8 is arranged between the peripheral edge of the sealing plate 7 and the inner surface of the upper opening of the container 1, and the sealing plate is attached to the container 1 by caulking to reduce the diameter of the upper opening inward. 7 is airtightly fixed via the gasket 8. One end of the positive electrode lead 9 is connected to the positive electrode 2, and the other end is connected to the lower surface of the sealing plate 7. Hat-shaped positive electrode terminal 1
Numeral 0 is mounted on the sealing plate 7 so as to cover the hole 6. A rubber safety valve 11 is disposed so as to close the hole 6 in a space surrounded by the sealing plate 7 and the positive electrode terminal 10. The holding plate 12 made of an insulating material having a hole in the center is provided on the positive electrode terminal 10 with the positive electrode terminal 10
The protrusions are arranged so as to protrude from the holes. The outer tube 13 covers the periphery of the holding plate 12, the side surface of the container 1, and the periphery of the bottom of the container 1.

Next, the positive electrode 2, the paste type negative electrode 4, the separator 3 and the electrolytic solution will be described. 1) Positive electrode 2 In this positive electrode 2, for example, a conductive material is added to a nickel compound which is an active material, and the mixture is kneaded with a binder and water to prepare a paste, and the paste is filled in a conductive substrate and dried. After that, it is manufactured by molding.

Examples of the nickel compound include nickel hydroxide and nickel oxide.
The conductive material is formed from at least one selected from cobalt compounds and metallic cobalt. Examples of the cobalt compound include cobalt monoxide, dicobalt trioxide, and cobalt hydroxide. In particular, a conductive material made of cobalt monoxide or cobalt hydroxide is suitable.

Examples of the binder include carboxymethyl cellulose, methyl cellulose, sodium polyacrylate, polytetrafluoroethylene and the like.

Examples of the conductive substrate include a mesh-like, sponge-like, fibrous, or felt-like porous metal body formed of nickel, stainless steel, or nickel-plated metal.

2) Paste type negative electrode 4 The negative electrode 4 is prepared by adding a binder and a conductive agent to hydrogen-absorbing alloy powder, and then kneading the mixture in the presence of water to prepare the conductive paste. It is manufactured by coating a flexible substrate, drying and rolling.

The hydrogen storage alloy is not particularly limited as long as it can store hydrogen electrochemically generated in the electrolytic solution and can easily release the stored hydrogen during discharge. . For example, LaNi ₅ , MmNi
₅ (Mm means a misch metal that is a mixture of lanthanum-based elements such as La, Ce, Pr, Nd, and Sm), LnNi ₅ (Ln; lanthanum-enriched misch metal), and one of these Nis. Parts are Al, Mn, Co,
Examples thereof include multi-element type elements substituted with elements such as Ti, Cu, Zn, Zr, Cr and B, or TiNi type elements and TiFe type elements. Among them, the general formula LnNi _x M
n _y A _z (where Ln is a misch metal composed of La, Nd, Ce and Pr, A is at least one metal selected from Al and Co, and the total value of atomic ratios x, y and z is 4.8 ≦ It is preferable to use a multi-element hydrogen storage alloy represented by (x + y + z ≦ 5.4). The negative electrode containing such a hydrogen storage alloy suppresses pulverization accompanying the progress of the charge / discharge cycle, and thus the charge / discharge cycle life of the secondary battery is improved.

The binder has an average molecular weight of 200,000 to 100.
10,000 low molecular weight polytetrafluoroethylene, high molecular weight polytetrafluoroethylene having an average molecular weight of 2,000,000 to 10,000,000, and other polymers.

The other polymer preferably has resistance to an alkaline electrolyte. Examples of such a polymer include hydrophobic polymers such as polyethylene and polypropylene, such as carboxymethyl cellulose (CM
C), methylcellulose (MC), hydroxypropylmethylcellulose (HPMC), polyacrylates such as sodium polyacrylate (SPA), hydrophilic polymers such as polyvinyl alcohol (PVA) and polyethylene oxide, and rubber systems such as latex. Polymers, polyacrylamide (PA), polyvinylpyrrolidone (PVP), polyethylene oxide (PEO) and the like can be mentioned. Among them, it is preferable to use a mixed polymer composed of polyacrylic acid salt and carboxymethyl cellulose. Polyacrylate improves the dispersion stability of the paste. On the other hand, carboxymethyl cellulose improves the adhesion of the paste to the conductive substrate.

The above-mentioned polytetrafluoroethylene having an average molecular weight of 200,000 to 1,000,000 has high water repellency although it has a low binding property because it is difficult to be fibrillated due to the shear stress applied to the paste when the paste is kneaded. The amount of polytetrafluoroethylene added is the same as that of the hydrogen storage alloy powder 1
It is desirable to set the range of 0.1 to 2.1 parts by weight with respect to 00 parts by weight. This is due to the following reasons. If the amount added is less than 0.1 parts by weight, the total amount of polytetrafluoroethylene will be less than 1.0 parts by weight, and it may be difficult to improve the water repellency of the negative electrode. If the amount added exceeds 2.1 parts by weight,
If the total amount of polytetrafluoroethylene exceeds 3.0 parts by weight, the alloy density of the hydrogen storage alloy may decrease, and the capacity of the negative electrode may decrease. The more preferable addition amount of low-molecular-weight polytetrafluoroethylene is 1.0 to 2.0 parts by weight with respect to 100 parts by weight of the hydrogen storage alloy powder.

The polytetrafluoroethylene having an average molecular weight of 2,000,000 to 10,000,000 has a high binding property as well as a high water repellency because it is easily made into fibers by the shear stress applied to the paste during the kneading of the paste. The amount of polytetrafluoroethylene added is 0.9 parts by weight to 2.0 parts by weight based on 100 parts by weight of the hydrogen storage alloy powder.
It is desirable that the content be in the range of parts by weight. This is due to the following reasons. If the addition amount is less than 0.9 parts by weight, the strength of the negative electrode may be reduced and the hydrogen storage alloy powder may fall off from the negative electrode during battery assembly. If the added amount exceeds 2.0 parts by weight, the paste may have poor fluidity and adhesiveness, and thus the applicability of the paste to the conductive substrate may be impaired. More preferable high molecular weight polytetrafluoroethylene is added,
1.0 part by weight to 100 parts by weight of hydrogen storage alloy powder
It is 1.5 parts by weight.

The paste contains 100 hydrogen absorbing alloy powders.
0.1 parts by weight to 2.1 parts by weight of polytetrafluoroethylene having an average molecular weight of 200,000 to 1 million is added to 0.9 parts by weight of polytetrafluoroethylene having an average molecular weight of 2 million to 10 million. It is desirable to add 2.0 parts by weight to 2.0 parts by weight and make the total amount of them 1.0 part by weight to 3.0 parts by weight. The reason why the total amount of polytetrafluoroethylene is limited to the above range is as follows. If the total amount is less than 1.0 part by weight, it may be difficult to improve the water repellency of the negative electrode. On the other hand, if the total amount exceeds 3.0 parts by weight, the capacity of the negative electrode may decrease because the alloy density of the hydrogen storage alloy decreases. The paste contains hydrogen storage alloy powder 1
0.5 parts by weight to 2.0 parts by weight of low molecular weight polytetrafluoroethylene, and 1.0 parts by weight to 1.5 parts by weight of high molecular weight polytetrafluoroethylene are added to 00 parts by weight, And the total amount of these is 1.5 parts by weight to 2.5.
It is more desirable to use parts by weight.

The other polymer is contained in the paste in an amount of 0.015 part by weight to 2.25 parts by weight per 100 parts by weight of the hydrogen storage alloy powder.
It is preferable to add 0 part by weight. This is due to the following reasons. The addition amount of the other polymer was set to 0.
If the amount is less than 015 parts by weight, it may be difficult to stably disperse the hydrogen storage alloy powder in the paste,
It may be difficult to firmly hold the hydrogen-absorbing alloy powder on the current collector, and further, the paste dried during the rolling step may be separated from the current collector to make it impossible to produce a negative electrode. On the other hand, the addition amount of the other polymer is 2.
If it exceeds 0 part by weight, not only the dispersion stability of the paste and the holding power of the hydrogen storage alloy powder cannot be expected, but also the flatness of the coated surface when the paste is coated on the current collector may be impaired. A more preferable addition amount of the other polymer is 0.05 part by weight to 100 parts by weight of the hydrogen storage alloy powder.
1.0 part by weight.

The conductive agent has a specific surface area of 700 m ² / g.
Mainly the above carbon black. When the specific surface area is less than 700 m ² / g, the conduction between the hydrogen storage alloy powders and the conduction between the hydrogen storage alloy powders and the conductive substrate may decrease in the negative electrode. More preferred specific surface area range is 800m ² / g~1300m ² / g.

The carbon black having such a specific surface area preferably has a three-dimensional chain structure formed by secondary aggregation of carbon particles (primary particles) having a particle diameter of 10 to 30 nm. The negative electrode containing carbon black having such a structure and specific surface area dramatically improves the conduction between the hydrogen storage alloy powders and the conduction between the hydrogen storage alloy powders and the conductive substrate.

Furnace black and Ketjen black are preferably used as the carbon black. The negative electrode containing carbon black of this kind and having a specific surface area in the above range can improve the negative electrode capacity, and can improve the battery capacity of the secondary battery including the negative electrode. Further, since the reactivity between the oxygen gas generated from the positive electrode and the hydrogen storage alloy powder when the secondary battery is overcharged can be improved, it is possible to suppress an increase in battery internal pressure during overcharge. it can.

The mixing ratio of the conductive agent is preferably 0.1 to 4 parts by weight with respect to 100 parts by weight of the hydrogen storage alloy powder. This is due to the following reasons. If the blending ratio of the conductive agent is less than 0.1 part by weight, it may be difficult to sufficiently achieve the effect of adding the conductive agent in the negative electrode. On the other hand, if the blending ratio of the conductive agent exceeds 4 parts by weight, the amount of hydrogen storage alloy per unit volume of the negative electrode may decrease, and a large capacity may not be obtained. A more preferable mixing ratio of the conductive agent is 0.1 part by weight to 2 parts by weight with respect to 100 parts by weight of the hydrogen storage alloy powder.
Parts by weight.

Examples of the conductive substrate 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.

3) Separator 3 As the separator 3, for example, a nonwoven fabric made of polyamide synthetic resin fiber (for example, nylon 6,6 fiber), a nonwoven fabric made of polyolefin synthetic resin fiber, which has been subjected to hydrophilic treatment, etc. Can be mentioned. Examples of the polyolefin include polyethylene and polypropylene. Examples of the hydrophilic treatment include plasma treatment, sulfonation treatment, and a method of graft-copolymerizing a vinyl monomer having a hydrophilic group. In particular, those obtained by subjecting the polyolefin synthetic resin fiber nonwoven fabric to a hydrophilic treatment,
It is suitable because it has a high electrolytic solution retention performance and excellent oxidation resistance, and thus self-discharge during storage of the secondary battery at high temperatures is suppressed.

4) Alkaline Electrolyte Solution Examples of the alkaline electrolyte solution include an aqueous solution of sodium hydroxide (NaOH) and lithium hydroxide (LiOH).
Aqueous solution, potassium hydroxide (KOH) aqueous solution, NaO
H and LiOH mixed solution, KOH and LiOH mixed solution, K
A mixed solution of OH, LiOH, and NaOH can be used.

It should be noted that although the description has been made by applying it to the cylindrical alkaline secondary battery, it can be similarly applied to the prismatic alkaline secondary battery. Further, the electrode group housed in the battery container is not limited to the spiral shape, but may be a form in which a plurality of positive electrodes, separators, and negative electrodes are stacked in this order.

[0031]

According to the alkaline secondary battery of the present invention, polytetrafluoroethylene having a high water repellency but a low binding property and an average molecular weight of 200,000 to 1,000,000 is contained in the paste constituting the hydrogen storage alloy negative electrode, It contains polytetrafluoroethylene having a high binding property and an average molecular weight of 2 to 10 million. Such a paste maintains good fluidity and has excellent coatability. Therefore, by coating the conductive substrate with the paste, it is possible to obtain a negative electrode in which the water repellency of the whole including the inside is improved.

Further, carbon black having a specific surface area of 700 m ² / g or more is added to the paste of the negative electrode as a conductive agent, so that the hydrogen storage alloy powders are electrically connected to each other in the negative electrode and the hydrogen storage alloy powders and the conductive substrate. It is possible to make good conduction with. As a result, the hydrogen storage alloy powder is efficiently used in the negative electrode and the surface area of the hydrogen storage alloy powder involved in the charge / discharge reaction is increased, so that the gas reaction rate of the hydrogen storage alloy powder can be improved.

Therefore, since the hydrogen storage alloy powder of the negative electrode has a three-phase interface over the whole and has high gas reactivity, the negative electrode can quickly generate gas generated from the positive electrode during overcharge and overdischarge. Can be absorbed into. For this reason, it is possible to suppress the increase in internal pressure during overcharging, which is manufactured more easily than the negative electrode in which the suspension of polytetrafluoroethylene is applied on the surface of the conventional method, and is provided with a negative electrode having excellent gas absorption performance. An alkaline secondary battery that can be provided can be provided. Furthermore, since the negative electrode has a large surface area of the hydrogen storage alloy powder involved in the charge / discharge reaction, it is possible to provide an alkaline secondary battery having excellent large current discharge characteristics.

[0034]

Embodiments of the present invention will now be described in detail with reference to the drawings. Example 1 First, LmNi _4.2 Mn _0.3 Al _0.3 Co _0.2 was pulverized by absorbing and desorbing gaseous hydrogen before use to prepare a 200-mesh pass hydrogen-absorbing alloy powder. Subsequently, to 100 g of the hydrogen storage alloy powder, 0.5 g of sodium polyacrylate and 0.1 g of carboxymethyl cellulose were added.
25 g and a specific surface area of 700 m ² / g as a conductive material,
An average molecular weight of 200,000 to 1 is obtained after adding 1.0 g of carbon black having a trade name of Ketjen Black EC manufactured by Ketjen Black International Co., Ltd.
Dispersion of 1,000,000 low molecular weight polytetrafluoroethylene (specific gravity 1.28, solid content 40 wt.%) Was 1.95 ml (1.0 part by weight in terms of solid content), and an average molecular weight of 2,000,000 to 10,000,000. 1.11 ml of high molecular weight polytetrafluoroethylene (specific gravity 1.5, solid content 60 wt.%) (1.0 part by weight in terms of solid content) and water 60
ml and kneaded with a mixer to prepare a paste. The obtained paste was applied to a punched metal as a conductive substrate, dried at 80 ° C., and pressure-molded with a roller press to produce a negative electrode.

On the other hand, nickel hydroxide powder 9 which is an active material
0 parts by weight and 10 parts by weight of cobalt monoxide powder as a conductive material, 0.3 part by weight of carboxymethyl cellulose, 0.3 part by weight of sodium polyacrylate, 4 parts by weight of polytetrafluoroethylene as a binder A paste was prepared by adding 60 parts by weight of water and kneading them. Subsequently, this paste was filled in a nickel-plated fiber substrate as a conductive substrate, dried and molded to prepare a paste-type positive electrode.

A test cell A shown in FIG. 2 was assembled using the obtained negative electrode and positive electrode. That is, in the container 21, 8
An alkaline electrolyte solution 22 made of a prescribed KOH solution is contained. The electrode group 23 has a negative electrode 24 with a thickness of 0.2 mm.
It is produced by sandwiching it between two positive electrodes 26 with a separator 25 made of a polyamide non-woven fabric interposed therebetween, and is housed in the container 21. The two pressing plates 27 sandwich the electrode group 23 therebetween. The reference electrode 28 is
It is immersed in the alkaline electrolyte 22 in the container 21. Example 2 Carbon black having a specific surface area of 800 m ² / g as a negative electrode conductive material and a product name of Ketjen Black EC manufactured by Ketjen Black International Co., Ltd. (the addition amount is 1.0 g per 100 g of hydrogen storage alloy 100 g). ) Was used to assemble the test cell A shown in FIG. 2 having the same configuration as in Example 1. Example 3 A negative electrode conductive material having a specific surface area of 1300 m ² / g, manufactured by Ketjen Black International Co., Ltd.,
The test cell A shown in FIG. 2 having the same structure as in Example 1 was used except that carbon black having a trade name of Ketjen Black EC (the amount of addition was 1.0 g per 100 g of the hydrogen storage alloy) was used. Assembled Comparative Example 1 The test cell A shown in FIG. 2 was assembled with the same configuration as in Example 1 except that 1 g of acetylene black having a specific surface area of 40 m ² / g was used as the conductive agent for the negative electrode.

With respect to the obtained test cells A of Examples 1 to 3 and Comparative Example 1, charging / discharging was repeated at a current of 150 mA / g of hydrogen storage alloy, and the change in the negative electrode potential at the 10th cycle of discharging was measured. The results are shown in Fig. 3.

As is clear from FIG. 3, the test cells A of Examples 1 to 3 can keep the potential of the negative electrode at the time of discharging high for a long period of time. This is a binder containing high molecular weight polytetrafluoroethylene and low molecular weight polytetrafluoroethylene, and a specific surface area of 700 m.
^This is because the negative electrode prepared from the paste containing the conductive agent made of carbon black of ² / g or more was used.

On the other hand, it can be seen that the test cell A of Comparative Example 1 has a lower potential of the negative electrode at the time of discharging, as compared with Examples 1 to 3. In addition, an electrode group was produced by spirally winding between the obtained negative electrodes of Examples 1 to 3 and Comparative Example 1 and the positive electrode with a separator made of a polyamide fiber non-woven fabric having a thickness of 0.2 mm interposed therebetween. did. This electrode group was inserted into an AA size space of an acrylic resin container equipped with a pressure detector, and an electrolyte consisting of 8N KOH solution was injected into this space and sealed, and the test as shown in FIG. 4 was performed. Cell B (capacity 1000 mA
h) was assembled.

That is, the test cell B includes a battery case composed of the case body 31 made of the acrylic resin and the cap 32. At the center of the case body 31, the AA
A space 33 having the same inner diameter and height as the metal container of the size battery is formed. The electrode group 34 is housed in the space 33, and further, an electrolytic solution is housed therein. On the case body 31, the cap 32 is airtightly fixed by a bolt 37 and a nut 38 via a rubber sheet 35 and an O ring 36. A pressure detector 39 is attached to the cap 32. One end of the negative electrode lead 40 is attached to the negative electrode, and the other end is led out through between the rubber sheet 35 and the O ring 36. One end of the positive electrode lead 41 is attached to the positive electrode, and the other end is led out through between the rubber sheet 35 and the O-ring 36.

The test cells B obtained in Examples 1 to 3 and Comparative Example 1 were initially charged at a current of 100 mA for 15 hours and then discharged to 0.8 V at a current of 1 A. Furthermore,
After charging with a current of 1 A for 1.5 hours, a current of 1 A gives a voltage of 0.
Charging / discharging to discharge up to 8V was repeated 50 times, the maximum internal pressure at the end of charging at the 50th cycle was measured, and the results are shown in Table 1.
Shown in An open state of 30 minutes as a pause time was provided between the charge and the discharge and the discharge and the charge, respectively.

[0042]

[Table 1]

As is clear from Table 1, the test cells B of Examples 1 to 3 can suppress the increase in internal pressure due to the progress of charge / discharge cycles. Furthermore, the obtained Examples 1-3
And a thickness of 0.2 m between the negative electrode of Comparative Example 1 and the positive electrode.
A separator made of polyamide fiber non-woven fabric of m was interposed and spirally wound to prepare an electrode group. The above-described structure shown in FIG. 1 has a theoretical capacity of 1000 mAh and an AA-sized cylindrical nickel-hydrogen nickel alloy having the structure shown in FIG. The next battery was assembled.

The obtained secondary batteries of Examples 1 to 3 and Comparative Example 1 were initially charged at a current of 100 mA for 15 hours, and then discharged to 0.8 V at a current of 1 A. Furthermore, 1
After charging for 1.5 hours with the current of A, 0.8 with the current of 1A
The charging / discharging to discharge to V was repeated, and the overcharge test in which the battery was charged with a current of 1 A for 2 hours at the 30th cycle was performed to measure the change in the battery internal pressure with respect to the elapsed time.
Shown in

As is apparent from FIG. 5, the secondary batteries of Examples 1 to 3 have a smaller increase in internal pressure when overcharged than in Comparative Example 1. It was confirmed that such improvement of the gas absorption characteristics of the negative electrode can be achieved not only during overcharging but also when hydrogen gas is generated from the positive electrode during reverse charging. Examples 4 to 8 100 g of hydrogen storage alloy powder having the same composition as in Examples 1 to 3
In addition, 0.5 g of sodium polyacrylate, 0.125 g of carboxymethyl cellulose, a specific surface area of 1300 m ² / g as a conductive material, carbon black manufactured by Ketjen Black International Co., Ltd. under the trade name Ketjen Black EC And 1.0 g of low molecular weight polytetrafluoroethylene having an average molecular weight of 200,000 to 1,000,000 and an average molecular weight of 2,000,000 to 100
The high molecular weight polytetrafluoroethylene of 0,000 is shown in Table 2 below.
The suspension prepared by mixing in a ratio as shown in (proportion to 100 parts by weight of hydrogen storage alloy powder) and 60 ml of water were added and kneaded by a mixer to prepare a paste. The obtained paste was applied to a punched metal as a conductive substrate, dried at 80 ° C., and pressure-molded with a roller press to produce a negative electrode.

An electrode group was produced by spirally winding the obtained negative electrode and a positive electrode similar to those in Examples 1 to 3 with a separator made of a polyamide fiber nonwoven fabric having a thickness of 0.2 mm interposed therebetween. This electrode group was inserted into an AA size space of an acrylic resin container equipped with a pressure detector, and an electrolyte consisting of 8N KOH solution was injected into this space and sealed, and the test shown in FIG. 4 was performed. Cell B (capacity 1000 mAh) was assembled. Conventional Example A suspension containing 1.5 parts by weight of high molecular weight polytetrafluoroethylene having an average molecular weight of 2 to 10 million as a binder for a negative electrode, 0.5 g of sodium polyacrylate, and 0.125 g of carboxy. Negative electrodes similar to those in Examples 4 to 10 were produced except that methyl cellulose was used. Subsequently, a water repellent treatment was performed by applying a suspension of high molecular weight polytetrafluoroethylene to the surface of the negative electrode and drying the suspension.

An electrode group was produced by spirally winding the obtained negative electrode and a positive electrode similar to those in Examples 1 to 3 with a separator made of a polyamide fiber nonwoven fabric having a thickness of 0.2 mm interposed therebetween. This electrode group was inserted into an AA size space of an acrylic resin container equipped with a pressure detector, and an electrolyte consisting of 8N KOH solution was injected into this space and sealed, and the test shown in FIG. 4 was performed. Cell B (capacity 1000 mAh) was assembled.

With respect to the obtained negative electrodes of Examples 4 to 8, Comparative Examples 2 to 5 and the conventional example, the coating state of the paste was examined, and the results are also shown in Table 2 below. In addition, it was investigated whether or not the hydrogen storage alloy powder was peeled from these negative electrodes when the spiral electrode group was produced, and the results are also shown in Table 2 below.

Further, the obtained Examples 4 to 8 and Comparative Examples 2 to 2 were obtained.
5 and the test cell B of the conventional example were subjected to a charge-discharge cycle test of charging 150% at a current of 0.3 C and then discharging to 0.8 V at a current of 1 C, and measuring the internal pressure at the 50th cycle, and the result Is also shown in Table 2 below.

[0050]

[Table 2]

As is clear from Table 2, the negative electrodes of Examples 4 to 8 are high in strength because the paste filling amount is uniform and the hydrogen storage alloy powder is not peeled off when the spiral electrode group is manufactured. I understand. Further, it can be seen that the test cell B provided with these negative electrodes can suppress an increase in internal pressure with the progress of charge / discharge cycles.

On the other hand, in the test cells B of Comparative Examples 3 and 5 equipped with the negative electrode containing only low molecular weight PTFE, the internal pressure at the 50th cycle was relatively low, but the amount of hydrogen storage alloy powder that had fallen off was large. . On the other hand, in the test cell B of Comparative Example 2 provided with the negative electrode containing only a small amount of high molecular weight PTFE, the internal pressure at the 50th cycle was high, and the amount of hydrogen storage alloy powder that had fallen off was large. In addition, as in Comparative Example 4, high molecular weight PTFE
The paste containing a large amount of only could not be applied to the conductive substrate because the viscosity was too high.

On the other hand, in the conventional example, although the internal pressure at the 50th cycle was low, the work of applying the suspension of polytetrafluoroethylene to the surface of the negative electrode was required, and the production of the negative electrode was complicated. Examples 9 to 12 Hydrogen storage alloy powder 1 having the same composition as in Examples 1 to 3
0.5 g of sodium polyacrylate, 0.125 g of carboxymethyl cellulose, a specific surface area of 800 m ² / g as a conductive material, and a product name of Ketjen Black EC manufactured by Ketjen Black International Co., Ltd. Carbon black 0.1g, 1.0
g, 2.0 g, and 4.0 g, a dispersion of low molecular weight polytetrafluoroethylene having an average molecular weight of 200,000 to 1,000,000 (specific gravity: 1.28, solid content: 40 w)
t. %) Is 1.95 ml and the average molecular weight is 2,000,000 to 1
1.11 ml of 10 million high molecular weight polytetrafluoroethylene (specific gravity 1.5, solid content 60 wt.%) And water 6
0 ml was added and kneaded with a mixer to prepare a paste. The obtained paste was applied to a punched metal as a conductive substrate, dried at 80 ° C., and pressure-molded with a roller press to produce a negative electrode.

An electrode group was produced by spirally winding the obtained negative electrode and a positive electrode similar to those in Examples 1 to 3 with a separator made of a polyamide fiber nonwoven fabric having a thickness of 0.2 mm interposed therebetween. This electrode group was inserted into an AA size space of an acrylic resin container equipped with a pressure detector, and an electrolyte consisting of 8N KOH solution was injected into this space and sealed, and the test shown in FIG. 4 was performed. Cell B (capacity 1000 mAh) was assembled.

The test cells B obtained in Examples 9 to 12 were initially charged with a current of 100 mA for 15 hours, and then,
It was discharged to 0.8 V with a current of 1 A. Furthermore, after charging with a current of 1 A for 1.5 hours, charging / discharging to discharge 0.8 V with a current of 1 A was repeated 30 times, and the voltage change at the time of discharging with a current of 5 A was measured in the 30th cycle. Results are shown in FIG. An open state of 30 minutes as a pause time was provided between the charge and the discharge and the discharge and the charge, respectively.

As is apparent from FIG. 6, Examples 9 to 12
It can be seen that the test cell B of 1. has excellent large current discharge characteristics. In particular, Example 9 provided with a negative electrode containing 0.1 to 2.0 parts by weight of a conductive agent with respect to 100 parts by weight of hydrogen storage alloy powder.
It can be seen that the test cells B of Nos. 11 to 11 are superior to Example 12 in the large current discharge characteristics.

[0057]

As described in detail above, according to the alkaline secondary battery of the present invention, it is possible to suppress an increase in internal pressure due to the progress of charging / discharging cycles, and it is possible to greatly improve large current discharge characteristics. Moreover, there is a remarkable effect that the negative electrode can be produced by a simple method.

[Brief description of drawings]

FIG. 1 is a perspective view showing a cylindrical alkaline secondary battery according to the present invention.

FIG. 2 is a test cell A used in Examples 1 to 3 of the present invention.
FIG.

FIG. 3 is a characteristic diagram showing changes in the negative electrode potential when the electrode capacitance is changed in Examples 1 to 3 of the present invention.

FIG. 4 is a sectional view showing a test cell B used in Examples 1 to 12 of the present invention.

FIG. 5 is a characteristic diagram showing changes with time in battery internal pressure in Examples 1 to 3 of the present invention.

FIG. 6 is a characteristic diagram showing changes over time in battery voltage in Examples 9 to 12 of the present invention.

[Explanation of symbols]

1 ... Container, 2 ... Positive electrode, 3 ... Separator, 4 ... Negative electrode, 5 ...
Electrode group, 7 ... Sealing plate, 8 ... Insulation gasket.

Claims (1)

[Claims] 1. A positive electrode, a negative electrode composed of a conductive substrate filled with a paste containing a hydrogen storage alloy, a binder and a conductive agent, a separator interposed between the positive electrode and the negative electrode, and an alkali. In an alkaline secondary battery provided with an electrolytic solution, the binder of the negative electrode contains polytetrafluoroethylene having an average molecular weight of 200,000 to 1,000,000 and polytetrafluoroethylene having an average molecular weight of 2,000,000 to 10,000,000, The conductive material of the negative electrode is mainly composed of carbon black having a specific surface area of 700 m ² / g or more.