JPH1186864A - Sealed nickel hydrogen secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nickel hydrogen secondary battery having a negative electrode on which high capacity is attained, without impairing strength and liquid absorptivity of an electrolyte. SOLUTION: In a nickel hydrogen secondary battery having a vessel 1, an electrode group 5 which is housed in this vessel and has a structure such that a separator 3 is interposed between a positive electrode 2 and a negative electrode 4 containing hydrogen storage alloy powder, a high polymer binding agent and conductive powder and an alkaline electrolyte, the high polymer binding agent is polytetrafluoroethylene having an average molecular weight of 4,000,000 to 20,000,000, and the conductive powder is carbon having a specific surface area of not less than 700 m<2> /g.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel-hydrogen secondary battery having an improved negative electrode containing a hydrogen storage alloy.

[0002]

2. Description of the Related Art A nickel-hydrogen secondary battery has a structure in which an electrode group produced by interposing a separator between positive and negative electrodes is housed in a container together with an electrolytic solution. Such a nickel-hydrogen secondary battery is voltage-compatible with a nickel-cadmium secondary battery having a negative electrode having a cadmium compound instead of a hydrogen storage alloy, and has a higher capacity than a nickel-cadmium secondary battery. It has the feature of.

[0003] By the way, when the nickel-hydrogen secondary battery is used as an operating power supply for electronic equipment, there is a demand for higher capacity. For this reason, the ratio of the volume of the electrode group in the container is increased, that is, the degree of tightness is increased. However, when the volume of the electrode group occupied in the container is increased, the amount of the electrolyte in the container, particularly the amount of the electrolyte involved in the battery reaction of the electrode group, becomes low, and the cycle characteristics are deteriorated. .

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a nickel-metal hydride secondary battery provided with a negative electrode which achieves a high capacity without impairing the strength and the liquid absorption of the electrolyte.

[0005]

A nickel-hydrogen secondary battery according to the present invention comprises a container, a positive electrode, a negative electrode containing a hydrogen storage alloy powder, a polymer binder and a conductive powder, which are housed in the container. In a nickel-metal hydride secondary battery including an electrode group having a structure in which a separator is interposed therebetween and an alkaline electrolyte, the polymer binder has an average molecular weight of 4,000.
It is a polytetrafluoroethylene of 000 to 20,000,000, and the conductive powder is a carbon having a specific surface area of 700 m ² / g or more.

According to the present invention, the polymer binder constituting the negative electrode has an average molecular weight of 4,000,000.
By using a polytetrafluoroethylene of up to 20,000,000, a binder having a network structure developed in the negative electrode can be formed. Therefore, even if the amount of addition to the negative electrode is reduced, the negative electrode strength (current collector (Adhesion force of the negative electrode agent layer containing the hydrogen storage alloy to the anode) can be sufficiently improved, and the amount of electrolyte absorbed can be increased. In addition, by using carbon having a specific surface area of 700 m ² / g or more as the conductive powder constituting the negative electrode, the amount of electrolyte absorbed can be increased.

Therefore, by adding the specific polymer binder and the conductive powder, it is possible to reduce the amount of addition in the negative electrode while maintaining the strength of the negative electrode and the high liquid absorbing property of the electrolytic solution of the negative electrode. The amount of occlusion alloy can be increased. As a result, a nickel-hydrogen secondary battery having a high capacity and excellent cycle characteristics can be obtained.

In the nickel hydrogen secondary battery according to the present invention, 0.3 to 2.0 parts by weight of polytetrafluoroethylene in the negative electrode is added to 100 parts by weight of the hydrogen storage alloy, and It is preferable that 0.5 to 2.0 parts by weight of the conductive powder is added to 100 parts by weight of the hydrogen storage alloy. By thus defining the amounts of the specific polymer binder and the conductive powder to be added, it is possible to obtain a nickel-hydrogen secondary battery having a higher capacity and excellent cycle characteristics.

In the nickel-metal hydride secondary battery according to the present invention, the dimension of each member constituting the electrode group in the layer thickness direction in the container is A, and the total thickness of the members constituting the electrode group is A. When B is set, the thickness (B / A) obtained by dividing the B by the A (B / A) of the thickness of the electrode group in the layer direction before being housed in the container is 1 or more. Is preferred. By increasing the degree of tightness of the electrode group housed in the container in this way, it is possible to increase the capacity by taking into account the increase in the amount of hydrogen storage alloy of the negative electrode itself, and to improve the negative electrode. A nickel-hydrogen secondary battery having good cycle characteristics can be obtained due to the liquid absorbing property of the electrolytic solution.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A nickel-metal hydride secondary battery (cylindrical nickel-metal hydride secondary battery) according to the present invention will be described below with reference to FIG.

An electrode group 5 formed by laminating a positive electrode 2, a separator 3, and a negative electrode 4 and winding them in a spiral shape is accommodated in a cylindrical container 1 having a bottom. 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 first sealing plate 7 having a hole 6 in the center is arranged at the upper opening of the container 1. The ring-shaped insulating gasket 8 is
Is arranged between the periphery of the container and the inner surface of the upper opening of the container 1,
The sealing plate 7 is airtightly fixed to the container 1 via the gasket 8 by caulking to reduce the diameter of the upper opening inward. 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. The positive electrode terminal 10 having a hat shape is attached on the sealing plate 7 so as to cover the hole 6. Rubber safety valve 1
1 is arranged so as to close the hole 6 in a space surrounded by the sealing plate 7 and the positive electrode terminal 10. A circular holding plate 12 made of an insulating material having a hole in the center is provided on the positive electrode terminal 10 so that a protrusion of the positive electrode terminal 10 is provided on the holding plate 1.
2 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 negative electrode 4, the positive electrode 2, the separator 3
And the electrolyte will be described.

1) Negative electrode 4 The negative electrode was made of a hydrogen storage alloy powder having an average molecular weight of 4,000.
A polymer binder comprising polytetrafluoroethylene having a specific surface area of from 70,000 to 20,000,000;
Contains conductive powder of 0 m ² / g or more carbon.
Such a negative electrode 4 is prepared, for example, by adding a conductive material to the hydrogen storage alloy powder, kneading the mixture with a polymer binder and water to prepare a paste, filling the paste into a conductive substrate,
After drying, it is produced by molding.

The hydrogen storage alloy is not particularly limited, and may be any alloy that can store hydrogen electrochemically generated in an electrolyte and can easily release the stored hydrogen during discharge. . As this hydrogen storage alloy,
For example LaNi _5, MmNi ₅ (Mm; misch metal), LmNi ₅ (Lm; lanthanum enriched misch metal), or some of these Ni Al, Mn, C
o, Ti, Cu, Zn, Zr, Cr, B, etc.
e-type ones can be mentioned. Among them, the general formula Lm
Ni _x Mn _y A _z (However, A is shown Al, at least one metal selected from Co, the atomic ratio x, y, z is the total value of 4.8 ≦ x + y + z ≦ 5.4) is represented by It is preferable to use one.

The polytetrafluoroethylene (PTF)
The reason why the average molecular weight of E) is specified is that if the average molecular weight is less than 4,000,000, it becomes difficult to form a sufficiently developed network structure in the negative electrode. On the other hand, if the average molecular weight of the PTFE exceeds 20,000,000, the viscosity of the negative electrode paste containing the PTFE may increase, and the applicability to the conductive substrate may be deteriorated. More preferably, the average molecular weight of the PTFE is 5,000,0
00 to 15,000,000.

The PTFE is made of the hydrogen storage alloy 100
It is preferable to add 0.3 to 2.0 parts by weight per part by weight. If the amount of the PTFE is less than 0.3 parts by weight, the strength of the negative electrode (the strength of adhesion of the negative electrode layer to the conductive substrate) may be reduced. On the other hand, if the amount of the PTFE exceeds 2.0 parts by weight, it is difficult to increase the capacity of the negative electrode. A more preferable addition amount of the PTFE is 0.5 to 1.5 parts by weight.

The negative electrode may be allowed to contain, in addition to the PTFE, a polymer binder such as carboxymethylcellulose, methylcellulose, and sodium polyacrylate.

The specific surface area of carbon as the conductive powder is specified. If the specific surface area is less than 700 m ² / g, it becomes difficult to sufficiently increase the liquid absorption of the electrolyte. More preferable specific surface area of the carbon is 1,000
0 to 1,500 m ² / g.

The conductive powder is made of the hydrogen storage alloy 10
It is preferable to add 0.5 to 2.0 parts by weight to 0 parts by weight. If the amount of the conductive powder is less than 0.5 part by weight, the liquid absorbing property of the electrolyte of the negative electrode and the conductivity of the negative electrode itself may be reduced, and the cycle characteristics may be reduced. On the other hand, if the amount of the conductive powder exceeds 2.0 parts by weight, the capacity of the negative electrode may decrease. A more preferable addition amount of the conductive powder is 0.7 to 1.5 parts by weight.

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, and a three-dimensional substrate such as a felt-like metal porous body and a sponge-like metal substrate. be able to.

2) Positive Electrode 2 The positive electrode 2 has a structure in which a positive electrode material containing nickel hydroxide particles as an active material, a conductive material and a polymer binder is supported on a conductive substrate. Such a positive electrode 2 is prepared by adding a conductive material to, for example, nickel hydroxide particles as an active material, kneading the mixture with a polymer binder and water to prepare a paste,
This paste is filled in a conductive substrate, dried, and then molded.

As the nickel hydroxide particles, for example, a single nickel hydroxide particle or a nickel hydroxide particle in which a metal such as zinc, cobalt, bismuth, or copper is coprecipitated with metallic nickel can be used. In particular, the latter positive electrode containing nickel hydroxide particles can further improve the charging efficiency in a high-temperature state.

Examples of the conductive material include metal cobalt, cobalt oxide, cobalt hydroxide and the like.

Examples of the polymer binder include carboxymethylcellulose, methylcellulose, sodium polyacrylate, polytetrafluoroethylene and the like.

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

3) Separator 3 Examples of the separator 3 include a nonwoven fabric made of polyamide fiber, a nonwoven fabric made of polyolefin fiber such as polyethylene and polypropylene, and a nonwoven fabric provided with a hydrophilic functional group.

4) Alkaline Electrolyte As the alkaline electrolyte, for example, a mixed solution of sodium hydroxide (NaOH) and lithium hydroxide (LiOH),
A mixture of potassium hydroxide (KOH) and LiOH, KOH
And a mixed solution of LiOH and NaOH.

The electrode group 5 has a dimension A in the layer thickness direction of each of the members 2 to 4 constituting the electrode group 5 in the layer thickness direction, and a total of the layer thicknesses of the members constituting the electrode group. When B, the value (B / A) obtained by dividing B by A in the layer direction thickness of the members 2 to 4 before the electrode group 5 is housed in the container 1 is 1 or more. It is preferable to set as follows.

In FIG. 1 described above, the separator 3 is interposed between the positive electrode 2 and the negative electrode 4 and spirally wound and accommodated in the cylindrical container 1 having a bottom. The battery is not limited to such a structure. For example, a prismatic nickel-metal hydride secondary battery may be configured by interposing a separator between a positive electrode and a negative electrode, and stacking a plurality of the laminated members in a bottomed rectangular cylindrical container.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

Example 1 <Preparation of Paste-Type Negative Electrode> A commercially available lanthanum-enriched misch metal Lm and each element of Ni, Co, Mo, and Al were put into a high-frequency furnace, heated and melted, and then cooled to cool LmNi. A hydrogen storage alloy having a composition of _4.0 Co _0.4 Mn _0.3 Al _0.3 was produced. This alloy is mechanically ground to 200
A hydrogen storage alloy powder of a mesh pass was obtained. To 100 parts by weight of the obtained hydrogen storage alloy powder, 0.5 part by weight of sodium polyacrylate, carboxymethyl cellulose (CMC)
0.12 parts by weight of polytetrafluoroethylene dispersion having an average molecular weight of 5,000,000 (specific gravity: 1.
5, solid content of 60% by weight) in terms of solid content of 1.0 part by weight,
And a specific surface area of 1,300 m ² /
A paste was prepared by adding 0.3 parts by weight of carbon powder and mixing with 50 parts by weight of water. This paste was applied to a punched metal as a conductive substrate, dried, and then pressed to produce a negative electrode.

<Preparation of Paste-Type Positive Electrode> A mixture of 90 parts by weight of nickel hydroxide powder and 10 parts by weight of cobalt monoxide powder was mixed with carboxymethyl cellulose (CM).
C) 0.3 parts by weight of polytetrafluoroethylene dispersion (specific gravity 1.5, solids content 60% by weight) is added in an amount of 0.5 parts by weight in terms of solids, and mixed with 45 parts by weight of pure water. To prepare a paste. Subsequently, this paste was filled in a nickel-plated metal porous body, dried, and then rolled by roller pressing to produce a positive electrode.

Next, a separator made of a nonwoven fabric made of polypropylene fiber subjected to a hydrophilic treatment was interposed between the negative electrode and the positive electrode, and spirally wound to form an electrode group. After storing such an electrode group in a bottomed cylindrical container,
An electrolytic solution composed of 7N potassium hydroxide and 1N lithium hydroxide was accommodated, sealed, and the like, and the cylindrical nickel-metal hydride secondary battery of 4 / 3A size having the structure shown in FIG. 1 described above was assembled. In addition, when the dimension of each member constituting the electrode group in the layer thickness direction in the container is A, and the sum of the layer thicknesses of the members constituting the electrode group is B, the inside of the container of the electrode group is The value (B / A) obtained by dividing B by A in the thickness in the layer direction of those members before being housed in the container is 1.01.
It was set to become.

(Examples 2 to 11) A negative electrode was produced using a paste to which PTFE and carbon powder were added at the ratios shown in Table 1 below, and had the same structure as that of Example 1 and the structure shown in FIG. A 4/3 A size cylindrical nickel-metal hydride secondary battery was assembled.

(Comparative Example 1) <Preparation of Paste Type Negative Electrode> Commercially available lanthanum-enriched misch metal Lm and each element of Ni, Co, Mo, and Al were put into a high-frequency furnace, heated and melted, and then cooled to obtain LmNi. A hydrogen storage alloy having a composition of _4.0 Co _0.4 Mn _0.3 Al _0.3 was produced. This alloy is mechanically ground to 200
A hydrogen storage alloy powder of a mesh pass was obtained. To 100 parts by weight of the obtained hydrogen storage alloy powder, 0.5 part by weight of sodium polyacrylate, carboxymethyl cellulose (CMC)
0.12 parts by weight of polytetrafluoroethylene dispersion having an average molecular weight of 1,000,000 (specific gravity: 1.
5, solid content of 60% by weight) in terms of solid content of 1.0 part by weight,
And a specific surface area of 1,300 m ² /
A paste was prepared by adding 1.0 part by weight of carbon powder and mixing with 50 parts by weight of water. This paste was applied to a punched metal as a conductive substrate, dried, and then pressed to produce a negative electrode.

Next, a separator made of a nonwoven fabric made of a polypropylene fiber subjected to a hydrophilic treatment was interposed between the negative electrode and the same positive electrode as in Example 1, and spirally wound to form an electrode group. After storing such an electrode group in a cylindrical container having a bottom, an electrolytic solution composed of 7N potassium hydroxide and 1N lithium hydroxide is stored, and sealing is performed. A / 3 A cylindrical nickel-metal hydride secondary battery was assembled. Note that the dimensions of the members constituting the electrode group in the container in the layer thickness direction are A,
A value obtained by dividing the thickness of the electrode group in the layer direction before the electrode group is housed in the container by dividing the B by the A, where B is the total of the layer thicknesses of the members constituting the electrode group. (B /
A) was set to 1.01.

Comparative Example 2 A commercially available lanthanum-enriched misch metal Lm and each element of Ni, Co, Mo, and Al were heated and melted in a high-frequency furnace, and then cooled to obtain LmNi _4.0 Co _0.4 Mn _0.3 Al _0.3 A hydrogen storage alloy having the following composition was produced. This alloy is mechanically ground to 200
A hydrogen storage alloy powder of a mesh pass was obtained. To 100 parts by weight of the obtained hydrogen storage alloy powder, 0.5 part by weight of sodium polyacrylate, carboxymethyl cellulose (CMC)
0.12 parts by weight of polytetrafluoroethylene dispersion having an average molecular weight of 5,000,000 (specific gravity: 1.
5, solid content of 60% by weight) in terms of solid content of 1.0 part by weight,
A paste was prepared by adding 1.0 part by weight of a carbon powder having a specific surface area of 300 m ² / g as a conductive material and mixing with 50 parts by weight of water. This paste is applied to punched metal as a conductive substrate, dried,
Further pressing was performed to produce a negative electrode.

Next, a separator made of a nonwoven fabric made of polypropylene fiber subjected to hydrophilic treatment was interposed between the negative electrode and the positive electrode similar to that in Example 1, and spirally wound to form an electrode group. After storing such an electrode group in a cylindrical container having a bottom, an electrolytic solution composed of 7N potassium hydroxide and 1N lithium hydroxide is stored, and sealing is performed. A / 3 A cylindrical nickel-metal hydride secondary battery was assembled. Note that the dimensions of the members constituting the electrode group in the container in the layer thickness direction are A,
A value obtained by dividing the thickness of the electrode group in the layer direction before the electrode group is housed in the container by dividing the B by the A, where B is the total of the layer thicknesses of the members constituting the electrode group. (B /
A) was set to 1.01.

The obtained Examples 1 to 11 and Comparative Examples 1 and 2
In 2, the negative electrode layer containing the hydrogen-absorbing alloy when the spirally wound electrode group was produced was examined for the presence or absence of peeling from the punched metal.

The secondary batteries of Examples 1 to 11 and Comparative Examples 1 and 2 were repeatedly charged and discharged at a current of 2 C and discharged to 1 C at 80% of the discharge capacity in the first cycle. The number of cycles at the time of was determined.

The results are shown in Table 1 below.

[0042]

[Table 1]

As is clear from Table 1, PTFE having an average molecular weight of 4,000,000 to 20,000,000 is used.
It can be seen that the secondary batteries of Examples 1 to 11 provided with the negative electrode including the carbon powder having a specific surface area of 700 m ² / g or more did not peel off the negative electrode layer of the negative electrode and had excellent cycle characteristics.

On the other hand, the same amount of PTF as in Example 2 was used.
The secondary battery of Comparative Example 1 provided with a negative electrode containing E and carbon powder but having an average molecular weight of PTFE less than the above range resulted in peeling of the negative electrode layer and the same amount as in Example 2. The secondary battery of Comparative Example 2 provided with the negative electrode to which PTFE and carbon powder were added, but the specific surface area of the carbon powder was less than 700 m ² / g, had higher cycle characteristics than the secondary batteries of Examples 1 to 11. Is inferior.

In particular, PTF having an average molecular weight in the above range
E and carbon powder having a specific surface area of 700 m ² / g or more, and the amount of each of the PTFE and carbon powder is 0.3 to 100 parts by weight of the hydrogen storage alloy.
The secondary batteries of Examples 2 to 10 provided with a negative electrode of 0.5 to 2.0 parts by weight and 0.5 to 2.0 parts by weight of Examples 1 and 11 in which the addition amounts of PTFE and carbon powder were out of the above ranges.
It can be seen that cycle characteristics are more excellent than those of.

[0046]

As described above, according to the present invention, a nickel-metal hydride secondary battery having a high capacity and excellent cycle characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is a perspective view of a nickel-metal hydride secondary battery as an example of a nickel-metal hydride secondary battery according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Container, 2 ... Positive electrode, 3 ... Separator, 4 ... Negative electrode, 5 ... Electrode group, 7 ... Sealing plate, 8 ... Insulating gasket.

Claims (3)

[Claims] 1. An electrode group having a structure in which a separator is interposed between a positive electrode and a negative electrode containing a hydrogen storage alloy powder, a polymer binder and a conductive powder, the container being housed in the container,
In a nickel-metal hydride secondary battery comprising an alkaline electrolyte, the polymer binder has an average molecular weight of 4,000,000.
-20,000,000 polytetrafluoroethylene, and the conductive powder has a specific surface area of 700 m ^2.
/ G or more of carbon. 2. The polytetrafluoroethylene in the negative electrode contains 0.3 to 2.0 parts by weight of 100 parts by weight of the hydrogen storage alloy.
2. The nickel-metal hydride secondary battery according to claim 1, wherein 0.5 to 2.0 parts by weight of the conductive powder in the negative electrode is added to 100 parts by weight of the hydrogen storage alloy. 3. When the dimension of each member constituting the electrode group in the layer thickness direction in the container is A, and the sum of the layer thicknesses of each member constituting the electrode group is B, The thickness of the members in the layer direction before being stored in the container is set so that a value (B / A) obtained by dividing the B by the A (B / A) is 1 or more. Nickel-metal hydride secondary battery.