JP2000090903A - Secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary battery having long charge/discharge cycle life. SOLUTION: This secondary battery has an electrode group 2 formed by placing a separator 5 between a positive electrode 3 and a negative electrode 4, a container 1 for housing the electrode group 2 and also serving as a terminal, and conductors 6a, 6b which are compressed between at least one portion on the outside of the electrode group 2 and the inside surface of the container 1, returned to a specified shape in charge/discharge, and has elasticity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a secondary battery.

[0002]

2. Description of the Related Art Alkaline secondary batteries such as nickel cadmium secondary batteries and nickel hydrogen secondary batteries, nickel zinc secondary batteries and lithium ion secondary batteries are known as batteries used in portable electronic equipment. ing. As a prismatic nickel-metal hydride secondary battery which is an example of an alkaline secondary battery, one having a structure as illustrated in FIG. 6 is known. That is, the electrode group 22 is housed in the bottomed rectangular cylindrical container 21 also serving as the negative electrode terminal. The electrode group 22 has a structure in which four positive electrodes 23 and five negative electrodes 24 are alternately stacked with a separator 25 interposed therebetween. The outermost layer of the electrode group 22 is the negative electrode 24 and is in contact with the inner surface of the container 21. The alkaline electrolyte is contained in the container 21. A rectangular sealing plate 26 (not shown) having a hole in the center is
Is arranged in the upper opening. Insulating gasket 27
Is formed of a synthetic resin such as nylon, for example, and is disposed between the periphery of the sealing plate 26 and the inner surface of the upper opening of the container 21. The sealing plate 26 is air-tightly fixed to the container 21 via the gasket 27 by caulking to reduce the diameter of the upper opening of the container 21 inward. One end of the positive electrode lead 28 is connected to the positive electrode 23, and the other end is connected to the lower surface of the sealing plate 26.
The positive electrode terminal 29 is mounted on the sealing plate 26 so as to cover the hole. An elastic valve element (not shown) is disposed in a space surrounded by the sealing plate 26 and the positive electrode terminal 29 so as to close the hole.

[0003]

In the prismatic nickel-metal hydride secondary battery having the above-mentioned structure, the positive electrode 23 and the positive electrode terminal 29 are electrically connected by the lead 28. On the other hand, the container 21 also serving as the negative electrode terminal and the negative electrode 24 are electrically connected by the contact of the outermost negative electrode 24 of the electrode group with the inner surface of the container 21. Since the conduction between the negative electrode and the negative electrode terminal (container) is performed by bringing the two into contact with each other, there are the following problems.

In a nickel-hydrogen secondary battery, when the electrode group repeatedly expands and contracts as the charge / discharge reaction progresses, the shapes of the positive and negative electrodes are lost, the elasticity of the separator is reduced, and the like. The group shrinks, creating a gap between the electrode group and the container. As a result, the nickel-hydrogen secondary battery has a problem that the capacity is reduced and the cycle life is shortened because the electrical connection between the negative electrode and the container serving as the negative electrode terminal is insufficient with the progress of the charge / discharge cycle. Is generated.

An object of the present invention is to provide a secondary battery having an improved charge / discharge cycle life.

[0006]

A secondary battery according to the present invention comprises: an electrode group having a structure in which a separator is interposed between a positive electrode and a negative electrode; a container accommodating the electrode group and also serving as a terminal; It is arranged in a compressed state between at least one portion of the outer surface of the electrode group and the inner surface of the container, returns to a predetermined shape at the time of charging and discharging, and has an elastic conductor. Is what you do.

In another secondary battery according to the present invention, an electrode group having a structure in which a positive electrode and a negative electrode are alternately stacked with a separator interposed therebetween, and the outermost layer is a negative electrode, and the electrode group is housed. A bottomed rectangular cylindrical container also serving as a negative electrode terminal, and is disposed between at least one of the outermost layers of the electrode group and the inner surface of the container, and returns to a predetermined shape during charging and discharging, and has a resilient conductor. And characterized in that:

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an example in which the present invention is applied to a prismatic alkaline secondary battery will be described. This prismatic alkaline secondary battery will be described in detail with reference to FIGS.

First, a prismatic alkaline secondary battery in a state where charging and discharging are not performed will be described with reference to FIGS.

As shown in FIG. 1, an electrode group 2 is accommodated in a bottomed rectangular cylindrical container 1 also serving as a negative electrode terminal.
The electrode group 2 has a structure in which four positive electrodes 3 and five negative electrodes 4 are alternately stacked with a separator 5 interposed therebetween. The outermost layer of the electrode group 2 is the negative electrode 4 and is in contact with the inner surface of the container 1. Here, the conductors 6a and 6b before being housed in the container 1 are shown in FIG. As shown in FIG. 2A, the conductors 6a and 6b
Is a leaf spring having a shape in which the center is bent in a V shape.
The conductors 6a and 6b are arranged in a compressed state between the outermost layer of the electrode group 2 and the inner surface of the container 1 so that a bending point contacts the outermost layer. The conductors 6a and 6b have the property of returning to the original shape shown in FIG. The alkaline electrolyte is contained in the container 1. A rectangular sealing plate 7 (not shown) having a hole in the center is arranged at the upper opening of the container 1. The insulating gasket 8 is formed of a synthetic resin such as nylon, for example, and is disposed between the peripheral edge of the sealing plate 7 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 of the container 1 inward. One end of the positive electrode lead 9 is connected to the positive electrode 3, and the other end is connected to the lower surface of the sealing plate 7. The positive electrode terminal 10 is connected to the sealing plate 7.
It is attached so as to cover the hole. An elastic valve element (not shown) is disposed in a space surrounded by the sealing plate 7 and the positive electrode terminal 10 so as to close the hole.

When the secondary battery having the structure shown in FIG. 1 is charged and discharged, the state shown in FIG. 3 is obtained.
That is, the conductors 6a and 6b are bent to return to the shape shown in FIG.
The electrode group 2 is pressed by the conductors 6a and 6b,
The adhesion between the positive electrode 3, the negative electrode 4, and the separator 5 is improved. In addition, since the conductors 6a and 6b which are bent as described above press the inner surface of the container 1,
The adhesion between the conductors 6a and 6b and the inner surface of the container 1 is improved. As a result, the secondary battery is charged and discharged,
The conduction between the container 1 also serving as the negative electrode terminal and the negative electrode 4 can be improved.

Hereinafter, the conductors 6a and 6b, the positive electrode 3, the negative electrode 4, the separator 5, and the alkaline electrolyte will be described in detail.

1) Conductors 6a and 6b The conductors 6a and 6b have a shape in which the center is bent in a V-shape as shown in FIG. It is made of a leaf spring that has the property of returning to the normal state. As shown in FIG. 1 described above, such conductors 6a and 6b are each in a compressed state such that a bending point is in contact with the outermost layer between the outermost layer of the electrode group 2 and the inner surface of the container 1. Be placed.

It is preferable that the conductor returns to its original shape by heat generated when the nickel-hydrogen secondary battery is charged and discharged. The conductor can be formed from, for example, a shape memory alloy, a bimetal, a functional polymer, or the like. In particular, as for the conductor, the temperature at which shape return occurs is 30 ° C.
Those having a temperature in the range of -85 ° C, more preferably 35-75 ° C are preferred. The conductor at which the temperature at which the shape return occurs is 35 to 75 ° C. can be formed from, for example, a Ti—Ni alloy.

The shape of the conductor is as described in FIG.
In addition to the shape described in (a), for example, a corrugated plate shape as shown in FIG. 2B or a zigzag bent shape as shown in FIGS. Can be. In particular, the shape shown in FIG. 2D is preferable because the contact area between the container or the electrode group and the conductor increases.

2) Positive electrode 3 This positive electrode 3 contains nickel hydroxide.

The positive electrode 3 is prepared, for example, by kneading a nickel hydroxide powder, a conductive agent and a binder in the presence of water to prepare a paste, filling the conductive substrate with the paste, drying, and rolling. It is manufactured by performing molding.

As the nickel hydroxide powder, for example, a powder composed of nickel hydroxide or a nickel hydroxide powder in which zinc and cobalt are eutectic can be used. The latter positive electrode containing nickel hydroxide powder can improve charge efficiency and charge / discharge cycle characteristics in a high temperature state.

As the conductive agent, at least one selected from a cobalt compound and metallic cobalt can be used. Examples of the cobalt compound include cobalt monoxide and cobalt hydroxide.
Also, instead of adding the conductive agent to the paste,
The surface of the nickel hydroxide powder may be coated with at least one selected from a cobalt compound and metallic cobalt, and this may be added to the paste.

Examples of the binder include fluorine resins such as polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), polyacrylates (eg, sodium polyacrylate, potassium potassium acrylate), acrylic Copolymer of acid and vinyl alcohol, copolymer of acrylate and vinyl alcohol, water-soluble cellulose derivative (for example, methyl cellulose (MC),
One or more selected from carboxymethylcellulose (CMC), hydroxypropylmethylcellulose (HPMC)), polyacrylamide (PA), polyvinylpyrrolidone (PVP), polyethylene oxide (PEO) and the like can be used.

Examples of the conductive substrate include a two-dimensional substrate such as a punching metal and an expanded metal, a fibrous metal porous body (non-plating type) by chattering vibration, a sponge-like metal porous body of a plating type, and a felt. A three-dimensional substrate such as a porous metal body can be used.

3) Negative electrode 4 This negative electrode 4 contains a hydrogen storage alloy.

The negative electrode 4 is prepared by, for example, kneading a hydrogen storage alloy powder, a conductive material and a binder together with pure water to prepare a paste, applying the paste to a conductive substrate, drying the paste, and then rolling and forming the paste. It is manufactured by doing.

The hydrogen storage alloy is not particularly limited, as long as it can store hydrogen electrochemically generated in an electrolytic solution and can easily release the stored hydrogen during discharge. For example, LaNi ₅ , MmNi
₅ (Mm is Misch metal enriched in Ce), LmNi ₅
(Lm is La-enriched misch metal), and part of Ni of these alloys is Al, Mn, Co, Ti, Cu, Zn, Z
multi-elements substituted with elements such as r, Cr, B,
Alternatively, TiNi-based and TiFe-based materials can be used. In particular, the general formula _{LmNi w Co x Mn y Al z} ( atomic ratio w, x, y, the total value of z is 5.00 ≦ w + x + y +
a hydrogen storage alloy having a composition represented by z ≦ 5.50) or a general formula AB _x (where A is Ti and / or Zr, and B is Mn, Ni, V, Co, Cr, A
and at least one element selected from the group consisting of 1, Fe, Cu, Mo, La, Ce, Pr, and Nd, and x is 1.8 ≦ x ≦
It is preferable to use a hydrogen storage alloy represented by the following formula (2.5), wherein the main component of the alloy phase is a C14 or C15 Laves phase.

Examples of the conductive material include carbon black and graphite.

As the binder, one or more selected from the polymers described above for the positive electrode can be used.

Examples of the conductive substrate include a two-dimensional substrate such as a punched metal, an expanded metal and a nickel net, and a three-dimensional substrate such as a felt-like metal porous body and a sponge-like metal porous body. it can.

4) Separator 5 As the separator 5, a non-woven fabric made of a polyamide fiber or a non-woven fabric made of a polyolefin fiber such as polyethylene or polypropylene provided with a hydrophilic functional group can be used.

5) Alkaline Electrolyte As the alkaline electrolyte, for example, potassium hydroxide (KOH) alone or sodium hydroxide (Na)
OH) and lithium hydroxide (LiOH), or an aqueous solution having a composition to which both are added.

As described in detail above, the secondary battery according to the present invention includes an electrode group having a structure in which a separator is interposed between a positive electrode and a negative electrode, a container in which the electrode group is housed, and which also serves as a terminal; An elastic conductor is disposed between at least one of the outer surfaces of the electrode group and the inner surface of the container in a compressed state, and returns to a predetermined shape when charged and discharged, and has elasticity. The conductor arranged in a compressed state between the electrode group and the container as illustrated in FIG. 1 described above tries to return to a predetermined shape at the time of charging and discharging. In addition, the electrode group can be pressed during charging and discharging to increase the adhesion between the positive and negative electrodes and the separator, and the inner surface of the container can be pressed to improve the adhesion to the side surface. Further, since the conductor has elasticity, it can be deformed following expansion and contraction of the electrode group during charge and discharge, and does not hinder the expansion and contraction reaction of the electrode group. As a result, the secondary battery can secure a desired degree of tightness and conductivity in the electrode group from the beginning of the charge / discharge cycle, so that excellent charge / discharge characteristics can be realized. When the charge and discharge cycle is repeated, the electrode group gradually shrinks, but the conductor attempts to return to a predetermined shape each time the charge and discharge cycle is performed. Can maintain the degree of tightness and conductivity. As a result, a secondary battery having an excellent charge / discharge cycle life can be realized.

In another secondary battery according to the present invention, an electrode group having a structure in which a positive electrode and a negative electrode are alternately stacked with a separator interposed therebetween, and the outermost layer is a negative electrode, and the electrode group is housed. And a bottomed rectangular cylindrical container also serving as a negative electrode terminal,
It is arranged between at least one of the outermost layers of the electrode group and the inner surface of the container, and returns to a predetermined shape during charge and discharge,
And an elastic conductor. According to such a secondary battery, the electrode group can maintain a desired degree of tightness and conductivity for a long period of time from the initial stage of the charge / discharge cycle. Discharge cycle life can be improved.

[0032]

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

[0033] (Example 1) <Production of Negative Electrode> composition LmNi _5.0-xyz Co _x Mn _y
0.5 part by weight of sodium polyacrylate to 100 parts by weight of the hydrogen storage alloy powder represented by al _z, carboxymethyl cellulose (CMC) 0.12 parts by weight, dispersion (specific gravity 1.5 of polytetrafluoroethylene solids 60 parts by weight) and 1.0 part by weight of carbon black as a conductive material were added thereto, and mixed with 30 parts by weight of water to prepare a paste. These pastes were applied to a punched metal as a conductive substrate, dried, and pressed to produce a negative electrode.

<Preparation of Positive Electrode> A mixed powder comprising 90 parts by weight of nickel hydroxide powder and 10 parts by weight of cobalt monoxide powder was mixed with 0.3 parts of carboxymethyl cellulose (CMC).
A paste was prepared by adding 0.5 parts by weight of a polytetrafluoroethylene dispersion (specific gravity 1.5, solid content 60% by weight) in terms of solid content and mixing with 45 parts by weight of pure water. . Subsequently, the paste was filled in a foamed nickel substrate, dried, and then rolled by roller pressing to produce a positive electrode.

A separator made of a nonwoven fabric made of polyamide fiber was folded in two and molded into an envelope, and the positive electrode was stored in the envelope.

Next, an electrode group was prepared by alternately stacking the five negative electrodes and the four positive electrodes housed in the separator such that the outermost layer was the negative electrode. In the outermost layer of the electrode group, a conductor made of a shape memory alloy (Ti-Ni alloy) having the structure shown in FIG. Each was arranged so that it might contact an outer layer. The electrode group thus sandwiched between the two conductors is housed in a bottomed rectangular cylindrical container also serving as a negative electrode terminal, and the two conductors are placed between the outermost layer of the electrode group and the inner surface of the container. Placed in a compressed state. An electrolytic solution composed of 7N potassium hydroxide and 1N lithium hydroxide is accommodated in such a container, and the container is sealed and the like, thereby having the structure shown in FIG. 1 described above and having a theoretical capacity of 650 mAh. A hydrogen secondary battery was assembled.

(Embodiment 2) The outermost layer of the laminated electrode group having the same structure as in Embodiment 1 has the structure shown in FIG. 2B described above and is made of the same type of shape memory alloy as in Embodiment 1. Conductors were arranged. The electrode group thus sandwiched between the two conductors is housed in a bottomed rectangular cylindrical container also serving as a negative electrode terminal, and the two conductors are placed between the outermost layer of the electrode group and the inner surface of the container. Placed in a compressed state. A prismatic nickel-metal hydride secondary battery having the structure shown in FIG. 1 described above by containing an alkaline electrolyte having the same composition as in Example 1 in such a container and performing sealing or the like, and having a theoretical capacity of 650 mAh. Was assembled.

(Embodiment 3) The outermost layer of the laminated electrode group having the same structure as in Embodiment 1 has the structure shown in FIG. 2C described above, and is made of the same type of shape memory alloy as in Embodiment 1. Conductors were arranged. The electrode group thus sandwiched between the two conductors is housed in a bottomed rectangular cylindrical container also serving as a negative electrode terminal, and the two conductors are placed between the outermost layer of the electrode group and the inner surface of the container. Placed in a compressed state. A prismatic nickel-metal hydride secondary battery having the structure shown in FIG. 1 described above by containing an alkaline electrolyte having the same composition as in Example 1 in such a container and performing sealing or the like, and having a theoretical capacity of 650 mAh. Was assembled.

(Embodiment 4) The outermost layer of the laminated electrode group having the same structure as in Embodiment 1 has the structure shown in FIG. 2D described above, and is made of the same type of shape memory alloy as in Embodiment 1. Conductors were arranged. The electrode group thus sandwiched between the two conductors is housed in a bottomed rectangular cylindrical container also serving as a negative electrode terminal, and the two conductors are placed between the outermost layer of the electrode group and the inner surface of the container. Placed in a compressed state. A prismatic nickel-metal hydride secondary battery having the structure shown in FIG. 1 described above by containing an alkaline electrolyte having the same composition as in Example 1 in such a container and performing sealing or the like, and having a theoretical capacity of 650 mAh. Was assembled.

(Comparative Example) After a laminated electrode group having the same structure as in Example 1 was housed in a bottomed rectangular cylindrical container also serving as a negative electrode terminal, an alkaline electrolyte having the same composition as in Example 1 was housed.
By performing sealing and the like, a prismatic nickel-metal hydride secondary battery having the structure shown in FIG. 1 and having a theoretical capacity of 650 mAh was assembled.

The obtained secondary batteries of Examples 1 to 4 and Comparative Example were charged at a current of 130 mA for 90 minutes, and charged.
After leaving it for 0 minutes, a voltage of 1.0 V throughout with a current of 650 mA
The battery voltage when the battery was discharged to the maximum was measured, and the result is shown in FIG.

As is clear from FIG. 4, the secondary batteries of Examples 1 to 4 have a higher voltage at the time of discharge than the secondary batteries of the comparative examples, and can suppress a decrease in the battery voltage at the time of discharge. Understand.

The secondary batteries of Examples 1 to 4 and Comparative Example were charged with a current of 130 mA for 90 minutes, left for 30 minutes, and then repeatedly charged and discharged with a current of 650 mA to a voltage of 1.0 V throughout. The discharge capacity in each cycle was measured, and the results are shown in FIG.

As is apparent from FIG. 5, the secondary batteries of Examples 1 to 4 have a longer charge / discharge cycle life than the secondary batteries of the comparative example.

In the above-described embodiment, the conductor is disposed on both outermost layers of the electrode group. However, the conductor may be disposed on only one of the outermost layers of the electrode group.

In the above-described embodiment, an example in which the present invention is applied to a prismatic nickel-metal hydride secondary battery has been described. However, the present invention can be similarly applied to a cylindrical nickel-metal hydride secondary battery. In this case, a group of electrodes wound spirally so that the outermost periphery becomes a negative electrode is accommodated in a bottomed cylindrical container with a separator interposed between the positive electrode and the negative electrode, and the electrode group and the inner surface of the container ( Between the inner peripheral surface), a leaf spring having a folding screen type and having a property of returning to the original shape at the time of charging and discharging may be arranged in a compressed state.

[0047]

As described in detail above, according to the present invention,
A secondary battery having excellent charge / discharge cycle life can be provided.

[Brief description of the drawings]

FIG. 1 is a partially cutaway sectional view showing an example of a secondary battery (for example, a prismatic alkaline secondary battery) according to the present invention.

FIG. 2 is a side view showing a specific example of a conductor incorporated in the secondary battery of FIG.

FIG. 3 is a cross-sectional view showing a state of the secondary battery of FIG. 1 during charge and discharge.

FIG. 4 is a characteristic diagram showing a relationship between a discharge time and a battery voltage in the prismatic nickel-metal hydride secondary batteries of Examples 1 to 4 and Comparative Example.

FIG. 5 is a characteristic diagram showing the relationship between the number of charge / discharge cycles and the discharge capacity in the prismatic nickel-metal hydride secondary batteries of Examples 1 to 4 and Comparative Example.

FIG. 6 is a sectional view showing a conventional prismatic nickel-metal hydride secondary battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Container, 2 ... Electrode group, 3 ... Positive electrode, 4 ... Negative electrode, 5 ... Separator, 6a, 6b ... Conductor, 7 ... Sealing plate, 8 ... Insulating gasket.

Claims (2)

[Claims] 1. An electrode group having a structure in which a separator is interposed between a positive electrode and a negative electrode, a container accommodating the electrode group and also serving as a terminal, and at least one location on an outer surface of the electrode group and the container. Placed in a compressed state with the inner surface of the
A rechargeable battery comprising: a conductor that returns to a predetermined shape when charged and discharged and has elasticity. 2. An electrode group having a structure in which a positive electrode and a negative electrode are alternately laminated with a separator interposed therebetween, and the outermost layer is a negative electrode, and a bottomed rectangular tubular housing the electrode group and serving also as a negative electrode terminal. A container, which is disposed between at least one of the outermost layers of the electrode group and the inner surface of the container, returns to a predetermined shape at the time of charging and discharging, and includes an elastic conductor. Rechargeable battery.