JP2001273874A - Rectangular alkaline secondary battery - Google Patents

Abstract

(57) [Problem] To provide a prismatic alkaline secondary battery having a high volume energy density and a long charge / discharge cycle life. SOLUTION: A metal container 1 having a rectangular cross section,
In a prismatic alkaline secondary battery including an electrode group 5 containing a positive electrode 3 and a negative electrode 4 containing nickel hydroxide and contained in the container 1 and an alkaline electrolyte contained in the container 1, The secondary battery has a volume energy density of 15
0 WH / L or more, the hardness of the container 1 is 120 HV1 or more, and the thickness of the container 1 is 0.20 to 0.40 mm.
It is characterized by being within the range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a prismatic alkaline secondary battery.

[0002]

2. Description of the Related Art With the recent development of electronic equipment, the demand for a battery as a driving power source for the equipment has been increasing. Among these batteries, alkaline secondary batteries such as nickel-hydrogen secondary batteries and nickel-cadmium secondary batteries are widely used as power sources for personal computers and mobile phones.
Cylindrical and prismatic alkaline secondary batteries are known. The cylindrical alkaline secondary battery has a structure in which an electrode group in which a separator is interposed between a positive electrode containing nickel hydroxide as an active material and a negative electrode, and an alkaline electrolyte are accommodated in a bottomed cylindrical container. On the other hand, the prismatic alkaline secondary battery has a structure in which an electrode group in which a separator is interposed between a positive electrode and a negative electrode containing nickel hydroxide as an active material and an alkaline electrolyte are contained in a bottomed rectangular cylindrical container. .

[0003] The positive electrode of an alkaline secondary battery has the property of swelling during overcharge and as the charge / discharge cycle progresses. Since the container of the cylindrical alkaline secondary battery has a bottomed cylindrical shape as described above, the container has high shape retention against internal stress. Therefore, in the cylindrical alkaline secondary battery, swelling of the positive electrode is suppressed by the container. On the other hand, the container of the prismatic alkaline secondary battery is a bottomed rectangular tube having a rectangular cross section, so that when an internal stress such as swelling of the positive electrode is applied, the side surface on the long side is easily curved, and the Promotes swelling. When the positive electrode swells, voids increase in the positive electrode, and the electrolyte in the separator moves to the voids, so that the amount of electrolyte retained in the separator decreases. As a result, the internal resistance of the secondary battery increases as the charge / discharge cycle progresses, so that the charge / discharge cycle life is shortened. In addition, the size of the battery deviates from the standard value due to the deformation of the container due to the swelling of the positive electrode, causing a problem that the battery cannot be incorporated into the electronic device.

[0004] In view of the above, in the prismatic alkaline secondary battery, the swelling of the positive electrode is achieved by making the thickness of the container about 1.5 to 2 times larger than the thickness of the container of the cylindrical alkaline secondary battery. It has been done to suppress.

[0005] Incidentally, the prismatic alkaline secondary battery has an advantage that the volume efficiency of the assembled battery is superior to that of the cylindrical alkaline secondary battery. For this reason, demand has been increasing in recent years, and there is a demand for improving the volume energy density.

[0006]

However, since the container of the prismatic alkaline secondary battery has a small inner volume due to the large thickness, when the volume of the electrode group increases with an increase in the volume energy density, the electrolytic solution storage Insufficient space makes it impossible to inject a sufficient amount of alkaline electrolyte. As a result, the depletion of the alkaline electrolyte in the separator is apt to proceed, which causes a problem that the cycle life is shortened.

An object of the present invention is to provide a rectangular alkaline secondary battery having a high volume energy density and a long charge / discharge cycle life.

[0008]

SUMMARY OF THE INVENTION The present invention comprises a metal container having a rectangular cross section, an electrode group housed in the container and including a positive electrode and a negative electrode containing nickel hydroxide, and In the prismatic alkaline secondary battery including the contained alkaline electrolyte, the secondary battery has a volume energy density of 150 WH / L or more, and the hardness of the container is 12 WH / L.
0 HV1 or more, and the thickness of the container is 0.20-0.
A prismatic alkaline secondary battery characterized by being within a range of 40 mm.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A prismatic alkaline secondary battery according to the present invention comprises a metal container having a rectangular cross section, a separator housed in the container, and a positive electrode and a negative electrode containing nickel hydroxide. It comprises an electrode group interposed and an alkaline electrolyte contained in the container.

The volume energy density of the secondary battery is 15
0 WH / L or more. This volume energy density C (W
H / L) is defined by the following equation.

C = (C _T × Z) / V (1) where C _T (Ah) is the theoretical capacity of the secondary battery and Z (V)
Represents the voltage of the secondary battery, and V (L) represents the volume of the secondary battery (volume obtained from the external dimensions of the secondary battery).

The hardness of the container is 120 HV1 or more, and the thickness of the container is in the range of 0.20 to 0.40 mm.

The electrode group may be manufactured by alternately stacking a positive electrode containing nickel hydroxide and a negative electrode with a separator interposed therebetween, or alternatively, the positive electrode and the negative electrode may be separated by a separator. It is produced by spirally winding while being interposed, and then press-molding into a flat shape.

The container, positive electrode, negative electrode, separator and alkaline electrolyte will be described.

1) Container The container having a rectangular cross section is, for example, a container C having a rectangular cylinder with a bottom as shown in FIG. 1, a rectangular cylinder with a bottom having a step portion having an inwardly projecting shape. And the like.

In the present application, the thickness of the container means the thickness of a metal plate constituting the container. For example, in FIG. 1, T is the thickness of the container.

The reason for limiting the thickness of the container to the above range is as follows. When the plate thickness is less than 0.2 mm, the container tends to swell due to internal stress when the positive electrode swells, and it becomes difficult to suppress the swelling of the positive electrode, so that a long life cannot be obtained. On the other hand, when the plate thickness is 0.
If it exceeds 4 mm, although the resistance of the container to internal stress increases and the swelling of the positive electrode can be suppressed, the volume in the container becomes small, and a sufficient amount of the alkaline electrolyte cannot be injected. Long life cannot be obtained. The more preferable range of the plate thickness is 0.25 to 0.38 m
m.

The reason why the hardness of the container is defined in the above range is as follows. When the hardness is less than 120 HV1, the container tends to swell due to internal stress when the positive electrode swells, and it becomes difficult to suppress the swelling of the positive electrode, so that a long life cannot be obtained. A more preferable range of the hardness is 150 HV1 or more, and a further preferable range is 160 HV1 or more. The upper limit of the hardness is 190
HV1 is preferred.

2) Positive electrode This positive electrode contains nickel hydroxide.

For the positive electrode, for example, a paste containing an active material containing nickel hydroxide, a conductive agent, a binder and water is prepared, and the paste is filled in a current collector, which is dried and pressed. It is produced by doing. The conductive agent can be added to the paste as a powder or as a coating covering the surface of the active material.

Examples of the active material containing nickel hydroxide as a main component include nickel hydroxide particles, zinc,
Nickel hydroxide particles in which at least one metal selected from cobalt, bismuth and copper is eutectic can be used.

As the conductive agent, for example, at least one selected from cobalt and a cobalt compound can be used. Examples of the cobalt compound include dicobalt trioxide (Co ₂ O ₃ ), cobalt monoxide (CoO), and cobalt hydroxide {Co (OH) ₂ }.

Examples of the binder include carboxymethylcellulose, methylcellulose, sodium polyacrylate, polytetrafluoroethylene, and polyvinyl alcohol.

The current collector may be a two-dimensional substrate such as a mesh-like, sponge-like, fiber-like, or felt-like porous metal body made of nickel, stainless steel, or nickel-plated metal, or punched metal. Having irregularities on the periphery of the hole.

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

The negative electrode is prepared, for example, by kneading a hydrogen storage alloy powder together with a conductive agent, a binder and water to prepare a paste, filling the paste into a conductive substrate, drying, and then molding. Manufactured.

The hydrogen storage alloy is not particularly limited, and may be any 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), LmNi ₅ (Lm is La
At least one element selected from the group consisting of rare earth elements containing Al, Mn, Co, Ti, and C.
Examples thereof include a multi-element-based material substituted with an element such as u, Zn, Zr, Cr, and B, or a TiNi-based or TiFe-based material. In particular, the general formula LmNi _w Co _x Mn _y
Al _z (the total value of atomic ratios w, y, and z is 5.00 ≦ w + x
+ Y + z ≦ 5.5) The hydrogen storage alloy having the composition represented by the following formula (1) is preferable because the charge-discharge cycle life can be improved.

Examples of the conductive agent include carbon black and graphite.

Examples of the binder include polyacrylates such as sodium polyacrylate and potassium polyacrylate, fluorine resins such as polytetrafluoroethylene (PTFE), and carboxymethyl cellulose (CM).
C) and the like.

Examples of the conductive substrate include a two-dimensional substrate such as a punched metal, an expanded metal, a nickel net, and a nickel plate, and a three-dimensional substrate such as a felt-like porous metal or a sponge-like porous metal. Can be mentioned.

4) Separator As the separator, for example, a nonwoven fabric made of polyamide fiber or a nonwoven fabric made of 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, an aqueous solution of sodium hydroxide (NaOH), 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.

FIG. 2 shows an example of the prismatic alkaline secondary battery according to the present invention.

The metal container 1 also serving as the negative electrode terminal and having a rectangular cross section has a thickness of 0.2 to 0.4 mm.
Hardness is 120 HV1 or more. The container 1 has a bottomed rectangular cylindrical shape having a bent portion 1a formed by bending an upper end of an opening inward and a stepped portion 1b formed at the lower end of the opening and projecting inward. . In the container 1, an electrode group in which positive electrodes 3 and negative electrodes 4 housed in the bag-shaped separator 2 are alternately stacked is housed such that the stacking direction is orthogonal to the longitudinal direction of the container 1. ing. The outermost negative electrode 4 of the electrode group is in contact with the inner surface of the container 1. The alkaline electrolyte is contained in the container 1. A sealing member 6 serving both as an explosion-proof function and a positive electrode terminal is fixed by caulking to the opening of the container 1 via an insulating gasket 7, and has a rectangular sealing plate 9 having a gas vent hole 8 at the center, and A protruding positive electrode terminal 10 arranged to surround the gas vent hole 8;
And an elastic valve element 11 arranged in a compressed state so as to close the gas vent hole 8 in a space surrounded by the positive electrode terminal 10. The positive electrode terminal 10 is provided with a plurality of gas vent holes 12. One end of the positive electrode lead 13 is connected to the positive electrode 3, and the other end is connected to the lower surface of the sealing plate 9.

According to the present invention described above, a metal container having a rectangular cross section, an electrode group housed in the container and including a positive electrode and a negative electrode containing nickel hydroxide, and an electrode group housed in the container The secondary battery has a volume energy density of 150 WH / L or more, a hardness of the container of 120 HV1 or more, and a thickness of the container of 0.20 or more.
When the thickness is in the range of about 0.40 mm, a rectangular alkaline secondary battery having a high capacity and a long life can be provided.

That is, since a container having a hardness of 120 HV1 or more and a plate thickness of 0.20 to 0.40 mm has a high internal volume, a sufficient amount of alkali is required when the volume energy density is 150 WH / L or more. An electrolyte can be accommodated. Further, this container is hardly deformed by internal stress, and can suppress swelling of the electrode group having a volume energy density of 150 WH / L or more. As a result, since the internal resistance can be suppressed from increasing with the progress of the charge / discharge cycle, the charge / discharge cycle life can be improved, and a high-capacity, long-life rectangular alkaline secondary battery can be obtained. Can be provided.

[0037]

Embodiments of the present invention will be described below in detail with reference to the drawings.

Example 1 <Preparation of Positive Electrode> A mixed powder consisting of 90 parts by weight of nickel hydroxide powder and 7.5 parts by weight of cobalt hydroxide powder was added to 0.3 parts of carboxymethyl cellulose with respect to the nickel hydroxide powder. Parts by weight and dispersion of polytetrafluoroethylene (specific gravity 1.5, solid content 60% by weight)
A paste was prepared by adding 1.5 parts by weight, adding 30 parts by weight of pure water thereto and mixing. Subsequently, the paste was filled in a nickel-plated foamed metal substrate, dried, and then roll-pressed to form a paste-type positive electrode.

<Preparation of Negative Electrode> A commercially available hydrogen-absorbing alloy of MmNi _3.6 Co _0.8 Mn _0.4 Al _0.2 was prepared using a commercially available lanthanum-enriched misch metal Mm, Ni, Co, Mn, and Al in a high-frequency furnace. The hydrogen storage alloy is mechanically pulverized, and a dispersion of sodium polyacrylate 0.4 part by weight, carboxymethyl cellulose (CMC) 0.1 part by weight, and polytetrafluoroethylene with respect to 100 parts by weight of the obtained hydrogen storage alloy powder. (Specific gravity 1.5, solid content 60% by weight), 1.5 parts by weight in terms of solid content, 0.8 parts by weight of carbon powder and 55 parts by weight of water were added and kneaded to prepare a paste. Each paste was applied to a punched metal as a conductive substrate, dried, and then subjected to pressure molding with a roller press to produce a negative electrode.

<Separator> A nonwoven fabric made of long fibers having an average diameter of 3 μm, a basis weight of 42 g / m ² and a thickness of 0.18 mm was prepared from a polypropylene resin by a melt blow method. The nonwoven fabric is immersed in an aqueous solution of acrylic acid, irradiated with ultraviolet light to graft polymerize the acrylic acid monomer, washed to remove unreacted acrylic acid, and then dried to obtain a carboxyl group (COOH) as an ion exchange group. ) Was obtained.

The obtained paste-type positive electrode was covered with the separator. Such a positive electrode and a negative electrode were alternately laminated such that the outermost layer became the negative electrode, to prepare an electrode group. The electrode group is placed in a bottomed rectangular cylindrical container having an opening, a step formed below the opening by expanding the opening, and a body present below the step. Was stored. At this time, the negative electrode in the outermost layer of the electrode group was brought into contact with the inner surface on the long side of the container. The container was made of steel having a grade specified by JIS standards of SPCC-SB, and had the hardness and plate thickness shown in Table 1 below.

Next, 7 mol / m ³ of K was placed in the container.
An alkaline electrolyte composed of OH and 1 mol / m ³ LiOH was injected in an amount occupying 30% of the volume in the container. The injection amount at this time was 1.08 cm ³ as shown in Table 1 below. However, the container internal volume V is calculated by the following equation (1).

V (cm ³ ) = (L ₁ −2T) × (L ₂ −2T) × H (1) In the formula (1), L ₁ is the width of the outer diameter of the container on the long side. Where L ₂ is the width of the shorter side of the outer diameter of the container,
T is the thickness of the container, and H is the height inside the container.

Subsequently, a member (sealing member) in which a sealing member also serving as an explosion-proof function and a positive electrode terminal was housed in an insulating gasket was prepared, and after connecting the sealing member and the positive electrode housed in the container with a lead, The closure was placed on the step in the container. Then, after reducing the diameter of the opening of the container, the upper end of the opening is bent inward to fix the sealing member to the opening of the container via the insulating gasket, and the structure shown in FIG. Having a volume energy density of 150 WH / L and a height of 47.5 m.
m, a prismatic nickel-metal hydride secondary battery having a long width of 16.5 mm and a short width (battery thickness) of 5.6 mm.

(Examples 2 and 3) A prismatic nickel-metal hydride secondary battery was assembled in the same manner as described in Example 1 except that the thickness of the container was changed as shown in Table 1 below.

(Examples 4 and 5) A prismatic nickel-metal hydride secondary battery was manufactured in the same manner as described in Example 1 except that the thickness and hardness of the container were changed as shown in Table 1 below. Assembled.

Comparative Example 1 A prismatic nickel-metal hydride secondary battery was assembled in the same manner as described in Example 1 except that the container hardness and the container plate thickness were changed as shown in Table 1 below. .

Comparative Example 2 A square nickel metal hydride secondary battery was prepared in the same manner as in Example 1 except that the container hardness, the container plate thickness, and the volume energy density were changed as shown in Table 1 below. The battery was assembled.

(Comparative Example 3) The same as in Comparative Example 2 described above except that the volume energy density was changed as shown in Table 1 below.
A prismatic nickel-metal hydride secondary battery was assembled in the same manner as described above.

Regarding the obtained secondary batteries of Examples 1 to 5 and Comparative Examples 1 to 3, 1 CmA in an atmosphere of 25 ° C.
After charging the battery at −ΔV (10 mV), the battery was repeatedly charged and discharged at 1 CmA until the battery voltage reached 1.0 V, the cycle life was measured, and the results are shown in Table 1 below. However, the discharge capacity for each cycle is as follows:
Calculated from the time to reach. The cycle life was defined as the number of cycles at which the discharge capacity decreased to 80% in the first cycle.

Further, the discharge capacity is reduced to 80% in the first cycle.
The amount of change in the battery thickness at the time of the cycle when the battery life was lowered was measured.

[0052]

[Table 1]

As is clear from Table 1, the hardness is 120H.
The secondary batteries of Examples 1 to 5 including a container having a plate thickness of 0.20 to 0.40 mm and having a plate thickness of 0.20 to 0.40 mm and a volume energy density of 150 WH / L or more have a small deformation of the container and a cycle. It can be seen that the life is long.

On the other hand, it is understood that the secondary battery of Comparative Example 1 provided with a container having a hardness lower than 120 HV1 and a plate thickness smaller than 0.20 mm has a large amount of deformation of the container and a short cycle life. Comparative Example 3 provided with a container having a hardness lower than 120 HV1 and a plate thickness larger than 0.40 mm
It can be seen that the secondary battery has a small amount of electrolyte that can be accommodated and has a short cycle life. Furthermore, it is understood from Comparative Example 2 that when the volume energy density is lower than 150 WH / L, a long life can be obtained even with a thick container as in Comparative Example 3.

In the above-described embodiment, an example was described in which the present invention was applied to a square alkaline secondary battery which was sealed using a bottomed rectangular cylindrical container having an inwardly projecting step, and which was sealed. The present invention can be similarly applied to a square alkaline secondary battery that is laser-sealed using a bottomed rectangular cylindrical container.

[0056]

As described in detail above, according to the prismatic alkaline secondary battery of the present invention, a high capacity can be achieved,
In addition, remarkable effects such as improvement of the charge / discharge cycle life can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of a container included in a prismatic alkaline secondary battery according to the present invention.

FIG. 2 is a partially cutaway sectional view showing an example of the prismatic alkaline secondary battery according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Container, 2 ... Separator, 3 ... Positive electrode, 4 ... Negative electrode, 5 ... Electrode group, 6 ... Sealing member which doubles as an explosion-proof function and a positive electrode terminal, 7 ... Insulating gasket.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hiroyuki Shibaoka 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo Toshiba Battery Corporation F-term (reference) 5H011 AA01 BB04 CC06 KK01 KK07 5H028 AA07 HH00 HH05 HH10

Claims (1)

[Claims] 1. A metal container having a rectangular cross section, an electrode group housed in the container and containing a positive electrode and a negative electrode containing nickel hydroxide, and an alkaline electrolyte solution housed in the container. In the prismatic alkaline secondary battery provided, a volume energy density of the secondary battery is 150 WH / L or more, a hardness of the container is 120 HV1 or more, and a plate thickness of the container is in a range of 0.20 to 0.40 mm. A prismatic alkaline secondary battery characterized by the following.