JPH11149938A - Nickel hydrogen secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent liquid leakage during storage and fast power charge by housing and sealing a positive electrode, a negative electrode, and a separator in a bottomed cylindrical container and making an actual volume of the positive and negative electrodes and the separator excluding a cavity part to this sealed container after sealing a specific ratio. SOLUTION: In a bottomed cylindrical container 1, an electrode group 5 fabricated by laminating a positive electrode 2, a separator 3a, and a negative electrode 4 each other, and winding them in spiral shape is housed. The negative electrode 4 is disposed in the outer-most periphery of the electrode group 5, and is brought into electrical contact with the container 1, and an alkali electrolyte is housed in the container 1. A first circular sealing plate 7 having a hole 6 at its center is disposed at the top opening of the container 1, and the sealing plate 7 is fixed with air tightness in the container 1 via a ring-shaped insulation gasket 8 by means of caulking process in which this top opening diametrically is contracted is inwardly. With this arrangement, the actual volume of the positive and negative electrodes 2 and 4 and the separator 3a excluding the cavity part is 50 to 70% to the volume of the container 1, more preferably, 55 to 65%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nickel-metal hydride secondary battery.

[0002]

2. Description of the Related Art A nickel-cadmium secondary battery has been conventionally known. In recent years, lighter weight and higher capacity are possible compared with this secondary battery, and LaNi ₅ and CaNi which reversibly occlude and release hydrogen, which is a negative electrode active material, at a low pressure are particularly available.
Nickel-metal hydride secondary batteries comprising a negative electrode containing a hydrogen storage alloy such as ₅ and a positive electrode containing a nickel compound such as nickel hydroxide have been developed and put into practical use.

When the hydrogen storage alloy in the negative electrode is used as a negative electrode and a suitable positive electrode such as a nickel electrode is used as a counter electrode in an alkaline electrolyte, the negative electrode itself absorbs hydrogen generated during charging and occludes hydrogen during discharging. As the hydrogen is released, the hydrogen gas is oxidized and returns to the original water. For this reason, the nickel-hydrogen secondary battery can store a large amount of hydrogen in the hydrogen storage alloy of the negative electrode, so that the capacity can be increased.

In order to further increase the capacity in a limited battery capacity, it is necessary to increase the amount of the active material of the positive electrode and the amount of the electrolytic solution in order to increase the amount of oxidation-reduction reaction involved in charging and discharging. is there. As a method for responding to such a high capacity, a reduction in the basis weight and volume of the separator has been conventionally studied.

[0005] However, the following problems arise as the weight per unit area and volume of the separator are reduced. 1) When manufacturing an electrode group, there is an increased risk that a burr of a positive electrode or a negative electrode penetrates through the separator and comes into contact with a counter electrode to cause an internal short circuit.

2) The amount of electrolyte held between the positive electrode and the negative electrode required for the oxidation-reduction reaction, that is, the amount of electrolyte held by the separator is reduced, so that the charge / discharge cycle life is shortened. Since the problems 1) and 2) described above hinder the stability of battery production and quality, there is a limit to reducing the basis weight and volume of the separator.

[0007] Therefore, in order to obtain a battery having a high capacity, it is necessary to increase the amount of the active material of the positive and negative electrodes. However, an increase in the amount of the active material is accompanied by an increase in the volume of the electrode group including the positive and negative electrodes and the separator, so that the amount of the injectable electrolytic solution is reduced, and the capacity is deteriorated as the charge and discharge cycle progresses. Further, if the injection amount of the electrolyte is increased to a possible amount in the container, there is a problem that the liquid leaks during long-term storage at a high temperature or rapid charging.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a nickel-hydrogen secondary battery suitable for increasing the capacity and capable of preventing the occurrence of liquid leakage during storage and rapid charging. is there.

[0009]

A nickel-metal hydride secondary battery according to the present invention is a nickel-metal hydride secondary battery in which a positive electrode, a negative electrode and a separator are housed in a bottomed cylindrical container and an alkaline electrolyte is housed. The actual volume (excluding voids) of the positive and negative electrodes and the separator occupies 50 to 70% of the volume of the container after closure. That is, assuming that the volume of the container after sealing is V ₁ and the actual volumes of the positive and negative electrodes and the separator are V ₂ (excluding voids), the actual volume is (V ₂ / V ₁ ) × 100 = 50.
Satisfies the equation of ~ 70%.

[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 produced by stacking the positive electrode 2, the separator 3, and the negative electrode 4 and winding them in a spiral shape is accommodated in the bottomed cylindrical container 1.
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 disposed 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 formed on the container 1 by caulking to reduce the diameter of the upper opening inward. 7 is hermetically 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. The positive electrode terminal 10 having a hat shape is attached 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. A circular holding plate 12 made of an insulating material having a hole in the center is arranged on the positive electrode terminal 10 such that a protrusion of the positive electrode terminal 10 projects from the hole of the holding plate 12. 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.

The actual volumes of the positive and negative electrodes 2 and 4 and the separator 3 (excluding voids) are 50 to 70 with respect to the volume of the container.
%. If the actual volume is less than 50%, it becomes difficult to obtain a high capacity secondary battery. On the other hand, if the actual volume exceeds 70%, leakage may occur when gas is generated during a charge / discharge cycle or the like. A more preferable actual volume is 55 to 65%.

Next, the positive electrode 2, the negative electrode 4, the separator 3
And the electrolyte will be described. 1) Positive Electrode 2 The positive electrode 2 contains nickel compound particles such as nickel hydroxide particles as an active material.

As the nickel hydroxide particles, for example, single nickel hydroxide particles or nickel hydroxide particles 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.

The nickel hydroxide particles have a peak half width at (101) plane of 0.8 面 / 2θ by X-ray powder diffraction.
(Cu-Kα) or more is preferable. More preferable peak half width of nickel hydroxide particles is 0.9 to 1.0.
゜ / 2θ (Cu-Kα).

The positive electrode (paste type positive electrode) is prepared by adding a conductive material to nickel hydroxide particles, kneading the mixture with a polymer binder and water to prepare a paste, filling the paste into a conductive substrate, and drying the paste. After that, it is produced by molding.

Examples of the conductive material include cobalt oxide and cobalt hydroxide. Examples of the polymer binder include carboxymethyl cellulose, methyl cellulose, sodium polyacrylate,
Polytetrafluoroethylene and the like can be mentioned.

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

2) Negative electrode 4 This negative electrode 4 contains a hydrogen storage alloy powder. 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. Examples of this hydrogen storage alloy include LaNi ₅ , M
mNi ₅ (Mm; misch metal), LmNi ₅ (L
m; lanthanum-enriched misch metal), or a part of these Nis is Al, Mn, Co, Ti, Cu, Zn,
Examples thereof include a multi-element-based material substituted with an element such as Zr, Cr, and B, or a TiNi-based or TiFe-based material. Among them, the formula LmNi _x Mn _y A _z (However, A is Al, at least one metal selected from Co, the atomic ratio x, y, z is the total value 4.8 ≦ x + y +
It is preferable to use a compound represented by the following formula: z ≦ 5.4).

The negative electrode (for example, a paste type negative electrode) is prepared by adding a conductive material to a 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.

Examples of the polymer binder include those similar to those used for the positive electrode. As the conductive material, for example, carbon black or the like can be used.

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.

3) Separator 3 The separator 3 is made of, for example, a nonwoven fabric made of a polyolefin fiber or a nylon fiber, a woven fabric made of the same fiber, or a composite sheet made of the nonwoven fabric and the woven fabric. In particular, it is preferable that the separator is formed from a sheet containing polyolefin-based synthetic resin fibers, and the sheet is formed from a graft copolymerized with a vinyl monomer having a carboxyl group.

The polyolefin-based synthetic resin fibers include a polyolefin single fiber, a core-sheath composite fiber in which a polyolefin fiber different from the polyolefin fiber is coated on the surface of a core material made of the polyolefin fiber, and polyolefin fibers different from each other. A composite fiber having a divided structure joined in a circle can be used. Examples of the polyolefin include polyethylene and polypropylene.

Examples of the sheet-like material containing the polyolefin-based synthetic resin fiber include a nonwoven fabric made of the above-mentioned polyolefin-based synthetic resin fiber, a woven fabric made of the same, or a composite sheet made of the nonwoven fabric and the woven fabric. be able to. The nonwoven fabric is, for example, a dry method,
It is produced by a wet method, a spun bond method, a melt blow method, or the like. The average fiber diameter of the polyolefin-based synthetic resin fibers is preferably 1 to 20 μm from the viewpoint of mechanical strength and prevention of short circuit between the positive electrode and the negative electrode. If the average fiber diameter of the synthetic resin fibers is less than 1 μm, the mechanical strength of the separator may be reduced, which may make battery assembly difficult. On the other hand, if the average fiber diameter of the synthetic resin fibers exceeds 20 μm, the coverage of the separator may decrease, and short-circuits between positive and negative electrodes may occur frequently. The more preferable average fiber diameter of the synthetic resin fibers is 3 to 15 μm.

Examples of the vinyl monomer having a carboxyl group include acrylic acid, methacrylic acid, and esters of acrylic acid and methacrylic acid. Among the vinyl monomers, acrylic acid is preferred.

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 concentration of KOH in these electrolytes is 2.0 N to
It is desirable to set it to 6.0N. The concentration of NaOH is
1.0N to 6.0N, more preferably 2.0N to 5.0N
It is desirable to set the range of N. The concentration of LiOH is
0.3N to 2.0N, more preferably 0.5N to 1.5N
It is desirable to set the range of N.

It is preferable that the electrolytic solution is injected into the container in an amount of 60 to 90% of the remaining space volume obtained by subtracting the actual volumes of the positive and negative electrodes and the separator from the volume of the container after sealing. When the injection amount of the electrolyte is less than 60%, the amount of the electrolyte in the battery (particularly, the amount of the electrolyte held between the positive electrode and the negative electrode) is reduced, and the charge / discharge cycle life may be reduced. If the injection amount of the electrolytic solution exceeds 90%, there is a possibility that leakage occurs during storage or during quick charging.

According to the present invention described above, the actual volume (excluding voids) of the positive and negative electrodes and the separator occupies 50 to 70% of the volume of the container after sealing, thereby achieving high capacity. It is possible to obtain a nickel-metal hydride secondary battery having good charge / discharge cycle characteristics that is suitable for use, prevents leakage during storage and rapid charging, and has stable quality and high reliability.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. (Examples 1 to 3) <Preparation of paste type negative electrode> LmNi _4.0 Co _0.4 Mn _0.3 Al using a commercially available lanthanum-enriched misch metal Lm and Ni, Co, Mn, Al in a high frequency furnace.
_A hydrogen storage alloy having a composition of _0.3 was prepared. The hydrogen storage alloy was mechanically pulverized and passed through a 200-mesh sieve. 0.5 part by weight of sodium polyacrylate, 0.125 part by weight of carboxymethylcellulose (CMC), and a dispersion of polytetrafluoroethylene (specific gravity: 1.50 parts by weight) based on 100 parts by weight of the obtained hydrogen storage alloy powder.
5, a solid content of 60 wt%) and a paste were prepared by mixing 2.5 parts by weight of carbon powder as a conductive material and 1.0 part by weight of carbon powder together with 50 parts by weight of water. This paste was applied to punched metal, dried and then molded under pressure to produce a paste type negative electrode.

<Preparation of Paste-Type Positive Electrode> In a mixed powder consisting of 90 parts by weight of nickel hydroxide powder and 10 parts by weight of cobalt oxide powder, 0.3 parts by weight of carboxymethylcellulose with respect to the nickel hydroxide powder, A paste was prepared by adding 0.5 parts by weight of an ethylene dispersion (specific gravity 1.5, solids content 60% by weight) in terms of solids content, adding pure water 45 parts by weight thereto and kneading them. Subsequently, after this paste was filled in a nickel-plated fiber substrate, the paste was further applied to both surfaces thereof, dried, and rolled by roller pressing to produce a paste-type positive electrode.

<Preparation of Separator> A polypropylene resin is made of long fiber having a fiber diameter of 10 μm by a spunbond method, and has a basis weight of 50 g / m ² and a thickness of 0.20 m.
m of non-woven fabric. Subsequently, a first roll having a smooth surface and a second roll having a plurality of pinpoint-shaped irregularities formed on the surface are arranged to face each other. After heating the non-woven fabric between these rolls,
Embossing was performed by applying pressure to the roll and the convex portion of the second roll and performing heat fusion. Subsequently, after irradiating the non-woven fabric with ultraviolet rays, the non-woven fabric was immersed in an aqueous solution of acrylic acid to graft copolymerize an acrylic acid monomer. The nonwoven fabric was washed to remove unreacted acrylic acid, dried, and cut to produce a separator.

Next, the separator was interposed between the negative electrode and the positive electrode so that the embossed surface thereof faced the positive electrode, and was spirally wound to form an electrode group. At this time, the capacity ratio of the positive electrode was 0.9 or more with respect to the negative electrode. When such an electrode group is housed in a bottomed cylindrical container, the value obtained by calculating and adding the volumes of the positive electrode, the negative electrode, and the separator is regarded as the actual volume (excluding the void portion), and the volume of the container after sealing is determined. The ratio was set to be 50 to 70%. Thereafter, an electrolytic solution composed of 7N KOH and 1N LiOH is injected into the container so as to have a ratio of 80% with respect to the remaining space volume obtained by subtracting the actual volume from the volume of the container, and sealing is performed. By performing the above, three types of cylindrical nickel-metal hydride secondary batteries having the structure shown in FIG. 1 described above and having a size of 4 / 3A were assembled.

In Table 1 below, the volume of the container after closure, the volumes of the positive electrode, the negative electrode, and the separator, the added volume (actual volume), and the ratio of the actual volume to the volume of the container are shown. .

(Comparative Examples 1 to 3) When the same electrode group as in Example 1 was spirally wound using the same separator, negative electrode and positive electrode to form an electrode group, and this electrode group was stored in a bottomed cylindrical container,
The value obtained by calculating and adding the volumes of the positive electrode, the negative electrode, and the separator was defined as an actual volume (excluding voids), and was set so as to have a ratio shown in Table 1 below with respect to the volume of the container after sealing. Thereafter, an electrolytic solution composed of 7N KOH and 1N LiOH is injected into the container so as to have a ratio of 80% with respect to the remaining space volume obtained by subtracting the actual volume from the volume of the container, and sealing is performed. FIG. 1 described above by performing
The three types of 4 / 3A cylindrical nickel-metal hydride secondary batteries having the structure shown in Table 3 were assembled. In Table 1 below, the volume of the container after sealing, the volumes of the positive electrode, the negative electrode, and the separator, and the added volume (actual volume) are also shown.

[0035]

[Table 1]

The obtained Examples 1 to 3 and Comparative Examples 1 to 3
The secondary battery was aged for 24 hours in a thermostat at 45 ° C., and the initial charge was performed. After this, 1Cm
After charging at 150% with A, the battery was paused for 30 minutes, and repeated charging and discharging at 1 CmA until the battery voltage reached 1.0 V was repeated. FIG. 2 shows the discharge capacity ratio with respect to the cycle number ratio.

As is apparent from FIG. 2, the secondary batteries of Examples 1 to 3 in which the actual volumes (excluding voids) of the positive and negative electrodes and the separator were 50 to 70% with respect to the volume of the container after sealing are as follows. It can be seen that the battery has excellent charge / discharge cycle characteristics.

On the other hand, the actual volumes of the positive and negative electrodes and the separator (excluding voids) with respect to the volume of the container after sealing are 5%.
It can be seen that the secondary batteries of Comparative Examples 1 to 3 deviating from 0 to 70% have lower charge / discharge cycle characteristics than those of Examples 1 to 3. In the secondary battery of Comparative Example 3 in which the above value exceeded 70%, the internal pressure increased during the charge / discharge cycle.

In particular, in the secondary batteries of Comparative Examples 1 and 2, when the amount of the electrolytic solution was small, the charge / discharge reaction became non-uniform due to the uneven distribution of the electrolytic solution. The falling or floating of the hydrogen storage alloy is promoted, and the charge / discharge cycle life is shortened. When the amount of the electrolyte in the secondary battery of Comparative Example 3 is small, the internal resistance increases, the efficiency decreases in the charging reaction, and insufficient charging occurs. In the discharging reaction, the capacity decreases due to the lack of the reactant hydroxide ion. On the other hand, when the amount of the electrolyte is large, the internal pressure rises during the charge / discharge cycle to cause a liquid leakage.

[0040]

As described above, according to the present invention, there is provided a high-performance and highly reliable nickel-metal hydride secondary battery suitable for increasing the capacity and preventing the occurrence of liquid leakage during storage and rapid charging. can do.

[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.

FIG. 2 is a characteristic diagram showing a relationship between a cycle number ratio and a discharge capacity ratio in the nickel-hydrogen secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 3 of the present invention.

[Explanation of symbols]

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

Claims (1)

[Claims] 1. A nickel-metal hydride secondary battery in which a positive electrode, a negative electrode and a separator are housed in a bottomed cylindrical container, and an alkaline electrolyte is housed, wherein the positive and negative electrodes and A nickel-metal hydride secondary battery, wherein the actual volume (excluding voids) of the separator occupies 50 to 70%.