JP2002184380A - Alkali secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alkali secondary cell restraining self-discharge at high temperature storage, with improved cycle characteristics. SOLUTION: For the alkali secondary cell having a positive electrode, a negative electrode, and a separator, at least one side surface of the separator is negatively charged, and the charged electricity quantity is less than -1 nQ.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an alkaline secondary battery, and more particularly, to an alkaline secondary battery having an improved separator.

[0002]

2. Description of the Related Art A nickel-hydrogen secondary battery, which is a kind of alkaline secondary battery, is formed, for example, by a spiral in which a separator is interposed between a positive electrode containing a nickel compound as an active material and a negative electrode containing a hydrogen storage alloy as an active material. It has a structure in which an electrode group wound in a shape is housed in a container together with an electrolytic solution. Nickel-metal hydride rechargeable batteries are the same alkaline rechargeable batteries, and are voltage compatible with nickel cadmium rechargeable batteries, which are currently used as power supplies for many portable devices, and have the advantage of higher capacity than nickel cadmium batteries. Because of these characteristics, it is widely used as a power source for personal computers, mobile phones, portable information terminals, electric tools, electric vehicles, and the like.
However, the nickel-hydrogen secondary battery, like the nickel-cadmium secondary battery, has a problem in self-discharge during high-temperature storage.

That is, the self-discharge of a conventional nickel cadmium secondary battery at a high temperature is mainly caused by (1) a reduction reaction of a nickel compound (NiOOH) as a positive electrode active material by a substance generated by oxidative decomposition of a separator, and (2). NiOOH
Autolysis reaction occurs in two ways. this house,
Since the self-decomposition reaction of (2) is slower than the reaction of (1), it is considered that the main cause of the self-discharge reaction during high-temperature storage is due to the oxidative decomposition of the separator of (1).

[0004] Oxidative decomposition of the separator is remarkable when a nonwoven fabric made of a polyamide resin widely used in nickel cadmium secondary batteries is used. This is because nitrate ions, nitrite ions, ammonium and the like generated by decomposition of the polyamide-based resin with acid reduce NiOOH. For this reason, in order to prevent the oxidative decomposition, a polyolefin-based resin fiber having excellent oxidation resistance is used. This polyolefin resin fiber is
Since it is hydrophobic compared to polyamide-based resins, various hydrophilic treatments have been studied and attempts have been made to improve self-discharge.

However, in the case of a nickel-metal hydride secondary battery, a hydrogen storage alloy is used for the negative electrode, and the secondary battery is constructed utilizing the property of electrochemically storing and releasing hydrogen gas. In addition, the hydrogen equilibrium pressure of the hydrogen storage alloy increases, and the amount of hydrogen gas stored decreases, so that hydrogen gas that cannot be stored at high temperatures is released. as a result,
When a nickel-metal hydride secondary battery is stored at a high temperature, hydrogen gas is released from the negative electrode to fill the battery, and the NiO of the positive electrode is charged.
There is a problem that a reaction for reducing OH occurs.

As a means for solving such a problem, there is known a method in which a vinyl monomer having a carboxyl group is graft-copolymerized on a nonwoven fabric made of a polyolefin resin fiber. The high-temperature storage characteristics are correlated with the ion exchange capacity, and the higher the ion exchange capacity, the better the properties. However, the use of the graft copolymerized separator deteriorates the cycle characteristics of the secondary battery. In particular, when a separator having a high ion exchange capacity is used, the tendency is remarkably exhibited.

[0007] It has also been studied to copolymerize a polyolefin-based resin with a monomer having a sulfone group to introduce a sulfone group into the resin constituting the fiber. However, it was difficult to sufficiently suppress self-discharge.

Further, a separator in which the nonwoven fabric made of a polyolefin resin fiber is treated with a sulfuric acid solution to sulfonate the nonwoven fabric itself to improve the hydrophilicity has been developed, and self-discharge has been considerably suppressed. Was difficult to secure. In addition, since the polyolefin-based fiber itself is damaged, the strength is remarkably reduced, and its use is restricted.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide an alkaline secondary battery which suppresses self-discharge during high-temperature storage and has improved cycle characteristics.

[0010]

An alkaline secondary battery according to the present invention is an alkaline secondary battery having a positive electrode, a negative electrode, a separator and an electrolytic solution, wherein at least one surface of the separator is negatively charged, and The charge amount is -1
nQ or less.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an alkaline secondary battery (for example, a cylindrical nickel metal hydride secondary battery) according to the present invention will be described with reference to FIG.

An electrode group 5 formed by laminating a positive electrode 2, a separator 4, and a negative electrode 3 and winding them in a spiral shape is accommodated in a bottomed cylindrical container 1. The negative electrode 3 is arranged at the outermost periphery of the electrode group 5 and is in electrical contact with the container 1.

An alkaline electrolyte is contained in the container 1. The sealing plate 7 having a hole 6 in the center is
Is arranged in the upper opening. 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. Hat-shaped positive electrode terminal 10
Is mounted on the sealing plate 7 so as to cover the hole 6.

A rubber safety valve 11 is disposed in a space surrounded by the sealing plate 7 and the positive electrode terminal 10 so as to close the hole 6. 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.

Next, the positive electrode 2, the negative electrode 3, the separator 4
And the electrolyte will be described.

1) Positive electrode 2 This positive electrode 2 contains a nickel compound as an active material.

Examples of the nickel compound include nickel hydroxide, nickel oxide and nickel oxide in which nickel hydroxide, zinc and cobalt are co-precipitated.
Particularly, nickel hydroxide in which zinc and cobalt are coprecipitated is preferable.

The positive electrode (paste type positive electrode) is prepared, for example, by kneading a nickel compound as an active material, a conductive material and a binder together with water to prepare a paste, filling the paste into a conductive core, and drying the paste. It is produced by performing pressure molding as required.

As the conductive material, for example, at least one selected from a cobalt compound and metallic cobalt is used. As the cobalt compound,
For example, cobalt hydroxide [Co (OH) ₂ ], cobalt monoxide (CoO), and the like can be given. In particular, it is preferable to use cobalt hydroxide, cobalt monoxide, or a mixture thereof as the conductive material.

Examples of the binder include hydrophobic polymers such as polytetrafluoroethylene, polyethylene, and polypropylene; cellulosic materials such as carboxymethylcellulose, methylcellulose and hydroxypropylmethylcellulose; acrylic esters such as sodium polyacrylate; Examples include hydrophilic polymers such as polyvinyl alcohol and polyethylene oxide; and rubber-based polymers such as latex.

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

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

The hydrogen storage alloy is particularly restricted.
Not electrochemically generated water in the electrolyte
Element can be occluded and the occluded hydrogen can be easily released during discharge
Anything that can be done is acceptable. As this hydrogen storage alloy,
For example, LaNi_Five, MmNi _Five(Mm; Mishmeta
L), LmNi_Five(Lm: lantern-enriched misch
Al), Mn, C
o, Ti, Cu, Zn, Zr, Cr, B
Substituted multi-element type, TiNi type, TiF
e-type ones can be mentioned. Among them, the general formula Lm
Ni_xMn_yA_z(However, A is selected from Al and Co
At least one metal, and the atomic ratios x, y, z are the sum of
The value is 4.8 ≦ x + y + z ≦ 5.4)
It is preferred to use

For the negative electrode (paste type negative electrode), for example, a paste is prepared by kneading the hydrogen storage alloy powder, a conductive material and a binder together with water, filling the paste into a conductive core, and drying. It is produced by performing pressure molding as necessary.

Examples of the binder include those similar to those used for the positive electrode 2. This binder is
0.5 to 6 with respect to 100 parts by mass of the hydrogen storage alloy powder
It is preferable to mix parts by mass.

As the conductive material, for example, carbon black such as acetylene black, Ketjen black (trade name, manufactured by Lion Aguso), furnace black, or graphite can be used. This conductive material is preferably blended in an amount of 5 parts by mass or less with respect to 100 parts by mass of the hydrogen storage alloy powder.

Examples of the conductive core include a two-dimensional structure such as a punched metal, an expanded metal, a perforated steel plate, and a wire mesh, and a three-dimensional structure such as a foamed metal and an Amejo sintered metal fiber. Can be.

3) Separator 4 The separator 4 is made of, for example, a non-woven fabric made of cellulose resin or various synthetic resin fibers such as polyolefin, polyimide, aramid, ethylene-vinyl alcohol copolymer and the like, and at least one surface thereof is -1 nQ or less. Negative charge. For such negative charging, for example, a method of applying a negatively charging fine powder such as a silica powder, or a gas phase sulfonation treatment of irradiating ultraviolet rays in the presence of SO ₃ gas may be employed. it can. Before or after such treatment, a vinyl monomer having a hydrophilic group such as acrylic acid, methacrylic acid, maleic acid or vinyl propionate is allowed to polymerize with the graph.

The average fiber diameter of the polyolefin fiber is as follows:
Mechanical strength, from the viewpoint of densifying the nonwoven fabric 0.1 to 0.1
It is preferably 15 μm. As the polyolefin fiber, a polyolefin single fiber, a composite fiber having a core-sheath structure in which a polyolefin fiber different from the polyolefin fiber is coated on a core material surface composed of polyolefin fiber, and a division in which different polyolefin fibers are circularly joined to each other. And the like. Examples of the polyolefin include polyethylene and polypropylene.

The non-woven fabric of the polyolefin fiber is produced by, for example, a dry method, a wet method, a spun bond method, a melt blow method, or the like.

The reason why the amount of charge on at least one side of the separator is specified is that when the amount of charge exceeds -1 nQ (for example, -0.9 nQ), self-discharge during long-term storage can be suppressed. It becomes difficult.

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. In particular, an electrolytic solution obtained by mixing an aqueous KOH solution with an aqueous NaOH solution or an aqueous LiOH solution is preferable.

The alkaline secondary battery according to the present invention described above includes a positive electrode, a negative electrode, a separator, and an electrolytic solution. At least one surface of the separator is negatively charged, and the amount of charge is -1 nQ or less. To have the configuration,
Suppression of self-discharge during high-temperature storage and cycle characteristics can be greatly improved.

That is, in an open circuit state, for example, the equilibrium pressure of the hydrogen storage alloy slightly changes at a high temperature, for example, so that a very small potential difference is generated between the positive and negative electrodes so that the OH ions pass through the separator and shift the equilibrium. If a very weak reaction occurs,
By imparting a negative charge (-1 nQ or less) to the separator, the movement of the OH ions can be prevented, and a change in the concentration of the OH ions can be suppressed. For this reason, a further shift in equilibrium is prevented, and a cycle in which hydrogen gas generated from the negative electrode reduces the positive electrode is cut off. As a result, it shows a remarkable improvement effect on self-discharge and decrease in open voltage during long-term storage at high temperatures.

Therefore, by using a separator having a predetermined negative chargeability, an alkaline secondary battery having improved high-temperature storage characteristics and cycle characteristics by suppressing self-discharge can be obtained.

[0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIG.

(Examples 1 to 4) <Preparation of Positive Electrode> 0.3 parts by mass of carboxymethylcellulose and polytetrafluoroethylene were mixed with 90 parts by mass of nickel hydroxide particles and 10 parts by mass of cobalt monoxide powder. Add 0.5 parts by mass of the dispersion,
A paste was prepared by adding 45 parts by mass of pure water and kneading them. Subsequently, the paste was filled into a nickel-plated metal porous body, dried, and roller-pressed to a predetermined thickness to produce a paste-type positive electrode.

<Preparation of Paste Type Negative Electrode> LmNi _4.0 C
o _0.4 Mn _0.3 Al _0.3 (where Lm is a lanthanum-enriched misch metal) and 100 parts by mass of a hydrogen storage alloy powder having a composition of 0.5% sodium polyacrylate.
Parts by mass, carboxymethylcellulose (CMC) 0.1
A paste is prepared by mixing 25 parts by mass, 2.5 parts by mass of a polytetrafluoroethylene dispersion (specific gravity 1.5, solid content 60% by mass) and 1.0 part by mass of carbon powder together with 50 parts by mass of water. did. This paste was applied to punched metal, dried, and then molded under pressure to produce a paste-type negative electrode.

<Preparation of separator> The center part was covered with a polypropylene resin, and the outside was covered with ethylene vinyl alcohol.
A nonwoven fabric having a so-called core-sheath structure, a basis weight of 50 g / m ² and a thickness of 0.20 mm was produced by a spun bond method. After irradiating this nonwoven fabric with ultraviolet rays in the presence of SO ₃ gas, the nonwoven fabric was immersed in aqueous solutions of acrylic acid of various concentrations to graft copolymerize acrylic acid monomers. Subsequently, unreacted acrylic acid was washed with water and dried to produce four types of separators having various graft ratios.

The contact charge amount of each separator is measured by a cascade-type contact charge amount measuring device (trade name: T;
S100). The amount of contact charge was determined by measuring the amount of charge (nQ / 5 seconds) generated when 1.1 g of reference powder (FeO carrier powder) was flown over the separator surface using an electrometer. The charge amounts of these separators are shown in Table 1 below.

Then, each of the separators was interposed between the negative electrode and the positive electrode and spirally wound to produce four types of electrode groups. Subsequently, after each electrode group was respectively housed in a bottomed cylindrical metal container, an electrolyte solution consisting of 7M KOH and 1M LiOH was housed in the bottomed cylindrical metal container, and a lid was attached. Four types of AA-size cylindrical nickel-metal hydride secondary batteries having the structure shown in FIG. 1 described above were assembled.

Comparative Example 1 The same procedure as in Examples 1 to 4 was carried out except that a separator made of the same nonwoven fabric as in Examples 1 to 4 (without irradiation of ultraviolet rays in the presence of SO ₃ gas and without graft copolymerization) was used. An AA size cylindrical nickel-metal hydride secondary battery was assembled in the same manner. The charge amount of the separator (measured in the same manner as in Examples 1 to 4) is shown in Table 1
Shown in

In the obtained secondary batteries of Examples 1 to 4 and Comparative Example 1, 150% at 1 C after the initial activation.
After charging, charging / discharging at 1 C until the battery voltage reached 1.0 V was repeated three times. Subsequently, each secondary battery was charged to 150% at 1 C, stored in a high-temperature bath at 60 ° C. for 3 days, and then discharged at 1 C until the battery voltage reached 1.0 V. Discharge capacity before storage is 10
The residual capacity ratio after storage at high temperature was determined as 0.

A rechargeable battery with similar charging conditions was charged at 45 ° C.
Stored in a constant temperature bath for 6 months, once discharged, charged,
The capacity recovery rate of the secondary battery was measured under the same conditions as described above.
The results are shown in Table 1 below.

[0045]

[Table 1]

As is apparent from Table 1, Examples 1 to 4 using the separator to which a negative charge of -1 nQ or less was applied.
It can be seen that the secondary battery of Example 1 has excellent storage characteristics by suppressing self-discharge at high temperature as compared with the secondary battery of Comparative Example 1.

Further, the secondary batteries of Example 4 and Comparative Example 1 were charged at 150% at 1C, and charged at a battery voltage of 1.0 at 1C.
Charge / discharge was repeatedly performed, with one cycle of discharging until reaching 0 V as one cycle. FIG. 2 shows the measurement results of the discharge capacity in such a cycle. The cycle number ratio on the horizontal axis indicates the number of cycles in Example 4 and Comparative Example 1 with the number of cycles in which the discharge capacity of the secondary battery of Example 4 reached 80% of the discharge capacity in the first cycle as 100. I have.
The discharge capacity ratio on the vertical axis is shown as the discharge capacity in Example 4 and Comparative Example 1 with the discharge capacity in the first cycle of the secondary battery in Example 4 as 100.

As is apparent from FIG. 2, the secondary battery of Example 4 has better cycle characteristics than the secondary battery of Comparative Example 1.

[0049]

As described above, according to the present invention, there is provided an alkaline secondary battery having improved high-temperature storage characteristics and cycle characteristics by suppressing self-discharge by using a separator having a predetermined negative chargeability. be able to.

[Brief description of the drawings]

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

FIG. 2 is a characteristic diagram showing a capacity retention ratio with respect to a cycle number of an alkaline secondary battery in Example 4 and Comparative Example 1.

[Explanation of symbols]

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

Claims (1)

[Claims] 1. An alkaline secondary battery comprising a positive electrode, a negative electrode, a separator and an electrolytic solution, wherein at least one surface of the separator is negatively charged, and the amount of charge is -1 nQ or less. Alkaline secondary battery.