JPH117938A - Alkaline storage battery - Google Patents

Abstract

(57) Abstract: The present invention relates to an improvement of an alkaline storage battery, and regulates the amount of a hydrophilic compound having a carboxyl group which is not bonded to a constituent resin of a separator in the battery, thereby enabling self-discharge as a battery. Improve properties. SOLUTION: This is a sealed alkaline storage battery using a woven fabric, a nonwoven fabric, or a porous membrane mainly composed of a polyolefin resin modified with a hydrophilic compound having at least a carboxyl group in a resin surface layer as a separator. The amount of the hydrophilic compound having a carboxyl group, which is not bonded to the resin in the battery, is set to 0.1 per 1 Ah of the battery capacity.
35 mg or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement in the characteristics of an alkaline storage battery, and more particularly to an improvement in a separator thereof.

[0002]

2. Description of the Related Art Alkaline storage batteries currently used in a wide range of fields are expected to have high reliability. Large batteries are used as industrial power supplies, and small batteries are used in recent years in the development of various portable devices such as mobile phones and personal computers. As a result, demand for such power sources is expanding.

[0003] The separator for an alkaline storage battery has low electric resistance, excellent alkali resistance and oxidation resistance, good electrolyte retention for a long period of time, and a moderate air permeability. Is required.

Based on these required properties, nonwoven fabrics made of polyolefin-based resin fibers which have been subjected to a discharge treatment, or those which have been given a surfactant treatment or a fluorine treatment to impart hydrophilicity have been used as separator materials. I have.

At present, nonwoven fabrics made of polyolefin resin fibers are treated with sulfuric acid or fuming sulfuric acid to impart a hydrophilic property by introducing a sulfone group. −
It has been put to practical use as a separator for hydrogen storage batteries. Furthermore, the demand for higher capacity of secondary batteries from the portable equipment industry in recent years has been increasing more and more. As a prescription for increasing the capacity, a method of packing a larger amount of active material in a battery is conceivable. For this reason, a thinner separator is required. However, in general, when the thickness of the separator is reduced, the amount of retained electrolyte decreases,
It is not preferable as a battery because it causes the electrolyte to wither. Therefore, as a separator material capable of sufficiently holding the electrolytic solution even when thinned, a hydrophilic compound having a carboxyl group in a nonwoven fabric made of polyolefin resin fibers having a larger liquid holding capacity than the above-mentioned sulfonated polyolefin nonwoven fabric. Which have been imparted hydrophilicity by graft polymerization of

[0006]

However, in the study of the present inventors, a battery using a separator obtained by graft-polymerizing a hydrophilic compound having a carboxyl group on a nonwoven fabric made of the above-mentioned polyolefin-based resin fiber is disclosed in US Pat. There is a problem that self-discharge characteristics are inferior to batteries using a non-woven fabric made of a polyolefin-based resin fiber as a separator. One of the factors is considered to be the effect of a hydrophilic compound that is not polymerized during the graft polymerization treatment and is not bonded to the nonwoven fabric fibers that is not removed in the subsequent steps.

The present invention solves the above-mentioned conventional problems. By controlling the amount of a hydrophilic compound having a carboxyl group, which is not bonded to a resin in a battery, to a certain amount or less, An object is to provide an alkaline storage battery having excellent self-discharge characteristics.

[0008]

In order to solve the above-mentioned problems, the present invention provides, as a separator, a woven fabric mainly composed of a polyolefin resin modified with a hydrophilic compound having at least a carboxyl group in a resin surface layer. Using a cloth, a nonwoven fabric or a porous membrane, and not binding to the resin in the battery, the amount of the hydrophilic compound having a carboxyl group,
0.35 mg or less per 1 Ah of battery capacity. More preferably, the modification of the hydrophilic compound to the resin surface layer is obtained by graft-polymerizing at least one of acrylic acid and methacrylic acid. By controlling the amount of the hydrophilic compound having a carboxyl group that is not bonded to the separator resin in the battery to a certain amount or less, the elution of these substances into the alkaline electrolyte is reduced, and the reduction reaction with this is reduced. The capacity of the positive electrode that is consumed as a result can be extremely small. Therefore the above woven cloth,
In a battery using a non-woven fabric or a porous membrane as a separator, the capacity deterioration during storage is extremely small, and the self-discharge characteristics can be improved.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION
As a separator, a woven fabric, a nonwoven fabric, or a porous membrane mainly composed of a polyolefin resin modified with a hydrophilic compound having at least a carboxyl group in the resin surface layer is used. An alkaline storage battery in which the amount of the hydrophilic compound having a carboxyl group that is not bonded to the battery is 0.35 mg or less per 1 Ah of battery capacity.

[0010] The invention according to claim 2 relates to hydrophilization of a woven fabric, a nonwoven fabric or a porous membrane made of polyolefin-based resin fibers. A carboxyl group is modified to impart long-term hydrophilicity.

(Embodiment) FIG. 1 shows an amount of a hydrophilic compound having a carboxyl group which is not bonded to a resin fiber constituting a separator (hereinafter referred to as a residual COOH amount).
FIG. 5 is a diagram showing a relationship between the battery capacity and the remaining capacity ratio of the battery. Residual CO
When the OH content is 0.35 mg / Ah or less, the residual capacity after storing the battery in a charged state at 65 ° C. for 2 weeks is 45% or more of the initial capacity, which is a good result.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.
In this embodiment, a nonwoven fabric of polypropylene fiber (hereinafter referred to as AGP) treated with acrylic acid as a separator was used.
P will be described using a nickel-hydrogen storage battery as an example. A polypropylene fiber nonwoven fabric subjected to an acrylic acid graft polymerization treatment was produced by the following procedure. First, a splittable conjugate fiber having a nominal fiber diameter of 9 μm and a polypropylene / polyethylene core-sheath fiber having a nominal fiber diameter of 1 μm.
The fiber of 5 μm is weighed by a method such as wet entanglement and the like.
g / m ² and a thickness of 180 μm. The compounding ratio of the splittable conjugate fiber and the polypropylene / polyethylene core-sheath fiber was 80:20 by weight. In a solution comprising 20% by weight of acrylic acid, 65% by weight of distilled water, 0.5% by weight of benzophenone, 0.3% by weight of Mohr's salt, 13.7% by weight of methoxyethanol and 0.5% by weight of nonionic surfactant. For 10 minutes. The solution used was previously deoxygenated with nitrogen in order to minimize the influence of oxygen during the subsequent polymerization treatment. After removing the excess solution from the polypropylene nonwoven fabric, acrylic acid was graft-polymerized by irradiating ultraviolet rays for 2 minutes using a 110-watt low-pressure mercury lamp from a distance of 5 cm on both sides in a deoxygenated atmosphere. Thereafter, the separator was washed with water by immersing it in distilled water at a temperature of 40 ° C. for 30 minutes. Then, it is dried and calendered, and has a basis weight of 58 g / m ² and a thickness of 130.
A nonwoven fabric 1 of a polypropylene fiber subjected to an acrylic acid graft polymerization treatment of μm was obtained. The manufacturing conditions other than the water washing were the same, and the water washing time during the water washing was 15 minutes, 10 minutes, respectively.
After 5 minutes and 3 minutes, the non-woven fabric 2, non-woven fabric 3, non-woven fabric 4, and non-woven fabric 5 of polypropylene fibers were obtained by adjusting the amount of residual COOH and performing an acrylic acid graft polymerization treatment. The measurement of the residual COOH amount was performed as follows. First, the separator in the battery is taken out, stored in 100 ml of pure water at 60 ° C. for 1 hour, and the electrolytic solution is washed with water. Thereafter, the nonwoven fabric is taken out, and the nonwoven fabric is treated with 100 ml of pure water at 50 ml for 30 minutes.
By repeating the operation of stirring for 5 seconds five times, the vinyl monomer in the nonwoven fabric is extracted into the solution. The solution was subjected to neutralization titration and calculated from the titer. For comparison, a non-woven fabric of polypropylene fiber was treated with fuming sulfuric acid to give a sulfonated basis weight of 55 g / m ² and a thickness of 1
25 μm sulfonated polypropylene nonwoven fabric 6 (hereinafter referred to as S
PP). Table 1 shows the basis weight, thickness, washing time, and residual COOH content of the above nonwoven fabric.

[0013]

[Table 1]

The battery was prepared in the following procedure.
For the positive electrode, a sponge-like porous nickel body was filled with a mixture obtained by mixing 6 parts by weight of cobalt hydroxide powder and water with respect to 100 parts by weight of nickel hydroxide powder as an active material and forming a paste. The one cut to the dimensions of was used. The negative electrode has a composition formula of MmNi _3.55 Mn _0.4 Al _0.3 Co
_{A 0.75} (Mm is a mixture of rare earth elements) hydrogen-absorbing alloy is converted into fine powder having an average particle size of about 30 μm by a ball mill, immersed in a KOH solution at 80 ° C., washed with water, and then dispersed with styrene-butadiene rubber and carboxymethyl cellulose. And carbon and water are mixed to form a paste, which is applied to a punching metal plated with nickel on iron, dried,
After pressing, one cut to desired dimensions was used. Next, the above-mentioned paste type positive electrode and a length twice as long as the length of the positive electrode +
A 27 mm (Table 1) separator, the theoretical capacity is 1.6 to 1.7 times the theoretical capacity of the positive electrode, and the length is the positive electrode length +21.
The combination with the negative electrode of mm was formed in a spiral shape, and an AAA size sealed battery having a capacity of 550 mAh was formed. The electrolyte is KOH aqueous solution with specific gravity 1.30 and LiOH
Was dissolved in 40 g / l, and 0.1 g was dissolved per cell.
97 cc of the solution was injected to prepare six types of batteries 1 to 6. Table 1 shows the battery numbers and the separator numbers used at that time.

The prepared batteries 1 to 6 were precharged and discharged for two cycles at 20 ° C. under the conditions of charging at 120% with a charging current of 0.2 C and discharging up to 1 V at a discharging current of 1 C to stabilize the capacity. Next, the battery was charged at a charging current of 1 C and discharged to 1.0 V at a discharging current of 1 C, and the discharge capacity of the battery before storage was determined. Thereafter, the battery was charged at a charging current of 1 C, and each battery was stored in a constant temperature room at 65 ° C., one by one, for two weeks. After the storage, each battery was taken out, discharged to 1.0 V at a discharge current of 1 C, and the remaining capacity of each battery was measured. The ratio of the capacity after storage to the capacity before storage was defined as the remaining capacity ratio, and was calculated as (Equation 1).

[0016]

[Formula 1] Residual capacity ratio = capacity after storage / capacity before storage × 100 (%) (Table 2) shows the remaining capacity ratio of each of the batteries 1 to 6.
FIG. 1 shows the relationship between the residual COOH amount and the residual capacity ratio.

[0017]

[Table 2]

From Table 2 and FIG. 1, it can be seen from the results that the batteries 1 and 2 had a residual COOH content of less than 0.35 mg / Ah in the separator.
As for the batteries 2 and 3, the reduction in capacity is smaller than that of the battery 6 using the SPP separator for comparison, and the remaining capacity ratio is high.
On the other hand, in the batteries 4 and 5 using the separator having the residual COOH amount larger than 0.35 mg / Ah, the residual capacity ratio is SP
It is lower than the battery 6 using P. Also, the residual capacity ratio shows a tendency to decrease as the residual COOH amount increases. Although the cause is not clear yet, it is considered that a compound having COOH which is not bonded to the separator elutes into the alkaline electrolyte during storage of the battery and promotes the reduction reaction of the positive electrode. From the above, the amount of the hydrophilic compound having a carboxyl group remaining in the separator can be reduced to 0.35 mg / Ah or less by increasing the water washing time of the separator after the graft polymerization. This can improve the self-discharge characteristics of the alkaline storage battery. In the present invention, a polypropylene nonwoven fabric obtained by graft polymerization of acrylic acid is described as an example of the separator, but the form of the separator is a woven fabric or a porous film in addition to the nonwoven fabric.
Any shape may be used, and the material may be a polyolefin-based resin such as polyethylene or a copolymer of polypropylene and polyethylene. Such an effect can be obtained not only when the amount of residual COOH is reduced by changing the washing time, but also by increasing the washing efficiency by increasing the water flow. In addition, by optimizing the conditions at the time of the grafting treatment, for example, the composition of the treatment solution, the treatment temperature, the treatment time, the ultraviolet irradiation conditions, etc., as the hydrophilic compound having a carboxyl group, not only acrylic acid, but also acrylic ester The same effect can be obtained by using methacrylic acid, methacrylic acid ester, or the like. Further, similar effects can be observed in other alkaline storage batteries that do not use a nickel hydroxide positive electrode or a hydrogen storage alloy negative electrode, such as nickel-zinc storage batteries other than nickel-hydrogen storage batteries and manganese dioxide-hydrogen storage batteries.

[0019]

According to the present invention, there is provided an alkaline storage battery using any one of a woven fabric, a nonwoven fabric, and a porous film as a separator, the main constituent of which is a polyolefin resin modified with a hydrophilic compound having at least a carboxyl group in the resin surface layer. By setting the amount of the hydrophilic compound having at least a carboxyl group, which is not bonded to the resin in the battery, to 0.35 mg or less per 1 Ah of battery capacity, the residual capacity ratio during storage is high and the self-discharge characteristics are excellent. Thus, an alkaline storage battery can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the amount of residual COOH in a separator according to the present invention and the remaining capacity ratio of a nickel-hydrogen storage battery using the separator.

Claims (2)

[Claims] 1. A woven or non-woven fabric comprising a positive electrode, a negative electrode, a separator and an alkaline electrolyte, wherein the separator is a woven or non-woven fabric mainly composed of a polyolefin resin modified with a hydrophilic compound having at least a carboxyl group in a resin surface layer. And an amount of the hydrophilic compound having a carboxyl group in the battery, which is not bonded to the resin, is 0.35 mg or less per 1 Ah of battery capacity. 2. The alkaline storage battery according to claim 1, wherein the modification of the hydrophilic compound having a carboxyl group to the resin surface layer of the separator made of a polyolefin resin is graft polymerization of at least one of acrylic acid and methacrylic acid. .