JP2590520B2 - Sealed alkaline storage battery separator and method for producing the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separator for a battery, particularly a sealed alkaline storage battery, and a method for producing the same.

2. Description of the Related Art As a secondary battery among various power sources, a lead storage battery and an alkaline storage battery are widely used. Among the latter alkaline storage batteries, the most widely used one is a nickel-cadmium storage battery, and the use of a sealed structure has been a major factor in expanding the range of practical use.

As a separator used in these batteries, a polyamide nonwoven fabric is most common. However, since this separator is not sufficient in terms of alkali resistance, in a battery used at high temperature or under severe conditions such as continuous overcharge / discharge, the temperature rise of the electrolyte and electrochemical changes are remarkable. Intense embrittlement. Therefore, it cannot be said that it is sufficient for high-temperature use or extremely long-term use. Furthermore, it cannot be said that the separator is excellent in self-discharge.

Further, a method has been proposed in which a nonwoven fabric in which a polyamide fiber and a polyethylene-polypropylene composite fiber are bonded by a polyethylene component is used as a separator. But,
According to this method, the alkali resistance and the oxidation resistance of the polyamide fiber in the portion in contact with the polyethylene-polypropylene conjugate fiber can be improved, but the embrittlement of the polyamide fiber in the bare portion can be avoided. Can not.

On the other hand, a polyolefin, that is, a porous body made of polyethylene or polypropylene, for example, a nonwoven fabric, is sufficient in alkali resistance, but is inferior in electrolyte solution retention as compared with a polyamide nonwoven fabric. Therefore, in order to improve this, a method of impregnating a polyolefin porous body with a surfactant in advance has been adopted. However, when this means is adopted, the electrolyte retention ability is too large at the beginning, and impairs the negative electrode gas absorption ability in a closed form. In addition, there is a problem that the charge / discharge characteristics are deteriorated because the surface activity ability is reduced and the electrolyte retention ability is also reduced when charge / discharge is repeated.

Further, for the purpose of preventing short-circuiting, which is a major role as a separator, it has long been proposed to form a polyvinyl alcohol coating, which is an ion-permeable substance, on these nonwoven fabrics. However, there is no consideration that can be applied to a sealed alkaline storage battery that requires gas permeation. That is, when polyvinyl alcohol is applied to the separator without special consideration, the polyvinyl alcohol becomes a film and the gas permeability decreases. As a result, the gas absorption capacity is reduced, and the gas absorption capacity can be used for, for example, an open type storage battery using a large amount of an electrolytic solution, but cannot be used for a closed type storage battery requiring gas permeation.

In addition, a method has been proposed in which a polyolefin porous body is treated with fuming sulfuric acid or immersed in high-temperature concentrated sulfuric acid. However, since fuming sulfuric acid or concentrated sulfuric acid is used, there is a problem in the material and handling of the apparatus, and it is also troublesome to remove these acids from the separator. Therefore, the process becomes complicated and expensive.

Problem to be Solved by the Invention In view of the above problems, the present invention is a battery separator, in particular, as a separator for a sealed alkaline storage battery, while being obtained at low cost, while maintaining a porous body made of polyolefin electrolyte resistance, An object of the present invention is to provide a separator which suppresses a decrease in gas absorption characteristics due to an excessively large electrolyte retention capacity at an initial stage and does not deteriorate charge / discharge characteristics for a long period of time.

Means for Solving the Problems The sealed alkaline storage battery separator of the present invention is formed of a porous body composed of a polyvinyl alcohol fiber into which a sulfone group has been introduced by sulfuric acid treatment and a polyolefin fiber. The polyolefin is made of polyethylene or polypropylene, and the porous body is preferably a nonwoven fabric.

The simplest method of obtaining the separator of the present invention is a method of impregnating a solution containing sulfuric acid into a porous body composed of polyvinyl alcohol-based fibers and polyolefin fibers, followed by heating and drying. In addition, as the polyvinyl alcohol-based fibers, those obtained by treating polyvinyl alcohol with various aldehydes are generally used, and one obtained by formalizing and then heat-treating is a preferable example.

Action When a sulfuric acid solution is added to a porous body composed of a polyvinyl alcohol fiber and a polyolefin fiber and heated at about 60 to 100 ° C., the porous body turns black-brown. This treatment introduces a small amount of a sulfone group into the polyvinyl alcohol-based fiber, thereby imparting lyophilicity. On the other hand, polyolefin fibers are hardly affected by this level of treatment, so that the strength of the porous body does not decrease.

Furthermore, the porous body composed of the polyvinyl alcohol fiber into which the sulfone group is introduced by the sulfuric acid treatment and the polyolefin fiber is not abnormally lyophilic and has a moderate lyophilicity as compared with a porous body impregnated with a known surfactant. Can be kept for a long time.

As described above, the separator according to the present invention has an effect of removing the difficulty of the oxygen gas from reaching the positive electrode to the negative electrode during charging, and has excellent charge / discharge characteristics and a longer life.

In addition, since the separator according to the present invention does not have a nitrogen-containing functional group such as polyamide, a nitrogen compound such as nitrogen oxide is not generated during charge and discharge of a battery. Therefore, self-discharge is smaller than that of the polyamide-based separator.

Example: Polyvinyl alcohol fiber consisting of 40% vinylon fiber and 60% polypropylene obtained by heat treatment after folimarization (0.16mm thickness including commercially available surfactant)
After immersing the nonwoven fabric in concentrated sulfuric acid solution diluted 5 times,
Heat and dry at ℃ for 1 hour. Thereafter, washing is performed with water to remove unreacted sulfuric acid and most of the surfactant. The color changes from dark brown to slightly light brown due to washing with water. It is dried again to obtain a separator.

As the battery, a sealed nickel-cadmium storage battery of SubC type was taken as an example. As the nickel electrode, a known foamed nickel electrode was selected, with a width of 3.3 cm and a length of 17 cm. The thickness is 0.
7 mm. On the other hand, as a cadmium electrode, a known paste-type cadmium electrode is selected, and nickel plating is performed on the electrode surface to improve the gas absorbing ability. This electrode was cut into a width of 3.3 cm and a length of 20 cm, and lead plates were attached to two predetermined spots by spot welding. Since the separators were arranged on both sides of the negative electrode, the length was about 40 cm.

In addition, in order for the negative electrode to hold a discharge compensation capacity,
This electrode is set to a current density of 14 A / dm ² , a time of 5 minutes, an electrolytic bath, and a specific gravity.
The battery was charged using a nickel plate as the counter electrode under the conditions of a caustic potassium solution of 1.15 and a temperature of 25 ° C. This charge is calculated as
Equivalent to about 18-20% of the total cadmium logic capacity,
Since the charging efficiency is low, it can be considered that about 10% is actually charged.

As an electrolytic solution, 25 g / l of lithium hydroxide was dissolved in an aqueous solution of caustic potassium having a specific gravity of 1.22. Nominal capacity is 2.3Ah. This battery is referred to as (A).

Next, for comparison, the thickness including the commercially available surfactant
A battery using the same conditions as the battery (A) was used as a separator (B), and a battery using a known polyamide nonwoven fabric was also used as a separator (C).

First, the quick charging characteristics of each battery were examined. Each battery used 10 cells. With the ambient temperature set to 5 ° C., the change in pressure in the battery when charged at each charging rate was measured. In addition, charge
The test was performed at each charging rate up to 1.5 times the discharge capacity. 1C charge (2.3
The maximum internal pressure of each battery at the time of A) is 0.3 to 0.1 for the battery (A).
For 5 kg / cm ² , battery (B), 2.1 to 2.5 kg / cm ² , battery (C)
Was 0.4 to 0.7 kg / cm ² .

In other words, the battery (A) is inferior to the battery (A) particularly in gas absorption. The reason seems to be that, as described above, in the case of the battery (B), it is difficult to reach oxygen gas from the positive electrode to the negative electrode during charging due to abnormal lyophilicity of the surfactant. .

Next, the life characteristics due to charge / discharge cycles were examined. Each battery was repeatedly charged at 0.2 C and discharged at 1.0 C. As a result, first, the discharge capacity in 5 cycles was 2.350 Ah for battery (A) and 2.362 Ah for (B), and 2.29 A for (C).
7Ah. However, at 500 cycles, the average is 2.338 Ah, 1.987 Ah, and 2.165 Ah, respectively, and the decrease in the capacity of the battery (A) is extremely small.

Finally, self-discharge was examined. Operate each battery at 25 ° C
After charging at 150% of the previous discharge capacity at 0.3 C, the battery was left at 50 ° C. for 10 days. Thereafter, the temperature was returned to 25 ° C. and the battery was discharged at 0.2 C. As a result, the capacity retention rate of the battery (A) was 78% on average, whereas it was 73% in (B) and 55% in (C). .

With respect to the ratio of the polyvinyl alcohol fiber and the polyolefin fiber, if the former is too large, the strength is reduced after the sulfuric acid treatment, and if the latter is too large, the effect of sulfuric acid is small. Therefore, the former is suitably about 20 to 50%.

Effect of the Invention By using a separator composed of a porous body composed of polyvinyl alcohol-based fibers and polyolefin fibers into which sulfone groups have been introduced by sulfuric acid treatment, improvement in gas absorption characteristics during charging of a sealed alkaline storage battery,
The service life can be further extended. In addition, the self-discharge can be improved.

Claims (5)

(57) [Claims] 1. A sealed alkaline storage battery separator comprising a porous body comprising a polyvinyl alcohol fiber into which a sulfone group has been introduced by sulfuric acid treatment and a polyolefin fiber. 2. The sealed alkaline storage battery separator according to claim 1, wherein the polyolefin fiber is made of polyethylene or polypropylene, and the porous body is a nonwoven fabric. 3. The sealed alkaline storage battery separator according to claim 1, wherein the polyvinyl alcohol-based fiber is obtained by formalizing polyvinyl alcohol. 4. A method for producing a separator for a sealed alkaline storage battery, comprising impregnating sulfuric acid into a porous body comprising polyvinyl alcohol-based fibers and polyolefin fibers and heating and drying. 5. The method according to claim 4, wherein the porous body is immersed and heated in a solution containing sulfuric acid.