JPH01255162A - Battery separator and its manufacturing method - Google Patents

Abstract

PURPOSE:To improve gas absorptiveness at the time of charging a sealed battery and enhance the self-charging property by using as separator a porous substance formed by placing a polyvinyl alcohol film over the surface of a polyolefin fiber. CONSTITUTION:A porous substance is used which is formed by coating polyvinyl alcohol over the surface of polyolefin fiber. Therein the polyvinyl alcohol does not form a film as in a conventional arrangement, but merely covers surfaces of the polyolefin fiber itself. Accordingly inclusion of polyvinyl alcohol still allows keeping of porosity for passage of gas This provides separators for sealed type alkaline battery at low cost wherein possible drop of gas absorption characteristic due to too large electrolyte retaining capacity is suppressed in the early period while the porous body consisting of polyolefin maintains its resistance against electrolyte, and in a long-term view the charging/discharging characteristic is prevented from deterioration.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a separator for batteries, particularly for sealed alkaline storage batteries, and a method for manufacturing the separator.

BACKGROUND OF THE INVENTION Among various power sources, lead-acid batteries and alkaline batteries are widely used as secondary batteries. Among the latter alkaline storage batteries, the most widely used one is the nickel-cadmium storage battery, and the adoption of a sealed structure was a major factor in expanding the range of practical use.

The most common separator used in these batteries is polyamide nonwoven fabric. However, this separator does not have sufficient alkali resistance, so for example,
It is not sufficient for high-temperature applications or extremely long-term applications. Furthermore, it cannot be said to be an excellent separator in terms of self-discharge.

On the other hand, a porous material made of polyolefin, such as polyethylene or polypropylene, such as a nonwoven fabric, has sufficient alkali resistance, but is inferior to a polyamide nonwoven fabric in terms of electrolyte retention.

Therefore, in order to improve this problem, a method has been adopted in which the porous polyolefin material is impregnated with a surfactant in advance. However, when this means is adopted, the electrolyte retention capacity is initially too large, which inhibits the negative electrode gas absorption capacity in a closed type. Further, when charging and discharging are repeated, the surfactant ability decreases, and the electrolyte retention ability also decreases, so there is a problem that the charging and discharging characteristics deteriorate.

Furthermore, for the purpose of preventing short circuits, which plays a major role as a separator, it has been proposed for a long time to form a polyvinyl alcohol coating, which is an ion-permeable substance, on these nonwoven fabrics. However, none of these considerations are particularly applicable to the sealed storage battery of the present application, that is, the sealed storage battery that requires gas permeation.
Therefore, the current situation is that the gas absorption capacity is reduced.

In other words, if applied without special consideration, it will form a film, and while it can be used for open storage batteries that use a large amount of electrolyte, it cannot be used for sealed storage batteries that require gas permeation. is the current situation.

In addition, methods have been proposed in which the porous polyolefin material is treated with oleum or immersed in high-temperature VIA sulfuric acid. A battery using a separator obtained by this method has excellent rapid charging characteristics, long life, and self-discharge characteristics. However, since fuming sulfuric acid and AI acid are used,
There are problems with the materials and handling of the device, and it is also complicated to remove these acids from the separator. Therefore, the process becomes complicated and expensive.

Problems to be Solved by the Invention A separator for batteries, particularly a separator for sealed alkaline storage batteries, can be obtained at low cost, and the porous body made of polyolefin maintains electrolyte resistance while maintaining electrolyte retention capacity in the initial stage ζ. To suppress deterioration of gas absorption characteristics due to excessively large values, and also to solve the problem of deterioration of charge/discharge characteristics over a long period of time. Additionally, improvements in self-discharge will also be attempted.

Means for Solving the Problems The present invention uses as a separator a porous body made of polyolefin fibers whose surface is coated with polyvinyl alcohol, polyvinyl alcohol treated with sulfuric acid, or polyvinyl alcohol treated with sulfuric acid and aldehyde. , and its manufacturing method.

Function In this way, a porous body is used in which the surface of polyolefin fibers is coated with polyvinyl alcohol. This prevents polyvinyl alcohol from forming a film like in the past.
It only coats the surface of the polyolefin fiber itself.

Therefore, even though it contains polyvinyl alcohol, it maintains porosity that allows gas to pass through.

Furthermore, when the surface of polyolefin fibers is coated with polyvinyl alcohol containing a small amount of sulfuric acid and heated at about 60 to 100°C, this porous body turns black. It is thought that this treatment introduces sulfone groups into the polyvinyl alcohol, albeit in a small amount, and also improves the adhesion of the polyvinyl alcohol to the porous body. and,
Since excess solution is removed from polyvinyl alcohol containing sulfuric acid during impregnation, it does not form a film as in conventional methods, but only coats the surface of the polyolefin fiber itself. Therefore, even if this sulfuric acid-treated polyvinyl alcohol is contained, it maintains porosity that allows gas to pass through.

Furthermore, this sulfuric acid-treated polyvinyl alcohol does not have the unusual lyophilic properties of known surfactants, and is more lyophilic than the original polyvinyl alcohol. From this, it seems that the separator has the effect of eliminating the difficulty of oxygen gas reaching from the positive electrode to the negative electrode during charging, and also provides excellent charge-discharge characteristics. Moreover, this sulfuric acid-treated polyvinyl alcohol has better electrolyte resistance and oxidation resistance than general surfactants, so that the life of the -layer can be extended.

Furthermore, the surface of the polyolefin fiber is coated with polyvinyl alcohol containing a small amount of sulfuric acid and aldehyde.
When heated at about 0 to 100°C, this porous body turns black. Through this treatment, a sulfone group is introduced into the polyvinyl alcohol, albeit in a small amount, and acetalization is also performed. Furthermore, it is believed that the adhesion of polyvinyl alcohol to the porous body is improved. For boat fishing, the introduction of sulfuric acid groups increases electrolyte affinity, and acetalization, on the contrary, increases electrolyte resistance.

Furthermore, since the excess solution is removed after impregnation, the surface of the polyolefin fiber itself is coated instead of forming a film as in the conventional method. Therefore, this riR
Even though it contains only polyvinyl alcohol treated with acids and aldehydes, it remains porous to allow gas to pass through. Roughly,
Polyvinyl alcohol treated with sulfuric acid and aldehyde does not have unusual electrolyte-philic properties like known surfactants, and is resistant to electrolytes. Therefore, when used as a separator, it has the effect of eliminating the difficulty of oxygen gas reaching from the positive electrode to the negative electrode during charging, and provides excellent charge-discharge cycle characteristics.

In addition, if these separators are made of aldehydes that do not have nitrogen-containing functional groups, such as polyamide, nitrogen compounds such as nitrogen oxides will not be generated during charging and discharging of the battery. Therefore, self-discharge can also be reduced compared to polyamide separators.

Examples (Example 1) A 0.16 mm thick polypropylene nonwoven fabric containing a commercially available surfactant was impregnated with a 3% (by weight) aqueous solution of polyvinyl alcohol, and then passed between two rollers to remove the excess solution contained. remove. It is necessary to keep the polypropylene nonwoven fabric wet with polyvinyl alcohol. Dry this. After that, it is preferable to wash with water to remove most of the surfactant. Dry again to obtain a separator. In this case, the amount of polyvinyl alcohol added depends on the thickness and porosity of the porous body, but the amount is 0.5 to 1.5.
A range of mg/cm2 is suitable.

As an example of the battery, a 5ubC type close-locked nickel-cadmium storage battery was used. As the nickel electrode, a well-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, a known paste-type cadmium electrode was selected as the cadmium electrode, and the surface of the electrode was plated with nickel in order to improve the gas absorption ability. This electrode has a width of 3.3 cm and a length of 20 cm.
It was cut into cm pieces, and lead plates were attached to two predetermined locations 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 to maintain the capacity for discharge compensation in the negative electrode, this electrode was heated in an electrolytic bath at a current density of 14 A/di2 for 2 hours and 5 minutes.
Charging was carried out using a nickel plate as a counter electrode under conditions of a caustic potassium aqueous solution having a specific gravity of 1.15 and a temperature of 25°C. This charge 1 corresponds to about 18 to 20% of the total theoretical capacity of the quad drum 1 according to calculation, but since the charging efficiency is low, it can be considered that about 10% was actually charged.

As the electrolytic solution, 25 g/I of lithium hydroxide was dissolved in a caustic potassium aqueous solution having a specific gravity of 1.22.

The nominal capacity is 2.3 Ah. This battery is referred to as (A1).

Next, for comparison, a thickness of 0 containing a commercially available surfactant was prepared.
．． A battery (B1) using a 16 mm polypropylene nonwoven fabric as it is and using the same conditions as the battery (AI),
As the same separator, a battery (cl) also using a known polyamide nonwoven fabric was added.

First, we investigated the quick charging characteristics of each battery. In each case, 20 cells were used. The ambient temperature was set to 3° C., and the change in pressure inside the battery was measured when charging was performed at each charging rate. For charging,
The charging was carried out at each charging rate up to 1.4 times the discharge capacity. After that,
The charge was reduced to 0.20, and the total charge was 1.5 times the discharge capacity.

First, the maximum internal pressure of each battery during IC charging (2,3A) is 0.2 to 0.4kg7cm2 for battery (A1). In the battery (B1), 2. 5-3.3kg/cm2. battery(
C1), 0. 7-1. It was 2 kg/Cm2. Next, when setting it to 1.25C (2,875A1), the battery (
A + ), 1. 4.9 at 4-1.8° (B1)
~6.4. For (C+), it was 3.1 to 4.0. In other words, compared to battery (A + ), (B+) is particularly inferior in terms of gas absorption. The reason for this is that, as already mentioned, in the case of battery (B1), it is difficult for oxygen gas to reach from the positive electrode to the negative electrode during charging due to the abnormal lyophilicity caused by the surfactant.

In addition, as in battery (A1), polypropylene nonwoven fabric is impregnated with polyvinyl alcohol, but it becomes (AI),
We also investigated separators obtained by a conventionally known method, which is obtained by drying without passing through rollers, but we have already
During charging in a cycle, the internal pressure increased due to gas and leaked, so it was not included in the test.

Finally, we investigated self-discharge. After charging each battery to 150% of the previous discharge capacity at 0.3C at 25℃,
It was left for 10 days. Afterwards, when the temperature was returned to 25℃ and discharged at 0.2C, the capacity retention rate was 67-72% for batteries (AI) and (B+), whereas battery (C1) was discharged at 0.2C.
), it remained at 50-55%.

(Example 2) Concentrated sulfuric acid 90c diluted five times with 10QOcc of a 3% (weight!!l) aqueous solution of polyvinyl alcohol on a commercially available surfactant-containing polypropylene with a thickness of 0.16mm and 6mm
After impregnating with the added solution, remove the excess solution by passing it between two slits. In other words, it is necessary to keep the polypropylene nonwoven fabric wet with polyvinyl alcohol containing sulfuric acid. This is heated and dried at 85° C. for 1 hour. Thereafter, it is washed with water to remove unreacted sulfuric acid and most of the surfactant. When washed with water, it changes from black to a slightly lighter blackish brown. Dry again to obtain a separator. In this case, the amount of sulfuric acid-treated polyvinyl alcohol added is polyolefin! ! Although it depends on the thickness and porosity of the male porous body, a range of 0.65 to 1.5 mg/cm2 is appropriate.

As an example of the battery, a 5ubC type close-locked nickel-cadmium storage battery was used. As the nickel electrode, a well-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, a known paste-type cadmium electrode was selected as the cadmium electrode, and the surface of the electrode was plated with nickel in order to improve the gas absorption ability. This electrode has a width of 3.3 cm and a length of 20 cm.
It was cut into cm pieces, and lead plates were attached to two predetermined locations by spot welding. Since the separators were arranged on both sides of the negative electrode, the length was about 40 ctn.

In addition, in order to maintain the discharge compensation capacity in the negative electrode, this electrode was heated in an electrolytic bath at a current density of 14 A/dm2 for 9 hours and 5 minutes.
Charging was carried out using a nickel plate as a counter electrode under conditions of a caustic potassium aqueous solution having a specific gravity of 1.15 and a temperature of 25°C. According to calculations, this charge 5iffi is about 18 to 18% of the total theoretical cadmium capacity.
This corresponds to 20%, but due to low charging efficiency, it is actually about 1
It can be considered that 0% is charged.

As the electrolytic solution, 25 g/+ of lithium hydroxide was dissolved in a caustic potassium aqueous solution having a specific gravity of 1.22.

The nominal capacity is 2.3 Ah. This battery is referred to as (A2).

Next, for comparison, a thickness of 0 containing a commercially available surfactant was prepared.
．． A battery (B2) using a 16 mm polypropylene nonwoven fabric as it is and using the same conditions as the battery (A2),
Similarly, a battery (C2) using a known polyamide nonwoven fabric was added as a separator.

First, we investigated the quick charging characteristics of each battery. In each case, 10 cells were used. The ambient temperature was set to 5° C., and changes in pressure inside the battery were measured when charging was performed at each charging rate. For charging,
The charging was carried out at each charging rate up to 1.4 times the discharge capacity. After that,
The battery charge was reduced to 0.062C, and the battery was charged to 1.5 times the discharge capacity in total.

First, the maximum internal pressure of each battery during IC charging (2, 3A) is 0.2 to 0.0 for battery (A2). 31 (g7cm2.
In the battery (B2), 2.1 to 2.5 kg/Cm2. In pond M (C2), it was 0.4 to 0.7 kg/Cm2.

Next, when charging at 1.25C (2,875A), the battery (
A2), 1.1 to 1°4 kg/c to 2, (
B2) and 2. 9 to 4.5 kg/cm2+ (C2) is 2. 6-3. It was 2 kg/cm2.

That is, compared to battery (A2), battery (B2) is particularly inferior in terms of gas absorption. The reason for this seems to be that, as already mentioned, in the case of battery (B2), the abnormal lyophilicity caused by the surfactant makes it difficult for oxygen gas to reach the negative electrode from the positive electrode during charging. .

Next, the life characteristics due to charge/discharge cycles were investigated. Each battery was subjected to 0.30 charge-1, OC discharge cycles. As a result, first, the discharge capacity in 5 cycles was the same as that of the battery (A2
), the average is 2.360Ah (B2) is the same <2.36
2, (C2) was 2°297. However, 50
When it comes to 0 cycles, the average is 2.338 respectively.
．． It becomes 1.987.2.165 Ah, and the decrease in the capacity of the battery (A2) is extremely small.

In addition, we have also investigated separators made by a conventionally known method in which a polypropylene nonwoven fabric is impregnated with polyvinyl alcohol containing sulfuric acid, but then dried without passing it through slits, as in battery (A2).
During charging in a cycle, the internal pressure increased due to gas and leaked, so it was not included in the test. The reason for this is that a polyvinyl alcohol film containing sulfuric acid was formed on the polypropylene nonwoven fabric, which prevented oxygen gas from reaching the negative electrode from the positive electrode.

Finally, we investigated self-discharge. Each battery was charged to 150% of the previous discharge at 3C at 25°C, and then left at 55°C for 10 days. When the temperature was then returned to 25°C and discharged at 0.2C, the capacity weight retention rate of battery (A2) was 75% on average, while that of battery (B2) was 71% (
In C2), it was only 53%.

(Example 3) 60 cc of a sulfuric acid diluted 5 times and 80 cc of formalin (35% formaldehyde aqueous solution) to 1000 cc of a 3% (heavy @) aqueous solution of polyvinyl alcohol on a 0.16 mm 6 mm thick polypropylene containing a commercially available surfactant.
After being impregnated with the added solution, the excess solution is removed by passing it between two slits. In other words, it is necessary to keep the polypropylene nonwoven fabric wet with this solution.

This is heated and dried at 85° C. for 1 hour. Afterwards, it is washed with water to remove unreacted sulfuric acid, formalin, and residual surfactant. When washed with water, it changes from black to a slightly lighter blackish brown.

Dry again to obtain a separator. In this case, the amount of polyvinyl alcohol treated with sulfuric acid and aldehyde is:
Although it depends on the thickness and porosity of the porous body made of polyolefin fibers, a range of 0.5 to 1.5 mg/cm2 is appropriate.

As an example of the battery, a 5ubC type closed-circuit nickel-cadmium storage battery was used. As the nickel electrode, a well-known foamed nickel electrode was selected, with a width of 3.3 cm and a length of 17 cm. The thickness is 0-7mm. On the other hand, a known paste-type cadmium electrode was selected as the cadmium electrode, and the surface of the electrode was nickel-plated to improve the gas absorption ability. This electrode was cut to a width of 3.3 cm and a length of 20 cm, and lead analyzers were attached to two predetermined locations by spot welding. Since the separators were arranged on both sides of the negative electrode, their length was approximately 40 cm.

In addition, in order to maintain the capacity for discharge compensation in the negative electrode, this electrode was heated in an electrolytic bath at a current density of 14 A/dm2 for 2 hours and 5 minutes.
Charging was carried out using a nickel plate as a counter electrode under conditions of a caustic potassium aqueous solution having a specific gravity of 1.15 and a temperature of 25°C.

As the electrolytic solution, 25 g/I of lithium hydroxide was dissolved in a caustic potassium aqueous solution having a specific gravity of 1.22.

The nominal weight is 2.3 Ah. This battery is referred to as (A3).

Next, for comparison, a thickness of 0 containing a commercially available surfactant was prepared.
．． A battery (B3) using a 16 mm polypropylene nonwoven fabric as it is and using the same conditions as the battery (A3),
Similarly, a battery (C3) using a known polyamide nonwoven fabric was added as a separator.

・ First, we investigated the quick charging characteristics of each battery. In each case, 10 cells were used. The ambient temperature was set at -3° C., and changes in pressure inside the battery were measured when charging was performed at each charging rate. Note that charging was performed at each charging rate up to 1.4 times the discharge capacity. First, the maximum internal pressure of each battery during IC charging (2, 3A) is
For batteries (A3), 1°2 to 1. 4 kg/c ~
2. 3 for battery (B3). 1-3. 5kg/
cm2. 1.7 to 2.5 kg/cm2 for battery (C3)
Met. Next, when charging at 1.25C (2,875A), the internal pressure of each battery was approximately 1.4 times the value when charging with IC.

That is, compared to battery (A3), battery (B3) is particularly inferior in terms of gas absorption. The reason for this is thought to be that, as already mentioned, in the case of battery (B3), the abnormal electrolyte property due to the surfactant makes it difficult for oxygen gas to reach from the positive electrode to the negative electrode during charging. It will be done.

Next, the life characteristics due to charge/discharge cycles were investigated. For each battery, 0.3C charge-1 and OC discharge were repeated. As a result, firstly, the discharge capacity in 5 cycles of the battery (A3
), the average is 2.371Ah.

(B3) is the same <2.362, (C3) is 2°2
It was 97. However, when it comes to 500 cycles, the average is 2.369.1.987.2.165.
Ah, and the decrease in capacity of the battery (A3) is extremely small.

In addition, we also investigated a separator made by a conventionally known method, in which a polypropylene nonwoven fabric was impregnated with polyvinyl alcohol containing sulfuric acid and formalin, but was then heated and dried without passing it through slits, similar to battery (A3). However, the internal pressure increased due to the gas during charging in one cycle, causing leakage, so it was not included in the test. The reason for this is that a polyvinyl alcohol film treated with sulfuric acid and formalin was formed on the polypropylene nonwoven fabric, which prevented oxygen gas from reaching the negative electrode from the positive electrode.

Finally, we investigated self-discharge. After charging each battery to 150% of the previous discharge capacity at 0.3C at 25℃,
So I left it alone for 10 days. Afterwards, when the temperature was returned to 25℃ and discharged at 0.20, the capacity retention rate was 77% on average for the battery (A3), while it was 71% for the battery (B3).
, (C3) remained at 53%.

In addition, although formaldehyde was described as an example of aldehyde in the examples, other acetaldehyde, butyraldehyde, etc. can of course be used.

Effects of the Invention As described above, in the present invention, by using a porous material with a polyvinyl alcohol film formed on the surface of polyolefin fibers as a separator, it is possible to improve gas absorption characteristics during charging of a closed-cell battery and to improve self-discharge. improvements have become possible.

Claims (7)

[Claims] (1) A battery separator characterized by being a porous body made of polyolefin fibers whose surface is coated with polyvinyl alcohol. (2) A battery separator made of a porous body made of polyolefin fibers whose surface is coated with polyvinyl alcohol treated with sulfuric acid. (3) A battery separator made of a porous body made of polyolefin fibers whose surface is coated with polyvinyl alcohol treated with sulfuric acid and aldehyde. (4) Claim 1, characterized in that the porous body is a nonwoven fabric.
, 2 or 3. (5) A method for producing a battery separator, which comprises impregnating a polypropylene nonwoven fabric with a polyvinyl alcohol solution, removing excess solution, and then drying. (6) A method for producing a battery separator, which comprises impregnating a porous body made of polyolefin fibers or polypropylene nonwoven fabric with a polyvinyl alcohol solution containing sulfuric acid, removing excess solution, and then heating and drying. (7) A method for producing a battery separator, which comprises impregnating a porous body made of polyolefin fibers or polypropylene nonwoven fabric with a polyvinyl alcohol solution containing sulfuric acid and aldehyde, removing excess solution, and then heating and drying.