JP2000340233A - Lead-acid battery additives - Google Patents

Abstract

(57) [Problem] To provide an inexpensive additive for a lead storage battery, which can significantly improve the charge and discharge cycle life. SOLUTION: The amount of hydrogen-containing functional groups present on the surface is 3 μm.
An additive for a lead storage battery, wherein carbon black having a value of at least eq / m ² and a maximum agglomerate particle diameter Dupa99% (nm) of 500 nm or less in an aqueous dispersion is dispersed in water. However, the value of the maximum particle diameter Dupa99% (nm) of the agglomerate is determined by irradiating an aqueous dispersion of carbon black with a laser beam, and calculating the agglomerate particle diameter in the cumulative frequency distribution curve prepared from the frequency modulation degree of the scattered light.
Indicates the value of% cumulative frequency. The amount of the hydrogen-containing functional group is the sum of the carboxyl group and the hydroxyl group.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an additive for a lead storage battery capable of significantly improving the cycle life of charge and discharge.

[0002]

2. Description of the Related Art Lead storage batteries, which are rechargeable secondary batteries, are:
Despite shortcomings such as short charge / discharge cycle life, heavy weight, and low energy density per unit weight, automotive power supplies, emergency power supplies,
It is widely used for power supplies for uninterruptible power supplies.

[0003] A lead-acid battery uses lead dioxide (Pb) as a positive electrode.
O _2), using a metal lead (Pb) in the negative electrode, a sulfuric acid aqueous solution as an electrolytic solution, the following (1) during discharging, (2) reacting the PbSO ₄ generates the. Positive ^{_{electrode; PbO 2 + 4H + + SO}} 4 2- + 2e - → PbSO 4 + 2H 2 O ...... (1) ^{_{anode; Pb + SO 4 2- → PbSO}} 4 + 2e - ...... (2) Further, by the reverse reaction during discharge during charging, By electrochemically changing PbSO ₄ generated at the time of discharging to PbO ₂ , Pb and sulfuric acid, the electromotive force is recovered, and discharging and charging can be repeated.

The reason why the cycle life of charge / discharge of this lead storage battery is short is that the electronic conductivity of lead sulfate (PbSO ₄ ) generated by the discharge is extremely low. That is, PbSO ₄ and the conductive material come into contact with each other where the charging reaction proceeds,
Furthermore, since these are limited to the region in contact with the electrolytic solution, the charging reaction hardly proceeds as compared with the discharging reaction, and P
It is difficult to completely change bSO ₄ to PbO ₂ or Pb. As a result, PbSO ₄ is accumulated as charge and discharge are repeated, and the dischargeable capacity decreases and charging becomes impossible.

[0005] In order to impart conductivity to a substance having a low electron conductivity and allow the electrochemical reaction to proceed smoothly, a method of mixing a conductive material such as graphite powder or acetylene black is generally used. For example, when producing a positive electrode of a manganese dry battery, manganese dioxide (MnO ₂ ) having low conductivity is used.
Is mixed with acetylene black. However, this technique cannot be applied to lead-acid batteries.

That is, in the discharge reactions of the above formulas (1) and (2), both the positive electrode and the negative electrode are once dissolved in the electrolyte as Pb ²⁺ ions, and react with sulfate ions in the electrolyte to form PbS ^+.
O ₄ is generated and precipitated. Therefore, even if a conductive material such as acetylene black is mixed in the positive electrode or the negative electrode,
Since acetylene black and the like are dispersed in the electrolytic solution with the elution of b ²⁺ ions, it becomes difficult to electrochemically change to PbO ₂ and Pb by contacting PbSO ₄ during charging to give conductivity.

Therefore, Japanese Patent Application Laid-Open No. Hei 8-7916 discloses that
A lead-acid battery in which negatively-charged carbon powder is electrodeposited on the anode surface of a lead-acid battery, and an electrolyte in a lead-acid battery in which negatively-charged carbon powder is suspended in an acid aqueous solution constituting an electrolytic solution. Proposed. According to this publication, the electrical resistance between active materials is reduced by electrodepositing negatively charged carbon powder on the anode of a lead-acid battery, and the coating of carbon powder prevents PbSO ₄ from adhering to the active material. To prevent the passivation of the anode.
It is presumed that it effectively acts on bSO ₄ separation and decomposition.

Japanese Patent Application Laid-Open No. 10-228922 discloses that conductive fine particles having a hydrophilic group on the surface and having a median diameter of 600 nm or less are placed in an aqueous electrolyte and / or on the surface of electrode active material particles. A secondary battery additive characterized by containing has been proposed, in which the conductive fine particles are made of carbon, and the hydrophilic group contains a carbonyl group, a carboxyl group, a hydroxyl group, or a sulfo group. I have.

According to Japanese Patent Application Laid-Open No. Hei 10-228922, specifically, carbon black is preferable as the conductive fine particles, and black or black ink obtained by adding glue or gum arabic to the electrolyte is added to the electrolyte of the lead storage battery. By doing so, the size of the conductive fine particles is much smaller than before, the adsorption on the electrode active material surface is faster than the precipitation rate in the electrolytic solution, and the deterioration due to the charge-discharge cycle is caused by the coexistence of the organic protective colloid. According to the company, it can be reduced.

[0010]

However, according to Japanese Patent Application Laid-Open No. Hei 8-7916, the preparation of negatively charged carbon powder is carried out by modifying the surface by oxidation treatment, and particularly by electrolytically oxidizing a carbon material such as a graphite rod. However, there is a disadvantage that the cost is extremely high. Also, Japanese Patent Application Laid-Open No. 10-22
According to the publication 8922, the protective colloid adsorbed on the carbon black surface has a poor conductivity, which impairs the conductivity of the carbon black itself. Further, the protective colloid is charged to undergo electrochemical oxidation and reduction at the positive electrode and the negative electrode. There are problems such as a decrease in discharge efficiency and deterioration of battery performance due to generated substances.

Therefore, the present inventors have conducted intensive studies to develop an inexpensive additive for a lead-acid battery that can smoothly transfer electrons to PbSO ₄ and facilitate the charging reaction. As a result, it has been found that the accumulation of PbSO ₄ can be suppressed by using a specific carbon black. The present invention has been developed on the basis of this finding, and an object of the present invention is to provide an inexpensive additive for a lead-acid battery that can significantly improve the cycle life of charge and discharge.

[0012]

The additive for a lead-acid battery according to the present invention for achieving the above object has a hydrogen-containing functional group present on the surface of 3 μeq / m ² or more, A structural feature is that carbon black having a maximum particle diameter Dupa99% (nm) value of agglomerate of 500 nm or less is dispersed in water. However, the value of the maximum particle diameter Dupa99% (nm) of the agglomerate is determined by irradiating the aqueous dispersion of carbon black with a laser beam, and obtaining a 99% cumulative value in the cumulative frequency distribution curve of the agglomerate particle diameter created from the frequency modulation degree of the scattered light. Indicates the frequency value.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Carbon black is hydrophobic and has low wettability with water, and it is extremely difficult to stably disperse it in water. This is because the amount of functional groups having high affinity for water molecules existing on the surface of the carbon black particles is extremely small. Therefore, it has long been known to improve the water dispersion performance by oxidizing carbon black to form a hydrophilic functional group on the surface of the carbon black particles.

When carbon black is oxidized, various functional groups are generated depending on the oxidizing agent and the oxidizing conditions. Among these functional groups, the amount of functional groups having a high affinity for water molecules is important for effectively improving the water dispersion performance.

When carbon black is dispersed in water, the amount of hydrophilic functional groups present at the contact interface between carbon black and water molecules plays an important role.
That is, there are various varieties of carbon black having different specific surface areas, and in order to provide an accurate index of the amount of hydrophilic functional groups present at the contact interface with water molecules, in the present invention, the unit of carbon black particles is The amount of the hydrogen-containing functional group existing per surface area is specified, and the value is regulated to a value of ³ μeq / m ² or more. 3μeq of hydrogen-containing functional group
If it is less than / m ² , sufficient water dispersion performance cannot be imparted.

The hydrogen-containing functional groups are specifically a carboxyl group (—COOH) and a hydroxyl group (—OH), and the amount of the hydrogen-containing functional group is the sum of the carboxyl group and the hydroxyl group. That is, when the carbon black is oxidized, various functional groups such as a carboxyl group (—COOH) and a hydroxyl group (—OH) as well as a hydronium group (—H) and a quinone group (> C ＝ O) are generated. .
Among these functional groups, the affinity for water molecules is high, and in order to maintain and maintain a stable dispersion state in water, the abundance of carboxyl groups and hydroxyl groups containing active hydrogen greatly affects, and hydronium groups are unstable The quinone group has a low affinity for water molecules and rather inhibits water dispersibility.

These hydrogen-containing functional groups can be formed by oxidizing carbon black. The oxidizing treatment is performed by using a halogen acid such as hypochlorous acid, chlorous acid, chloric acid, or an acid such as persulfuric acid. An appropriate oxidation method such as wet oxidation with a commonly used aqueous solution of an oxidizing agent such as a salt or aqueous hydrogen peroxide, or dry oxidation with oxygen or ozone can be applied.

The values measured for the functional groups by the following method are used. Carboxyl group content: 2 to 5 g of carbon black was added to 50 ml of 0.976N sodium hydrogen carbonate and shaken for 6 hours. Then, the carbon black was filtered off from the reaction solution, and a 0.05N aqueous hydrochloric acid solution was added to the filtrate. pH 7.0
The neutralization titration test is performed with a 0.05N aqueous solution of sodium hydroxide until the carboxyl group is measured. This measured value is the nitrogen adsorption specific surface area of carbon black (N ₂ SA; m ² / g)
Is defined as the amount of carboxyl groups formed per unit surface area of carbon black (μeq / m ² ).

Hydroxyl group content: 2,2'-Diphenyl-
1-picrylhydrazyl (DPPH) is dissolved in carbon tetrachloride to prepare a solution having a concentration of 5 × 10 ⁻⁴ mol / l, and 0.1 to 0.6 g of carbon black is added to the solution, and the solution is kept at a constant temperature of 60 ° C. Stir in the bath for 6 hours. Thereafter, carbon black is separated from the reaction solution by filtration, and the absorbance of the filtrate at a wavelength of 520 nm is measured by an ultraviolet absorption spectrophotometer to quantify the hydroxyl group.
The value obtained by dividing the value measured in this manner by the nitrogen adsorption specific surface area of carbon black (N ₂ SA; m ² / g) is the amount of hydroxyl groups formed per unit surface area of carbon black (μeq / m ² ). And

The additive for a lead storage battery of the present invention is characterized in that, in addition to the above-mentioned hydrogen-containing functional group content, carbon black having a maximum agglomerate particle diameter Dupa99% (nm) value of 500 nm or less in an aqueous dispersion is added to water. It is an essential requirement that they be distributed.

When carbon black is dispersed in water, it is easy to disperse in water, and in order to maintain the dispersion state stably, carbon black particles are dispersed in water in a finer aggregated form and reagglomerated. To form a large aggregated form. In other words, the aggregate form of carbon black is such that several to several tens of basic fine particles of carbon black are fused and bonded in an irregular and complex chain form to form an aggregate. Are formed of aggregates (agglomerates) that are entangled with each other or adhere and re-aggregate.

Therefore, the aggregated form of carbon black dispersed in water is such that the aggregates, which are the smallest aggregate units of carbon black, are dispersed in water, and the aggregates in which the aggregates are reagglomerated are less agglomerated. The state is effective for improving the dispersion performance, and the dispersion state free of agglomerates is ideal. However, aggregates exhibiting a complicated three-dimensional morphology are entangled and re-agglomerated, tend to form agglomerates, and it is almost impossible to obtain a dispersed state free of agglomerates. On the other hand, a larger agglomerate is more advantageous in terms of electron conductivity.

Therefore, in the present invention, by setting the value of the maximum particle diameter Dupa99% (nm) of agglomerate to 500 nm or less, the dispersion stability of carbon black in water can be maintained and improved, and the electron conductivity can be improved. In order to maintain the high level. Dupa99%
If the value of (nm) exceeds 500 nm, the aggregates are reaggregated and the agglomerates are large, so that the aggregates are likely to reaggregate or sediment in an aqueous medium, and the dispersion stability is significantly reduced.

The maximum particle size of agglomerate Dupa9
The value obtained by the following measurement method is used for 9% (nm). Disperse carbon black in water 0.1-0.5g /
l, and prepare a heterodyne laser Doppler type particle size distribution analyzer (Microtrac, UPAmode
19340), the dispersion is irradiated with laser light, and the particle size of agglomerate in the dispersion is measured from the degree of frequency modulation of the scattered light. The carbon black in the dispersion liquid undergoes Brownian motion, and the frequency of scattered light is modulated by the size of the dispersed carbon black aggregate due to the Doppler effect. Therefore, since the intensity of the Brownian motion differs depending on the size of the aggregate, the size of the aggregate in a state of being dispersed in water, that is, the particle diameter of agglomerate can be measured. A cumulative frequency distribution curve is created from the particle diameters of the agglomerates measured in this way, and the value of the 99% cumulative frequency is defined as the maximum particle diameter Dupa99% (nm) of the agglomerates.

The additive for a lead storage battery according to the present invention has a hydrogen-containing functional group content of 3 μeq / m ² or more on the surface and a maximum agglomerate particle size Dupa of 99% in an aqueous dispersion.
The value of (nm) is obtained by dispersing carbon black having a value of 500 nm or less in water, and a method of adding the additive of the present invention to a part of the electrolyte is preferable as a method of adding the black to the electrolyte of the lead storage battery. . It is possible to completely remove water by drying the wet-oxidized carbon black and add it to the electrolyte in the form of a powder.However, part of the carbon black is easily aggregated by the drying treatment, This is because redispersion is not easy, and handling is inconvenient because of the fine powder.

Since the additive of the present invention exerts a great effect even in a small amount, the amount to be replaced with the electrolyte is
About 0.05 to 0.3 g of carbon black equivalent per ml is sufficient, and the water dispersion concentration of carbon black should be 1 to suppress a decrease in the sulfuric acid concentration in the substituted electrolyte.
It is preferable to set it to wt% or more.

The additive for a lead storage battery of the present invention is prepared by, for example, adding carbon black to an aqueous solution of an acid such as a halogen acid such as hypochlorous acid, chlorous acid or chloric acid, or a salt thereof such as persulfuric acid, and stirring. After mixing and oxidizing, the reduced salts are removed using an ultrafiltration membrane, a microfiltration membrane, a reverse osmosis membrane, or the like. Next, the pH of the dispersion is adjusted to about 8 to 11 to improve the dispersibility of the carbon black, and then the ultrafiltration membrane and the microfiltration membrane described above are used to adjust the dispersion concentration of the carbon black to a predetermined concentration. Concentration and desalting are performed with a separation membrane such as a reverse osmosis membrane. Thus, the additive for a lead storage battery of the present invention can be produced.

Hereinafter, examples of the present invention will be specifically described in comparison with comparative examples.

Example 1 150 g of carbon black (Tokai Carbon Co., Ltd., Toka Black # 7550F) was added to 3000 ml of a 1.5 N aqueous sodium persulfate solution at a temperature of 60 ° C. and a rotation speed of 300.
The mixture was stirred and mixed at a rotation speed of rpm for 10 hours, oxidized, and filtered. Next, after neutralizing the oxidized carbon black with an aqueous solution of sodium hydroxide, an excess salt remaining in the dispersion is separated with an ultrafiltration membrane (Asahi Kasei Corporation, AHP-1010, molecular weight cut off 50,000), Purified. Thus, the additive for a lead storage battery of the present invention comprising an aqueous dispersion of carbon black was produced. In addition, carbon black was separated from the aqueous dispersion, and carboxyl groups and hydroxyl groups were measured as surface functional groups, and the maximum particle diameter Dupa 99% of agglomerate was determined. As a result, the sum of the carboxyl group and the hydroxyl group (the amount of the hydrogen-containing functional group) was 4.12.
The value of μeq / m ² and the maximum particle size Dupa 99% of the agglomerate was 156 nm.

The thus prepared additive having a carbon black aqueous dispersion concentration of 3% by weight was replaced with 6 ml of an electrolyte of a commercially available motorcycle battery (capacity: 2 AHr, 6 V). This battery was charged at 0.2 A for 12 hours, and then repeatedly discharged at 0.2 A to 5.2 V. Battery life is as follows: discharge capacity is 70% of nominal capacity (1.4 AHr)
It was the time when it decreased to. As a result, the battery life was 321
It was a cycle. FIG. 1 shows a change in discharge capacity depending on the number of charge / discharge cycles.

Example 2 An aqueous carbon black dispersion was produced by the same oxidation treatment as in Example 1, except that Toka Black # 7400F was used instead of carbon black. The sum of the carboxyl group and the hydroxyl group (the amount of the hydrogen-containing functional group) of the carbon black in the aqueous carbon black dispersion was 4.36 μeq / m ² , and the maximum particle size of the agglomerate Dupa9
The value of 9% was 360 nm.

The thus prepared additive having a carbon black aqueous dispersion concentration of 3% by weight was replaced with 6 ml of an electrolyte of a commercially available motorcycle battery (capacity: 2 AHr, 6 V). The battery was charged at 0.4 A for 6 hours and then charged at 0.
The discharge was repeated up to 4.8 V at 4 A. The life of the battery was determined when the discharge capacity decreased to 70% (1.4 AHr) of the nominal capacity. As a result, the battery life was 218 cycles. FIG. 2 shows the change in discharge capacity depending on the number of charge / discharge cycles.

Comparative Example 1 Commercially available motorcycle battery (capacity: 2 AHr, 6 V)
Is charged at 0.2 A for 12 hours and then at 0.2 A for 5.
The discharge to 2V was repeated. The battery life was determined when the discharge capacity dropped to 70% of the nominal capacity (1.4 AHr). As a result, the battery life was 162 cycles. FIG. 1 shows a change in discharge capacity depending on the number of charge / discharge cycles.

Comparative Example 2 Commercially available motorcycle battery (capacity: 2 AHr, 6 V)
Is charged at 0.4 A for 6 hours and then 4.8 at 0.4 A
The discharge to V was repeated. The battery life was determined when the discharge capacity dropped to 70% of the nominal capacity (1.4 AHr). As a result, the battery life was 74 cycles. FIG. 2 shows the change in discharge capacity depending on the number of charge / discharge cycles.

Example 3 An aqueous carbon black dispersion was produced by the same oxidation treatment as in Example 1 except that Toka Black # 7240F was used instead of carbon black. The sum of the carboxyl group and the hydroxyl group (the amount of the hydrogen-containing functional group) of the carbon black in the aqueous carbon black dispersion was 4.31 μeq / m ² , and the maximum particle size of the agglomerate Dupa9
The value of 9% was 420 nm.

The thus prepared additive having a carbon black dispersion concentration of 3% by weight was replaced with 6 ml of the electrolyte of the battery which had reached the end of its life in Comparative Example 2. This battery is 0.2A at 1
The battery was charged for 2 hours and repeatedly discharged at 0.2 A to 5.2 V. As a result, the discharge capacity once lowered was recovered to a level close to the initial capacity. Thereafter, 147 cycles of charge / discharge were possible before the capacity was reduced and the life was reached again.

Comparative Example 3 An aqueous carbon black dispersion was produced by the same oxidation treatment as in Example 1 except that thermal black (N990) was used. The sum of the carboxyl group and the hydroxyl group (the amount of the hydrogen-containing functional group) of the carbon black in the aqueous carbon black dispersion was 2.80 μeq / m ² , and the maximum particle diameter Dupa 99% of the agglomerate was 1240 nm. A charge / discharge test was performed using this dispersion and the same commercially available motorcycle battery as in Example 1 under the same conditions as in Example 1. As a result, almost no effect was observed, and the battery life was 182 cycles. Met. FIG. 3 shows a change in discharge capacity depending on the number of charge / discharge cycles. FIG. 3 also shows the results of Example 1.

Comparative Example 4 An aqueous carbon black dispersion was prepared in the same manner as in Example 1 except that the temperature of the oxidation treatment was set at 40 ° C. The sum of the carboxyl group and the hydroxyl group (the amount of the hydrogen-containing functional group) of the carbon black in this dispersion was 2.0 μeq /
m ² , the value of the maximum particle diameter Dupa99% of agglomerate is 156
nm. This aqueous dispersion (carbon black concentration: 3
(wt%), a charge / discharge test of the battery was performed in the same manner as in Example 1, but almost no effect was observed, and the battery life was 168 cycles. FIG. 3 shows a change in discharge capacity depending on the number of charge / discharge cycles.

FIGS. 1 and 2 show that the replacement of the aqueous carbon black dispersions of Examples 1 and 2 with a part of the electrolyte solution of an unused battery greatly improves the charge / discharge cycle life. In addition, it is recognized that the discharge rate exceeding 2 AHr can be achieved by increasing the utilization rates of the active materials of the positive electrode and the negative electrode. In addition, even in the case of the battery whose battery performance has been deteriorated by use from Example 3, it is recognized that the discharge capacity is recovered by replacing the additive of the present invention with a part of the electrolytic solution, thereby prolonging the battery life. .

In addition, if the requirements of the surface functional group amount of carbon black and the maximum particle size of agglomerate specified in the present invention are not satisfied from FIG. 3, the cycle life of charge / discharge cannot be improved. I understand.

[0041]

As described above, the additive for a lead storage battery according to the present invention uses an inexpensive carbon black to adjust the amount of a hydrogen-containing functional group, which is the sum of a carboxyl group and a hydroxyl group, to 3 μeq. / M ² or more, the value of the maximum particle size Dupa99% (nm) of agglomerate in the aqueous dispersion is 50
0 nm or less, since the carbon black of the specified properties is formed from a dispersion liquid dispersed in water, it exhibits excellent dispersion performance with respect to the electrolyte solution of a lead storage battery, and can be stably dispersed over a long period of time. Pb with a small amount added
The conductivity can be imparted to SO _4, and the cycle life of charge and discharge of the lead storage battery can be greatly improved.

[Brief description of the drawings]

FIG. 1 is a graph comparing the change in discharge capacity with the number of charge / discharge cycles in Example 1 and Comparative Example 1.

FIG. 2 is a graph comparing the change in discharge capacity with the number of charge / discharge cycles in Example 2 and Comparative Example 2.

FIG. 3 is a graph comparing the change in discharge capacity with the number of charge / discharge cycles in Example 1 and Comparative Examples 3 and 4.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masataka Kono 1-3-2 Kitaaoyama, Minato-ku, Tokyo Tokai Carbon Co., Ltd. (72) Inventor Yoshihiko Muto 1-3-2 Kitaaoyama, Minato-ku, Tokyo Tokai F term in Carbon Co., Ltd. (reference) 5H003 AA04 BA07 BB04 BB15 BC05 BD02 BD03

Claims (2)

[Claims] 1. The amount of a hydrogen-containing functional group present on a surface is 3 μm.
An additive for a lead storage battery, wherein carbon black having a value of at least eq / m ² and a maximum agglomerate particle diameter Dupa99% (nm) of 500 nm or less in an aqueous dispersion is dispersed in water. However, the value of the maximum particle diameter Dupa99% (nm) of the agglomerate is determined by irradiating an aqueous dispersion of carbon black with a laser beam, and calculating the agglomerate particle diameter in the cumulative frequency distribution curve prepared from the frequency modulation degree of the scattered light.
Indicates the value of% cumulative frequency. 2. The additive for a lead storage battery according to claim 1, wherein the amount of the hydrogen-containing functional group is the sum of a carboxyl group and a hydroxyl group.