JPH08162147A - Electrolyte for lead-acid battery - Google Patents

Abstract

PURPOSE: To improve the discharging capacity of a lead-acid battery and extend the service life by designing the additive to the electrolyte. CONSTITUTION: This electrolyte is used for lead-acid battery, and a hydrogensulfide is added thereto. Since the hydrogensulfide has a high solubility to electrolyte, compared with a conventional sulfate, the effect for suppressing the generation of Pb<2+> , at an over discharge, to suppress the crystal growth of PbSO4 or the reduction in conductivity of the electrolyte is improved by the portion that the adding concentration to the electrolyte can be increased. The precipitation of the hydrogensulfide on a grid-active material critical surface under low temperature can be also suppressed to suppress the problem that the shielding between grid-active materials by the precipitated material. Further, although PbSO4 repeats dissolution and precipitation to grow the crystal when the pH of the electrolyte is increased, the hydrogensulfide is advantageous for suppressing the crystal growth of PbSO4 because it has a high acidity, compared with the sulfate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic solution for a lead storage battery, and more particularly to an electrolytic solution for a lead storage battery which can improve the discharge capacity and life of the lead storage battery.

[0002]

2. Description of the Related Art Conventionally, sulfuric acid was used as an electrolytic solution, Pb powder was used as a negative electrode active material, and PbO ₂ was used as a positive electrode active material, and these active materials were placed in the middle of a separator and placed in a glass or synthetic resin battery container. Lead acid batteries are known. In this lead acid battery, the negative electrode Pb and the positive electrode PbO ₂ become PbSO ₄ during discharging, and the negative electrode returns to Pb and the positive electrode returns to PbO ₂ during charging. Further, the dilute sulfuric acid in the electrolytic solution is converted into water by electrolysis during discharge, and returns from water to dilute sulfuric acid during charge.

Generally, lead-acid batteries are left for a long time,
If left over-discharged, it becomes unchargeable due to self-discharge. That is, when over-discharged, the concentration of sulfuric acid in the electrolytic solution is lowered and the specific gravity of the electrolytic solution is lowered. In particular, the specific gravity of the electrolytic solution is remarkably reduced in the vicinity of the grid inside the electrode plate from the surface of the electrode plate.
When the specific gravity of the electrolytic solution decreases in this way, Pb as a grid
And the solubility of PbSO ₄ formed in the electrode plate increases
^A large amount of ²⁺ is eluted, and this Pb ²⁺ combines with OH ⁻ and O ^{2 −} to produce PbO _x . Further, since the pH of the electrolytic solution increases and the potential decreases due to such an oxidation reaction, a reduction reaction of PbO ₂ → PbSO ₄ occurs near the positive electrode lattice, and PbSO ₄ repeats dissolution and precipitation when the pH increases. Huge non-reducing PbSO ₄ crystals are deposited at the lattice-active material interface. Therefore, a high resistance film is formed on the lattice-active material interface due to the generation and growth of PbO _x and PbSO ₄ , resulting in a non-chargeable state.

Therefore, Na ₂ SO ₄ and K ₂ S are added to the electrolytic solution.
It has been conventionally performed to improve the over-discharge leaving performance by adding an alkali metal sulfate such as O ₄ or ammonium sulfate (Japanese Patent Laid-Open No. 1-267965).
(See the official gazette). Sulfates and ammonium sulfates of these alkali metals, when the specific gravity of the electrolyte decreases during overdischarge,
It functions to suppress the generation of Pb ²⁺ and suppress the generation of PbO _x and the crystal growth of PbSO ₄ . Also, during over discharge, H ₂ SO ₄
Becomes H ₂ O or PbSO ₄ , so that the number of ions that carry the charging current is extremely small, and the conductivity of the electrolytic solution is extremely reduced. However, the alkali metal sulfate or ammonium sulfate added to the electrolytic solution Ions suppress the decrease in conductivity and improve the recovery charge characteristics.

[0005]

However, it is difficult to sufficiently improve the discharge capacity even by the technique of adding an alkali metal sulfate or ammonium sulfate to the above-mentioned conventional electrolytic solution, and further improvement of the discharge capacity and Life extension is desired. The present invention has been made in view of the above circumstances, and it is a technical problem to be solved to further improve the discharge capacity and extend the life by devising an additive in the electrolytic solution.

[0006]

An electrolytic solution for a lead-acid battery of the present invention which solves the above-mentioned problems is an electrolytic solution used for a lead-acid battery, characterized in that hydrogen sulfate is added. Is.

[0007]

[Action] Hydrogen sulfate is added to the electrolytic solution for a lead storage battery of the present invention, which improves the discharge capacity of the lead storage battery and improves the discharge capacity of the lead storage battery as compared with a conventional electrolytic solution containing an alkali metal sulfate or ammonium sulfate. The life can be extended more effectively. The reason for this is considered as follows.

Hydrogen sulphate has the effect of suppressing the production of Pb ²⁺ and suppressing the crystal growth of PbSO ₄ and suppressing the decrease of the electric conductivity of the electrolytic solution at the time of over-discharge, like the above-mentioned conventional sulphate. To contribute. That is, when the sulfuric acid concentration in the electrolytic solution decreases and the specific gravity of the electrolytic solution decreases during overdischarge, the solubility of PbSO ₄ increases and the production of Pb ²⁺ increases, but PbSO _{4 of the} weak electrolyte is called SO ₄ ^2-. When hydrogensulfate having a common ion coexists, its ionization degree decreases, so that the production of Pb ²⁺ can be suppressed. Also, during over discharge, H ₂ SO ₄
Changes to H ₂ O or PbSO ₄ , the presence of the ions that carry the charging current is extremely low, and the conductivity of the electrolyte is extremely reduced. However, due to the hydrogen sulfate ion added to the electrolyte, the conductivity decreases. The decrease is suppressed and the recovery charge characteristics are improved, which contributes to the improvement of the discharge capacity and the life.

Here, the hydrogen sulfate is compared with the conventional sulfate.
All of them have high solubility in the electrolyte solution and
It is possible to increase the degree. For example, K₂SO_Fourof
Solubility in water is 12.05g / 100g (25 ℃)
While KHSO_FourSolubility in water is 5
It is 1.5 g / 100 g (25 ° C.). For this reason sulfuric acid water
Elementary salt is a component that can increase the concentration of addition to the electrolyte.
However, at the time of over discharge, Pb ²⁺Generation of PbSO_Fourof
It suppresses crystal growth and suppresses the decrease in the conductivity of the electrolyte.
Is superior to conventional sulfates. Also, for electrolyte
The high solubility of hydrogen sulphate makes it
-Precipitation at the active material interface can be suppressed,
The material shields the lattice-active material and reduces the discharge capacity.
You can suppress the problem.

Further, as described above, when the pH of the electrolytic solution becomes high, a reduction reaction of PbO ₂ → PbSO ₄ occurs near the positive electrode lattice, and PbSO ₄ is repeatedly dissolved and precipitated to form a large non-reducing PbSO ₄ Although crystals are deposited at the lattice-active material interface, hydrogen sulfate has a higher acidity than sulfates, which is advantageous for suppressing the crystal growth of PbSO ₄ .

[0011]

EXAMPLES Examples of the present invention will be specifically described below. Example 1 An electrolytic solution was prepared by adding 0.1 mol / L of potassium hydrogen sulfate (KHSO ₄ ) to dilute sulfuric acid (concentration 42.4 wt%). This electrolytic solution was injected into a battery case made of synthetic resin in which positive and negative electrode plates were arranged via a separator made of fine glass fibers, to produce a lead storage battery of 2Ah-6.0V. The positive electrode active material is PbO ₂ and the negative electrode active material is Pb.

(Example 2) Potassium hydrogensulfate (KHSO
₄ ) instead of ammonium hydrogen sulfate (NH ₄ · HSO
_A lead acid battery was produced in the same manner as in Example 1 except that ₄ ) was added to the electrolytic solution. Except that (Comparative Example 1) without the addition of potassium hydrogen sulfate (KHSO ₄₎ in the electrolytic solution, to prepare a lead-acid battery in the same manner as in Example 1.

Comparative Example 2 Potassium hydrogen sulfate (KHSO
_A lead acid battery was prepared in the same manner as in Example 1 except that calcium sulfate (CaSO ₄ ) was added to the electrolytic solution instead of ₄ ). (Comparative Example 3) A lead storage battery was prepared in the same manner as in Example 1 except that hydrazine sulfate (N ₂ H ₄ · H ₂ SO ₄ ) was added to the electrolytic solution instead of potassium hydrogen sulfate (KHSO ₄ ). did.

(Comparative Example 4) Potassium hydrogen sulfate (KHSO
_A lead acid battery was prepared in the same manner as in Example 1 except that sodium sulfate (Na ₂ SO ₄ ) was added to the electrolytic solution instead of ₄ ). (Comparative Example 5) except that added to the electrolytic solution of potassium sulfate (K ₂ SO ₄₎ in place of potassium hydrogen sulfate (KHSO ₄₎ was prepared lead-acid batteries in the same manner as in Example 1.

Comparative Example 6 Potassium hydrogen sulfate (KHSO
_A lead acid battery was prepared in the same manner as in Example 1 except that magnesium sulfate (MgSO ₄ ) was added to the electrolytic solution instead of ₄ ). Except that the addition (Comparative Example 7) Instead of ammonium sulfate potassium hydrogen sulfate _{(KHSO 4) ((NH 4} ) 2 SO 4) to the electrolytic solution, to prepare a lead-acid battery in the same manner as in Example 1.

(Evaluation of Discharge Capacity) The discharge capacities of the lead storage batteries of Examples 1 and 2 and Comparative Examples 1 to 7 were evaluated. This is the lead according to Comparative Example 1, which was charged / discharged under the conditions of discharge: 2 A (1 CA) up to 4.2 V, charge: 0.2 A (0.1 CA) and 7 Hr, and nothing was added to the electrolytic solution. Others were compared based on the discharge capacity of the storage battery. The result is shown in FIG.

As is apparent from FIG. 1, the lead storage batteries according to Examples 1 and 2 in which hydrogen sulfate was added to the electrolytic solution were the lead storage batteries according to Comparative Examples 2 to 7 in which sulfate was added to the electrolytic solution. In both cases, the discharge capacity was improved. Further, regarding the lead storage battery according to Example 2 in which ammonium hydrogen sulfate was added to the electrolytic solution and the lead storage battery according to Comparative Example 1 in which nothing was added to the electrolytic solution, the discharge time and the discharge voltage were changed under the same conditions as above. I investigated the relationship. The results for Example 2 are shown in FIG. 2, and the results for Comparative Example 1 are shown in FIG.

As is clear from FIGS. 2 and 3, the lead-acid battery according to Example 2 has a longer discharge time during the second and subsequent discharges than the lead-acid battery according to Comparative Example 1 and has a discharge capacity of Has improved. (Evaluation of Life) The lead storage batteries according to Example 1 and Comparative Example 1 manufactured under the specifications of 45 Ah and 12 V were evaluated for life. This was performed based on the evaluation of JIS light load life characteristics in an atmosphere of 75 ° C. FIG. 4 shows the results.

As is apparent from FIG. 4, the lead storage battery according to Example 1 in which potassium hydrogen sulfate was added to the electrolytic solution has a life longer than that of the lead storage battery according to Comparative Example 1 in which nothing was added to the electrolytic solution. It was extended by about 20%. In the above examples, as hydrogen sulfate, an example using potassium hydrogen sulfate and ammonium hydrogen sulfate was described, but similar effects can be obtained for other hydrogen sulfate such as hydrogen sulfate of alkali metal such as sodium hydrogen sulfate. It is thought to be obtained.

The amount of hydrogen sulfate added to the electrolytic solution can be appropriately set depending on, for example, the environmental temperature of the lead storage battery and the solubility of the hydrogen sulfate in the electrolytic solution. The effect of the present invention can be maximized by adding the maximum amount of hydrogen sulfate that can be dissolved in the electrolytic solution at a temperature. A preferred range of the amount of hydrogen sulfate added to the electrolytic solution is 2 to 100 g / l (liter), and a more preferred range is 10 to 30 g / l.
(Liter).

[0021]

As described in detail above, when the electrolytic solution containing hydrogen sulfate of the present invention is used in a lead storage battery, a lead storage battery using a conventional electrolytic solution containing alkali metal sulfate or ammonium sulfate is used. Compared with the above, it is possible to more effectively improve the discharge capacity and extend the life of the lead storage battery.
Then, by adding the maximum amount of hydrogen sulfate that can be dissolved in the electrolytic solution under the environment temperature in which the lead storage battery is used, it becomes possible to improve the discharge capacity at low temperature more than before.

[Brief description of drawings]

FIG. 1 is a diagram showing a result of evaluation of discharge capacities of lead acid batteries according to Examples 1 and 2 and Comparative Examples 1 to 7.

FIG. 2 is a diagram showing a relationship between a discharge time and a discharge voltage of a lead storage battery according to a second embodiment.

FIG. 3 is a diagram showing a relationship between a discharge time and a discharge voltage of the lead storage battery according to Comparative Example 1.

FIG. 4 is a diagram showing the results of evaluating life characteristics of lead acid batteries according to Example 1 and Comparative Example 1.

Claims (1)

[Claims] 1. An electrolytic solution used in a lead storage battery, comprising:
An electrolytic solution for a lead storage battery, characterized in that hydrogen sulfate is added.