JPH01302660A - Sealed type lead-acid battery - Google Patents

Abstract

PURPOSE:To enhance the rate of utilization and prolong the cycle lifetime of charging/discharging by changing the active substance density (porosity) across the thickness of the electrode plate, and making in multi-layer construction. CONSTITUTION:A double construction is incorporated by laying positive electrode active substance in layers in the thickness direction of the electrode plate from its center toward outside with a lower density (higher porosity) layer 2 situated in the central part of the electrode and with a higher density (lower porosity) layer 3 situated in the part contacting separator of the electrode plate surface. Accordingly, even repetitive charging and discharging does not cause the active substance to be turned into fine particles at the layer in the electrode plate surface part. Also the central part of the electrode plate has high porosity, which facilitates dispersion of the electrolyte and enriches existence of the electrolyte. This enhances the rate of utilization of the active substance and accomplishes a battery with large capacity and an excellent cycle lifetime of charging and discharging.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a sealed lead-acid battery that is widely used in portable devices such as portable videos, emergency lights, and the like.

Conventional technology Conventionally, the positive electrode active material of sealed lead-acid batteries was made by kneading lead oxide made by oxidizing pure lead and a fine powder mixture of pure lead with water and dilute sulfuric acid to form a paste. were mainly used. These materials were then dried, aged, and chemically converted into positive electrode active materials. Depending on the mixing ratio of these lead oxide powders, water and dilute sulfuric acid, and the kneading method, the density, or porosity, of the lead dioxide electrode plate obtained as the active material will vary, and the selection is made according to the purpose of the battery. It was Generally, when the porosity is high, the utilization rate of the active material is high, but the active material tends to become fine particles, and when the porosity is low, the opposite tendency is observed.

Problem to be solved by the invention The theoretical energy density of the active material of a lead-acid battery is 167Wh/
In contrast, the energy density of conventional lead-acid batteries is as low as 30 to 40 Wh/Ky, and there is an increasing demand for smaller, higher capacity, and lighter batteries.

On the other hand, in a lead-acid battery having a relatively low actual energy density as described above, the amount of positive and negative active materials in the total weight of the battery is approximately 45 cm in a 12 2Ah battery.

Therefore, by improving the utilization rate of the active material, it is possible to reduce the weight of the battery, and it is possible to obtain a battery with high energy density.

In order to improve the utilization rate of the active material, a method is generally used to reduce the density of the active material and increase its porosity. That is, by increasing the reaction surface area of the active material and by allowing a large amount of the electrolyte to exist in the active material, a decrease in the utilization rate due to diffusion of the electrolyte is suppressed.

On the other hand, according to these methods, due to repeated charging and discharging reactions, the contact between active material particles decreases and the active material particles become fine particles. Therefore, problems arise in that the discharge capacity decreases early in the cycle of charging and discharging, or that the charging efficiency decreases even during charging, making it difficult to be charged.

The present invention solves the above problems (1) and provides a sealed lead-acid battery that has a high utilization rate and has an excellent charging/discharging vehicle life.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention is characterized in that the active material density (porosity) is varied in the thickness direction of the electrode plate to form a multilayer structure. The density of the active material may be changed by filling a paste made of lead oxide, water, dilute sulfuric acid, etc. multiple times, or by directly filling lead dioxide with different densities.

Furthermore, by applying a liquid-absorbing material to the interface between these layers of different densities, it is possible to improve the utilization rate of the active material and reduce the weight of the battery.

Function: By layering the IE electrode active material in the thickness direction of the electrode plate,
It has a two-layer structure, with a low density (high porosity) layer at the center of the plate and a high density (low porosity) layer on the surface of the plate in contact with the separator, facing outward from the center of the plate. can do. Therefore, even after repeated charging and discharging, the active material becomes less likely to become fine particles in the layer on the surface of the electrode plate.
This results in a battery with excellent charge/discharge cycle life. On the other hand, the center of the electrode plate has high porosity, which facilitates the diffusion of the electrolyte and increases the presence of the electrolyte, which improves the utilization rate of the active material and increases the capacity of the battery. I can figure it out.

Furthermore, by coating a liquid-absorbing substance on the interface between these active material layers, the electrolytic solution can be easily diffused into the active material.

On the other hand, the porosity of the center of the electrode plate should be reduced to 1~. When the porosity of the surface of the electrode plate is increased, the density due to contact between the lattice, which is a current collector, and the active material is improved.

Therefore, the battery becomes easy to charge, has excellent charging efficiency, and has excellent recovery properties after deterioration such as self-discharge.

Example The present invention will be explained below using examples.

As the positive electrode plate, as shown in FIG.
A lattice body 1 made of an n-alloy was filled with a paste formed by kneading lead oxide, water, dilute sulfuric acid, etc. 7 and chemically formed. As the base i-state active material, two types of lead dioxide were used: 2 with a porosity of 68 mm and 3 with a porosity of 70 mm. The electrode plate is 3rm thick.

It is 50 meters long and 20 meters wide. Note that silica powder (Aerosil powder) is used as the liquid-absorbing material 4, and M of the active material is
It was applied as a layer between 2.3 and 0.1 mm thick.

The negative electrode plate has lead oxide, lead oxide, and a grid made of Pb-Ca alloy.
A paste made by kneading water, dilute sulfuric acid, barium sulfate, organic fibers, etc. was filled and chemically formed. We prepared one with a thickness of 1.6 mm, a length of 50 mm, and a width of 20+ m.

Two and three of these electrode plates were assembled, a mat separator made of fine glass fiber was inserted between the electrode plates, and dilute sulfuric acid with a specific gravity of 1.3° was used as the electrolyte.

The prototype battery has a 10 hour rate capacity of 2AH and an output voltage of 1
Six cells were assembled in series at 2V.

FIG. 2 shows the results of the charge/discharge cycle life of each of the batteries a to f. Here, charging was performed for 2 hours at a constant voltage and current of 14.8 V and 10.8 A, and discharging was performed using a constant resistance of 15 Ω to a discharge end voltage of 1 o, sV.

Further, FIG. 3 shows the change in discharge time after charging was left in an atmosphere of 60° C. for 3 months.

Effects of the Invention According to the present invention, it is possible to provide a battery with a larger capacity and an excellent charge/discharge cycle life.

In addition, in the case of cells with one positive electrode plate and one negative electrode plate facing each other with a separator in between, the active material layer can have a two-layer structure, making it possible to produce electrode plates with good performance and ease of production. The effect is great.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a positive electrode plate according to the present invention, and FIGS. 2 and 3 are characteristic diagrams as a battery. 1... Lattice, 2... Inner active material, 3.
...Outer active material, 4...Liquid-absorbing material layer. Name of agent: Patent attorney Toshio Nakao and 1 other person/-
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Claims (3)

[Claims] (1) A sealed lead-acid battery having a positive electrode plate using lead dioxide as a positive electrode active material, and having layers having different densities (porosity) in the thickness direction of the positive electrode plate. (2) The sealed lead-acid battery according to claim 1, wherein a liquid-absorbing material is coated or interposed on the interface between the active materials having different densities. (3) The sealed lead-acid battery according to claim 3, which uses silica powder as the liquid-absorbing material.