JPH0524626B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to lead-acid batteries, particularly sealed type (hereinafter referred to as sealed type) lead-acid batteries.

BACKGROUND ART Conventionally, this type of sealed lead-acid battery has been used for cycle applications and overcharge applications. These batteries are composed of positive and negative polar plates, a separator, an electrolyte, and a battery container.The electrolyte is contained in the positive and negative polar plates and the separator, and there is almost no free electrolyte. There is. Furthermore, the discharge capacity of a battery is determined by the electrolyte when the battery is new. When a battery without free electrolyte is charged in this manner, oxygen gas is generated from the positive electrode plate after the middle stage of charging, and this generated oxygen gas is dissipated by contacting the negative electrode plate. This oxygen loss mechanism generally occurs when it comes into contact with active metal lead (the active material in the charged state of the negative electrode plate) and becomes lead oxide, and when it comes into contact with sulfuric acid, which is an electrolytic solution, it becomes lead sulfate, which dissipates water. generate. This reaction is exothermic.

If all of the generated gas is fixed within the battery due to this oxygen loss reaction, there will be no decrease in the electrolyte, but if rapid charging, such as constant current rapid charging, is performed, the oxygen generation rate will be greater than the oxygen absorption reaction rate. , oxygen gas flows out of the battery, and the electrolyte decreases. Furthermore, the exothermic reaction promotes evaporation of the electrolytic solution whose sulfuric acid specific gravity has become low, and the amount of electrolytic solution on the negative electrode plate decreases. Even if the decrease in the amount of electrolyte in the negative plate is greater than that in the positive plate or separator, if the liquid absorption capacity of the negative plate is greater than that of the positive plate or separator, the electrolyte will move from them and the electrolyte distribution within the battery will change. However, in the conventional configuration, no measures were taken to improve the liquid absorption ability of the negative electrode plate.

Problems to be Solved by the Invention When a conventional battery as described above is cycle serviced, overcharged, or overdischarged, the amount of electrolyte in the battery decreases. In particular, the amount of electrolyte on the negative electrode plate decreases. When the amount of electrolyte decreases, the internal resistance increases and the contact state between the electrolyte and the active material deteriorates, resulting in a decrease in discharge capacity. Particularly in the negative electrode plate, lead sulfate is generated due to the oxygen loss reaction, making it difficult to charge the battery when the electrolyte is low, resulting in a severe decrease in capacity.

The present invention solves the above problems. In other words, the purpose is to improve battery characteristics such as cycle life of sealed lead-acid batteries.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention aims to electrolyze a negative electrode plate having a liquid absorption capacity larger than that of the separator and the positive electrode plate to such an extent that no free electrolyte exists. This is used in sealed lead-acid batteries with limited fluid volume.

As a means to make the liquid absorption capacity of the negative electrode plate larger than that of the separator and the positive electrode plate, there is a method of making the pore diameter of the negative electrode plate smaller than the pore diameter of the separator and the positive electrode plate that absorb electrolyte, or a method of making the pore size of the negative electrode plate smaller than the pore diameter of the separator and the positive electrode plate, which absorbs the electrolyte, or a method of making the pore size of the negative electrode plate smaller than the pore diameter of the separator and the positive electrode plate, which absorbs the electrolyte, or A method is used to add and contain a substance that has better liquid absorption ability than the plate. Further, although the initial discharge capacity is slightly reduced, the relative liquid absorption capacity of the negative electrode plate can be increased even if a water-repellent material or a material with low liquid absorption capacity is used for the separator.

Effects Due to the above configuration, when used in cycling applications or applications involving overcharging, overdischarging, etc., the negative electrode plate, which has a reduced amount of electrolyte, has a higher liquid absorption capacity than the separator or positive electrode plate. The electrolyte volume distribution becomes uniform, and charging performance can be improved and a decrease in discharge capacity can be suppressed.

Example Examples of the present invention will be described below.

The conventional structure of the positive electrode plate and separator described above was used, and only the negative electrode plate was changed. Specifically, a battery was constructed by using a positive electrode plate with an average pore diameter of approximately 2.5 μm and a separator with an average pore diameter of approximately 10 μm, and by varying the average pore diameter of the negative electrode plate. The pore size of the negative electrode plate was adjusted by varying the amounts of sulfuric acid and water in the negative electrode plate manufacturing method, which involves kneading lead powder, sulfuric acid, and water, applying the mixture to a current collector (grid), drying it, and chemically forming it. In general, increasing the sulfuric acid content increases the small pore size, and increasing the water amount increases the large pore size. In addition, the amount of sulfuric acid and the amount of water greatly affect the viscosity of the kneaded product, which affects the workability when applying it to the current collector, so there are cases where it is not possible to manufacture electrode plates by adjusting only one of them. There is.

In this example, the specific gravity of sulfuric acid, the amount of sulfuric acid, and the amount of water were adjusted to 1 kg of lead oxide powder, and the results were 1.3 μ, 2.0 μ, and 2.2 μ.
A negative electrode plate having an average pore diameter of The negative electrode plate with an average pore diameter of 1.3μ is made of 120c.c. of sulfuric acid with a specific gravity of 1.55 and 45% of water.
cc, 2.0μ is 120c.c. of sulfuric acid with a specific gravity of 1.40 and 40c.c. of water, 2.2
μ is shown for an example obtained by kneading 150 c.c. of sulfuric acid with a specific gravity of 1.35 and 35 c.c. of water. We also created a negative electrode plate to which a liquid-absorbing substance was added to improve the liquid-absorbing ability. There are many types of substances that have high liquid absorption properties, but when used in lead-acid batteries, they have acid resistance and also have good battery characteristics.
In particular, it must be a material that does not deteriorate self-discharge characteristics. As an example of such a material, finely powdered silica or an alumina-based material is preferable.
This example shows an example in which calcium silicate with a particle size of about 2 μm is used. Mix 1 kg of lead oxide powder with sulfuric acid and water with a specific gravity of 1.40, and then add 20 g of calcium silicate per 1 kg of lead oxide and mix to prepare a mixture with an apparent specific gravity of approximately 3.5 g/cc. This was then applied to a current collector grid to form a negative electrode plate.

These two negative electrode plates and three positive electrode plates were combined to produce a battery with a 10 hour rate discharge capacity of 2.0 Ah.
Note that dilute sulfuric acid with a specific gravity of 1.32 was used as the electrolyte for the battery.

These batteries were charged at a current rate of 10 hours and discharged at a current rate of 7 hours to confirm the initial capacity, and then their cycle life characteristics were evaluated. Charging is done within 1 hour with a constant current of 2.1A, and charging is stopped by detecting a rise in the potential of the negative electrode plate due to the oxygen loss reaction on the negative electrode plate, and when this rise reaches approximately 50mV, the current is cut off using a circuit. The discharge was performed at a constant current of 1.7 A, and the final voltage was 1.70 V per cell. This cycle was repeated and the discharge capacity relative to the initial capacity was measured.

Evaluation battery No. 1 had a negative electrode plate with an average pore diameter of 1.3μ, and No. 2 had a negative electrode plate with an average pore diameter of 1.3μ.
Battery No. 3 uses a 2.0 μ negative electrode plate, No. 4 uses a 2.2 μ negative electrode plate, and No. 4 uses a negative electrode plate containing calcium silicate.
For reference, a conventional battery (No. 5) was also evaluated at the same time.

Figure 1 shows an example of the results. Curve No. in the same figure.
indicates the battery number. From FIG. 1, it is clear that the product of the present invention has a significantly improved cycle life compared to the conventional battery.

FIG. 2 shows the results of comparing the liquid absorption abilities of Nos. 1 to 5 of the negative electrode plates, positive electrode plates, and separators. The evaluation method was to stand the object to be measured upright in a dilute sulfuric acid solution with a specific gravity of 1.32, and compare the time for the dilute sulfuric acid to crawl up to a height of 10 cm. In FIG. 2, the negative electrode plate number indicates the negative electrode plate number of the battery shown in FIG. 1. From FIG. 2, it can be seen that the liquid absorption capacity of the product of the present invention is greater than that of the conventional negative electrode plate, separator, and positive electrode plate.

Effects of the Invention From the above results, the product of the present invention in which the liquid absorption capacity of the negative electrode plate is larger than that of the separator and the positive electrode plate has the effect of improving the cycle life, especially the cycle life associated with rapid charging. In the examples, only three types of average pore diameters and one type using an additive for improving liquid absorption ability were shown, but similar effects can be obtained by other methods. Furthermore, although the cycle life characteristics associated with rapid charging were shown in the example, the same phenomenon occurs during overcharging, that is, an oxygen loss reaction occurs on the negative electrode plate during charging, so the cycle life is improved and the overcharge characteristics are also improved. be able to.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the cycle life characteristics of a battery in an example of the present invention, and FIG. 2 is a diagram showing the liquid absorption capacity of the negative electrode plate, positive electrode plate, and separator of the battery of the present invention.

Claims (1)

[Claims] 1. A lead-acid battery in which an electrolyte is held in both positive and negative electrode plates and a separator, and the amount of electrolyte is limited to such an extent that there is no free electrolyte, the negative electrode plate being a positive electrode plate and a separator. A lead-acid battery is characterized by having a larger liquid absorption capacity than a separator. 2. The lead-acid battery according to claim 1, wherein the negative electrode plate has a smaller average pore diameter than the positive electrode plate and the separator. 3. The lead-acid battery according to claim 1, wherein the negative electrode plate contains a substance having a better liquid absorption ability than the positive electrode plate and the separator.