JPH088104B2 - Sealed lead acid battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement of a sealed lead-acid battery.

Conventional technology and its problems Conventional lead-acid batteries often have a long life due to a decrease in the capacity of the positive electrode plate, and a method of increasing the paste density and the filling amount of the positive electrode active material has been adopted to extend the life. However, this has a drawback that the porosity of the positive electrode is lowered and thus the initial capacity is reduced, and a battery having satisfactory performance has not been obtained yet. On the other hand, in a sealed lead-acid battery, its capacity is limited by the amount and concentration of the electrolyte, so using such a high-density paste reduces the porosity and does not supply sulfuric acid to the deep part of the electrode plate, resulting in a capacity Will be less. It is possible to increase the porosity of the active material in order to increase the capacity, but the lead sulfate sulfate generated by the discharge clogs the pores of the active material and interrupts the supply of sulfuric acid from the separator, thus increasing the porosity. There is a limit to the capacity improvement by. Moreover, if the porosity is extremely increased, it will be too soft during the kneading and cannot be produced. From this point as well, the upper limit of the active material density is about 2.8 g / cc.

It is known, for example, from Japanese Examined Patent Publication No. 62-31787 etc. to add hollow porous fine particles having a particle size of 20 to 300 μm to the paste to give the positive electrode plate an appropriate porosity to increase the active material utilization rate.

Japanese Examined Patent Publication No. 62-31787 discloses a particle size of aluminosilicate as one of the additives for a positive electrode plate for a lead-acid battery, which has a free liquid and is not hermetically sealed, as is clear from the examples.
It is stated that 300 μ, a sphere wall thickness of 2 to 25 μ, and a bulk specific gravity of 0.2 to 0.5 are suitable.

In a sealed lead-acid battery, normally, positive and negative electrode plates are alternately stacked via separators formed by sheet-shaped separators mainly made of glass fiber having a diameter of 1 μm or less, to form a pole group. The amount of dilute sulfuric acid equal to or less than the amount that can be retained in, is injected, oxygen gas generated in the positive electrode at the end of charging is moved to the negative electrode through the voids in the separator,
Sealing is performed using a so-called oxygen cycle that prevents the electrolytic solution from disappearing outside the system by reacting with the negative electrode active material. In a lead-acid battery, dilute sulfuric acid is directly involved in the discharge reaction, and thus the obtained capacity is determined by the amount of sulfuric acid held in the electrode group. Therefore, when trying to increase the capacity of the sealed lead-acid battery, one of the major points is how to increase the pore volume of the pole group. The porosity of the separator is usually 90-95%,
It is much higher than 50-65%, and it is difficult to raise it more than this, and in order to increase the capacity, it is necessary to concentrate on increasing the pore volume of the positive and negative active materials.

As one of the measures, the proposal of the above publication is also effective. By the way, in the sealed lead-acid battery, the separator and the electrode plate are overlapped with each other by applying a high pressure of, for example, 30 kg / dm ² , and since there is no free liquid flowing, there is a risk that the active material may fall off in the embodiment of the above publication. It is extremely small compared to the battery of. Therefore, if the shape and amount of the micro hollow body for a positive electrode are properly selected, it has a much higher addition effect than the conventional one.

OBJECT OF THE INVENTION The present invention uses a sealed lead acid battery, in particular, a glass mat separator mainly formed of fine glass fibers having a size of 1 μm or less and formed into a sheet shape. The purpose is to improve the capacity and the life of the sealed structure by generating an oxygen cycle.

The present invention aims to increase the initial capacity of a sealed lead-acid battery, maintain this high capacity even after repeated charge and discharge, and to extremely improve the capacity at high rate discharge. Then, the addition of hollow fine particles to the positive electrode active material is studied to propose the optimum configuration as a sealed lead acid battery.

Examples Hereinafter, examples will be described. Hollow porous fine particles of 98% or more of silica are porous bodies having a large number of fine pores of 2 to 20 mμ on the wall surface, and have a specific surface area of about 800 m ² / g and have the ability to suck sulfuric acid into the hollow portion. The average particle size is about 3μ
After adding an amount of 8% by weight to the amount of the completed positive electrode active material in the positive electrode paste of 456 g / cm ³ , the above paste was applied to the positive electrode grid and 30 kg / dm together with the fine glass separator and the negative electrode plate. A cell A was assembled by applying a pressure of ² to the cell. Further, the above fine particles were mixed in the positive electrode paste in the same amount of 2% by weight, and a battery prepared in the same manner was designated as B. Finally, a battery similarly prepared by using a paste in which the above fine particles are not mixed was designated as C. Battery C has a nominal capacity of 4 AH (2
0 hour rate).

Table 1 shows the results of measuring the initial capacity by discharging these at a rate of 25 ° C. for 5 hours. Further, FIG. 1 shows the result of measuring the capacity change by repeating charge and discharge with a constant current of 75% depth of discharge (DOD).

Thus, the battery using the paste in which the fine particles are mixed so as to be 8% by weight with respect to the amount of the active material after chemical formation maintains a high capacity. It is also seen that the capacity is particularly large at high rate discharge.

It is considered that the effect of the hollow fine particles is that the particles incorporated in the positive electrode plate occlude and supply a large amount of SO ₄ ²⁻ ions in the electrode plate due to its large surface area. Here, the particle size is 0.
1μ ~ 50μ, more preferably limited to 6.1 ~ 15μ,
If the diameter of the lead powder is the same as that of the lead powder, the hollow fine particles will not enter the lead powder when it is added and kneaded, and the lead powder will be removed without entering the lead powder. This is because the conductivity of the abdomen is impaired.

The diameter of a large number of micropores existing on the wall surface of the hollow fine particles must be smaller than 100 millimicrons (mμ), and more preferably smaller than 20 mμ. When the pore size is larger than 100 mμ, the pores are blocked by the active material by repeated charging and discharging, impairing the role of supplying the electrolytic solution to the active material, and the original addition effect is lost as the cycle is repeated. I will go away.

It is thought that most of the electrolyte absorption capacity of hollow particles depends on the diameter of the fine pores existing on the wall surface, but considering the retention by adsorption on the surface, the specific surface area is also important.
0-900m ² / g is good. If it is less than 200 m ² / g, the absorption capacity is insufficient, and if it is more than 900 m ² / g, not only is it unreasonable due to the high price, but also the effect of unnecessarily slowing the electrolyte supply rate is expected. Is not demonstrated.

The amount of the hollow fine particles added was 0 by weight ratio of the positive electrode active material after chemical conversion.
An extremely wide range of 5-10% can be adopted. If less than 0.5%, the effect is not recognized, so 0.5%
Above 10% and 0.1% to 50% compared to the conventional example
This is because even if it is made extremely small, the electronic bond between the lead particles is damaged, so that the capacity cannot be taken out, the bonding force as the electrode plate becomes weak, and the particle easily falls off. The best range for this amount is 2-5%. 20 with particle size of 0.1 to 15μ and wall micropore size of 20mμ or less
It is optimal to add 2 to 5% of hollow fine particles mainly composed of silicon dioxide having a specific surface area of 0 to 900 m ² / g to the positive electrode active material. At that time, the electrolytic solution is stored in the hollow portion, so the thinner the wall of the hollow fine particles, the better. But,
If the thickness is extremely thin, the strength will be weak, so there is an appropriate range, and the pore volume per 1 g of fine particles should be 0.3 to 2.0 cc. If it is less than 0.3cc, the effect is too small, and if it is more than 2.0cc, the wall becomes too thin and it collapses during electrode plate production. This pore volume can be calculated by measuring the weight of the fine particles, impregnating the hollow fine particles with a liquid having a known density, and then measuring the weight.

In addition, as the material of the hollow fine particles, silicon dioxide is 50 ~
60% so-called chemical glass can also be used. However, since it is in contact with a positive electrode active material that is a strong oxidizer, it is most suitable that it is made of quartz glass having excellent oxidation resistance, and at least 95% or more of silicon dioxide is preferable.

In the example, as a separator, a sheet-shaped material of fine glass fiber was closely arranged under positive and negative pressure of 30 kg / dm ² between the positive and negative electrode plates, and the amount of liquid was reduced so that there was no flowing electrolytic solution. Although shown, the invention is not so limited. That is, the separator may be a separator that can minimize the amount of flowing electrolyte and can support and fix the active material in as many points as possible, such as a polymer separator that swells and gels with dilute sulfuric acid and fine silicon dioxide particles. A gel type in which an electrolytic solution is gelled and fixed by powder may be used. However, the most effective method is the isolation method shown in the above embodiment.

Further, the above results can be similarly expected for the negative electrode plate.

EFFECTS OF THE INVENTION Since the present invention has the structure as described in the claims, it is possible to increase the initial capacity of the sealed lead-acid battery, maintain the high capacity even after repeated charging and discharging, and achieve a high rate. The capacity at the time of discharge is also improved.

[Brief description of drawings]

Figure 1 shows that each of the A, B, and C prototype batteries was discharged at a temperature of 25 ° C to a discharge depth of 75% at a rate of 3 hours of the initial capacity, and
5 is a graph in which a 5 hour rate discharge capacity is measured every 50 cycles in a cycle test of charging the battery at a rate of 5 hours.

Claims (5)

[Claims] 1. A positive electrode plate in which hollow fine particles having SiO ₂ as a main component and having a large number of fine pores smaller than 100 mm on the wall surface and a specific surface area of 200 to 900 m ² / g are added to a positive electrode active material. Sealed lead acid battery using 2. The method according to claim 1, wherein the positive electrode plate and the separator mainly composed of fine glass fibers are closely contacted with each other.
The sealed lead-acid battery according to item. 3. The hollow fine particles have a diameter of 0.1 to 50 μm, more preferably 0.1 to 15 μm, and the amount added to the positive electrode active material is 0.5 to 10% by weight, more preferably 2 to 5% by weight. The sealed lead-acid battery according to item 1 and item 2 in the range. 4. The volume of pores per 1 g of hollow fine particles is 0.3 to 2.0.
The sealed lead-acid battery according to claim 1, claim 2 or claim 3, which is cc. 5. The sealed lead-acid battery according to claim 4, wherein the hollow fine particles are composed of SiO ₂ 95% by weight or more.