JPS6327827B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lead-acid battery using colloidal sulfuric acid as an electrolyte, and particularly aims to suppress short circuits between positive and negative electrodes during charging.

Conventionally, lead-acid batteries that use pure lead or Pb-Ca alloy for the positive electrode grid become difficult to charge after deep discharge, and if the battery is left in a deeply discharged state for a long period of time, the charging characteristics deteriorate further. There was a tendency for it to deteriorate. One reason for this was that insulating lead sulfate with developed crystallinity was formed at the interface between the positive electrode lattice and the active material due to deep discharge and leaving the battery in a deep discharge state. In recent years, lead alloys have been developed that are less likely to produce crystalline lead sulfate on the surface of the lattice even when deep discharge is performed, and this problem seemed to have been solved for the time being.

However, even with lead-acid batteries using lattice alloys that have good charging characteristics even after such deep discharge,
In particular, lead-acid batteries using a sulfuric acid colloid electrolyte have the disadvantage that short circuits between the positive and negative electrodes tend to occur at the top of the electrode plates when repeated charge-discharge cycles with deep discharges occur.

The reason for this is thought to be as follows. That is,
Oxygen gas generated at the end of charging of a lead-acid battery accumulates as bubbles in the upper part of the colloidal electrolyte, and a small amount of sulfuric acid aqueous solution synergized from the sulfuric acid colloid accumulates in the bubble cavity. The sulfate ions inside are consumed and the sulfuric acid concentration decreases. Furthermore, if left in a deep discharge state,
As sulfate ions are further consumed by the self-discharge reaction, the electrolyte approaches a neutral region, which increases the solubility of lead and leads to dissolution in the electrolyte. When charging under such conditions, the electrolyte resistance is lower than other parts of the current-carrying path that includes the sulfuric acid aqueous solution part synergized in the bubbles, and the current density becomes higher, leading to the precipitation of lead ions dissolved in the negative electrode. As the charge and discharge cycles are repeated, they develop into needle-like shapes,
Finally, the positive electrode is reached. It is thought that the short circuit phenomenon occurs in this way.

An object of the present invention is to prevent short circuits caused by bubbles generated in the upper part of the electrode plate. That is,
The present invention uses a water-absorbing compound that has a high water-absorbing ability when the pH of the electrolyte is around 7 and exhibits almost no water-absorbing ability when the pH of the electrolyte is around 1, to be used in areas where air bubbles tend to accumulate in the electrolyte, that is, on the electrode plate. It is characterized by being added to the upper electrolyte.

With this configuration, the water-absorbing compound retains the electrolyte that synergates into bubbles when the battery enters a deep discharge state and the electrolyte reaches a neutral region, and the current density during charging is reduced to the bubble cavity. This can prevent short circuits from occurring. When the pH of the electrolyte is lowered by subsequent charging, the water held in the water-absorbing compound is returned to the electrolyte and does not deteriorate the discharge characteristics. In this way, the present invention suppresses short circuits at the upper portions of the battery plates.

Note that, as in Japanese Patent Publication No. 54-112570, it has been proposed to add a water-absorbing compound to the entire colloidal electrolyte for another purpose, but especially in high-rate discharge, even a small amount of such a water-absorbing compound is For high rate discharge applications, it should be avoided to add the above-mentioned water-absorbing compound to the entire composition, since it becomes a factor that increases the electrolyte resistance and deteriorates the high rate discharge characteristics. In addition, it is not preferable especially for small sealed lead-acid batteries because it is necessary to secure as much sulfuric acid as possible in the limited internal volume of the battery to increase the capacity. From these viewpoints, the present invention concentrates the addition to the upper portion that does not contribute to the resistance of direct discharge.

The present invention will be explained below using examples.

FIG. 1 shows an embodiment of a lead-acid battery according to the present invention.

In the figure, 1 is a battery case, and there are 3
An electrode plate group consisting of two negative electrode plates 2, two positive electrode plates 3, and a frame-shaped separator plate 5 with projections 4 is inserted, and a sulfuric acid colloid electrolyte 6 is injected. Sulfuric acid colloid 7 to which 10% by weight of the dependent water-absorbing compound has been added is injected. The lattice of the positive electrode 3 contains Pb-Ca (0.08% by weight), which has relatively good charging characteristics even during deep discharge.
-Sn (0.5% by weight) alloy was used. 8 is a lid adhered to the opening of the battery case with epoxy resin, 9 is a negative terminal, 10 is a positive terminal, 11 is a safety valve, and 12 is acid-resistant resin fiber cotton.

In addition, compounds whose water absorption power depends on pH are:
Starch obtained by graft copolymerizing acrylic acid-based monomers or methacrylic acid-based monomers is a compound with remarkable effects, and one example is the one sold under the name Sunwet 1M-300 by Sanyo Chemical Industries, Ltd. In this example, powdered Sunwet 1M-300 was used.

A battery having the above configuration with a 10-hour rate discharge capacity of 3 Ah and a capacity determined by the amount of electrolyte is designated as A, and a normal sulfuric acid colloid is used for both electrolyte layers 6 and 7 without providing a layer containing a water-absorbing substance. Let the battery be B.

These batteries were subjected to a charge/discharge cycle in which they were discharged for 20 hours at 20°C under a constant resistance load equivalent to a 10-hour rate and charged at 350 mA for 12 hours. Figure 2 shows the transition of discharge time until the voltage reaches 1.75V per cell.
The reason why the characteristics of battery B have deteriorated as shown by the S mark is because
This was due to lead depositing in the form of needles from the negative electrode in the air bubbles accumulated between the positive and negative electrodes and reaching the positive electrode.

3 and 4 illustrate this short-circuit phenomenon, in the upper part of the colloidal electrolyte layer 6,
The syneresis sulfuric acid aqueous solution 14 accumulates in the bubbles 13 formed by the accumulation of oxygen gas generated at the end of charging under the frame-shaped separator 5 with the protrusion 4, and the pH increases due to deep discharge of the battery. This is because lead ions are dissolved in the electrolyte when the battery rises, and needle-shaped lead 15 is precipitated from the negative electrode 2 during the next charging and reaches the positive electrode 4.

In the battery according to the present invention, short circuits due to such phenomena do not occur. Electrolyte layer 7 mixed with water-absorbing substance
Considering the size of the bubbles normally generated, it is effective to provide the layer 7 5 to 15 mm below the lower end 6a of the upper piece of the separator 6, and it is highly unlikely to make the layer 7 thicker than necessary. This may cause adverse effects such as deterioration of discharge characteristics. Also, said portion 6a of the separator
If it is only provided within 5mm from the air bubble 13
Since the electrolytic solution 14 that has synercised inside may not be able to be absorbed, a minimum width of 5 mm or more is required.

As described above, the present invention provides short-circuiting of the positive and negative electrodes by providing a layer containing a sulfuric acid colloid and a compound whose water absorption power is dependent on pH in the upper electrolyte that includes a part of the electrode plate group. The effect of this is extremely large, as it suppresses this and lengthens the charge/discharge cycle life of the battery.

[Brief explanation of drawings]

Fig. 1 is a longitudinal cross-sectional view of a lead-acid battery showing an embodiment of the present invention, Fig. 2 is a comparison diagram of repeated cycle characteristics of deep discharge and charging, and Fig. 3 is a diagram showing the short circuit phenomenon of the conventional positive and negative electrodes. Front view of the section, Figure 4 is Figure 3-
FIG. 2...Negative electrode, 3...Positive electrode, 5...Separator, 6...
...Electrolyte, 7...An electrolyte to which a water-absorbing compound is added.

Claims (1)

[Scope of Claims] 1. In a lead-acid battery whose electrolyte is a colloid containing sulfuric acid, the colloid containing sulfuric acid has a PH-dependent water absorption ability, and the water absorption ability decreases in the neutral region and its vicinity. 1. A lead-acid battery characterized in that a mixture layer containing a high-density compound is provided in an upper electrolyte that includes a part of the electrode plate group. 2. The lead-acid battery according to claim 1, wherein the water-absorbing compound having pH dependence is starch obtained by graft copolymerizing an acrylic acid monomer or a methacrylic acid monomer. 3. The lead-acid battery according to claim 1, wherein the sulfuric acid colloid mixture layer containing a pH-dependent water-absorbing compound is provided to a portion 5 to 15 mm below the lower end of the upper piece of the frame-shaped separator.