JPH0610991B2 - Sealed lead acid battery - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to suppression of thermal runaway that occurs when a sealed lead acid battery is charged.

2. Description of the Related Art In general, a sealed lead-acid battery keeps a sealed state by absorbing oxygen gas generated from a positive electrode during charging in a negative electrode. Therefore, in order to facilitate the contact between the oxygen gas and the negative electrode, a gel electrolyte is used between the electrodes or a porous body impregnated with an electrolytic solution is used. The battery is equipped with a safety valve for exhausting gas when the amount of gas generated increases, such as when the battery is charged with a large current.This safety valve is used to increase the reactivity of oxygen gas absorption at the negative electrode. , Is designed to operate at a high pressure of 100 to 200 mmHg. Further, in order to prevent hydrogen gas from being generated from the negative electrode during charging, the discharge capacity of the negative electrode is usually made larger than that of the positive electrode.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention This type of battery does not need to be supplemented such as replenishing water, and has a widespread use as an emergency power source in the event of a power failure, taking advantage of the feature of no leakage.
When installing batteries, it is becoming more common to place multiple batteries in close contact and to use them in a storage box that does not have much room.Batteries generate heat during charging, resulting in poor heat dissipation. If this happens, the temperature of the battery will rise. Normally, this type of battery is charged by constant voltage charging, and the charging overvoltage of the battery decreases as the temperature rises, so a larger current flows as the temperature rises. Then, while a large current flows, the amount of oxygen gas generated from the positive electrode increases, while the high temperature increases the gas absorption capacity of the negative electrode, so that the negative electrode charging overvoltage and the increase of heat generation due to the oxygen gas absorption occur. Then, a larger current flows again, the amount of oxygen gas generated from the positive electrode increases, and heat generation due to oxygen gas absorption in the negative electrode further increases. If the heat generation and heat dissipation of this battery are balanced, the battery temperature will stabilize, but if it is in the direction of heat storage, the battery temperature will rise further and a phenomenon of heat escape will occur. When heat escape occurs, the battery case is usually made of thermoplastic resin, so deformation occurs due to high temperature and increase in internal pressure, and a large current flows to accelerate the expansion of the positive electrode grid or electrolysis by electrolysis of water. Battery performance is reduced due to the reduction of the liquid.

It is an object of the present invention to provide means for suppressing this thermal runaway phenomenon.

Means for Solving the ProblemsThe present invention, in order to achieve the above-mentioned object, first reduces the discharge capacity of the negative electrode plate to 0.55 to 0.70 with respect to the weight of the positive electrode active material relative to the weight of the positive electrode active material, and further reduces the discharge capacity of the positive electrode plate. Is equipped with a safety valve that opens when the pressure rises within 80 mmHg from atmospheric pressure.

Function By making the weight of the negative electrode active material smaller than that of the positive electrode, it is easy to raise the overvoltage of the negative electrode during charging.By doing so, the negative electrode charging overvoltage decreases due to oxygen gas absorption in the negative electrode Reduces the flow of a large amount of current in order to complete the drop. On the other hand, since the charging overvoltage of the negative electrode is likely to rise, the charging overvoltage of the positive electrode does not need to rise so much, so that oxygen gas generation is suppressed, and lowering of the charging overvoltage and heat generation of the negative electrode due to oxygen gas absorption in the negative electrode are suppressed.
This effect is exhibited when the weight of the active material of the negative electrode is 0.70 or less with respect to that of the positive electrode, and when the value is smaller than 0.55, insufficient charge of the positive electrode plate is caused and the amount of hydrogen gas generated from the negative electrode is increased, which is not preferable. However, even if the weight ratio of the active material of the negative electrode / positive electrode is in the range of 0.55 to 0.70, a larger current flows as the temperature becomes higher, and the amount of oxygen gas generated from the positive electrode increases, while the oxygen gas absorption capacity at the negative electrode increases. However, it is inevitable to reduce the decrease in charging overvoltage of the negative electrode. Therefore, in order to reduce the absorption of oxygen gas at the negative electrode, the pressure at which the safety valve opens is kept low, which makes it possible. The effect of reducing the heat generation due to the absorption of oxygen gas at the negative electrode by lowering the valve opening pressure of the safety valve is remarkable when the valve opening pressure is 80 mmHg or less. Due to the above characteristics, the thermal escape phenomenon can be suppressed.

Example An example of the present invention will be described.

The battery tested was a sealed lead-acid battery of 6V, 10Ah and had the structure shown in Table 1. The active material weight of the positive electrode plate was constant, the active material weight of the negative electrode plate was changed, and the valve opening pressure of the safety valve was changed. ing.

Then, eight batteries were connected in series according to the specifications shown in Table 1, and the long side surfaces of the batteries were closely contacted and subjected to an array test. In the test, overcharging was performed in a constant temperature bath at 60 ° C. with a charging voltage of 2.3 V / cell, and the battery temperature at that time was measured. The results are shown in FIG. FIG. 1 shows the temperature range indicated by the batteries of each of the batteries A to D. As can be seen from this figure, in the batteries other than the product of the present invention, the battery temperature gradually rises, causing thermal escape. The reason for this is as described above.

EFFECTS OF THE INVENTION By preventing heat escape according to the present invention, excessive gas generation and battery heat generation can be suppressed, and the deformation of the battery case due to the influence can be prevented, and lattice corrosion due to the effect of heat escape and reduction of electrolyte solution can be prevented. It is possible to provide a highly reliable battery that can prevent the battery from having an early capacity decrease due to the above.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing changes in battery temperature during overcharge.

Claims (1)

[Claims] 1. The weight of the negative electrode active material is 0.
A sealed lead-acid battery comprising a 55 to 0.70 electrode group and having a safety valve that opens when the internal pressure of the battery rises within 80 mmHg from atmospheric pressure.