The Reason For The Swelling Of Lead-acid Batteries Is Here

- Nov 19, 2018-

The reason for the swelling of lead-acid batteries is here!

 

First, the cause of battery bulging

1. There are mainly the following situations:

A. The vent hole on the liquid filling cap is blocked or not clear.

During the charging process, especially at the end of charging, a large amount of explosive gas will be generated inside the battery. If the vent hole on the battery filling cap is blocked or not clear, the gas will not be discharged in time, and thus accumulated in the battery case. Inside, the pressure is getting bigger and bigger, and finally the battery is inflated.

B. The battery charging current is too large or the charging time is too long

When the charging current of the battery is too large or the charging time is too long, the temperature of the electrolyte will rapidly increase, and a large amount of gas will be generated, causing the active material on the battery plate to loosen and fall off, causing the battery to swell.

C. The battery plate is vulcanized

During the charging process of the battery with vulcanization of the plate, the voltage of the single cell and the temperature of the electrolyte will rise rapidly, and the bubble generation is early and intense, which easily causes the battery to swell.

D. Continuous start motor is too long

When starting the electric vehicle motor, the battery should supply a large current (usually 20-40A) to the motor in a short time, so that a large starting current will inevitably cause a severe chemical reaction inside the battery, if the battery plate is accompanied by light When the degree of vulcanization occurs, the temperature of the electrolyte suddenly rises and a large amount of gas is generated. Once these gases are not released in time, they are prone to explosions. If the starter is used for a long time, it will increase the generation of gas and increase the possibility of battery bursting.

E. The inner pole of the battery and the pole and the bus bar are not welded firmly.

When the tabs and poles of the inner plate of the battery are welded to the busbar, they must be welded firmly and integrated to meet the needs of the battery during high-current discharge. Otherwise, in the case of large current discharge, the welding site may cause sparking or ablation due to too thin contact points or poor contact, thus causing sparks, which will ignite the explosive gas generated by the battery, causing the battery to explode.

F. The electrolyte viscosity is too large

When the temperature is too low, the viscosity of the electrolyte is large, the rate of penetration into the pores of the plate is slow, the internal resistance is increased, and the voltage drop on the internal resistance during discharge is large, which causes the electrolyte temperature to rise rapidly, resulting in a large amount of The gas increases the gas pressure inside the battery. If the battery is over-discharged at this time, the temperature of the electrolyte rises faster, the gas is generated more, and the gas pressure inside the battery is larger, which results in battery collapse. In addition, if an explosive gas is generated during the charging process of the battery, it will immediately cause an explosion, causing the battery to burst. Therefore, the charging room must be well ventilated and fireworks are strictly prohibited.

G. Electrolyte drying

When the battery is used for a long time, there will be water loss, which will cause the electrolyte to dry up. At this time, the battery will bulge when the battery is overcharged, and it will cause a burst. If the battery has water loss, the battery may be supplemented with distilled water. The amount of the battery and the method of operation can be carried out according to the instruction manual of the battery.

2. Preventive measures for battery bursting

Judging from the reasons for the bursting of the battery mentioned above, in order to avoid battery cracking accidents, first of all, to avoid sparks during the use of the battery, it is necessary to install the battery firmly during use, wire joints The connection with the electric pile should be fastened, and the welding quality of the electrode plate group should be ensured during overhaul.

Secondly, in order to make the gas generated in the working process of the battery overflow from the vent hole of the filling port in time, the internal pressure of the battery is not too high, and the liquid filling cap of the battery must be tightened normally, and the vent hole is often unblocked.

Third, in order to avoid excessive battery discharge, the starter cannot be used continuously when starting the vehicle using the starter, especially when starting the vehicle under low temperature conditions. When the vehicle is started by a cold car, the vehicle must be preheated. The combined time of the starter must not exceed 5-10s, and it must be started once every 10-15s.

Fourth, when charging the battery, be sure to avoid excessive current or overcharging. For this reason, for the battery that has been installed on the vehicle, the rated voltage of the generator must be adjusted; for the battery that is charged in the charging room, the charging current and charging time must be grasped.

Second, the analysis of the deformation of the battery casing

The battery casing material, such as ABS engineering plastic, should not be deformed when used at 45 °C. The deformation of the battery casing is not sudden. There is often a process. After the battery is discharged, when the charger charges the battery to about 80% of the battery capacity, the charging enters the high-voltage charging zone. Oxygen is evolved. Oxygen passes through the micropores in the AGM separator to reach the negative electrode, and the oxygen composite reaction is performed on the negative electrode plate. Heat is generated during the reaction. When the charging capacity reaches 90%, the oxygen generation rate increases, and the negative electrode begins to generate hydrogen gas. The increase of a large amount of gas causes the internal pressure of the battery to exceed the pressure-opening valve, the safety valve is opened, and the gas escapes with water, and finally the water is lost.

As the number of battery cycles increases, the water gradually decreases, resulting in the following conditions:

The oxygen "channel" becomes smooth, and the oxygen generated by the positive electrode easily reaches the negative electrode through the "channel";

The heat capacity is reduced, and the heat capacity in the battery is the largest. After the water is lost, the heat capacity of the battery is greatly reduced, and the generated heat causes the temperature of the battery to rise rapidly;

Due to the shrinkage of the AGM separator in the battery after water loss, the adhesion to the negative electrode plate is deteriorated, the internal resistance is increased, and the heat generation during charging and discharging is increased. After the above process, the heat generated inside the battery can only be dissipated through the wall of the battery compartment. If the amount of heat dissipation is less than the amount of heat generated, the temperature rises. When the temperature rises, the battery's gassing overpotential decreases, and the gassing amount increases. A large amount of oxygen in the positive electrode reacts on the surface of the negative electrode through the “channel”, generating a large amount of heat, causing the temperature to rise rapidly, forming a vicious circle, so-called “thermal runaway”. When the final temperature reaches 80 ° C or above, the battery casing deformation phenomenon occurs.