The principle of lead-acid battery and the analysis of the cause of explosion

Because people do not know very much about the use of batteries, there will be some mistakes in the use of batteries.

Product Overview

Lead acid battery (VRLA) is an electrode made mainly of lead and its oxides. The electrolyte is a battery of sulfuric acid solution. Under the charge state of lead-acid battery, the positive electrode is mainly composed of lead dioxide, and the main component of the negative electrode is lead; Under the discharge state, the main components of the positive and negative poles are lead sulfate. The nominal voltage of a single-cell lead-acid battery is 2.0 V, which can discharge to 1.5 V and can be charged to 2.4 V; In applications, six single-cell lead-acid batteries are often used in series to form lead-acid batteries with a nominal 12V, as well as 24V, 36V, and 48V.

The VRLA battery is designed as follows: In the battery, a part of the electrolyte is absorbed in the electrode and partition to increase the negative oxygen absorption capacity, prevent the loss of the electrolyte, and enable the battery to seal.

VRLA battery structure

Parts Component Materials

Positive positive pole lead-antimony-calcium alloy plate, containing lead oxide as an active substance to ensure sufficient capacity to maintain battery capacity during prolonged use, reducing self-discharge

Negative negative pole lead-antimony-calcium alloy plate containing spongy fiber active material to ensure sufficient capacity to maintain battery capacity during long-term use and reduce self-discharge

Advanced multi-microporous AGM partition keeps the electrolyte and prevents the positive and negative poles from short-circuiting. Prevention of short circuit of positive and negative poles; maintenance of electrolyte; prevention of release of active material from electrode surface

In the electrochemical reaction of a battery, sulfuric acid acts as an electrolyte to conduct ions that enable electrons to transfer between positive and negative polar active substances in the battery

The shell and lid provide the battery space for the ABS resin to be placed in the positive-negative combination panel without specific instructions

The safety valve is made of synthetic rubber with excellent acid resistance and anti-aging. When the internal pressure of the battery is higher than normal pressure, release gas and maintain normal pressure to prevent oxygen from entering

According to the different batteries, positive and negative extremes can be connected pieces, rods, screw columns or lead lines. Sealed terminals contribute to high current discharge and long service life

Electrochemical reactions in electrodes

The electrochemical reaction of the valve controlled lead-acid battery is shown below. Charging is to connect the external DC power supply to the battery for charging, so that the electrical energy is converted into chemical energy storage. The discharge is the release of electrical energy from the battery to drive the external device.

When the VRLA battery charging will reach its peak, the charging current is only used to decompose the water in the electrolyte. At this time, the positive electrode of the battery produces oxygen and the negative electrode produces hydrogen. The gas will overflow from the battery, causing the electrolyte to decrease. Water is added at irregular times.

On the other hand, at the end of the charging period or under overcharging conditions, the charging energy is used to decompose water. The oxygen produced by the positive pole reacts with the negative sponge lead, leaving part of the negative pole in an incomplete state and inhibiting the production of negative hydrogen.

New and old batteries used in Series

Due to the large number of chemical reaction substances, the end voltage is high, the internal resistance is small, while the old battery end voltage is low, and the internal resistance is large. Generally, the internal resistance of the new 12V battery is 0.015-0.018oumu, and the internal resistance of the old battery is mostly 0.085 Ohm or more, If the old and new batteries are used in series, the charging voltage at both ends of the old battery will be higher than the charging voltage at both ends of the new battery. As a result, the new battery has not yet been filled, and the old battery is already too high, and in the discharge state, Since the capacity of the new battery is larger than that of the old battery, the result is an excessive discharge of the old battery, and even the old battery is reversed, and the battery swelling causes side effects. It will consume the electricity of the new battery, and it will also cause the internal voltage of the electrical appliance to be unstable. There is also the danger of overuse of the old battery.

Three causes of the explosion:

High internal pressure of battery causes battery shell explosion

According to the working principle of lead-acid batteries, it is known that during the charging process of batteries, especially at the end of the charging period, the water is decomposed into hydrogen and oxygen due to overcharging, and the temperature of the electrolyte increases sharply when short-circuit, severe vulcanization, and charging, will cause large amounts of water to evaporate. At this time, if the air hole of the liquid hole cover is blocked, the pressure inside the battery will rise very high due to too much gas overflowing, causing the battery tank to deform first. When the internal pressure reaches a certain pressure, it will be from the combination of the battery tank cover or other weak points. Burst, This is a physical process. When the internal pressure of the battery is higher than 0.25 MPa, the battery bursts, and the burst position is located at the hot air junction of the tank cover or at the corner of the stress concentration.

A battery explosion of hydrogen in an open fire.

The explosion limit of hydrogen and oxygen mixture gas is 4 % -96 % of the gas volume of the mixture, and the explosion limit of hydrogen and air mixture gas is 4 % -74 % of the gas volume of the mixture. If 80 % of the excess charge is used for electrolyzing water, the hydrogen content inside the battery is greater than the explosion range. When the hydrogen content in the battery or in the air accumulates to the explosion limit, an open fire will form an explosion. This is a chemical reaction. The study found that the explosion of the battery belongs to the chain explosion reaction. Too many of these explosions occur under overcharging conditions. If there are virtual welding spots in the inner pole of the battery, wear wall welding, etc., the battery has a higher chance of explosion. A qualified battery will not have a self-heating explosion reaction under normal operating conditions. When the battery charging voltage gasoline car is higher than 14.4 V and the diesel car is higher than 28.8 V, an explosion may occur under the condition that the fire exists at the same time. Through the vehicle inspection of the battery explosion, it was found that most of the voltage regulators have defects, and the battery is in a serious over-charging state.

Vent blockage, explosion.

As the exhaust hole of the battery is blocked, the battery bursts first, causing the battery to vibrate, and the pole wiring does not produce sparks, thus forming an explosion.

The page contains the contents of the machine translation.