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| Why are there individual deformation in the use of accumulator batteries |
| Time：2019-04-02 Source： Views：6229 |
Battery deformation is caused by excessive gas pressure inside the battery. In order to ensure high oxygen recombination efficiency, it is necessary to maintain a certain pressure inside the battery. On the premise of high oxygen compound efficiency, the quality of safety valve is very important. According to JISC8707-1992, the open and close pressure of battery safety valve is below 49 kPa and above lkPa. The original rules of the Ministry of Posts and Telecommunications in China are that the opening pressure is 10-4gkPa and the closing pressure is 1-lOkPa.
The theory proves that the opening pressure should be slightly lower, 10-l5kPa is more suitable, and the closing pressure value close to the opening pressure value is better. In order to solve the problem of battery shrinkage, it is necessary to ensure that the oxygen recombination efficiency is above 98%. For this reason, the void fraction (should be greater than 93%), base weight, acid absorption value and other indicators are very important. The use of high-quality partitions is the basis to ensure the above technical indicators. The wall thickness margin is fully considered in the design to deal with the battery deformation.
Battery deformation is not sudden, often has a gradual process. When the battery enters the high-voltage charging area at about 80% of its charging capacity, oxygen is first released on the positive plate, and then reaches the negative plate through the hole in the partition, stopping the oxygen reactions on the negative plate and generating heat in the process of the reactions. When the charging capacity reaches 90%, the rate of oxygen generation increases, and hydrogen is generated at the beginning of the negative electrode. With the increase of a large number of gases, the internal pressure of the battery exceeds the pressure of the open valve, and the safety valve opens and the gas escapes, which eventually results in water loss. With the increase of the number of battery cycles, the water content decreases gradually, resulting in the following situation of the battery:
(1) The heat capacity decreases. The biggest heat capacity in the battery is water. After water loss, the heat capacity of the battery decreases greatly, and the heat generated makes the temperature of the battery rise rapidly.
(2) Some batteries exhibit irreversible sulfation of the plate, increase internal resistance, and heat is generated during charging. When the temperature rises to the critical temperature of the shell, the heat generated cannot be fully distributed, which will lead to the deformation of the battery shell.
(3) The shrinkage of ultrafine fiberglass separators in batteries after water loss makes the adhesion between the separators and positive and negative plates worse, the internal resistance increases, and the heat increases during charging and discharging. After the above process, the heat generated inside the battery can only be lost through the battery tank, such as heat dissipation less than heat, that is, temperature rise phenomenon. As the temperature rises, the overpotential of battery gas evolution decreases and the volume of gas evolution increases, and a great deal of oxygen passes through the "channel". In the negative exterior response, a lot of heat is emitted, so that the temperature rises rapidly, forming a vicious circle, that is, the so-called "thermal runaway", the final temperature reaches more than 80%, that is, deformation occurs.
When a group of batteries are deformed at the same time, the voltage should be checked first. If the voltage is basically normal, the unit voltage should also be measured to determine whether the short circuit is possible or not. If there is no short circuit, it is explained that the deformation is caused by "thermal runaway" caused by overcharging. At this time, the charging parameters of the charger should be checked. If the charging voltage is too high, there is no overcharge maintenance, the floating charging voltage is too high or the trickle current conversion point current is too low, the charger should be adjusted or changed. If only one or two of a group of batteries (3 batteries) are deformed, the causes of their faults are as follows:
1) An accumulator exhibits irreversible sulfation of the plate, increases the internal resistance, and warms up and deforms during charging.
2) When a certain battery is connected to the wire, the reverse pole forms charging heating deformation.
3) There is no difference in the charge of batteries. Some batteries are overcharged and deformed when they are charged. Charging indifference may be caused by single cell short circuit or by user discharging or self-discharging of the battery.
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