Causes of deformation of lead-acid batteries

by:Power Kingdom     2021-07-15

  Fault phenomenon

  The deformation of the battery is not sudden, it is often a process. The battery enters the high-voltage charging zone when it is charged to about 80% of its capacity. At this time, oxygen gas is first precipitated in the positive electrode, and the oxygen gas passes through the pores in the separator and reaches the negative electrode. Oxygen resurrection reaction on the negative plate:

  2Pb+O2u003d2PbO+H2O+Q

  PbO+H2SO4u003dPbSO4+H2O +Q

   generates heat during the reaction. When the charging capacity reaches 90%, the rate of oxygen generation increases, and the negative electrode begins to generate hydrogen. The increase of a large amount of gas is that the internal pressure of the battery exceeds the valve opening pressure, the safety valve opens, and the gas escapes, which is finally manifested as water loss.

  2H2Ou003dH2+O2

  As the number of battery cycles increases, the moisture decreases gradually, and the results of the battery appear as follows :

   (1) The oxygen 'channel' becomes unblocked, and the oxygen generated by the positive electrode can easily reach the negative electrode through the 'channel'.

   (2) The heat capacity is reduced, and the largest heat capacity in the battery is water. After the water is lost, the heat capacity of the battery is greatly reduced, and the heat generated makes the temperature of the battery rise quickly.

   (3) After the loss of water, the ultrafine glass fiber separator in the battery shrinks, which makes the adhesion to the positive and negative plates worse and the internal resistance increases. Heat generation increases during charging and discharging. After the above process, the heat generated inside the battery can only be dissipated through the battery slot. If the heat dissipation is less than the calorific value, the temperature will rise, which will reduce the overpotential of the battery gassing and increase the gassing capacity. A large amount of oxygen from the positive electrode passes through the 'channel' and reacts on the negative surface, emitting a large amount of heat to make the temperature rise rapidly. The formation of a vicious circle leads to 'thermal runaway' and deformation.

  Failure inspection and treatment

   A group of batteries deforms at the same time, first check the voltage. If the voltage is basically normal. The single cell voltage should also be measured to determine whether there is a short circuit. If there is no short circuit, it means that the deformation is caused by 'thermal runaway' caused by overcharging. Should focus on checking the charging parameters of the charger. If the voltage is too high (above 44.7V) without overcharge protection or the trickle conversion current is too low, the charger must be replaced.

  

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