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Thermal runaway problem of electric scooter lead-acid batteries
May 25, 2018

Deformation of the battery is not sudden, it is often a process. When the battery is charged to 80% of the capacity, it enters into the high voltage charging zone. At this time, oxygen is precipitated on the positive electrode plate. Oxygen gas passes through the pores in the separator to reach the negative electrode, and oxygen reactivation reaction is performed on the negative electrode plate: 2Pb+O2 (Oxygen) = 2PbO + Q (heat); PbO + H2SO4 = PbSO4 + H2O + Q (heat). When the reaction generates heat, when the charging capacity reaches 90%, the oxygen generation rate increases, the negative electrode starts to generate hydrogen, and the increase of a large amount of gas causes the internal pressure of the battery to exceed the valve pressure, the safety valve opens, the gas escapes, and finally the performance is water loss. 2H2O=2H2↑+O2↑. As the number of battery cycles increases, moisture gradually decreases, resulting in the following conditions for the battery:

(1) Oxygen "channels" become unobstructed, and the oxidation produced by the positive electrode can easily reach the negative electrode through the "channel";

(2) The heat capacity is reduced. 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 increases the temperature of the battery.

(3) Due to the phenomenon of shrinkage of the ultra-fine glass fiber separator in the battery after dehydration, the adhesion to the positive and negative plates deteriorates, the internal resistance increases, and the heat generation during charge and discharge increases. After the above process, the heat generated inside the battery can only be dissipated through the battery slot. If the heat is less than the amount of heat, the temperature rises. As the temperature rises, the over-potential of the battery gas is reduced, and the amount of gas evolution increases. A large amount of oxidation of the positive electrode passes through the “channel” and reacts on the surface of the negative electrode to generate a large amount of heat, so that the temperature rises rapidly and a vicious circle is formed, that is, the so-called “thermal runaway”. http://www.jianmoddc.com/


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