National service hotline① water loss ② vulcanization ③ imbalance ④ thermal runaway (filling drum)
The first two (1) and (2) account for 97% of battery damage on the market.
(1) Analysis ① : The main cause of water loss in lead-acid batteries
Electric vehicle charger
The electrolyte in a lead-acid battery is as valuable as human blood, and its loss means the battery is dead. The electrolyte consists of dilute sulfuric acid and water. In the process of charging, it is difficult to avoid water loss, and water loss is not the same with different charging modes. The water loss of the ordinary three-stage charging mode is more than twice that of the Collin pulse mode. Batteries also have a water-loss life in addition to their natural life: if a single battery loses more than 90 grams of water, the battery is useless. At room temperature (25℃), the loss of water of the ordinary charger is about 0.25 grams, while the Colin pulse is 0.12 grams. At high temperature (35℃), the loss of water in the ordinary charger is 0.5 g, while the Colin pulse is 0.23 g. According to this calculation, the ordinary charger after 250 cycles of water dry, while the Colin pulse after 600 cycles of water dry. As a result, the Colin pulse can extend the battery life by more than double. (Show the report and draw a graph.)
The big problem in lead-acid battery charging process is gas extraction.
According to the American scientist J.A.M. 's research on the causes and rules of gas evolution in the charging process of lead-acid battery, in order to achieve very low gas evolution rate, lead-acid battery can accept the charging current curve as follows:
The formula of the critical gas evolution curve is: I=I0e-at %h^2
In the charging process, the charging current exceeds the critical gas evolution curve, can only lead to the battery electrolytic water reaction and produce gas and temperature rise, can not improve the capacity of the battery
(1) In the constant current charging stage, the charging current remains constant, the charged amount increases rapidly, and the voltage rises;
(2) In the constant voltage charging stage, the charging voltage remains constant, the charged amount continues to increase, and the charging current decreases;
(3) When the battery is full, the current drops to lower than the float charging conversion current, and the charging voltage drops to the float charging voltage;
(4) In the floating charging stage, the charging voltage remains the floating charging voltage;
Common three-stage charging stage for constant current charging, this is mainly to consider the design of the circuit is more convenient, not to make the battery performance is very good design.
In the late period of constant current charging and the early period of constant voltage charging (shadow area), the current exceeds the critical gas evolution curve, resulting in gas evolution of the battery, resulting in reduced life.
The current exceeding the critical gas evolution curve only makes the battery produce gas and temperature rise, and does not convert into battery power, thus reducing the charging efficiency.
(2) Analysis ② : the cause of lead-acid battery vulcanization
Long-term battery retention, long-term overcharge and undercharge in the charging process, large current discharge in the use of the process, easy to cause the vulcanization of the battery. Its appearance is: as soon as the light, as soon as the full, we call it the battery "false damage". Sulphide substance sulphate adhered to the plate, reduced the electrolyte and plate reaction area, so that the capacity of the battery rapidly attenuated. The loss of water will aggravate the vulcanization of the battery; Vulcanization will increase the battery water loss, easy to form a vicious cycle.
(3) Analysis ③ : lead acid battery imbalance problem
A battery group consists of three or four cells. Due to manufacturing process problems, can not do the effective balance of each battery, ordinary charger using the average current, so that the small capacity of the single battery is very full, and the formation of overcharge, discharge, the small capacity of the battery is very first, and the formation of overrelease. In the long run, the vicious cycle makes the whole group of batteries lag behind, thus making the whole group of batteries scrapped. The floating charge stage of the three-stage charger, with a small current of 500mA, its function is to compensate the charge, so that the battery is full. But it also brings two side effects :1, after full, the excess current is not related to break off, electric energy into heat, water decomposition, accelerate the distribution of water; 2. 2, small current charging, the current bifurcation is large, more likely to cause the imbalance of the battery pack.
(4) Analysis ④ : Lead acid battery thermal runaway problem
Battery deformation is not sudden, is often a process. When the battery is charged to 80% of its capacity, it enters the high-voltage charging zone. At this time, oxygen is precipitated on the positive plate, and oxygen passes through the hole in the separator to the negative electrode, where oxygen is revived: 2Pb+O2 (oxygen) =2PbO+Q (heat); PbO+H2SO4=PbSO4+H2O+Q. Heat is generated during the reaction. When the charging capacity reaches 90%, the oxygen rate increases and the negative electrode begins to produce hydrogen. The increase of a large number of gases makes the internal pressure of the battery exceed the valve pressure, and the safety valve opens and the gas escapes, which is ultimately manifested as water loss. 2H2O is equal to 2H2↑+O2↑. As the number of battery cycles increases, the water gradually decreases, resulting in the following situations:
The oxygen "channel" becomes smooth, the oxidation generated by the positive electrode is easy to reach the negative electrode through the "channel";
The heat capacity is reduced, in the battery heat capacity is very big water, water loss, the heat capacity of the battery is greatly reduced, the heat generated by the battery temperature rises quickly;
(3) Due to the shrinkage phenomenon of the ultrafine glass fiber separator in the battery after water loss, the adhesion with positive and negative plates becomes worse, the internal resistance increases, and the heat increase in the process of charging and discharging. After the preceding process, the heat generated inside the battery can only be dissipated through the battery slot. If the heat loss is less than the heat gain, the temperature rises. The temperature rises, so that the battery gas evolution over potential reduction, gas evolution increases, a large number of positive electrode oxidation through the "channel", in the negative surface reaction, emit a lot of heat, so that the temperature rises rapidly, the formation of a vicious cycle, the so-called "thermal runaway".