① Water loss ② Vulcanization ③ Unbalance ④ Thermal runaway (drum charging)

The first two ① and ② account for 97% of battery damage on the market.

(1) Analysis ①: The main cause of lead-acid battery water loss

Electric car charger

The electrolyte in a lead-acid battery is as valuable as the blood in the human body. Once the electrolyte is lost, it means that the battery is scrapped. The electrolyte is composed of dilute sulfuric acid and water. During the charging process, it is difficult to avoid water loss. The charging mode is different and the water loss is different. Ordinary three-stage charging mode, the water loss during charging is more than twice that of Colin pulse mode! In addition to the natural life of the battery, there is also a water loss life: a single battery loses more than 90 grams of water, and the battery is scrapped. At room temperature (25 ℃), the water loss of ordinary charger is about 0.25 grams, while the colin pulse is 0.12 grams. At high temperature (35 ℃), the water loss of ordinary charger is 0.5g, while the colin pulse is 0.23g. According to this calculation, the ordinary charger will dry the water after 250 cycles, while the Colin pulse will dry the water after 600 cycles. Therefore, Colin pulse can extend the battery life more than double.

A big problem in the charging process of lead-acid batteries is gas evolution.

According to the American scientist Mas (J.A.Mas) on the lead-acid battery charging process of gas evolution causes and laws of research, in order to achieve a very low gas evolution rate, lead-acid batteries can accept the charging current curve is as follows:

The formula of critical gas evolution curve is: I = I0e-at h 2

During the charging process, the part of the charging current exceeding the critical gas evolution curve can only cause the electrolytic water reaction of the battery to produce gas and temperature rise, and cannot increase the capacity of the battery.

① In the constant current charging stage, the charging current remains constant, the charged quantity increases rapidly, and the voltage rises;

In the constant voltage charging phase, the charging voltage remains constant, the charged quantity continues to increase, and the charging current decreases;

③ When the battery is fully charged, the current drops below the floating charge conversion current, and the charging voltage drops to the floating charge voltage;

④ During the floating charging phase, the charging voltage is kept at the floating voltage;

Ordinary three-stage charging stage for constant current charging, this is mainly considering the circuit design is more convenient, not to make the battery performance is very good and design.

In the late stage of constant current charging and the early stage of constant voltage charging (shaded area), the current exceeds the critical gas evolution curve, resulting in gas evolution of the battery and a decrease in life.

The current exceeding the critical gas evolution curve only causes the battery to produce gas and temperature rise, not converted into battery power, and the charging efficiency is therefore reduced.

(2) Analysis ②: Causes of vulcanization of lead-acid batteries

Long-term retention of the battery, long-term overcharge and undercharge during charging, and high current discharge during use, can easily cause battery vulcanization. Its appearance is: light as soon as it is released and full as soon as it is charged. We call it "false damage" to the battery ". Sulfide substance sulfate adheres to the plate, which reduces the reaction area between the electrolyte and the plate, and makes the battery capacity decay rapidly. Water loss will increase the battery vulcanization; vulcanization will increase the battery water loss, easy to form a vicious circle.

(3) Analysis ③: Imbalance of lead-acid batteries

A group of batteries consists of three to four. Due to manufacturing process problems, it is impossible to achieve the effective balance of each battery. Ordinary chargers use average current to make a single battery with small capacity fully charged first and form overcharge. When discharging, this battery with small capacity is discharged first and overdischarge is formed. For a long time, the vicious circle, so that the whole group of batteries appear single behind, so that the whole group of batteries scrapped. The floating charging phase of the three-stage charger has a small current of 500mA. Its function is to compensate for charging and make the battery full. But it also brings two side effects: 1. After full charging, the excess current is not turned off, and the electric energy is converted into heat energy, which decomposes water and accelerates the distribution of water; 2. When charging with small current, the generated current bifurcates greatly, which is more likely to cause imbalance of the battery pack.

(4) Analysis ④: Thermal runaway of lead-acid batteries

Battery deformation is not sudden, often there is a process. When the battery is charged to 80% of its capacity, it enters the high-voltage charging area. At this time, oxygen is first precipitated on the positive plate, and oxygen passes through the holes in the separator to reach the negative electrode. Oxygen resurrection reaction is carried out on the negative plate: 2Pb + O2 (oxygen) = 2PbO + Q (heat);PbO + H2SO4 = PbSO4 + H2O + Q (heat). Heat is generated during the reaction. When the charging capacity reaches 90%, the oxygen generation rate increases, and the negative electrode begins to generate hydrogen. 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 shows water loss. 2H2O = 2H2 ↑ + O2 ↑. As the number of battery cycles increases, the moisture gradually decreases, resulting in the following battery:

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

⑵ The heat capacity is reduced. The large 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 battery temperature rise quickly;

⑶ Due to the shrinkage of the ultra-fine glass fiber separator in the battery after water loss, the adhesion to the positive and negative plates becomes worse, the internal resistance increases, and the 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 heat generation, the temperature rise will occur. The temperature rises, so that the battery gas evolution potential is reduced, the amount of gas evolution increases, a large number of positive oxidation through the "channel", in the negative surface reaction, a large amount of heat, so that the temperature rises rapidly, the formation of a vicious circle, the so-called "thermal runaway".