While the majority of electric vehicle users feel the convenience brought by the electric vehicle side, they are also almost distressed by the batteries that are replaced once a year. According to the statistics of an authoritative electric vehicle magazine, the replacement rate of electric vehicle batteries in summer is as high as 70~80%, and more than 80% of these replaced batteries are scrapped due to battery bulge. The main causes of the battery bulge are the thermal runaway of the battery and the runaway internal circuit of the charger; The method to prevent the battery from bulging is to add nano carbon sol battery activator or install temperature controlled circuit breaker.

1、 Causes of battery bulge

The battery bulges because the battery enters into a thermal runaway state when charging. The battery enters into a thermal runaway state because the charging current is too large or the internal resistance of the battery is increased due to battery vulcanization after a certain period of use. After the internal resistance increases, the battery temperature will rise under the effect of current when charging, and the temperature rise will further increase the current, thus forming a vicious cycle, the internal pressure will rise, and finally the battery will be deformed. The main causes of the battery bulge are the thermal runaway of the battery and the runaway internal circuit of the charger.

（1） The thermal runaway of the battery causes the battery to bulge

Thermal runaway refers to the cumulative enhancement of current and battery temperature during battery charging and gradual damage. After the lead-acid battery is seriously dehydrated and sulfurized, the internal resistance of the battery increases, which leads to an increase in the heat output of the battery during the charging and discharging process, reducing the overpotential of gas evolution of the battery, and increasing the gas evolution amount. A large amount of oxygen released from the positive electrode reacts on the negative electrode surface through the internal "channel", releasing a large amount of heat, and causing a large increase in the battery temperature, forming a vicious cycle. This is the "heat runaway" of the lead-acid battery. When the internal temperature of the lead-acid battery with "thermal runaway" reaches or exceeds the softening temperature (thermal deformation temperature) of its plastic shell material, the battery will produce "thermal deformation" and the battery will bulge. In summer, when the external temperature is high, the internal electrochemical reaction rate of the battery will be accelerated and the battery temperature will be accelerated, which is more likely to cause the battery to bulge due to "thermal runaway".

1. The characteristics of electric vehicle battery cause "thermal runaway"

The electric vehicle battery is designed as a lean solution battery, that is, a valve regulated lead-acid maintenance free battery. Water loss is a unique phenomenon of electric vehicle batteries. The battery will lose water after 6 months of use, which will cause the increase of the specific gravity of electrolyte, that is, the increase of the concentration of sulfuric acid. It will accelerate the formation of irreversible lead sulfate crystals, which will lead to the increase of the internal resistance of the battery. The battery voltage will rise during charging. Once the terminal voltage reaches 2.30-2.35V/single battery, It is found that the hydrogen and oxygen gas move to form the "boiling" phenomenon of electrolyte. When the voltage rises again, the current entering the battery will almost all be used in the electrolytic water. The electrolytic water will produce gas, so it will blow up. That is to say, the heat loss of the battery is the prelude to the thermal runaway of the battery. When the water loss develops to a certain extent, it will turn into thermal runaway

2. The quality of electric vehicle battery causes "thermal runaway"

Due to the different manufacturing processes of each battery manufacturer, such as plate manufacturing, assembly, formation, bus bar welding and other processes, the battery cell lags behind. During the use of the electric vehicle battery pack, it is usually that the backward single cell battery fails ahead of time. When charging the battery, the backward single cell battery shows that the voltage does not rise or rises very slowly when the charging constant voltage is unchanged. Prolonging the charging time will make the voltage of the good single cell battery relatively high, and will also make this battery or the whole battery overheat due to overcharging, leading to the thermal runaway of the battery.

3. "Thermal runaway" caused by charging of electric vehicle battery

The habit of charging electric vehicles is also easy to make the batteries of electric vehicles bulge. Many users charge at night until tomorrow morning. Although the indicator light of the charger has turned green, the charger still has a large trickle and floating charge. The battery has been charged for a long time at a single time, resulting in the electrolytic loss of water in the electrolyte, causing the battery to heat and deform the charging drum, causing the plate to break or short circuit. In addition, the charger does not match the battery pack of the electric vehicle, and the voltage of the charger is too high, which is higher than the specified value of the lead-acid battery pack, which greatly increases the gas evolution of the battery. When the oxygen circulation gas path inside the battery is too smooth, the oxygen released from the positive plate directly acts on the negative plate for oxygen circulation, and the heat generated cannot be discharged in time, causing the battery to lose control of heat.

（2） Battery bulge caused by out of control internal circuit of charger

1. The working mechanism of the three-stage charger causes the battery to bulge. The vast majority of chargers in the market are three-stage chargers. They start charging, limit the current by 1.8A, and the setting of the maximum limit voltage jumps to 44V (not 42V). When the charging current is less than 0.5A, the green light jumps, and the maximum setting voltage returns to 42V, and the floating charge starts. We have set up a special test bench and found that the current of almost all chargers after charging to the green light is enough to drive the motor of an electric vehicle to idle above 10 meters, so almost all of them have always had the problem of large trickle and floating charge, which is the culprit of battery charging.

2. The internal voltage stabilizing circuit of the charger is out of control, which causes the output voltage to be higher than 15.5V/single charger for a long time, and the charger cannot enter the low voltage charging, causing the battery to "heat out of control", resulting in battery charging drum.

3. The current conversion circuit inside the charger is out of control, which causes that the charger cannot jump to the floating charge low voltage maintenance stage according to the normal procedure when the battery is close to the completion of charging. The battery is in the high-level charging stage for a long time, which causes the battery to heat up inside and cause the battery to bulge

2、 Precursor of Electric Vehicle Battery Bulging

All kinds of omens will appear when anything changes, and the battery drum is no exception. If we find that the battery changes before it starts to bulge, we should take precautions to prevent it from happening. Pay attention to the following phenomena to prevent the battery from bulging.

1. Check the change of charger indicator

A. The green light will jump when the battery of the electric vehicle is charged for 4 hours (green light means full).

B. The green light does not jump when the electric vehicle battery is charged for a long time.

C. After charging the battery of the electric vehicle, the green light came on an hour later, and the red light came on an hour later.

D. The green light does not jump after the battery of the electric vehicle is charged for a long time. When you unplug the power plug and plug it in, the green light turns strange.

2. Feel the change of battery shell temperature

When the electric vehicle is charged for 6 hours, if the temperature of the electric vehicle charger rises to 40 ° C or the battery shell temperature reaches 50 ° C, the battery may bulge.

3、 Prevention Method of Electric Vehicle Battery Bulging

It is very simple to prevent the battery of electric vehicles from bulging. As long as the following three points are achieved, the battery of electric vehicles can be used for more than two years.

1. Use electric vehicles and charging methods correctly. The specific methods and contents are concerned with the battery repair of the small coppersmith. The official vxin official account is xtj400-004-1090.

2. Nano carbon sol was added to electric vehicle battery. After adding nano carbon sol battery activator, the active component of the activator can solidify the electrode plate under the action of electric field; Disintegration irreversible sulfate crystallization; Open the diaphragm ion channel; Active substance for activating the battery; Reduce the internal resistance of the battery and improve the electrochemical reaction of the battery. It can effectively prevent "thermal runaway" caused by the increase of battery internal resistance.

3. The battery pack shall be equipped with temperature control circuit breaker. The temperature control breaker is close to the battery surface. When the battery temperature rises to 50 degrees, the temperature controller will automatically disconnect the charging current of the charger. When the temperature of the battery surface drops, the temperature controller will automatically connect the power supply to continue charging. When the charger circuit is out of control, the temperature controller will automatically identify and disconnect the charging power supply, stop the charger from charging the battery for a long time with large current, and effectively protect the battery.