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cnhl 6s lipo battery safety problems and preventive measures

Electric vehicles are the main development direction of new energy vehicles, and the biggest safety hazard is the power cnhl 6s lipo battery.

Although there are quite a lot of regulations on the safety of the cnhl 6s lipo battery system and battery performance in China, due to the inherent chemical characteristics of the power battery, unstable factors in some special conditions will lead to spontaneous combustion, and the cnhl 6s of electric vehicles The thermal runaway rate of lipo battery is difficult to estimate, and it is more difficult to extinguish than traditional gasoline vehicles.

Today, CNHL will give you a comprehensive interpretation of the new safety technology and new trends of cnhl 6s lipo battery!

cnhl 6s lipo battery thermal runaway process:

The thermal runaway of the cnhl 6s lipo battery is caused by the fact that the heat generation rate of the cnhl 6s lipo battery is much higher than the heat dissipation rate, and a large amount of heat is accumulated and not dissipated in time. In essence, "thermal runaway" is an energy-positive feedback loop process: increased temperature causes the system to heat up, which in turn makes the system hotter. Without strict division, battery thermal runaway can be divided into three stages

Stage 1: Internal thermal runaway stage of cnhl 6s lipo battery
Due to internal short circuit, external heating, or the cnhl 6s lipo battery itself heats up during high current charging and discharging, the internal temperature of the battery rises to about 90℃~100℃, and the lithium salt LiPF6 begins to decompose;

for the chemical activity of the carbon negative electrode in the charged state Very high, close to metal lithium, the SEI film on the surface decomposes at high temperature, and the lithium ions embedded in the graphite react with the electrolyte and the binder, which further pushes the temperature of the cnhl 6s lipo battery to 150 ℃, and there are new products at this temperature. The violent exothermic reaction occurs, for example, a large amount of electrolyte is decomposed to generate PF5, and PF5 further catalyzes the decomposition reaction of organic solvents.

Stage 2: cnhl 6s lipo battery drumming stage
When the temperature of the cnhl 6s lipo battery reaches above 200°C, the positive electrode material decomposes, releasing a large amount of heat and gas, and the temperature continues to rise. At 250-350°C, the lithium intercalated negative electrode begins to react with the electrolyte.

Stage 3: cnhl 6s lipo battery thermal runaway, explosion failure stage
During the reaction process, the charged cathode material begins to undergo a violent decomposition reaction, and the electrolyte undergoes a violent oxidation reaction, releasing a large amount of heat, generating high temperature and a large amount of gas, and the cnhl 6s lipo battery burns and explodes.

cnhl 6s lipo battery process design and thermal runaway:

The production process of cnhl 6s lipo battery is very complicated, and even with strict control, metal impurities or burrs in the production process cannot be completely avoided. If impurities, burrs or dendrites appear inside the cnhl 6s lipo battery, the electrical conductivity will rise after amplification and deterioration, the temperature will rise, and the heat generated by the chemical reaction and discharge heat will accumulate, which may eventually lead to the thermal runaway of the cnhl 6s lipo battery.

cnhl 6s lipo battery has insufficient negative capacity

When the capacity of the negative electrode opposite the positive electrode is insufficient, or there is no capacity at all, part or all of the lithium generated during charging cannot be inserted into the interlayer structure of the negative electrode graphite, and will precipitate on the surface of the negative electrode to form protruding "branches". During the next charge, this protruding part is more likely to cause the precipitation of lithium. After dozens to hundreds of cycles of charge and discharge, the "dendrite" will grow, and finally pierce the separator paper, causing a short circuit inside. . The battery cell is rapidly discharged, generating a lot of heat, burning the diaphragm, and causing a larger short circuit phenomenon. The high temperature will cause the electrolyte to decompose into gas, and the negative electrode carbon and the diaphragm paper will burn, resulting in excessive internal pressure. When exposed to this pressure, the cells explode.

cnhl 6s lipo battery moisture content is too high

Moisture can react with the electrolyte in the cnhl 6s lipo battery cell to produce gas. When charging, it can react with the generated lithium to generate lithium oxide, which will cause the capacity loss of the cnhl 6s lipo battery cell and easily cause the cnhl 6s lipo battery to lose its capacity. The cell is overcharged to generate gas, the decomposition voltage of water is low, and it is easy to decompose to generate gas during charging. When this series of generated gases will increase the internal pressure of the cell, when the outer shell of the cell cannot withstand it, The cnhl 6s lipo battery will explode.

cnhl 6s lipo battery internal short circuit

Due to the internal short-circuit phenomenon, the cnhl 6s lipo battery cell is discharged with a large current, which generates a lot of heat, burns out the diaphragm, and causes a larger short-circuit phenomenon. In this way, the cell will generate high temperature, causing the electrolyte to decompose into gas, causing internal If the pressure is too high, when the shell of the cnhl 6s lipo battery cell cannot withstand this pressure, the cell will explode. During laser welding, the heat is conducted to the positive tab through the shell, which makes the temperature of the positive tab high. If the upper tape does not separate the positive tab and the diaphragm, the hot positive tab will burn or shrink the separator paper, resulting in an internal short circuit. to form an explosion.

Measures to prevent the explosion of cnhl 6s lipo battery:

Improve thermal stability of cnhl 6s lipo battery material
Cathode material: The cathode material can be improved by optimizing synthesis conditions, improving synthesis methods, and synthesizing materials with good thermal stability; or using composite technology (such as doping technology), surface coating technology (such as coating technology) to improve cnhl 6s lipo battery Thermal stability of cathode materials.

Negative electrode material:

The thermal stability of the negative electrode material is related to the type of negative electrode material, the size of the material particles and the stability of the SEI film formed by the negative electrode.

If the size particles are made into a negative electrode according to a certain ratio, the contact area between the particles can be expanded, the electrode impedance of the cnhl 6s lipo battery can be reduced, the electrode capacity of the cnhl 6s lipo battery can be increased, and the possibility of the precipitation of active metal lithium can be reduced.

6s lipo battery SEI film:

The quality of SEI film formation directly affects the charge and discharge performance and safety of cnhl 6s lipo battery. Weakly oxidize the surface of carbon materials, or reduce, doped, surface-modified carbon materials and use spherical or fibrous carbon materials The material helps to improve the quality of cnhl 6s lipo batterySEI membrane.

6s lipo battery Electrolyte:

The stability of the electrolyte is related to the type of lithium salt and solvent. The thermal stability of the battery can be improved by using a lithium salt with good thermal stability and a solvent with a wide potential stability window. Adding some high boiling point, high flash point and non-flammable solvents to the electrolyte can improve the safety of the battery.

Conductive agent and binder:

The type and quantity of conductive agent and binder also affect the thermal stability of the battery. The binder and lithium react at high temperature to generate a lot of heat. Different binders have different calorific values. The calorific value is almost twice that of the non-fluorine binder, and replacing the PVDF with the non-fluorine binder can improve the thermal stability of the battery.

The safety issue of cnhl 6s lipo battery is a complex and comprehensive issue. The biggest hidden danger in the safety of cnhl 6s lipo battery is the random internal short circuit of the battery, resulting in on-site failure and thermal runaway. Therefore, the development and use of materials with high thermal stability is the fundamental way and the direction of efforts to improve the safety performance of cnhl 6s lipo battery in the future.

Well, the above is the whole content about the safety issues and preventive measures of the cnhl 6s lipo battery brought to you today by the die flash. Since the thermal runaway of the cnhl 6s lipo battery is difficult to control, the cnhl 6s lipo battery is in danger of explosion. This problem It can be improved by synthesizing materials with good thermal stability, the quality of SEI film formation, and the stability of electrolytes. I hope the above content is helpful to you, more information will be continuously updated, see you in the next issue.

Vorig artikel What is 4s lipo battery thermal runaway expansion?

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