Influence of high temperature on lithium ion battery
Among all environmental factors, temperature has the greatest influence on the battery's charge and discharge performance. The electrochemical reaction at the electrode / electrolyte interface is related to the ambient temperature. The temperature rise means that the output power of the lithium ion battery will rise. The temperature also affects the transfer speed of the electrolyte. The temperature rises faster, the transfer temperature decreases, and the transfer slows down. The battery charge and discharge performance will also be affected. However, if the temperature is too high above 45 ° C, the chemical balance in the battery will be destroyed, causing side reactions.
The influence of temperature on the discharge performance directly reflects the discharge capacity and discharge voltage. As the temperature decreases, the internal resistance of the battery increases, the electrochemical reaction rate slows down, the polarization internal resistance increases rapidly, and the battery discharge capacity and discharge platform decrease, affecting the output of battery power and energy. Lithium-ion battery capacity decline has the effect of battery polarization, that is, the diffusion speed of lithium ions can not keep up with the transfer speed of electrons, which makes the battery positive electrode contain less and less lithium ions. This polarization process is further exacerbated at a high temperature of 60 ° C, which is the root cause of capacity decay of lithium-ion batteries.
The high-temperature failure mechanism of lithium-ion batteries is far more complicated than previous reports. In actual research, it is difficult to distinguish between the loss of active lithium and the loss of active materials. During the lithium intercalation of lithium iron phosphate materials, part of the lithium intercalated lithium iron phosphate phase will be isolated from the electronic conductive channel formed by the conductive agent due to the internal stress application, so that the lithium cannot be irreversibly deintercalated and cause the loss of active material.
Is high temperature the cause of the bulging of lithium-ion batteries?
1. The main reason for the bulging of lithium-ion batteries is that gas appears inside the lithium-ion battery. The first manifestation of almost all lithium-ion batteries when they are damaged is the appearance of gas inside the battery; It manifests as cell bulging, so cell bulging is also an early warning of cell damage or possible safety issues.
2. The cell is affected by high temperature. Most of the time the cell is stored at a higher temperature for a long time, the temperature will accelerate some chemical reactions inside the cell to form gas, especially when the cell is fully charged or slightly overcharged. The effect of high-temperature storage is more obvious, so it is necessary to prevent long-term storage of batteries at high temperatures.
3. Overcharge will cause all the lithium atoms in the positive electrode material to run into the negative electrode material, resulting in the deformation and collapse of the originally full grid of the positive electrode, which is also an important reason for the decrease in the capacity of the lithium ion battery. In this process, there are more and more lithium ions in the negative electrode, and excessive accumulation causes the lithium atoms to grow out of the stump crystal and cause the battery to swell.
4. The SEI film will have a protective effect on the negative electrode material, so that the material structure is not easy to collapse, and the cycle life of the electrode material can be added. The SEI film is not static, and there will be a little change in the process of charging and discharging. The important thing is that some organic substances will change reversibly. After the battery is over-discharged, the reversible ring of the SEI film occurs, and the SEI that protects the negative electrode material collapses so that the negative electrode material collapses, thereby forming a bulge phenomenon.
The chemistry and electrochemical reaction of lithium-ion batteries at high temperatures are very complicated. It is essential to study the reaction mechanism between the internal components of the battery. It is essential to suppress the occurrence of various exothermic reactions and improve the safety performance under battery abuse . Lithium-ion batteries are greatly affected by temperature. In the application field of power lithium battery applications and the temperature-intensive application environment, it is necessary to thermally manage the battery to improve the efficiency of the battery and extend the service life of the battery system.
