Process of lithium iron phosphate battery -Lithium - Ion Battery Equipment
Formation is an important process in the production process of lithium batteries. During chemical formation, a passivation layer is formed on the surface of the negative electrode, that is, a solid electrolyte interface film (SEI film). The quality of the SEI film affects the battery's cycle life, stability, The electrochemical properties such as self-discharge and safety meet the requirements of "maintenance-free" sealing of secondary batteries. However, the SEI films formed by different chemical processes are different, and the impact on the performance of the battery is also very different.
The traditional low-current precharging method is helpful for stable SEI film formation, but long-term low-current charging will lead to an increase in the resistance of the formed SEI film, thereby affecting the rate discharge performance of lithium-ion batteries, and the long process time will affect production efficiency. Different lithium battery systems have different formation processes. This paper analyzes the lithium iron phosphate battery system as the object.(Lithium - Ion Battery Equipment)
The formation process of the lithium iron phosphate system is usually selected as follows:
Charging current 0.05C~0.2C, cut-off voltage 3.6~3.7V, charging cut-off current 0.025C~0.05C, after standing for a period of time (10-20min), 0.1~0.2C discharge to 2.5V, standing for a period of time (20 -60min). Under different charge-discharge mechanisms, the difference of charge current affects the formation and quality of SEI, and the resting time and charge cut-off current affect the formation process time of the battery.
The battery formation process of the lithium iron phosphate system needs to select an appropriate cut-off voltage. From the crystal structure of the material, when the charging voltage is greater than 3.7V, the lattice structure of the lithium iron phosphate may be damaged, thereby affecting the cycle performance of the battery. Partial internal resistance experiments and pole piece SEM observation results also prove that the following conclusions are correct:
1. Appropriately reducing the formation voltage and formation time can effectively reduce the generation of lithium precipitation on the negative electrode surface, so that a negative electrode sheet with a relatively smooth surface can be obtained. This is because when the formation voltage is high, the gas production rate inside the battery is fast, so that the gas inside the battery cannot be discharged in time, and deposits on the surface of the separator, which affects the contact balance between the separator and the negative electrode. In the process of lithium ion de-intercalation, due to the influence of the unbalanced contact between the two, lithium ions are over-inserted in some areas, causing the surface of the negative electrode to be uneven, and finally affecting the performance of the battery.
2. After the formation of the battery internal resistance test, it is found that appropriately reducing the formation voltage and formation time can reduce the internal resistance of the battery. The high internal resistance caused by the high formation voltage is also related to the non-smooth surface of the negative electrode and the formation of white spots. Because the white spots are lithium compounds and have poor conductivity, the internal resistance of the battery is too large.
3. Properly reducing the formation voltage in the design of the formation process can increase the first charge and discharge capacity of the battery and improve the cycle performance of the battery. Excessive formation voltage can easily lead to the deposition of lithium and its compounds on the surface of the negative electrode, which increases the irreversible capacity of the battery and will inevitably affect the capacity of the battery. fast, affecting battery cycle life.
The traditional low-current precharging method is helpful for stable SEI film formation, but long-term low-current charging will lead to an increase in the resistance of the formed SEI film, thereby affecting the rate discharge performance of lithium-ion batteries, and the long process time will affect production efficiency. Different lithium battery systems have different formation processes. This paper analyzes the lithium iron phosphate battery system as the object.(Lithium - Ion Battery Equipment)
The formation process of the lithium iron phosphate system is usually selected as follows:
Charging current 0.05C~0.2C, cut-off voltage 3.6~3.7V, charging cut-off current 0.025C~0.05C, after standing for a period of time (10-20min), 0.1~0.2C discharge to 2.5V, standing for a period of time (20 -60min). Under different charge-discharge mechanisms, the difference of charge current affects the formation and quality of SEI, and the resting time and charge cut-off current affect the formation process time of the battery.
The battery formation process of the lithium iron phosphate system needs to select an appropriate cut-off voltage. From the crystal structure of the material, when the charging voltage is greater than 3.7V, the lattice structure of the lithium iron phosphate may be damaged, thereby affecting the cycle performance of the battery. Partial internal resistance experiments and pole piece SEM observation results also prove that the following conclusions are correct:
1. Appropriately reducing the formation voltage and formation time can effectively reduce the generation of lithium precipitation on the negative electrode surface, so that a negative electrode sheet with a relatively smooth surface can be obtained. This is because when the formation voltage is high, the gas production rate inside the battery is fast, so that the gas inside the battery cannot be discharged in time, and deposits on the surface of the separator, which affects the contact balance between the separator and the negative electrode. In the process of lithium ion de-intercalation, due to the influence of the unbalanced contact between the two, lithium ions are over-inserted in some areas, causing the surface of the negative electrode to be uneven, and finally affecting the performance of the battery.
2. After the formation of the battery internal resistance test, it is found that appropriately reducing the formation voltage and formation time can reduce the internal resistance of the battery. The high internal resistance caused by the high formation voltage is also related to the non-smooth surface of the negative electrode and the formation of white spots. Because the white spots are lithium compounds and have poor conductivity, the internal resistance of the battery is too large.
3. Properly reducing the formation voltage in the design of the formation process can increase the first charge and discharge capacity of the battery and improve the cycle performance of the battery. Excessive formation voltage can easily lead to the deposition of lithium and its compounds on the surface of the negative electrode, which increases the irreversible capacity of the battery and will inevitably affect the capacity of the battery. fast, affecting battery cycle life.
