What is battery formation?
Battery formation is a key step in battery manufacturing. It activates the electrochemical properties and forms a stable solid electrolyte interface (SEI) film by charging and discharging the newly assembled battery for the first time. This process is crucial to the performance, life and safety of the battery.
Formation is usually carried out after the battery is assembled and is a key step in the transformation of the battery from a “semi-finished battery” to a “finished battery”.
Changes in the battery during the formation process
During the battery formation process, a series of complex physical and chemical changes occur inside the battery, mainly including the following aspects:
1.Activation of battery chemistry:
During the first charge process, lithium ions are separated from the cathode electrode material (such as lithium cobalt oxide, lithium iron phosphate, etc.) and enter the electrolyte. This process activates the electrochemical activity of the cathode electrode material, enabling it to reversibly embed and extract lithium ions. At the same time, lithium ions migrate to the anode electrode (usually graphite or silicon-based materials) through the electrolyte and embed into the anode electrode material. This process activates the electrochemical activity of the negative electrode material.
2.Formation of solid electrolyte interface (SEI) film
During the first charge process, the electrolyte undergoes a reduction reaction on the surface of the negative electrode and decomposes to form a layer of solid products, namely the SEI film. The SEI film is mainly composed of inorganic salts (such as LiF, Li2CO3) and organic polymers (such as ROCO2Li). The functions of the SEI film include:
- Ionic conductivity: The SEI film allows lithium ions to pass through, but blocks electrons from passing through, thereby preventing further decomposition of the electrolyte.
- Stability: SEI film can stabilize the negative electrode surface and prevent direct contact between the electrolyte and the negative electrode material, thereby improving the cycle life and safety of the battery.
- Self-repairability: During the battery cycle, the SEI film will continue to repair and reorganize to maintain its protective effect.
3.Gas generation and discharge
During the formation process, the decomposition of the electrolyte not only generates the SEI film, but also may generate a small amount of gas (such as H2, CO2, CH4, etc.). These gases mainly come from the decomposition reaction of solvents and additives in the electrolyte. During the aging process after formation, the battery usually goes through a period of static state so that the gas can be discharged from the inside of the battery. This process helps to reduce the internal pressure of the battery and improve the safety of the battery.
4.Stability of battery performance
Through the first charge and discharge, the capacity of the battery gradually stabilizes. The charge and discharge conditions during the formation process (such as current, voltage, temperature, etc.) have an important influence on the final capacity of the battery. At the same time, the internal resistance of the battery gradually decreases, which helps to improve the power performance of the battery. By forming a stable SEI film, the cycle life of the battery is significantly improved. The SEI film can effectively prevent the continuous decomposition of the electrolyte and reduce the loss of active lithiu
Key parameters of the battery formation process
Charging current: The charging current during the formation process has an important influence on the formation of the SEI film and the battery performance. Too high a current may cause an uneven SEI film, while too low a current will prolong the formation time.
Charging voltage: The upper limit of the charging voltage is usually slightly lower than the rated voltage of the battery to prevent overcharging and excessive decomposition of the electrolyte.
Temperature control: The temperature during the formation process has a significant effect on the formation of the SEI film and the battery performance. It is usually necessary to carry out the formation under constant temperature conditions to ensure the uniformity and stability of the SEI film.
Formation is an indispensable and key step in battery manufacturing. It activates the electrochemical properties of the battery through the first charge and discharge and forms a stable SEI film. This process has a decisive influence on the performance, life and safety of the battery.
During the formation process, complex physical and chemical changes occur inside the battery, including the activation of electrochemical properties, the formation of SEI film, the generation and discharge of gases, and the stabilization of battery performance. By precisely controlling the formation process parameters, the performance and consistency of the battery can be significantly improved.
