Chemical conversion and capacity separation belong to the core processes of the later stage of lithium batteries, which are the stages of electrochemical activation and performance screening and grading of battery cells. They determine the final quality and consistency of battery cells, and are also important quality control checkpoints before leaving the factory.
Chemical conversion is the first controlled charging and discharging process of a battery cell. Under the constant temperature environment, small current is used to gradually charge, so that the electrolyte reacts on the negative electrode surface to form a layer of solid electrolyte interface facial mask, referred to as SEI film. High quality SEI film can conduct lithium ions, reduce electrolyte side reactions, protect negative electrode materials, and is crucial for battery cycle life. The formation process will be accompanied by a small amount of gas production, and some processes will be combined with exhaust processes. The current curve, temperature, and pressure parameters of the formation need to be matched with the material system. Improper parameters can easily cause uneven SEI film thickness and high internal resistance.
After the formation is completed and left to stand, it enters the volume separation process. The device performs standardized charge and discharge cycles on the battery cells, accurately collecting multiple parameters such as actual capacity, DC internal resistance, voltage platform, and self discharge rate. The same batch of battery cells may exhibit performance variability due to slight deviations in the front-end processing; Capacity division refers to the classification of battery cells based on detection data, with cells with similar parameters assigned to the same level.
After classification, it enters the aging and retesting stage, which is generally divided into room temperature aging and high temperature aging. After a period of standing, the open circuit voltage is retested again to calculate the voltage change rate and screen for cells with excessive discharge and unstable performance.
After passing all the tests, the battery cells will be assembled into battery modules or packs according to application requirements, with protective structures and management systems; Unqualified battery cells shall be separately divided and treated. The data of the entire subsequent process will be retained and recorded to achieve traceability of battery cell information, providing data support for process optimization of the production line.
