Reason for formation
After the battery is manufactured, the internal positive and negative electrode materials are activated by a certain way of charge to improve the battery's charge and discharge perfromance, self-discharge, storage and other comprehensive performance. The process is called formation.
What is formation?
1. The formation of lithium cell is the intial initation of battery, so that the active substance of the cell is activated, which is a process of energy conversion.
2. The formation of lithium cell is a very complicated process, and it is also an important one for the battery's perfomance, because Li+ is first to be inserted into graphite when it is first charged. The electrochemical reaction will occur in the battery. During the first charging process of the battery, it is inevitable to form a passivation thin layer covering the surface of the carbon electrode on the interface between the negavice carbon electrode and the electrolyte, which is called the soild electrolyte phase interface or SEI film (Soild Electrolyte Interface).
3. On the one hand, the formation of SEI film consumes the limited ions in the battery, which requires the use of more lithium containing material to compensate for the lithium consumption in the initial charging process. On the other hand, it also increases the resistance of the electrode/electrolyte interface, resulting in a certain voltage lag.
The principle of formation
The positive electrode of a lithium-ion battery usually consists of an active compound of lithium, while the negative electrode is carbon with specific molecular structure. The main component of the common cathode material is LiCoO2. When charging, the electric potential applied at the two poles of the battery forces the cathode compound to release lithium ions and embed them in the lamellar carbon where the cathode molecules are arranged. When discharged, the lithium ions precipitate out of the lamellar carbon and recombine with the positive compound. The movement of lihtium ions creates electric current.