The Concept of Lithium-ion Battery Formation
What is battery formation?
Battery formation refers to the process of charging a battery cell for the first time, also known as initial charging or forming. In this process, the positive and negative electrode materials in the battery are charged and form an electrochemical reaction, so that the chemical reaction system inside the battery reaches a stable state, forming an SEI film (solid electrolyte interface), thereby ensuring the battery has better performance in the future use.
Battery formation is a very important part of the battery manufacturing process and one of the key steps to ensure battery quality. Through cell formation, various materials and components inside the battery can be made more stable and uniform, avoiding unnecessary safety problems. At the same time, it also can improve the capacity, cycle life and performance stability of the battery.
The process of battery formation includes multiple steps, such as initial charging, constant current charging, constant voltage charging, etc.
- Among them, the purpose of initial charging is to quickly form the chemical reaction system inside the battery and activate the chemical properties of the positive and negative materials of the battery.
- Constant current charging and constant voltage charging are to make the chemical reaction system inside the battery more stable, so as to ensure better performance of the battery in future use.
The steps of battery formation
Battery formation usually includes the following steps:
* Initial charging
In this step, the positive and negative electrode materials in the battery are initially charged, allowing them to quickly form a chemical reaction system, thus laying the foundation for the subsequent battery formation.
* Constant current charging
In this step, the battery will be charged with a constant current, so that the internal chemical reaction system can be better activated and stabilized, thereby improving the capacity and cycle life of the battery.
* Constant voltage charging
In this step, the battery will be charged at a constant voltage, so that the chemical reaction system inside the battery can be better stabilized, thereby improving the performance stability and safety performance of the battery.
* Discharge test
fter the cell formation is completed, the battery needs to be discharged to test whether the performance and safety performance of the battery meet the requirements.
It should be noted that different types of batteries may have some differences in the cell formation process, so corresponding treatments need to be carried out according to the specific battery type and manufacturing process. Meanwhile, the process of cell formation also needs to be carried out under strict control conditions to ensure the quality and safety of the battery.
Common setting parameters for battery formation
Different types and specifications of batteries may have different charge and discharge setting parameters during the formation process, and generally need to be adjusted according to specific battery specifications, manufacturing processes and design requirements. The following are formation setup parameters for some common batteries:
* Lithium cobalt oxide battery
The initial charging current is 0.5C, constant current charging to 4.2V, keep for 2 hours, then charging at 0.05C to the end voltage, and discharging to 3V to stop.
* Lithium iron phosphate battery
The initial charging current is 0.3C, constant current charging to 3.65V, keeping it for 2 hours, then charging at 0.05C to the end voltage, and discharging to 2.5V to stop.
* Ternary Lithium Battery
The initial charging current is 0.3C, constant current charging to 4.2V, keep it for 2 hours, then charging at 0.05C to the end voltage, and discharging to 3V to stop.
The above are only the formation setting parameters of common batteries, and the specific parameters need to be adjusted according to the specific battery type and specification. What’s more, the formation process needs to be carried out under strict control conditions to ensure the quality and safety performance of the battery.
What is SEI film?
The SEI film is a very thin film on the electrochemical interface, which is formed between the electrolyte and the electrode material. It is formed by a chemical reaction and composed of the solvent in the electrolyte and the reaction product on the surface of the electrode material. Its formation has a very important impact on the performance and safety performance of the battery. The following are some specific explanations about the SEI film:
* The role of the SEI film
The SEI film can prevent the chemical reaction process inside the battery from getting out of control, meanwhile protect the interface between the electrolyte and the electrode material, thereby improving the cycle life and safety performance of the battery.
* The characteristics of SEI film
SEI film is a very thin film, the thickness is usually between several nanometers to tens of nanometers. It is composed of a variety of chemicals, including fluorides, carbonates, polymers, and more. The characteristics and composition of the SEI film will change with the service time and cycle number of the battery, so it needs special attention during the battery formation process.
* The formation process of SEI film
The formation of SEI film is a complex chemical reaction process, which needs to be carried out under specific conditions. In general, the process of battery formation requires specific current and voltage for charge and discharge cycles to promote the formation of the SEI film. Besides, special attention should be paid to the temperature and environmental conditions of the battery during the formation process to ensure the formation effect of the SEI film.