Activation and Detection of 18650 Lithium ion Battery.
After the initial process, the functional structure of the lithium battery cells has been formed. Subsequently, it is necessary to carry out chemical capacity separation, testing, sorting, and assembly to form a lithium battery product that is safe to use and has stable performance.
Among them, chemical transformation activates the battery by charging it for the first time after high-temperature aging, forming an SEI film on the negative electrode surface, which is a layer of film on the surface of the electrode material. It is formed by the consumption of lithium ions by the electrolyte and can effectively block the passage of electrons and solvent molecules.
The general steps are:
(1) Shelf: Assemble the battery on the bed forming cabinet and let it sit for 5 minutes;
(2) Constant current charging: 0.02C constant current charging to 3.0V;
(3) Suspend: Suspend for 5 minutes;
(4) Constant current charging: 0.05C, 0.1C, 0.15C constant current charging to 3.5V;
(5) Suspend: Suspend for 5 minutes;
(6) Constant current discharge: 0.1C constant current discharge, discharge depth 50% SOC;
(7) Aging: stored at room temperature for 15 days;
Charge from 0.02C to 3V, and charge with a slightly higher current after the SEI film is formed, which not only saves more time; And the formed SEI film is dense and has better thermal stability. At this time, the SEI film completely separates the electrolyte from the graphite, allowing only ions to pass through and reach the graphite layer.
Capacity division is the process of using a charging and discharging machine to charge and discharge a battery. A "fully charged discharged" cycle is carried out according to certain standards, and the capacity of the battery is determined using the ampere hour integral method. The result obtained by multiplying the cycle time by the discharge current is the capacity of the battery. Only batteries with a tested capacity that meets or exceeds the design capacity are qualified, and the consistency of the batteries needs to be ensured.
After being divided into two parts, the open circuit voltage, AC internal resistance, and shell cover insulation of the battery are measured using testing equipment such as OCV and DCIR. Qualified individual batteries are selected and finally subjected to high-temperature aging to complete the production of the battery.
