During the charging process, a power source provides electrical energy to a lithium battery. Electrons at the positive electrode migrate to the negative electrode through an external circuit. Simultaneously, positive lithium ions leap from the positive electrode into the electrolyte, traverse the winding paths in the separator, and travel to the negative electrode, where they combine with the electrons that have already arrived. At this point, the following reactions occur at the positive electrode:
The following reactions occur at the negative electrode:
• Detailed Explanation of the Battery Discharge Process
Batteries can be discharged in two ways: constant-current discharge and constant-resistance discharge. In constant-current discharge, a variable resistor is added to the external circuit, whose resistance value adjusts with voltage. In constant-resistance discharge, a resistor is added between the positive and negative electrodes to allow electrons to pass through. The key to battery discharge is whether electrons can migrate from the negative electrode to the positive electrode. During discharge, electrons flow from the negative electrode to the positive electrode through an electronic conductor. Simultaneously, lithium ions (Li+) also enter the electrolyte from the negative electrode, travel through the small holes in the separator, and finally reach the positive electrode to combine with electrons.
• Discussion of Charge and Discharge Characteristics
Battery cells often use LiCoO2, LiNiO2, or LiMn2O2 as positive electrode materials. LiCoO2 has a stable layered structure. However, when x Li ions are removed from LiCoO2, its structure may change, depending on the value of x. Research has shown that when x > 0.5, the structure of Li1-xCoO2 becomes extremely unstable, potentially leading to crystal collapse and thus affecting battery cell performance. Therefore, during battery cell use, the value of x must be limited by controlling the charge voltage. Typically, the charge voltage should not exceed 4.2V to ensure x is less than 0.5, thereby maintaining the stability of the Li1-xCoO2 crystal structure.
