The optimal charging current for lithium batteries.

The optimal charging current for lithium batteries.

The term 'lithium battery charging current' in daily expressions refers to the charging current during the rapid charging stage of lithium batteries. As a dynamic process, the maximum charging current of lithium batteries is actually divided into three stages.

1. The optimal current for pre charging: When the initial/no-load voltage of a lithium battery is below the pre charging threshold, it first needs to go through a pre charging stage. For a single lithium-ion battery, this threshold is generally 3.0V. During this stage, the pre charging current is about 10% of the current in the next stage - constant current charging stage.

2. The optimal current for constant current charging: Constant current refers to a constant current, gradually increasing voltage, and entering the fast charging stage. Most constant current charging currents are set between 0.4~0.6C, which can be understood as 0.5C, meaning that it can be fully charged in about two hours without considering other factors. The reason for choosing 0.5C is that this current achieves a good balance between charging time and charging safety.

3. Charging current during constant voltage charging: For a single lithium-ion battery, when the battery reaches a certain voltage value, it enters constant voltage charging, which is generally 4.2V. At this stage, the voltage remains constant and the current decreases; This decrease in current is a gradual process, and most lithium battery protections choose 0.01C as the termination current, which means that the charging process enters the end state. Once the charging is completed, the charging current drops to zero.

The core of the optimal charging current for lithium batteries is the current design during constant current charging. It should be emphasized that most portable lithium batteries are more suitable for 0.5C charging. For example, 18650 lithium batteries have a conventional capacity of 1800-2600mAh and can choose 1A charging, while rate type batteries have a capacity of 1200-1500mAh and a charging current of 0.7A at 0.5C.

Strictly speaking, the maximum charging current of lithium batteries is determined by the battery structure. Therefore, various lithium battery manufacturers have different regulations on this, some set it at 0.6C, and the highest regulation for portable lithium batteries is 1C.

Of course, the current design for pre charging and constant voltage charging cannot be ignored. In these two processes, if the initial voltage is not lower than the pre charging threshold of 3.0V, there is no pre charging process. Overall, a pre conditioning and exercise rest process before and after constant current charging is beneficial for the long-term use of lithium batteries.