The optimal charging process for lithium-ion batteries can be divided into four stages: trickle charging, constant current charging, constant voltage charging, and charging termination.
Phase 1: Trickle Charging. Trickle charging is used to pre-charge (recovery charging) fully discharged lithium-ion battery cells. When the battery voltage is below approximately 3V, a constant current of up to 0.1C is used to charge the battery.
Phase 2: Constant Current Charging. When the battery voltage rises above the trickle charging threshold, the charging current is increased to perform constant current charging. The constant current charging current is between 0.2C and 1.0C. The current during constant current charging does not need to be highly precise; a quasi-constant current is also acceptable. In linear charger designs, the current often increases with the battery voltage to minimize heat dissipation issues on the transmission transistors.
Phase 3: Constant Voltage Charging. When the lithium-ion battery voltage rises to 4.2V, constant current charging ends, and constant voltage charging begins. To achieve optimal performance, the voltage regulation tolerance should be better than +1%.
Phase 4: Charging Termination Unlike nickel batteries, continuous trickle charging of lithium-ion batteries is not recommended. Continuous trickle charging can cause plate plating in the lithium metal. This can destabilize the battery and potentially lead to sudden, rapid disintegration.
What precautions should be taken when charging lithium-ion batteries?
1. Prevent charging at excessively high temperatures.
If lithium-ion batteries are used in environments exceeding the specified operating temperature (above 35°C), the battery capacity will continuously decrease, meaning the battery's operating time will not be as long as usual. Charging devices at such temperatures will further damage the lithium-ion batteries. Even storing batteries in relatively hot environments will inevitably cause some damage to their quality. Therefore, maintaining a suitable operating temperature is the best way to extend the lifespan of lithium-ion batteries.
2. Prevent charging at excessively low temperatures.
If you use lithium batteries in low-temperature environments, i.e., below 4C, you will also find that the battery life is reduced, and some original lithium batteries in mobile phones may not even charge in low-temperature environments. But don't worry too much, this is only a temporary situation. Unlike use in high-temperature environments, once the temperature rises, the molecules in the lithium-ion battery are heated and immediately recover their previous capacity.
3. Frequent use
Life is about movement. To maximize the performance of a lithium-ion battery, use it frequently to keep the electrons inside constantly flowing. If you don't use your lithium battery often, remember to complete a full charging cycle each month and perform a charge calibration, i.e., a deep discharge followed by a deep charge.
