Charging Process of Lithium ion recgargeable batteries

The charging process of lithium-ion battery can be divided into four stages: trickle charging (low voltage precharge), constant current charging, constant voltage charging, and charging termination.   

The basic requirements of lithium battery chargers are a specific charging current and charging voltage to ensure a safe charging of the battery. Other charging aids are added to improve battery life and simplify the operation of the charger, including trickle charging of over-discharged batteries, battery voltage detection, input current limits, switching off the charger after charging, automatic start-up charging after partial discharge of the battery, etc.   

The charging method of lithium battery is to limit the constant flow, is controlled by the IC chip, the typical charging method is: first to detect the voltage of the battery to be recharged, if the voltage is less than 3V, to pre-charge, charging current is set by 1/10 of the current, the voltage to 3V, into the standard charging process. The standard charging process is: to set the current for constant current charging, the battery voltage to 4.20V, change to constant pressure charging, keep the charging voltage of 4.20V. At this point, the charging current gradually decreases, and when the current drops to 1/10 of the set charging current, the charging ends.

Stage 1: Trickle charging - Trickle charging is used to pre-charge (restorative charging) of a fully discharged battery cell first. In the battery voltage is less than 3V or so when the use of a trickle charging, trickle charging current is one-tenth of the constant current charging current, or 0.1c (with a constant charging current of 1A for example, then the trickle charging current is 100mA), 

Stage 2: constant current charging - when the battery voltage rises above the trickle charging threshold, increase the charging current for constant current charging. Constant current charging current stake is between 0.2C and 1.0C. The battery voltage increases gradually with the constant current charging process, and the voltage set by the general single cell is 3.0-4.2V. 

Stage 3: Constant voltage charging - When the battery voltage rises to 4.2V, the constant current charge ends and the constant voltage charging phase begins. The current is determined to terminate the charge when reduced to 0.01C as the charging current continues to be reduced from the maximum. (C is a representation of the battery's nominal capacity-to-current, such as the battery is 1000mAh capacity, and 1C is the charging current of 1000mA.) 

Stage 4: Charging termination - There are two typical charging termination methods: the minimum charging current is used to judge or the timer (or a combination of the two). The minimum current method monitors the charging current during the constant voltage charging phase and terminates the charging when the charging current is reduced to the range of 0.02C to 0.07C. The second method is to time from the beginning of the constant pressure charging phase and stop the charging process after two hours of continuous charging. The above four-stage charging method takes about 2.5 to 3 hours to complete charging a fully discharged battery. Advanced chargers also incorporate additional security measures. For example, if the battery temperature exceeds the specified window (usually 0 to 45 degrees C), then charging will pause.

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