It seems standard for a lithium-ion charger to cut off the applied voltage when the CV-mode current draw dips below 0.1C (or thereabouts). Why is this necessary? Why can’t the charger continue to apply 4.2V indefinitely? According to Battery University: Li-ion cannot absorb overcharge. When fully charged, the charge current must be cut off.
Below this voltage, the cell's capacity is considered to be exhausted, and continuing to discharge it further could damage the cell or reduce its overall lifespan. The cut-off voltage varies depending on the type of cell or battery being used, as well as its specific chemistry and construction.
Going below this voltage can damage the battery. Charging Stages: Lithium-ion battery charging involves four stages: trickle charging (low-voltage pre-charging), constant current charging, constant voltage charging, and charging termination. Charging Current: This parameter represents the current delivered to the battery during charging.
This initial phase is characterized by a gentle voltage increase. Steady Voltage and Declining Current: As the battery charges, it reaches a point where its voltage levels off at approximately 4.2V (for many lithium-ion batteries). At this stage, the battery voltage remains relatively constant, while the charging current continues to decrease.
Here is a general overview of how the voltage and current change during the charging process of lithium-ion batteries: Voltage Rise and Current Decrease: When you start charging a lithium-ion battery, the voltage initially rises slowly, and the charging current gradually decreases. This initial phase is characterized by a gentle voltage increase.
Current dependency of cycle aging of lithium ion battery. Thermal and current effects decoupled on cycle aging. Constant battery temperature during cycle aging at different cycle currents using Peltier cells.