This target charge current is relative to the battery capacity ("C"). For standard Li-ion or Li-polymer batteries, chargers often target 0.5C charge current. In other words, if the battery is rated at 500 mA-h, the target current is 250 mA. It is not unusual to charge at 1C (500mA), but this compromises the battery's capacity over time.
Typically, PMICs charge LiPo and Lithium-Ion batteries using the CC-CV method. The battery gets charged with a constant current until the cell reaches its maximum voltage. From then on, the charger gradually decreases the charge current until the battery is fully charged. Modern charge ICs apply a few more steps to the process to increase safety.
During the bulk charging phase, lithium batteries need a controlled charge at a specific voltage level. This ensures equal charging across cells, preventing imbalance issues within the battery pack.
When designing a single-cell Lithium-Ion charger, record the allowed maximum charge current and voltage of the battery in use. Then determine the voltage and maximum charge current of the power supply you want to use for charging. Usually, this will be five volts and between 500 mA and 900 mA (USB 2.0 and USB 3.0).
Charging properly a lithium-ion battery requires 2 steps: Constant Current (CC) followed by Constant Voltage (CV) charging. A CC charge is first applied to bring the voltage up to the end-of-charge voltage level. You might even decide to reduce the target voltage to preserve the electrode.
Charging lithium batteries with solar power requires careful consideration, and the use of a solar charge controller is paramount. This controller serves as a crucial link between solar panels and batteries, regulating voltage and current to optimize charging.