Charging a lithium-ion battery involves precise control of both the charging voltage and charging current. Lithium-ion batteries have unique charging characteristics, unlike other types of batteries, such as cadmium nickel and nickel-metal hydride.
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 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.
Higher currents result in faster charging, but beware of excessive currents leading to overheating and potential damage. Different batteries have specific requirements for maximum charging currents, vital for safe and optimal performance. Knowing your battery’s allowable charging current is crucial to avoid damage caused by incompatible chargers.
For Li-ion batteries at a temperature of between 0˚ and 15˚C, the fast-charge current is limited to 50% of its programmed rate, and if the battery temperature rises above 60˚C the current is cut altogether until the temperature drops to a safe level.
Charging Termination: The charging process is considered complete when the charging current drops to a specific predetermined value, often around 5% of the initial charging current. This point is commonly referred to as the “charging cut-off current.” II. Key Parameters in Lithium-ion Battery Charging