Lithium ion batteries can be charged using different methods, with the simplest being constant voltage charging. When using constant voltage charging, the battery voltage remains unchanged, while the charging current will gradually decrease. When the charging current drops below 0.1C, it is considered that the battery has been fully charged. To prevent defective batteries from charging endlessly, a backup timer is used to terminate the charging cycle.
Taking into account the safety, speed, and efficiency of the charging process, lithium-ion batteries usually use constant current and constant voltage charging methods. The charging process can be divided into three stages: pre charging, constant current charging, and constant voltage charging.
1. Pre charging stage
In this state, first check if the voltage of a single lithium-ion battery is low (<3.0V). If so, use trickle charging, which means charging the battery with a relatively small constant current until the battery voltage rises to a safe value. Otherwise, this stage can be omitted, which is also the most common situation. Because pre charging is mainly used to repair over discharged lithium batteries.
2. Constant current charging
After trickle charging, the charger enters a constant current charging state. In this state, the charging current remains constant at a larger value, and the maximum charging current of the battery is determined by its capacity.
Under constant current charging and pre charging conditions, by continuously monitoring the voltage and temperature of the battery, the following two constant current charging termination methods can be used to terminate constant current charging.
(1) Battery maximum voltage termination method: When the voltage of a single lithium battery reaches 4.2V, the constant current charging state should be immediately terminated;
(2) Battery maximum temperature termination method: During the constant current charging process, when the temperature of the battery reaches 60 ℃, the constant current charging state should be immediately terminated.
3. Constant voltage charging stage
After the constant current charging is completed, it enters the constant voltage charging state. In this state, the charging voltage remains constant. Because lithium-ion batteries require high precision in charging voltage, the constant voltage charging voltage of a single battery should vary within 1% of the specified value. Therefore, the charging voltage of lithium-ion batteries must be strictly controlled. During the constant voltage charging process, the charger continuously monitors the voltage, temperature, charging current, and charging time of the battery.
There are four commonly used methods for terminating constant voltage charging:
(1) Maximum battery voltage: When the voltage of a single lithium-ion battery reaches 4.25V, the constant voltage charging state automatically terminates;
(2) Maximum temperature of the battery: When the maximum temperature of the lithium-ion battery reaches 60 ℃, the constant voltage charging state automatically terminates;
(3) Maximum charging time: In order to ensure the safe charging of lithium-ion batteries, in addition to setting the highest voltage and temperature, the longest constant voltage charging time should also be set. In the event of temperature and voltage detection failure, it can ensure the safe charging of lithium-ion batteries;
(4) Minimum charging current: During the constant voltage charging process, the charging current of lithium-ion batteries gradually decreases. When the charging current drops to a certain value (usually 1/10 of the constant current charging current), the constant voltage charging state automatically terminates.
Taking into account the safety, speed, and efficiency of the charging process, lithium-ion batteries usually use constant current and constant voltage charging methods. The charging process can be divided into three stages: pre charging, constant current charging, and constant voltage charging.
1. Pre charging stage
In this state, first check if the voltage of a single lithium-ion battery is low (<3.0V). If so, use trickle charging, which means charging the battery with a relatively small constant current until the battery voltage rises to a safe value. Otherwise, this stage can be omitted, which is also the most common situation. Because pre charging is mainly used to repair over discharged lithium batteries.
2. Constant current charging
After trickle charging, the charger enters a constant current charging state. In this state, the charging current remains constant at a larger value, and the maximum charging current of the battery is determined by its capacity.
Under constant current charging and pre charging conditions, by continuously monitoring the voltage and temperature of the battery, the following two constant current charging termination methods can be used to terminate constant current charging.
(1) Battery maximum voltage termination method: When the voltage of a single lithium battery reaches 4.2V, the constant current charging state should be immediately terminated;
(2) Battery maximum temperature termination method: During the constant current charging process, when the temperature of the battery reaches 60 ℃, the constant current charging state should be immediately terminated.
3. Constant voltage charging stage
After the constant current charging is completed, it enters the constant voltage charging state. In this state, the charging voltage remains constant. Because lithium-ion batteries require high precision in charging voltage, the constant voltage charging voltage of a single battery should vary within 1% of the specified value. Therefore, the charging voltage of lithium-ion batteries must be strictly controlled. During the constant voltage charging process, the charger continuously monitors the voltage, temperature, charging current, and charging time of the battery.
There are four commonly used methods for terminating constant voltage charging:
(1) Maximum battery voltage: When the voltage of a single lithium-ion battery reaches 4.25V, the constant voltage charging state automatically terminates;
(2) Maximum temperature of the battery: When the maximum temperature of the lithium-ion battery reaches 60 ℃, the constant voltage charging state automatically terminates;
(3) Maximum charging time: In order to ensure the safe charging of lithium-ion batteries, in addition to setting the highest voltage and temperature, the longest constant voltage charging time should also be set. In the event of temperature and voltage detection failure, it can ensure the safe charging of lithium-ion batteries;
(4) Minimum charging current: During the constant voltage charging process, the charging current of lithium-ion batteries gradually decreases. When the charging current drops to a certain value (usually 1/10 of the constant current charging current), the constant voltage charging state automatically terminates.