What is the principle of LiFePO4 battery charging?
Lithium iron phosphate batteries have different charging characteristics due to their different materials. The charging curve is different from that of lead-acid batteries. LiFePO4 batteries are known for their simpler charging process and method. They have a relatively flat charging curve, which means they can charge at a constant voltage without the need for complex charging algorithms.
Lithium iron phosphate battery charging mode
This curve shows the charging pattern of a LiFePO4 battery, covering two stages.
T1: CC (constant current) phase
The CC stage performs constant current charging on the lifepo4 battery. The voltage gradually increases until it reaches a constant voltage set point, which may vary depending on the charging method.
T2: CV (constant voltage) phase
During the CV phase, the battery is maintained at a constant voltage. At the same time, the charging current gradually decreases until it reaches a termination current of 2A (0.02C), also known as trickle current. Once the termination current is reached, the charging process is interrupted, indicating that the battery is fully charged.
It should be noted that the CC and CV stages during the charging process are to control the charging current and voltage to ensure the safety and effectiveness of the battery charging process. The specific parameters and duration of these stages may vary depending on the charger and battery type.
Lead-acid battery charging method
This curve shows the lead-acid battery charging pattern, consisting of three stages.
T1: Bulk/boot stage
During this phase, the battery is charged at its maximum current capacity. The voltage will rise steadily until it reaches the absorption voltage set point. This phase is similar to the constant current (CC) phase in lithium iron phosphate (LiFePO4) battery charging.
T2: absorption stage
Once the battery voltage reaches the absorption voltage set point, the voltage remains constant while the current gradually decreases until the battery is fully charged (within 10-20%). To prevent overcharging, the absorption phase generally does not exceed 3 hours. This phase is similar to the constant voltage (CV) phase in LiFePO4 battery charging.
T3: Floating stage
After the absorption phase, the battery voltage decreases to the float voltage set point and the current decreases to the low maintenance level. This phase prevents the battery from discharging and counteracts any self-discharge. If the battery experiences significant discharge, the controller can switch the charging process back to the bulk/boost or absorption phase to replenish the energy lost during self-discharge.
The charging patterns of lead-acid batteries are similar to those of lithium iron phosphate batteries, but there are some key differences. Lead-acid batteries typically have a lower absorption voltage setting and a slightly lower float voltage setting compared to LiFePO4 batteries. In addition, lead-acid batteries may produce sulfate crystals during the charging process and require regular equalization charging to prevent capacity loss.