LFP battery is the short name for LiFePO4, also as known Lithium Ferro(Iron) Phosphate Battery. An LFP battery refers to a li-ion battery using lithium iron phosphate as a positive electrode material.
Knowing the relevant voltage of the LFP battery helps to set the reasonable end voltages, so the LFP battery could be working in the most effective and reasonable condition, and offer a safe, stable, and long-lasting power supply.
As the safest lithium technology, the LFP battery has many advantages in energy storage applications.
l Safe
l Super Long Cycle Life
l Light Weight for Easy Handling and Installation
l Suitable for High Temperature
l Environmentally friendly
LFP Battery Cell Voltage
Due to the difference in various raw materials used by each manufacturer(including positive, negative electrode materials, and electrolytes), the performance and voltage of the batteries are not exactly the same. In general conditions, the nominal voltage of the LFP battery cell is 3.2V, the high-end voltage is 3.6V, and the low-end voltage is 2.0V.
The charging voltage of the LFP battery cell is recommended as 3.65V, 14.6V+-0.2V for a 12.8V battery. 3.65V per cell is proven to be a reasonable charging voltage after long-time practical use.
The relevant voltage of the LFP battery is different in different conditions. Mainly in 3 cases, open-circuit voltage (OCV), charging condition, and discharging condition. In applications, the charging and discharging voltage are more useful, involving a reasonable set of end voltages to ensure that the battery works in a good and stable situation.
LFP Battery Voltage In Charging Condition(0.5C, 25℃)
Here, 0.5C means charging at a current of 0.5*(number of capacity)A. For example, a 12.8V100Ah LFP battery is charged at 14.6V with 50A current. SOC means the State Of Charge, which means the percentage of energy remaining.
Related Voltage in Charging Condition
The charging curve is shown below:
The voltage will be different if charge with a different number of current. The bigger the current, the higher the voltage.
LFP Battery Voltage In Discharge Condition(0.5C, 25℃)
Just like the above condition in CHARGE, here for a 12.8V100Ah battery, it means discharge at 50A.
Related Voltage in Discharge Condition
Note the related voltage will also be different if the discharge current is different.
For most energy storage applications, a DOD of 80% is reasonable and effective.
Based on the above data, the end voltage can be set at 12.55V, but please note that for smaller currents such as 10A, the discharge depth will still exceed 80% even when the voltage is higher than 12.55V.
And it is recommended to set the overcharge voltage at 15.60V to avoid overcharging the battery.
Notes for Voltage Difference
1. The voltages of different lithium batteries from different materials are different.
2. For the same LFP battery, same SOC (for example 20%), the voltage varies depending on the discharge current. The higher the discharge current, the lower the voltage.
3. The effect of ambient temperature on the battery voltage. The lower the temperature, the lower the voltage.
4. The impact after cycle use. After a long time of use, the voltage will also be different.
5. Different manufacturers, the different capacities of LFP batteries, the discharge voltage is slightly different.