Tips About Lithium Iron Phosphate Battery Charge & Discharge Operation

Lithium iron phosphate battery(LiFePO4 Battery) is a new type of lithium-ion battery, which has the advantages of high energy density, long life, good safety, and environmental protection, and has gradually become a popular choice for various applications. However, to give full play to the performance and life of lithium iron phosphate batteries, it is necessary to master the correct charging and discharging methods. This blog will introduce the following aspects of lithium iron phosphate battery charging and discharging tips:

Charging Method

Is the charging way of lithium iron phosphate batteries the same as lithium-ion batteries?
The charging method of lithium iron phosphate batteries is different from common lithium-ion batteries.
Lithium batteries usually use a three-stage charging method, that is, constant current charging, constant voltage charging, and trickle charging, the whole process takes 8 to 11 hours.

While lithium iron phosphate batteries only need two-stage charging methods, i.e., constant current charging and constant voltage charging, the whole process only needs 3 to 4 hours.

When constant current charging, the appropriate charging current and time should be determined according to the rated capacity of the battery and the termination charging voltage.

For example, a 3.2 volt 100 mAh single cell battery with a termination charging voltage of 3.65 volts will take about 2 hours to fill the battery to about 80% if it is charged at a constant current of 50 mA (0.5C). At this point, switch to constant voltage charging mode and continue to energize the battery at a constant voltage of 3.65 volts until the charging current is reduced to a very small value (generally 0.02C or 0.01C), at which point the battery can be considered to be fully charged.

Is it possible to charge the Lithium batteries with the lead-acid battery charger?
Although we can’t charge the LiFePO4 batteries with the previous lead-acid battery charger, it is possible to use the LiFePO4 battery charger with the Lithium battery charger, which we should also pay attention to the following points:

1. The charger can’t come with an overcharge function, otherwise it will damage the LiFePO4 battery.
2. The float charging voltage of the 12-volt LiFePO4 battery pack is 14.6 volts, and the recommended trickle charge (maintenance) voltage is 13.8 volts.
3. The charger should have a low-temperature activation function to wake up the LiFePO4 battery in the over-discharge protection state.

(Especially for solar inverter systems, it should also be friendly to Li-FePO4 battery, in addition to lead-acid mode and communication mode, it should also have a user-defined setting mode, which can support Li-FePO4 battery packs without communication, and it can set its own charging and discharging parameters to better adapt to the battery characteristics.)

Discharge Method

The discharge method of lithium iron phosphate battery should also pay attention to the following aspects:

1. The influence of temperature. Temperature has a great influence on the discharge performance of the battery. At low temperatures, the electrodes contract, making it difficult for ions to be released, the conductivity of the electrolyte decreases, and the movement of ions between the two electrodes slows down. At high temperatures, the electrodes expand, making it easier for ions to move and the electrolyte more conductive. However, too high a temperature can damage the electrodes, so it is important to maintain a suitable temperature condition to keep the battery in optimal condition when discharging.

2. The amount of discharge current. The discharge current of a battery is controlled by the BMS, which means that each battery has a maximum operating current limit. Therefore, when using lithium iron phosphate batteries, as long as the operating current does not exceed the BMS limit, the battery can power the system. However, from the perspective of longevity, a low discharge rate can optimize the capacity efficiency and prolong the life of the battery.

3. Depth of discharge selection. Depth of discharge is the percentage consumed from full to empty. Depth of discharge has a direct relationship with the cycle life of the battery; the shallower the depth of discharge, the more cycles. So, if you don’t need to use up all the energy, you can use shallow discharge and shallow charging to extend the life. However, this should also be done with care to do a full charge-discharge cycle (100% discharge) periodically, which allows the BMS to update and calibrate the SOC (remaining capacity).

4. Handling of self-discharge. Self-discharge is the gradual loss of energy from the battery itself when not in use. Self-discharge is non-linear and varies over time. The rate of self-discharge is largely dependent on temperature; the higher the temperature, the faster the self-discharge. Most lithium iron phosphate
batteries have a self-discharge rate of 0.5% to 3% per month, which means that the battery loses 0.5% to 3% of its energy in a month. At low temperatures, this discharge rate increases dramatically. Therefore, it is important to check the voltage and capacity of the battery regularly to avoid over-discharge and over-charge.

The above is the introduction of lithium iron phosphate battery charging and discharging tips, I hope it is helpful to you. If you have other questions, please leave a message, and I will reply to you as soon as possible. Thank you!