LiFePO4 batteries are a type of rechargeable battery that utilizes lithium ion phosphate(LFP) as its cathode material. This technology offers many advantages over traditional lead acid or nickel-based chemistries, such as improved safety, higher specific energy density, and better voltage output. However, improper charging can lead to battery damage, reduced lifespan and even safety incidents. In this article, Bely will offer the guidance on the proper procedures for lithium battery charging to enhance your understanding and ensure optimal battery utilization.

Use a Lithium-specific charger

Using a Lithium-specific charger provides an efficient and safe way to charge LiFePO4 batteries, with precise voltage and current control, automatic charge termination, balancing technology, temperature monitoring and compatibility with BMS systems. These features help maintain the battery's performance and extend its overall lifespan, making such chargers highly recommended for LiFePO4 battery charging.

Lithium battery chargers can behave in several different ways during the charging process. First, the charger can steadily increase its voltage in order to keep the current flow constant. This is the first stage of the charging process, typically called the bulk charging stage. During this stage, the charger adjusts its applied voltage to deliver the maximum current to the battery.

Once the bulk voltage is reached, the charger enters a second stage which called the absorption charging stage. During absorption, the charger applies a constant voltage called the absorption voltage. As the battery's open-circuit voltage approaches the absorption voltage, the current flow steadily decreases down to zero. At this point, the battery is fully charged.

Constant Current (CC) Charge

Constant charging current, the voltage is continuously increasing during the charge, reaching the max. voltage(14.6V). The recommended charging current for a LiFePO4(Lithium Iron Phosphate) battery can vary depending on the specific battery size and application. It is recommended to keep the charging current of LiFePO4 batteries below 0.5C, as overheating due to rapid charging can cause a negative effect on the battery. Although the current limit for your battery is 1C or higher.

Constant Voltage (CV) Charge

Constant voltage, slowly the current decreases to below 0.05C. The charge voltage of LiFePO4 battery is recommended to be 14V to 14.6V at 25℃, meaning 3.5V to 3.65V per cell. The best recommended charge voltage is 14.4V, which is 3.6V per cell. Compared to 3.65V per cell, there is only a little of the capacity reduced, but you will have a lot more cycles.

A battery's SOC(state of charge) can indicate the remaining capacity that can be discharged over the battery pack's total capacity. When the battery is charged, the voltage increases. The higher the battery voltage, the fuller the battery is. In order to get accurate results, you must keep the battery at rest for at least four hours before measuring.

Charge Temperature

The charging temperature range for LiFePO4 batteries is 0℃ to 55℃. It is not recommended to charge below 0℃ theoretically. However, charge under 0℃ will crystallize the lithium ions, thus reducing the effective capacity. 

Bely batteries has an advanced type of low-temperature LiFePO4 battery integrated strong heating films with the highest possible effectiveness and efficiency which can be charged at around -30℃. The BMS controls to heat the battery internally to 5-10℃, which made the battery allowed to charge. The heating system automatically activates once charging below 0℃ is attempted, and it automatically deactivates  when it's no longer needed.

Charging LiFePO4 batteries in Parallel

It is recommended to charge each battery individually before making the parallel connection. After charging, use a voltmeter to check the voltage of each battery a few hours later and ensure they are within 50mV(0.05V) of each other before paralleling. This procedure helps minimize the chance of any imbalance between the batteries, enhancing system performance.

Charging LiFePO4 batteries in Series

When charging LiFePO4 batteries in series, it's crucial to balance the voltages across each battery during the charging process to prevent imbalances that could lead to reduced performance and shorter lifespan. It is advisable to charge each battery up individually and check the voltage to ensure they are within 50mV(0.05V) of each other before making the series connections. Ensure that the charge controller comes with cell-balancing capabilities or use a separate cell-balancer to ensure each battery receives an equal amount of charge.

Charging LiFePO4 batteries with Solar Panels

Charging LiFePO4 batteries with solar energy is becoming increasingly popular due to its environmental and economic benefits. However, it is not advisable charge battery directly with solar panel, because the output voltage and current of solar panels will vary depending on the intensity and angle of sunlight, which may exceed the charging range of LiFePO4 batteries, resulting in overcharging or undercharging, affecting the performance and lifespan of the batteries. Therefore, to safely use a solar panel to charge a LiFePO4 battery, you will need to add a charge controller between the solar panel and the battery. Here is an overview of how to charge a LiFePO4 battery with solar panels.

1. Choose a compatible solar panel: The first step is to select a solar panel that is compatible with the LiFePO4 battery's voltage and capacity requirement. Check the manufacturer's specifications to ensure that the solar panel provides the necessary voltage and current to charge the battery.

2. Connect the charge controller to the LiFePO4 battery: After connecting the solar panel to the charge controller, connect the charge controller to the LiFePO4 battery. Eusure that the connections are secure and follow the manufacturer's instructions carefully.

3. Connect the solar panel to a charge controller: To regulate the charging process, you need to connect the solar panel to a charge controller. The charge controller will prevent overcharging and control the charging rate to ensure safe and efficient charging.

4. Monitor the charging process: During the charging process, monitor the battery's voltage, charge rate and temperature regularly. If the temperature rises above the recommended level, reduce the charge rate or pause the charging process to avoid overheating.

5. Disconnect the solar panel: Once the battery is fully charged, disconnect the solar panel from the charge controller to prevent overcharging which can damage the battery.

Charging LiFePO4 batteries with Generator

When you find yourself in situation where access to electricity is limited, such as during outdoor activities or in remote locations, generators can serve as an excellent solution for charging LiFePO4 batteries. However, it is crucial to ensure compatibility between the charging voltage and current of the generator and the speficications of your LiFePO4 battery. If the generator supports DC output, it becomes necessary to incorporate a DC-to-DC charger between the battery and the generator.

Conclusion

Proper charging is crucial for ensuring optimal performance and extending the lifespan of LiFePO4 batteries. By following the recommended charging techniques, monitoring the charging progress, and using lithium-ion specific or adjustable chargers, you can maximize the benefits of LiFePO4 batteries. Remember to avoid overcharging, maintain a partial state of charge when storing the battery, and consult the manufacturer's instructions for charging recommendations. With these best practices, you can enjoy the superior performance and longevity of LiFePO4 batteries for years to come.