SOC and Charge of LiFePO4 Battery

Introduction to LiFePO4 Battery

As the frontrunner of a new generation of battery, lithium battery is known for its remarkable performance,high energy density, longer lifespan, and enhanced safety  features. It has been applied widespreadly in various industries: electric vehicles (EVs) , renewable energy storage, marine applications and consumer electronics.

What is the SOC?

SOC refers to the State of Charg, indicating the amount of energy remaining in the battery relative to its fully charged capacity. For LiFePO4 batteries, SOC is usually expressed as a percentage, with 0% indicating a fully discharged battery and 100% representing a fully charged battery. Monitoring SOC is crucial for optimizing battery performance, extending its lifespan, and preventing over-discharge or overcharge scenarios. At the same time, when users are confused about the charging and discharging voltages, the SOC can also clearly show the voltage and charge at each stage of the battery's charging and discharging.

 

Several factors will influence the SOC of LiFePO4 battery:

  1. Current: higher charge/discharge current lead to faster change of SOC.
  2. Temperature: the temperature of the battery is also the important factors in influencing SOC. Extreme temperatures, both high and low, can affect the accuracy of SOC measurements and impact battery performance.
  3. Cycle times: the number of battery cycle affects the SOC estimation and longevity.

Voltage change while charged:

While charging, the voltage of a lithium battery increases gradually as it accumulates energy. This voltage increase occurs due to the movement of lithium ions between the positive and negative electrodes. During the battery charging process, the voltage will continue to increase until it reaches the maximum safe voltage. Beyond this point, further charging can lead to damage or safety hazards.

Generally, a higher SOC corresponds to a higher voltage, reflecting the amount of energy stored in the battery. Conversely, a lower SOC correlates with a lower voltage.

However, it's essential to note that the voltage alone doesn't provide a precise measure of the battery's capacity. Factors like internal resistance, load characteristics, and aging affect the voltage response. 

When the battery energy is at 0%, it means that the battery is fully discharged, and there is no more usable energy left to power devices or perform work. However, the voltage reading might still display 13.2V or another value, depending on the battery chemistry and the characteristics of the voltage measurement system.

 

To maximize the performance and longevity of LiFePO4 batteries, what should we pay attention to?

Charging a lithium battery requires careful considertion of various parameters to ensure its optimal performance and safety.

Voltage: Even if you have other chargers at home, you should pay attention to whether it can adjust to the lithium battery charging mode. Different batteries have different voltage requirements, and lithium battery voltage limit ranges generally from 3.6V to 3.8V per cell. It's also to prevent overcharging.

Current: Charging current should be controlled to avoid overheating and degradation of the battery. The optimal current refer to the battery capacity and manufacturer recommendations.

BMS: BMS systems help monitor SOC, prevent overcharging, and balance battery voltage to improve safety and longevity.

Last but not least, following the manufacturer guidelines for charging profiles, cycle limits and storage conditions to optimize battery performance and life. When you can not determine the optimal voltage, current, and appropriate operating temperature of the battery charging and discharging, please consult the relevant service personnel, so as to avoid causing safety problems.