The voltage method for estimating the state of charge (SoC) in lithium-ion batteries is generally inaccurate for most types due to their flat discharge curves. This characteristic, especially prevalent in Lithium Iron Phosphate (LiFePO4) and other lithium-based chemistries like Li-manganese and NMC, makes it difficult to determine SoC based solely on voltage readings. The flat discharge curve means that a small change in voltage can indicate a large change in SoC, and environmental factors such as temperature can further distort these readings.
Specific Challenges with Voltage Method:
- Flat Discharge Curve: Most lithium-ion chemistries exhibit a relatively flat voltage profile over a significant portion of their discharge cycle, making it challenging to accurately determine SoC based on voltage alone.
- Temperature and Material Effects: Variations in temperature and material properties can cause voltage fluctuations unrelated to SoC, further complicating accurate measurement.
- Rest Period Required: To obtain somewhat accurate readings, batteries need to be in an open-circuit state for several hours, which is impractical for batteries in active use.
Therefore, while the voltage method can provide some indication of full charge and deep discharge, it is not reliable for accurately determining the SoC in most operational conditions for lithium-ion batteries. Advanced methods involving calibrated charge indicators or models that account for these factors are typically required for higher accuracy.
Original article by NenPower, If reposted, please credit the source: https://nenpower.com/blog/can-the-voltage-method-be-used-accurately-in-all-lithium-ion-battery-types/
