The presentation aims to explain why manufacturers recommend charging LFP batteries to 100% and to highlight the key differences between LFP and NMC batteries.
1. Why Manufacturers Recommend 100% Charge for LFP
SOX Algorithm
Limitations: SOX algorithms, including State of Charge (SOC) and State of Health (SOH), are crucial for battery management. These algorithms struggle to accurately determine the battery’s state when it is not fully charged due to the flat voltage curve in LFP batteries. Charging to 100% helps ensure accurate SOC predictions.
Battery Degradation: NMC batteries degrade faster than LFP when charged to 100% without considering other stress factors.
EV owners should note the two main points: algorithm limitations and different degradation effects of full charge for LFP vs. NMC.
2. SOX Algorithm Limitations Direct Measurements in BMS:
BMS relies on current, voltage, and temperature to predict SOX. Accurate voltage measurement is crucial for SOC estimation. Small voltage changes in the flat region of LFP batteries make it difficult for the BMS to predict SOC accurately.
3. Equivalent Circuit Models (ECM) ECMs are used to estimate SOC and SOH.
Voltage plays a key role in these calculations. Small voltage changes in the flat region of LFP batteries make precise algorithm development challenging. This is another reason for recommending 100% charge for LFP batteries.
4. Degradation
The first table shows four scenarios with DOD, C-rate, and temperature.
The second table shows the number of cycles according to these scenarios. NMC and LFP have similar cycle numbers in normal conditions (low-duty I). However, LFP lasts longer at 30 degrees (low-duty II), but performs worse in high-duty with high C-rate. It’s incorrect to say LFP always has better cycle life performance; operating conditions and EV specifications must be considered. NMC batteries are more sensitive to DOD and temperature, while LFP is more sensitive to discharging C-rate. This sensitivity explains why LFP batteries are harder to adopt for high-speed cars requiring high max power.
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