Continuous high charge levels damage LFP cells, US researchers say
Repeated charging cycles at a higher state of charge can damage LFP cells over time. However, the researchers also recommend that high charge levels in electric cars should not be avoided as a matter of principle. What do the new findings mean in everyday life?
For the study, the research team only analysed the service life or capacity retention within the LFP cell, while the vehicle manufacturers focus on the entire car and the customer benefit, in this case, the battery management system (BMS), for example. That is where the aforementioned different voltage curve of the LFP cells comes into play. LFP battery systems must be calibrated regularly due to the flatter voltage curve so that the BMS has a fixed point. It would theoretically also be possible in an empty state, i.e. with zero per cent SoC. However, it is difficult to convince customers to drive their electric car completely empty once a week or month – charging to 100 per cent is easier to communicate. The BMS then knows the exact charge level of all cells and can subsequently specify the charge level and remaining range more precisely.
The study authors’ conclusion should also be seen against this background. On the one hand, the results show that operation at charge levels of zero to 25 per cent extends the service life of the LFP battery cell. On the other hand, they write: “There is clearly a tradeoff between useful capacity and capacity retention. […] It is not realistic to recommend cycling LFP cells between 0%–25% SoC only, because that is a waste of capacity.”
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Repeated charging cycles at a higher state of charge can damage LFP cells over time. However, the researchers also recommend that high charge levels in electric cars should not be avoided as a matter of principle. What do the new findings mean in everyday life?
For the study, the research team only analysed the service life or capacity retention within the LFP cell, while the vehicle manufacturers focus on the entire car and the customer benefit, in this case, the battery management system (BMS), for example. That is where the aforementioned different voltage curve of the LFP cells comes into play. LFP battery systems must be calibrated regularly due to the flatter voltage curve so that the BMS has a fixed point. It would theoretically also be possible in an empty state, i.e. with zero per cent SoC. However, it is difficult to convince customers to drive their electric car completely empty once a week or month – charging to 100 per cent is easier to communicate. The BMS then knows the exact charge level of all cells and can subsequently specify the charge level and remaining range more precisely.
The study authors’ conclusion should also be seen against this background. On the one hand, the results show that operation at charge levels of zero to 25 per cent extends the service life of the LFP battery cell. On the other hand, they write: “There is clearly a tradeoff between useful capacity and capacity retention. […] It is not realistic to recommend cycling LFP cells between 0%–25% SoC only, because that is a waste of capacity.”
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