Meaning
Experimental voltage profiles provide the baseline measurements required to calculate the rates of potential change during lithiation. Plotting logarithmic voltage derivatives against capacity reveals peaks that correspond to the staging of lithium within the electrode materials. These graphs allow researchers to see electrochemical events that are invisible on a standard voltage curve.
Data Transformation
Converting the measured voltage into a differential form requires high resolution sensors to avoid noise. The resulting plot typically shows the rate of change in voltage for each unit of charge added to or removed from the battery.
Peak Identification
Shifts in the position or height of the peaks indicate changes in the chemistry of the cell. By analyzing the logarithmic voltage derivatives over many cycles, engineers can pinpoint which electrode is losing capacity or if the electrolyte is breaking down. A reduction in peak height often signifies a loss of active material, while a shift in peak position suggests an increase in internal resistance.
This method is particularly useful for assessing the health of commercial cells where the internal components cannot be directly measured.
State Estimation
Advanced algorithms use these derivative signatures to provide more accurate readings of the remaining charge. Knowing the exact state of the electrodes helps the battery management system optimize the power delivery for electric vehicles.
