Meaning
Analytical techniques measure the change in cell voltage relative to the change in capacity to identify specific electrochemical reactions. The differential voltage spectroscopy calculates the derivative of voltage with respect to capacity to transform a smooth discharge curve into a series of peaks. These peaks correspond to phase transitions in the electrode materials.
Chemical Signature
Every electrode material has a unique profile that acts as a fingerprint during operation. As a cell ages, the peaks in the differential voltage spectroscopy plot shift or decrease in height. This movement indicates a loss of active material or the depletion of lithium inventory.
State Assessment
Comparing the current derivative plot to a fresh cell baseline allows for precise estimation of health. Subtle changes in the graphite phase transitions are visible here before they appear in total capacity measurements. Modern differential voltage spectroscopy provides a non-destructive way to look inside the chemistry.
Diagnostic Resolution
High precision equipment is necessary to capture the small voltage increments required for an accurate derivative. Noise in the raw data can obscure the features of the plot. Sophisticated differential voltage spectroscopy algorithms filter this noise to reveal the underlying thermodynamic behavior.
Numerical smoothing techniques are often applied to ensure the resulting curves are clear enough for automated analysis.
