Meaning
Differential capacity analysis measures the voltage spacing between corresponding charge and discharge peaks to quantify polarization and degradation inside an electrochemical cell. In lithium-ion cell testing, dq dv peak separation tracks increases in internal resistance caused by solid electrolyte interphase growth and contact loss. The metric isolates ohmic losses from kinetic mass transfer limitations across distinct state of charge ranges.
It reaches its boundary when structural phase changes alter peak morphology completely, preventing accurate pairing of charging and discharging features.
Polarization Origin
Kinetic hysteresis causes charge features to appear at higher potentials than corresponding discharge features. As current flows, dq dv peak separation widens proportional to total cell impedance. High rate operation amplifies this voltage gap through combined ohmic drop and slow charge transfer kinetics.
Degradation Tracking
State of health monitoring relies on tracking peak movement over long cycling intervals. Internal resistance growth shifts charge peaks to higher potentials and discharge peaks to lower potentials. Analyzing individual peak pairs reveals whether capacity fade stems from active material loss or lithium inventory loss.
Battery management software uses these shifts to adjust end-of-charge voltage thresholds and prevent localized lithium plating.
Measurement Boundary
Low C-rates are required during data collection to separate kinetic polarization from true thermodynamic phase shifts. If testing rates exceed C over 20, thermal effects and concentration gradients blur the differential curves. Smooth mathematical filtering prevents noise from creating false local peaks in numerical derivative calculations.
