Quantifying Transient Resistance Measurement Errors Driven by Data Acquisition Delay
Data acquisition delay inflates cell transient resistance measurements by capturing double-layer charging decay rather than pure ohmic voltage drops.
Phase Lag
Meaning
A time delay occurs between an excitation signal and the resulting output of an electrochemical system. During electrochemical impedance spectroscopy, phase lag describes the delay in current response relative to the applied voltage perturbation. This parameter reveals the capacitive and inductive properties of the cell chemistry.
Frequency Dependency
The timing offset varies widely across the scan range of the instrumentation. At high frequencies, phase lag is dominated by double-layer capacitance and inductive effects of the cell terminals. As the frequency decreases to millihertz levels, the delay reflects the diffusion kinetics of lithium ions in the active material.
Designers must map these frequency-dependent shifts during the characterization phase to ensure the diagnostic software interprets the raw impedance data correctly under all operating conditions.
Measurement Distortion
Analog front-end filters can introduce additional timing delays that corrupt the calculated impedance. If this parasitic phase lag is not subtracted from the measurement, the battery management system will miscalculate the cell temperature and internal resistance. This error leads to incorrect state of health estimation in the field.
Algorithm Calibration
Software routines must compensate for these delays to ensure accurate real-time diagnostics. Sourcing high-speed analog front-ends with known phase behavior simplifies the calibration of the state of health algorithms. When the system is properly calibrated, the corrected measurements allow the pack to operate safely at its performance limits.