Optimised Pulse-Fitting for Robust Time-Domain Impedance Analysis of Automotive Lithium-Ion Cells under Application-Specific Pulse Conditions

A pulse-fitting methodology for time-domain analysis of lithium-ion battery impedance is presented and systematically extended to address automotive-relevant measurement constraints under controlled test conditions, including non-ideal current profiles, limited stabilization times, measurement noise, low sampling frequencies, and SOC-dependent OCV contributions. Since no universally applicable test pulse exists for large-format automotive lithium-ion cells, pulse-based diagnostics require evaluation methods that remain robust under application-specific excitation conditions. In this work, a pulse-fitting methodology for time-domain analysis of lithium-ion battery impedance is systematically extended. The approach models the voltage response to current pulses using a physically motivated RC network, enabling the extraction of diffusion-related time constants without relying on frequency-domain techniques. Key enhancements include numerical convolution for non-ideal current profiles, incorporation of a dynamic open-circuit voltage, Tikhonov regularisation, and weighting and scaling strategies to improve robustness against noise and low sampling frequencies. ... mehrFurthermore, a quadratic programming solver is introduced to increase stability for ill-conditioned problems, and an extrapolation method is proposed to account for insufficient voltage stabilization times. The methodology is validated using both synthetic and experimental pulse data, demonstrating reliable access to low-frequency impedance characteristics. The results highlight the potential of the approach for advanced state estimation and model development.