Dynamic Electrochemical Impedance Spectroscopy‐Based Diagnosis of Electrochemical and Thermal Behavior in Li‐Ion Batteries under Varying Current Rates, State of Charge, and Temperature

Abstract Dynamic Electrochemical Impedance Spectroscopy (D‐EIS) enables real‐time evaluation of lithium‐ion battery performance by capturing electrochemical and thermal responses under dynamic conditions, surpassing static EIS. This study applies D‐EIS to LiCoO 2 cells at 25 and 35 °C, varying C‐rates and state of charge (SOC). Ohmic resistance (R₀) was highest at low C‐rate and temperature (98.50 mΩ at 0.5C, 25 °C) due to reduced ionic conductivity and interfacial contact resistance but declined at higher C‐rates and temperature (70.55 mΩ at 3C, 35 °C), showing improved electrode/electrolyte interface. Charge transfer resistance decreased strongly (11.35 mΩ at 0.5C, 25 °C to 0.43 mΩ at 3C, 35 °C), reflecting enhanced interfacial kinetics. Double‐layer capacitance rose substantially (0.14 F at 0.5C to 9.13 F at 3C, 25 °C; ≈11.65 F at 35 °C), indicating greater ion accumulation and surface activity. Diffusion resistance increased at low C‐rate and deep discharge but fell ≈40% at 3C, 35 °C, evidencing improved diffusion. Heat generation peaked at 3C‐rate, reaching 4.48 W at 25 °C and 4.39 W at 35 °C. Over 45 cycles, R₀ increased from 74.5 to 88.1 mΩ (50% SOC), with broader mid‐frequency semicircles confirming degradation. Thus, D‐EIS effectively diagnoses transient behavior and early degradation in Li‐ion cells.