Can Electrochemical Impedance Spectroscopy be Replaced by Direct Current Techniques in Battery Diagnosis?

Electrochemical impedance spectroscopy (EIS), a conventional and alternating-current-(AC)-based technique for impedance measurement, is commonly used in battery diagnosis. However, it requires expensive equipment and demanding operating conditions and is complex and model-dependent in data analysis. Recently, novel direct current (DC) analytics have emerged as an alternative to EIS. They are simple yet powerful, being capable of revealing impedance information that traditionally could only be obtained through EIS and determining Li-ion diffusion coefficient. Besides, a complete EIS spectrum can be predicted based on constant current charging curves in the support of machine learning methods. This work highlights the similarities and discrepancies between DC techniques and EIS in the electrochemical analysis of Liion batteries. Looking ahead, DC techniques may be a promising substitute for EIS in future battery diagnosis, requiring simplified equipment while offering a deep understanding of battery impedance and its underlying electrochemical processes.

Fast formation of anode-free Li-metal batteries by pulsed current.

Anode-free Li-metal batteries offer high energy density but are prone to dendrite formation during charging which can cause catastrophic failures. Ensuring dendrite-free smooth Li deposits during charging is therefore necessary. Suppressing dendrite growth can be achieved by pulsed current charging, especially during the formation cycle that largely determines the corrosion trajectory of a cell. As opposed to the constant-current technique, pulsed current techniques apply intermittently stopped current flows. This work investigates the electroplating of metallic Li onto a Cu foil current collector under constant-current and pulsed current formation protocols. In addition to smoother, less resistive electroplated metallic Li deposits and increased Coulombic efficiency, we show that by employing an optimized pulsed current formation protocol, the formation process is accelerated by a factor of 2 and the Coulombic efficiency was increased by 10% compared to a C/20 protocol. Finally, by employing a simple regression coupled to experimentation, we propose the pseudo-IR-drop to be used for live adjustment of pulsed current protocols i.e., individually approach each cell at all SOC during formation.