Hysteresis of the charge transfer resistance between the charge and discharge processes obtained from electrochemical impedance measurements using a thin-film cathode for a lithium-ion cell

Abstract

• A thin-film LiNi 1/3 Co 1/3 Mn 1/3 O 2 was formed on a single-crystal Si substrate. • Preparing a pouch-type cell using the thin-film with flat surface as a cathode. • Conducting EIS measurements at a precisely controlled state of charge of the cell. • Hysteresis of the charge transfer resistance during charge/discharge was observed. A thin-film LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NMC) material preferentially oriented to the platinum (Pt) layer, NMC (0 0 3) plane parallels to Pt (1 1 1) plane, was successfully formed on a single-crystal silicon substrate using pulsed laser deposition. A pouch-type thin-film cell (thin-film NMC cell) was prepared using the thin-film NMC on the substrate as a cathode. The resistance components of the prepared thin-film NMC cell were compared with those of a composite NMC cell using electrochemical impedance spectroscopy (EIS). Consequently, the charge transfer resistance ( R 1 ) based on the state of charge in the thin-film cells showed large hysteresis between the charge and discharge processes, whereas those in the composite NMC cells almost coincided. Furthermore, a similar large hysteresis of R 1 was obtained in the composite NMC cells using a diluted electrolyte solution. The discordance between the thin-film cells and the composite cells is not inconsistent, by considering the difference of an effective surface area of each electrode exposed to an electrolyte. Thus, the obtained results indicate that the thin-film NMC cell having flat surface can be used as an ideal interface model to analyze the charge transfer mechanism at the cathode–electrolyte interface during charge and discharge in a standard electrolyte concentration.