Kinetic Analysis of Sodium-Ion Intercalation Reaction into Graphene-Like Graphite by Electrochemical Impedance Spectroscopy

Abstract

Graphene-like graphite (GLG) is a promising anode material for sodium-ion batteries, which is believed to have unique kinetic properties compared to hard carbon due to its different intercalation mechanism. In this study, electrochemical impedance spectroscopy was used to investigate the kinetic properties of sodium-ion intercalation in GLG. Our results indicated that the activation energies for interfacial sodium-ion transfer of GLGs were nearly identical to those reported for graphite, regardless of the heat treatment temperature of the GLGs. Furthermore, these activation energies were lower than those observed for hard carbon, suggesting better sodium-ion intercalation kinetics. In addition, the diffusion coefficient of sodium ions in the GLG was similar to that of graphite, with the highest value observed for GLG800, the GLG heat-treated at the highest temperature of 800 °C. This may indicate that the diffusion coefficient increases with the presence of nanopores in the graphene layer of GLG. It has also been reported that GLG800 is superior in terms of reversible capacity and working potential compared to GLGs synthesized at other temperatures. Consequently, the results clearly demonstrated that GLG800 has the best electrochemical properties in terms of both thermodynamics and kinetics among the GLGs investigated in this study.