Differentiating Cyclability and Kinetics of Na+ Ions in Surface-Functionalized and Nanostructured Graphite Using Electrochemical Impedance Spectroscopy

Abstract

The revolution in lithium-ion battery (LIB) technology was partly due to the invention of graphite as a robust negative electrode material. However, equivalent negative electrode materials for complementary sodium ion battery (NIB) technologies are yet to be commercialized due to sluggish reaction kinetics, phase instability, and low energy density originating from the larger size of Na+-ion. Therefore, in search of the next-generation electrode materials for NIBs, we first analyze the failure of graphite during reversible Na+ ion storage. Building upon that, we suggest surface-functionalized and nanostructured forms of analogous carbon allotropes for enhancing Na+ ion storage. During long-term rigorous cycling conditions, Graphene Oxide (GO) and Graphene nanoplatelets (GNP) exhibit higher Na+ ion storage (157 mAh g−1 and 50 mAh g−1 after 60 cycles, respectively) compared to graphite (27 mAh g−1). Optimizing alternative NIBs requires a comprehensive analysis of cycling behavior and kinetic information. Therefore, in this investigation, we further examine ex-situ electrochemical impedance spectroscopy (EIS) at progressive cycles and correlate capacity degradation with impedance arising from the electrolyte, solid electrolyte interphase formation, and charge transfer.