Graphite dual-ion batteries (GDIBs) have gained attention in recent years due to their low cost and low environmental impact. The understanding of the anion storage behaviour which possesses a coupling mechanism of intercalation and capacitive processes remains unclear. Differentiating the nature of charge storage that are capacitive, pseudocapacitive, or battery-like behaviour of electrode materials is essential in structural design for optimized energy storage. Although conventional voltammetric analysis is a reliable approach to determine the capacitive contribution of charge-storing materials by measuring the current response against varying scan rates, it is usually time-consuming and requires a large number of complicated steps for analysis. In this study, a three dimensional (3D) Bode analysis is adopted as a complementary technique to characterize the capacitive contribution and oxidation kinetics of the fundamental anion storage processes. The anion storage mechanism of graphite electrodes in electrolytes containing anions with different ionic radius including PF 6 - , TFSI - , AlCl 4 - was investigated using AC impedance technique. Real capacitance C’ versus frequency and the applied direct-current (DC) cell voltage are used as key descriptors to reveal the effect on the ionic sizes on the charge storage behaviour. 3D Bode plot of graphite electrode shows high C’ at multiple voltages, indicating the staging mechanism which is consistent with the results obtained from cyclic voltammetric (CV) analyses. The proposed method in this work presents a facile characterization technique for anion storage processes compared to the complex in-situ microscopic and spectroscopic approaches.
