Anion-intercalated graphite is one of the feasible solutions for high-energy devices. Various characteristics of graphite may influence its overall performance. In this work, three homologous graphites with different particle sizes are selected as positive electrodes to accommodate tetrafluoroborate anion from propylene carbonate, based on activated carbon/graphite capacitors. In situ X-ray diffraction, Raman spectroscopy and electrochemical dilatometry are combined organically to identify the hierarchical storage behavior of anions in graphite electrodes. The graphite with minimal size exhibits a prior anion accumulation in the shallow region before notable expansion in the crystal structure. This extra charge storage leads to a higher capacity at the normal current density (0.1 A g −1 ), however, also drags down the anionic de-intercalation process and causes a significant capacity fade at high discharge rate.

The electrolyte solutions of 1 M LiBF 4 dissolved in ethyl methyl carbonate (EMC)/sulfone mixtures are applied for dual-ion batteries using graphite positive electrodes. The representative sulfone solvents include sulfolane (SL) and 3methylsulfolane. Graphite electrodes can deliver higher capacity of anion storage in the solutions of the mixed solvents than those of pure solvents. Traditional electrochemical and in situ X-ray diffraction measurements are performed on Li/graphite cells to probe the anion intercalation process at the interface between graphite electrode and electrolyte solutions. Ionic conductivity, viscosity, and NMR tests are carried out to characterize electrolyte solutions. The effects of ion-pairing between Li + and BF 4 − and the anion solvations by EMC or sulfones on the anion storage in graphite have been addressed.