Hierarchical Intercalation of Solvated Tetrafluoroborate Anions into Graphite Electrodes: The Case Studies of Methyl Acetate and γ-Butyrolactone Solutions

Intercalation of anions unlocks graphite as a positive material in energy storage devices, and the performance could be affected by solvents in solutions. In this context, it is vital to investigate the role of solvents in anion intercalation. Herein, a hierarchical intercalation phenomenon, in which different graphite intercalation compounds are generated in the same solution, is studied in lithium tetrafluoroborate (LiBF4) solutions of carboxylate ester solvents γ-butyrolactone (GBL) and methyl acetate (MA). The evolution modes of the graphite cathode structure during electrochemical intercalation and deintercalation are discussed via in situ X-ray diffraction (XRD) measurements. Based on this, the relationship between GICs and potentials, together with concentrations, is compared in detail. Furthermore, various graphite materials with different surface properties are applied to adjust the anions’ solvation status inside graphite sheets.