Intercalation Behavior of Tetrafluoroborate Anion in a Graphite Electrode from Mixed Cyclic Carbonates

In a dual-ion battery with an electrolyte solution, the anion storage behavior of graphite positive electrode is heavily dependent on anion solvation. In 1 M LiBF4 solutions dissolved in cyclic carbonates including ethylene carbonate, propylene carbonate, butylene carbonate, and their mixtures, the performance of graphite positive electrode is investigated by traditional electrochemical tests in conjunction with ex situ and in situ X-ray diffraction (XRD) characterizations. The intimate correlation between the storage capacity of tetrafluoroborate anion in the graphite electrode and electrolyte solution’s composition has been found. Graphite intercalation compounds based on various types of solvated tetrafluoroborate anion have been identified. From the solutions based on carbonate mixtures, the co-intercalation of different carbonate species together with the anion has been discovered. The preferential affinity between the anion and ethylene carbonate is disclosed.