Intercalation of Tetrafluoroborate Anions into Graphite Electrodes from Mixed Sulfones

Solvents have an effect on anions’ intercalation into graphite and therefore partly determine the electrochemical performance of dual-ion batteries. Lithium tetrafluoroborate (LiBF4) together with a mixture of ethyl methyl sulfone and sulfolane is employed as electrolyte solutions and graphite electrodes charged to 5.5 V deliver a reversible capacity as high as 90 mA h g–1. In situ X-ray diffraction measurements are performed for graphite electrodes in Li/graphite cells to investigate the formation process of anion–graphite intercalation compounds (AGICs). Intercalation gallery heights are found to change discontinuously from 0.8 to 1.07 nm with potentials in certain solutions, which means that the species inside graphite sheets are altered. Besides, variable factors of the AGICs’ evolution process such as potentials, LiBF4 concentration, and past experience of electrochemical intercalation have been discussed.