PF6− Intercalation into Graphite Electrode from Gamma-butyrolactone/ethyl Methyl Carbonate

PF6− intercalated graphite compounds have found promising applications in dual-ion batteries. However, the anion storage mechanisms of graphite positive electrode in different organic solvents have not been well understood yet, especially in the mixed solvents. In this report, PF6− storage behavior in graphite electrode in 1 M LiPF6-GBL/EMC solutions is studied by conventional electrochemical tests like galvano-static charge-discharge and cyclic voltammetry at first. Then the combined electrochemical in situ characterizations including both in situ X-ray diffraction and electrochemical quartz crystal balance on graphite electrodes are carried out to trace their changes of crystal structure and mass during the anion storage. It is discovered that with EMC addition in the solutions, EMC rather than GBL will preferentially solvate with PF6− anion as the intercalant species. Moreover, ionic conductivity values and NMR spectra of the solutions were measured to investigate the interactions between ions and solvents inside, and are correlated with the performance of graphite electrode.