Hexafluorophosphate Anion Intercalation into Graphite Electrodes from Propylene Carbonate/Gamma-Butyrolactone Solutions

The PF6– intercalation behavior of graphite positive electrodes has been investigated in the solutions of 1 M LiPF6–propylene carbonate (PC)/gamma-butyrolactone (GBL). Conventional electrochemical tests including galvanostatic charge–discharge and cyclic voltammetry are conducted on Li/graphite cells to assess the anion storage capability of the graphite electrode in these solutions. We find an abnormal undulation of capacity with the rise in GBL content. Ex situ and in situ X-ray diffraction (XRD) measurements are performed on graphite electrodes to identify the co-intercalating solvents and stage transitions. The intercalation of the anion cosolvated by both GBL and PC into the graphite electrode has been discovered at low GBL contents. Infrared (IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopic studies on the solutions are carried out to evaluate interactions between ions and solvents inside. The intercalation behavior of the anion in the graphite electrode is correlated with the solvation environments of the solution.