Intercalation behaviour of magnesium into natural graphite using organic electrolyte systems

Abstract

The focus of this study is on the investigation of electrochemical intercalation and deintercalation behaviour of Mg²⁺ into natural graphite electrodes in organic electrolyte. We used as a conductive salt magnesium bis(trifluoromethylsulfonyl)imide (Mg(TFSI)₂) dissolved in N,N-dimethylformamide (DMF) as organic solvent. By utilization of conductivity measurements within a broad temperature range (−20 °C to +60 °C), a conductivity maximum is to be found at a concentration of 0.5 M for all temperatures. Thus, in this study all electrochemical investigations dealing with magnesiation of graphite anodes are made with the electrolyte system 0.5 M Mg(TFSI)₂/DMF. In three electrode cells (Swagelok© T-cells) we obtain cathodic and anodic currents, which are highly reversible and last for more than 100 cycles showing a coulombic efficiency above 98%. SEM images reveal a non-destructive intercalation of cationic species into graphite and the formation of a magnesiated graphite intercalation compound is confirmed by ex situ XRD diffraction measurements.