Cointercalation of Mg²⁺ Ions into Graphite for Magnesium-Ion Batteries

Natural graphite was examined as a host material for the intercalation of Mg²⁺ ions in magnesium-ion batteries. To demonstrate the cointercalation of Mg²⁺ions into graphite with linear ether solvents, galvanostatic cycling was performed with 0.3 M Mg(TFSI)₂ in EC/DEC (1:1 v:v) and 0.3 M Mg(TFSI)₂ in DME/DEGDME (1:1 v:v). To measure each contribution of the graphite and Mg electrodes to the large polarization of the graphite/Mg cell, two symmetric cells, one comprising two graphite/graphite electrodes and the other with two Mg/Mg electrodes, were examined by galvanostatic cycling. To fabricate the graphite/graphite symmetric cell, two graphite electrodes were first discharged with Mg counter electrodes. To clarify the cointercalation mechanism of graphite with Mg²⁺ ions, structural changes in the natural graphite were investigated through ex situ XRD analysis at various states during charge and discharge. This finding provides a new avenue for developing promising anode materials for magnesium-ion batteries.