Defective Graphene and Graphene Allotropes as High-Capacity Anode Materials for Mg Ion Batteries

Although rechargeable Mg ion batteries have recently received renewed interest as a promising alternative to Li ion batteries, the Mg metal used for anodes in state-of-the-art Mg ion batteries is not compatible with conventional battery electrolyte solvents. On the other hand, graphite electrode materials function well with common battery electrolyte solvents, but Mg intercalation into graphite is very difficult. In the case of two-dimensional (2D) carbon-based materials, pristine graphene, the most well-studied 2D material, is known to have no capacity for Li or Mg. Here we demonstrate the potential of defective 2D carbon-based structures to be used as high-capacity anode materials for Mg ion batteries. Adsorption of divalent Mg ions on defective graphene and graphene allotropes is predicted by first-principles density functional theory. Our results show enhanced Mg adsorption on both defective graphene and graphene allotropes. Moreover, we show that Mg storage capacity can be improved by increasing the defect concentration or changing the local arrangement of carbon rings. A Mg storage capacity as high as 1042 mAh/g can be achieved in graphene with 25% divacancy defects. These new insights, together with the fact that carbon-based materials are very compatible with a wide range of battery electrolyte solvents, will pave the way for developing carbon-based anode materials for practical Mg ion batteries.