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Based on the intrinsic restrictions in current lithium-ion battery, Mg-based batteries are regarded as one of the most potential candidates because of their higher volumetric energy density and fewer Mg dendrites in the process of charge and discharge. However, the improved energy density of the Mg-based battery is expected to further promote their practical application. Compared with metal chalcogenides, the selenides have high electrical conductivity and special electron orbit mixing effect between the Se and the transition metal atoms. As a result, the conversion-type selenides are promising cathodes for Mg batteries with high-energy- density. Herein, this review focuses on the recent investigations on the metal selenides as cathode materials for Mg-based batteries. Their crystal structures, the preparation methods, and electrochemical properties/mechanism of transition metal selenides are unveiled. Finally, the issues and the future research of selenides for Mg batteries are discussed, such as advanced characterization methods and rational design strategies. These advances of selenides provide new ideas for realizing the characteristics of high-energy-density Mg-based batteries.

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The low specific capacity and Mg non-affinity of graphite limit the energy density of ion rechargeable batteries. Here, we first identify that the monolayer C12‑3‑3 in sp 2–sp 3 carbon hybridization with high Li/Mg affinity is an appropriate anode material for Li-ion batteries and Mg-ion batteries via the first-principles simulations. The monolayer C12‑3‑3 can achieve high specific capacities of 1181 mAh/g for Li and 739 mAh/g for Mg, higher than those of most previous anodes. The Li storage reaction is an “adsorption–conversion–intercalation mechanism”, while the Mg storage reaction is an “adsorption mechanism”. The 2D carbon material of C12‑3‑3 displays fast diffusion kinetics with low diffusion barriers of 0.41 eV for Li and 0.21 eV for Mg. As a new carbon-based anode material, the monolayer C12‑3‑3 will promote the practical application of batteries with high-capacity and high-rate performance.

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