Theoretical prediction of MoN₂ monolayer as a high capacity electrode material for metal ion batteries

Benefiting from the advantages of environmental friendliness, easy purification, and high thermal stability, the recently synthesized two-dimensional (2D) material MoN₂ shows great potential for clean and renewable energy applications. Here, through first-principles calculations, we show that monolayered MoN₂ is promising as a high capacity electrode material for metal ion batteries. Firstly, identified by phonon dispersion and exfoliation energy calculations, MoN₂ monolayer is proved to be a structurally stable material that can be exfoliated from its bulk counterpart in experiments. Secondly, all the studied metal atoms (Li, Na and K) can be adsorbed on MoN₂ monolayer; both the pristine and doped MoN₂ are metallic. Thirdly, the metal atoms possess moderate/low migration barriers on MoN₂, which ensures excellent cycling performance as battery electrodes. In addition, the calculated average voltages suggest that MoN₂ monolayer is a suitable cathode for Li-ion batteries and a suitable anode for Na-ion and K-ion batteries. Most importantly, as a cathode for Li-ion batteries, MoN₂ possesses a comparable average voltage but a capacity 1 to 2 times larger (432 mA h g^-1) than that of standard commercial cathode materials; as an anode for Na-ion batteries, the theoretical capacity (864 mA h g^-1) of MoN₂ is 2 to 5 times larger than that of typical 2D anode materials, such as MoS₂ and most MXenes. Finally, we also provide an estimation of the capacities of other transition-metal dinitride materials. Our work suggests that the transition-metal dinitride MoN₂ is an appealing 2D electrode material with high storage capacity.