Tetragonal and trigonal Mo2B2 monolayers: two new low-dimensional materials for Li-ion and Na-ion batteries

Abstract

In this study, we report two new Mo₂B₂ monolayers and investigate their stabilities, electronic structures, lattice dynamics, and properties as anode materials for energy storage by using the crystal structure prediction technique and first-principles method. The calculated phonon spectra and electrical structures indicate that our predicted tetragonal and trigonal Mo₂B₂ (tetr- and tri-Mo₂B₂) monolayers possess excellent electronic conductivity and great stability. The adsorption energies of Li/Na on them are negative enough to ensure stability and safety under operating conditions. Besides, tetr-Mo₂B₂ possesses a theoretical specific capacity of ∼251 mA h g⁻¹ for both Li- and Na-ion batteries (LIBs and NIBs), while tri-Mo₂B₂ possesses ∼251 and ∼188 mA h g⁻¹ for LIBs and NIBs, respectively. The diffusion energy barriers of Li/Na over tetr- (0.029/0.010 eV) and tri- (0.023/0.013 eV) Mo₂B₂ are very small, indicating their excellent charge/discharge capability. In addition, the low electrode potential of Li/Na-intercalated tetr- and tri-Mo₂B₂ is beneficial to their performance as anode materials. This work is of great importance for widening the families of both anode materials for LIBs/NIBs and two-dimensional transition metal borides.