A new high capacity cathode material for Li/Na-ion batteries: dihafnium sulfide (Hf₂S)

Structural and electronic properties of the newly synthesized dihafnium sulfide (Hf₂S) monolayer were investigated in this study. The Hf₂S monolayer is a magnetic metal and it retains its metallicity despite external factors, such as tensile/compressive strain or various atom terminations. This robust metallic Hf₂S monolayer has a high storage capacity of 1377.7 mA h g^-1 for both Li and Na atoms, which is much higher than conventional battery electrodes. The minimum diffusion barrier value is 131 meV for Li, and 117 meV for Na. The average open-circuit voltage values of Li and Na were calculated as 2.37 V and 1.69 V, respectively. Investigation of the mechanical properties showed that it is softer than graphene due to the Young's modulus of 111.7 N m^-1, but comparable with the molybdenum disulfide (MoS₂) monolayer. In light of the results of this study, the Hf₂S monolayer can serve as a useful cathode material for Li-ion and Na-ion batteries. In addition, the interactions of the Hf₂S monolayer with aluminium nitride (AlN) and MoS₂ monolayers were presented. While AlN behaves like a substrate for the Hf₂S monolayer, the MoS₂ monolayer forms a heterostructure with the Hf₂S monolayer. This study is a guide for the Hf₂S monolayer and its functions in nanotechnology.