Exploration of the two-dimensional transition metal phosphide MoP₂ as anode for Na/K ion batteries

Transition metal phosphides are regarded to be potential anode materials for alkali metal ion batteries with abundant availability of the constituent elements. However, the volume changes and resulting structure deterioration during the charge-discharge process are challenges. Using evolutionary search combined with ab initio calculations, we discover a dynamically, thermally, and mechanically stable MoP₂ monolayer, which turns out to be an excellent anode material for Na-ion batteries providing a high specific capacity of 339 mA h g⁻¹, low diffusion barrier of 0.12 eV, and low open-circuit voltage of 0.48 V. The volume expansion (125%) is found to be decisively smaller than in the case of black phosphorus (443%), for example.