Gismondine cobalt phosphate (CoPO4) as a monovalent-ion battery cathode material: a first-principles study

Abstract

Using density functional theory calculations, we investigated the electrochemical properties of gismondine CoPO₄, a polymorph from the well-studied polyanionic transition metal phosphate family, for its suitability as a monovalent (Li or Na) battery cathode material. We found gismondine CoPO₄ to be promising for Na-ion battery cathodes. It exhibits a high cell voltage of ∼4 V (vs. bulk Na) and a theoretical specific capacity of 152 mA h g⁻¹. Multiple Na-ion diffusion channels in 3D within the compound were identified with low barriers ranging from 0.13 to 0.28 eV, and high ionic diffusivities ranging from 10⁻⁴ to 10⁻⁷ cm² s⁻¹. It also displays a small volume change of ∼−7% upon complete sodiation to NaCoPO₄.