Crystal and electronic structures of nitridophosphate compounds as cathode materials for Na-ion batteries
Abstract
Using density-functional theory, we have studied the electronic and magnetic properties of two promising compounds that can be used as cathode materials, namely, Na2Fe2P3O9N and Na-3 TiP3O9N. When Na is extracted, we found the volume change to be quite small, with values of similar to-0.6% for Na3TiP3O9N and -5% for Na2Fe2P3O9N. Our calculated voltageswith theHubbard-type correction (GGA+U) approximation are 2.93 V for Na3TiP3O9N/Na2TiP3O9N and 2.68 V for Na2Fe2P3O9N/NaFe2P3O9N, in good agreement with the experimental data. Our results confirm that these compounds are very promising for rechargeable Na-ion batteries.