First-principle calculation for inherent stabilities of LixCoPO4, NaxCoPO4 and the mixture LixNayCoPO4

Abstract

We have synthesized NaCoPO4 and LiCoPO4 via microwave-assisted solvothermal synthesis. The local atomic structure around Co atoms was characterized by means of Co K-edge XANES spectroscopy. Using X-ray diffraction, we have identified two NaCoPO4 phases with Pnma and P65 space groups (lattice parameters a = 10.26 Å, b = 5.93 Å, c = 4.74 Å, and a = 10.16 Å,b = 10.16 Å,c = 23.87 Å, respectively) and one LiCoPO4 phase has Pnma space group with lattice parameters a = 10.22 Å, b = 5.93 Å and c = 4.71 Å. Within GGA + U approximation we have calculated the variation of the cell voltage versus Li foil and atomic Bader charges for a wide range of alkali metal concentration in the material. Considering the low cost of the material and high intercalation voltage the synthesized sodium-based material is a good candidate for novel cathode materials.