Synthesis, structural, and electrochemical properties of NaCo(PO3)3 cathode for sodium ion batteries
A new Co base sodium metaphosphate compound, NaCo(PO3)3, has been synthesized here by solid state method. The crystal structure is refined by the Rietveld method, and the results reveal that NaCo(PO3)3 has an orthorhombic structure with the space group of P212121 and lattice parameters of a 14.2453(2) A, b 14.2306(1) A, and c 14.2603(2) A. Its typical morphology and chemical composition are confirmed by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) The valence states of all elements and the internal/external vibrational modes of NaCoP3O9 compound are measured by X ray photoelectron and vibrational spectrum, where a typical feature of the (PO3) polyanion group is observed. Meanwhile, the electrochemical properties of NaCo(PO3)3 cathode for sodium ion batteries are also elevated and an initial discharge capacity of 33.8 mAh/g can be obtained at 0.05 C within 1.5 4.2 V. After 20 cycles, a discharge capacity of 26.7 mAh/g can be obtained and a well kept oxidation reduction plateau is still observed for NaCo(PO3)3 cathode, indicating the good reversibility of this metaphosphate electrode.
Journal of Solid State Electrochemistry