Solid state synthesis of layered sodium manganese oxide for sodium-ion battery by in-situ high energy X-ray diffraction and X-ray absorption near edge spectroscopy

Abstract In situ high energy X-ray diffraction (HEXRD) and in situ X-ray absorption near edge spectroscopy (XANES) were carried out to understand the solid state synthesis of Na x MnO 2 , with particular interest on the synthesis of P2 type Na 2/3 MnO 2 . It was found that there were multi intermediate phases formed before NaMnO 2 appeared at about 600 °C. And the final product after cooling process is a combination of O′3 NaMnO 2 with P2 Na 2/3 MnO 2 . A P2 type Na 2/3 MnO 2 was synthesized at reduced temperature (600 °C). The influence of Na 2 CO 3 impurity on the electrochemical performance of P2 Na 2/3 MnO 2 was thoroughly investigated in our work. It was found that the content of Na 2 CO 3 can be reduced by optimizing Na 2 CO 3 /MnCO 3 ratio during the solid state reaction or other post treatment such as washing with water. We expected our results could provide a good guide for future development of high performance cathode materials for sodium-ion batteries.