Abstract
P2 Na(2/3)MnO(2) can be used as a cathode material in sodium-ion batteries. Here, the electrochemical-temperature-dependent evolution of P2 Na(2/3)MnO(2) is investigated using X-ray powder diffraction. P2 Na(2/3)MnO(2) powder under a N(2) atmosphere shows evidence of the formation of a monoclinic C2/m phase, from about 450 °C. The P2 Na(2/3)MnO(2) electrode sealed in a capillary undergoes a sequence of phase transitions from the as-prepared hexagonal P6(3)/mmc to a secondary hexagonal P6(3)/mmc phase followed by a transition to Mn(3)O(4) and subsequently MnO. NaF also appears parallel to the formation of the secondary hexagonal phase. These transitions suggest a local reducing environment as the Mn oxidation state evolves from 3(+)/4(+) to 2(+). The samples at various states of charge show similar thermal evolution with the exception of the discharged (Na-inserted) state which features a slightly more complex evolution. Understanding the structure and thermal evolution at various states of charge and under various conditions provides insight into the stability of these potential cathode materials.