Thermally and Electrochemically Driven Topotactical Transformations in Sodium Layered Oxides NaxVO2
2016-02-05T00:00:00Z (GMT) by
Phase diagrams and structural transformations in the complex NaxVO2 system have been studied using electrochemical (de)intercalation and in situ and operando high resolution synchrotron powder diffraction. Starting from O′3-Na1/2VO2 obtained by sodium electrochemical deintercalation of O3-NaVO2, the structural details of irreversible and reversible thermally driven transformations to P′3 and P3 type structures are presented. Subsequently, these P′3-NaxVO2 phases provide a platform for operando studies exploring the NaxVO2 phase diagram as a function of sodium electrochemical (de)intercalation. In this system, three single phase domains have been found: a line phase P′3-Na1/2VO2, one solid solution for 0.53 ≤ x ≤ 0.55 characterized by an incommensurate modulated structure, and a second solid solution for 0.63 ≤ x ≤ 0.65 with a defective structure resulting from a random stack of O′3 and P′3 layers. With further sodium intercalation (x > 0.65), the structure irreversibly transforms to the starting parent phase O3-NaVO2. This work reveals new details about the diverse structural polymorphs found in sodium layered oxides used as electrode battery materials and the transitional pathways between them as a function of temperature and composition.