A fundamental understanding of the Fe/Ti doping induced structure formation process to realize controlled synthesis of layer-tunnel Na0.6MnO2 cathode

Abstract

It's well known that ion-doping could modify the crystal structure and adjust the corresponding performance of cathode, but how the doped ions affect the structure formations during high-temperature calcination still remains a daunting challenge, which is critical for the ideal controlled synthesis. In our pervious study, we have found that the cationic ion doping can both tune the single phase structure and adjust the phase ratio in layer-tunnel Na0.6MnO2. And in the present study, we furtherly try to track the influence of varied Fe3+ and Ti4+ on the formation process of layer-tunnel hybrid structures and focus on the thermal behavior, structure evolution and morphology change. The kinetics-preferred layered structure can be detected at the initial stage and transfer to the thermodynamic-stable tunnel structure at increased temperature. The Fe3+ can stabilize the formed layer structure while the Ti4+ promote the latter transformation. More interesting, the Ti4+ plays a dominant role when Fe3+/Ti4+ were co-doped. The impressive results can be related with the more orderly structure of layer phase and distorted coordination in tunnel phase. This research correlates the synthesis process and the final structure, as well as the ultimate electrochemical performance, which shed new light on the development of advanced oxides cathode.