Effects of Mn‐Doping on the Structural and Electrochemical Properties of Na 3 Ni 2 SbO 6 for Sodium‐Ion Battery.

Recently, layered O′3‐Na 3 Ni 2 SbO 6 has been investigated as a unique cathode material for Na‐ion batteries due to the good electrochemical performance via O′3‐P′3 phase transitions in the voltage range between 2.0 and 4.0 V vs Na + /Na. However, at present it is not well understood whether transition metal doping of the pristine structure could improve the phase transition kinetics during charge/discharge. In this study, we synthesized Mn‐doped Na 3 Ni 2‐x Mn x SbO 6 ( x =0, 0.25, 0.5) layered oxides and investigated their feasibility as cathode materials for Na‐ion batteries using ex‐situ X‐ray diffraction (XRD) coupled with DFT calculations. The results show that light Mn doping ( x =0.25) energetically enhances the O′3‐P′3 phase transition kinetics with smaller unit‐cell‐volume changes. However, the heavily doped ( x =0.5) sample suffers from large polarization, which could be attributable to the reduced two‐phase reaction range and a large unit‐cell‐volume change upon sodium extraction.