Effects of Mn‐Doping on the Structural and Electrochemical Properties of Na₃Ni₂SbO₆ for Sodium‐Ion Battery.

Abstract Recently, layered O′3‐Na₃Ni₂SbO₆ 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 Na₃Ni_2‐xMn_xSbO₆ (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.