Effects of elemental doping on phase transitions of manganese-based layered oxides for sodium-ion batteries

Due to unprecedented growing demand for renewable and clean energy, as well as the shortage and uneven distribution of lithium resources, sodium-ion batteries (SIBs) are attracting increasing attention as a competitive alternative for lithium-ion batteries. Sodium ion layered oxide materials, particularly manganese-based layered oxide materials, including P2-NaxMnO2, P′2-NaxMnO2, P2-Na0.67Ni0.33Mn0.67O2, and O3-NaNi0.5Mn0.5O2, have shown high feasibility for commercialization due to their simple structures and facile synthetic methods. However, a general challenge for these materials is the poor cycling performance caused by irreversible phase transitions. Elemental doping is an effective strategy to suppress the irreversible phase transitions and improve the performance. In this paper, we review the recent progress of elemental doping in manganese-based layered oxides and explore the effects of elemental doping on crystal structure and structural evolution of manganese-based layered oxide cathode materials.