Investigation on the Air Stability of P2-Layered Transition Metal Oxides by Nb Doping in Sodium Ion Batteries

Sodium-ion batteries are regarded as a substitution for lithium-ion batteries for its abundant resources, wide distribution, low cost, etc. The P2-layered sodium transition metal oxides (P2-NaxTMO2) have attracted extensive attention due to their high rate and cycling properties. However, P2-NaxTMO2 often undergoes structural transformations when exposed in ambient air, which restricts its practical applications. Herein we studied the effect of Nb doping on the air stability of P2-NaxTMO2. We demonstrated that the Nb-induced surface preconstructed layer inhibited the surface dissolution of the P2 material in the electrochemical reaction and formed a stable and thin (cathode–electrolyte interphase) CEI film, which prevented water molecules from entering the P2-NaxTMO2 lattice. Na0.67Mn0.67Ni0.33Nb0.03O2 could exhibit superior rate performance (a reversible capacity of 72.5 mAh g−1 at 20 C) and outstanding cycling performance (84.43% capacity retention after 1000 cycles at 5 C) in a half cell after exposed in a moisture atmosphere (RH93%) for 20 days.