Exceptionally increased reversible capacity of O3-type NaCrO2 cathode by preventing irreversible phase transition

Although O3-type NaCrO2 has various merits as a promising cathode material for Na-ion batteries, only ∼0.5 mol Na+ in O3-type NaCrO2 can be used because of irreversible phase transition by Cr migration to the Na layers. Thus, it is important to increase the Na+ content that can be reversibly de/intercalated by O3-type NaCrO2. Through combined studies using first-principles calculation and experiments, we demonstrate that the presence of Sb5+ in the NaCrO2 structure can suppress Cr migration even after charging to 4.1 V (vs. Na+/Na) and enables an increase in the Na content that can be reversibly de/intercalated. During charge/discharge at C/20 (1C = 175 mA g−1), O3-type Na0.72Cr0.86Sb0.14O2 delivers a specific capacity of ∼175 mAh g−1 corresponding to ∼0.72 mol Na+ de/intercalation, representing highly enhanced electrochemical performance compared with that of O3-type NaCrO2, which exhibits poor coulombic efficiency of only ∼37% under the same conditions.