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

Abstract

Although O3-type NaCrO2 has various merits as a promising cathode material for Na-ion batteries, only ~& nbsp;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 ~& nbsp;175 mAh g(-1) corresponding to ~& nbsp;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 ~& nbsp;37% under the same conditions.