O3–NaxMn1/3Fe2/3O2as a positive electrode material for Na-ion batteries: structural evolutions and redox mechanisms upon Na+(de)intercalation

O3–Na_0.77Mn_1/3Fe_2/3O₂was studied byin situXRPD. The system undergoes several structural transitions from 1.5 V to 4.3 V: O′3 → O3 → P3 → “X”.