Mn-Rich P ' 2-Na-0.67[Ni0.1Fe0.1Mn0.8]O-2 as High-Energy-Density and Long-Life Cathode Material for Sodium-Ion Batteries

Herein, P ' 2-type Na-0.67[Ni0.1Fe0.1Mn0.8]O-2 is introduced as a promising new cathode material for sodium-ion batteries (SIBs) that exhibits remarkable structural stability during repetitive Na+ de/intercalation. The O-Ni-O-Mn-O-Fe-O bond in the octahedra of transition-metal layers is used to suppress the elongation of the Mn-O bond and to improve the electrochemical activity, leading to the highly reversible Na storage mechanism. A high discharge capacity of approximate to 220 mAh g(-1) (approximate to 605 Wh kg(-1)) is delivered at 0.05 C (13 mAg(-1)) with a high reversible capacity of approximate to 140 mAh g(-1) at 3 C and excellent capacity retention of 80% over 200 cycles. This performance is associated with the reversible P ' 2-OP4 phase transition and small volume change upon charge and discharge (approximate to 3%). The nature of the sodium storage mechanism in a full cell paired with a hard carbon anode reveals an unexpectedly high energy density of approximate to 542 Wh kg(-1) at 0.2 C and good capacity retention of approximate to 81% for 500 cycles at 1 C (260 mAg(-1)).