Mn‐Rich P′2‐Na<sub>0.67</sub>[Ni<sub>0.1</sub>Fe<sub>0.1</sub>Mn<sub>0.8</sub>]O<sub>2</sub> as High‐Energy‐Density and Long‐Life Cathode Material for Sodium‐Ion Batteries
Ji Ung Choi, Jae Hyeon Jo, Yun Ji Park, Kug‐Seung Lee, Seung‐Taek Myung
Abstract
Abstract Herein, P′2‐type Na 0.67 [Ni 0.1 Fe 0.1 Mn 0.8 ]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 ONiOMnOFeO bond in the octahedra of transition‐metal layers is used to suppress the elongation of the MnO bond and to improve the electrochemical activity, leading to the highly reversible Na storage mechanism. A high discharge capacity of ≈220 mAh g −1 (≈605 Wh kg −1 ) is delivered at 0.05 C (13 mAg −1 ) with a high reversible capacity of ≈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 (≈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 ≈542 Wh kg −1 at 0.2 C and good capacity retention of ≈81% for 500 cycles at 1 C (260 mAg −1 ).