Regulating Na Occupation in P2‐Type Layered Oxide Cathode for All‐Climate Sodium‐Ion Batteries

Abstract P2‐type Na_2/3Ni_1/3Mn_2/3O₂ (NNMO) has been investigated as one of the promising cathode materials of sodium‐ion batteries (SIBs) due to a low‐cost and wide‐temperature‐range adaptability. However, its application faces a number of obstacles because of the poor cycling stability and bad rate capabilities. Herein, by accommodating more Na‐ions at the e‐site (Na_e) in P2‐type NNMO, which is thermodynamically more stable, P2‐type layered oxides (Na_e/Na_f > 1.64) with outstanding electrochemical performance are obtained. Specifically, the Na_0.696Ni_0.329Mn_0.671O₂ (NM‐2) exhibits a remarkable capacity retention of 71.9% after 1000 cycles at 1C and an excellent rate capability of 54.33 mAh g⁻¹ at 50C. In addition, NM‐2 exhibits a wide temperature working range, even at extreme temperatures for batteries (−30 or 60 °C), it still shows a capacity close to room temperature and good cycle stability compared with 25 °C. These performances are demonstrated to be attributed to the fast kinetics of the Na ions in the Na_e site, which has a lower energy barrier compared to Na_f (0.8301 eV for edge sites and 1.0664 eV for face sites). This work gives a fundamental understanding of the Na‐storage mechanism in Na_2/3Ni_1/3Mn_2/3O₂, and also provides a universal strategy to improve the rate and cycling life of P2‐type layered oxide cathode materials.