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

Abstract P2‐type Na 2/3 Ni 1/3 Mn 2/3 O 2 (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 0.696 Ni 0.329 Mn 0.671 O 2 (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 2/3 Ni 1/3 Mn 2/3 O 2 , and also provides a universal strategy to improve the rate and cycling life of P2‐type layered oxide cathode materials.