P3‐Na0.45Ni0.2Mn0.8O2/Na2SeO4 Heterostructure Enabling Long‐Life and High‐Rate Sodium‐Ion Batteries

Abstract Sodium‐based layered oxide cathodes are competitive candidates for commercial sodium‐ion batteries owing to their high theoretical capacities, low costs, and simple synthesis. P3‐type layered oxides with large open channels enable fast Na + transport and hence good rate performance. However, the lower crystal symmetry of P3‐type oxides and variation of Na + contents in the Na layer during desodiation/sodiation lead to large electrostatic repulsion changes between TMO 2 slabs (TM=Transition Metal), resulting in irreversible phase transitions, and fast performance degradation. Herein, a potential Na + conductor Na 2 SeO 4 is first found that it can be easily in situ grown on P3‐Na 0.45 Ni 0.2 Mn 0.8 O 2 to form a novel heterostructure P3‐Na 0.45 Ni 0.2 Mn 0.8 O 2 /Na 2 SeO 4 . The synergy between P3‐Na 0.45 Ni 0.2 Mn 0.8 O 2 and Na 2 SeO 4 functions in promoting Na + diffusion and suppressing P3‐O3 phase transitions upon deep sodiation, which results in recorded high‐rate capability (68.2% capacity retention with retained 83.9 mAh g −1 capacity at 6400 mA g −1 ) and superior cycling stability (capacity retention 75% after 1000 cycles) among all reported P3‐type cathodes. Thus, it is believed that this novel heterostructure design opens a new pathway to promote practical applications for layered oxide cathodes in sodium‐ion batteries.