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

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 TMO2 slabs (TM=Transition Metal), resulting in irreversible phase transitions, and fast performance degradation. Herein, a potential Na+ conductor Na2SeO4 is first found that it can be easily in situ grown on P3-Na0.45Ni0.2Mn0.8O2 to form a novel heterostructure P3-Na0.45Ni0.2Mn0.8O2/Na2SeO4. The synergy between P3-Na0.45Ni0.2Mn0.8O2 and Na2SeO4 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.