P3-Na_0.45Ni_0.2Mn_0.8O₂/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-Na_0.45Ni_0.2Mn_0.8O₂ to form a novel heterostructure P3-Na_0.45Ni_0.2Mn_0.8O₂/Na₂SeO₄. The synergy between P3-Na_0.45Ni_0.2Mn_0.8O₂ 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. © 2023 Wiley-VCH GmbH.