Hierarchical O3/P2 heterostructured cathode materials for advanced sodium-ion batteries

O3-type layered materials are considered as promising cathode materials for advanced sodium-ion batteries owing to their low cost and high energy density. However, resultant cathodes undergo complex phase transitions and severe electrochemical corrosion during cycling, causing rapid capacity decay. To overcome these limitations, a heterostructured cathode, consisting of P2-Na2/3MnO2–coated O3-NaNi0.5Mn0.5O2 that combines a high-capacity core and structurally stable shell, is rationally designed. A half cell with an optimized heterostructured cathode yields a high reversible capacity of 141.4 mA h g−1 at 0.1 C and exhibits excellent rate capability, with a capacity of 103.7 mA h g−1 at 15 C. In addition, the surface-modified cathode also shows improved cycling stability in both Na half cell (i.e. 85.3% capacity retention after 150 cycles at 1 C) and full cell systems (i.e. 83.6% capacity retention after 200 cycles at 3 C). The protective P2-Na2/3MnO2 layer not only enhances the reversibility and air/thermal stability of the cathode, but also improves the electrochemical kinetics and reduces the charge transfer resistance. Hence, the sodium storage performance of O3-NaNi0.5Mn0.5O2 is greatly improved by employing the proposed heterostructure design approach, which can be extended to other Mn-based layered oxide cathode materials.