Core-Shell Layered Oxide Cathode for High-Performance Sodium-Ion Batteries.

Sodium layered oxides are considered to be cathode candidates with the most potential for large-scale energy storage because of their high reversible capacity and wide availability of sodium resources. A significant hurdle to wide application of these layered oxides lies in simultaneously satisfying high-energy density and long cycle life because of the intrinsic problems associated with their structural irreversibility. Herein, a O3/O'3-P2 core-shell composite that integrates a high specific capacity from O-type Ni-based core and good structural stability from P2-type Mn-rich shell is presented. Multiscale electron microscopy and affiliated spectroscopy analyses reveal that, in addition to the microscale O3/O'3-P2 core-shell structure, a nanoscale coherent P2/O3 intergrown structure can also be identified in the composite. Such well-tailored structures not only constrain the structural damages (microscale cracks) induced by repeated volumetric changes upon desodiation and resodiation but also facilitate fast Na ions diffusion through the exterior P2-type layered structure. This work may provide new clues into the design of high-performance cathode materials for sodium-ion batteries.