Roles of Coherent Interfaces on Electrochemical Performance of Sodium Layered Oxide Cathodes

Sodium layered cathode materials with higher specific capacity and enhanced cyclability are desired for advanced Na-ion batteries (NIBs). This work presents the controlled synthesis of a class of multiphasic P-/O-type Li-substituted NaxLi0.18Mn0.66Ni0.17Co0.17O2 layered composites. Complementary electron microscopy and X-ray-based spectroscopy analyses at multilength scales reveal that nanoscale intergrown nanostructures with various coherent-interface densities are featured in these layered composites. Improvements in electrochemical kinetics and cycling performance are observed in the triphasic P3/P2/O′3 composite with a larger amount of coherent-interface density. The interphasic strain induced by the lattice mismatch along the a/b plane between the Na–P3, Na–P2, and Li–O′3 phases may not only effectively suppress P3–P3″ and P2–P2″ phase transitions that account for enhanced cyclability but also facilitate smooth and fast Na diffusion between the prismatic sites leading to enhanced rate capability. Moreover, the gradual electrochemical activation process triggered by Li–O′3 phase in P2-containing composites is believed to play a positive role on the electrochemical kinetics of the composite materials.