Na-Rich Layered Transition Metal Oxides with Core/Shell Structures for Improved Performance of Sodium-Ion Batteries

While P2-type layered transition metal oxides are regarded as potential cathode candidates for sodium-ion batteries because of the high theoretical capacity and a wide operating voltage window, they still suffer from low capacity and sluggish sodium-ion kinetics. Here, we report a Na0.67Mn0.66Co0.17Ni0.17O2 cathode material with a core/shell structure. P2-Na0.67Mn0.66Co0.17Ni0.17O2 has exhibited excellent discharge specific capacity (266 mAh g-1 at 0.1 C and 89 mAh g-1 at 5 C) and ultralong cycle stability, which are among the best state-of-the-art values for Na-based Na-ion batteries. The superior stability results from core/shell structures composed of nanosheets, and the space between the core and shell effectively relieves the volume expansion caused by the deintercalation of sodium ions. Transition metal doping effectively improves the structural distortion caused by the Jahn-Teller effect and provides high sodium mobility, creating higher specific capacity. These findings provide new ideas for the design and development of high-performance sodium-ion battery cathode materials.