Tailoring Cu-rich surface spinel phase for high-performance O3-type layered cathode materials for sodium-ion batteries

O3-type layered oxide cathodes are primarily limited by complex phase transitions and sluggish kinetics resulting in rapid capacity drop and poor rate capability. Even worse, its inherent air sensitivity leads to spontaneous extraction of lattice Na-ions and the deactivation of the cathode. Simultaneous modification of both the bulk phase and the surface structure is promising to offset the above deficiencies. A spinel@O3 type layered composite structure Na0.9Mn0.5Ni0.5Cu0.1O2+x (NMNCO-SL) was constructed for the design of cathodes with higher cycling, rate and air stability. The atomic-level Cu-rich spinel structure on the surface was identified by scanning transmission electron microscopy, elemental linear scanning analysis and Raman spectra. In situ charge-discharge X-ray diffraction results show that the phase transition of NMNCO-SL is significantly suppressed. Finally, the material maintains good electrochemical properties after exposure to stringent humidity environments. The results indicate that the spinel structure at the surface plays a significant role in improving ion-diffusion dynamics, enhancing structural integrity, and increasing air stability. 1 Ah pouch cell based on NMNCO-SL showed 92% capacity retention after 500 cycles of charge/discharge cycling at 1 C, demonstrating the potential prospects of customizing the surface phase structure for materials engineering applications.