High Energy Density Heterostructured Sodium Layered Oxide Cathodes Enabled by Mechanical-Chemical Coupling Effect

Designing cobalt-free manganese-based oxide cathode materials with high energy density and excellent stability is of great significance and a challenge. Here, we construct a P2/O3 core-shell heterostructured layered oxide cathode material with a mechanical-chemical coupling effect to achieve precise structural modulation and superior electrochemical performance. Using O3-NaNi_0.4Fe_0.2Mn_0.4O₂ as the core material, the P2/O3 core-shell heterostructured cathode was obtained by accurately regulating the epitaxial layer. Benefiting from the synergistic effect of the O3 bulk phase and P2 shell layer, this heterostructured cathode shows a high energy density (587.34 Wh·kg^-1, based on cathode active materials), excellent structure, superior air stability, and full cell performance. The phase transition mechanism of the cathode as well as the atomic arrangement characteristics were analyzed by in situ X-ray diffraction and spherical aberration-corrected scanning transmission electron microscopy (STEM), respectively. Most importantly, it was verified using stress simulation calculations that the P2 shell layer can share the mechanical stress of the internal O3 bulk phase on a micro-scale, suppressing the plastic yielding and structural degradation of the material during electrochemical processes, and dramatically enhancing the structural stability. The heterostructured cathode with the mechanical-chemical coupling effect designed in this study will provide new insights for the optimization of other electrode materials.