Layered transition-metal oxides are among the most promising sodium-ion battery cathodes owing to their high specific capacities and structurally tunable frameworks. However, the prototypical P2-Na0.67Ni0.33Mn0.67O2(NM) undergoes an irreversible P2 → O2 phase transition at high voltages, accompanied by severe lattice strain and capacity fade, which hinders practical deployment. Here, we propose a cooperative regulation strategy that couples Zn/Al co-doping with Na enrichment, and successfully synthesize P2-Na0.80Ni0.14Zn0.14Mn0.58Al0.14O2(NMZA-N14). The optimized NMZA-N14 delivers an initial discharge capacity of 125 mAh g−1at 0.1C and demonstrates exceptional cycling and rate performance, retaining 98.6% of its capacity after 100 cycles at 0.2C and 93.6% after 200 cycles at 1C. Kinetic analyses indicate a higher Na+diffusion coefficient and a lower charge-transfer resistance in NMZA-N14, evidencing substantially accelerated ion transport. In situ X-ray diffraction further reveals a reversible P2 → OP4 phase transition in the high-voltage regime with a unit-cell volume change of only ~2.27%, thereby avoiding the irreversible structural degradation observed in NM. This synergistic modulation markedly enhances structural stability and electrochemical kinetics, providing a viable pathway for the rational design of high-performance sodium-ion battery cathodes.
Mingxing Li,Wenda Zhang,Xiaoge Wang,Xiaofan Cao,Chunjun Liang,Xiaojun Kuang,Jing Ju,Fangtian You
Despite remarkable progress in the synthesis of rare-earth nanomaterials, achieving precise control over the distribution of lanthanide ion (Ln3+) dopants remains a formidable challenge. Previous studies that utilized NaYF4 with mixed cation occupancy have offered valuable insights into nonuniform elemental doping and its influence on the emission properties of the materials. However, the complex interplay among cation distribution, structural transformation, and luminescent characteristics has not been fully understood and elucidated. This lack of comprehensive knowledge significantly hinders the optimization of the performance of nanomaterials. In this study, the structural transformation of individual β-NaYF4:Eu3+ nanoparticles under electron beam irradiation was systematically investigated. A discovery was made regarding the transition to a cubic phase. Elemental analysis of the pristine samples revealed that sodium was enriched at the edges of the nanoparticles. This sodium enrichment seemingly initiates the structural transition, which propagates from the surface toward the interior of the particles. Correlated cathodoluminescence electron microscopy (CCLEM) was employed in this research. The results confirmed that the emission intensity is highly correlated with the elemental distribution. Moreover, the structural disorder within the cubic phase leads to a decrease in the site symmetry compared to the theoretical Eu3+ luminescence. Overall, this study provides a more in-depth understanding of how elemental distribution impacts both the structural features and luminescent behavior of these materials. As a result, it makes a significant contribution to the development of optimized nanomaterials with enhanced performance.
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