Interfacial and lattice synergy enabled by Cu/Al dual doping and carbon coating in O3-type sodium-ion battery cathodes

Sodium ions in the O3 structure not only have more potential Na⁺ deintercalation and intercalation, but also have a higher sodium storage capacity. O3-type layered transition metal oxides are regarded as promising cathode materials for sodium-ion batteries owing to their high theoretical capacity. However, their practical application is severely hindered by structural degradation, aggravated interfacial side reactions, and sluggish Na⁺ diffusion kinetics during cycling. To address these challenges, an integrated Cu/Al dual-doping and carbon coating strategy is proposed in this work to regulate both the lattice and interfacial characteristics, leading to the construction of a highly stable composite cathode material (denoted as NFMCA@C). Structural characterizations reveal that the synergistic incorporation of Cu and Al effectively tailors the local lattice environment of the transition metal layers, thereby mitigating structural distortion and phase instability induced by the Jahn-Teller effect during repeated Na⁺ insertion/extraction. Meanwhile, the uniform carbon coating forms a continuous conductive network on the particle surface, which not only enhances electronic conductivity but also suppresses detrimental electrode-electrolyte interfacial reactions. As a result, the NFMCA@C cathode delivers improved cycling stability and rate capability while maintaining a considerable specific capacity. Kinetic analyses further demonstrate that the combined effects of dual doping and carbon coating significantly reduce charge-transfer resistance and facilitate Na⁺ diffusion. This work provides an effective multiscale design strategy for simultaneously stabilizing the lattice structure and interface of O3-type layered cathodes for advanced sodium-ion batteries.