A Novel Rare-Earth/Anion Synergistic Doping Strategy Enhances the Structural Stability and Sodium-Ion Diffusion Kinetics of Superlattice Layered Oxide Cathode

Sodium-ion batteries (SIBs) are highly promising for large-scale energy storage due to the abundance and low cost of sodium resources. Among various cathode materials, layered transition metal oxides are considered one of the most commercially viable systems, thanks to their high theoretical capacity, mature synthesis processes, and favorable two-dimensional ion diffusion pathways that enable fast ion transport. However, their practical application is still hindered by challenges such as structural instability and interfacial side reactions. Conventional single-element doping strategies often struggle to address these multiple issues simultaneously. This study focuses on the superlattice-structured P2–Na 0.80 Li 0.13 Ni 0.20 Mn 0.67 O 2 cathode material. A TbF 3 synergistic doping strategy is employed to achieve concurrent optimization of the crystal structure and interfacial chemistry. The doping effectively promoted reversible anionic redox reactions while suppressing electrolyte decomposition and interfacial side reactions. Electrochemical tests reveal that the optimized sample exhibits a capacity retention of 84.01% after 200 cycles at 0.5 C within the voltage range of 2–4.5 V and delivers a capacity of 94.08 mAh g –1 at a high rate of 5 C, significantly outperforming the undoped sample. This work provides a novel rare-earth and anion synergistic doping strategy for designing high-performance SIBs.