Dopant alliance: K/Cu cooperative bonds lock structural stability in P2-type sodium cathodes

Sodium-ion batteries (SIBs) are gaining traction for large-scale energy storage due to sodium's abundance and cost efficiency, yet the structural instability and slow ion transport of P2-type cathodes remain critical challenges. This study employs a high-temperature solid-state approach to develop K/Cu co-doped cathodes, demonstrating that co-doping preserves the P2 phase while optimizing lattice parameters to expand interlayer spacing. The reduction in Mn 3+ content suppresses the Jahn-Teller effect and mitigates P2-O2 phase transitions, enhancing structural reversibility. The optimal K 0.05 Na 0.7 Ni 0.23 Mn 0.67 Cu 0.1 O 2 exhibits a high initial discharge capacity of 123.8 mAh·g −1 at 20 mA·g −1 and maintains 96.80 % capacity after 200 cycles at 200 mA·g −1 , outperforming single K-doped samples (89.83 % retention). Kinetic analyses reveal a sodium-ion diffusion coefficient of 1.06 × 10 −10  cm 2 ·s −1 , attributed to enlarged interlayers and reduced charge transfer resistance. In-situ XRD confirms minimal (002) peak shift (0.42°) during cycling, validating structural stability from K + -pinned interlayers. DFT calculations indicate that Cu doping induces spin-polarized half-metallic behavior, enhancing electron conductivity by increasing density of states near the Fermi level. This work presents a “dual-functional co-doping” strategy in which K + stabilizes interlayers and Cu 2+ optimizes the electronic structure, thereby simultaneously suppressing phase transitions and enhancing ion/electron transport. The proposed approach provides a scalable route for developing high-performance SIBs cathodes, which is crucial for advancing affordable and durable energy storage solutions.