Polyanion-induced interfacial reconstruction enabling the development of air-stable single-crystal high-nickel cathodes

Single-crystal high-nickel layered oxides are regarded as highly promising cathode materials for next-generation lithium-ion batteries with high energy density because of their crack-resistant morphology and high packing density. However, their large-scale applications are still severely restricted by poor air-storage stability during storage and electrode fabrication. Even short-term air exposure can trigger Li⁺/H⁺ exchange, surface carbonate accumulation, and irreversible phase transitions, leading to pronounced kinetic deterioration and rapid capacity decay. Herein, a small-amount (∼0.5 wt%) polyanion interfacial engineering strategy is proposed to enable the development of single-crystal high-Ni cathodes with markedly improved air stability and electrochemical durability. By constructing a chemically bonded and Li⁺-conducting LPO-derived phosphate-rich interphase, this strategy not only protects the highly reactive surface from air attack but also preserves interfacial lithium transport. As a result, after 7 days of air exposure, the modified cathode retains 97.8% of its initial capacity, whereas only 76.6% is retained for the unmodified pristine materials. Meanwhile, the modified sample exhibits improved cycling stability and superior rate capability. HRTEM, soft X-ray absorption spectroscopy, Fourier-transform infrared spectroscopy and depth-resolved XPS collectively reveal that polyanion-induced near-surface reconstruction enables a chemically coupled phosphate-rich interphase to suppress parasitic surface reactions, inhibit Ni reduction and rock-salt phase formation and stabilize lattice oxygen coordination. This small-amount and scalable modification strategy thus provides an effective solution for improving the storage and processing reliability of single-crystal high-nickel cathodes under practical ambient storage conditions.