In situ formation of NaTi 2 (PO 4 ) 3 coating layers to enhance the high-temperature performance of NaNi 1/3 Fe 1/3 Mn 1/3 O 2 cathode materials

The insufficient structure and interfacial stability of O3-type layered oxide cathode materials hinder their practical application in sodium-ion batteries, particularly at high temperatures. In this study, a thin, island-like NaTi₂(PO₄)₃ coating layer (∼15 nm) is constructed on the surface of NaNi_1/3Fe_1/3Mn_1/3O₂ through an in situ reaction involving nano-TiO₂, Na₂CO₃ and NH₄H₂PO₄. During the high-temperature calcination process, partial Ti-atom diffusion into the NaNi_1/3Fe_1/3Mn_1/3O₂ lattice results in the expansion of the interslab of the sodium layer and a reduction in lattice oxygen vacancies. Benefitting from the stable NaTi₂(PO₄)₃-modified interface and enhanced structural stability, the NaNi_1/3Fe_1/3Mn_1/3O₂ coated with 2 wt% NaTi₂(PO₄)₃ exhibits optimal cycle stability at high temperature. It retains 90.3% of its initial capacity after 100 cycles at 0.5C (1C = 130 mA g^-1, 45 °C). This dual-modification strategy, obtained from a facile approach, has the potential to facilitate the practical application of O3-type layered oxide cathode materials.