In-situ forming NaTi2(PO4)3 coating layer to enhance the high-temperature performance of NaNi1/3Fe1/3Mn1/3O2 cathode material

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 NaNi1/3Fe1/3Mn1/3O2 through an in situ reaction involving nano-TiO2, Na2CO3 and NH4H2PO4. During the high-temperature calcination process, partial Ti-atom diffusion into the NaNi1/3Fe1/3Mn1/3O2 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 NaNi1/3Fe1/3Mn1/3O2 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.