NaTi2(PO4)3 modified O3-type NaNi1/3Fe1/3Mn1/3O2 as high rate and air stable cathode for sodium-ion batteries

Layered transition metal oxides O3-NaNi1/3Fe1/3Mn1/3O2(NFM) have been extensively studied due to their low cost and high reversible specific capacity. However, the inferior rate and cycle performance, as well as the poor air stability severely limit its practical applications. In this work, O3-NaNi1/3Fe1/3Mn1/3O2 is successfully modified with an unintermittent and thin NaTi2(PO4)3 (NTP) coating layer, which plays a critical role in pre-venting the highly corrosive hydrofluoric acid (HF) attacks from decomposition of electrolyte and subsequent dissolution of the redox-active metal from the cathode particles. Meanwhile, partial Ti4+ ions were doped in the bulk NaNi1/3Fe1/3Mn1/3O2, which can enlarge the interslab spacing. DFT calculations confirm the reduced Na+ migration energy barrier for the as produced sample. As a consequence, the NTP coated NFM sample presents a superior rate capacity (103.1 mAh g-1 at 5 C), significantly enhanced capacity retention (77.5% at 1 C after 100 cycles), outperforming the state of the art literatures. Besides, the air stability of the sample is well improved and the full cells deliver good cyclic performance when coupled with hard carbon, which will promote the large-scale application of O3-tpye cathode material.