Enhanced sodium-ion storage with Fe3O4@Na2Ti3O7 nanoleafs

In this work, uniform Fe3O4@Na2Ti3O7 (FNTO) nanoleafs coated with N-doped C (FNTO-CN) were synthesized through the hydrothermal reaction of Fe nanoparticles and TiO2 powders in concentrated NaOH solution. FNTO exhibited a wider layer spacing and a more fluent Na-ion exchange effect than pure Na2Ti3O7 (NTO). Afterwards, FNTO-CN composites were prepared via a facile solid-state method, with folic acid as C and N sources, as coated C could increase the overall conductivity. When FNTO or FNTO-CN was tested as a working electrode in a half-cell versus Na metal, they exhibited high-capacity densities of 142 and 175 mAh g−1 ​at 5C, respectively. They also showed stability of 1000 cycles owing to the high Na-ion diffusion rate and electron transport capability. Besides, a full cell assembled using the FNTO-CN anode with Na2/3(Ni1/3Mn2/3)O2 cathode afforded an energy density of ~117 ​Wh kg−1 (based on the mass of both electrodes). This interlayer engineering may provide a useful tool to develop high-performance anode materials, and folic acid is a promising dual C and N source for modifying the properties of anode/cathode materials.