Low-Cost Orthorhombic Nax[FeTi]O4 (x = 1 and 4/3) Compounds as Anode Materials for Sodium-Ion Batteries

Abundant and low-cost sodium, iron, and titanium have great potentials to act as raw materials for large-scale power sources. Here we report the synthesis of novel orthorhombic Nax[FeTi]O4 (x = 1 and 4/3) anode materials by a solid-state reaction method and their electrochemical behaviors in sodium-ion batteries. These materials are able to reversibly insert additional Na+ ions and show very good cycling stabilities. In particular, the Na4/3[FeTi]O4 material can deliver a high reversible capacity of 120 mA h g-1 at 0.1 C, and cyclic voltammetry (CV) investigation proves that there is no phase transformation during testing cycles. The Na[FeTi]O4 material exhibits an even higher initial charge capacity of 181 mA h g-1 at 0.1 C, and in situ X-ray diffraction (XRD) results indicate that Na+ ions behave in topotactic insertion and extraction manners inside this material. Meanwhile, gas evolutions during the initial redox process are analyzed by an operando mass spectrometry technique. The result suggests that the Na[FeTi]O4 material exhibits an enhanced safety.