Single-step solid-state synthesis and characterization of Li₄Ti_{5-: X}Fe_xO_{12- y} (0 ≤ x ≤ 0.1) as an anode for lithium-ion batteries

We carried out a single-step doping reduction, Li₄Ti_5-xFe_xO_12-y (0 ≤ x ≤ 0.1) with Fe, by a facile solid-phase method with the objective of improving the electrochemical performance of Li₄Ti₅O₁₂ (LTO). Unlike the conventional method of using an Fe salt as a dopant, elemental Fe is used here as both a reducing agent and a dopant. The Fe first reacts with TiO₂ to form Ti³⁺ and Fe³⁺ ions; the Fe³⁺ ions then incorporate into the TiO₂ crystal lattice through substitution of Ti by Fe; the amount of Ti³⁺/Ti⁴⁺ is increased as a result of charge compensation, which further improves the conductivity of the LTO, resulting in high electrochemical performance. The investigation of the electrochemical performance of lithium-ion batteries under low-voltage conditions is important for assessing their safety. Because LTO can provide a higher battery voltage and a discharge capacity at a lower voltage, the electrochemical behavior of LTO in the voltage range 0-3 V was also investigated. The modified Li₄Ti_5-xFe_xO_12-y exhibits a capacity of 228.7 mA h g^-1 after 200 cycles, which is substantially higher than that of pure LTO (176.3 mA h g^-1). In addition, the band structure and density of states (DOS) of the original and Fe-doped Li₄Ti₅O₁₂ were calculated by first-principles calculations. The Li₄Ti_5-xFe_xO_12-y (0 ≤ x ≤ 0.1) can provide a higher voltage, enabling its broad application in lithium-ion batteries because of its large discharge range, good electrochemical performance, and simple synthesis process.