Preparation and electrochemical properties of Mg2+ and F− co-doped Li4Ti5O12 anode material for use in the lithium-ion batteries

Abstract Spinel Li 4 Ti 5 O 12 co-doped with Mg 2+ and F − was synthesized by solid-state reaction of anatase TiO 2 , Li 2 CO 3 , NH 4 F, and Mg(NO 3 ) 2 . For comparison, Mg 2+ -doped and F − -doped Li 4 Ti 5 O 12 were prepared using the same method. The structure and electrochemical performance of the prepared materials were investigated by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, electrochemical impedance spectroscopy, and galvanostatic charge-discharge tests. Using an internal standard and Rietveld refinement, we calculated the lattice parameters of the samples. After co-doping with Mg 2+ and F − , the dopant ions enter the Li 4 Ti 5 O 12 lattice, resulting in the reduction of Ti 4+ to Ti 3+ , and increasing the conductivity of the material. Furthermore, the Mg 2+ and F − co-doping technique resulted in smaller primary particles with a narrow size distribution, factors that can accelerate transfer of Li + between the electrode and electrolyte. Consequently, the Mg 2+ and F − co-doped Li 4 Ti 5 O 12 material exhibits a superior rate performance and delivers discharge capacities of 159.4, 154.1, 146.5, 120.8, 102.7, and 76 mAh g −1 at 0.2C, 0.5C, 1C, 3C, 5C, and 10C, respectively, significantly higher than those of pure Li 4 Ti 5 O 12 (155.4, 138.6, 124.2, 94.1, 76.7, and 52.2 mAh g −1 at the same C-rates). Moreover, the Mg 2+ and F − co-doped Li 4 Ti 5 O 12 showed outstanding cycling stability, and the capacity retention was 99.62% after 150 cycles at 5C rate. Therefore, the Mg 2+ and F − co-doping technique has proven an effective approach to improve the electrochemical performance of Li 4 Ti 5 O 12 .