Preparation and electrochemical performance of F-doped Li4Ti5O12 for use in the lithium-ion batteries

Spinel Li 4 Ti 5 O 12 doped with F was synthesized via the solid-state reaction of anatase TiO 2 , Li 2 CO 3 , and NH 4 F. The structural characterization and electrochemical performance evaluation of the prepared materials were carried out utilizing X-ray diffraction, scanning electron microscopy, galvanostatic charge-discharge, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) tests. The lattice parameters of all samples were calculated using an internal standard and Rietveld refinement method. The results indicate that the F was successfully doped into the lattice structure of Li 4 Ti 5 O 12 , and this process did not influence the crystal structure and superficial morphology. Moreover, the best-performing material, Li 4 Ti 5 O 11.9 F 0.1 delivers superior rate capacities of 165, 162.1, 160.0, 142.3, 125.1, and 99.2 mAh g −1 , at 0.2 C, 0.5 C, 1 C, 3 C, 5 C, and 10 C, respectively, which is higher than those of Li 4 Ti 5 O 12 (150.0, 135.0, 123.5, 93.7, 76.4, and 56.8 mAh g −1 at the same C-rates), and the cycling retention is 82.7% after 150 cycles at 5 C. Meanwhile, the charge-transfer resistance (R ct ) of Li 4 Ti 5 O 11.9 F 0.1 (56.4 Ω) is lower than that of pure Li 4 Ti 5 O 12 (80.6 Ω), and the lithium-ion diffusion coefficients (D Li + ) of Li 4 Ti 5 O 11.9 F 0.1 (2.505 × 10 −10  cm 2  s −1 ) is higher than that of pure Li 4 Ti 5 O 12 (1.694 × 10 −10  cm 2  s −1 ).