Spinel Li4–2xCo3xTi5–xO12 (0 ≤ x ≤ 0.5) for Lithium-Ion Batteries: Crystal Structures, Material Properties, and Battery Performances

Although disordered spinel Li 4 Ti 5 O 12 with Fd 3̅ m space group is an attracting anode material for lithium ion batteries, it suffers from its poor rate performance. Moreover, there are very limited studies of ordered spinel anode materials with P 4 3 32 space group. Here, spinel Li 4–2 x Co 3 x Ti 5– x O 12 materials with Fd 3̅ m (0 ≤ x ≤ 0.2) or P 4 3 32 (0.25 ≤ x ≤ 0.5) space group have been synthesized. The lattice parameter and occupancy of Co 2+ ions in tetrahedral 8a/8c sites quasi-linearly increase with the amount of Co 2+ substitutes. Due to the increased lattice parameter and free 3d electrons in Co 2+ ions, Co 2+ -substituted samples exhibit improved Li + ion diffusion coefficients and electronic conductivities. The optimized sample, Li 3.5 Co 0.75 Ti 4.75 O 12 with P 4 3 32 space group, shows the highest Li + ion diffusion coefficient of 9.07 × 10 –11 cm 2 s –1 and electronic conductivity of 1.49 × 10 –7 S cm –1 . Consequently, Li 3.5 Co 0.75 Ti 4.75 O 12 has the best rate performance with a large capacity of 158 mAh g –1 at a current density of 1000 mA g –1, while Li 4 Ti 5 O 12 only possesses 70 mAh g –1 . Furthermore, the considerable occupancy of Co 2+ ions in the tetrahedral sites tailors the shape of discharge profiles. Li 3.5 Co 0.75 Ti 4.75 O 12 exhibits a much smaller plateau hysteresis than the previously developed spinel anode materials with the same space group.