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

Although disordered spinel Li4Ti5O12 with Fd (3) over barm 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 P4(3)32 space group. Here, spinel Li4-2xCo3xTi5-xO12 materials with Fd (3) over barm (0 <= x <= 0.2) or P4(3)32 (0.25 <= x <= 0.5) space group have been synthesized. The lattice parameter and occupancy of Co2+ ions in tetrahedral 8a/8c sites quasi-linearly increase with the amount of Co2+ substitutes. Due to the increased lattice parameter and free 3d electrons in Co2+ ions, Co2+-substituted samples exhibit improved Li+ ion diffusion coefficients and electronic conductivities. The optimized sample, Li3.5Co0.75Ti4.7O12 with P4332 space group, shows the highest Li+ ion diffusion coefficient of 9.07 X 10(-11) cm(2) s(-1) and electronic conductivity of 1.49 X 10(-7) S cm(-1). Consequently, Li3.5Co0.75Ti4.75O12 has the best rate performance with a large capacity of 158 rnAh g(-1) at a current density of 1000 mA g(-1), while Li4Ti5O12 only possesses 70 mAh g(-1). Furthermore, the considerable occupancy of Co2+ ions in the tetrahedral sites tailors the shape of discharge profiles. Li3.5Co0.75Ti4.75O12 exhibits a much smaller plateau hysteresis than the previously developed spinel anode materials with the same space group.