The formation mechanism of Li4Ti5O12−y solid solutions prepared by carbothermal reduction and the effect of Ti3+ on electrochemical performance

摘要

Samples of Li4Ti5O12−y solid solutions are synthesized by one-step solid-state carbothermal reduction reaction using Li2CO3, anatase, and carbon black under a nitrogen atmosphere. The underlying formation mechanism that leads to Li4Ti5O12−y solid solutions is proposed. The formation mechanism of the Li4Ti5O12−y solid solution is investigated by in situ variable temperature X-Ray diffraction (VT-XRD) and thermogravimetric analysis/differential scanning calorimetry (TGA-DSC). First, some Ti⁴⁺ centers are converted to Ti³⁺ (TiO2-TiO2−x) because of the presence of carbon black. Secondly, Li2CO3 reacts with TiO2−x (anatase) to form Li₂TiO₃. Thirdly, Li₂TiO₃ reacts with TiO_2−x to form the Li₄Ti₅O_12−y solid solution, while anatase starts to transform into rutile at the same time. Rutile reacts with Li₂TiO₃ to form Li₄Ti₅O_12−y at higher temperatures. The presence of Ti³⁺ not only improves the electrical conductivity but also improves the ionic conductivity. As a result, the as-prepared material exhibits good rate capability and cycling stability with 99.3% capacity retention after 200 cycles.