The formation mechanism of Li(4)Ti(5)O(12−y) solid solutions prepared by carbothermal reduction and the effect of Ti(3+) on electrochemical performance

Samples of Li(4)Ti(5)O(12−y) solid solutions are synthesized by one-step solid-state carbothermal reduction reaction using Li(2)CO(3), anatase, and carbon black under a nitrogen atmosphere. The underlying formation mechanism that leads to Li(4)Ti(5)O(12−y) solid solutions is proposed. The formation mechanism of the Li(4)Ti(5)O(12−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 Ti(4+) centers are converted to Ti(3+) (TiO(2)-TiO(2−x)) because of the presence of carbon black. Secondly, Li(2)CO(3) reacts with TiO(2−x) (anatase) to form Li(2)TiO(3). Thirdly, Li(2)TiO(3) reacts with TiO(2−x) to form the Li(4)Ti(5)O(12−y) solid solution, while anatase starts to transform into rutile at the same time. Rutile reacts with Li(2)TiO(3) to form Li(4)Ti(5)O(12−y) at higher temperatures. The presence of Ti(3+) 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.