High power and high safety materials for Li-ion battery

The photos and X-ray diffraction patterns of TNO annealed in air and vacuum are compared in Fig. 1. Although the crystal structure is not changed by the different annealing atmosphere, the color of TNO is changed from white to dark blue by vacuum annealing, indicating the presence of the mixed Ti⁴⁺/Ti³⁺ ions.

Thermogravimetric analysis clearly shows that a small amount of oxygen vacancy is introduced by vacuum annealing, which causes partial reduction from Ti⁴⁺ to Ti³⁺ in TNO. By addressing this fact, vacuum-annealed TNO (V-TNO) shows much higher electronic conductivity (10^-6-10^-5 S cm^-1) than air-annealed TNO (A-TNO) at room temperature.

Fig. 2 shows a comparison of the charge and discharge curves of both A-TNO and V-TNO electrodes at various fixed current densities per unit electrode area of 0.5, 2, 4 and 7 mA cm^-2. The charge and discharge capacities for both electrodes are decreased monotonically with increasing current densities, but V-TNO shows larger capacity than A-TNO under the current density above 2 mA cm^-2. This tendency becomes more remarkable as the current density is increased.

The improved electrochemical performance of V-TNO electrode at high current rate is mainly attributed to the enhancement of its intrinsic electronic conductivity. V-TNO can potentially be used as a novel negative electrode material for Li-ion batteries capable of high power and high safety for large scale applications such as hybrid electric vehicles and energy storage systems.