Microwave-assisted synthesis of Li₄Ti₅O₁₂ from TiO(OH)₂ and its application for hybrid capacitors

We report two types of spinel Li₄Ti₅O₁₂ synthesized from the mixtures of two different nano-sized Ti precursors (TiO(OH)₂ and TiO₂) using microwave heating. The mixed precursors were heated at various temperatures ranging from 450 to 750°C using microwave heating processing. Spinel Li₄Ti₅O₁₂ prepared from TiO(OH)₂ as a Ti precursor exhibits lower synthesis temperature of 550°C than Li₄Ti₅O₁₂ prepared from TiO₂. Two types of spinel Li₄Ti₅O₁₂ obtained from TiO(OH)₂ and TiO₂ were characterized using X-ray diffraction, particle size distribution, and scanning electron microscopy. Hybrid capacitors to evaluate the electrochemical performance of spinel Li₄Ti₅O₁₂ were fabricated using activated carbon as a cathode material. TiO(OH)₂ has the advantage of low-temperature synthesis in comparison with rutile or anatase phase TiO₂, because TiO(OH)₂ possesses a high concentration of defects in the structure. As a result, the rate capability of the hybrid capacitor improved with the decreasing particle size of the Li₄Ti₅O₁₂ prepared from TiO(OH)₂ owing to the increasing contact area between electrode and electrolyte, as well as reduced diffusion path of lithium ions. In this study, we demonstrated that the high-rate performance and long-term cycle stability of Li₄Ti₅O₁₂ obtained from TiO(OH)₂ for hybrid capacitors. The presented hybrid capacitor could be a competitive candidate for use in promising energy storage devices.