Development of an efficient CVD technique to prepare TiO2/porous-carbon nanocomposites for high rate lithium-ion capacitors.

Titanium dioxide is a promising electrode material for lithium-ion capacitors. When using TiO2 as an electrode material, it is necessary to combine it with carbon at the nanometer level to improve its low electrical conductivity and low reactivity with Li+. However, preparation methods of reported TiO2/porous-carbon nanocomposites are generally not cost-effective, and their productivities are low. In this study, the vacuum liquid-pulse chemical vapor deposition (VLP-CVD) technique was developed to easily prepare TiO2/porous-carbon nanocomposites, where TiO2 nanoparticles with a diameter of ∼4 nm could be homogeneously deposited inside the pores of meso- or macroporous carbons. Because the deposited TiO2 nanoparticles had access to effective electrically conductive paths formed by the porous-carbon substrate, they showed a high discharge capacity of ∼200 mA h g-1-TiO2 (based on TiO2 weight). In particular, the composite prepared from macroporous carbon showed an extremely high rate performance, where 50% of the discharge capacity was retained at a current density of 15 000 mA g-1 when compared to that measured at 50 mA g-1. In addition, the composite also showed very high cyclability, where 80% of the discharge capacity was retained at the 10 000th cycle. Because the VLP-CVD technique can be performed using simple apparatus and commercially available starting materials, it can be expected to boost industrial production of TiO2/porous-carbon for lithium-ion capacitors.