Amorphous Ultrathin TiO₂Atomic Layer Deposition Films on Carbon Nanotubes as Anodes for Lithium Ion Batteries

Amorphous TiO 2 (a-TiO 2 ) thin films were conformally coated onto the surface of hydroxyl functionalized multi-walled carbon nanotubes (CNTs) using atomic layer deposition (ALD). The electrochemical characteristics of the a-TiO 2 /CNT nanocomposites were then determined using cyclic voltammetry and galvanostatic charge/discharge curves. The ultrathin TiO 2 ALD films displayed high specific capacity and high rate capability. The specific capacities of the a-TiO 2 /CNT nanocomposites after 50 and 100 TiO 2 ALD cycles at 100 mA/g were 220 mAh/g and 240 mAh/g, respectively. For CNTs coated with 100 TiO 2 ALD cycles, 88% of the capacity at 100 mA/g could be maintained at 1 A/g. When the voltage window for the a-TiO 2 /CNT nanocomposites was extended down to 0.5 V versus Li/Li + , the CNTs coated with 50 and 100 TiO 2 ALD cycles exhibited specific capacities at 100 mA/g of 275 mAh/g and 312 mAh/g, respectively. These high capacities are higher than the bulk theoretical values and are attributed to additional interfacial charge storage resulting from the high surface area of the a-TiO 2 /CNT nanocomposites. Free-standing TiO 2 -CNT electrodes were also fabricated and displayed excellent capacity and rate capability. These results demonstrate that TiO 2 ALD on high surface area CNT substrates can provide high power and high capacity anodes for lithium ion batteries.