Layer-by-Layer Synthesis of Thick Mesoporous TiO2 Films with Vertically Oriented Accessible Nanopores and Their Application for Lithium-Ion Battery Negative Electrodes

TiO2 films of varying thicknesses (up to approximate to 1.0 mu m) with vertically oriented, accessible 7-9 nm nanopores are synthesized using an evaporation-induced self-assembly layer-by-layer technique. The hypothesis behind the approach is that epitaxial alignment of hydrophobic blocks of surfactant templates induces a consistent, accessible mesophase orientation across a multilayer film, ultimately leading to continuous, vertically aligned pore channels. Characterization using grazing incidence X-ray scattering, scanning electron microscopy, and impedance spectroscopy indicates that the pores are oriented vertically even in relatively thick films (up to 1 mu m). These films contain a combination of amorphous and nanocrystalline anatase titania of value for electrochemical energy storage. When applied as negative electrodes in lithium-ion batteries, a capacity of 254 mAh g(-1) is obtained after 200 cycles for a single-layer TiO2 film prepared on modified substrate, higher than on unmodified substrate or nonporous TiO2 film, due to the high accessibility of the vertically oriented channels in the films. Thicker films on modified substrate have increased absolute capacity because of higher mass loading but a reduced specific capacity because of transport limitations. These results suggest that the multilayer epitaxial approach is a viable way to prepare high capacity TiO2 films with vertically oriented continuous nanopores.