Mesoporous TiO2 with high packing density for superior lithiumstorage

Abstract

Micrometre-sized mesoporous materials have characteristic grains as well as pores nearly in the same scale. Electrodes of mesoporous materials for lithium batteries have short transport lengths for Li⁺ ions due to their nano-sized grains (10–20 nm), and easy access for electrolytes due to their nanopores (5–10 nm). Such mesoporous materials have high packing densities unlike nanopowders, nanowires, nanorods and nanotubes. Despite such advantages, electronic conduction over micrometre-sized particles limits the rate performance of mesporous materials. Occasionally counductive thin layers (2–5 nm) of carbon or RuO₂ have been used to overcome such kinetic limitations and to achieve high storage performances. In this manuscript, we present a simple approach for the synthesis of mesoporous TiO₂ anatase using a soft-template method, which shows superior storage performance without such conductive surface layers. Various cationic surfactants with different chain lengths have been selected for this investigation to assist the formation of the mesoporous TiO₂ structure. Among these, cetyl trimethylammoniumbromide templated C16-TiO₂ has the highest surface area of 135 m² g⁻¹ and reversible capacity of 288, 220, 138,134 and 107 mAh g⁻¹ at 0.2, 1, 5, 10 and 30C respectively. The storage performance of the as-synthesized mesoporous TiO₂ is nearly five times better than the commercially available TiO₂ nanopowder. The packing density of meso-TiO₂ is found to be 6.6 times higher than the TiO₂ nanopowder. In addition, battery testing using mesoporous TiO₂ electrodes without the 15% carbon additive exhibits nearly the same performance at low rate as the meso-TiO₂ with carbon additives. These exciting results suggest a facile conduction path for electrons, a unique character of micrometre-sized mesoporous TiO₂ with highly interconnected nanograins of 15–20 nm.