Improving the volumetric capacity of TiO₂ nanomaterials used as anodes in lithium-ion batteries

Abstract

The experimental data presented in this thesis demonstrates the preparation and characterization of TiO₂ polymorphs (anatase and TiO₂-(B)) in the form of nanomaterials. The reduced dimension of the nanomaterials amplifies the properties compared to the bulk TiO₂; however, this is often at the cost of the tapped density. The anatase nanomaterials with pseudo-spherical nanoparticles of 5 to 70 nm in size were synthesized and their volumetric capacities compared. Both the gravimetric and volumetric capacity is higher for nanoparticles of less than 10 nm in diameter. The volumetric capacity is also dependent on the agglomerate size. For example at the very lowest rate of 50 mA/g, the agglomerate larger than 50 μm leads to the highest volumetric capacity; while at a rate higher than 600 mA/g the smaller agglomerates are preferred. Following this, we reported the synthesis of mesoporous TiO₂-(B) with the particle size along the [010] direction ranged from 3 to 300 nm, and the pore size increasing from 2.5 to more than 20 nm. By comparing the volumetric capacity of these TiO₂-(B) mesoporous materials, the optimal morphology for an improved volumetric capacity was identified. TiO₂-(B) with a novel microstructure was synthesized via a hydrothermal reaction. The primary particles are brick-like in shape with the shorter dimensions (4 - 10 nm) in parallel to the [100] and [010] directions, facilitating the Li⁺ ion diffusion in the particle. This TiO₂-(B) offers a superior rate capability compared to many other titanate anodes reported in the literature. In addition, it exhibits a great cycleability due to its exceptional structural stability and minimal SEI layer. Surface treatments could reduce its first cycle irreversible capacity to ~10%.