Titanium based oxides as high performing materials for lithium batteries

© 2016 Dr. Erwin Franco Rodriguez TolavaEnergy density, power density, cycle-life and safety are great challenges for high performance lithium batteries. Titanium-based oxides (TBOs) are promising materials for such application. Herein mesoporous anatase TiO2 and Li4Ti5O12 (LTO) were investigated as safe anodes for lithium ion batteries (LIBs), and hollow anatase microspheres (HMs) were employed as excellent hosts for lithium sulfur batteries (LSB). The physical and chemical properties of these TBOs were adjusted to investigate their effect on the electrochemical performance. The physical properties of the monodisperse mesoporous anatase beads, including pore diameter, bead diameter and degree of sintering, were tailored to investigate their influence on the performance of LIBs. While the pore diameter showed little effect on the performance, crystal size and surface area influenced the rate capability and overall lithium storage capacity. Additionally, the conductive carbon content was varied in conjunction with the bead diameter. For the beads with a small diameter, a larger quantity of conductive carbon was required in the electrode. Mesoporous nitrogen doped LTO (N-LTO) was fabricated via a hydrothermal treatment followed by calcination. The nitrogen doping enhanced the electron transfer property of the anode, and the N-LTO with optimised properties was prepared by calcining at 550 °C. The precursor was composed of protonated titanate (LHT) nanosheets, and these LHT were transformed into cubic LTO upon calcination. The resulting N-LTO delivered an excellent and reversible capacity of 95.4±16.5 mAh/g even at 120 C rate due to their integrated features including abundant mesoporosity, high surface area, nanosheet morphology, water-free property and high crystallinity. Six LHTs with varied Li/Ti ratios were synthesised as the precursors and the resulting calcined LTO contained small quantities of anatase or monoclinic Li2TiO3 (m-LTO). Intercalation of Li+ into the (200) plane of the orthorhombic LHT increased when the Li/Ti ratio was raised. LHTs with a Li/Ti ratio higher than 0.91 can result in trace amount of m-LTO, whereas those with a ratio lower than 0.88 produced trace amount of anatase. Anatase can take part in lithium storage but m-LTO is inactive. All the LTO materials had high electrochemical performance, showing high capacities, rate capabilities and long cycle-life. For instance, the LTO prepared using LHT with a Li/Ti ratio of 0.88 showed 87 % retention in its initial capacity after 2634 cycles. LSBs were investigated as high energy density alternatives to LIBs. HMs were used to contain highly-soluble lithium polysulfides (PSs) to improve the cycle-life. The HMs had a hollow chamber within a mesoporous shell, which physically confined the PSs. These LSBs had a long cycle-life with over 82 % capacity retention after 500 cycles at 1 C rate. Additionally, carbon coated HMs (CHMs) were synthesised using ionic liquids and the resulting CHM-sulfur composite showed high rate capability, being able to cycle well at 5 C rate. Controlling physical and chemical properties of TBOs was demonstrated to have a great influence on the performance for lithium batteries. TBOs with nanostructured and porous features delivered high electrochemical performance in LIBs and LSBs