Novel expanded titanate based materials for energy applications
Yarali, Miad (2015) Novel expanded titanate based materials for energy applications. [Thesis]
Development of lithium-ion batteries operating at high charge and discharge rates is highly demanded especially for electronic devices and electric vehicles. For this purpose, improvement of ion transport in the crystal structure is needed. In this respect, the general strategy is reducing down the particle size to a nanometer scale. This helps to decrease the ion diffusion length. Titanate nanotubes are promising materials because of their special morphology and high specific surface area. These titanates provide high rate capability and low volume expansion upon lithiation. More importantly their tubular structure helps the transport of ions through the crystal. In this study, we synthesized titanate nanotubes hydrothermally from commercial and sol-gel TiO2. Moreover, the interlayer distances of the nanotubes were modified by changing the pH and the addition of surfactants. For the characterization, SEM, XRD, BET and TEM techniques were used. In addition, the effect of interlayer distance on energy capacity and rate capability was investigated. The shortest interlayer distance was observed at pH value of 4.4. Getting further away from this point, interlayer distances increased and this also increased the nanotube diameter. Conversely, specific surface area reaches its maximum value of 334 m2/g at pH of 4.4. Potential-capacity profiles of TiO2 (anatase) nanoparticles showed distinct potential plateaus at 1.7 and 2.2 V for discharging and charging, respectively. However, the capacity dropped from 254 mAh/g to 87 mAh/g in 10 cycles. For titanates, broad peaks appear in CV measurement, thus no distinct plateau was observed at potential-capacity profile. For titanates before surfactant treatment capacities as high as 980 mAh/g were obtained. After surfactant treatment the capacity reached to 1232 mAh/g. More importantly, titanates showed exceptional rate capabilities especially at wider interlayer distances due to higher mobility of ions in the structure. It was found that interlayer distance plays an important role in rate capability. In addition, we achieved significant expansion in interlayer distances after post-treatment with the surfactants which can enhance the ion mobility.
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