Synthesis and Applications of Lithium-Doped Lanthanum Titanate Nanomaterials

Abstract

Ceramic electrolytes have attracted much interest in research, as they represent a safer alternative to flammable organic electrolytes. In particular, perovskite-type lithium lanthanum titanate (LLTO) is one of the most promising solid electrolytes because of its high ionic conductivity. However, it is a great challenge to synthesize LLTO nanomaterial with high purity at low temperature, which is essential for practical applications. In this dissertation, lanthanum titanate and lithium lanthanum titanate nanomaterials were successfully prepared by a modified hydrothermal process and their crystalline structures were characterized by X-ray diffraction and transmission electron microscopy. It has been found that both lanthanum titanate and lithium lanthanum titanate show layered structure, which can be attributed to the stratified monoclinic crystalline structure and weak bonding between layers. In addition, the effects of reaction parameters, including reaction time, surfactants and agitation on crystal growth, have been systematically investigated. Pure lanthanum titanate (LaTiO3) was used to fabricate resistive random access memory devices. The device shows excellent performance, such as the OFF / ON ratio of more than 100, over 200 cycles of resistance performance and a holding time longer than 105 s. A conductive filament model based on oxygen vacancies was proposed to explain the switching mechanism A number of different film preparation techniques were used to prepare LLTO films. The experimental results show that compared to drop coating and convective assembly, the layer-by-layer technique is superior for preparing nanoparticle films of structure in 2D layers. In addition, the LLTO was also combined with commercial LiCo1/3 Ni1/3Mn1/3O2 (CNM) for lithium battery applications, which indicated that the LLTO can facilitate the diffusion of lithium ions between active materials and electrolytes. This thesis demonstrated the great potential of the bottom up technology to manufacture nanosheets based on lanthanum titanate for promising applications of electrochemical devices.