Development of Li0.33La0.56TiO3 based Solid Electrolyte Materials

Abstract

As the increasing need for electronic products like smartphones, lithium-ion batteries have been a vital topic in this era. For developing batteries with higher electrochemical performance and safety, solid electrolytes play a significant role in increasing safety owing to less risk of electrolytes leakage and a wider electrochemical window for higher energy density. Among various materials, inorganic ceramic solid electrolytes lead the intention because of their high electrochemical performance, such as ionic conductivity. However, compared to traditional liquid electrolytes, the ionic conductivity of ceramic solid electrolytes is still below current requirements. To optimize ionic conductivity, strategies of decreasing grain and grain boundary resistance are required. In this thesis, three different strategies for optimizing Li0.33La0.56TiO3 materials’ ionic conductivity were developed. Lithium lanthanum titanate (LLTO) powder was prepared using a modified sol-gel process with three chelating agents. After initial structural characteristics, LLTO pellets were prepared by spark plasma sintering. To investigate alternation of grain and grain boundary resistance of the LLTO, Ag dopants were introduced to LLTO, and composite pellets of LLTO and silver nanowires were also fabricated. The LLTO synthesized by acetic acid was found to have the strongest intensity, minor impurity, and the biggest crystallite size from XRD patterns and Rietveld refinement compared with LLTO synthesized by citric acid and a mix of citric acid and glucose. According to the XRD patterns, Ag doping of LLTO (Li0.33-xLa0.56AgxTiO3) was positively proved by shifting away from the original target Li0.33La0.56TiO3. The composite pellet (LLTO/AgNWs) was successfully fabricated by spark plasma sintering, and the LLTO/AgNWs pellet showed a more apparent grain boundary from the SEM image. The modified sol-gel method has been proved that it is an efficient way to synthesize LLTO with low reaction temperature and short reaction time compared with the traditional physical reaction method. The pure LLTO pellet was fabricated with a 10(-4) S/cm grain conductivity via spark plasma sintering (SPS). Due to successful chemical composition alteration, the Ag-doped LLTO pellet reached higher grain conductivity by 2 *10(-5) S/cm than the pure LLTO pellet. The composite LLTO/AgNWs pellet was also efficiently fabricated through SPS