Experimental and DFT analysis of structural, optical, and electrical properties of Li3xLa2/3-xTiO3 (3x = 0.1, 0.3 and 0.5) solid electrolyte

Abstract

The perovskite material, lithium lanthanum titanate Li3xLa2/3-xTiO3 (LLTO) is one of the interesting prospects that may be employed as a solid-state inorganic electrolyte for Li-ion batteries. Here, three various formulations corresponding to: (i) 3x = 0.1 (Li0.1La0.63TiO3), (ii) 3x = 0.3 (Li0.3La0.57TiO3), and (iii) 3x = 0.5 (Li0.5La0.5TiO3) were synthesized using sol-gel method. The impacts of lithium concentration, calcination temperature, elemental composition, microstructure, optical properties, and conductivity of the ceramics were studied using a plethora of techniques. DFT calculations were performed on Li0.5La0.5TiO3 to get an in-depth understanding on the relationship between the structure –electronic– optical properties of LLTO materials. Our results show that the grain and crystallite sizes behave inversely proportional to the band gap. Maximum grain ionic conductivity on the order of 10−3S/cm and grain boundary ionic conductivity on the order of 10−6S/cm were obtained for both samples (3x = 0.3 and 3x = 0.5) at higher temperatures. The total density of states indicates that the titanium d-bands (Ti-d) and oxygen p–bands (O-p) form covalent Ti-O bond character. The formation of localized states is suggested to result in the lowering of the band gap energy, when lithium content is increased. Finally, the calculated mechanical properties show that LLTO (3x = 0.5) possess high elastic moduli as compared to other solid electrolytes.