Ionic conductivity of Li1.3Al0.3Ti1.7 (PO4)3 solid electrolyte synthesized by solution-based method

LiTi2(PO4)3 based compounds with nasicon type structures are known as low temperature solid electrolytes with fast Li+ ion transport. Substitution of Ti4+→M3++Li+ in the system Li1+xMxTi2−x(PO4)3 (where M=Fe, Sc, Al, Y, B, In, Ga) leads to higher conductivities by several orders higher than those of host compounds. Li1.3Al0.3Ti1.7(PO4)3 (LATP) is one of the most highly conductive, air stable, lithium ceramic electrolytes that have been used in li-airbatteries recently as solid electrolyre interface . The significant advantage of ceramic based artificial SEI in li air batteries is that it protects the lithium metal from all atmospheric contamination.Most studies on LATP have adopted solid state reaction and melting–quenchingmethods for the LATP preparation .These methods cannot be easily applied to the mass production due to high energy consumption and contamination of impurities in the final products. On the other hand solution based synthesis method favors the preparation of powderwith controlled composition and metallurgy. In this study we have prepared LATP powders by a solution based synthesis method continued by sintering to obtain the highest ionic conductivity. 50 mL of NH4OH and 25 mL of Ti(OC3H8)4 was used as precursor producing a white gelatinous precipitate.The precipitate was washed with 500 mL of deionized water to remove the excess base and placed in 100 mL of deionized water. To this solution was added 200 mL of a 1M solution of anhydrous oxalic acid. Al(NO3)3·9H2O, (NH4)2HPO4, and 5% excess LiNO3 were added under stirring with stoichiometric ratios to the solution. The final solution was then heated on a hot plate until all the water was evaporated, which produces a white precipitate ofwell mixed precursors for annealing. The dried mixture was heated at 850°C for 5 hours to obtain crytalline structure. The Xrdpatterns of grounded powder were depicted in fig.1. As seen diffraction peaks were well matched with the standard pattern of LTP, and no impurity phase was observed. The peak intensities shows high crystallinity of grownded powders. The milled powder was used to form the pellet,which was then calcined at 650 and 850 ° for 3 hours. Li ion conductivity of the LATP pellet was measured by AC impedance method. Prior to measure, Au was sputtered on both side of thepellet to ensure electrical contact. Data was obtained at 10 mV voltage signal in a frequencyrange of 1Hz to 1MHz at room temperature. The density of the pellets was determined via Archimede’s method. Sample properties and obtained value for conductivity and density was depicted in Table 1. SEM micrographs (fig.2) of pulished surfaces shows two different areas . More well sintered areas with higher density was observed in sample 1 as a result of higher sintering temperature . The measured densities are in agreement with SEM micrographs. Furthermore higher total conductivity of sample 1 in comparsion with sample 2 is a result of its lower porosity. According to this total conductivity LATP pellets could be used as solid electrolyte in a Li-air battery.

کلیدواژه ها:

NASICON ، Solid electrolyte ، Ionic conductivity ، LATP