Thermokinetic and thermodynamics of Pechini derived Li7-3xAlxLa3Zr2O12 (X=0.0-0.2) xerogel decomposition under oxidative conditions

Abstract

Solid electrolytes for all-solid-state Li-ion batteries have attracted significant interest with their outstanding safety. But their poor ionic conductivity limits their widespread use. Li7La3Zr2O12 solid electrolytes have the potential of showing comparable ionic conductivities with commercially available electrolytes. However, its high ion conductive cubic phase is not stable at room temperature. Studies demonstrated that the cubic Li7La3Zr2O12 phase can be stabilized easier than solid-state method by modified Pechini method and very little work has been done in order to understand what makes the phase transformation easier. For this purpose, thermal decomposition behavior, model-free kinetics and thermodynamics of Li7La3Zr2O12 xerogels synthesized by modified Pechini method were investigated and the effect of stabilizer (Al) addition was discussed in this study. The results showed the presence of four peak zones and the main reaction zone includes multiple reactions. Different statistical functions were tested for deconvolution of main reaction zone and the best fits were obtained by Bigaussian and Asym2sig statistical functions. The multiple reactions in the main thermal degradation zone were separated into three reaction zones and thermokinetic and thermodynamic calculations were employed using model-free approach. The results also showed that Al incorporation expanded the main thermal decomposition zone of LLZO and resulted in changes in kinetic and thermodynamic parameters.