Effects of a dual doping strategy on the structure and ionic conductivity of garnet-type electrolyte

Garnet solid electrolyte is the most promising candidate among inorganic solid electrolytes due to its wide potential window, good compatibility and high safety. In this work, a dual doping strategy is offered for the development of garnet-type electrolytes with high ionic conductivity. Te6+ is introduced into the Zr sites to stabilize the high-ionic conductivity cubic phase. Simultaneously, Sr2+ enter the La sites to achieve a fine-tuning of the Li+ concentration by charge compensation, acting as a sintering agent of Te6+/Sr2+ doped electrolytes. The structure, chemical composition and ionic conductivity of Li7-2y+xLa3-xSrxZr2-yTeyO12 (x = 0-0.25, and y = 0.35) electrolytes are systematically investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscope, Energy Dispersive X-ray Spectroscopy, Inductively Coupled Plasma-Optical Emission Spectrometry and Alternating Current impedance. The results show that the optimal amount of Sr2+ substitution helps to reduce the total resistance by promoting the growth of grains and ceramic densification. Among the investigated compositions, the composition with Li6.425La2.875Sr0.125Zr1.65Te0 35O12 exhibits excellent performance with relative density of 97.95%, conductivity of 4.27 x 10(-4) S cm(-1) at 25 degrees C and activation energy of 0.30 eV. The assembled Li/Li6.425La2.875Sr0.125Zr1.65Te0 35O12/Li symmetrical batteries are cycled galvanostatically under different current densities. The results show that the symmetrical battery can achieve good cyclic stability, good Li+ stripping and plating process and low overpotential.