Effects of alkali-earth metals (Mg, Ca, Sr, Ba) doping on the microstructure and conductivity of Li13.9Sr0.1Zn(GeO4+δ)4 electrolyte

Abstract

In this work, alkali-earth metal elements (Mg, Ca, Sr, Ba) doped Li13.9Sr0.1Zn(GeO4+δ)4 electrolyte is prepared by sol-gel method. The influence of alkali-earth metal doping on the phase structure, morphology, Li+/H+ ion exchange and electrical conduction behavior of Li13.9Sr0.1Zn(GeO4+δ)4(LSZG) electrolyte is characterized by X-ray diffraction, scanning electron microscopy，thermal gravimetric analyzer and electrochemical impedance spectroscopy. The powders of Mg, Ba and Sr doped Li13.9Sr0.1Zn(GeO4+δ)4 electrolyte are found to possess the same phase structure as LSZG powders. The grain size and density of Mg, Ba and Sr doped LSZG samples increase significantly after sintering at 1050 °C. Ca is partially doped into the LSZG lattice, and some is precipitated in the form of CaGeO3 second phase. The doping elements can promote the ion exchange of Li+/H+ in LSZG electrolyte. With the increase of ion radius of doping elements, the Li+/H+ ion exchange rate of samples gradually decreases. The proton conductivity of all doped samples is significantly higher than that of pure LSZG electrolyte pellets. Mg is considered to be the best doping element. In 5% H2-Ar humid atmosphere, the proton conductivity of Li13.8Mg0.1Sr0.1Zn(GeO4+δ)4(LMSZG) electrolyte at 0.9 V bias voltage is about 0.053 S/cm at 600 °C. The proton conductivity of LMSZG sample with BaZr0.4Ce0.4Y0.1Ni0.1O3 (BZCYN) barrier layer is about 0.049 S/cm at 600 °C.