Ga-substituted La3Zr2Li7O12 garnet is shown to be a promising Li-ion conducting electrolyte material. The strategy adopted in this study is the substitution of Li by Ga, thereby creating Li vacancies and enhancing the Li conductivity. Solid State Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) measurements have been used to identify the location of the substituted Ga in the structure and its effect on the Li distribution and mobility. In addition MAS NMR was used to follow the effect of protonation due to atmospheric moisture on the sintering behavior of these materials. In particular, it is shown that the Ga atoms are located in tetrahedral positions promoting the random distribution of lithium over the available sites, hence promoting an increase in the conductivity. Control of the sintering conditions by using a dry O2 atmosphere leads to the formation of dense ceramic materials and avoids the degradation process due to the exchange of Li+ by H+ from atmospheric moisture. Electrochemical Impedance Spectroscopy data show total conductivities as high as 1.3 and 2.2 mS cm–1 at 24 and 42 °C, respectively, which are among the highest Li ion conductivities reported for garnet-structured materials to date.

All-solid-state batteries promise significant safety and energy density advantages over liquid-electrolyte batteries. The interface between the cathode and the solid electrolyte is an important contributor to charge transfer resistance. Strong bonding of solid oxide electrolytes and cathodes requires sintering at elevated temperatures. Knowledge of the temperature dependence of the composition and charge transfer properties of this interface is important for determining the ideal sintering conditions. To understand the interfacial decomposition processes and their onset temperatures, model systems of LiCoO2 (LCO) thin films deposited on cubic Al-doped Li7La3Zr2O12 (LLZO) pellets were studied as a function of temperature using interface-sensitive techniques. X-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS), and energy-dispersive X-ray spectroscopy (EDS) data indicated significant cation interdiffusion and structural changes starting at temperatures as low as 300⁰C. La2Zr2O7 and Li2CO3 were identified as 2 decomposition products after annealing at 500°C by synchrotron X-ray diffraction (XRD). X-ray absorption spectroscopy (XAS) results indicate the presence of also LaCoO3, in addition to La2Zr2O7 and Li2CO3. Based on electrochemical impedance spectroscopy, and depth profiling of the Li distribution upon potentiostatic hold experiments on symmetric LCO|LLZO|LCO cells, the interfaces exhibited significantly increased impedance, up to 8 times that of the as-deposited samples after annealing at 500 o C. Our results indicate that lower-temperature processing conditions, shorter annealing time scales, and CO2-free environments are desirable for obtaining ceramic cathode-electrolyte interfaces that enable fast Li transfer and high capacity.

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The effect of Mo doping on the crystal structure and thermal, electrical, and electrochemical properties of the SrCo1–x Mo x O3−δ (x = 0.05, 0.1) system has been studied. The introduction of Mo as a substitution for Co in SrCoO3−δ leads to a change from a hexagonal to a tetragonal perovskite structure at room temperature. The electrical conductivity is largely enhanced by the introduction of Mo at intermediate temperature due to the stabilization of the 3D-perovskite structure. However, the increase in Mo content decreases the total conductivity probably due to partial disruption of the electronic pathway. The use of these materials as cathodes in a solid-oxide fuel cell (SOFC) and as anodes in a solid oxide electrolyzer (SOE) has been evaluated, showing low values of electrode polarization resistances in both configurations over the intermediate temperature range. Interestingly, better performance was obtained under anodic polarization conditions reaching overpotential values as low as 28 mV for a current density of 210 mA·cm–2 at 700 °C. The good performance of the SrCo1–x Mo x O3−δ compounds in both cathodic and anodic conditions makes this system a promising candidate for reversible oxygen electrodes in cells that could operate as both SOFC and SOE.