Garnet solid electrolytes are regarded as amongst the most promising class of materials for the realization of all-solid-state Li ion batteries, demonstrating good stability vs Li metal (anode) and exhibiting conductivity values that come close to conventional liquid- and/or organic-based electrolytes (on order order of 10^-3 S/cm)^1,2. These properties are strongly governed by structure stability (thermodynamic and electrochemical), doping effects, and the dominating Li ion conduction mechanism in the garnet framework. In this respect, a clear and fundamental understanding of the garnet material itself is crucial for the formulation of effective strategies for property optimization. Unfortunately, elucidation by experiment alone are met with difficulties. Even conductivity values for the same garnet composition can vary significantly as can be seen in the literature. In the case of electrochemical stability, the decomposition product(s) in the oxidative voltage regime, for example, could be difficult to detect. Meanwhile, ascertaining the actual site preference and distribution of dopants is also not straightforward and could depend on the preparation condition of the garnet powder. When determining bulk and grain boundary conductivity, separating the bulk and grain boundary contributions of resistance in impedance measurements can also become problematic.

By experiment and computational modelling, we attempted to clarify some of the above issues as well as tried to resolve some of the discrepancies existing in the literature. Specifically, we studied the electrochemical stability,^3,4 dopant distribution and local structure,⁵ and Li ion transport properties^5,6,7. As an example, for experiment, results will be shown related to the charge process behavior of an air-isolated Li ion battery with a garnet solid electrolyte, and then use modelling to aid in clarifying the origin of capacity fading. Another example, for computation, we employed various techniques such as first-principles density functional theory (DFT), augmented plane-wave method, computational NMR, force-field approach, and molecular dynamics in order to analyze the effects of gallium doping in garnet Li₇La₃Zr₂O₁₂. Our results could provide insights and fresh view, for both experimentalists and computationalists, on the state and the future direction that could be taken for solid electrolyte research.

REFERENCES

¹Li et al., J. Mater. Chem. 2012, 22, 15357-15361.

² Bernuy-Lopez et al., Chem. Mater. 2014, 26, 3610-3617.

³ Nakayama et al., Phys. Chem. Chem. Phys. 2012, 14, 10008-10014.

⁴ Jalem et al., J. Mater. Chem. A 2016, 4, 14371-14379.

⁵Jalem et al., Chem. Mater. 2015, 27, 2821-2831.

⁶ Jalem et al., J. Phys. Chem. C 2015, 119, 20783-20791.

⁷ Jalem et al., Chem. Mater., 2013, 25, pp 425-430.