Correlating structure and transport properties in pristine and environmentally-aged superionic conductors based on Li1.3Al0.3Ti1.7(PO4)3 ceramics

Li-ion superionic conductors play an important role in next-generation energy storage devices. To be applicable, they should meet a wide range of specifications such as safety, efficiency, affordability, and stability. The NASICON-type Li1.3Al0.3Ti1.7(PO4)3 (LATP) compound is a well-known lithium-conductive solid electrolyte, suitable for all-solid-state and redox-flow battery prototypes offers great potential. Yet, despite the high scientific attention paid to LATP, its stability towards environmental exposure to reactive components such as water, carbon dioxide, and oxygen is poorly elucidated. Herein we evaluate under controlled conditions the structure and transport properties of LATP in both air and argon atmosphere to understand the influence of environmental processing effects over a three-month set of experiments. We demonstrate that LATP ceramics (total conductivity σt of 4·10−4 S cm−1 at room temperature; porosity of 18.5 vol %) degrade drastically showing 76% and 28% of the σt losses (for ceramics stored in the air and argon correspondingly). Based on experimental and theoretical approaches, we propose a degradation mechanism supported by Electrochemical Impedance Spectroscopy (EIS), Powder X-Ray Diffraction Analysis (PXRD), Scanning Electron Microscopy (SEM), Energy-Dispersive X-Ray spectroscopy (EDX), and Density Functional Theory (DFT) calculations.