Atomistic mechanism of high ionic conductivity in lithium ytterbium-based halide solid electrolytes: A first-principles study

As the next generation of commercial automotive power batteries begins replacing liquid lithium batteries, many look towards all-solid-state batteries to pioneer the future. All-solid-state batteries have attracted the attention of countless researchers around the world because of their high safety and high energy density. In recent times, halide solid-state electrolytes have become a research hotspot within solid-state electrolytes because of their potentially superior properties. In this paper, in the framework of DFT, we investigated the atomic mechanisms of improving the ionic conductivity and stability of Li3YbCl6. Our calculations show that both trigonal and orthorhombic Li3YbCl6 exhibit wide electrochemical windows and metastable properties (100 meV/atom > Ehull > 0 meV/atom). However, the orthorhombic Li3YbCl6 can be stabilized at high temperatures by taking the vibrational entropy into account, which is supported by the experimental results. Moreover, it is expected that because of the Yb/Li synergistic interactions that, due to their strong mutual coulomb repulsion, influence the Li+ transport behavior, the orthorhombic Li3YbCl6 might have superior ionic conductivities with appropriate Li + migration paths determined by the Yb3+ distribution. Also, higher ionic conductivities can be obtained by regulating the random distribution of Li+ ions. Further Li+-deficiency can also largely increase the ionic conductivity by invoking vacancies. This study helps gain a deeper understanding of the laws that govern ionic conductivities and stabilities and provides a certain theoretical reference for the experimental development and design of halide solid-state electrolytes.