Correlate phonon modes with ion transport via isotope substitution

• Published in: Science China. Chemistry Vol. 66; no. 3; pp. 768 - 777
• Main Authors: Gao, Yirong, Huang, Jianxing, Cheng, Jun, Bo, Shou-Hang
• Format: Journal Article
• Language: English
• Published: Beijing Science China Press 01.03.2023; Springer Nature B.V
• Subjects: Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Electrolytes; Ion currents; Ion transport; Lattice vibration; Lithium; Molecular dynamics; Molten salt electrolytes; Phonons; Solid electrolytes; Solid state; Substitutes; Transport properties; phonon modes; isotope substitution; lattice dynamics; solid-state electrolytes; ion transport
• ISSN: 1674-7291; 1869-1870
• DOI: 10.1007/s11426-022-1488-9

Understanding the correlations between lattice dynamics (phonons) and ion transport is important for improving the ionic conductivity of solid-state electrolytes. This understanding largely hinges on selective tuning or excitation of specific phonon modes without changing the chemical environments of atoms, which is, however, challenging to be achieved. In this work, we used 6 Li isotope substitution to selectively change the phonon properties associated with lithium, without introducing additional defects or disorders which would affect the ion transport properties. The changes in the phonon modes were then related to ion transport properties through impedance measurements and deep potential molecular dynamics simulations. Our results demonstrated that lower lithium vibration frequency leads to higher ionic conductivity and lower activation energy in the garnet solid-state electrolyte of Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 . We furthermore quantified the effect of lithium-related phonons on the migration entropy and attempt frequency, which would be difficult to be achieved otherwise. Our work suggests an effective isotope substitution method to decouple the effect of phonon modes to ion transport from that of other complex structural factors. The obtained insights can contribute to innovative understanding of ion transport in solids and strategies to optimize the ionic conductivity of solid-state electrolytes.