How Concerted Are Ionic Hops in Inorganic Solid-State Electrolytes?

Area of Science:

• Materials Science
• Solid-State Chemistry
• Computational Materials Science

Background:

• Understanding ion transport in solid-state electrolytes (SSEs) is crucial for advanced battery technologies.
• The degree of ion coordination during diffusion events in SSEs remains poorly understood.
• This lack of comprehension hinders the rational design and optimization of SSE materials.

Purpose of the Study:

• To develop and apply a novel unsupervised k-means clustering approach to identify ion-hopping events and correlations.
• To analyze these correlations across various inorganic SSE families using ab initio molecular dynamics (MD) data.
• To elucidate the relationship between ion coordination and fast-ionic diffusion properties.

Main Methods:

• Utilized an unsupervised k-means clustering algorithm to detect ion-hopping events.
• Applied the method to a large ab initio MD database of inorganic SSEs.
• Analyzed millions of ionic configurations to identify many-ion correlations.

Main Results:

• Higher-order (n > 2) ion correlations are more frequent than two-body interactions in SSEs.
• A general exponential decay law was identified for the probability of concerted mobile ions.
• For Li-based SSEs, an average of 10 ± 5 correlated ions were observed, independent of temperature.
• Fast-ionic diffusion correlates positively with hopping length and span, not frequency or residence time.

Conclusions:

• Many-ion correlations significantly influence ion diffusion in SSEs.
• The developed clustering approach provides a new tool for analyzing ion dynamics.
• Neglecting these correlations can lead to overestimations of ion hopping frequency, impacting material performance predictions.