Equilibration of ion distribution at polymer/ceramic interfaces.

Area of Science:

• Materials Science
• Electrochemistry
• Computational Chemistry

Background:

• Composite solid electrolytes (CSEs) are promising for solid-state batteries.
• Non-homogeneous ion distribution in CSEs poses challenges for molecular dynamics (MD) simulations at typical battery operating temperatures.
• Limited timescales in classical MD (<μs) hinder achieving interfacial ion equilibration.

Purpose of the Study:

• To investigate equilibrium ion distributions in CSEs using MD simulations at elevated temperatures (400-700 K).
• To assess the transferability of high-temperature simulation insights to lower, experimentally relevant temperatures.
• To predict ion transfer barriers and hopping rates for solid-state battery applications.

Main Methods:

• Molecular dynamics (MD) simulations of composite solid electrolytes (CSEs) comprising Li$_{7}$La$_{3}$Zr$_{2}$O$_{12}$ (LLZO) ceramic and LiTFSI in PEO polymer electrolyte.
• Simulations conducted at elevated temperatures ranging from 400 K to 700 K.
• Analysis of interfacial ion (Li$^{+}$ and TFSI$^{-}$) distributions and free energy curves.

Main Results:

• Equilibrium interfacial structures, independent of temperature above 600 K, show significant Li$^{+}$ transfer to the LLZO ceramic phase.
• Below 600 K, Li$^{+}$ distribution is not fully equilibrated, though TFSI$^{-}$ distribution appears to follow Li$^{+}$.
• High-temperature simulations enable estimation of Li$^{+}$ free energy barriers and hopping rates at lower temperatures.

Conclusions:

• Elevated temperature MD simulations are crucial for achieving equilibrium ion partitioning in CSEs.
• Insights from high-temperature simulations can predict ion dynamics at lower, experimentally relevant temperatures.
• This approach aids in designing efficient solid-state batteries by understanding ion transport mechanisms.