Atomic-scale study clarifying the role of space-charge layers in a Li-ion-conducting solid electrolyte

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Space-charge layers are often cited as the cause of high interfacial resistance in all-solid-state lithium batteries.
• Previous assumptions about Li-deficient space-charge layers lack detailed atomic-scale investigation into their structure and ion transport properties.

Purpose of the Study:

• To elucidate the true role of space-charge layers in Li$_{0.33}$La$_{0.56}$TiO$_{3}$ (LLTO), a solid electrolyte exhibiting significant grain-boundary resistance.
• To investigate the atomic configuration and ion transport behavior within space-charge layers at the atomic scale.

Main Methods:

• Combined experimental and computational approaches.
• Atomic-scale characterization of space-charge layers in LLTO.
• Analysis of ion transport mechanisms.

Main Results:

• Contrary to prevailing theories, Li-deficient space-charge layers were not observed in LLTO.
• Actual space-charge layers were found to be Li-excess, with additional Li$^{+}$ ions occupying 3c interstitial sites.
• These Li-excess space-charge layers demonstrate efficient ion transport capabilities.

Conclusions:

• Space-charge layers are not the primary bottleneck for interfacial resistance in LLTO.
• The study identifies Li-depleted grain-boundary cores as the principal source of high grain-boundary resistance in LLTO.
• This finding necessitates a re-evaluation of interfacial resistance mechanisms in solid-state electrolytes.