Electrochemical Stability and Reduction Mechanism of LLZO Interfaces in Li Batteries from First Principles

Area of Science:

• Materials Science
• Electrochemistry
• Computational Chemistry

Background:

• Lithium lanthanum zirconium oxide (LLZO) is a promising solid electrolyte for lithium-ion batteries.
• Understanding the electrochemical stability of LLZO interfaces is crucial for battery performance and longevity.

Purpose of the Study:

• To investigate the electrochemical stability of pristine and doped Li7La3Zr2O12 (LLZO) in contact with Li metal.
• To elucidate the mechanisms behind the observed instability of doped LLZO during battery cycling.

Main Methods:

• Density-functional theory (DFT) and GW many-body perturbation theory were employed.
• Calculations included energy level alignment across Li-LLZO interfaces and grand-canonical phase analysis.
• Interface structures with minimal lattice mismatch were analyzed.

Main Results:

• Direct interface energy level alignment provides more accurate stability predictions than vacuum-slab models.
• Pristine LLZO is predicted to be electrochemically stable against Li.
• Doped LLZO exhibits intermediate electronic states localized on dopant atoms during lithiation, causing instability.

Conclusions:

• The formation of intermediate electronic states in doped LLZO is an intrinsic source of reductive decomposition.
• Electron transfer to dopant atoms initiates a degradation pathway, leading to phase separation.
• This study establishes a holistic mechanism for LLZO degradation in Li batteries.