Local Distortion Balancing Entropy-Enthalpy Compensation for Fast Li⁺ Migration in Garnet Solid-State Electrolytes.

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Garnet-type solid-state electrolytes (SEs) are crucial for high-safety batteries due to their 3D ion transport channels.
• Cation substitutions enhance ionic conductivity, but the role of the pre-exponential factor is often overlooked compared to activation energy.

Purpose of the Study:

• To investigate the impact of configurational entropy and local lattice distortion on phase formation and ionic conductivity in garnet-type SEs.
• To elucidate the interplay between activation energy and the pre-exponential factor in determining overall ionic transport.

Main Methods:

• Utilized neutron diffraction and density functional theory (DFT) calculations.
• Employed multiple lattice site substitution to introduce controlled local distortions and configurational entropy.

Main Results:

• Highly distorted Li coordination environments were observed, decreasing activation energy.
• Decreased migration entropy and hopping frequency compensated for lower activation energy, limiting conductivity enhancement.
• Li$_{6.3}$Ga$_{0.1}$La$_{3}$Zr$_{0.8}$Hf$_{0.8}$Ta$_{0.2}$Nb$_{0.2}$O$_{12}$ exhibited optimized ionic conductivity due to a balanced trade-off between activation energy and the pre-exponential factor.

Conclusions:

• Local lattice distortion significantly influences ionic conductivity by affecting both activation energy and pre-exponential factor.
• A high-entropy strategy offers a viable approach to advance ionic transport in solid-state electrolytes for battery applications.