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

Pivoting toward high-safety solid-state batteries, garnet-type solid-state electrolytes (SEs) with 3D ion transport channels are highly promising candidates. Complex cation substitutions are proved efficacious in enhancing ionic conductivity, while the role of pre-exponential factor in Arrhenius equation receives insufficient attention compared to the activation energy term. Herein, multiple lattice site substitution is employed to elucidate the contribution of increased configurational entropy to phase formation and the predominance of local distortion on ionic conductivity. Neutron diffraction and density functional theory calculations reveal the highly-distorted Li coordination environments leading to a decrease of activation energy. However, this effect is simultaneously compensated by decreased migration entropy and hopping frequency, hampering the enhancement of ionic conductivity. In the study, LiGaLaZrHfTaNbO with rational-designed local distortion shows the optimized ionic conductivity due to the trade-off between activation energy and pre-exponential factor. This work demonstrates an approach of high-entropy strategy to advancing the ionic transport behavior of SEs.