Non-equilibrium kinetics for improving ionic conductivity in garnet solid electrolyte.

Solid-state electrolytes (SSEs), as an essential component of all solid-state batteries, exhibit limited ionic conductivity. The fractional occupancy of Li + ions, regulated by the doping of hetero-valent transition metals, is an important characteristic to enable high Li + conductivity. However, the structural and kinetic mechanism of this is still unclear, preventing the rational design of higher-conductivity SSEs. Here, taking the typical garnet SSE Li 7- x La 3 Zr 2- x Ta x O 12 (0≤ x ≤0.625) as an example, we revealed that a Ta 5+ -doping concentration of x = 0.25 leads to a high amount of non-equilibrium Li + configurations in the form of [LiO 6 ]-[LiO 4 ]-[ V Li O 6 ]. Non-equilibrium configurations induce high off-center shifts and high electrostatic energies of Li + ions, reducing the activation energy of Li + -ionic transport. As a result, the doping of hetero-valent ions has a great effect on Li + -ionic conductivity through controlling the amount of non-equilibrium Li + ions. These findings provide important insight into the understanding of ionic transport and pave the way towards optimizing Li + distribution to improve ionic conductivity.