Low electronic conductivity of Li7La3Zr2O12 solid electrolytes from first principles

Abstract

The formation of lithium dendrites in solid-state lithium-ion batteries leads to short-circuiting and cell failure. One proposed mechanism for dendrite growth is the direct reduction of lithium ions, due to residual electronic conductivity in the nominally insulating solid electrolyte. This article presents a fully first-principles scheme for modeling the electronic conductivity of nominally insulating materials, such as solid electrolytes, as a function of synthesis protocol, and applies this to the prototypical lithium-ion solid electrolyte Li${}_{7}$La${}_{3}$Zr${}_{2}$O${}_{2}$ (LLZO). LLZO is predicted to have low bulk electronic carrier mobilities and negligible carrier concentrations. This suggests that the bulk electronic conductivity of LLZO is not sufficiently high to enable lithium-dendrite growth, implicating extended defects and surface contributions in any non-negligible electronic conductivity in lithium garnet solid electrolytes.