The Electronic Conductivity of Single Crystalline Ga-Stabilized Cubic Li₇La₃Zr₂O₁₂: A Technologically Relevant Parameter for All-Solid-State Batteries

The next-generation of all-solid-state lithium batteries need ceramic electrolytes with very high ionic conductivities. At the same time a negligible electronic conductivity σ_eon is required to eliminate self-discharge in such systems. A non-negligible electronic conductivity may also promote the unintentional formation of Li dendrites, being currently one of the key issues hindering the development of long-lasting all-solid-state batteries. This interplay is suggested recently for garnet-type Li₇La₃Zr₂O₁₂ (LLZO). It is, however, well known that the overall macroscopic electronic conductivity may be governed by a range of extrinsic factors such as impurities, chemical inhomogeneities, grain boundaries, morphology, and size effects. Here, advantage of Czochralski-grown single crystals, which offer the unique opportunity to evaluate intrinsic properties of a chemically homogeneous matrix, is taken to measure the electronic conductivity σ_eon. Via long-time, high-precision potentiostatic polarization experiments an upper limit of σ_eon in the order of 5 × 10⁻¹⁰ S cm⁻¹ (293 K) is estimated. This value is by six orders of magnitude lower than the corresponding total conductivity σ_total = 10⁻³ S cm⁻¹ of Ga-LLZO. Thus, it is concluded that the high values of σ_eon recently reported for similar systems do not necessarily mirror intragrain bulk properties of chemically homogenous systems but may originate from chemically inhomogeneous interfacial areas.