Electronic Conductivity of Lithium Solid Electrolytes

While significant efforts have been devoted to improving the ionic conductivity of lithium solid electrolytes (SEs), electronic transport, which has an important role in the calendar life, energy density, and cycling stability of solid-state batteries (SSBs), is rarely studied. In this talk, we will present our recent results on the electronic conductivities of three representative SEs, including Li3PS4, Li7La3Zr2O12, and Li3YCl6 for sulfide-, oxide-, and halide-based SEs, respectively. By revisiting direct current polarizations using two-blocking-electrode cells and the Hebb-Wagner approach, we propose that the electronic conductivities of SEs are overestimated from the conventional measurements. We will discuss the limitations and sources of inaccuracy for these measurements and highlight the anodic decomposition of SE as the key source for the overestimated result. Modifications in the electrode selection and data interpretation are also proposed to approach the intrinsic electronic conductivity of SEs. To estimate the electronic conductivity of sulfides that decompose during measurement, a two-step polarization method will also be introduced. The electronic conductivities of all SEs measured by the modified approach are one or two orders of magnitude lower than the reported value. Despite that, the electronic conductivity of sulfides seems to be still quite high to enable SSBs with a long calendar life of >10 years, highlighting the critical need for a more careful study of electronic transport in lithium SEs.