Ion transport limitations in all-solid-state lithium battery electrodes containing a sulfide-based electrolyte

We study ion transport limitations in composite electrodes for all-solid-state lithium batteries. These electrodes are composed of variable volume fractions of active material particles (Li4Ti5O12) and of a sulfide-based solid electrolyte, while the volume fraction of carbon black acting as conductive additive is held constant. The ion transport limitations are characterized by impedance spectroscopic measurements on different types of symmetrical solid-state cells. Ion transport resistances are calculated either based on a transmission line model or from the Li+ ion current under electron-blocking conditions. In addition, we demonstrate a cell setup, for which both types of measurements can be carried out on the same composite electrodes. Effective ion transport tortuosities tau(eff) are then derived from the resistance values and analyzed in dependence on the volume fraction of the solid electrolyte in the composite electrodes, epsilon . We show that for epsilon >= 0.4, both methods yield very similar tortuosity values, while discrepancies between the results obtained from the two methods are found for epsilon < 0.4. Our results give strong indication that the power density of solid-state batteries with volume fractions epsilon around 0.4 of the best solid Li+ electrolytes should be at least equal that of commercial liquid electrolyte-based Li-ion batteries.