Transport processes in all-solid-state batteries: At the In−Li anode | separator interface, a laterally inhomogeneous interphase is formed during decomposition of the solid electrolyte, causing a finite-length Li transport impedance inside the In−Li alloy. Inside the composite cathode, the LiNbO₃ layer coated onto the cathode active material (CAM) particles acts as artificial interphase with relatively high Li⁺ ion conductivity and improves the accessibility of the CAM particle surface by the Li⁺ ions.

Abstract

All-solid-state-batteries (ASSBs) are considered as promising next-generation batteries in order to achieve improvements in both energy density and safety. The complex electrochemical processes in ASSBs taking place on different time scales can be probed by means of electrochemical impedance spectroscopy. However, the separation of anode and cathode contributions to the impedance and the understanding of the underlying electrochemical processes in both electrodes is a challenging task. Here, we compare the impedance spectrum of a prototypical full ASSB to those of symmetric cells anode | separator | anode and cathode | separator | cathode. We use Ni-rich polycrystalline LiNi_0.85Co_0.10Mn_0.05O₂ particles as active material inside the composite cathode and an indium-lithium alloy as anode. Based on the comparison, we show that the charge transfer process inside the cathode is remarkably fast, i. e., even faster than observed for cathodes of batteries with liquid electrolyte. Our results give indication that the differences in the time scales of cathode and anode processes are related to the distinct transport properties of interphases inside the cathode and at the anode | separator interface, respectively.