Timescale identification of electrochemical processes in all-solid-state batteries using an advanced three-electrode cell setup

Two-electrode (2E) setups commonly employed in solid-state batteries (SSBs) are often not sufficient to deconvolute electrochemical processes of anode/cathode. To address this issue, herein we introduce a three-electrode (3E) cell setup, making use of an electrochemically prelithiated lithium titanate composite as reference electrode (LTO-RE). The potential/state of charge/kinetics relationship of LTO was revisited by conducting both ex situ and in situ electrochemical impedance spectroscopy measurements and corresponding distribution of relaxation times (DRT) analyses. The proposed LTO-RE maintains a stable reference potential of about 1.57 V vs. Li + /Li with minimal drift (by 8 mV over 600 h) and negligible growth in charge-transfer resistance, enabling long-term use in 3E SSB cells. Time constants representing the involved kinetic processes are often quite close and obscure reliable assessment of contributions from different electrodes. By implementing the 3E approach, the overlap of kinetic processes between LTO working electrode and In/InLi counter electrode across a broad range of timescales can be effectively separated and identified. The proposed 3E setup offers a viable approach for thoroughly studying the interfacial kinetics of individual electrodes, thereby enhancing understanding of the underlying degradation processes in SSBs and ensuring stable long-term testing.