Operando Detection of Void Formation during Lithium Stripping in Solid-State Batteries Using Single-Frequency Impedance Analysis

Solid-state batteries with lithium (Li) metal anodes experience stability issues at the Li|solid electrolyte (SE) interface during stripping due to void formation. In this work, an operando detection strategy for void formation at the Li|SE interface is developed based on galvanostatic electrochemical impedance spectroscopy (GEIS). The stripping behaviors of in situ-formed Li on Li 6 PS 5 Cl and Li 7 La 3 Zr 2 O 12 SEs in an “anode-free” configuration are studied. By comparing the impedance data in the frequency domain to the cell voltage trace in real time, we identify descriptors that enable early detection of void formation. It is found that the imaginary component of the impedance in specific frequency ranges enables earlier detection of void formation compared to other descriptors. To describe these trends, a three-dimensional (3-D) model of the interfacial void geometry is developed to predict the impedance response, which agrees well with experiments. Informed by these GEIS results, we demonstrate the potential of an operando impedance measurement using only one frequency to enable early detection of voids, without the need for broadband impedance equipment or real-time fitting with equivalent circuit models. This approach can be integrated into a control system to enable early diagnosis of interfacial degradation in solid-state batteries.