Defect Detection in Solid-State Battery Electrolytes Using Lock-in Thermal Imaging

Defective regions in battery materials often generate excess or non-uniform heat profiles during operation. Here, we discuss lock-in thermography as a high-sensitivity, spatially-resolved, and non-destructive technique to characterize defects and guide the targeted optimization of new battery materials and cell designs. As an example, we thermally image all-solid-state cells with β-Li₃PS₄ electrolyte, showing point-like heat signatures that correlate with cell breakdown. Based on the current/voltage cycling characteristics and electrochemical impedance spectroscopy, we attribute heating at the breakdown sites primarily to resistive current flow through dendrites. To assist in enabling wider application of lock-in thermography to emerging battery materials, we discuss several parameters necessary to optimize this technique, including the influences of surface thermal emissivity, thermal diffusivity, and lock-in modulation frequency.