Operando spatial mapping of lithium concentration using thermal-wave sensing

The development of battery sensing techniques is crucial for safe, reliable, and fast operation of lithium-ion batteries (LIBs). There is a growing realization that the spatially averaged chemical information provided by existing battery diagnostic tools is insufficient for understanding degradation of LIBs. Here, we report the use of thermal waves for operando probing of the local lithium concentration as a function of depth inside battery electrodes. The dependence of the thermal conductivity of electrodes on lithiation is used for lithium detection for the first time. A proof-of-concept study of graphite anodes demonstrates that thermal-wave sensing provides spatial information of lithium concentration comparable with experimental results using synchrotron X-ray diffraction. Therefore, a valuable battery sensing technique based on thermal waves is developed for studying the lithium concentration and the degradation of electrodes during fast charge, which may lead to much cheaper and faster sensing techniques compared with synchrotron-based techniques.