Operando Liquid-Phase TEM Experiments for the Investigation of Dissolution Kinetics: Application to Li-Ion Battery Materials

We present here a novel and universal sample preparation method for liquid-phase transmission electron microscopy (TEM) experiments involving powder materials. Thanks to this new protocol, we demonstrate the ability to study the dissolution of cathode materials by sulfuric acid using operando TEM. Based on ultramicrotomy, this method has been developed to avoid compatibility issues between sample size and liquid cell geometry. The observation parameters have been optimized to get the best contrast in scanning TEM (STEM) images. The reaction kinetics have been investigated by image analysis and compared to those obtained ex situ. By taking into account the sample geometry and the reacting surfaces in both experiments, we show that the reaction kinetics are equivalent and could be overlaid. This proves that the protocol developed enables real operando experiments, as it provides quantitative data at the nanoscale that are representative of the bulk specimen. The main challenges of such a protocol for operando liquid-phase TEM, as well as the accuracy of the image analysis method used, are also discussed.