High-throughput mechanical characterization methods for composite electrodes and in-situ analysis of Li-ion batteries

Electrodes in commercial rechargeable batteries are microscopically heterogeneous materials. The constituents often have large variation in their mechanical properties, making the characterization process a challenging task. In addition, the mechanical properties and mechanical behaviors of electrodes are closely coupled with the electrochemical processes of lithium insertion and extraction. There is an urgent need to develop an experimental platform to characterize the chemomechanical response of electrodes under the in-situ conditions of charge and discharge. In the first part of this thesis, instrumented grid indentation is employed to determine the elastic modulus and hardness of the constituent phases of a composite cathode. The approach relies on an array of indentations and statistical analysis of the experimental output. The statistically interpreted properties of the active particles and matrix are further validated through indentation at selected sites. The combinatory technique of grid indentation and statistical deconvolution is demonstrated to be a fast and reliable route to quantify the mechanical properties of composite electrodes. In the second part of work, a nanoindenter, a liquid cell, and an electrochemical station are integrated into an inert gas filled glovebox. The developed experimental platform makes it possible to perform mechanical tests of thin film electrodes during in-situ charge and discharge cycles and to monitor the evolution of the mechanical properties as a function of the state of charge. The technique overcomes practical issues related with environment requirements and instrument limitations, and enables comprehensive and consistent data acquisition. Furthermore, the procedure allows experiments to be carried out in a considerably shorter time than existing methods. In a preliminary study, this technique is applied to the in-situ characterization of silicon thin film and it is validated against the literature results. Overall, the thesis work focuses on the mechanical characterization, both ex-situ and in-situ, of electrodes in Li-ion batteries. The developed methodology and experimental platform are significant toward the complete understanding of the chemomechanical behaviors of high-performance batteries