Evaluation of Degradation Processes in Lithium-Based Thick Film Electrodes by Laser-Induced Breakdown Spectroscopy

Studying degradation processes in lithium-ion batteries provides beneficial information for further improvement of electrode concepts and cell design. One specific characteristic, which is strongly connected to a homogeneous lithium distribution within entire electrodes, is a uniform intercalation / deintercalation process of lithium-ions, which in turn assigns cell properties such as lifetime, combined with failure mechanisms during electrochemical cycling. The homogeneity of lithium distribution was investigated for three types of thick film electrodes: (i) electrodes after manufacturing, (ii) electrochemically cycled electrodes with locally compressed porosity regions, and (iii) electrochemically cycled electrodes with laser-generated electrode architectures. 3D mapping of lithium in thick film electrodes was performed by laser-induced breakdown spectroscopy (LIBS), which is an analytical tool offering a full 3D elemental analysis of the entire electrode surface and volume. Within a few seconds, a chemical map including quantitative lithium concentration values could be obtained. Additionally, post-mortem LIBS analyses were correlated with electrochemical data, offering new perspectives in studying and visualizing degradation processes during battery operation. Briefly, critical points of cell failure were reliable localized on electrodes. It is worth mentioning that one main mechanism of cell failure was attributed to the electrical short cut at cathode side indicated by an enormous increase in lithium concentration which we assign to the metallic phase. Using the information obtained by LIBS, the continuous evolution of degradation processes could be illustrated. This enabled a model-like description of the degradation behaviour of thick-film electrodes, which in final consequence follows the scenario of spontaneous cell failure. Four characteristic electrode segments were detected in which the lithium concentration and its distribution showed a strong deviation from electrochemically uncycled reference electrodes (after manufacturing). The significant increase in lithium content - as starting point for degradation - could be initiated by mechanical compression inside the cell or dendrite grow processes. Depending on the electrode design and properties such as porosity, tortuosity, or film adhesion, design criteria for optimized 3D electrodes could be derived.