The Nanoscale Cryo-Microscopy of the Nucleation and Growth of Dendrites in Lithium-Ion Batteries

Internal short-circuits (ISC) are a major cause of failure in lithium-ion batteries and typically occur due to the dendrite formation, although the actual mechanism of the nucleation and growth of these microstructures is still not well understood. This is especially true at the nanoscale due to the limitations presented by current techniques, such as scanning electron microscopy (SEM). The purpose of this research project is to present the application of a new cryo-microscopy set-up, the Imperial Centre for the Cryo-Microscopy of Materials (I(CM)2), at Imperial College London. This has the capability of combining cryo-transmission electron microscopy (cryo-TEM) with cryo-atom probe tomography (cryo-APT) to study dendrite nucleation at a sub-atomic scale. When correlated, these techniques will provide information on the local chemistry, particularly degradation-related defects, and a highly resolved compositional mapping of the atomic arrangement, respectively, thus painting a clearer image of the dendrite nucleation mechanism than what is currently known.

It is well known that lighter elements, such as hydrogen, carbon, lithium and sulphur, have been key in advancing battery technology as we know it. Yet, due to their susceptibility to beam damage and challenges associated with their quantification, there are clear limitations associated with the study of such elements. APT is a growing technology that exhibits nearly uniform capabilities in identifying even the lightest of elements, making it a high-potential candidate in its application to lithium-ion battery systems. Achieving an improved understanding of the local chemistry and structural variations, made possible with this workflow, associated with dendrite nucleation and evolution will improve our understanding of their mechanism and growth. These results will subsequently be crucial in devising dendrite-suppression measures and contributing to the development of next-generation LIBs. Industry and consumers will also benefit from an improved understanding of the root causes of ISCs, a key limitation in battery technology today and a challenge that researchers globally are committed to overcoming.

This workflow will be used to investigate the effects of ambient temperature variation, electrolyte composition, excess current density and state of charge (SoC) on dendrite evolution and chemistry, which will also help to improve our understanding of the interplay of these factors on battery degradation. As this research project is one of the first to use this set-up, a crucial aspect will be developing a suitable protocol for the sample (electrode) preparation, transfer and characterisation. This information can then be used for subsequent projects, particularly those relating to energy materials, while the more general site-selective analysis techniques will be beneficial to a wider reach of scientists using cryo-methods.