Abstract
Li-Ion batteries, which are now an integral part of our everyday lives, are essentially based on the use of insertion compounds. These have a major impact, controlling the battery's capacity, output potential, autonomy and energy density. What are these insertion materials or sponges for Li, Na... ? That's what this first lecture aims to answer.
Throughout this lecture, I have briefly described the principle of battery operation before focusing on the chemical and physical principles underlying these insertion reactions. In addition, I recalled the necessary knowledge of crystallography (dimensionality of structures and symmetry of docking sites) and electronic structure (band structure, Fermi level, redox couple). These notions are essential for understanding this series of lectures. It was also an opportunity to present the excitement generated by the genesis of the first intercalation materials (graphite, lithium alloys and transition metal dichalcogenides) in the world of batteries. Despite the great scientific advances that were made, leading to the identification of a multitude of lamellar transition metal disulfides (MS2), the numerous attempts to industrialize batteries (Li-MS2) only met with setbacks that eventually led to their abandonment. This can be explained by the safety issues associated with the formation of highly divided and reactive Li during cycling, which can form dendrites, creating short-circuits and possibly an explosion. Finally, from a more fundamental point of view , numerous examples of materials with atomic or molecular redox centers have shown that electrochemistry can be used as spectroscopy to test/probe the band structure of certain insertion compounds.
