Characterization and quantification of lithiation heterogeneities in graphite electrodes

International audience ; The need of an ecological transition at the international scale imposes to find solution to store clean energies. In this regard, Li-ion technology represents a mature solution providing a reasonable energy density that can still be improved and a low power density that needs in depth investigation. Currently, power and energy are antagonist terms when it comes to batteries and this limitation requires better investigation. One of the reasons is the commercial graphite electrode which is still limited in terms of kinetics especially at fast charging rate, leading us to rethink the electrode engineering to improve fast charging while keeping high energy. Several parameters could be tuned to improve power and energy density: the electrode loading (allowing high energy density with high loading), the graphite particle size (determining the lithium solid state diffusion) and the electrode porosity (impacting the ionic diffusion and the electronic percolation)1. In this regard, we investigated the power limitations of graphite electrodes, especially the impact of the electrode engineering on fast charging. We performed an experiment at ID31 beamline (ESRF synchrotron) where we scanned half-cell composed of graphite as working electrode and Li metal as counter electrode in liquid organic electrolyte. The WAXS experiment leads us to scan the cell as Z profile (each 5 µm) in the depth of the graphite electrode to identify possible ionic limitation (Li gradient). As graphite electrode possesses several phase transitions, it is easy to attribute a particular angle to a specific phase and thus, as can be seen in Figure 1a, we correlated the LiC6 peak integration extracted from the diffraction patterns as a function of the cell cycling and of the Z profile of the electrode. It revealed a Li intercalation gradient from the slices near the separator to the ones near the current collector, gradient coming most probably from the electrode engineering and impacting the lithium diffusion in the ...