23March 2021 ESRFnews
Synchrotron X-ray holotomography shows Renault the best makeup for lithium-ion battery electrodes.
Electrodes play a big role in the performance of lithium-ion batteries, but their microstructures are often developed by trial and error. Now a team from the Laboratory for the Reactivity and Chemistry of Solids (LRCS, run by the CNRS and the University of Amiens Jules Verne) in France, together with the French network for Research and Technology on the Electrochemical Storage of Energy (RS2E), the ESRF and the vehicle manufacturer Renault, have found an evidence-based way to determine the best electrode microstructures: synchrotron X-ray holotomography. Lithium-ion battery electrodes
consist of three components: the active material, which is lithium nickel manganese cobalt oxide (NMC); the carbon binder domain (CBD), in which carbon promotes the electrical connectivity of a polymer binder; and finally, a network of pores, which are filled with a liquid electrolyte. Thanks to its exploitation of phase contrast, X-ray holotomography on the ESRF ID16B beamline allowed the researchers to distinguish between the heavier elements in this mix, such as NMC, and the lighter elements, such as the CBD, in composite electrodes of varying proportions of CBD all in three dimensions, at nanoscale resolution and in very short acquisition times. As a result, the researchers could quantitatively analyse the spatial relation of the electrodes three components in an ensemble of 500 individual active particles, with a spatial resolution of 50 nm in a volume of 50 × 60 × 60 μm. From each particle they could derive statistics about the surface contact with CBD, the porosity and even
the particle-to-particle connectivity, to monitor the evolution in performance as a function of interfacial areas.
U-turn According to Arnaud Demortière of LRCS, there had been a prevailing belief among battery scientists that a greater proportion of CBD delivers greater battery performance. He and his colleagues, however, found the complete opposite : better performance from less carbon binder. They believe lower proportions of CBD allow the liquid electrolyte to circulate more easily to reach the active material. Without our synchrotron experiments, we could not have
Basing electrodes on evidence
Electrodes are crucial to the performance of lithium-ion batteries in electric vehicles, such as the Renault Zoe. Via holotomography on ID16B, the ESRF can help to hone their microstructures.
R E N A U LT
reached this conclusion, he says. The team now want to monitor the
lithiation delithiation process inside the electrode of a custom-made cell during electrochemical cycling, in the cell s normal working environment. That would allow the researchers to correlate, in three-dimensions, the lithiation mechanism of several individual NMC particles with the local configuration of CBD and the porous network inside the cathode thereby painting a complete picture of what is going on in battery electrodes during the charge discharge process. The EBS will improve the
spatial and temporal resolution for nanotomography, opening new opportunities for operando experiments, says Julie Villanova, scientist on ID16B.
Montserrat Capellas Espuny
Without synchrotron experiments, we could not have reached this conclusion
ESRFMar21_Industry_v2.indd 23 26/02/2021 10:49