Researchers from Russia’s Skoltech Center for Energy Science and Technology (CEST) have used a bespoke lithium-ion cell to visualise solid electrolyte interphrase (SEI) formation on battery-grade materials.
The specially designed cell allowed the measurements necessary for this direct observation of SEI formation on battery-grade carbonaceous electrode materials using in-situ atomic force microscopy (AFM).
The results of this work, supported by the Russian Science Foundation, were published in the journal Scientific Reports.
Previously, measurements were carried out on Highly Oriented Pyrolytic Graphite (HOPG), a very pure and ordered form of graphite that has a clean and atomically flat basal plane surface, but which is a poor replacement for battery-grade electrode materials.
The researchers found the SEI on battery-grade materials nucleated at different potential than that on HOPG, and was more than two times thicker and mechanically stronger.
They were therefore able to demonstrate that SEI was better bound with the rough surface of battery-grade graphite than with the flat surface of HOPG.
Research scientist Sergey Luchkin and professor Keith Stevenson led the Skoltech team.
Luchkin said: “Battery-grade materials are powders, and visualising dynamic processes on their surface by AFM, especially in liquid environment, is challenging.
“A standard battery electrode is too rough for such measurements, and isolated particles tend to detach from substrate during scanning. To overcome this issue, we embedded the particles into epoxy resin and made a cross section, so the particles were firmly fixed in the substrate.
Stevenson said: “Spatially-resolved investigations of battery interfaces and interphases detailed in this work provide significant new insights into the structure and evolution of the anode SEI. Therefore, they provide firm guidelines for rational electrolyte design to enable high performance batteries with improved safety.”