Benoît VAN TROEYE has received the 2018 IMCN Best Thesis Award on May 29, 2019.
His work was entitled "First-principles investigation of interface in composite layered materials : application to lithium-ion batteries".
This Prize, which is granted yearly by the IMCN Institute, rewards the most outstanding PhD work among those who graduated during the previous civil year (2018 in the present case).
A selection Committee chaired by Prof. Jacques DEVAUX and composed of one member per pole and the VPR noticed the high quantity and quality of research carried out by Benoît, as well as his communication skills at various levels (conferences, publications, PhD defense). This initiative aims at promoting excellence in scientific research within the Institute.
Graphite is the prototypical anode material in lithium-ion batteries, as it can withstand hundreds of lithiation-delithiation cycles without breaking. Other materials, like silicon and black phosphorus (a layered material, like graphite), show much larger theoretical storage capacity than that of graphite. Still, this large specific capacity cannot be exploited in practice due to the important volume expansion associated with lithiation in these materials, leading quickly to their mechanical fracture. For sodiation, it has been recently demonstrated that a composite layered material constructed by stacking alternately graphene and phosphorene layers (the monolayers counterparts of graphene and black phosphorus) on top of the others combines both the advantages of graphite and black phosphorus (good cyclability and high capacity storage) . Still, the origin of these improved performances was unknown at that time.
In this thesis, I investigate using first-principles computations (Density Functional Theory) the nanoscopic origin of these improved performances. It is found that the graphene layers do not only play the role of an electrical conductivity enhancer but also that of an elastic buffer in the composite layered material. In addition, an original intercalation process is identified at the interface between graphene and the lithiated phase of phosphorene. I predict that the material with the perfect alternation between graphene and phosphorene layers should show the most interesting properties for lithium-ion battery applications . In addition, an extension of the Frenkel Kontorova model is proposed to investigate the interface nature between graphene and phosphorene, as well as that between other 2D materials.