Improving the Li-Electrochemical Properties of Monodisperse Ni2P Nanoparticles by Self-Generated Carbon Coating
Résumé
Carbon coating of electrode materials is nowadays a major tool to improve the electronic percolation of the electrode. In this study, a self-generated carbon coating is described as a new way to deposit a regular thin layer of carbon on the surface of nanoparticles. It relies on the soft decomposition of the nanoparticles surface native ligands, containing alkyl chains, under inert atmosphere at 400 °C, a route particularly suited for oxidation-sensitive nanoparticles. Using 25 nm monodispersed Ni2P nanoparticles as a model phase, we succeeded in forming nonsintered and nonoxidized carbon-coated nanoparticles. The carbon coating is then tuned in thickness by modifying the ligands set. Electrochemical properties of the resulting Ni2P/C nanoparticles vs Li are compared with those of bulk Ni2P. Both materials are shown to undergo a conversion reaction. The capacity of the bulk material collapses after a few cycles while Ni2P/C nanoparticles show much better retention. The self-generated carbon coating is thus found to promote Li uptake by providing a Li-permeable electron-conductive percolating network and by improving the mechanical integrity of the electrode.