Reinforcement of binder adhesion for nickel-rich layered oxide in lithium-ion batteries using perfluorinated molecular surface modification

Abstract

Ni-rich layered oxides are considered the most promising candidates for cathode materials for use in electric vehicles because of their high energy density and low cost. However, the cyclability of Ni-rich layered oxide needs to be improved because it suffers from contact loss by microcracks owing to the large anisotropic volume changes during cycling. Furthermore, its unstable surface, which releases lithium impurities by water contamination, must also be mitigated. To improve the adhesive force with a polyvinyl fluoride (PVdF) binder as well as the air-stability, a self-assembled monolayer of 1H,1H–2H,2H-perfluorodecyltriethoxysilane (PFDTES) is introduced onto the surface of Ni-rich layered oxide cathode powder. A molecular functional monolayer with fluorocarbons on Ni-rich layered oxide powder is delivered to achieve an ∼ 13 Å thin homogeneous molecular-level functional coating at a negligible weight ratio. The functionalized surface improves the adhesion between PVdF and cathode powder by F⋯F interaction, relieving the electrode detachment. As a result, cycling failure mode is remarkably mitigated. The fluorinated hydrophobic surface alleviates water contamination, thereby reducing lithium impurities.