Covalent organic framework@graphene composite as a high-performance electrode for Li-ion batteries

As emerging candidates for the electrode materials of next-generation rechargeable batteries, covalent organic frameworks (COFs) have large charge capacity, wide ion diffusion paths and low potential range. However, organic electrodes generally suffer from low conductivity. Graphene (G) possesses great strength, flexibility and has been widely used as a type of conductive additive due to its remarkable electrical conductivity. Here we propose a composite constructed by a certain kind of COF and a pristine G sheet (COF@G), the characteristics of which have been systematically investigated based on density functional theory calculations and molecular dynamics simulations. Results indicate that the COF@G (COF/G, COF/COF/G, COF/G/G) can exhibit good electronic conductivity and ultrahigh capability, which can be used as high-performance electrodes of Li-ion batteries. For Li-ions (Li+), they can provide strong adsorption sites and smooth diffusion channels leading to high specific capacity and good rate capability. More importantly, the coupling interaction of the COF and the G can greatly inhibit the structure changes of the COF during the lithiation process, and the volumetric change rate is less than 23%. Among them, the COF/G is the most suitable for Li+ adsorption and corresponding theoretical capacity can reach 353 mAh/g.