Origin of Bonding between the SWCNT and the Fe3O4(001) Surface and the Enhanced Electrical Conductivity

Recent experiments have demonstrated that adding single-wall carbon nanotubes (SWCNTs) to Fe3O4 nanoparticle electrodes leads to dramatically improved electrical conductivity and performance of Li ion batteries. Our density functional theory (DFT) calculations reveal that the interactions between both pristine and B- or N-doped SWCNTs and the Fe3O4(001) surface are very weak. Although C vacancies in SWCNTs can lead to stronger chemical bonding between SWCNTs and Fe3O4(001) surfaces, the binding and electrical conductivity in this case are not ideal. Interestingly, we show that transition-metal (Fe, Ni) atoms or clusters facilitate the formation of strong chemical bonding between SWCNTs and Fe3O4(001) surfaces, providing excellent channels for electrons flowing between SWCNTs and Fe3O4(001) surfaces, which is essential for improving electrical conductivity of the mixed electrodes. The calculated electron conductance of the transition-metal-decorated system is improved by more than 2 orders of magnitude, in agreement with experimental observations. Our results, therefore, suggest a viable way for functionalizing SWCNTs.