Interface and Doping Effects on Li Ion Storage Behavior of Graphene/Li2O

Graphene/metal oxide nanocomposites have been widely used as the anode materials for Li ion batteries, which exhibit much higher Li storage capacity beyond their theoretical capacity. In order to make clear the Li storage mechanism in graphene/metal oxide, we systematically investigated the interface and (B, N, O, S) doping effects on Li ion storage behavior in graphene/Li2O using first-principles total energy calculations. It is revealed that the doping elements increase the van der Waals interface interaction of graphene/Li2O by changing the electronic structure of graphene through different mechanisms. The Li storage at the graphene/Li2O interface exhibits the synergistic effect resulting from the enhanced interface interaction by the Li insertion at the interface. The p-type and n-type doping induced by B and N dopants in graphene enhance and reduce the Li storage capability of graphene/Li2O, respectively. O and S doping result in the localization of the electronic states in graphene which benefits the Li adsorption at the interface. The localization of electronic states combined with the appropriate dopant electronegativity can enhance the Li atoms adsorption and diffusion simultaneously. Thereby, the highest interfacial lithium storage (0.330 mhA/m(2)) is obtained for the O-doped system, while the S-doped system possesses the good balance between interfacial Li storage (0.220 mhA/m(2)) and diffusion energy barrier (0.27 eV). The results open a new insight for the design of graphene/metal oxide composites as energy storage materials.