Interfacial Li Ion Storage And Doping Effects In Graphene/Li₂O

Graphene/metal-oxide nanocomposites have been widely used as the anode materials for lithium ion batteries.The synergistic effects between graphene and metal oxide,such as the higher lithium storage capacity beyond their theoretical capacity,have been revealed experimentally.The graphene/metal-oxide interface plays a crucial role in the formation of the synergistic effects.Moreover,the doping in graphene can enhance the electrochemical properties of graphene/metal-oxide.With the formation of lithium oxide during the charging/discharging process for most of metal oxides under consideration,in this study,interface and doping effects on Li ion storage behavior in graphene/Li₂O have been systematically investigated using first-principles total energy calculations.Compared to the Li adsorption on the surface of graphene and Li₂O,Li adsorption at the interface exhibits the synergistic effect which results in interfacial Li storage and benefits the specific capacity.Doping atom can adjust the performance of graphene,which will further affect the electrochemical performance of graphene/metal oxide nanocomposites.Due to the p-type and n-type doping resulting from B and N dopants,the Li storage capability is enhanced and reduced in the B and N doped graphene/Li₂O,respectively.O and S doping results in the enhancement of Li adsorption due to the localization of the electronic states in graphene.The localization of electronic states combined with the appropriate dopant electronegativity can enhance the Li atoms adsorption and diffusion simultaneously.As a result,the highest interfacial lithium storage is obtained for O-doped system,while S-doped system possesses the well balance between interfacial Li storage and diffusion energy barrier.The research opens a new insight to the design of graphene/metal oxide composites as energy storage materials.