Abstract
Boron-substituted disordered carbons indicate large Li storage compared to pristine carbons and can be apromising anode-material in high-energy Li-ion batteries. In order to clarify the reason why boron-substituted carbonscan store more Li atoms than pristine carbons, we employed polyaromatic hydrocarbons as model clusters for disordered carbons and investigated the effect of boron and nitrogen substitutions on the stable structures and electronic propertiesof model clusters, by using a semiempirical molecular orbital method. By boron-substitution into carbon clusters, anelectron acceptor level is created in a lower energy region than that for the pristine carbon cluster. This lower levelaccepts electrons from the absorbed Li atoms more easily, so that the stabilization energy by Li absorption for the boronsubstituted cluster is much larger than that for the pristine carbon cluster. Onthe other hand, for the nitrogen-substitutedclusters, the electron acceptor level is almost the same as that for the pristine carbon, so that the stabilization energyis not enhanced by nitrogen-substitution. Therefore, we conclude that the large Li storage in boron-substituted disorderedcarbons is related to the creation of a lower electron-acceptor level caused by boron-substitution, which makes easierelectron transfer from absorbed Li atoms to host materials.
