First Principle Calculations On Electrical Properties Effect Of Li On Graphene, BC_x, C_xN Surfaces

Lithium ion battery (LIBs) has been widely used in mobile devices, and also thepotential power source of electric vehicles and hybrid electric vehicle. Lithium intercalationcompounds and graphite-based materials are usually used in anodes for LIBs nowadays.However, due to lithium storage capacity of graphite is limited, and can’t meet therequirements for higher Li storage capacity. Graphene due to their excellent electronicproperties and structure has attracted the interest of people. Electrical properties and lithiumstorage capacity of Boron (Nitrogen)-doped graphene have changed. The geometrical structuresof Li atom adsorption on the most stable sites of pristine and Boron (Nitrogen)-dopedconcentration for25%、16.67%、12.5%(atom fraction) graphene were optimized by using firstprinciple method based on density functional theory (DFT). The band structures, density ofstates (DOS), electron transferring, electron density differences and binding energies of bothpristine and Boron (Nitrogen)-doped graphene were calculated theoretically. Throughthe calculation we can mainly draw the following conclusions:(1) Electrical properties effect of Li on graphene: after single Li atoms adsorption ongraphene surface, the graphene-Li system presents metal property. There is a mixture of ionicbond and covalent bond between graphene and Li. After lithium atom adsorption on graphenethere is a2s state degradation phenomenon.(2) Electrical properties effect of Li on BC3、C3N: when B-doped concentration which is25%form a lack of electronic state, it is beneficial to adsorption Li atom with free electrons andenhances remarkably the adsorbing energy of Li atom on graphene. When N-dopedconcentration which is25%form a rich electronic state, and decreases the adsorbing energy ofLi atom on graphene. After Li adsoption on BC3and C3N surface, the Fermi level ofcorresponding system rising relative to before Li adsorption, and BC3-Li and C3N-Li systemshow metal properties, from semiconductor to a conductor. There is a mixture of ionic bond andcovalent bond between BC3、C3N and Li.(3) Electrical properties effect of Li on BC7、C7N: when B-doped concentration which is12.5%form a lack of electronic state, the adsorbing energy of Li on BC7surface is larger thanthat on BC3surface. When N-doped concentration which is12.5%form a rich electronic state, the adsorbing energy of Li on C7N surface is larger than that on C3N surface. After single Liatom adsoption on BC7and C7N surface, BC7-Li and C7N-Li system both showmetal properties. There is a mixture of ionic bond and covalent bond between BC7、C7N and Li.(4) Electrical properties effect of Li on BC5、C5N: when B-doped concentration which is16.67%form a lack of electronic state, the adsorbing energy of Li on BC5surface is the largestof all systems. When N-doped concentration which is16.67%form a rich electronic state, theadsorbing energy of Li on C5N surface is larger than that on C3N surface and smaller than thaton C7N surface. After single Li atom adsoption on BC5and C5N surface, BC5-Li and C5N-Lisystem both show metal properties. There is a mixture of ionic bond and covalent bond betweenBC5、C5N and Li.