First Principles Study Of Electronic Properties Of Corner Bilayer Graphene And Its Sodium Storage Properties

Sodium ion batteries have many excellent properties and a wide range of applications.In order to improve the adsorption capacity of sodium ions,bilayer graphene prepared from graphene is usually enhanced by defects and doping.In this paper,the electronic structures of defective corner bilayer graphene,boron-doped corner bilayer graphite and vacancy-defective boron-doped corner bilayer graphene and their sodium storage properties are investigated using the first-principles approach to provide references for the optimal design of sodium storage anode materials.The main research works are as follows:1.The energy band structures of bilayer graphene with different turning angles(21.8°,13.2°,9.4° and AB stacks)are analyzed computationally based on the first nature principle.In particular,the electronic structures of corner(21.8°)bilayer graphene,vacancy defect corner(21.8°)bilayer graphene,boron-doped corner(21.8°)bilayer graphite and boron-doped corner(21.8°)bilayer graphene with vacancy defects are analyzed in more detail.The calculation results show that the corner bilayer graphene has some characteristics of both AA and AB stacked bilayer graphene,and the dispersion relation of its electrons is still linear at the M-point attachment in k-space,and the band gap is small and metallic,which is favorable for use as an electrode material.The specific conclusions are as follows:(1)The band gap value of the corner(21.8°)bilayer graphene,calculated by GGA,is nearly zero;the band gap value calculated by HSE06 is 9.2 meV,which exhibits semimetallicity;the corner(13.14°)and(9.4°)bilayer graphene also exhibit semimetallicity.(2)The vacancy defect makes the energy states near the Fermi energy level increase,which is beneficial to improve its electrical conductivity.However,the smooth energy band constrains the electron motion and the tendency of localization,which means the increase of the effective mass and the decrease of the mobility of electrons in this energy region.(3)In the boron-doped corner(21.8°)bilayer graphene,energy states(extra energy bands)are introduced near the Fermi energy level,but they are not smooth energy bands,which is beneficial to the conductivity.The boron-doped corner(21.8°)bilayer graphene presents stronger metallicity.(4)By analyzing the energy band structure diagram of the vacancy-defective borondoped corner(21.8°)bilayer graphene,the smooth energy band appears near the Fermi energy level,but compared with the vacancy-defective corner(21.8°)bilayer graphene,the smooth energy band out of the Fermi energy level is reduced,and the vacancy-defective boron-doped corner(21.8°)bilayer graphene still shows metallicity.(5)The external electric field can change the band gap of corner graphene;the electric field applied in the<001>direction has a more pronounced change in the band gap value than the band gap in other directions.2.A computational study was conducted for the sodium adsorption performance of corner(21.8°)bilayer graphene.A model of sodium-turned-corner graphene adsorption system was developed and the sodium adsorption performance of its different adsorption sites was analyzed computationally.The main conclusions are as follows:(1)The best sodium adsorption site for sodium atoms adsorbed by corner(21.8°)bilayer graphene is the H-site.for H-site adsorption,the total energy of the system is-258.7229 eV,the adsorption energy of a single sodium atom is-0.3663 eV,and the adsorption distance is 2.34 ? at this time.(2)The best adsorption position for sodium atom adsorption by bilayer graphite is also the H-position.The adsorption energy of single sodium atom of vacancy defect corner graphene is smaller than that of single sodium adsorption energy of corner(21.8°)bilayer graphene,so the adsorption effect of boron-doped corner(21.8°)bilayer graphene on sodium atom is stronger than that of corner(21.8°)bilayer graphene has a stronger adsorption capacity.(3)The best adsorption position of sodium adsorption by boron doped corner(21.8°)bilayer graphite is T-site with total energy of-256.2749 eV,adsorption distance of 2.0689 ?and adsorption energy of-1.5946 eV.The adsorption ability is stronger than that of vacancy defect corner(21.8°)bilayer graphene.(4)The best adsorption position of vacancy-defective boron-doped corner(21.8°)bilayer graphite is H-site with total energy of-242.2202eV,adsorption distance of 1.9988?,and adsorption energy of-1.7596eV.(5)The adsorption energy of bilayer graphene with vacancy defect boron doping angle(21.8°)is the smallest.H-site is the best adsorption site for bilayer graphite with vacancy defect boron doping angle(21.8°)and has the strongest adsorption capacity.