First-Principles Study Of Borophene-Based Two-Dimensional Materials As Anodes For Li/Na-Ion Batteries

In recent years,due to the intermittent supply of renewable energy such as wind and solar energy for the power system,developing electrochemical energy storage technologies become valued and urgent.Rechargeable metal-ion batteries,especially Li-ion batteries and Na-ion batteries have been extensively applied from portable electronic equipment to electric vehicles and large-scale power plants.To meet the greater demand for energy storage technologies in the future,a large number of research work is focused on improving the performance of Li/Na-ion batteries,including the aspects of rate capability,energy density,reversible capacity and cycling stabilit.Improving the existing manufacturing technology of Li/Na-ion batteries,cannot fundamentally solve the problem of its slow development.In this context,the development of new anode materials with good conductivity,high capacity and excellent rate performance has become a new research trend.Recently,the study of anode materials based on two-dimensional structure has achieved great success,because the unique layered structure is very conducive to the Li/Na ions insertion and diffusion processes.More importantly,two-dimensional anodes with atomic thickness have a large specific surface area and maintain the desired stability that accompany the battery operation,thus can fully embody their storage potential.Computational materials science is a new subject and has developed rapidly in the field of materials science in recent decades,which can conduct extensive and in-depth research on physical and chemical properties of materials through computer technology.Computational materials science has been widely used by theorists and experimentalists because of its low cost,short period and the ability to discuss problems at the atomic level.First-principles method based on density functional theory,has certain advantages in material design,simulation and evaluation,and is one of the very important computational methods in computational materials science.In this paper,the application potential of three borophene-based two-dimensional materials and one two-dimensional MOF material with planar periodic structure as anodes for Li/Na-ion batteries are predicted and discussed by first-principles methods.The details are as follows:1.A novel two-dimensional single-layer material Fe B₆is designed in theory,in which Fe atoms located at the center of partial boron rings can stabilize the structure of hexagonal borophene.The key performance parameters as anode material for Li/Na-ion batteries were simulated by first-principles method.The results show that the two-dimensional Fe B₆anode not only has good structural stability and electronic conductivity,but also exhibits strong adsorption energy,low diffusion barrier and high theoretical storage capacity for Li/Na atoms.The corresponding battery system also exhibits moderate open circuit voltage,which ensures the safety of battery operation.Therefore,Fe B₆can be an ideal candidate anode material for Li/Na-ion batteries.2.Another method to stabilize the planar hexagonal borophene structure is proposed,which is to substitute partial boron atoms in hexagonal borophene by oxygen atoms.Using this method,a new two-dimensional borophene oxide h-B₃O was predicted in theory,and its structural stability was confirmed by phonon spectrum and molecular dynamics simulation.First-principles results show that two-dimensional h-B₃O anode has strong adsorption energy and low diffusion barrier for Li/Na atoms,and the corresponding battery system exhibits moderate open circuit voltage.Especially for Li atoms,the high theoretical storage capacity of 1161 m Ah/g can well meet the requirements of anode materials for Li-ion batteries in the future.3.A novel two-dimensional beryllium-boron compound Be₂B₂is theoretically predicted by CALYPSO structure search technique based on the structure configuration of triangular borophene.Combined with first-principles method,the structure was proved to possess good thermodynamic stability,and then its potential application as anode material for Li/Na-ion batteries was systematically explored.The results show that two-dimensional Be₂B₂anode has strong adsorption energy and low diffusion barrier for Li/Na atoms,and maintains good electronic conductivity in the whole lithiation/sodiation process.The corresponding battery system exhibits moderate open circuit voltage and very high theoretical specific capacity,which are ideal for anode materials.4.At present,most studies are focused on MOFs containing transition metal,while the exploration of main group based MOFs is even in its infancy.In order to solve this problem,a new two-dimensional MOF,Ga₃C₆N₆,which is composed of the main group metal gallium and hexaminobenzene organic ligand,was designed in theory.The feasibility of Ga₃C₆N₆as anode material for Li/Na-ion batteries was investigated by first-principles method.The results show that Ga₃C₆N₆anode possesses strong adsorption energy,low diffusion barrier and high theoretical storage capacity for Li/Na atoms,and the corresponding battery system also exhibits moderate open circuit voltage.Therefore,two-dimensional Ga₃C₆N₆is expected to be an anode material with excellent comprehensive performance for Li/Na-ion batteries.