Study On The Application Of Two-dimensional Material Structure Modification In The Anode Of Alkali Metal Ion Battery

Two-dimensional（2D） materials,due to the quantum confinement effects brought by its structural properties,have caused novel mechanical,electrical and thermal properties.Which makes it an important kind of material in many fields.Compared with traditional 3D materials,2D materials have large specific surface area and unique electronic properties.Thus,they have been proved to have a good application prospect in the preparation of energy storage devices.Due to the inevitable introduction of impurities and defects in the processes of preparation.Therefore,the investigation of exploring the effects of doping and defects on the properties of 2D materials has become a hot spot in the research of low-dimensional materials.In addition,the growing demands for energy storage put forward higher performance requirements for lithium-ion batteries.The graphite,as the main commercialized anode material,has low theoretical lithium storage capacity.At the same time,the reserves of lithium on the earth are small and uneven.So looking for stable anode materials with larger lithium storage capacity and developing new ion batteries have also become the focus of attention.In this paper,the structural modification of 2D materials,doping engineering and defect engineering,is employed.And the first-principles method based on density functional theory is used to systematically study the effects of doping and defects on the performance of 2D materials as anodes for alkali metal ion batteries.A brief description as follows:（1）The demand for rechargeable batteries with higher energy density promotes the design of higher performance electrode materials.Based on the first-principles calculation method,we studied the doped C₃N monolayer as the anode material for Li,Na and K ion batteries.First of all,a variety of light elements doping were carried out,and after comparing the optimized structure and related properties.It was found that the effect of B atom doping was the best.At the same time,the electron loss of C₃N monolayer caused by B doping will enhance the adsorption of alkali metal atoms on the substrate,which is helpful to prevent the formation of alkali metal clusters on the substrate surface.Therefore,it is beneficial to improve the cycle stability of alkali metal ion batteries and the B-doped systems have higher specific capacity for these alkali metal atoms than the intrinsic C₃N monolayer.In addition,the saturated adsorption model of B-doped C₃N monolayer was studied by ab initio molecular dynamics method and it was also found that it had good thermal stability.Although the diffusion barriers of Li,Na and K atoms on B-doped substrate increase slightly,the barriers still less than the threshold of metal ion migration at room temperature（0.5 e V）.The above results show that B doping in two-dimensional C₃N can effectively improve its performance as battery anode material.（2）Based on the new 2D Dirac material NiB₆,we have studied the properties of anode materials for alkali metal ion batteries on intrinsic and defective NiB6substrates.Our calculated results show that the pristine NiB₆monolayer might has promising application for alkali-ion batteries due to its large adsorption energy,high specific capacity(1301.61 m A·h·g^-1),and fast migration capability（energy barrier is0.43/0.23/0.14e V for Li/Na/K）.And the pristine NiB₆also provides a more suitable average open circuit voltage（0.96/0.71/0.69V for Li/Na/K）.At the same time,the adsorption and diffusion mechanism of alkali metal atoms on NiB6 substrates with defects show that the defect sites tend to act as metal atom trapping sites,which improves the adsorption capacity of alkali metal atoms on NiB₆substrates,but reduces the diffusion performance of alkali metal atoms on the substrate.These studies lay a foundation for the application of 2D NiB₆in the field of ion batteries,and provide a certain reference significance for the study of the effect of defects on materials as electrodes.