Ab Initio Study of the Electronic Properties of a Silicene Anode Subjected to Transmutation Doping.

In the present work, the electronic properties of doped silicene located on graphite and nickel substrates were investigated by first-principles calculations method. The results of this modeling indicate that the use of silicene as an anode material instead of bulk silicon significantly improves the characteristics of the electrode, increasing its resistance to cycling and significantly reducing the volume expansion during lithiation. Doping of silicene with phosphorus, in most cases, increases the electrical conductivity of the anode active material, creating conditions for increasing the rate of battery charging. In addition, moderate doping with phosphorus increases the strength of silicene. The behavior of the electronic properties of doped one- and two-layer silicene on a graphite substrate was studied depending on its number and arrangement of phosphorus atoms. The influence of the degree of doping with silicene/Ni heterostructure on its band gap was investigated. We considered the single adsorption of Li, Na, K, and Mg atoms and the polyatomic adsorption of lithium on free-standing silicene.

Computer simulation of obtaining thin films of silicon carbide.

Silicon carbide films are potential candidates for the development of microsystems with harsh environmental conditions. In this work, the production of high-purity silicon carbide films by the electrolytic method is reproduced in a computer model. Single-layer SiC films were deposited on nickel, copper, and graphite substrates. The kinetic and structural characteristics related to the Si and C atoms in this compound are presented. The coefficient of self-diffusion of C atoms on all substrates is higher than that of Si atoms. In addition, the diffusion of atoms on a graphite substrate occurs much more intensively than on metallic (Ni and Cu) substrates. The first maximum of the radial distribution function g(r)SiC is at a shorter distance when the film is deposited on the graphite substrate. A detailed analysis of the structure, based on the construction of Voronoi polyhedra, indicates that the degree of crystallinity of the film increases when changing the substrate in the order from nickel to graphite. The resulting SiC films are subject to local stresses, the strongest of which appear on the copper substrate, however the average stresses in the film do not appear to be high.

Two-Layer Silicene on the SiC Substrate: Lithiation Investigation in the Molecular Dynamics Experiment.

The functioning of the lithium-ion battery anode composed of silicene/SiC composite is studied by molecular dynamics. In this composite, silicene has multiple vacancy defects. Approximately the same degree of lithium filling in such an anode is considered for both horizontal and vertical intercalations. During the horizontal intercalation lithium atoms not only fill the channel and deposit on its walls, but also penetrate into the substrate. In both cases, the self-diffusion coefficients of lithium atoms have similar values. However, the process of filling the system with lithium occurs with a smoother total energy change when the intercalation is performed vertically. A detailed study of the lithium atoms packing via the construction of Voronoi polyhedra for each of the systems under consideration shows the better uniformity of the Li atoms distribution over the volume of the system during the vertical intercalation.

Study of the structure of a multicomponent salt melt using molecular dynamics modeling.

The composition of the electrolyte is critical in the electrodeposition of high-purity silicon. In this work, molecular dynamics modeling of the preparation of liquid salt melt KF-KCl-KI and a detailed study of its structure based on the method of statistical geometry have been performed. Partial radial distribution functions reflect the size of the ions under consideration and the averaged structure of the generated ionic subsystems. Halogen subsystems have domed angular distributions of nearest geometric neighbors, a wide range of face types of combined polyhedra, and fifth order rotational symmetry. The shape of the distribution of distances to the nearest neighbors of a given type depends on the amount of these ions in the melt. Small-scale thermal fluctuations in the halogen subsystems are predominantly represented by small triangular faces in combined polyhedra. The electrodeposition of silicon was carried out in a homogeneous salt melt, in which each halogen ion had from one to three close contacts with halogen ions of any other type. The simulations performed provide a fundamental understanding of the structure of the electrolyte molten salts used to produce solar silicon.

Computer Test of a Modified Silicene/Graphite Anode for Lithium-Ion Batteries.

Despite the considerable efforts made to use silicon anodes and composites based on them in lithium-ion batteries, it is still not possible to overcome the difficulties associated with low conductivity, a decrease in the bulk energy density, and side reactions. In the present work, a new design of an electrochemical cell, whose anode is made in the form of silicene on a graphite substrate, is presented. The whole system was subjected to transmutation neutron doping. The molecular dynamics method was used to study the intercalation and deintercalation of lithium in a phosphorus-doped silicene channel. The maximum uniform filling of the channel with lithium is achieved at 3% and 6% P-doping of silicene. The high mobility of Li atoms in the channel creates the prerequisites for the fast charging of the battery. The method of statistical geometry revealed the irregular nature of the packing of lithium atoms in the channel. Stresses in the channel walls arising during its maximum filling with lithium are significantly inferior to the tensile strength even in the presence of polyvacancies in doped silicene. The proposed design of the electrochemical cell is safe to operate.

Computational investigation of a promising Si-Cu anode material.

The lack of suitable anode materials is a limiting factor in the creation of a new generation of lithium-ion batteries. We use the molecular dynamics method to explore the processes of intercalation and deintercalation of lithium in the anode element, represented by two sheets of silicene, on a copper substrate. It is shown that the presence of vacancy-type defects in silicene increases the electrode capacitance, which becomes especially significant with bivacancies. However, the enlargement of defect sizes reduces the strength of the silicene channel during cycling and in the presence of hexavacancies it suffers a strong deformation and becomes impassable for Li+ ions during intercalation. The presence of a copper substrate greatly changes the electronic properties of silicene. The calculated DOS spectrum shows that silicon on a copper substrate acquires metallic properties. To analyze the structure we used the statistical geometry method. Lithium atoms in the channel are predominantly irregularly packed. However, part of the Li atoms are located above the hexagonal Si cells. The average stresses in silicene, calculated with limiting filling of the channel with lithium, are usually small. However, in the case of silicene with monovacancies, the tensile stress reaches 12.5% of the ultimate tensile stress. Evaluation of the dynamic stress observed in silicene during cycling shows that its value is less than 5% of the ultimate tensile stress.

Atomistic simulations of methane interactions with an atmospheric moisture.

Methane is an extremely effective absorber of radiation, i.e., it is a relatively potent greenhouse gas, and the increased concentration of methane in the atmosphere must influence earth's radiation balance. The adsorption of one to six methane molecules by water clusters is studied by the method of molecular dynamics under near-atmospheric conditions. The capture of methane molecules by water clusters produces an increase in the integrated intensity of IR absorbance and the reflection coefficient. The Raman spectrum of the system is considerably depleted due to the addition of methane molecules to the disperse water system. The observed emission power of a dispersed aqueous system with adsorbed methane molecules has appreciably increased relative to the analogous characteristics of the pure water cluster system. The Voronoi polyhedra and simplified ones constructed within the framework of molecular-dynamic model of clusters are used for the analysis of the structure changes occurring with increasing the number of adsorbed CH4 molecules.