STUDY OF THE EFFECT OF N-TYPE DOPING ON LITHIUM DIFUSIVITY AND ELECTRONIC CONDUCTIVITY PROPERTIES IN SILICONE NANOWIRE

• Main Author: Fadhlan Anshor, Muhammad
• Format: Final Project
• Language: Indonesia
• Subjects: Teknik (Rekayasa, enjinering dan kegiatan berkaitan)
• Online Access: https://digilib.itb.ac.id/gdl/view/64893
• Institution: Institut Teknologi Bandung

In recent decades the need for energy storage based on lithium ion batteries has increased significantly for use in electronic devices ranging from smartphones to electric vehicles. The performance of a lithium ion battery is generally determined by the ability of its electrodes. The anode is important to develop because it determines the amount of Li stored during the first charging process. So we need an anode that has the ability to store more Li ions to increase the energy density of a battery. One of the anode materials that has a large capacity is silicon which has a theoretical capacity of 4200 mAh/g, which is about 10 times the capacity of graphite (372 mAh/g) which is widely used today. Many experimental studies have been conducted on silicon as a battery anode, it was found that there was a large volumetric increase during intercalation, causing cracks in the material which caused the battery cycle to not last long. Furthermore, silicon with nanowire structure is used to overcome the cracks. The problem of cracking has been minimized by reducing the mechanical strain due to the shape of the nanowire which makes expansion only in the radial direction, but silicon nanowire (SiNW) still has a drawback, namely poor electronic conductivity. One strategy that has been done to increase the electronic conductivity of SiNW is to provide doping. Previously, experimental studies on doping SiNW have been carried out and the anode performance has increased compared to pure SiNW, especially its electronic conductivity, but there has been no theoretical study that comprehensively discusses this. Therefore, in this final project, a theoretical review with computational methods will be carried out to explain the effect of n-type doping on SiNW on lithium diffusivity properties and electronic conductivity. In this final project, calculations were carried out using Density Functional Theory (DFT) to see the effect of n-type doping, namely arsenic (As), phosphorus (P), nitrogen (N), and antimony (Sb) on the energy of the diffusion barrier Li and the electronic conductivity of SiNW. The VASP software is used to perform the calculations. There are 3 doping sites that may be occupied by doping atoms, namely surface (s), intermediate (i), and core (c), where the energy of doping formation for As, P, and Sb is relatively not different at each site. NEB (Nudged Elastic Band) calculations were performed to obtain the minimum energy path for further calculation of the Li diffusion activation energy in SiNW. It was found that the energy of the Li diffusion barrier decreased by 0.12 - 0.48 eV when Li diffuse into the SiNW with doping compared to pure SiNW. The highest Li diffusivity with P doping at site i is 4 x 10-6 cm2/s, which is about 106 times the diffusivity value in pure SiNW (8 x 10-12 cm2/s). This increase in diffusivity is due to the electron-rich effect on SiNW brought about by the doping atoms. Qualitatively, the electronic conductivity increases by looking at the electronic band structure of the doped SiNW where the Fermi energy level rises below the conduction band due to the addition of electrons. Coupled with the increase in the number of Li in SiNW, there will be more state bands in the band-gap so that it will be closer to the conductor properties. By doing this research, it is hoped that it can provide initial predictions for experimental research to develop battery anodes with high capacity and good ionic and electronic conductivity.