DFT STUDY OF PHOSPHOROUS DOPING EFFECT ON LITHIUM INSERTION TOWARD STABILITY OF SILICION-NANOWIRE AS ANODE MATERIAL OF LITHIUM ION BATTERY

• Main Author: Zahrah Fitriana Syafira, Az
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/65176
• Institution: Institut Teknologi Bandung

Lithium-ion battery are commonly used as electrochemical energy storage system. However, these batteries are far from perfect. Energy density of a lithium-ion battery is affected by storage capacity of electrode. Graphite as commonly used anode material has low theoritical capacity which around 372 mAh g-1. One of the alternative is silicon, a material with higher theoritical capacity around 4200 mAh g-1. Nevertheless, this silicon-based anode has disadvantage, where large volume expansion (up to 400%) happens during litiation and leads to pulverization. One of the solution proposed to solve this problem is using silicon-nanowire (SiNW), which has larger surface to volume ratio compare to silicon bulk and can perform well due to their strain relaxation capability. Better performance of SiNW can be achieved using type-n doping. Previous experimental study shows that phosphorous-doped SiNW (P-doped SiNW) with (100) orientation can enhance battery performance. Further understanding on SiNW based battery is needed to enhance performance even better. In this undergraduate thesis, P-doped SiNW (100) is modelled using ab inito (first principle) approach with Density Functional Theory (DFT) and Vienna Ab Initio Simulation Package (VASP) as the software. This study calculates electronic and mechanical stability of P-doped SiNW while inserting lithium to analyse the effect. Electronic stability is tested using Li insertion energy, Density of States, and band structure. Li insertion energy is calculated to examine bonding between Li and SiNW structure. Density of States and band structure is calculated to identify electronic stability of P-doped SiNW. These calculation is also done for pristine SiNW as comparation. Meanwhile, mechanical stability is examined by calculating Young’s Modulus. Either electronic or mechanical stability is calculated at various Li concentration, namely 0%, 0,93%, 1,85%, 3,70%, 7,40%, 11,12%, 14,81%, 18,51%, and 22,23%. Result shows that Li insertion energy is relatively increased as Li cocentration increased. This indicates that Li-SiNW bond tend to be stronger when Li concentration increased. Moreover, it is examined that P-doped SiNW create stronger bond with Li than that of the pristine SiNW. Up to concentration of Li = 22,23%, all SiNW system shows tendency to accept Li, as shown by positive value of insertion energy. Calculation of Density of states shows that Fermi energy approaching conduction band because of increasing amount of electrons from iv addition of P-doped and Li insertion. The implementation is that Li insertion can also be considered as doping. Meanwhile, band structure calculation shows that conductivity of SiNW increased either when P-doped or Li insertion is added. In this case, P-doped is giving contribution to enhance electronic conductivity of SiNW. Calculation of Young’s Modulus shows that pristine SiNW has good mechanical stability. When P-doped is added, SiNW has relatively similar mechanical stability to that pristine SiNW. This mechanical stability is examined only at elastic zone. Thus, addition of P-doped does not break mechanical stability of SiNW. Overall result shows that P-doped is good for enhancing electronic stability of SiNW, especially electronic conductivity. In the other hand, P-doped is also good to maintain mechanical stability since it does not cause breaking in elastic zone. Therefore, P-doped can be applied to SiNW as anode material of lithium ion battery to enhance electronic properties without breaking mechanical properties.