FIRST-PRINCIPLES INVESTIGATION OF COPPER SULFIDE (CUS) SUPERCAPACITOR PERFORMANCES

• Main Author: Al Ghiffari, Ahmad
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/62783
• Institution: Institut Teknologi Bandung

Various technologies that exist today require electrical energy storage devices that have the best performance. These technological developments encourage the development of energy storage devices for better performance. Supercapacitors have received more attention from various energy storage devices in recent years because of their ability to provide high power and energy density. Some materials based on Transition Metal Sulfide (TMS) have been widely developed as energy storage devices because they provide the best current capacitance results. One type of TMS interesting to study is Copper Sulfide (CuS) as it conduct high conductivity, high specific capacity, and cost-effectiveness to applied as electrode material in supercapacitors. The perfomance improvement of copper sulfide supercapacitors has been widely studied, but there is no theoretical explanation for the increase in supercapacitor performance. In this research, a study based on Density Functional Theory (DFT) was conducted using the Vienna Ab-Initio Simulation Package (VASP) software to analyze the relationship between Density of State (DOS) and CuS capacitance. In the calculations, the addition of potassium electrolyte ions on the CuS Surface was also carried out to study the effect of charging on the CuS surface structure which is known as Rigid Band Approximation. From this charged CuS surface structure, it is possible to calculate the redox pseudocapacitance, which was previously needed to determine the Work Function (WF) change for the charged and uncharged structure. The geometry of the CuS structure was optimized using the interpolation method to obtain the most stable lattice constant. Functional variations were carried out in the form of Hubbard functional and van der Waals functional so that we get the lattice constant a is 3.785 Å and the lattice constant c is 16.343 Å. The CuS pristine structure resulting from this geometry optimization is given a vacuum gap in the z-direction with 16 Å. This structure is then expanded by 3×3×1 so that in the expansion model, there are 54 Cu atoms and 54 S atoms. Based on the calculation of the WF from the variation of the additional charge, the maximum WF at charge -9 is 2.58 eV. From the surface structure of CuS pristine, which added one to nine Potassium ions on the surface, it was obtained that the average amount of charge transferred by the electrolyte ions to the structure was 1e. From these two variations, the maximum pseudocapacitance value for the CuS surface structure is 611.4 F/g. In addition to the pseudocapacitance value, the quantum capacitance for the CuS surface structure is higher with a value of 2441 F/g. The quantum capacitance is increase in the surface structure so that we need to more consider about this in the surface structure. The phenomenon of capacitance was also observed by doping Fe and Mn on the surface structure of CuS pristine. The pseudocapacitance values were obtained from the addition of charge -1, and one potassium electrolyte ion to the surface for the surface structure of CuS pristine, CuS doped with Fe, and CuS doped with Mn are 16.95 F/g, 90.49 F/g, and 25.03 F/g. From the pseudocapacitance value, it is found that the redox pseudocapacitance value can be increased by doping on the surface structure of CuS pristine. Meanwhile, for the integrated quantum capacitance in the negative potential region of the CuS pristine bulk structure, CuS doped with Fe bulk structure, and CuS doped with Mn bulk structure are 790.5 F/g, 860.9 F/g, and 973.6 F/g. The integrated quantum capacitance values in the positive potential region of the CuS pristine bulk structure, CuS doped with Fe bulk structure, and CuS doped with Mn bulk structure are 476 F/g, 490.1 F/g, and 552.8 F/g. For the surface structure of CuS pristine, CuS doped with Fe, and CuS doped with Mn, the integrated quantum capacitance in the negative potential region are 1855.7 F/g, 1700.3 F/g, and 1748.5 F/g. As for the surface structure of CuS pristine, CuS doped with Fe, and CuS doped with Mn, the integrated quantum capacitance in the positive potential region are 1075.6 F/g, 1016.8 F/g, and 1034.9 F/g. From the integrated quantum capacitance values for the two types of structures, the integrated quantum capacitance value in the negative potential region is higher than the positive potential region. This indicates the potential of CuS material as an anode electrode for supercapacitors. Meanwhile, from the quantum capacitance data for the bulk structure and surface structure, it is found that the quantum capacitance value will only increase when doped on the bulk structure of CuS.