Defect and Diffusion Forum Vol. 444

Abstract: Graphene, a 2D carbon allotrope with remarkable characteristics like high conductivity, large surface area has shown potential as a good candidate for high-performance supercapacitors. The processability of its derivative, graphene oxide, into fibers enables the development of miniaturized wearable energy storage devices. However, the synthesis of pure graphene oxide and its subsequent reduction to restore conductivity remain a focus for research. Herein, we employ the improved Hummers’ method for graphene oxide synthesis, followed by meticulous washing to remove residual acids. The obtained graphene oxide was then transformed into conductive graphene fibers through a wet-spinning and hydroiodic acid (HI) reduction process. The resulting fibers showed a high areal capacitance of 175 mA cm⁻² in a three-electrode system. When assembled into a flexible supercapacitor, these fibers delivered an energy density of 8 μWh cm⁻² and areal capacitance of 60 mA cm⁻². This study demonstrates the potential of our strategy for fabricating fiber-based energy storage devices based on graphene.

Abstract: Developing materials for electrodes with engineered interfaces is important for improving supercapacitor performance. Combining metal oxides and two-dimensional (2D) transition-metal dichalcogenides (TMDs) is a promising approach to develop enhanced supercapacitor electrodes. To the best of our knowledge, the electrochemical activity and energy storage of the Fe₃O₄/ReS₂ heterostructure-based electrodes have not been reported in the literature. Therefore, this study employed a two-step hydrothermal method to synthesize a Fe₃O₄/ReS₂ heterostructure and investigated its electrochemical performance. The developed material exhibited exceptional specific capacitance, capacity retention, and high energy and power densities. Moreover, various characterization techniques, including SEM, TEM combined with EDX, and XRD, were employed to examine the surface and structural properties of the produced heterostructures. Electrochemical measurements for supercapacitor application were conducted in 2 M KOH electrolytes for all the developed electrodes. The Fe₃O₄/ReS₂ electrode displayed an excellent energy density of 49.31 Wh/Kg, a power density of 550 W/Kg, a specific capacitance of 322.7 F/g, at a current density of 1A/g, and attained 118 % capacitance retention after 2000 cycles at 10 A/g. A specific capacitance of 789.65 F/g was obtained at 5 mV/s. This work uncovers the potential of Fe₃O₄/ReS₂ heterostructures as promising electrode materials for high-performance energy storage applications.

Abstract: Laser-induced graphene (LIG) has gained much attention as a promising material for advanced energy storage solutions, including supercapacitors, due to its many advantages. This study presents the fabrication and characterization of LIG electrodes for electrochemical energy storage, a significant contribution to the field. Laser writing parameters such as laser power and scanning speed were optimized to produce highly conductive and electrochemically active LIG material. Transmission electron microscopy and Raman spectroscopy confirmed the formation of high-quality graphene with excellent electrical conductivity. A systematic investigation of the electrochemical performance of the LIG electrodes was conducted using various aqueous electrolytes, including H₂SO₄ (sulfuric acid), KOH (potassium hydroxide), NaOH (sodium hydroxide), and Na₂SO₄(sodium sulfate), all at the same concentration. A solid-state supercapacitor was assembled using two separate LIG electrodes, and its electrochemical performance was analyzed using Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). The specific areal capacitance of the supercapacitor was determined to be 6.9 mF/cm² at a scan rate of 10 mV/s. The device demonstrated performance consistent with many previously reported LIG-based supercapacitors.

Abstract: Along with the rapid development of technology in this modern era, batteries have a significant role, used as energy storage devices. Lithium-ion batteries have reliable characteristics as energy sources for electronic devices and electric vehicles. Nickel Manganese Cobalt (NMC) is claimed to be the best cathode for high-energy-density lithium-ion batteries. This study aims to analyze the effect of the addition of TiO₂ nanoparticles as a coating material with variations of 1, 3, and 5 wt.% on the morphology and electrochemical performance of LiNi_0.9Mn_0.05Co_0.05O₂ (NMC 955). The coating process with the addition of TiO₂ through ball milling method at a speed of 600 rpm for 1 minute and 1000 rpm for 60 minutes. The results obtained are an increase in particle diameter in the 5 wt.% variation with particle size in the range from 0.1 to 0.5 μm. NMC 955 TiO₂ 1% has the highest specific capacity of 168 mAh g^-1 at 0.5 C. It is indicated that the process of adding TiO₂ coating on NMC 955, can improve the electrochemical performance in terms of specific capacity compared to NMC 955 without TiO₂ coating.

Abstract: Lithium-ion batteries (LIBs) are widely used in various applications such as portable devices and electric vehicles due to their long lifespan and high energy density. However, current LIBs have limited capacity, which can be attributed to the low theoretical capacity of graphite anode (~372 mAh/g). To enhance LIBs performance, silicon-based materials can be used as an alternative anode, offering a higher theoretical capacity of up to 4200 mAh/g. Nonetheless, silicon-based anodes in LIBs still face challenges of high-volume expansion and low electrical conductivity. To overcome these issues, combining silicon-carbon in the form of SiO_x/C has been developed to mitigate the effect of volume expansion and enhance the conductivity of the anode. Moreover, SiO_x/C can be directly synthesized from biomasses as they can serve as both silicon and carbon sources, providing a sustainable synthesis approach. In this study, SiO_x/C materials were synthesized from grey sedge, an abundant biomass in tropical and humid areas of Indonesia. The synthesis of grey sedge-derived SiO_x/C involved the activation using ZnCl₂ and one-step pyrolysis, resulting in carbon-rich SiO_x/C anode with an initial discharge capacity of 1595 mAh/g in pre-lithiation. The grey sedge-derived SiO_x/C anode demonstrated a higher actual capacity than graphite anodes, with 68% capacity retention after 85 charge-discharge cycles at 200 mA/g. These findings highlight the potential of grey sedge-derived silicon-carbon materials as the anode for next-generation LIBs, supporting the global transition to renewable energy sources.

Abstract: Energy storage devices have become essential in modern life, and supercapacitors are among the prominent choices. Reduced graphene oxide (rGO) is a promising material for electrochemical double layer capacitors (EDLC). However, its drawback lies in its relatively lower electrical conductivity compared to pristine graphene. Doping mechanism utilizing nitrogen could enhance the electrical conductivity of rGO. In parallel, CuCr₂O₄ has been identified as a suitable material for pseudocapacitor. In this study, hybrid supercapacitors of EDLC and pseudocapacitor were fabricated through the utilization of N-doped rGO/CuCr₂O₄ composites. The fabrication process involved varying the duration of microwave-assisted solvothermal radiation at 180 W to synthesize N-doped rGO, with variations of 30, 45, and 60 minutes. The impact of varying radiation duration on the structures and morphologies of the materials was investigated using X-Ray Diffractometer (XRD), Fourier-Transformed InfraRed (FTIR), Scanning Electron Microscope (SEM), and Energy Dispersive Spectroscope (EDS) instruments. The capacitive properties of the fabricated supercapacitors were evaluated through Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). From the CV measurements, the specific capacitances of the supercapacitors synthesized with radiation durations of 30, 45 and 60 minutes were found to be 397.72 Fg^-1, 245.79 Fg^-1, and 237.74 Fg^-1, respectively. The specific capacitance values were strongly influenced by the electrical conductivities of the materials, which were measured as 0.2, 0.18, and 0.13 Scm^-1 for radiation durations of 30, 45, and 60 minutes, respectively. It was observed that longer radiation durations appeared to induce structural damage to the material, leading to decreased conductivity in the resulting material.