COMPARATIVE HALF-CELL ANALYSIS OF SULFUR-, NITROGEN-, AND FLUORINE-DOPED REDUCED GRAPHENE OXIDE ANODES

Mohamad Taufiq Mohamad Alias; Nur Ezyanie Safie; Siti ‘Aishah Azman; Nurul Syuhada Mohd Shari; Najmiah Radiah Mohamad; Eleen Dayana Mohamed Isa; Mohd Asyadi Azam

Mohamad Taufiq Mohamad Alias Fakulti Teknologi dan Kejuruteraan Elektrik, Universiti Teknikal Malaysia Melaka, Malaysia.
Nur Ezyanie Safie Fakulti Teknologi dan Kejuruteraan Elektrik, Universiti Teknikal Malaysia Melaka, Malaysia.
Siti ‘Aishah Azman Fakulti Teknologi dan Kejuruteraan Elektrik, Universiti Teknikal Malaysia Melaka, Malaysia.
Nurul Syuhada Mohd Shari Fakulti Teknologi dan Kejuruteraan Elektrik, Universiti Teknikal Malaysia Melaka, Malaysia.
Najmiah Radiah Mohamad Fakulti Teknologi dan Kejuruteraan Elektronik dan Komputer, Universiti Teknikal Malaysia Melaka, Malaysia.
Eleen Dayana Mohamed Isa Malaysia-Japan International Institute of Technology, Universiti Teknologi Malaysia, Malaysia.
Mohd Asyadi Azam Fakulti Teknologi dan Kejuruteraan Industri dan Pembuatan, Universiti Teknikal Malaysia Melaka, Malaysia.

Keywords: Functionalized graphene, reduced graphene oxide, graphene anode, anode material, LFP battery

Abstract

Advanced lithium iron phosphate battery systems demand anode materials with higher capacity, better rate capability, and stronger structural stability than conventional graphite. This study investigates the electrochemical performance of functionalized reduced graphene oxide (rGO) as a potential anode material, focusing on sulfur (S), nitrogen (N), and fluorine (F) heteroatom doping. The materials were synthesized through controlled hydrothermal and thermal treatment methods and characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray (EDX) spectroscopy. Structural analysis showed that sulfur doping increased interlayer spacing and introduced more active defect sites, while nitrogen and fluorine doping enhanced graphitic alignment, as indicated by a sharper (002) peak near 26°, which corresponds to reduced interlayer spacing. Electrochemical properties were evaluated using cyclic voltammetry (CV) within a potential range of 0.01–3.0 V (vs. Li/Li⁺). Among all samples, sulfur-doped rGO exhibited the strongest electrochemical performance, with the largest CV curve area and an apparent capacitance of 492.32 F g⁻¹, corresponding to a specific capacity of 408.90 mAh g⁻¹. Pristine rGO achieved 417.66 F g⁻¹ (346.89 mAh g⁻¹), whereas nitrogen-doped and fluorine-doped samples showed lower values of 278.39 F g⁻¹ (231.21 mAh g⁻¹) and 223.07 F g⁻¹ (185.27 mAh g⁻¹), respectively. The results indicate that charge storage is mainly governed by pseudocapacitive surface reactions rather than bulk intercalation. Overall, sulfur-doped rGO demonstrated superior charge storage capability, highlighting its potential as an advanced anode material for next-generation LiFePO₄-based lithium-ion batteries.