Honeycomb shaped porous carbon from coconut rachis as a sustainable cathode for lithium metal capacitors /
Nurulhuda Binti Mohamed Shah
- xv, 140 pages : illustrations : 30 cm. 1 CD-ROM
Faculty of Industrial Sciences and Technology
Thesis (Master of Science) -- Universiti Malaysia Pahang – 2025
Include bibliographical reference
The lithium metal capacitors (LMCs) are electrochemical capacitors analogous to lithium metal batteries (LMBs) sharing similar anode but differing cathodes and are promising devices to combine high energy and power capabilities. While LMBs rely on costly metal oxides, LMCs can utilize porous carbon derived from renewable biomass. Among various morphologies, honeycomb-shaped porous carbon (HSPC) offers superior mechanical, surface, and electrochemical properties. However, current fabrication methods using sacrificial templates are expensive and time-intensive. This study aims to synthesize porous carbon from coconut rachis through carbonization, evaluate its electrochemical properties, and measure its charge storability by improving the electrical properties of its formulation. In this study, honeycomb-shaped porous carbon (HSPC) was synthesized from coconut rachis, through carbonizing phloem and xylem, with subsequent chemical activation yielding specific surface area ~1933 m²·g-1 and average pore diameter ~2.0 nm. Scanning Electron Microscopy revealed honeycomb morphology with wall thickness and tunnel diameter of 5.91±0.40 μm and 1.65±0.40, respectively. Energy dispersive X-ray analysis and X-ray Photoelectron Spectroscopy revealed high carbon content (>80%). The surface functional groups were analyzed by Fourier-Transform Infrared Spectroscopy. The X-ray diffraction analysis indicated the amorphous nature, of average lateral size ~2.20 nm and an average stacking height of ~0.93 nm. Disorders and defects in the carbon structure were obtained using Raman spectroscopy, two distinct peaks corresponding to D band (~1350 cm ⁻¹) and G band (~1585cm⁻¹) were observed with their intensity ratio to be 1.10, indicating defective structure ideal for charge storage. The lithium metal capacitor fabricated in the Li//LiPF6//HSPC coin cell configuration delivered a specific capacitance (Cs) ~133 F·g⁻¹ at a current density of 0.1 A·g⁻¹. Quasi-rectangular cyclic voltammetry curves and symmetric triangular charge/discharge profiles validated the electric double-layer capacitance behaviour. The device maintained 98% capacity retention with 100% coulombic efficiency after 1000 cycles with stable SEI layer formation and significant reduction of charge transfer resistance. To further improve storability, nominal substitution of conductive carbon by single walled carbon nanotubes (SWCNTs) (0.2-0.6 wt.%) in the cathode slurry showed a 30% enhancement in CS (~188 F·g-1) due to 100% increased the electrical conductivity of the films. The charge-discharge cycling demonstrated that the device retained ~84% of its initial capacity with 100% coulombic efficiency after 5000 cycles. The enhancements were validated by electrochemical impedance spectroscopy, which recorded significant decrease of charge transfer resistance from 640 to 213 Ω upon SWCNT addition. Moreover, low charge transfer (from ~29 to ~15 Ω) and stable SEI layer formation after repetitive charge/discharge cycling indicate efficient ion diffusion. The specific energy and specific power of the best performing devices were ~78 Wh·kg−1 and ~4785.57 W· kg−1, respectively. Together, these results highlight a sustainable and cost-effective electrode material for efficient charge storage applications.
THE0010195 (Local)
Faculty of Industrial Sciences and Technology--Dissertations
Universities and colleges--Dissertations Theses--Dissertations