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Synthesis and application of materials for next-generation lithium-ion batteries
Date
2025-09-30
Abstract
This thesis describes the development of high-capacity, next-generation battery materials using synthesis strategies designed to minimise cost, complexity and scalability issues commonly associated with the development of such materials. The experimental chapters are arranged as research articles with introductions at the beginning of each chapter.
Lithium-ion batteries (LIBs) have experienced a surge in widespread usage over the last decade, enabling technologies such as electric vehicles, mobile robotics, and portable electronics, thereby driving the demand for higher energy densities. While the low cost and excellent stability of graphite anodes have allowed LIBs to achieve commercial success for the last 30 years, the specific capacity of graphite (372 mAh g-1 ) is too low to meet the strict energy requirements of future LIBs. Higher-capacity alternatives such as silicon (3579 mAh g-1) and germanium (1384 mAh g-1) can, in principle, deliver greater energy densities, but undergo significant volume changes during cycling (~300% for Si and ~260% for Ge), leading to particle fracture, electrode delamination, and rapid capacity fade. Nanostructured Si and Ge mitigate these effects by enhancing transport and mechanical resilience. However, improvements achieved through nanostructuring quickly reach a point of diminishing returns, as they become constrained by high material and production costs, as well as poor scalability. Similarly, lithium-sulfur (Li-S) batteries are attracting interest due to the low-cost, abundance, and high theoretical capacity (1675 mAh g-1) of sulfur. However, like Si anodes, sulfur cathodes suffer from severe stability issues, including the insulating nature of sulfur species, which increases the resistance of the cathode, as well as the dissolution of polysulfide intermediates, which lead to rapid capacity loss. This thesis examines material design strategies that target these fundamental challenges across both high-capacity anodes and cathodes for next-generation LIBs, aiming to identify pathways where high capacity can be achieved alongside improved stability and scalability.
Chapter 3 describes the direct growth of silicon nanowires on Sn-decorated reduced graphene oxide (Sn-rGO) using a solvent vapour growth method. The resulting Si-Sn-rGO composite achieved 980 mAh g-1 at 0.1 A g-1 , retained 628 mAh g-1 after 100 cycles at 0.5 A g-1 and 542 mAh g-1 after 150 cycles at 2 A g-1 , with only 1 mAh g-1 capacity loss after 100 cycles at 2 A g-1. During rate capability testing from 0.1 – 5 A g-1 , the Si-Sn-rGO electrode consistently delivered more than twice the capacity of Sn-rGO. Differential capacity analysis confirmed the continued reversible alloying of amorphous LixSi phases which remained electrochemically active at high current densities. When evaluated as a lithium-ion capacitor, the Si-Sn-rGO material delivered 139 Wh kg-1 at 155 W kg-1 and 101 Wh kg-1 at 2306 W kg-1, highlighting its potential for fast-charging and high-power applications.
Chapter 4 investigates a more economical approach by combining recycled silicon kerf waste with novel binder systems. Recovered anionic polyacrylamide (PAM) improved capacity retention from 255 to 767 mAh g-1 after 100 cycles at 0.2 A g-1 relative to CMC. A LiPAA/PAM blend further enhanced mechanical stability and Li⁺ transport, achieving 1529 mAh g-1 after 100 cycles at 0.2 A g-1 (six times higher than CMC) and ~1.75 times the capacity of the Si-Sn-rGO electrodes from Chapter 3 at the same rate. Electrochemical analyses confirmed that LiPAA promoted interfacial stability and Li+ion mobility, enabling continued cycling of degraded Si particles despite SEI growth. The binder also reduced electrode cracking and maintained
adhesion to the current collector, demonstrating that targeted binder design can substantially improve the performance of recycled Si without requiring changes to electrode manufacturing methods.
Chapter 5 explores calcium tetragermanate (CaGe4O9) nanowires synthesised hydrothermally from GeO2 and CaCO3 precursors as a more sustainable alternative to conventional Ge anodes. The nanowires delivered 780 mAh g-1 after 150 cycles at 0.2 A g-1 and remained above the theoretical capacity of graphite after 400 cycles at 1 A g-1, with initial coulombic efficiencies of ~80% exceeding those reported for related germanates. Differential capacity analysis revealed a transition from mixed conversion-alloying to predominantly alloying behaviour after 50 cycles, while a porous framework formed during cycling buffered volume changes and maintained diffusion pathways. These results establish CaGe₄O₉ nanowires as a competitive anode system that reduces reliance on costly Ge nanostructures and provide similar performance to Si NW electrodes.
Chapter 6 investigates disordered carbon nitrides as a means of reducing the instability of Li-S batteries. The carbon nitride structures were prepared by room-temperature supramolecular self-assembly followed by calcination as hosts for sulfur cathodes. The porous carbon nitride CN600, composed mainly of triazine and tri-s-triazine units enriched with pyrrolic-N and pyridinic-N, exhibited strong polysulfide adsorption and coulombic efficiencies
above 99.5%. Boron doping (BCN600) was found to enhance polysulfide binding and high-rate performance, but the porosity was reduced by ~24% due to the thermal stability of B-C and B-N bonds during calcination. At C/5, CN600 retained 569 mAh g-1 compared with 437 mAh g-1 for BCN600, whereas BCN600 outperformed CN600 at higher rates owing to improved catalytic activity. Both materials maintained structural integrity and accommodated sulfur volume changes during cycling.
Together, these studies demonstrate that incremental but targeted modifications, whether through nanostructure design, binder optimisation, hydrothermal synthesis, or molecular self-assembly, can deliver meaningful improvements in electrochemical performance while addressing cost and scalability considerations. The findings provide mechanistic insight into electrode behaviour and establish a basis for translating material-level advances into practical next-generation battery technologies.
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Publisher
University of Limerick
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Sustainable Development Goals
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Thesis
Rights
http://creativecommons.org/licenses/by-nc-sa/4.0/