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The synthesis and development of nanostructured silicon-based anode materials for lithium-ion batteries
Date
2025
Abstract
This thesis focuses on the synthesis and development of high-capacity silicon-based anode materials for lithium-ion batteries (LIBs), based on the nanostructure silicon (Si) size effect, surface treatment, electrode designs, and electrochemical applications. Specifically, lithium-alloying Si with optimized sizes from micro to nano scales and surface modifications have been thoroughly investigated to reveal their electrochemical performance and morphology evolutions upon cycling. More importantly, the Si/graphite (Si/G) composite anode materials have been further developed and analysed in the practical full-cell configurations for electrochemical energy storage applications. The core chapters are arranged as research articles with introductory summaries at the beginning of each chapter.
Advancements in commercial LIB chemistries are struggling to keep pace with the increasing power demands of portable consumer electronics and electric vehicles. Graphite anodes (372 mAh/g) are approaching their theoretical maximum performance, and it is becoming more and more important to identify alternative anode materials that offer significantly higher practical gravimetric energy densities. Si (3579 mAh/g) has been identified as one of the most promising alternatives to traditional graphite anodes as they can offer significant improvements in terms of specific capacities and gravimetric energies. However, one of the main challenges is a huge volume expansion, and the subsequent material pulverisation with increased cycling leads to low Coulombic efficiency and severe capacity fading, which limits the cycling capabilities in the LIBs full-cell applications.
To this end, this thesis has developed synthesis techniques for nanostructured one-dimension architecture and a scalable method of surface coating for Si, which can mitigate the detrimental volume change issues and achieve high specific capacity with stable cycling performance. Moreover, the use of a Si/graphite composite anode allows the high specific capacities, lower costs and improved conductivity to be harnessed in a LIB.
Chapter 3 describes the development of an innovative method to effectively control the diameter of Si nanowires on the 3-dimensional stainless-steel mesh (SSM) substrates so that the influence of nanowire diameter on electrochemical performance can be thoroughly characterized and analysed. Si nanowires with smaller diameters (~ 35 nm) are more resistant to material pulverisation and offer higher levels of capacity retention compared to larger diameter Si nanowires over hundreds of galvanostatic cycles. Si NWs with an average size of 100 nm exhibited specific capacities of ~800 mAh/g. Reducing the diameters to 55 nm gave ~1200 mAh/g whereas Si NWs with an average diameter of ~35 nm demonstrated a specific capacity of ~1500 mAh/g when cycled with an applied specific current of 1 A/g. This work highlights the importance of controlling the critical dimensions of Si-based nanostructures to reduce pulverisation effects and increase capacity retention.
Chapter 4 describes a facile surface treatment method for applying a thin carbon layer on the surface of Si particles. A ∼ 8 nm carbon (C) layer is coated on the surface of Si after carbonization. This carbon coating serves to improve the electrical conductivity, and also acts as a buffer layer reducing the mechanical strain exerted on the Si nanoparticles, thus mitigating pulverization and maintaining structural integrity. The C-coated Si anodes demonstrated higher capacity (1330 mAh/g with 81% retention) compared to pristine Si anodes (610 mAh/g and 28%) after 100 cycles at an applied current density of 1 A/g. The improved electrochemical performance could be attributed to the C conductive surface and ensures effective electron transfer. The surface treatment of Si is scalable and economical, offering a fresh avenue for the commercial viability of Si-based anodes.
In Chapter 5, an efficient prelithiation method for Si/G anodes using a direct-short-circuit mechanism is presented, aimed at addressing the challenges of its low initial Coulombic efficiency (ICE) and safety issue in the LSBs full cells. This study demonstrated that a 6-hour prelithiation process loaded a capacity of ∼ 1226 mAh/g, achieving 97% of ICE from the Si/G anode. The prelithiated Si/G–S full cells (Li–S batteries) delivered an ICE of 97%, a reversible capacity of 218 mAh/g at C/5 and over > 90% Coulombic efficiency across 100 cycles with a minimal electrolyte to sulfur ratio amount of 20 µL/mg. This study demonstrates a facile prelithiation method with a prototype of prelithiated Si/G–S full cell, paving the way for enhancing the gravimetric and volumetric energy density of safer and cost-effective next-generation Li–S batteries.
In Chapter 6, a synthesis strategy of directly growing tin (Sn)-seed Si NWs on graphite flakes (Sn/Si NWs/G) via a vapour-liquid-solid (VLS) approach is demonstrated. The objective is to combine the high capacity of Sn and Si NWs with the stability of graphite as a composite anode material, improving the rate capability and cycling stability. The prepared Sn/Si NWs/G anode delivers a specific capacity of 980 mAh/g with a capacity retention of 76% after 100 cycles at an applied specific current of 200 mA/g. A better rate capability of ~ 500 mAh/g compared to < 200 mAh/g of pure Si at a higher specific current of 2A/g after 20 cycles. Full cells composing prelithiated Sn/Si NWs/G anode with lithium iron phosphate (LFP) cathode display a capacity of 104 mAh/g with a capacity retention of 84% (comparable to the capacity retention of LFP half-cell) at C/2 from the 2nd to 100th cycles, and a capacity retention of 77% over 400 cycles. This work provides insights into the synthesis and prelithiation of Sn/Si NWs/graphite composite anodes for promoting the practical application of Si-containing Li-ion batteries.
Supervisor
Ryan, Kevin M.
McNulty, David
McNulty, David
Description
Publisher
University of Limerick
Citation
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Li_2025_Synthesis.pdf
Adobe PDF, 12.54 MB
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Funding code
Funding Information
Sustainable Development Goals
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Type
Thesis
Rights
http://creativecommons.org/licenses/by-nc-sa/4.0/