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The development of earth abundant anode materials for sodium-ion batteries with full-cell applications
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Date
2025-12
Abstract
This thesis explores the development of anode materials for sodium-ion batteries (SIBs), with particular emphasis on availability and abundance when selecting the elements/materials used. The first chapter introduces the importance and relevance of energy storage devices, such as batteries, before detailing the individual components and working principle of an SIB. Anode materials are classified into three groups - intercalation, conversion, and alloying - which are discussed in detail, as both intercalation and conversion materials are investigated in the experimental chapters of this thesis. The discussion then transitions to focus on full-cell testing and key considerations for operation, such as various pre-sodiation methods and the N/P ratios, which are explored further in Chapters 3 and 5. The characterisation of the materials is also an important part of this thesis and the working principles of each technique used are presented in chapter 2.
Chapter 3 investigates whether an abundant waste material (LDPE plastic) can be successfully employed as a carbon-based, intercalation anode material in SIBs. The LDPE plastic was carbonised at three different temperatures (600 °C, 800 °C, and 1000 °C) to assess the effect it had on the material and its ability to reversibly store Na+. The higher temperatures (800 °C and 1000 °C) samples showed superior and similar capacities and stability over 1000 cycles. This chapter also explores if the 1000℃ LDPE-derived carbon was also suitable in a full-cell. The anode was paired versus Na3V2(PO4)3 (NVP) with an N/P ratio of 1.1. As the full-cell was delivering ~50 % of the expected capacity, a direct-contact pre-sodiation method was introduced to reduce the initial capacity loss (ICL). The degree of the pre-sodiation and the effect it had on the full-cell was also examined. It was determined that, that by employing the direct-contract pre-sodiation for 1 minute, the initial Coulombic efficiency (ICE) increased from 90.73 % compared to 45.85 % in pristine full-cell, alongside an increase in the charge capacity of 93.88 mAh g-1.
Chapter 4 focuses on shifting from the intercalation class of materials and towards a conversion-based material to achieve higher specific capacities. This chapter focuses on the use of colloidally synthesized Cu3VS4 nanocrystals (NCs) in SIBs for the first time. The motivation for selecting the Cu3VS4 material was to move beyond the well reported binary transition metal sulfide (TMS), CuxS. The colloidal synthesis also enabled the individual selection of the elements which are earth abundant and have distinct advantages such as high conductivity and multiple redox states in their binary forms, VSx and CuxS, respectively. Colloidal synthesis allows for fine tuning of the phase and morphology of the NCs, which is advantageous for battery research. During the reaction, CuxS (x= 1, 2) and amorphous V-containing nanoparticles (NPs) undergo a solid-state reaction to form the ternary compound, Cu3VS4. This work evaluates the overall performance and stability of the Cu3VS4 nanocrystals over 1000 cycles, with an electrolyte of 1M NaOTF in diethylene glycol dimethyl ether (DEGDME) within the voltage range of 0.5 – 2.5 V. By the 1000th cycle, the Cu3VS4 nanocrystals had a specific capacity of approximately 100 mAh g-1, displaying stable cycling over a long period of time.
Although the Cu3VS4 nanocrystals were successfully implemented as an anode material for long-term cycling in a half-cell, the effects of several operating parameters were investigated to further optimise the electrochemical performance. Firstly, the voltage profile was adjusted beyond the previous reported range (0.5 – 2.5 V). When operating in voltage ranges of 0.01 – 3 V and 0.1 – 3 V, a severe capacity fade was observed around cycle 40 and 140, respectively. This was attributed to the poor properties of the Na+ solvation sheet as a result of the high donor number (based off of the HSAB theory) of the OTF- anion. The second parameter investigated was the electrolyte salt to determine its contribution to the electrochemical performance. When the NaOTF salt was replaced by NaPF6, superior electrochemical performance was seen in each voltage range, with discharge capacities of 9.354, 72.28, and 183.58 mAh g-1, for the voltage windows of 0.01 – 3 V, 0.1 – 3 V, and 0.5 – 2.5 V, respectively. This was due to the weak interactions and coordination of the cation and anion, essentially increasing the transfer kinetic of the electrolyte. Once successfully optimised in a half-cell configuration, the anode was paired against an Na3V2(PO4)3 cathode to assess its suitability in a full-cell. Once again, the pre-sodiation step played a crucial role in minimising the ICL as the ICE increased from 60.38 % to 89.45 %. Additionally, the charge and discharge capacities of the pre-sodiated cell increased to 80.52 mAh g-1 and 78.07 mAh g-1 by the 20th cycle, compared to 60.04 mAh g-1 and 57.67 mAh g-1 in the pristine cell. This work highlights the importance of carefully selecting the cell components and composition as well as the operating conditions, to maximize the performance of the active material.
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University of Limerick
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Sustainable Development Goals
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Attribution-NonCommercial-ShareAlike 4.0 International