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As the world's second-largest alumina producer and the fourth-largest coal producer, Australia generates approximately 30 million tonnes of red mud (a byproduct of the Bayer process for alumina production) and 13 million tonnes of coal combustion products (fly ash and bottom ash) annually. While the recycling rate for coal combustion products in Australia is approximately 60%, the recycling rate for red mud (RM) is below 5%. This results in an increasing waste stockpile and poses a burden on the local environment. Therefore, there is a pressing need to find a sustainable solution for managing this expanding industrial waste stream. Geopolymer, as an alternative binder to traditional cement, offers improved sustainability due to its ability to utilize various industrial wastes as aluminosilicate precursors (APs). Extensive studies have predominantly verified the feasibility of using various types of industrial waste, including coal combustion products and RM, for geopolymer production. Therefore, the utilization of these local industrial byproducts in Australia for geopolymer production is becoming increasingly attractive, as it promotes both a circular economy and the valorisation of local industrial waste. The extreme variability in the inherent properties of these waste materials, however, including their chemical composition, particle size, and crystalline/amorphous phases, presents a significant obstacle to the wider application of geopolymer and hinders the valorisation of waste materials. To enable industrial-scale production, widely accepted standards for testing methods and material properties are crucial. These standards ensure the stability of the raw-material supply chain and the performance of the final product. [...], Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Eng & Built Env, Science, Environment, Engineering and Technology, Full Text

Nanochannels with nanoscale characteristic dimensions have sparked broad interest across scientific and engineering disciplines. The emergence of a versatile family of two-dimensional (2D) materials enables high-throughput engineering of nanochannels with tunable layered structural and functional properties in the form of laminar membranes, which opens up new opportunities for applications in liquid molecular separation, gas separation, and ion sieving. Despite significant progress in 2D-material-based nanochannel, thorough understanding of this field is still lacking. In this thesis, I systematically and in-depth explored the mechanism of nanochannel modification on filtration. I also fabricated a series of 2D-material-based nanochannel membranes for water treatment. My research demonstrated that interlayer spacing plays a crucial role in determining the selectivity and permeability of nanofiltration membranes. Proper tuning gives these membranes high throughput, precise selectivity, and multiple uses. [...], Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, Full Text

Thiophene-based materials are some of the most versatile conjugated materials due to their combination of environmental stability and ease of synthetic modification. They are widely employed for photoelectronic applications, such as Organic Photovoltaics, however, thiophene-based materials in emissive applications fall far behind, possibly because of the limited fluorescent quantum yields in both solution and the solid state. Regardless of this limitation, thiophene-based materials still provide a number of characteristics that have made them popular systems for technological applications. In addition to the stability and synthetic diversity already discussed, these characteristics include controllable color tuning of absorption and emission, good charge mobility, and the ability to produce materials with low band gaps. The interest in emissive thiophene derivatives has also increased due to various approaches for overcoming the commonly reduced fluorescence efficiencies, as well as new applications such as fluorescent biomarkers. Besides the emissive properties, thiophene-based functional materials for photochromic systems are also studied intensively. Molecules in this category are usually termed "dithienylethene" concerning the structural motif of two thiophene rings bridged at their third position with an ethene group. Dithienylethenes (DTEs) outperform other photochromic systems in many ways, such as their excellent thermal stability in both isomers, high fatigue resistance, and switchability in the crystalline state. Before and after the irradiation, the two isomers differ not only in the absorption spectra but also in various physical and chemical properties, such as refractive indices, dielectric constants, oxidation-reduction potentials, and geometrical structures. The instant property changes without processing lead to their use in various optoelectronic devices, such as optical memory, photo-optical switching, display, and nonlinear optics. […], Thesis (PhD Doctorate), Doctor of Philosophy (PhD), Institute for Glycomics, Full Text

Recent advancements in the domain of two-dimensional materials have taken a significant leap, with MXenes – a vibrant class of materials constituted of transition metals in conjunction with carbon, nitrogen or boron – gaining widespread attention from global scientific communities. Characterized by their atomic-level thickness, high aspect ratios, and superlative physicochemical attributes, MXenes exhibit immense potential within the realm of energy storage. Despite this potential, their practical application has been impeded due to the hazardous and costly nature of current mainstream MXene preparation methods, which involve the use of highly corrosive hydrofluoric acid. Moreover, challenges persist in the realm of high-rate performance, cycle stability, and environmental stability for pure phase MXenes, factors that are of paramount importance for commercial applications. Consequently, this research endeavors to develop environmentally friendly, cost-effective electrochemical methods conducive to MXene mass production, while also exploring MXene functionalization for superior performance in energy storage devices. [...], Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, Full Text

This thesis presents a novel approach to the electrochemical synthesis of functional nanomaterials, aimed at bolstering photocatalytic hydrogen production. The research encompasses a strategic manipulation of graphitic carbon nitride (g-C3N4), synthesis of iron oxyhydroxide (FeOOH) nanostructures, and the creation of a heterojunction nanostructure by coupling g-C3N4 with a two-dimensional MXene (Ti3C2). [...], Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, Full Text

Currently, the energy density of lithium ion batteries has reached a level of about 200 300 Wh kg-1, but the current energy density is still unable to meet the needs of long distance electric vehicles. In the future, the energy density of lithium ion batteries will need to continue to increase to more than 500 Wh kg-1 to meet the longer range and higher drive performance of electric vehicles. A lithium metal anode has the potential to increase the energy density and reduce the weight of batteries, making them more efficient and practical for use in electric vehicles and other applications. The advantages of lithium metal anodes include higher energy density, longer cycle life, and lower cost compared to other types of anodes. This is because lithium metal has a higher theoretical capacity (3860 mAh g-1) than graphite (372 mAh g-1), which is commonly used as an anode material in commercial lithium ion batteries. Additionally, the use of lithium metal anodes can reduce the weight of batteries and increase their energy efficiency, making them more practical for use in electric vehicles and portable electronic devices. However, there are still significant challenges that need to be overcome in order to fully realize the potential of lithium metal anodes. One major challenge is the formation of dendrites, which are branching structures that can grow from the surface of the lithium metal and cause short circuits within the battery. This can result in safety hazards and reduced cycle life. Another challenge is the issue of lithium metal oxidation and degradation during cycling, which can reduce the performance and cycle life of the battery. To overcome these challenges, researchers are exploring various strategies such as using protective coatings, designing new electrolytes, and optimizing the battery architecture. However, since there are so many factors affecting lithium dendrite generation, such as local current density, current density, flatness of lithium foil surfac, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, Full Text

Electro-catalyzed oxygen reactions, including ORR and OER, play a crucial role in future sustainable energy conversion, enabling a number of electrochemical devices (i.e., fuel cells, metal-air batteries, and water-splitting electrolyzers). The prerequisite for the practical application of these next-generation technologies is appropriate catalyst materials, which can accelerate reaction rate, decrease reaction overpotential, and enhance the selectivity toward the targeted reaction pathway. Nevertheless, the rational design and synthesis of electrocatalysts with favorable intrinsic characteristics are still challenging. Advanced design strategies and mechanism investigations are urgently needed to construct advanced materials for oxygen electrocatalysis. The combination of theoretical and experimental studies working in concert has proven to be a successful strategy in this respect, yielding a framework to understand catalytic trends that can ultimately provide rational guidance toward developing improved catalysts. This PhD thesis targets to rationally design and synthesize high-performance non-precious nano-electrocatalysts for oxygen electrocatalysis via theoretical and experimental means and explore their potential applications in electrochemical energy conversion.[…], Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, Full Text

The increasing concerns about environmental pollution, climate change, and the limited supply of fossil fuels have led to a growing demand for the development and distribution of renewable energy. Currently, lithium-ion batteries (LIBs) have gained dominance in the energy storage market, however, their further development is hindered due to limited natural resources and safety concerns, which calls for the search for low-cost and high-safety energy storage devices. Aqueous zinc ion batteries (AZIBs) have gained widespread attention due to their advantages of high safety, low cost, and high specific energy, in addition to abundant natural reserves and low cost of zinc metal. As such, AZIBs has emerged as promising candidate for the future development of electronics and electric vehicle and large-scale energy storage devices. The further practical application of AZIBs is highly restricted by Zn metal anode, since it suffers from uncontrolled dendritic and severe side reactions, including corrosion and hydrogen evolution reactions. The formation of dendrites can penetrate the separator, resulting in poor cycle life and strophic safety hazards. Regarding side reactions, the formation and accumulation of electronically insulating byproducts at the interface of the Zn anode would lead to an increase in interfacial resistance and polarization, thereby adversely affecting the reversibility of the Zn anode. And the occurrence of side reactions during battery cycling can result in volume expansion, which can negatively impact performance and cycle life. Here, this thesis presents viable solutions to the challenges mentioned above, which involve the electrolyte optimization and interface modification., Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, Full Text

Lithium-sulfur batteries (LSBs) are attractive candidates for post-lithium-ion battery technologies because of their ultrahigh theoretical energy density and low cost of active cathode materials. However, the commercialization of LSBs remains extremely challenging primarily due to poor cycling performance and safety concerns, which are inherently caused by low conductivity of S8 and Li2S, severe polysulfide shuttling, and high polarization by solid Li2S2/Li2S deposition. Catalytic materials could facilitate the large-scale practical application of LSBs by overcoming all these challenges. In this review, we investigate the sulfur species evolution in LSBs and explore the roles of catalytic materials in charge/discharge processes, highlighting the catalysis of solid S8 to liquid polysulfides and solid Li2S2 to Li2S. Furthermore, we offer systematic strategies from atomic to macro levels, including defect engineering, morphology engineering and catalyst compositing, to enhance catalysis efficiency in terms of sulfur supercooling, fast charge transfer, thiosulfate generation, disulfide bond cleavage, tuneable Li2S growth and Li2S decomposition enhancement. The design and availability of the proposed catalytic materials will further advance LSB technology from coin cells and pouch cells to the subsequent commercialization scale.

Rechargeable aqueous zinc-ion batteries (ZIBs) are promising in stationary grid energy storage due to their advantages in safety and cost-effectiveness, and the search for competent cathode materials is one core task in the development of ZIBs. Herein, the authors design a 2D heterostructure combining amorphous vanadium pentoxide and electrochemically produced graphene oxide (EGO) using a fast and scalable spray drying technique. The unique 2D heterostructured xerogel is achieved by controlling the concentration of EGO in the precursor solution. Driven by the improved electrochemical kinetics, the resultant xerogel can deliver an excellent rate capability (334 mAh g−1 at 5 A g−1) as well as a high specific capacity (462 mAh g−1 at 0.2 A g−1) as the cathode material in ZIB. It is also shown that the coin cell constructed based on spray-dried xerogel can output steady, high energy densities over a broad power density window. This work provides a scalable and cost-effective approach for making high performance electrode materials from cheap sources through existing industrialized materials processing.

Currently, achieving carbon neutrality is a historical global concern, including China 2060 and USA 2050, which refers to a dynamic balance between carbon emissions and carbon fixation. To address these concerns, human society is not only promoting the scale of artificial carbon sinks but also reducing carbon emissions. The latter plays a vital position in achieving carbon neutrality, necessitating high-efficiency energy consumption. Among the key drivers of energy consumption, buildings consume approximately 40%, more energy than the industry and transportation sectors. Half of building energy is used in ventilation and temperature control (heating and cooling for buildings), making it the largest unrealized cost-effective emission savings. The main reason is that traditional windows allow heat transfer in an undesirable direction that helps buildings gain heat in summer and release heat in winter. Moreover, the traditional daylighting control solutions, i.e., blinds, lead to the commonplace occurrence of closing blinds and lights on, with poor daylight utilization and more electric energy consumption. Smart windows, which can regulate illumination in buildings and heat exchange with the environment, are regarded as the ideal solution of this problem. The most widely used and investigated smart windows are based on electrochromism, with few researchers focusing on the unconventional ones based on mechanochromism. Electrochromism refers to the reversible and persistent changes of colour, transmittance, or other optical properties through electrochemical redox reactions under applied voltages. A typical electrochromic device is essentially a battery with electrochromic materials as electrodes. Our first two research chapters report electrochromic effects in traditional inorganic anode and cathode materials, namely LTO and TiS2, respectively. For LTO anode, we performed a detailed analysis of LTO’s optical properties during charging/discharging via a robust study of t, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, Full Text

Full Text, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, Bio-derived materials have attracted increased attention recently due to not only the sustainability, care-for-the-environment concerns, but also their naturally possessed unique structures, interesting mechanical properties, and abundant functional groups. These features endow them to potentially solve the issues that the next-generation high-capacity conversiontype lithium-ion batteries (LIBs) are facing, including but not limited to 1) great volume variation during charge/discharge for most conversion-type active materials (AMs), causing electrode pulverization, a phenomenon that active material particles are disassociated with the electrode and 2) serious shuttle effect brought by the dissolution of poly-intermediates into the electrolyte, leading to AMs loss, self-discharging, capacity fading, and shortened battery life. Bio-derived materials could provide strong binding forces and excellent mechanical strength to maintain the electrode integrity for high-capacity anodes, such as aluminum (Al) and silicon (Si) anodes. Meanwhile, Bio-derived materials possess abundant functional groups which could suppress the shuttle effect for high-capacity cathodes, such as lithium-iodine (Li-I2) batteries. These unique chemical, physical and mechanical properties of bio-derived materials make them promising in developing next-generation high-capacity LIBs. In the first study, aluminum with a high specific capacity, abundance, and electrical conductivity had been used as an active material to react with lithium ions and the electrical current collector simultaneously to save cost in the battery manufacturing process. However, its almost 100% volume variation will lead to serious electrode pulverization during lithiation/delithiation and reduce the cycle life of Al anode. Herein, a novel and robust biomassderived poly(furfuryl alcohol)/carbon black binder composite is prepared and applied on the surface of aluminum foil, and this hybrid Al anode had shown a superior 150 cycle

Full Text, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, With industrialization rapidly progressing in recent decades, great amounts of refractory organic pollutants are found in water bodies, which severely jeopardizes ecosystem health. Monitoring the organic compounds in water bodies and removing organic pollutants from wastewater is essential for ameliorating threats to aquatic life and human health. Photocatalytic (PC) and photoelectrocatalytic (PEC) degradation and detection of organic pollutants in wastewater are promising strategies for fulfilling these goals sustainably, since PC and PEC technologies can take advantage of solar energy, which is one of the most abundant energy sources on earth. Titanium dioxide (TiO2) is a commonly used photocatalyst due to its appropriate band position, high chemical stability, low cost, and nontoxicity. However, pristine TiO2 photocatalysts can only be stimulated by UV irradiation because the band gap of pristine TiO2 is higher than 3.0 eV, which seriously impedes its development with low-cost and environmentally friendly solar energy. There are several efficient strategies to overcome these disadvantages of pristine TiO2, such as morphology modification, bandgap engineering, and applying co-catalysts with the host photocatalysts. Herein, this thesis aims to utilize different strategies to enhance the photocatalytic performance of TiO2-based photocatalysts under visible light irradiation and apply those modified photocatalysts to degradation and detection of organics in wastewater. In the first study, a photoelectrochemical Chemical Oxygen Demand (COD) sensor based on a linear photocurrent-concentration analytical principle was designed for the on-site determination of COD. A high-performance anatase-branch@hydrogenated rutile-nanorod TiO2 (AB@H-RTNR) photoelectrode was fabricated. The as-prepared photoanodes successfully achieved sensitive determination of COD with a detection limit of 0.2 ppm (S/N = 3), an RSD% of 1.5 %, a wide linear detection range of 1.25−576 ppm, and an ave

Full Text, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Science, Science, Environment, Engineering and Technology, 2D materials have inspired the intrigue of researchers and industries for its potential to improve the performance of existing materials in energy storage field. However, wide application of 2D material such as graphene and transition metal dichalcogenides in batteries is not implemented since the tremendous challenges and issues, the quality, quantity, and cost concerns impede its commercialization. Electrochemical approach performs as a controllable and scalable method for exfoliating, expanding, and functionalizing the pristine bulk materials on-demand. Sodium ion batteries, a promising candidate for lithium ion batteries, and aqueous zinc ion batteries, a safe energy storage system have received considerable attention in recent decades. The research herein focuses on the electrochemical exfoliation of graphite for its application in sodium ion battery anode, adopting the electrochemical graphene oxide (EGO) as functional agent combining with vanadium oxide for aqueous zinc ion battery cathode, and electrochemical production of molybdenum disulfide in a packed bed reactor. The PhD thesis generally is composed of three parts. In the first part, graphite is exfoliated and oxidized in a packed bed reactor. The effects of boron doping and oxidation on the graphene-based material were studied for high performance sodium ion battery anode respectively in Chapter 2 and Chapter 3. The electrochemical route from natural graphite to graphene oxide is investigated in terms of concentration of acid electrolyte (sulfuric acid). It was found that 12 M sulfuric acid reacted graphene oxide could deliver higher capacity of sodium ion battery than other concentrations. Boron doped graphene was synthesized by a twostep reaction, electrochemical fabrication of the tetraborate anions intercalated graphite oxide followed by reduction by annealing at 900 °C for 3 h under Ar gas. It was found that the boron doped graphene containing 0.21 at. % of boron was highly defective delivers a go

Full Text, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, This success of Li-ion batteries (LIBs) is mainly built on inorganic electrode materials (IEMs). However, due to the inherent drawbacks of IEMs, such as short lifetime, potential fire risk, heavy dependence on unsustainable natural sources and energy in the course of mining (such as Li, Co and Ni), and high carbon footprint production processes, we must explore the use of other materials. Organic materials (OMs) can be fabricated from abundant and renewable natural sources and achieve sustainable energy storage. These materials can be used as organic electrode materials (OEMs) and organic additives (OAs) in modern metal ion batteries (MIBs). OMs can deliver remarkable battery performance for MIBs due to their unique molecular versatility, high flexibility, versatile structures, sustainable organic resources, and low environmental cost. Before OEMs can be widely used in MIBs, their inherent issues such as low intrinsic electronic conductivity, significant solubility in electrolytes, large volume change, and low tap density must be addressed. In this thesis, the potential roles, energy storage mechanisms, existing challenges, and possible solutions to these challenges are systematically summarized using molecular and morphological engineering. Molecular and morphological engineering could offer practical pathways for developing advanced OEMs in next-generation rechargeable MIBs. Molecular engineering, such as grafting electron-withdrawing or electron-donating functional groups, increasing various redox-active sites, extending conductive networks, and increasing the degree of polymerization, could enhance the electrochemical performance including specific capacity (such as voltage output and charge transfer number), rate capability, and cycling stability. Morphological engineering facilitates the preparation of different dimensional OEMs (inc uding 0D, 1D, 2D, and 3D OEMs) via bottom-up and top-down methods to enhance electrons/ions diffusion kinetics at the OEMs and s

Full Text, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, Since the fabrication of graphene, designing advanced atomically thin nanomaterials (ATMs) with few-atoms thick layers, special electronic structures, and excellent electrochemical properties for next-generation energy storage and conversion devices has attracted worldwide attention. Compared with traditional bulk materials, the ATMs exhibit several advantages: i) Their large specific surface area offers abundant active sites for ion insertion/deinsertion, and increases the contact with the electrolyte; ii) The atomic thickness of ATMs conspicuously shortens the ion diffusion pathway; iii) The distorted crystal lattice of ATMs could lead to increased electrical conductivity, and also facilitate vacancy generation, elemental doping and heterostructure construction; iv) The ATMs are regarded as an ideal 2D platform to explore the connection between electrochemical performance and electronic structures. However, they also face challenges like weak conductivity, large bandgap, and poor chemical activity. To solve these problems, various methods, including doping/phase engineering, vacancies/hole creation, and heterostructure construction have been utilized to optimize their properties. The goal of this thesis is to present a deep understanding of the impact of structural design and engineered defects on the electrochemical performance of ATMs. In the first study, holey graphene (HG) was created through an etching method, which acted as a template for the in-situ growth of atomically thin mesoporous NiCo2O4 nanosheets, leading to a NiCo2O4-HG heterostructure. The atomic-thin thickness and porous structures of NiCo2O4-HG was beneficial for electrolyte diffusion and ions/electrons transfer, and the subsequent numerous accessible surface atoms result in improved redox pseudocapacitance. In addition, the synergistic effect between NiCo2O4 and HG produced a broad interfacial area and increased electrical conductivity, dramatically accelerating the intercalation pseudocapacita

Full Text, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, Inorganic oxides have received wide attention as a new type of functional energy storage material, but their application prospects are usually limited due to their intrinsic properties, such as poor conductivity, limited active sites, and unstable crystal structure. Defect engineering is able to fine tune the concentration, mobility, and spatial distribution of carriers and electrons within crystalline structures, and these changed features radically optimize the electronic structure and physicochemical properties of the oxides. These optimized properties of oxides help to solve the kinetic problems of ion diffusion during the charge-storage process. However, defect engineering in oxides still faces the restriction of bottlenecks, which includes but is not limited to, defect preparation, defect preservation, and defect concentration adjustment. Defect preparation refers to the complicated process and harsh conditions required in the process of defect formation; these unstable defects will gradually recover or be refilled if the oxide is exposed to air or water leading to the disappearance of optimized properties; Controllable defect concentration is a further requirement for orderly regulation of oxide intrinsic properties in the development of defect engineering. In the first study, vacancy concentration varies with temperature exponentially according to the formation mechanism of defects. But these vacancies will gradually recover or be refilled in the slow cooling process. Based on this, commercial spinel-type lithium titanium oxide (LTO) was selected and quenched in this work, and we found the rapid cooling could interrupt the recovery of defects and preserve the defect state at high temperatures in the crystal lattice. More importantly, these preserved defects (oxygen vacancies and Li/Ti redistributions) can allow for an extraordinary capacity of 201.7 mAh g-1 beyond the theoretical value of pristine bulk LTO (175 mAh g-1) at a rate of 1 C with the voltage rang

Full Text, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, Intermittent electricity generation from renewable energy sources, such as wind energy, ocean energy, and solar energy, has significantly intensified the demand for high-energy-density, high-power, and low-cost energy storage devices. In this regard, tremendous efforts have been devoted to the development of electrode materials, electrolytes, and separators of energy-storage devices to address the fundamental needs of emerging technologies such as electric vehicles, artificial intelligence, and virtual reality. Polymer materials are ubiquitous in fabricating these energy storage devices and are widely used as binders, electrolytes, separators, and other components. However, binders, as an important component in energy-storage devices, are yet to receive sufficient attention. Polyvinylidene fluoride (PVDF) has been the dominant binder in the battery industry for decades despite several well-recognized drawbacks, i.e., limited binding strength due to the lack of chemical bonds with electroactive materials, insufficient mechanical properties, and low electronic and lithium-ion conductivities. The limited binding function cannot meet the inherent demands of emerging electrode materials with high capacities such as silicon anodes and sulfur cathodes. Polymers are also used as electrolyte matrices because they offer the advantages of low cost, lightweight, easy processability, excellent mechanical deformation, and better interfacial contact and compatibility with electrodes. However, the practical implementation of solid polymer electrolytes has been hindered by several challenging issues including low ionic conductivity, low ion transfer number, high-voltage instability, and lithium dendrite growth. Because of the increasingly growing demand for higher performance of energy storage devices, it is necessary to develop novel polymeric binders and solid electrolytes with advanced functionalities to help improve the operation of the currently existing energy storage systems.

Solid polymer electrolytes (SPEs) have become increasingly attractive in solid-state lithium-ion batteries (SSLIBs) in recent years because of their inherent properties of flexibility, processability, and interfacial compatibility. However, the commercialization of SPEs remains challenging for flexible and high-energy-density LIBs. The incorporation of functional additives into SPEs could significantly improve the electrochemical and mechanical properties of SPEs and has created some historical milestones in boosting the development of SPEs. In this study, we review the roles of additives in SPEs, highlighting the working mechanisms and functionalities of the additives. The additives could afford significant advantages in boosting ionic conductivity, increasing ion transference number, improving high-voltage stability, enhancing mechanical strength, inhibiting lithium dendrite, and reducing flammability. Moreover, the application of functional additives in high-voltage cathodes, lithium–sulfur batteries, and flexible lithium-ion batteries is summarized. Finally, future research perspectives are proposed to overcome the unresolved technical hurdles and critical issues in additives of SPEs, such as facile fabrication process, interfacial compatibility, investigation of the working mechanism, and special functionalities.

A mechanically strong binder with polar functional groups could overcome the dilemma of the large volume change during charge/discharge processes and poor cyclability of lithium-sulfur batteries (LSBs). In this work, for the first time, we report the use of poly(thiourea triethylene glycol) (PTTG) as a multifunctional binder for sulfur cathodes to enhance the performance of LSBs. As expected, the PTTG binder facilitates the high performance and stability delivered by the Sulfur-PTTG cathode, including a higher reversible capacity of 825 mAh g−1 at 0.2 C after 80 cycles, a lower capacity fading (0.123% per cycle) over 350 cycles at 0.5 C, a higher areal capacity of 2.5 mAh cm−2 at 0.25 mA cm−2, and better rate capability of 587 mAh g−1 at 2 C. Such superior electrochemical performances could be attributed to PTTG's strong chemical adsorption towards polysulfides which may avoid the lithium polysulfide shuttle effect and excellent mechanical characteristics which prevents electrode collapse during cycling and allows the Sulfur-PTTG electrode to maintain robust electron and ion migration pathways for accelerated redox reaction kinetics.

Binders could play crucial or even decisive roles in the fabrication of low-cost, stable and high-capacity electrodes. This is especially the case for the silicon (Si) anodes and sulfur (S) cathodes that undergo large volume change and active material loss in lithium-ion batteries during prolonged cycles. Herein, a hydrophilic polymer poly(methyl vinyl ether-alt-maleic acid) (PMVEMA) was explored as a dual-functional aqueous binder for the preparation of high-performance silicon anode and sulfur cathode. Benefiting from the dual functions of PMVEMA, i.e., the excellent dispersion ability and strong binding forces, the as-prepared electrodes exhibit improved capacity, rate capability and long-term cycling performance. In particular, the as-prepared Si electrode delivers a high initial discharge capacity of 1346.5 mAh g−1 at a high rate of 8.4 A/g and maintains 834.5 mAh g−1 after 300 cycles at 4.2 A/g, while the as-prepared S cathode exhibits enhanced cycling performance with high remaining discharge capacities of 663.4 mAh g−1 after 100 cycles at 0.2 C and 487.07 mAh g−1 after 300 cycles at 1 C, respectively. These encouraging results suggest that PMVEMA could be a universal binder to facilitate the green manufacture of both anode and cathode for high-capacity energy storage systems.

Silicon (Si), due to its wide availability and highest theoretical capacity (4200 mAh·g−1) amongst other anode candidates, has drawn tremendous attention as a promising alternative of the existing graphitic anode in current-generation lithium-ion batteries (LIBs). However, the greatest challenge associated with using Si anodes is the huge volume changes which occur during the lithiation-delithiation process and result in pulverization of the electrode which shortens battery life. In this work, the thick and slimy mucilage from commonly cultivated okra pods is extracted, precipitated, and used as the binder to solve the challenges of silicon anodes. The extracted okra gum (OG) consisting of abundant branched polysaccharides, a non-toxic, bio-friendly, and water-soluble polymer offers excellent penetrating binding network and interfacial chemical binding forces. As a result, the as-prepared Si-OG electrode displays a discharge capacity of 1434 mAh·g−1 at a rate of 0.1C after 50 cycles which is about 1.5 times greater than that of the Si- carboxymethylcellulose (CMC) electrode. This improvement could be attributed to the greater Si-anchoring and viscoelastic properties of the OG binder than that of the CMC binder. The success of this work suggests that this sustainable, green, and low-cost okra gum binder is promising in constructing reliable silicon anodes for next-generation large energy capacity LIBs.

Sodium-ion batteries (SIBs) are emerging as an inexpensive and more sustainable alternative to lithium-ion batteries in the energy storage market. To advance their commercialization, one major scientific undertaking is to develop low-cost, reliable anode materials from abundant resources, like the success of graphite in the lithium-ion batteries. However, graphite is chemically inactive in storing sodium ions and, to render it viable in sodium-ion batteries, additional modification of graphite is required. Herein, we demonstrate a green and facile method to prepare cost-effective and stable graphitic SIB anodes. The modification process started with the electrochemical oxidation of expanded graphite to widen the interlayer and functionalize graphite layers, followed by a fast (20 min) thermal treatment at 150 °C to achieve controlled deoxygenation. The thermally processed electrochemical graphite oxide could provide a high reversible capacity of 268 mAh g−1 at 100 mA g−1 and 163 mAh g−1 at 500 mA g−1 as well as low fading in capacity (in average 0.0198% loss per cycle) over 2000 cycles. The electrochemical route eliminates the need for the harsh chemical oxidation of graphite, offering a promising approach for industrial production of low-cost anodes for sodium-ion batteries.

Both industrious and academic research societies have considered silicon (Si) as the most promising anode for next-generation lithium ion batteries (LIBs) because silicon offers more than one order of magnitude higher capacity than conventional anode materials. However, huge volume changes and pulverization of the silicon particles during the charge/discharge processes damage the longevity of Si-based LIBs. Self-healing binders could tackle this problem by in-situ repairing the damage to the silicon anode. Herein, we synthesized a novel self-healing poly(ether-thioureas) (SHPET) polymer with balanced rigidity and softness for the silicon anode. The as-prepared silicon anode with the self-healing binder exhibits excellent structural stability and superior electrochemical performance, delivering a high discharge capacity of 3744 mAh g−1 at a current density of 420 mA g−1, and achieving a stable cycle life with a high capacity retention of 85.6% after 250 cycles at a high current rate of 4200 mA g−1. The success of this work suggests that the proposed SHPET binder facilitates fast self-healing, buffers the drastic volume changes and overcomes the mechanical strain in the course of the charge/discharge process, and could subsequently accelerate the commercialization of the silicon anode.

Silicon (Si) has been investigated as a promising anode material because of its high theoretical capacity (4200 mAh g-1). However, silicon anode suffers from huge volume changes during repeated charge–discharge cycles. In this work, inspired by a remarkable success of the glutinous rice mortar in the Great Wall with ca. 2000-year history, amylopectin (AP), the key ingredient responsible for the strong bonding force, is extracted from glutinous rice and utilized as a flexible, aqueous, and resilient binder to address the most challenging drastic volume-expansion and pulverization issues of silicon anode. Additionally, the removal of toxic N-methyl-2-pyrrolidone (NMP) organic solvent makes the electrode fabrication process environmentally friendly and healthy. The as-prepared Si-AP electrode with 60 wt% of Si can uphold a high discharge capacity of 1517.9 mAh g−1 at a rate of 0.1 C after 100 cycles. The cycling stability of the Si-AP has been remarkably improved in comparison with both traditional polyvinylidene fluoride (PVDF) and aqueous carboxymethylcellulose (CMC) binders. Moreover, when the content of silicon in the Si-AP electrode increases to 70 wt%, a high discharge capacity of 1463.1 mAh g−1 can still be obtained after 50 cycles at 0.1° C. These preliminary results suggest that the sustainably available and environmentally benign amylopectin binders could be a promising choice for the construction of highly stable silicon anodes.

Rechargeable batteries have recently solidified their role in society’s transition toward a cleaner energy future through the emergence of electric vehicles and grid-scale energy storage. The deployment of electrochemical energy storage near electricity generators and at home has increased the reliability of renewable energy, thus easing renewable energy’s emergence into power grids worldwide. Similarly, electric vehicles have continued to increase their implementation into global transportation networks, which reduces the reliance on fossil fuelbased vehicles and helps mitigate CO2 emissions. At present, lithium-ion batteries (LIBs) dominate the portable electronics market due to their superior energy density. However, as lithium-ion batteries are late in their development cycle, the limitations of the technology are becoming apparent, and researchers have turned to new battery chemistries to enhance the energy density, reduce the cost, and mitigate the environmental impacts of current-generation batteries. Lithium-sulfur batteries (Li−S) are an excellent example of next-generation batteries, and can deliver higher energy densities, reduce costs, and minimise environmental impacts over current-generation LIBs. However, Li−S batteries have technical limitations associated with their chemistry. The most troublesome limitation of the Li−S cell is the dubbed the polysulfide shuttle and refers to the dissolution and migration of soluble discharge intermediates which results in rapid capacity fading. Other limitations revolve around the limited conductivity of sulfur cathodes, volume expansion of electroactive materials, and poor performance at high current densities. Researchers have focused on various cell components to address the limitations, with substantial research on the cathode, anode, and electrolyte. This thesis employs strategies targeted at the composite sulfur cathode in lithium-sulfur cells., Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, Full Text

Bio-derived materials have attracted increased attention recently due to not only the sustainability, care-for-the-environment concerns, but also their naturally possessed unique structures, interesting mechanical properties, and abundant functional groups. These features endow them to potentially solve the issues that the next-generation high-capacity conversiontype lithium-ion batteries (LIBs) are facing, including but not limited to 1) great volume variation during charge/discharge for most conversion-type active materials (AMs), causing electrode pulverization, a phenomenon that active material particles are disassociated with the electrode and 2) serious shuttle effect brought by the dissolution of poly-intermediates into the electrolyte, leading to AMs loss, self-discharging, capacity fading, and shortened battery life. Bio-derived materials could provide strong binding forces and excellent mechanical strength to maintain the electrode integrity for high-capacity anodes, such as aluminum (Al) and silicon (Si) anodes. Meanwhile, Bio-derived materials possess abundant functional groups which could suppress the shuttle effect for high-capacity cathodes, such as lithium-iodine (Li-I2) batteries. These unique chemical, physical and mechanical properties of bio-derived materials make them promising in developing next-generation high-capacity LIBs. In the first study, aluminum with a high specific capacity, abundance, and electrical conductivity had been used as an active material to react with lithium ions and the electrical current collector simultaneously to save cost in the battery manufacturing process. However, its almost 100% volume variation will lead to serious electrode pulverization during lithiation/delithiation and reduce the cycle life of Al anode. Herein, a novel and robust biomassderived poly(furfuryl alcohol)/carbon black binder composite is prepared and applied on the surface of aluminum foil, and this hybrid Al anode had shown a superior 150 cycle, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, Full Text

2D materials have inspired the intrigue of researchers and industries for its potential to improve the performance of existing materials in energy storage field. However, wide application of 2D material such as graphene and transition metal dichalcogenides in batteries is not implemented since the tremendous challenges and issues, the quality, quantity, and cost concerns impede its commercialization. Electrochemical approach performs as a controllable and scalable method for exfoliating, expanding, and functionalizing the pristine bulk materials on-demand. Sodium ion batteries, a promising candidate for lithium ion batteries, and aqueous zinc ion batteries, a safe energy storage system have received considerable attention in recent decades. The research herein focuses on the electrochemical exfoliation of graphite for its application in sodium ion battery anode, adopting the electrochemical graphene oxide (EGO) as functional agent combining with vanadium oxide for aqueous zinc ion battery cathode, and electrochemical production of molybdenum disulfide in a packed bed reactor. The PhD thesis generally is composed of three parts. In the first part, graphite is exfoliated and oxidized in a packed bed reactor. The effects of boron doping and oxidation on the graphene-based material were studied for high performance sodium ion battery anode respectively in Chapter 2 and Chapter 3. The electrochemical route from natural graphite to graphene oxide is investigated in terms of concentration of acid electrolyte (sulfuric acid). It was found that 12 M sulfuric acid reacted graphene oxide could deliver higher capacity of sodium ion battery than other concentrations. Boron doped graphene was synthesized by a twostep reaction, electrochemical fabrication of the tetraborate anions intercalated graphite oxide followed by reduction by annealing at 900 °C for 3 h under Ar gas. It was found that the boron doped graphene containing 0.21 at. % of boron was highly defective delivers a go, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Science, Science, Environment, Engineering and Technology, Full Text

With industrialization rapidly progressing in recent decades, great amounts of refractory organic pollutants are found in water bodies, which severely jeopardizes ecosystem health. Monitoring the organic compounds in water bodies and removing organic pollutants from wastewater is essential for ameliorating threats to aquatic life and human health. Photocatalytic (PC) and photoelectrocatalytic (PEC) degradation and detection of organic pollutants in wastewater are promising strategies for fulfilling these goals sustainably, since PC and PEC technologies can take advantage of solar energy, which is one of the most abundant energy sources on earth. Titanium dioxide (TiO2) is a commonly used photocatalyst due to its appropriate band position, high chemical stability, low cost, and nontoxicity. However, pristine TiO2 photocatalysts can only be stimulated by UV irradiation because the band gap of pristine TiO2 is higher than 3.0 eV, which seriously impedes its development with low-cost and environmentally friendly solar energy. There are several efficient strategies to overcome these disadvantages of pristine TiO2, such as morphology modification, bandgap engineering, and applying co-catalysts with the host photocatalysts. Herein, this thesis aims to utilize different strategies to enhance the photocatalytic performance of TiO2-based photocatalysts under visible light irradiation and apply those modified photocatalysts to degradation and detection of organics in wastewater. In the first study, a photoelectrochemical Chemical Oxygen Demand (COD) sensor based on a linear photocurrent-concentration analytical principle was designed for the on-site determination of COD. A high-performance anatase-branch@hydrogenated rutile-nanorod TiO2 (AB@H-RTNR) photoelectrode was fabricated. The as-prepared photoanodes successfully achieved sensitive determination of COD with a detection limit of 0.2 ppm (S/N = 3), an RSD% of 1.5 %, a wide linear detection range of 1.25−576 ppm, and an ave, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, Full Text

This success of Li-ion batteries (LIBs) is mainly built on inorganic electrode materials (IEMs). However, due to the inherent drawbacks of IEMs, such as short lifetime, potential fire risk, heavy dependence on unsustainable natural sources and energy in the course of mining (such as Li, Co and Ni), and high carbon footprint production processes, we must explore the use of other materials. Organic materials (OMs) can be fabricated from abundant and renewable natural sources and achieve sustainable energy storage. These materials can be used as organic electrode materials (OEMs) and organic additives (OAs) in modern metal ion batteries (MIBs). OMs can deliver remarkable battery performance for MIBs due to their unique molecular versatility, high flexibility, versatile structures, sustainable organic resources, and low environmental cost. Before OEMs can be widely used in MIBs, their inherent issues such as low intrinsic electronic conductivity, significant solubility in electrolytes, large volume change, and low tap density must be addressed. In this thesis, the potential roles, energy storage mechanisms, existing challenges, and possible solutions to these challenges are systematically summarized using molecular and morphological engineering. Molecular and morphological engineering could offer practical pathways for developing advanced OEMs in next-generation rechargeable MIBs. Molecular engineering, such as grafting electron-withdrawing or electron-donating functional groups, increasing various redox-active sites, extending conductive networks, and increasing the degree of polymerization, could enhance the electrochemical performance including specific capacity (such as voltage output and charge transfer number), rate capability, and cycling stability. Morphological engineering facilitates the preparation of different dimensional OEMs (inc uding 0D, 1D, 2D, and 3D OEMs) via bottom-up and top-down methods to enhance electrons/ions diffusion kinetics at the OEMs and s, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, Full Text

Since the fabrication of graphene, designing advanced atomically thin nanomaterials (ATMs) with few-atoms thick layers, special electronic structures, and excellent electrochemical properties for next-generation energy storage and conversion devices has attracted worldwide attention. Compared with traditional bulk materials, the ATMs exhibit several advantages: i) Their large specific surface area offers abundant active sites for ion insertion/deinsertion, and increases the contact with the electrolyte; ii) The atomic thickness of ATMs conspicuously shortens the ion diffusion pathway; iii) The distorted crystal lattice of ATMs could lead to increased electrical conductivity, and also facilitate vacancy generation, elemental doping and heterostructure construction; iv) The ATMs are regarded as an ideal 2D platform to explore the connection between electrochemical performance and electronic structures. However, they also face challenges like weak conductivity, large bandgap, and poor chemical activity. To solve these problems, various methods, including doping/phase engineering, vacancies/hole creation, and heterostructure construction have been utilized to optimize their properties. The goal of this thesis is to present a deep understanding of the impact of structural design and engineered defects on the electrochemical performance of ATMs. In the first study, holey graphene (HG) was created through an etching method, which acted as a template for the in-situ growth of atomically thin mesoporous NiCo2O4 nanosheets, leading to a NiCo2O4-HG heterostructure. The atomic-thin thickness and porous structures of NiCo2O4-HG was beneficial for electrolyte diffusion and ions/electrons transfer, and the subsequent numerous accessible surface atoms result in improved redox pseudocapacitance. In addition, the synergistic effect between NiCo2O4 and HG produced a broad interfacial area and increased electrical conductivity, dramatically accelerating the intercalation pseudocapacita, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, Full Text

Inorganic oxides have received wide attention as a new type of functional energy storage material, but their application prospects are usually limited due to their intrinsic properties, such as poor conductivity, limited active sites, and unstable crystal structure. Defect engineering is able to fine tune the concentration, mobility, and spatial distribution of carriers and electrons within crystalline structures, and these changed features radically optimize the electronic structure and physicochemical properties of the oxides. These optimized properties of oxides help to solve the kinetic problems of ion diffusion during the charge-storage process. However, defect engineering in oxides still faces the restriction of bottlenecks, which includes but is not limited to, defect preparation, defect preservation, and defect concentration adjustment. Defect preparation refers to the complicated process and harsh conditions required in the process of defect formation; these unstable defects will gradually recover or be refilled if the oxide is exposed to air or water leading to the disappearance of optimized properties; Controllable defect concentration is a further requirement for orderly regulation of oxide intrinsic properties in the development of defect engineering. In the first study, vacancy concentration varies with temperature exponentially according to the formation mechanism of defects. But these vacancies will gradually recover or be refilled in the slow cooling process. Based on this, commercial spinel-type lithium titanium oxide (LTO) was selected and quenched in this work, and we found the rapid cooling could interrupt the recovery of defects and preserve the defect state at high temperatures in the crystal lattice. More importantly, these preserved defects (oxygen vacancies and Li/Ti redistributions) can allow for an extraordinary capacity of 201.7 mAh g-1 beyond the theoretical value of pristine bulk LTO (175 mAh g-1) at a rate of 1 C with the voltage rang, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, Full Text

Intermittent electricity generation from renewable energy sources, such as wind energy, ocean energy, and solar energy, has significantly intensified the demand for high-energy-density, high-power, and low-cost energy storage devices. In this regard, tremendous efforts have been devoted to the development of electrode materials, electrolytes, and separators of energy-storage devices to address the fundamental needs of emerging technologies such as electric vehicles, artificial intelligence, and virtual reality. Polymer materials are ubiquitous in fabricating these energy storage devices and are widely used as binders, electrolytes, separators, and other components. However, binders, as an important component in energy-storage devices, are yet to receive sufficient attention. Polyvinylidene fluoride (PVDF) has been the dominant binder in the battery industry for decades despite several well-recognized drawbacks, i.e., limited binding strength due to the lack of chemical bonds with electroactive materials, insufficient mechanical properties, and low electronic and lithium-ion conductivities. The limited binding function cannot meet the inherent demands of emerging electrode materials with high capacities such as silicon anodes and sulfur cathodes. Polymers are also used as electrolyte matrices because they offer the advantages of low cost, lightweight, easy processability, excellent mechanical deformation, and better interfacial contact and compatibility with electrodes. However, the practical implementation of solid polymer electrolytes has been hindered by several challenging issues including low ionic conductivity, low ion transfer number, high-voltage instability, and lithium dendrite growth. Because of the increasingly growing demand for higher performance of energy storage devices, it is necessary to develop novel polymeric binders and solid electrolytes with advanced functionalities to help improve the operation of the currently existing energy storage systems., Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, Full Text

© 2020 The Royal Society of Chemistry. Pseudocapacitive energy storage via Li+ storage at the surface/interface of the electrode is promising for achieving both high energy density and high power density in lithium-ion batteries (LIBs). Thus, we created holey graphene (HG) via an etching method, and then in situ grew atomically thin mesoporous NiCo2O4 nanosheets on the HG surface, resulting in a NiCo2O4-HG heterostructure. Since both NiCo2O4 and HG possess atomic thickness and porous structures, the as-prepared nanocomposite enables efficient electrolyte diffusion and mass transfer, providing abundant accessible surface atoms for enhanced redox pseudocapacitance. Moreover, the strong coupling effect between NiCo2O4 and graphene produces an ultra-large interfacial area and enhanced electrical conductivity, and subsequently promotes the intercalation pseudocapacitance. Consequently, the NiCo2O4@HG exhibits a high specific capacity of 1103.4 mA h g-1 at 0.2C, ∼88.9% contribution from pseudocapacitance at 1 mV s-1, excellent rate capability, and ultra-long life up to 450 cycles with 931.2 mA h g-1 retention, significantly outperforming previously reported electrodes. This work suggests that the maximum exposure and utilization of the surface/interfacial active sites is vital for the construction of high-performance pseudocapacitive energy storage devices.

© 2020 The Royal Society of Chemistry. Pseudocapacitive energy storage via Li+ storage at the surface/interface of the electrode is promising for achieving both high energy density and high power density in lithium-ion batteries (LIBs). Thus, we created holey graphene (HG) via an etching method, and then in situ grew atomically thin mesoporous NiCo2O4 nanosheets on the HG surface, resulting in a NiCo2O4-HG heterostructure. Since both NiCo2O4 and HG possess atomic thickness and porous structures, the as-prepared nanocomposite enables efficient electrolyte diffusion and mass transfer, providing abundant accessible surface atoms for enhanced redox pseudocapacitance. Moreover, the strong coupling effect between NiCo2O4 and graphene produces an ultra-large interfacial area and enhanced electrical conductivity, and subsequently promotes the intercalation pseudocapacitance. Consequently, the NiCo2O4@HG exhibits a high specific capacity of 1103.4 mA h g-1 at 0.2C, ∼88.9% contribution from pseudocapacitance at 1 mV s-1, excellent rate capability, and ultra-long life up to 450 cycles with 931.2 mA h g-1 retention, significantly outperforming previously reported electrodes. This work suggests that the maximum exposure and utilization of the surface/interfacial active sites is vital for the construction of high-performance pseudocapacitive energy storage devices.

Full Text, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, Carbon nitrides are a unique family of nitrogen-rich carbon materials with multiple beneficial properties for effective alkali metal ion transport/storage. Graphitic carbon nitride (g-C3N4) is considered the most viable member of the carbon nitride family because of its high nitrogen content, wide structure with several nitrogen-defect pore sites, ease of synthesis, affordability, and scalability. Also, g-C3N4 delivers a lithium ion battery (LIBs) theoretical capacity of 524 mAh/g unlike graphite which records only 327 mAh/g. However, due to the ineffective intercalation/deintercalation reaction of Li+ with C3N4 it suffers low capacity, poor conductivity and structural deformation when applied as an anode material for battery application. Due to this problem, the application of g-C3N4 for LIBs has slowed down, and the prospects of g-C3N4 for emerging battery systems such as potassium ion batteries (KIBs) have not been explored. In this thesis, we present unique strategies to resolve the problems of irreversible Li+ intercalation, poor conductivity, and structural destruction, and explore g-C3N4-based composites for KIB system. In the first study, one-dimensional carbon nitride nanofibers were designed and proved to be a more effective and better performing anode material for LIBs than bulk g-C3N4. This work was accomplished by combining theoretical computing and experimental techniques, Density functional theory calculation showed that the edges of the 1D-g- C3N4 nanofibers exhibited a suitable Li adsorption energy for stress-free adsorption and desorption of adsorbed Li-atoms. Moreover, our synthesized 1D-g-C3N4 nanofiber possessed edges and pores, as well as higher pyridinic nitrogen content unlike the bulk g-C3N4. The 1D-g-C3N4 nanofiber delivered a superior specific capacity of 181.7 mAh/g, a specific capacity of 138.6 mAh/g after 5000 cycles when cycled at 10C along with excellent stability and power density. This performance remains the highest amongst reporte

Stable and seamless interfaces among solid components in all-solid-state batteries (ASSBs) are crucial for high ionic conductivity and high rate performance. This can be achieved by the combination of functional inorganic material and flexible polymer solid electrolyte. In this work, a flexible all-solid-state composite electrolyte is synthesized based on oxygen-vacancy-rich Ca-doped CeO2 (Ca–CeO2) nanotube, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and poly(ethylene oxide) (PEO), namely Ca–CeO2/LiTFSI/PEO. Ca–CeO2 nanotubes play a key role in enhancing the ionic conductivity and mechanical strength while the PEO offers flexibility and assures the stable seamless contact between the solid electrolyte and the electrodes in ASSBs. The as-prepared electrolyte exhibits high ionic conductivity of 1.3 × 10−4 S cm−1 at 60 °C, a high lithium ion transference number of 0.453, and high-voltage stability. More importantly, various electrochemical characterizations and density functional theory (DFT) calculations reveal that Ca–CeO2 helps dissociate LiTFSI, produce free Li ions, and therefore enhance ionic conductivity. The ASSBs based on the as-prepared Ca–CeO2/LiTFSI/PEO composite electrolyte deliver high-rate capability and high-voltage stability.

Silicon (Si) anodes suffer from severe structural instability caused by volume expansion during lithium insertion and extraction. The extensive stress generated causes delamination at the anode/current collector interface and early capacity decay. We developed a novel anode structure by introducing a liquid metal layer in between Si and the Cu current collector. Both experiments and the density functional theory (DFT) simulation indicate an increased flexibility in the hybrid structure. No visible cracking or interface delamination was observed, attributed to the self-healing effect from the liquid metal. This work introduces a novel design for hybrid anodes with balanced mechanical strength and electrochemical performance.

In spite of the fact that there are plenty of recent studies on Si/graphene composite anodes, the influence of graphene on Li diffusion at the interface and lithiation associated mechanical behavior have not been well-understood. Furthermore, it is still a technical challenge to maintain a high capacity and an ultralong cycle life with high mass loading. Using a simple self-assembly approach, we have developed an all-integrated architecture of Si nanoparticles (SiNPs) encapsulated inside reduced graphene oxide (rGO) bubble films anchored in a 3D rGO macroporous network (encapsulated Si@rGO) as an anode for Li-ion batteries (LIBs). The enhanced electrochemical performance and structural stability of the anode are accomplished by the unique multifunctional rGO bubble film, which smoothly wraps SiNPs with notable void spaces. Its residual functional groups covalently bind with SiNPs, preventing their detachment from the electrode. The bubble wrap together with the outermost 3D framework accommodate the volume change, contributing to a stabilized solid electrolyte interphase (SEI) layer while maintaining ionic and electronic conductive pathways. Density functional theory (DFT) simulations show that the graphene coating boosts the mobility of the Li atoms at the Si-graphene interface. Molecular dynamics (MD) simulations confirm that graphene bubble film can effectively control the stress build-up near the Si surface, maintaining the structural integrity of the anode. The encapsulated Si@rGO anode with a mass loading of 2.6 mg cm -2 demonstrates exceptional cycling stability and superior rate capabilities. The anode demonstrates a high reversible capacity of 1346 mAh g -1 after 200 cycles at 500 mA g -1. Even at a high current density of 2.5 A g -1, a reversible capacity of 998 mAh g -1 is maintained after 1000 cycles with a capacity retention of 97%.

In this work, cross-linked dextrin as a low-cost and aqueous binder has been prepared for silicon (Si) based anodes in Li-ion batteries. A 3D network is achieved by the aldolization between the hydroxyl groups in dextrin and the aldehyde groups in glutaraldehyde. This inter-waving structure demonstrates good mechanical property and can mitigate the volume variation of Si anodes during cycling, resulting in a better electrochemical performance than that with PVDF, CMC and pristine dextrin binders. The initial capacity is 3276 mAh g−1 with Coulombic efficiency (CE) of 88.79% and only drops to above 1000 mAh g−1 after 150 cycles under 0.1C. Adding 20 wt% FEC in the electrolyte, the cycling performance is further improved to about 1700 mAh g−1 after 150 cycles under 0.1C, and over 1000 mAh g−1 after 150 cycles under 0.5C. Therefore, the cross-linked dextrin is considered to be a promising binder for Si based electrodes, with potential for other anodes as well.

Carbon nitrides are a unique family of nitrogen-rich carbon materials with multiple beneficial properties for effective alkali metal ion transport/storage. Graphitic carbon nitride (g-C3N4) is considered the most viable member of the carbon nitride family because of its high nitrogen content, wide structure with several nitrogen-defect pore sites, ease of synthesis, affordability, and scalability. Also, g-C3N4 delivers a lithium ion battery (LIBs) theoretical capacity of 524 mAh/g unlike graphite which records only 327 mAh/g. However, due to the ineffective intercalation/deintercalation reaction of Li+ with C3N4 it suffers low capacity, poor conductivity and structural deformation when applied as an anode material for battery application. Due to this problem, the application of g-C3N4 for LIBs has slowed down, and the prospects of g-C3N4 for emerging battery systems such as potassium ion batteries (KIBs) have not been explored. In this thesis, we present unique strategies to resolve the problems of irreversible Li+ intercalation, poor conductivity, and structural destruction, and explore g-C3N4-based composites for KIB system. In the first study, one-dimensional carbon nitride nanofibers were designed and proved to be a more effective and better performing anode material for LIBs than bulk g-C3N4. This work was accomplished by combining theoretical computing and experimental techniques, Density functional theory calculation showed that the edges of the 1D-g- C3N4 nanofibers exhibited a suitable Li adsorption energy for stress-free adsorption and desorption of adsorbed Li-atoms. Moreover, our synthesized 1D-g-C3N4 nanofiber possessed edges and pores, as well as higher pyridinic nitrogen content unlike the bulk g-C3N4. The 1D-g-C3N4 nanofiber delivered a superior specific capacity of 181.7 mAh/g, a specific capacity of 138.6 mAh/g after 5000 cycles when cycled at 10C along with excellent stability and power density. This performance remains the highest amongst reporte, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, Full Text

© 2020 The Royal Society of Chemistry. Pseudocapacitive energy storage via Li+ storage at the surface/interface of the electrode is promising for achieving both high energy density and high power density in lithium-ion batteries (LIBs). Thus, we created holey graphene (HG) via an etching method, and then in situ grew atomically thin mesoporous NiCo2O4 nanosheets on the HG surface, resulting in a NiCo2O4-HG heterostructure. Since both NiCo2O4 and HG possess atomic thickness and porous structures, the as-prepared nanocomposite enables efficient electrolyte diffusion and mass transfer, providing abundant accessible surface atoms for enhanced redox pseudocapacitance. Moreover, the strong coupling effect between NiCo2O4 and graphene produces an ultra-large interfacial area and enhanced electrical conductivity, and subsequently promotes the intercalation pseudocapacitance. Consequently, the NiCo2O4@HG exhibits a high specific capacity of 1103.4 mA h g-1 at 0.2C, ∼88.9% contribution from pseudocapacitance at 1 mV s-1, excellent rate capability, and ultra-long life up to 450 cycles with 931.2 mA h g-1 retention, significantly outperforming previously reported electrodes. This work suggests that the maximum exposure and utilization of the surface/interfacial active sites is vital for the construction of high-performance pseudocapacitive energy storage devices.

© 2020 The Royal Society of Chemistry. Pseudocapacitive energy storage via Li+ storage at the surface/interface of the electrode is promising for achieving both high energy density and high power density in lithium-ion batteries (LIBs). Thus, we created holey graphene (HG) via an etching method, and then in situ grew atomically thin mesoporous NiCo2O4 nanosheets on the HG surface, resulting in a NiCo2O4-HG heterostructure. Since both NiCo2O4 and HG possess atomic thickness and porous structures, the as-prepared nanocomposite enables efficient electrolyte diffusion and mass transfer, providing abundant accessible surface atoms for enhanced redox pseudocapacitance. Moreover, the strong coupling effect between NiCo2O4 and graphene produces an ultra-large interfacial area and enhanced electrical conductivity, and subsequently promotes the intercalation pseudocapacitance. Consequently, the NiCo2O4@HG exhibits a high specific capacity of 1103.4 mA h g-1 at 0.2C, ∼88.9% contribution from pseudocapacitance at 1 mV s-1, excellent rate capability, and ultra-long life up to 450 cycles with 931.2 mA h g-1 retention, significantly outperforming previously reported electrodes. This work suggests that the maximum exposure and utilization of the surface/interfacial active sites is vital for the construction of high-performance pseudocapacitive energy storage devices.

The poor cycling stability resulting from the large volume expansion caused by lithiation is a critical issue for Si-based anodes. Herein, we report for the first time of a new yolk-shell structured high tap density composite made of a carbon-coated rigid SiO2 outer shell to confine multiple Si NPs (yolks) and carbon nanotubes (CNTs) with embedded Fe2O3 nanoparticles (NPs). The high tap density achieved and superior conductivity can be attributed to the efficiently utilised inner void containing multiple Si yolks, Fe2O3 NPs, and CNTs Li+ storage materials, and the bridged spaces between the inner Si yolks and outer shell through a conductive CNTs "highway". Half cells can achieve a high area capacity of 3.6 mAh cm−2 and 95 % reversible capacity retention after 450 cycles. The full cell constructed using a Li-rich Li2V2O5 cathode can achieve a high reversible capacity of 260 mAh g−1 after 300 cycles.

The poor cycling stability resulting from the large volume expansion caused by lithiation is a critical issue for Si-based anodes. Herein, we report for the first time of a new yolk-shell structured high tap density composite made of a carbon-coated rigid SiO2 outer shell to confine multiple Si NPs (yolks) and carbon nanotubes (CNTs) with embedded Fe2O3 nanoparticles (NPs). The high tap density achieved and superior conductivity can be attributed to the efficiently utilised inner void containing multiple Si yolks, Fe2O3 NPs, and CNTs Li+ storage materials, and the bridged spaces between the inner Si yolks and outer shell through a conductive CNTs "highway". Half cells can achieve a high area capacity of 3.6 mAh cm−2 and 95 % reversible capacity retention after 450 cycles. The full cell constructed using a Li-rich Li2V2O5 cathode can achieve a high reversible capacity of 260 mAh g−1 after 300 cycles.

Silicon is a promising anode material for rechargeable Li-ion battery (LIB) due to its high energy density and relatively low operating voltage. However, silicon based electrodes suffer from rapid capacity degradation during electrochemical cycling. The capacity decay is predominantly caused by (i) cracking due to large volume variations during lithium insertion/extraction and (ii) surface degradation due to excessive solid electrolyte interface (SEI) formation. In this work, we demonstrate that coating of a-Si thin film with a Li-active, nanoporous SiOx layer can result in exceptional electrochemical performance in Li-ion battery. The SiOx layer provides improved cracking resistance to the thin film and prevent the active material loss due to excessive SEI formation, benefiting the electrode cycling stability. Half-cell experiments using this anode material show an initial reversible capacity of 2173 mAh g1 with an excellent coulombic efficiency of 90.9%. Furthermore, the electrode shows remarkable capacity retention of ~97% after 100 cycles at C/2 charging rate. The proposed anode architecture is free from Liinactive binders and conductive additives and provides mechanical stability during the charge/discharge process.

Si anodes suffer an inherent volume expansion problem. The consensus is that hydrogen bonds in these anodes are preferentially constructed between the binder and Si powder for enhanced adhesion and thus can improve cycling performance. There has been little research done in the field of understanding the contribution of the binder's mechanical properties to performance. Herein, a simple but effective strategy is proposed, combining hard/soft polymer systems, to exploit a robust binder with a 3D interpenetrating binding network (3D‐IBN) via an in situ polymerization. The 3D‐IBN structure is constructed by interweaving a hard poly(furfuryl alcohol) as the skeleton with a soft polyvinyl alcohol (PVA) as the filler, buffering the dramatic volume change of the Si anode. The resulting Si anode delivers an areal capacity of >10 mAh cm−2 and enables an energy density of >300 Wh kg−1 in a full lithium‐ion battery (LIB) cell. The component of the interweaving binder can be switched to other polymers, such as replacing PVA by thermoplastic polyurethane and styrene butadiene styrene. Such a strategy is also effective for other high‐capacity electroactive materials, e.g., Fe2O3 and Sn. This finding offers an alternative approach in designing high‐areal‐capacity electrodes through combined hard and soft polymer binders for high‐energy‐density LIBs.

The poor cycling stability resulting from the large volume expansion caused by lithiation is a critical issue for Si-based anodes. Herein, we report for the first time of a new yolk-shell structured high tap density composite made of a carbon-coated rigid SiO2 outer shell to confine multiple Si NPs (yolks) and carbon nanotubes (CNTs) with embedded Fe2O3 nanoparticles (NPs). The high tap density achieved and superior conductivity can be attributed to the efficiently utilised inner void containing multiple Si yolks, Fe2O3 NPs, and CNTs Li+ storage materials, and the bridged spaces between the inner Si yolks and outer shell through a conductive CNTs "highway". Half cells can achieve a high area capacity of 3.6 mAh cm−2 and 95 % reversible capacity retention after 450 cycles. The full cell constructed using a Li-rich Li2V2O5 cathode can achieve a high reversible capacity of 260 mAh g−1 after 300 cycles.

The poor cycling stability resulting from the large volume expansion caused by lithiation is a critical issue for Si-based anodes. Herein, we report for the first time of a new yolk-shell structured high tap density composite made of a carbon-coated rigid SiO2 outer shell to confine multiple Si NPs (yolks) and carbon nanotubes (CNTs) with embedded Fe2O3 nanoparticles (NPs). The high tap density achieved and superior conductivity can be attributed to the efficiently utilised inner void containing multiple Si yolks, Fe2O3 NPs, and CNTs Li+ storage materials, and the bridged spaces between the inner Si yolks and outer shell through a conductive CNTs "highway". Half cells can achieve a high area capacity of 3.6 mAh cm−2 and 95 % reversible capacity retention after 450 cycles. The full cell constructed using a Li-rich Li2V2O5 cathode can achieve a high reversible capacity of 260 mAh g−1 after 300 cycles.

Full Text, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, Low-dimensional nanomaterials have attracted much attention due to their unique morphology, including zero, one and two-dimensional structures. These unique morphologies introduce excellent optical, electrical and magnetic properties, which make these materials promising active materials in high-efficiency energy conversion and storage devices. In this thesis, a series of low dimensional nanomaterials have been designed and fabricated. Their uses in photoelectrochemical and electrochemical devices were then investigated in several studies. In the first study, one-dimensional plasmonic titanium dioxide nanorod arrays (TiO2) photoelectrodes were modified with zero-dimensional plasmonic gold (Au) nanoparticle deposition and subsequent hydrogenation treatment (i.e. Au@H-TiO2). The photoelectrode delivered a tunable oxidation capability to selectively detect organic compounds in water bodies as PEC sensors. Under visible light, the Au@H-TiO2 electrode exhibits selective detection capability to labile organic compounds due to surface plasmonic resonance effects. Furthermore, the modified electrode can also indiscriminately and rapidly detect all kinds of organic compounds under UV irradiation due to the strong oxidation capability. This unique tunable oxidation capability enables the use of Au@H-TiO2 photoelectrodes in new generation PEC sensors for selective and collective degradation of organic compounds. The hydrogenation process was further explored by the synthesis of two-dimensional nanomaterials. A top-down strategy using high-pressure hydrogen surface treatment and controlled etching to reduce the thickness of Fe2O3 nanoplates was proposed. As a result, the thickness of the two-dimensional Fe2O3 materials could be further reduced to ca. 4 nm. Such an ultrathin structure can enhance internal diffusion of lithium ions, shorten electron transport length and increase tolerance to large volume changes. When employed as an anode material in rechargeable lithium-ion batt