Ionic liquids as electrolytes for energy storage applications – A modelling perspective

Ionic liquids as electrolytes for energy storage devices is a promising field. Here, the various approaches of how ionic liquids can be modelled are discussed along with how the modelling connects to experimental results. Recent theoretical developments are highlighted along with extended discussion of what molecular dynamics simulation options are now available and what key results can be extracted. Ab initio work is also discussed, this includes some of the spectral properties, both of ionic liquids and their electrolyte formulations

High temperature supercapacitors

The scientific objective of this research program was to determine the feasibility of manufacturing an ionic liquid-based supercapacitor that could operate at temperatures up to 220 °C. A secondary objective was to determine the compatibility of ionic liquids with other cell components (e.g. current collectors) at high temperature and, if required, consider means of mitigating any problems. The industrial motivation for the present work was to develop a supercapacitor capable of working in the harsh environment of deep offshore boreholes. If successful, this technology would allow down-hole telemetry under conditions of mechanical vibration and high temperature. The obstacles, however, were many. All supercapacitor components had to be stable against thermal decomposition up to T ≥ 220 °C. Volatile components had to be eliminated. If possible, the finished device should be able to withstand voltages greater than 4 V, in order to maximise the amount of stored energy. The internal resistance should be as low as possible. Side reactions, particularly faradaic reactions, should be eliminated or suppressed. All liquid components should be gelled to minimise leakage in the event of cell damage. Finally, any emergent problems should be identified. [Continues.

Advances in Supercapacitor Technology and Applications

Energy storage is a key topic for research, industry, and business, which is gaining increasing interest. Any available energy-storage technology (batteries, fuel cells, flywheels, and so on) can cover a limited part of the power-energy plane and is characterized by some inherent drawback. Supercapacitors (also known as ultracapacitors, electrochemical capacitors, pseudocapacitors, or double-layer capacitors) feature exceptional capacitance values, creating new scenarios and opportunities in both research and industrial applications, partly because the related market is relatively recent. In practice, supercapacitors can offer a trade-off between the high specific energy of batteries and the high specific power of traditional capacitors. Developments in supercapacitor technology and supporting electronics, combined with reductions in costs, may revolutionize everything from large power systems to consumer electronics. The potential benefits of supercapacitors move from the progresses in the technological processes but can be effective by the availability of the proper tools for testing, modeling, diagnosis, sizing, management and technical-economic analyses. This book collects some of the latest developments in the field of supercapacitors, ranging from new materials to practical applications, such as energy storage, uninterruptible power supplies, smart grids, electrical vehicles, advanced transportation and renewable sources

Characterising, understanding and predicting the performance of structural power composites

Dramatic improvements in power generation, energy storage, system integration and light-weighting are needed to meet increasingly stringent carbon emissions targets for future aircraft and road vehicles. The electrification of transport could significantly reduce direct CO2 emissions; however, battery energy and power density limitations pose a major technological barrier. The introduction of multifunctional structural power composites (SPCs), which simultaneously provide mechanical load-bearing and electrochemical energy storage, offers new possibilities. By replacing conventional materials with SPCs, electrical performance requirements could be relaxed, and vehicle mass could be reduced; however, for SPCs to outperform monofunctional systems, significant performance and reliability improvements are still required. The use of computational models to support experimental efforts has so far been overlooked, despite wide recognition of the benefits of such a combined approach. The aim of this work was to develop predictive finite element models for structural supercapacitor composites (SSCs), and use them to investigate their mechanical, electrical, and electrochemical behaviour. A unit cell modelling technique was used to generate realistic mesoscale models of the complex microstructure of SSCs. The effects of composite manufacturing processes on the final performance of SSCs were investigated through characterisation and modelling of compaction and manufacturing defects. Numerical predictions of the elastic properties of SSCs were evaluated against data from the literature; and the presence of defects was shown to significantly degrade performance. Motivated by the large series resistance of SSCs, direct conduction models were developed to better understand electrical charge transport. Based on investigations of various current collector geometries, design strategies for the mitigation of resistive losses were proposed. To enable analysis of the combined mechanical-electrochemical behaviour of SSCs, an ion transport user element subroutine was developed but could not be validated. Overall, this work demonstrates that substantial improvements in the mechanical and electrical properties of SSCs are possible through control of the composite microstructure. The models developed in this work provide guidance for the optimisation of manufacturing processes and the design of new SSC architectures, and underpin the future certification and deployment of these emerging materials.Open Acces

The effects of morphological changes and carbon nanospheres on the pseudocapacitive properties of molybdenum disulphide

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in fulfilment of the requirements for the degree of Master of Science in Engineering. Johannesburg, 21 July 2016The use of supercapacitors for energy storage is an attractive approach considering their ability to deliver high levels of electrical power, unlimited charge/discharge cycles, green environmental protection and long operating lifetimes. Despite the satisfactory power density, supercapacitors are yet to match the energy densities of batteries and fuel cells, reducing the competitiveness as a revolutionary energy storage device. Therefore, the biggest challenge for supercapacitors is the trade-off between energy density and power density. This presents an opportunity to enhance the electrochemical capacitance and mechanical stability of an electrode. Previous attempts to get around the problem include developing porous nanostructured electrodes with extremely large effective areas. One of the emerging high-power supercapacitor electrode materials is molybdenum disulfide (MoS2), a member of the transition-metal dichalcogenides (TMDs). Its higher intrinsic fast ionic conductivity and higher theoretical capacity have attracted a lot of attention, particularly in supercapacitors. In addition to double-layer capacitance, diffusion of the ions into the MoS2 at slow scan rates gives rise to Faradaic capacitance. Analogous to Ru in RuO2, the Mo center atom displays a range of oxidation states from +2 to +6. This plays an important role in enhancing charge storage capabilities. However, the electronic conductivity of MoS2 is still lower compared to graphite, and the specific capacitance of MoS2 is still very limited when used alone for energy storage applications. As evident in several literature reports, there is a need to improve the capacitance of MoS2 with conductive materials such as carbon nanotubes (CNT), polyaniline (PANI), polypyrrole (PPy), and reduced graphene (r-GO). Carbon nanospheres (CNS) have, in the past, improved the conductivity of cathode material in Li-ion batteries, owing to their appealing electrical properties, chemical stability and high surface area. The main objective of this dissertation research is to develop nanocomposite materials based on molybdenum sulphide with carbon nanospheres for pseudocapacitors with simultaneously high power density and energy density at low production cost. The research was carried out in two phases, namely, (i) Symmetric pseudocapacitors based on molybdenum disulfide (MoS2)-modified carbon nanospheres: Correlating physico-chemistry and synergistic interaction on energy storage and (ii) The effects of morphology re-arrangements on the pseudocapacitive properties of mesoporous molybdenum disulfide (MoS2) nanoflakes. The physico-chemical properties of the MoS2 layered materials have been interrogated using the surface area analysis (BET), scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), Raman, fourier-transform infrared (FTIR) spectroscopy, and advanced electrochemistry including cyclic voltammetry (CV), galvanostatic cycling with potential limitation (GCPL), repetitive electrochemical cycling tests, and electrochemical impedance spectroscopy (EIS). In the first phase, Molybdenum disulfide-modified carbon nanospheres (MoS2/CNS) with two different morphologies (spherical and flower-like) have been synthesized using hydrothermal techniques and investigated as symmetric pseudocapacitors in aqueous electrolyte. The two different MoS2/CNS layered materials exhibit unique differences in morphology, surface areas, and structural parameters, which have been correlated with their electrochemical capacitive properties. The flower-like morphology (f-MoS2/CNS) shows lattice expansion (XRD), large surface area (BET analysis), and small-sized nanostructures (corroborated by the larger FWHM of the Raman and XRD data). As a contrast to the f-MoS2/CNS, the spherical morphology (s-MoS2/CNS) shows lattice contraction, small surface area with relatively large-sized nanostructures. The presence of CNS on the MoS2 structure leads to slight softening of the characteristic Raman bands (E12g and A1g modes) with larger FWHM. The MoS2 and its CNS-based composites have been tested in symmetric electrochemical capacitors in aqueous 1 M Na2SO4 solution. CNS improves the conductivity of the MoS2 and synergistically enhanced the electrochemical capacitive properties of the materials, especially the f-MoS2/CNS-based symmetric cells (most notably, in terms of capacitance retention). The maximum specific capacitance for f-MoS2/CNS-based pseudocapacitor show a maximum capacitance of 231 F g-1 with high energy density 26 Wh kg-1 and power density 6443 W kg-1. For the s-MoS2/CNS-based pseudocapcitor, the equivalent values are 108 F g-1, 7.4 Wh kg-1 and 3700 W kg-1. The high-performance of the f-MoS2/CNS is consistent with its physico-chemical properties as determined by the spectroscopic and microscopic data. In the second phase, Mesoporous molybdenum disulfide (MoS2) with different morphologies has been prepared via a hydrothermal method using different solvents, water or water/acetone mixtures. The MoS2 obtained with water alone gave graphene-like nanoflakes (g-MoS2) while the other with water/acetone (1:1 ratio) gave a hollow-like morphology (h-MoS2). Both materials are modified with carbon nanospheres as conductive materials and investigated as symmetric pseudocapacitors in aqueous electrolyte (1 M Na2SO4 solution). Interestingly, a simple change of synthesis solvents confers on the MoS2 materials different morphologies, surface areas, and structural parameters, correlated by electrochemical capacitive properties. The g-MoS2 exhibits higher surface area, higher capacitance parameters (specific capacitance of 183 F g-1, maximum energy density of 9.2 Wh kg-1 and power density of 2.9 kW kg-1) but less stable electrochemical cycling compared to the h-MoS2. These findings have opened doors for further exploration of the synergistic effects between MoS2 graphene-like sheets and CNS for energy storage.MT201

Energy challenges for ICT

The energy consumption from the expanding use of information and communications technology (ICT) is unsustainable with present drivers, and it will impact heavily on the future climate change. However, ICT devices have the potential to contribute signi - cantly to the reduction of CO2 emission and enhance resource e ciency in other sectors, e.g., transportation (through intelligent transportation and advanced driver assistance systems and self-driving vehicles), heating (through smart building control), and manu- facturing (through digital automation based on smart autonomous sensors). To address the energy sustainability of ICT and capture the full potential of ICT in resource e - ciency, a multidisciplinary ICT-energy community needs to be brought together cover- ing devices, microarchitectures, ultra large-scale integration (ULSI), high-performance computing (HPC), energy harvesting, energy storage, system design, embedded sys- tems, e cient electronics, static analysis, and computation. In this chapter, we introduce challenges and opportunities in this emerging eld and a common framework to strive towards energy-sustainable ICT

Uudsete süsinikmaterjalide süntees ja karakteriseerimine suure võimusega superkondensaatorite rakendusteks

Väitekirja elektrooniline versioon ei sisalda publikatsiooneViimastel aastatel on üsna kiiresti kasvanud nõudlus mitmekülgsete energiasalvestussüsteemide järele. Mõnedes piirkondades on pidevalt suurenev energiatarbimine ja selle mõju keskkonnale on tekitanud vajaduse uute suure võimsuse- ja energiatihedusega energiasalvestite järele. Superkondensaatorid on pälvinud palju tähelepanu, kuna neil on suur erimahtuvus, pikk tööiga, suur võimsustihedus ja väga madalad hoolduskulud. Superkondensaatoreid saab kombineerida koos kõrge energiatihedusega patareide ja kütuseelementidega erinevates rakendustes, kus on oluline samaaegselt nii suur energia kui ka võimsustihedus. Superkondensaatorites salvestatava kui ka sealt vabaneva energia väärtused sõltuvad olulisel määral selle elektrilisest mahtuvusest, süsteemi takistusest ja maksimaalsest rakupotentsiaalist, mis kõik sõltuvad kasutatavate elektroodide materjalide poorsusest ja elektrolüüdi omadustest. Üks enimkasutatud elektroodimaterjale superkondensaatorites on erinevad poorsed süsinikud ja nende hulgas ka karbiidist saadud süsinikud, millede korral on võimalik pooride suurust väga kontrollitult varieerida ning läbi selle suurendada süsteemis salvestatava energia hulka. Teiseks oluliseks energia salvestamist piiravaks teguriks superkondensaatorites on kasutatavate elektrolüütide mõõdukas tööpotentsiaal. Superkondensaatori suurepärase jõudluse saavutamiseks on seega oluline optimeerida nii elektroodimaterjali mikro- ja mesopoorsust ja selle sobivust kasutatava elektrolüüdiga kui ka optimeerida kasutatava elektrolüüdi korral selle maksimaalset rakendatavat rakupotentsiaali. Antud doktoritöös kasutati mikro- ja mesopoorsete elektroodimaterjalide valmistamiseks sool-geel meetodit, mis annab esialgsele karbiidile täiendava mesopoorsuse, mis jääb alles ka karbiidset päritolu süsinikmaterjali ja mida ei eksisteeri kommertsiaalsest karbiidist süsteesitud süsinikus. Teiseks töötati välja ″operando″ aktiveerimise ja passiveerimise meetod elektroodide maksimaalse rakendatava rakupotsntsiaali suurendamiseks, et suurendada süsteemi energiatihedust.In recent years, the demand for versatile energy storage systems has risen quite fast. The environmental impact of energy consumption for some regions has additionally increased the necessity for new energy storage devices with high power and energy densities. Supercapacitors have gained much attention because they have high specific capacitance, long cycle life, high power density, and very low maintenance costs. Supercapacitors complement batteries and fuel cells in applications where high power is important. The energy storage and power delivery characteristics of supercapacitors are largely determined by the electrical capacitance, system resistance, and maximum cell potential which are all dependent on the electrode materials porosity and electrolyte properties used. One of the most used electrode materials in supercapacitors are different carbide derived carbons, which have the possibility to fine-tune the pore size. One limiting factor in achieving high power density is the moderate working cell potential of different electrolytes that are used in supercapacitors. To achieve excellent performance of a supercapacitor it is important to optimize the electrode’s micro-mesoporosity and for the used electrolyte, it is important that it has a high electrochemical window and that the electrolyte ions suit the selected electrode material. In this thesis, firstly, a sol-gel method was used for the preparation of well developed micro- and mesoporous electrodes, which gives additional mesoporosity to the initial carbide material. This results also in the derived carbon material, unlike when the commercially synthesized titanium carbide is used. Secondly, the operando activation and passivation method was developed for future enlargement of the ideal polarizability region of electrodes, to achieve higher energy densities.https://www.ester.ee/record=b5487650https://www.ester.ee/record=b548765

Nanoengineered Materials for Energy Conversion & Storage Applications: A Density Functional Theory Study

The conventional approach for the development of novel materials has become long relative to the desired product development cycle. Thus, the sluggish pace of the development of materials within the conventional approach hinders the rapid transformation of the scientific outcomes into useful technological products. To this end, the field of hierarchical materials informatics evolved to bridge this gap. In this field, the multiscale material internal structure is considered the starting point and the core of this approach. This being said, the density functional theory (DFT) was used to generate useful materials data for the advancement of the hierarchical materials data-bases towards the novel efficient data-driven materials design approach. In this study, the DFT was employed to tackle energy materials arena as the global community is heading towards the renewable energies paradigm to secure the pillars of sustainability. Photoelectrochemical (PEC) water splitting proved to be one of the most trailblazing technologies serving this dazzling aspiration. Development of efficient photoelectrodes through defect engineering of wide-bandgap metal oxides has been the prime focus of materials scientists for decades. However, tuning the properties of m-ZrO2 was scarcely addressed in the context of photoelectrochemical (PEC) water splitting. In addition, the effect of carbon defects in wide-bandgap metal oxides for PEC applications raised numerous controversies and still elusive. To this end, herein, the effect of various carbon defects in mZrO2 for PEC applications was investigated using the density functional theory to probe the thermodynamic, electronic, and optical properties of the defective structures. The defect formation energies revealed that elevating the temperature promotes and facilitates the formation of carbon defects. Moreover, the binding energies confirmed the stability of all studied complex carbon defects. Furthermore, the band edge positions against the redox potentials of water species exemplified that all the studied defective structures can serve as photoanodes. Additionally, CO3c (carbon atom substituted O3c site) was the only defective structure that exhibited slight straddling of the redox potentials of water species. Importantly, all the defective structures enhanced the light absorption to different extents. Also, it is reported iii that CO3cVO3c (carbon atom substituted O3c associated with O3c vacancy) defective m-ZrO2 enjoyed low direct bandgap (1.9 eV), low defect formation energy, low exciton binding energy, high mobility of charge carriers, fast charge transfer, and low recombination rate. Concurrently, its optical properties were excellent in terms of high absorption, low reflectivity and improved static dielectric constant. Hence, the study recommends CO3cVO3c defective m-ZrO2 as the leading candidate defective structure to serve as a photoanode for PEC applications. Also, DFT was used to investigate the performance of energy storage electrodes. The DFT proved to be a reliable tool for investigating the quantum capacitance performance of the EDL supercapacitor electrodes. DFT was used to give insights on the capacitance performance of graphene, graphite, carbon nanotubes (CNTs), and N-doped graphene. The results revealed that the quantum capacitance of the CNTs was very high in both positive and negative potential windows and that the N-doping greatly enhanced the capacitance performance of the pristine graphene