| 1. |
- Ahmed, Mukhtiar, et al.
(författare)
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Aromatic Heterocyclic Anion Based Ionic Liquids and Electrolytes
- 2023
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 25:4, s. 3502-3512
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Tidskriftsartikel (refereegranskat)abstract
- Five new ionic materials comprising fluorine-free aromatic heterocyclic anions based on pyridine and pyrazine combined with a common n-tetrabutylphosphonium cation, (P4444)+, result in two room temperature ionic liquids (RTILs), one semi-solid, and two organic ionic plastic crystals (OIPCs) with melting points >20 °C. The OIPCs showed a plastic crystalline phase, multiple solid–solid transitions, and plastic crystalline and melt phases. For both the neat RTILs and the Li+ conducting electrolytes, the nature and strength of the ion–ion interactions mainly depend on the position of the nitrogen atom with respect to the carboxylate group in the anions. Furthermore, for the RTILs the ionic conductivity is effected by the electronic structure and flexibility of the ions and the anions diffuse faster than the (P4444)+ cation, but are slowed down in the electrolytes due to the strong electrostatic interactions between the carboxylate group of the anions and the Li+, as shown both experimentally and computationally. Overall, this study describes the effect of structural tuning of aromatic anions on the ion–ion interactions and introduces new ionic materials with promising properties to be used as solid and liquid electrolytes in energy storage devices.
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| 2. |
- Ahmed, Mukhtiar
(författare)
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Fluorine-Free Ionic Liquids and Electrolytes : From Synthesis to Energy Storage Applications
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since their introduction by Sony in 1990, lithium-ion batteries (LIBs) have acquired a sizable market share. They have the best energy densities, a high open circuit voltage, a low self-discharge rate, no memory effect, and a slow loss of charge when not in use. These properties make them the most popular rechargeable batteries for portable gadgets, electric vehicles and aerospace applications. They do, however, pose major safety issues since the conventional electrolytes are made of fluorinated salts dissolved in volatile organic solvents, the former being meta-stable at ambient temperature and the latter being flammable with a high vapour pressure. Thus, there is an urge to develop thermally and electrochemically stable non-fluorinated electrolytes to improve the safety and performance of batteries. Electrolytes based on ionic liquids (ILs) offer a range of advantages over traditional electrolytes including low volatility and high thermal and electrochemical stabilities, and can additionally be made fluorine-free and task-specific. In addition, the transport properties of ILs can be controlled by structural design of chemical functionalities to reduce the ionic interactions and enhance the ion mobilities.This thesis is focussed on the development of new fluorine-free ILs and electrolytes for safer energy storage applications. An overview of synthesis, physicochemical and electrochemical characterizations of six different families of ILs and their structurally analogous electrolytes based on the aromatic heterocyclic rings, oligoether based aromatic and aliphatic carboxylates, oligoether phosphates and aromatic sulfonyl anions coupled with n- tetrabutylphosphonium-, imidazolium-, pyrrolidinium-based and alkali metal cations is presented. The structures and purity of the new anions, their intermediate products and the ILs are characterized by using multinuclear NMR, FTIR and mass spectrometry. These studies are further complemented by using NMR diffusometry to investigate the relative anion and anion mobilities and understand the possible interaction mechanisms between the oppositely charged ions within the ILs and the electrolytes, and especially, the influence of Li+ addition in the IL-based electrolytes. Among the synthesized ILs, the sulfonyl-based ILs revealed highest thermal stabilities, aromatic oligoether-based ILs showed the best electrochemical stabilities and aromatic sulfonyl -based ILs exhibited highest ionic conductivities. Some of the synthesized salts displayed promising performance as electrolytes in energy storage devices.
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| 3. |
- Ahmed, Mukhtiar, et al.
(författare)
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Ionic Liquids and Electrolytes with Flexible Aromatic Anions
- 2023
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Ingår i: Chemistry - A European Journal. - : John Wiley & Sons. - 0947-6539 .- 1521-3765. ; 29:41
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Tidskriftsartikel (refereegranskat)abstract
- Five new n-tetrabutylphosphonium (P4444)+ cation based ionic liquids (ILs) with oligoether substituted aromatic carboxylate anions have been synthesized. The nature and position of the oligoether chain affect thermal stability (up to 330 ºC), phase behaviour (Tg < -55 ºC) and ion transport. Furthermore, with the aim of application in lithium batteries, electrolytes were created for two of the ILs by 10 mol% doping using the corresponding Li-salts. This affects the ion diffusion negatively, from being higher and equal for cations and anions to lower for all ions and unequal. This is due to the stronger ionic interactions and formation of aggregates, primarily between the Li+ ions and the carboxylate group of the anions. Electrochemically, the electrolytes have electrochemical stability windows up to 3.5 V, giving some promise for battery application.
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| 4. |
- Bhowmick, Sourav, et al.
(författare)
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Ambient temperature liquid salt electrolytes
- 2023
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1364-548X .- 1359-7345. ; 59:18, s. 2620-2623
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Tidskriftsartikel (refereegranskat)abstract
- Alkali metal salts usually have high melting points due to strong electrostatic interactions and solvents are needed to create ambient temperature liquid electrolytes. Here, we report on six phosphate-anion-based alkali metal salts, Li/Na/K, all of which are liquids at room temperature, with glass transition temperatures ranging from −61 to −29 °C, and are thermally stable up to at least 225 °C. While the focus herein is on various physico-chemical properties, these salts also exhibit high anodic stabilities, up to 6 V vs. M/M+ (M = Li/Na/K), and deliver some battery performance - at elevated temperatures as there are severe viscosity limitations at room-temperature. While the battery performance arguably is sub-par, solvent-free electrolytes based on alkali metal salts such as these should pave the way for conceptually different Li/Na/K-batteries, either by refined anion design or by using several salts to create eutectic mixtures.
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| 5. |
- Bhowmick, Sourav, et al.
(författare)
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Structurally Flexible Pyrrolidinium- and Morpholinium-based Ionic Liquid Electrolytes
- 2023
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 25:29, s. 19815-19823
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Tidskriftsartikel (refereegranskat)abstract
- Ion transport measures and details as well as physico-chemical and electrochemical properties are presented for a small set of structurally flexible pyrrolidinium (Pyrr) and morpholinium (Morph) cation-based ionic liquids (ILs), all with oligoether phosphate-based anions. All have high thermal stabilities, low glass transition temperatures, and wide electrochemical stability windows, but rather moderate ionic conductivities, whereas both the anions and the cations of the Pyrr-based ILs diffuse faster than those of the Morph-based ILs. Overall the former ILs have significantly more promise as high-temperature supercapacitor electrolytes, rendering a specific capacitance of 164 F g−1 at 1 mV s−1, a power density of 241 W kg−1 and a specific energy density of 30 Wh kg−1 at 90 °C in a symmetric graphite supercapacitor.
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| 6. |
- Su, Yiqun, et al.
(författare)
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Effect of Electrode Surface Chemistry on Ion Structuring of Imidazolium Ionic Liquids
- 2023
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 39:24, s. 8463-8474
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Tidskriftsartikel (refereegranskat)abstract
- Surface chemistry plays a critical role in the ion structuring of ionic liquids (ILs) at the interfaces of electrodes and controls the overall energy storage performance of the system. Herein, we functionalized the gold (Au) colloid probe of an atomic force microscope with −COOH and −NH2 groups to explore the effect of different surface chemical properties on the ion structuring of an IL. Aided by colloid-probe atomic force microscopy (AFM), the ion structuring of an imidazolium IL, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6], abbreviated as BP hereafter), on the Au electrode surface and the ion response to the change in the surface chemistry are investigated. AFM morphologies, contact angles, and approaching force–distance curves of the BP IL on the functionalized Au surfaces exhibited that the IL forms a more obvious layering structure on the −COOH-terminated Au surface (Au–COOH), while it forms heterogeneous and aggregating droplets on the −NH2 surface (Au–NH2). The formed uniform and aggregation-free ion layers in the vicinity of the Au–COOH surface are due to the π–π+ stacking interaction between the delocalized π+ electrons from the imidazolium ring in the IL [BMIM]+ cation and the localized π electrons from the sp2 carbon on the −COOH group. The in situ observation of nano-friction and torsional resonance frequency at the IL–electrode interfaces further demonstrated the ion structuring of the IL at Au–COOH, which results in a more sensitive electrochemical response associated with a faster capacitive process.
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| 7. |
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| 8. |
- Tatrari, Gaurav, et al.
(författare)
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Coconut-husk Derived Graphene for Supercapacitor Applications: Comparative Analysis of Polymer Gel and Aqueous Electrolytes
- 2023
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Ingår i: Materials Advances. - : Royal Society of Chemistry. - 2633-5409. ; 4:15, s. 3310-3322
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Tidskriftsartikel (refereegranskat)abstract
- Herein, we propose the synthesis of reduced graphene oxide (rGO) using coconut husk as a green and natural resource for supercapacitor (SCs) applications. The electrochemical performance of graphene sheets is studied over two different electrolytes, i.e., sulfuric acid (1M) and polymer-gel electrolyte. The polyvinyl alcohol, potassium iodide, and sulfuric acid-base polymer gel electrolyte are developed using a simple solvolysis approach. The developed polymer gel electrolyte membrane shows the fine pore structure, providing appropriate channels for the ionic transportation and charge transfer within materials, alternatively enhancing the overall performance of the device in comparison to commercial polyvinyl alcohol-base membranes and polyvinyl alcohol and acid-base membranes. This is accredited to lower resistance, higher ionic conductivity of the developed materials, and electrolytes within the supercapacitor device. The electrode with 1M H2SO4 exhibits outstanding performance with a decent equivalent resistance of 4.75 Ωcm-2 and specific capacitance (Cs) of 650 Fg-1 at 1 mVs-1. Conversely, the polymer gel-containing device shows an equivalent sheet resistance (ESR), of 8 Ωcm-2 and a high specific capacitance of 500 Fg-1 at 1 mVs-1. In 1M H2SO4, the device showed 88 % cycle stability after 4400 cycles with a coulombic efficiency of 67.56 % and an energy density of 50.00 Whkg-1 with a very high-power density of 1000.00 Wkg-1 at 1 Ag-1. The polymer-gel electrolyte-containing device shows 99 % cyclic stability after 4400 cycles with a coulombic efficiency of 70.27 % and an energy density of 36.11 Whkg-1 with a power density of 996.92 Wkg-1 at 1 Ag-1.
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| 9. |
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| 10. |
- Xu, Yanqi
(författare)
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Fluorine-Free Phosphorus-Based Ionic Materials and Electrolytes
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Due to the successful commercialization of lithium-ion batteries (LIBs), there is a growing interest in developing new battery materials with beneficial electrochemical properties. However, the uneven distribution of lithium resources and the low abundance of lithium in the earth crust are the main obstacles for further development and large-scale production of LIBs. Sodium-ion batteries (SIBs), an alternative that can partly meet the energy storage challenges, are getting attentions of researchers due to the wide availability and lower cost of sodium resources. Nevertheless, the conventional liquid electrolytes of either LIBs or SIBs composed of fluorinated salts dissolved in volatile organic solvents, posing serious safety issues due to the instability of the salts and flammability of the solvents. There is an urge to develop new fluorine-free electrolytes with improved physicochemical and electrochemical properties. In this context, the conventional fluorinated salts should be replaced with fluorine-free salts and the flammable solvents should be substituted with non-flammable solvents. There are a number of strategies to develop high-performant electrolytes including ambient-temperature ionic liquids (ILs), organic ionic plastic crystals (OIPCs) and highly concentrated electrolytes (HCEs) utilizing new salts and solvents.In this thesis, novel phosphorus-based ionic materials and electrolytes are introduced and their properties are thoroughly investigated. In the first part (Paper I), fluorine-free NaDEEP salt and TEOP solvent are employed to make “solvent-in-salt” (SIS) sodium electrolytes, also known as HCEs. Unexpectedly, the addition of TEOP solvent lead to an increase in the oxidation stability of the SIS electrolytes. In addition, an unusual ionic conductivity behavior is found – the ionic conductivities of Na electrolytes increase with increasing salt concentration. The “salt-rich” and “solvent-rich” phases formed within the electrolytes are investigated using multinuclear liquid-state NMR spectroscopy and NMR diffusometry. In the second part (Paper II), a series of orthoborate-based ionic materials, specifically OIPCs, containing phosphonium/ammonium cations are prepared to compare with the popular fluorine-free, bis(oxalato)borate (BOB) salts. The tetrabutyl phosphonium bis(glycolato)borate ([P4444][BGB]) OIPC displays much higher decomposition temperature than the structural analogous [P4444][BOB] IL. The crystal structures of LiBGB and NaBGB salts are resolved using single-crystal X-ray diffraction analysis. Unlike LiBOB, the BGB-based salts revealed excellent moisture stability over an extended time of up to 8-weeks air exposure. Multinuclear solid-state NMR spectroscopy indicates weaker cation-anion interactions in phosphonium-based salts than the ammonium-based ones. Finally, in the third part (Paper III), two-component and three-component eutectic electrolytes, composed of pyrrolidinium saccharin (PySc), lithium saccharin (LiSc) and/or [P4444][BGB] salt. The resulting mixtures showed significantly lower melting temperatures than the neat salts. The physicochemical and thermal properties of these salts are thoroughly investigated and discussed.
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