| 1. |
- Calcagno, Giulio, 1990, et al.
(författare)
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Effect of Nitrogen Doping on the Performance of Mesoporous CMK-8 Carbon Anodes for Li-Ion Batteries
- 2020
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 13:19
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Tidskriftsartikel (refereegranskat)abstract
- Designing carbonaceous materials with heightened attention to the structural properties such as porosity, and to the functionalization of the surface, is a growing topic in the lithium-ion batteries (LIBs) field. Using a mesoporous silica KIT-6 hard template, mesoporous carbons belonging to the OMCs (ordered mesoporous carbons) family, namely 3D cubic CMK-8 and N-CMK-8 were synthesized and thoroughly structurally characterized. XPS analysis confirmed the successful introduction of nitrogen, highlighting the nature of the different nitrogen atoms incorporated in the structure. The work aims at evaluating the electrochemical performance of N-doped ordered mesoporous carbons as an anode in LIBs, underlining the effect of the nitrogen functionalization. The N-CMK-8 electrode reveals higher reversible capacity, better cycling stability, and rate capability, as compared to the CMK-8 electrode. Coupling the 3D channel network with the functional N-doping increased the reversible capacity to similar to 1000 mAh center dot g(-1) for the N-CMK-8 from similar to 450 mAh center dot g(-1) for the undoped CMK-8 electrode. A full Li-ion cell was built using N-CMK-8 as an anode, commercial LiFePO4, a cathode, and LP30 commercial electrolyte, showing stable performance for 100 cycles. The combination of nitrogen functionalization and ordered porosity is promising for the development of high performing functional anodes.
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| 2. |
- Calcagno, Giulio, 1990, et al.
(författare)
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Fast charging negative electrodes based on anatase titanium dioxide beads for highly stable Li-ion capacitors
- 2020
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Ingår i: Materials Today Energy. - : Elsevier BV. - 2468-6069. ; 16
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Tidskriftsartikel (refereegranskat)abstract
- Hybrid energy storage systems aim to achieve both high power and energy densities by combining supercapacitor-type and battery-type electrodes in tandem. The challenge is to find sustainable materials as fast charging negative electrodes, which are characterized by high capacity retention. In this study, mesoporous anatase beads are synthetized with tailored morphology to exploit fast surface redox reactions. The TiO2-based electrodes are properly paired with a commercial activated carbon cathode to form a Li-ion capacitor. The titania electrode exhibits high capacity and rate performance. The device shows extremely stable performance with an energy density of 27 mWh g-1 at a specific current of 2.5 A g−1 for 10,000 cycles. The remarkable stability is associated with a gradual shift of the potential during cycling as result of the formation of cubic LiTiO2 on the surface of the beads. This phenomenon renews the interest in using TiO2 as negative electrode for Li-ion capacitors.
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| 3. |
- Calcagno, Giulio, 1990
(författare)
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Mesoporous Materials for Fast Charging Electrochemical Energy Storage
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High performing electrochemical energy storage (EES) devices are needed to cope with the increasing energy requirements of modern society. Electrode materials must store lots of energy, charge/discharge fast and be environmentally friendly. The present thesis discusses the advantages of using nanostructured porous materials as electrodes for fast-charging energy storage. High specific surface areas and short diffusion paths make this class of materials competitive for future EES applications. Structural, morphological and electrochemical characterizations were used to study the materials and their charge/discharge behaviours on both a fundamental and device level. Mesoporous titanium dioxide of different polymorphs can reversibly insert Li+ ions inside its structure. Ordered amorphous mesoporous titanium dioxide, produced by low temperature spray deposition, showed a quasi-linear voltage - capacity profile in organic electrolytes, suggesting a pseudocapacitive behaviour of insertion type. A high initial capacity loss is associated with the irreversible formation of lithium rich phases at the surface of the material. On the other hand, mesoporous anatase beads, produced via a solvothermal approach, were characterized by extended plateaus in the voltage profile, a typical feature for a faradaic insertion mechanism. However, the anatase beads electrodes also showed high pseudocapacitive contributions and delivered higher capacities and rate performance compared with the mesoporous amorphous titanium oxide material. By doping the mesoporous beads with different niobium concentrations, the semiconducting anatase acquired a metallic-like conductivity. High concentration of doping negatively affected the lithium insertion process, while a low level of niobium doping was beneficial for improving the rate performance of mesoporous anatase beads electrodes. The anatase material showed initial irreversible capacities in organic electrolytes based on carbonates. Limiting the potential window was found to be a suitable strategy to avoid parasitic reactions, although this limits the amount of storable energy. Moreover, by using an ionic liquid as electrolyte, the electrode/electrolyte interface can be stabilized, limiting the capacity fading. Finally, the mesoporous anatase beads were studied in a hybrid configuration against a porous carbon electrode, delivering very stable performance over 10000 cycles. Ordered mesoporous carbons of the CMK-8 type also showed interesting performance for different EES systems. When doped with nitrogen, CMK-8 carbons were able to store high amounts of lithium ions, both at low and fast rates of charging. In addition, CMK-8 carbons were used in hybrid supercapacitors as conductive electrodes to support surface redox reactions of active molecules added in water-based electrolytes. A pentyl viologen/bromide redox-active pair was studied on CMK-8 carbon electrodes at different operating voltages. By detailed studies of the electrochemistry of the system, high and stable energy and power densities were achieved.
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| 4. |
- Calcagno, Giulio, 1990
(författare)
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Mesoporous Titania for High Rate Electrochemical Energy Storage
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mesoporous titanium oxides are increasingly attracting interest as potential candidates for fast electrochemical energy storage. In this thesis, mesoporous titania of different polymorphs have been evaluated in relation to their ability to reversibly store Li+ ions inside their structure. Mesoporous anatase beads with high crystallinity and specific morphology show high electrochemical capacity and high rate performance. The materials store charge through Li+ ion insertion of both faradaic and extrinsic pseudocapacitive nature. Moreover, the discharge capacity retention after 150 cycles is >95%. On the other hand, ordered mesoporous titania, prepared via low-temperature spray deposition and mainly amorphous, shows a linear correlation between voltage and capacity, typical of an intrinsic pseudocapacitive material of insertion type. The material exhibits exceptionally high electrochemical capacity of 680 mAh g-1 during the first cycle, which, however, rapidly decreases over the following cycles. A combination of electrochemical and structural characterization techniques is used to study the charge/discharge behavior of the material and the origin of the irreversible capacity. X-ray absorption spectroscopy and energy-filtered TEM are carried out to analyse pristine and cycled samples in charged and discharged state. The results suggest that the irreversible loss in the capacity is due to the formation of electrochemically inactive phases mainly located at the surface of the material. Additionally, electrodes based on mesoporous anatase beads are paired with a commercial activated carbon electrode that presents a broad distribution of mesopores and very high surface area to design a hybrid asymmetric supercapacitor. The device shows extraordinary stable performance with energy densities of 27 Wh kg-1 at the relatively fast discharge current of 2.5 A g-1 for 10 000 cycles and high power densities during fast cycling.
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| 5. |
- Calcagno, Giulio, 1990, et al.
(författare)
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Understanding the Operating Mechanism of Aqueous Pentyl Viologen/Bromide Redox-Enhanced Electrochemical Capacitors with Ordered Mesoporous Carbon Electrodes
- 2021
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Ingår i: ACS Applied Materials & Interfaces. - : American Chemical Society (ACS). - 1944-8252 .- 1944-8244. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- Compared to traditional electric double-layer capacitors, redox-enhanced electrochemical capacitors (redox-ECs) show increased energy density and steadier power output thanks to the use of redox-active electrolytes. The aim of this study is to understand the electrochemical mechanisms of the aqueous pentyl viologen/bromide dual redox system at the interface of an ordered mesoporous carbon (CMK-8) and improve the device performance. Cells with CMK-8 carbon electrodes were investigated in several configurations using different charging rates and potential windows. The pentyl viologen electrochemistry shows a mixed behavior between solution-based diffusion and adsorption phenomena, with the reversible formation of an adsorbed layer. The extension of the voltage window allows for full reduction of the viologen molecules during charge and a consequent increase in the specific discharge energy delivered by the cell. Investigation of the mechanism indicates that a 1.5 V charging voltage with a 0.5 A g-1 charging rate and fast discharge rate produces the best overall performance.
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| 6. |
- Cavallo, Carmen, 1986, et al.
(författare)
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Effect of the Niobium Doping Concentration on the Charge Storage Mechanism of Mesoporous Anatase Beads as an Anode for High-Rate Li-Ion Batteries
- 2021
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Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 4:1, s. 215-225
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Tidskriftsartikel (refereegranskat)abstract
- A promising strategy to improve the rate performance of Li-ion batteries is to enhance and facilitate the insertion of Li ions into nanostructured oxides like TiO2. In this work, we present a systematic study of pentavalent-doped anatase TiO2 materials for third-generation high-rate Li-ion batteries. Mesoporous niobium-doped anatase beads (Nb-doped TiO2) with different Nb5+ doping (n-type) concentrations (0.1, 1.0, and 10% at.) were synthesized via an improved template approach followed by hydrothermal treatment. The formation of intrinsic n-type defects and oxygen vacancies under RT conditions gives rise to a metallic-type conduction due to a shift of the Fermi energy level. The increase in the metallic character, confirmed by electrochemical impedance spectroscopy, enhances the performance of the anatase bead electrodes in terms of rate capability and provides higher capacities both at low and fast charging rates. The experimental data were supported by density functional theory (DFT) calculations showing how a different n-type doping can be correlated to the same electrochemical effect on the final device. The Nb-doped TiO2 electrode materials exhibit an improved cycling stability at all the doping concentrations by overcoming the capacity fade shown in the case of pure TiO2 beads. The 0.1% Nb-doped TiO2-based electrodes exhibit the highest reversible capacities of 180 mAh g-1 at 1C (330 mA g-1) after 500 cycles and 110 mAh g-1 at 10C (3300 mA g-1) after 1000 cycles. Our experimental and computational results highlight the possibility of using n-type doped TiO2 materials as anodes in high-rate Li-ion batteries.
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| 7. |
- Lindberg, Simon, 1985, et al.
(författare)
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Electrochemical Behaviour of Nb-Doped Anatase TiO2 Microbeads in an Ionic Liquid Electrolyte
- 2020
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Ingår i: Batteries and Supercaps. - : Wiley. - 2566-6223. ; 3:11, s. 1233-1238
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Tidskriftsartikel (refereegranskat)abstract
- TiO(2)is a promising material for high-power battery and supercapacitor applications. However, in general TiO(2)suffers from an initial irreversible capacity that limits its use in different applications. A combination of a microbead morphology, Nb-doping, and the use of an ionic liquid electrolyte is shown to significantly decrease the irreversible capacity loss. A change in the electrochemical response in the first cycles indicates formation of a solid-electrolyte interphase (SEI) or a modification of the structure of the surface layer of the TiO2/Nb microbeads, which apparently stabilises the performance. The change in the response is manifested in an increased charge transfer resistance and the presence of two charge transfer contributions. During prolonged cycling the TiO2/Nb electrode shows an excellent stability over 5000 cycles. Ex situ analysis after cycling shows that the overall microbead morphology is intact and that there are no changes in the crystal structure. However, a decrease in the intensity of the XRD pattern can point to a decrease in size of the nanocrystals building up the microbeads or the formation of amorphous phases.
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| 8. |
- Örn Simonarson, Gunnar, 1986, et al.
(författare)
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Electrochemical and structural characterization of lithiation in spray deposited ordered mesoporous titania as an anode for Li ion batteries
- 2020
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 10:34, s. 20279-20287
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Tidskriftsartikel (refereegranskat)abstract
- Ordered mesoporous titania, preparedvialow-temperature spray deposition, was examined as an anode material for lithium ion batteries. The material exhibits an exceptionally high electrochemical capacity of 680 mA h g-1during the first discharge, which rapidly decreases over the following cycles. The capacity stabilizes at around 170 mA h g-1after 50 cycles and the material delivers 83 mA h g-1at high charge/discharge rates (10C). A combination of electrochemical and structural characterization techniques were used to study the charge/discharge behavior of the material and the origin of the irreversible capacity. To determine the effect of cycling on the structure of the material, X-ray absorption spectroscopy (XAS) and energy filtered TEM were carried out on pristine and cycled samples in intercalated and deintercalated states. Titanium K-edge XAS measurements showed that intercalated lithium affects the NEXAFS region. By comparing peak intensity ratios, we propose a method to quantify the amount of lithium inserted into the titania structure and to differentiate between lithium bound in close proximity to titanium, and lithium bound further away from titanium. Additionally, we suggest that the irreversible loss in capacity is due to the formation of phases that are stable, and thereby electrochemically inactive, over the electrochemical cycling conditions applied.
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