| 1. |
- Calcagno, Giulio, 1990, et al.
(author)
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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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In: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 13:19
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Journal article (peer-reviewed)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.
(author)
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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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In: Materials Today Energy. - : Elsevier BV. - 2468-6069. ; 16
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Journal article (peer-reviewed)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. |
- Cavallo, Carmen, 1986, et al.
(author)
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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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In: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 4:1, s. 215-225
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Journal article (peer-reviewed)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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| 4. |
- Fretz, Samuel Joseph, 1987, et al.
(author)
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Amine- and Amide-Functionalized Mesoporous Carbons: A Strategy for Improving Sulfur/Host Interactions in Li-S Batteries
- 2020
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In: Batteries and Supercaps. - : Wiley. - 2566-6223. ; 3:8, s. 757-765
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Journal article (peer-reviewed)abstract
- Lithium-sulfur (Li-S) batteries are of great interest due to their potentially high energy density, but the low electronic conductivity of both the sulfur (S-8) cathode active material and the final discharge product lithium sulfide (Li2S) require the use of a conductive host. Usually made of relatively hydrophobic carbon, such hosts are typically ill-suited to retain polar discharge products such as the intermediate lithium polysulfides (LiPs) and the final Li2S. Herein, we propose a route to increase the sulfur utilization by functionalizing the surface of ordered mesoporous carbon CMK3 with polar groups. These derivatized CMK3 materials are made using a simple two-step procedure of bromomethylation and subsequent nucleophilic substitution with amine or amide nucleophiles. We demonstrate that, compared to the unfunctionalized control, these modified CMK3 surfaces have considerably larger binding energies with LiPs and Li2S, which are proposed to aid the electrochemical conversion between S-8 and Li2S by keeping the LiPs species in close proximity to the carbon surface during Li-S battery cycling. As a result, the functionalized cathodes exhibit significantly improved specific capacities relative to their unmodified precursor.
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| 5. |
- Nitze, Florian, 1981, et al.
(author)
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A binder-free sulfur/reduced graphene oxide aerogel as high performance electrode materials for lithium sulfur batteries
- 2016
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322 .- 2045-2322. ; 6
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Journal article (peer-reviewed)abstract
- Societies' increasing need for energy storage makes it necessary to explore new concepts beyond the traditional lithium ion battery. A promising candidate is the lithium-sulfur technology with the potential to increase the energy density of the battery by a factor of 3-5. However, so far the many problems with the lithium-sulfur system have not been solved satisfactory. Here we report on a new approach utilizing a self-standing reduced graphene oxide based aerogel directly as electrodes, i.e. without further processing and without the addition of binder or conducting agents. We can thereby disrupt the common paradigm of "no battery without binder" and can pave the way to a lithium-sulfur battery with a high practical energy density. The aerogels are synthesized via a one-pot method and consist of more than 2/3 sulfur, contained inside a porous few-layered reduced graphene oxide matrix. By combining the graphene-based aerogel cathode with an electrolyte and a lithium metal anode, we demonstrate a lithium-sulfur cell with high areal capacity (more than 3 mAh/cm(2) after 75 cycles), excellent capacity retention over 200 cycles and good sulfur utilization. Based on this performance we estimate that the energy density of this concept-cell can significantly exceed the Department of Energy (DEO) 2020-target set for transport applications.
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| 6. |
- Nitze, Florian, 1981, et al.
(author)
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Sulfur-doped ordered mesoporous carbons: A stability-improving sulfur host for lithium-sulfur battery cathodes
- 2016
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In: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 317, s. 112-119
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Journal article (peer-reviewed)abstract
- We report on sulfur-functionalized ordered mesoporous carbons aimed for lithium-sulfur battery electrode applications with improved charge capacity retention. The carbons were obtained by a hard-template strategy using a mixture of furfuryl alcohol and furfuryl mercaptan. For the application as electrode material in lithium-sulfur batteries, the carbons were additionally loaded with sulfur following a traditional melt-diffusion approach. It was found that the sulfur interacts stronger with the sulfur-functionalized carbon matrix than with the non-functionalized material. Electrodes showed very high capacity in the second discharge-charge cycle amounting to approximately 1500, 1200 and 1400 mAh/g (sulfur) for carbon materials with no, medium and high degrees of sulfur functionalization, respectively. More importantly, the sulfur-functionalization of the carbon was found to increase the capacity retention after 50 discharge-charge cycles by 8 and 5% for the carbons with medium and high degrees of sulfur-functionalization, respectively, compared to carbon with no sulfur-functionalization. We attribute this significant improvement to the presence of covalently bound sulfur groups at the internal surface of the functionalized carbon providing efficient anchoring sites for catenation to the sulfur loaded into the pores of the carbons and provide experimental support for this in the form of results from cyclic voltammetry and X-ray photoelectron spectroscopy.
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| 7. |
- Nordström, Jonas, 1980, et al.
(author)
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Concentration- and pH-dependence of highly alkaline sodium silicate solutions
- 2011
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In: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 356:1, s. 37-45
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Journal article (peer-reviewed)abstract
- In this study two routes for the gelation of water glass have been investigated; the destabilization by a change in pH and by an increase in concentration through evaporation. Both methods produce optically transparent, highly viscous, homogeneous solutions. The structure and dynamics of the solutions along the two routes have been investigated with Dynamic Light Scattering, 29Si-Nuclear Magnetic Resonance spectroscopy, viscosity measurements and infrared spectroscopy. We find that the two routes are fundamentally different. Increasing the concentration of the sodium silicate system leaves the silica speciation apparently unchanged. Lowering the pH leads to condensation reactions, thus a change in the silica speciation.
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| 8. |
- Nordström, Jonas, 1980, et al.
(author)
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Silica/alkali ratio dependence of the microscopic structure of sodium silicate solutions
- 2013
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In: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 397, s. 9-17
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Journal article (peer-reviewed)abstract
- Alkaline sodium silicate solutions with SiO2:Na2O molar ratios in the range 4-10 are known to be colloidaily unstable manifested in phase separation or gelation. The mechanistic understanding of this instability is generally poor. To improve this situation the microscopic structure of a series of solutions with ratios in the range 3.3-8.9 has been characterised using small-angle X-ray scattering, Dynamic light scattering, Fourier transformed infrared spectroscopy, and Si-29 Nuclear magnetic resonance spectroscopy to cover the relevant length scales related to silica clusters, aggregates, and particles present. In the starting solution, with ratio 3.3, there are silica present in three fractions. The main part is present as small silica clusters with a radius of 0.7 nm. There are also a significant portion of monomers/small oligomeric silica species as well as a minute amount of larger colloidal silica particles. At a higher SiO2:Na2O ratio, above approximately 4, smaller spherical colloidal particles are formed due to condensation reactions. However, as a result of a too high ionic strength the suspension is not stable and the particles aggregate to fractal structures with a size that depends on ratio and ageing time. At the highest SiO2:Na2O ratio, fractals are not formed because of the lower ionic strength and the smaller colloidal particles are stable in the solution. By carefully adding small amounts of NaCl to the high ratio solution it is possible to induce gelation of the solution confirming the hypothesis that the instability region is due to too high electrolyte concentration for the silica species present under those conditions.
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