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7. Superior Wear-Resistance of Ti3C2Tx Multilayer Coatings

Author

Grützmacher, Philipp G., primary, Suarez, Sebastian, additional, Tolosa, Aura, additional, Gachot, Carsten, additional, Song, Guichen, additional, Wang, Bo, additional, Presser, Volker, additional, Mücklich, Frank, additional, Anasori, Babak, additional, and Rosenkranz, Andreas, additional

Published
2021
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21. Electrospun carbon hybrid fibers as binder-free electrodes for electrochemical energy storage

Author

Tolosa, Aura and Presser, Volker

Subjects
Electrospinning, ddc:540, ddc:660, ddc:530, ddc:620, Electrochemical energy storage
Abstract

There is a great need for the development and improvement of electrochemical energy storage devices for applications ranging from energy and power management to portable electronic devices. My work explores electrode materials for devices with higher energy storage capacity and rate handling, namely electrical double-layer capacitors, lithium-ion batteries, and sodium-ion batteries. To this end, I report the synthesis and properties of electrospun fiber mats composed of nanoporous carbon, transition metal oxide/carbon hybrid material, or silicon oxycarbide. Based on a comprehensive array of structural and chemical analysis and electrochemical benchmarking, this work evaluates the potential and drawbacks of electrospun materials as electrodes. Key findings demonstrate that electrospinning of molecular precursor is an attractive approach for the synthesis of carbon and hybrid fiber mats as free-standing electrodes. By following a one-pot synthesis approach, material properties such as phase composition, crystal structure, and phase distribution are well tuned to achieve the desired electrochemical properties. Compared to polymer-bound free-standing electrodes, the continuous fiber network yields a superior gravimetric electrochemical performance, related to the absence of additives and the continuous path for electron transport. However, the large interfiber space and low electrode density limit the usefulness of adopting electrospun fiber mats to size-sensitive applications Mobile Anwendungen und Strommanagement erfordern verstärkt die Entwicklung verbesserter elektrochemischer Energiespeicher. Diese Dissertation erforscht vor diesem Hintergrund elektrogesponnene Fasern als hochleistungsfähige Elektroden für elektrische Doppelschichtkondensatoren, Lithium-Ionen-Batterien und Natrium-Ionen- Batterien. Hierzu kommen Fasern aus nanoporösen Kohlenstoff, Kohlenstoff/Metalloxid- Hybridmaterialien oder Siliziumoxykarbid zum Einsatz. Diese werden umfangreicher Materialanalyse und elektrochemischer Charakterisierung unterzogen um die Grenzen und Chancen für den Einsatz als Elektroden aufzuzeigen. Meine Ergebnisse zeigen, dass Elektrospinnen eine vielversprechende Methode ist um nanoskalige Fasermatten zu erzeugen, die direkt ohne weitere Beaufschlagung mit Leitadditiv oder Polymerbinder als Elektroden für elektrochemische Energiespeicher verwendet werden können. Durch die dargestellte one-pot Synthese können wichtige Eigenschaften wie Phasenzusammensetzung, Kristallstruktur und Phasenverteilung gezielt auf die gewünschten elektrochemischen Eigenschaften hin optimiert werden. Im Vergleich zu polymergebundenen freistehenden Elektroden liefert das hochvernetzte Fasernetzwerk eine höhere gravimetrische Leistung. Der große freie Raum zwischen den einzelnen Fasern führt jedoch zu einer geringen Leistung bezogen auf das Elektrodenvolumen, wodurch die Verwendung von Fasermatten als Elektroden für platzsensitive elektrochemische Energiespeicher eingeschränkt wird.

Published
2019
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25. Continuous silicon oxycarbide fiber mats with tin nanoparticles as a high capacity anode for lithium-ion batteries

Author

Tolosa, Aura, Widmaier, Mathias, Kruener, Benjamin, Griffin, John M., Presser, Volker, Tolosa, Aura, Widmaier, Mathias, Kruener, Benjamin, Griffin, John M., and Presser, Volker

Abstract

Continuous fiber mats are attractive electrodes for lithium-ion batteries, because they allow operation at high charge/discharge rates in addition to being free of polymer binders and conductive additives. In this work, we synthesize and characterize continuous Sn/SiOC fibers (diameter ca. 0.95 mu m), as a Li-ion battery anode. Our synthesis employs electrospinning of a low-cost silicone resin, using tin acetate in a dual role both as a polymer crosslinker and as a tin precursor (6-22 mass%). The hybrid electrodes present very high initial reversible capacities (840-994 mA h g(-1)) at 35 mA g(-1), and retain 280310 mA h g(-1) at 350 mA g(-1). After 100 cycles at 70 mA g(-1), the hybrid fibers maintained 400-509 mA h g(-1). Adding low amounts of Sn is beneficial not just for the crosslinking of the polymer precursor, but also to decrease the presence of electrochemically inactive silicon carbide domains within the SiOC fibers. Also, the metallic tin clusters contribute to a higher Li+ insertion in the first cycles. However, high amounts of Sn decrease the electrochemical performance stability. In SiOC fibers synthesized at high temperatures (1200 degrees C), the C-free phase has a significant influence on the stability of the system, by compensating for the volume expansion from the alloying systems (Sn and SiO2), and improving the conductivity of the hybrid system. Therefore, a high amount of carbon and a high graphitization degree are crucial for a high conductivity and a stable electrochemical performance.

Published
2018

40. Influence of carbon substrate on the electrochemical performance of carbon/manganese oxide hybrids in aqueous and organic electrolytes

Author

Zeiger, Marco, primary, Fleischmann, Simon, additional, Krüner, Benjamin, additional, Tolosa, Aura, additional, Bechtel, Stephan, additional, Baltes, Mathias, additional, Schreiber, Anna, additional, Moroni, Riko, additional, Vierrath, Severin, additional, Thiele, Simon, additional, and Presser, Volker, additional

Published
2016
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44. Binder‐Free Hybrid Titanium–Niobium Oxide/Carbon Nanofiber Mats for Lithium‐Ion Battery Electrodes.

Author

Grobelsek, Ingrid, Lim, Eunho, Tolosa, Aura, Fleischmann, Simon, Presser, Volker, and Quade, Antje

Subjects
TITANIUM, NIOBIUM, CARBON nanofibers, LITHIUM-ion batteries, ELECTRODES, ENERGY storage, NANOSTRUCTURED materials
Abstract

Abstract: Free‐standing, binder‐free, titanium–niobium oxide/carbon hybrid nanofibers are prepared for Li‐ion battery applications. A one‐pot synthesis offers a significant reduction of processing steps and avoids the use of environmentally unfriendly binder materials, making the approach highly sustainable. Tetragonal Nb2O5/C and monoclinic Ti2Nb10O29/C hybrid nanofibers synthesized at 1000 °C displayed the highest electrochemical performance, with capacity values of 243 and 267 mAh g−1, respectively, normalized to the electrode mass. At 5 A g−1, the Nb2O5/C and Ti2Nb10O29/C hybrid fibers maintained 78 % and 53 % of the initial capacity, respectively. The higher rate performance and stability of tetragonal Nb2O5 compared to that of monoclinic Ti2Nb10O29 is related to the low energy barriers for Li+ transport in its crystal structure, with no phase transformation. The improved rate performance resulted from the excellent charge propagation in the continuous nanofiber network. [ABSTRACT FROM AUTHOR]

Published
2018
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46. Niobium carbide nanofibers as a versatile precursor for high power supercapacitor and high energy battery electrodes.

Author

Aslan, Mesut, Grobelsek, Ingrid, Tolosa, Aura, Krüner, Benjamin, Jäckel, Nicolas, Zeiger, Marco, Presser, Volker, and Fleischmann, Simon

Abstract

This study presents electrospun niobium carbide/carbon (NbC/C) hybrid nanofibers, with an average diameter of 69 ± 30 nm, as a facile precursor to derive either highly nanoporous niobium carbide-derived carbon (NbC–CDC) fibers for supercapacitor applications or niobium pentoxide/carbon (Nb2O5/C) hybrid fibers for battery-like energy storage. In all cases, the electrodes consist of binder-free and free-standing nanofiber mats that can be used without further conductive additives. Chlorine gas treatment conformally transforms NbC nanofiber mats into NbC–CDC fibers with a specific surface area of 1508 m2 g−1. These nanofibers show a maximum specific energy of 19.5 W h kg−1 at low power and 7.6 W h kg−1 at a high specific power of 30 kW kg−1 in an organic electrolyte. CO2 treatment transforms NbC into T-Nb2O5/C hybrid nanofiber mats that provide a maximum capacity of 156 mA h g−1. The presence of graphitic carbon in the hybrid nanofibers enabled high power handling, maintaining 50% of the initial energy storage capacity at a high rate of 10 A g−1 (64 C-rate). When benchmarked for an asymmetric full-cell, a maximum specific energy of 86 W h kg−1 was obtained. The high specific power for both systems, NbC–CDC and T-Nb2O5/C, resulted from the excellent charge propagation in the continuous nanofiber network and the high graphitization of the carbon structure. [ABSTRACT FROM AUTHOR]

Published
2016
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49. Superior Wear-Resistance of Ti3C2TxMultilayer Coatings

Author

Grützmacher, Philipp G., Suarez, Sebastian, Tolosa, Aura, Gachot, Carsten, Song, Guichen, Wang, Bo, Presser, Volker, Mücklich, Frank, Anasori, Babak, and Rosenkranz, Andreas

Abstract

Owing to MXenes’ tunable mechanical properties induced by their structural and chemical diversity, MXenes are believed to compete with state-of-the-art 2D nanomaterials such as graphene regarding their tribological performance. Their nanolaminate structure offers weak interlayer interactions and an easy-to-shear ability to render them excellent candidates for solid lubrication. However, the acting friction and wear mechanisms are yet to be explored. To elucidate these mechanisms, 100-nm-thick homogeneous multilayer Ti3C2Txcoatings are deposited on technologically relevant stainless steel by electrospraying. Using ball-on-disk tribometry (Si3N4counterbody) with acting contact pressures of about 300 MPa, their long-term friction and wear performance under dry conditions are studied. MXene-coated specimens demonstrate a 6-fold friction reduction and an ultralow wear rate (4 × 10–9mm3N–1m–1) over 100 000 sliding cycles, outperforming state-of-the-art 2D nanomaterials by at least 200% regarding their wear life. High-resolution characterization verified the formation of a beneficial tribolayer consisting of thermally/mechanically degraded MXenes and amorphous/nanocrystalline iron oxides. The transfer of this tribolayer to the counterbody transforms the initial steel/Si3N4contact to tribolayer/tribolayer contact with low shear resistance. MXene pileups at the wear track’s reversal points continuously supply the tribological contact with fresh, lubricious nanosheets, thus enabling an ultra-wear-resistant and low-friction performance.

Published
2021
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