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- ItemCurrent Advances in TiO2-Based Nanostructure Electrodes for High Performance Lithium Ion Batteries(Basel : MDPI, 2018-2-6) Madian, Mahmoud; Eychmüller, Alexander; Giebeler, LarsThe lithium ion battery (LIB) has proven to be a very reliably used system to store electrical energy, for either mobile or stationary applications. Among others, TiO2-based anodes are the most attractive candidates for building safe and durable lithium ion batteries with high energy density. A variety of TiO2 nanostructures has been thoroughly investigated as anodes in LIBs, e.g., nanoparticles, nanorods, nanoneedles, nanowires, and nanotubes discussed either in their pure form or in composites. In this review, we present the recent developments and breakthroughs demonstrated to synthesize safe, high power, and low cost nanostructured titania-based anodes. The reader is provided with an in-depth review of well-oriented TiO2-based nanotubes fabricated by anodic oxidation. Other strategies for modification of TiO2-based anodes with other elements or materials are also highlighted in this report.
- ItemStructural Aspects of P2-Type Na0.67Mn0.6Ni0.2Li0.2O2 (MNL) Stabilization by Lithium Defects as a Cathode Material for Sodium-Ion Batteries(Weinheim : Wiley-VCH, 2021) Yang, Liangtao; Kuo, Liang-Yin; López del Amo, Juan Miguel; Nayak, Prasant Kumar; Mazzio, Katherine A.; Maletti, Sebastian; Mikhailova, Daria; Giebeler, Lars; Kaghazchi, Payam; Rojo, Teófilo; Adelhelm, PhilippA known strategy for improving the properties of layered oxide electrodes in sodium-ion batteries is the partial substitution of transition metals by Li. Herein, the role of Li as a defect and its impact on sodium storage in P2-Na0.67Mn0.6Ni0.2Li0.2O2 is discussed. In tandem with electrochemical studies, the electronic and atomic structure are studied using solid-state NMR, operando XRD, and density functional theory (DFT). For the as-synthesized material, Li is located in comparable amounts within the sodium and the transition metal oxide (TMO) layers. Desodiation leads to a redistribution of Li ions within the crystal lattice. During charging, Li ions from the Na layer first migrate to the TMO layer before reversing their course at low Na contents. There is little change in the lattice parameters during charging/discharging, indicating stabilization of the P2 structure. This leads to a solid-solution type storage mechanism (sloping voltage profile) and hence excellent cycle life with a capacity of 110 mAh g-1 after 100 cycles. In contrast, the Li-free compositions Na0.67Mn0.6Ni0.4O2 and Na0.67Mn0.8Ni0.2O2 show phase transitions and a stair-case voltage profile. The capacity is found to originate from mainly Ni3+/Ni4+ and O2-/O2-δ redox processes by DFT, although a small contribution from Mn4+/Mn5+ to the capacity cannot be excluded. © 2021 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH
- ItemDevelopment and characterization of a metastable Al-Mn-Ce alloy produced by laser powder bed fusion(Amsterdam : Elsevier, 2021) Gabrysiak, Katharina; Gustmann, Tobias; Freudenberger, Jens; Neufeld, Kai; Giebeler, Lars; Leyens, Christoph; Kühn, UtaLaser powder bed fusion (LPBF) can help to overcome two challenges occurring by casting of metastable Al alloys: (1) the high amount of casting defects and (2) the limited part size while maintaining rapid solidification of the whole cross-section. In this study, an Al92Mn6Ce2 alloy was processed crack-free without baseplate heating by LPBF. The high cooling rate during fabrication has a significant impact on the microstructure, which was characterized by SEM, TEM and XRD. The processing through LPBF causes a high amount and a strong refinement of the intermetallic Al20Mn2Ce precipitates. This leads, compared to suction-cast specimens, to a higher hardness (180 HV 5) and a higher tolerable compressive stress (>1200 MPa) associated with a pronounced plasticity without failure up to a strain of 40%. The extraordinary mechanical properties of additively manufactured Al92Mn6Ce2 can extend the possibilities of producing novel LPBF lightweight structures for potential applications under harsh conditions.
- ItemTernary CNTs@TiO2/CoO nanotube composites: Improved anode materials for high performance lithium ion batteries(Basel : MDPI, 2017) Madian, Mahmoud; Ummethala, Raghunandan; El Naga, Ahmed Osama Abo; Ismail, Nahla; Rümmeli, Mark Hermann; Eychmüller, Alexander; Giebeler, LarsTiO2 nanotubes (NTs) synthesized by electrochemical anodization are discussed as very promising anodes for lithium ion batteries, owing to their high structural stability, high surface area, safety, and low production cost. However, their poor electronic conductivity and low Li+ ion diffusivity are the main drawbacks that prevent them from achieving high electrochemical performance. Herein, we report the fabrication of a novel ternary carbon nanotubes (CNTs)@TiO2/CoO nanotubes composite by a two-step synthesis method. The preparation includes an initial anodic fabrication of well-ordered TiO2/CoO NTs from a Ti-Co alloy, followed by growing of CNTs horizontally on the top of the oxide films using a simple spray pyrolysis technique. The unique 1D structure of such a hybrid nanostructure with the inclusion of CNTs demonstrates significantly enhanced areal capacity and rate performances compared to pure TiO2 and TiO2/CoO NTs, without CNTs tested under identical conditions. The findings reveal that CNTs provide a highly conductive network that improves Li+ ion diffusivity, promoting a strongly favored lithium insertion into the TiO2/CoO NT framework, and hence resulting in high capacity and an extremely reproducible high rate capability.
- ItemApproach to Estimate the Phase Formation and the Mechanical Properties of Alloys Processed by Laser Powder Bed Fusion via Casting(Basel : MDPI, 2022) Kühn, Uta; Sander, Jan; Gabrysiak, Katharina Nicole; Giebeler, Lars; Kosiba, Konrad; Pilz, Stefan; Neufeld, Kai; Boehm, Anne Veronika; Hufenbach, Julia KristinA high-performance tool steel with the nominal composition Fe85Cr4Mo8V2C1 (wt%) was processed by three different manufacturing techniques with rising cooling rates: conventional gravity casting, centrifugal casting and an additive manufacturing process, using laser powder bed fusion (LPBF). The resulting material of all processing routes reveals a microstructure, which is composed of martensite, austenite and carbides. However, comparing the size, the morphology and the weight fraction of the present phases, a significant difference of the gravity cast samples is evident, whereas the centrifugal cast material and the LPBF samples show certain commonalities leading finally to similar mechanical properties. This provides the opportunity to roughly estimate the mechanical properties of the material fabricated by LPBF. The major benefit arises from the required small material quantity and the low resources for the preparation of samples by centrifugal casting in comparison to the additive manufacturing process. Concluding, the present findings demonstrate the high attractiveness of centrifugal casting for the effective material screening and hence development of novel alloys adapted to LPBF-processing.
- ItemAdditively manufactured AlSi10Mg lattices – Potential and limits of modelling as-designed structures(Amsterdam [u.a.] : Elsevier Science, 2022) Gebhardt, Ulrike; Gustmann, Tobias; Giebeler, Lars; Hirsch, Franz; Hufenbach, Julia Kristin; Kästner, MarkusAdditive manufacturing overcomes the restrictions of classical manufacturing methods and enables the production of near-net-shaped, complex geometries. In that context, lattice structures are of high interest due to their superior weight reduction potential. AlSi10Mg is a well-known alloy for additive manufacturing and well suited for such applications due to its high strength to material density ratio. It has been selected in this study for producing bulk material and complex geometries of a strut-based lattice type (rhombic dodecahedron). A detailed characterisation of as-built and heat-treated specimens has been conducted including microstructural analyses, identification of imperfections and rigorous mechanical testing under different load conditions. An isotropic elastic–plastic material model is deduced on the basis of tension test results of bulk material test specimens. Performed experiments under compression, shear, torsion and tension load are compared to their virtual equivalents. With the help of numerical modelling, the overall structural behaviour was simulated using the detailed lattice geometry and was successfully predicted by the presented numerical models. The discussion of the limits of this approach aims to evaluate the potential of the numerical assessment in the modelling of the properties for novel lightweight structures.
- ItemRole of 1,3-dioxolane and LiNO3 addition on the long term stability of nanostructured silicon/carbon anodes for rechargeable lithium batteries(Pennington, NJ : ECS, 2016) Jaumann, Tony; Balach, Juan; Klose, Markus; Oswald, Steffen; Eckert, Jürgen; Giebeler, LarsIn order to utilize silicon as alternative anode for unfavorable lithium metal in lithium – sulfur (Li–S) batteries, a profound understanding of the interfacial characteristics in ether-based electrolytes is required. Herein, the solid electrolyte interface (SEI) of a nanostructured silicon/carbon anode after long-term cycling in an ether-based electrolyte for Li–S batteries is investigated. The role of LiNO3 and 1,3-dioxolane (DOL) in dimethoxy ethane (DME) solutions as typically used electrolyte components on the electrochemical performance and interfacial characteristics on silicon are evaluated. Because of the high surface area of our nanostructured electrode owing to the silicon particle size of around 5 nm and the porous carbon scaffold, the interfacial characteristics dominate the overall electrochemical reversibility opening a detailed analysis. We show that the use of DME/DOL solutions under ambient temperature causes higher degradation of electrolyte components compared to carbonate-based electrolytes used for Li–ion batteries (LIB). This behavior of DME/DOL mixtures is associated with different SEI component formation and it is demonstrated that LiNO3 addition can significantly stabilize the cycle performance of nanostructured silicon/carbon anodes. A careful post-mortem analysis and a discussion in context to carbonate-based electrolyte solutions helps to understand the degradation mechanism of silicon-based anodes in rechargeable lithium-based batteries.
- ItemMXenes and the progress of Li–S battery development - a perspective(Bristol : IOP Publishing, 2021) Balach, Juan; Giebeler, LarsLithium–sulfur (Li–S) battery has attracted tremendous interest owing to its high energy density at affordable costs. However, the irreversible active material loss and subsequent capacity fading caused by the uncontrollable shuttling of polysulfides have greatly hampered its commercial viability. MXenes, a novel class of 2D materials derived from nano-layered MAX phases, have been shown the potential to push the development of sulfur-based batteries to a next level owing to their high conductivity, strong polysulfide affinity and electrocatalytic properties. This perspective article focuses on the possible implications that MXene-based materials will have in the development of advanced sulfur-based batteries and their potential application in different upcoming technologies. In four sections possible developments are outlined which can be reached in the next 10 years, that enable a highly reliable, minimized Li–S battery finally combined with energy harvesters to fabricate autonomous power supplies for the next generation of microscaled devices like meteorological or geotechnical probes, wearable (medical) sensors or other suitable mobile devices. Finally, a flowchart illustrates the possible way to realize some important milestones for the certain possible steps with significant contributions of MXenes.
- ItemLifetime vs. rate capability: Understanding the role of FEC and VC in high-energy Li-ion batteries with nano-silicon anodes(Amsterdam : Elsevier, 2016) Jaumann, Tony; Balach, Juan; Langklotz, Ulrike; Sauchuk, Viktar; Fritsch, Marco; Michaelis, Alexander; Teltevskij, Valerij; Mikhailova, Daria; Oswald, Steffen; Klose, Markus; Stephani, Guenter; Hauser, Ralf; Eckert, Jürgen; Giebeler, LarsFluoroethylene carbonate (FEC) and vinylene carbonate (VC) are the most frequently used electrolyte components to enhance the lifetime of anode materials in Li-ion batteries, but for silicon it is still ambiguous when FEC or VC is more beneficial. Herein, a nanostructured silicon/carbon anode derived from low-cost HSiCl3 is tailored by the rational choice of the electrolyte component, to obtain an anode material outperforming current complex silicon structures. We demonstrate highly reversible areal capacities of up to 5 mA h/cm2 at 4.4 mg/cm2 mass loading, a specific capacity of 1280 mA h/gElectrode, a capacity retention of 81% after 500 deep-discharge cycles versus lithium metal and successful full-cell tests with high-voltage cathodes meeting the requirements for real application. Electrochemical impedance spectroscopy and post-mortem investigation provide new insights in tailoring the interfacial properties of silicon-based anodes for high performance anode materials based on an alloying mechanism with large volume changes. The role of fluorine in the FEC-derived interfacial layer is discussed in comparison with the VC-derived layer and possible degradation mechanisms are proposed. We believe that this study gives a valuable understanding and provides new strategies on the facile use of additives for highly reversible silicon anodes in Li-ion batteries.
- ItemSEI-component formation on sub 5 nm sized silicon nanoparticles in Li-ion batteries: The role of electrode preparation, FEC addition and binders(Cambridge : Royal Society of Chemistry, 2015) Jaumann, Tony; Balach, Juan; Klose, Markus; Oswald, Steffen; Langklotz, Ulrike; Michaelis, Alexander; Eckert, Jürgen; Giebeler, LarsSilicon is a promising negative electrode for secondary lithium-based batteries, but the electrochemical reversibility of particularly nanostructured silicon electrodes drastically depends on their interfacial characteristics, commonly known as the solid electrolyte interface (SEI). The beneficial origin of certain electrolyte additives or different binders is still discussed controversially owing to the challenging peculiarities of interfacial post-mortem investigations of electrodes. In this work, we address the common difficulties of SEI investigations of porous silicon/carbon nanostructures and study the addition of a fluoroethylene carbonate (FEC) as a stabilizing additive as well as the use of two different binders, carboxymethyl cellulose/styrene-butadiene rubber (CMC/SBR) and polyacrylic acid (PAA), for the SEI formation. The electrode is composed of silicon nanocrystallites below 5 nm diameter allowing a detailed investigation of interfacial characteristics of silicon owing to the high surface area. We first performed galvanostatic long-term cycling (400 times) and carried out comprehensive ex situ characterization of the cycled nanocrystalline silicon electrodes with XRD, EDXS, TEM and XPS. We modified the preparation of the electrode for post-mortem characterization to distinguish between electrolyte components and the actual SEI. The impact of the FEC additive and two different binders on the interfacial layer is studied and the occurrence of diverse compounds, in particular LiF, Li2O and phosphates, is discussed. These results help to understand general issues in SEI formation and to pave the way for the development of advanced electrolytes allowing for a long-term performance of nanostructured Si-based electrodes.