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- ItemSelf-Activation of Inorganic-Organic Hybrids Derived through Continuous Synthesis of Polyoxomolybdate and para-Phenylenediamine Enables Very High Lithium-Ion Storage Capacity(Weinheim : Wiley-VCH, 2023) Mohamed, Mana Abdirahman; Arnold, Stefanie; Janka, Oliver; Quade, Antje; Presser, Volker; Kickelbick, GuidoInorganic-organic hybrid materials with redox-active components were prepared by an aqueous precipitation reaction of ammonium heptamolybdate (AHM) with para-phenylenediamine (PPD). A scalable and low-energy continuous wet chemical synthesis process, known as the microjet process, was used to prepare particles with large surface area in the submicrometer range with high purity and reproducibility on a large scale. Two different crystalline hybrid products were formed depending on the ratio of molybdate to organic ligand and pH. A ratio of para-phenylenediamine to ammonium heptamolybdate from 1 : 1 to 5 : 1 resulted in the compound [C6H10N2]2[Mo8O26] ⋅ 6 H2O, while higher PPD ratios from 9 : 1 to 30 : 1 yielded a composition of [C6H9N2]4[NH4]2[Mo7O24] ⋅ 3 H2O. The electrochemical behavior of the two products was tested in a battery cell environment. Only the second of the two hybrid materials showed an exceptionally high capacity of 1084 mAh g−1 at 100 mA g−1 after 150 cycles. The maximum capacity was reached after an induction phase, which can be explained by a combination of a conversion reaction with lithium to Li2MoO4 and an additional in situ polymerization of PPD. The final hybrid material is a promising material for lithium-ion battery (LIB) applications.
- ItemDesign of high-performance antimony/MXene hybrid electrodes for sodium-ion batteries(London [u.a.] : RSC, 2022) Arnold, Stefanie; Gentile, Antonio; Li, Yunjie; Wang, Qingsong; Marchionna, Stefano; Ruffo, Riccardo; Presser, VolkerDue to their versatile properties and excellent electrical conductivity, MXenes have become attractive materials for alkali metal-ion batteries. However, as the capacity is limited to lower values due to the intercalation mechanism, these materials can hardly keep up in the ever-fast-growing community of battery research. Antimony has a promisingly high theoretical sodiation capacity characterized by an alloying reaction. The main drawback of this type of battery material is related to the high volume changes during cycling, often leading to electrode cracking and pulverization, resulting in poor electrochemical performance. A synergistic effect of combing antimony and MXene can be expected to obtain an optimized electrochemical system to overcome capacity fading of antimony while taking advantage of MXene charge storage ability. In this work, variation of the synthesis parameters and material design strategy have been dedicated to achieving the optimized antimony/MXene hybrid electrodes for high-performance sodium-ion batteries. The optimized performance does not align with the highest amount of antimony, the smallest nanoparticles, or the largest interlayer distance of MXene but with the most homogeneous distribution of antimony and MXene while both components remain electrochemically addressable. As a result, the electrode with 40 mass% MXene, not previously expanded, etched with 5 mass% HF and 60% antimony synthesized on the surfaces of MXene emerged as the best electrode. We obtained a high reversible capacity of 450 mA h g−1 at 0.1 A g−1 with a capacity retention of around 96% after 100 cycles with this hybrid material. Besides the successful cycling stability, this material also exhibits high rate capability with a capacity of 365 mA h g−1 at 4 A g−1. In situ XRD measurements and post mortem analysis were used to investigate the reaction mechanism.
- ItemChoosing the right carbon additive is of vital importance for high-performance Sb-based Na-ion batteries(London [u.a.] : RSC, 2020) Pfeifer, Kristina; Arnold, Stefanie; Budak, Öznil; Luo, Xianlin; Presser, Volker; Ehrenberg, Helmut; Dsoke, SoniaElectrodes based on alloying reactions for sodium-ion batteries (NIB) offer high specific capacity but require bespoken electrode material design to enable high performance stability. This work addresses that issue by systematically exploring the impact of carbon properties on antimony/carbon composite electrodes for NIBs. Since the Sb surface is covered by an insulating oxide layer, carbon additives are crucial for the percolation and electrochemical activity of Sb based anodes. Instead of using complex hybridization strategies, the ability of mechanical mixing to yield stable high-performance Sb/C sodium-ion battery (NIB) electrodes is shown. This is only possible by considering the physical, chemical, and structural features of the carbon phase. A comparison of carbon nanohorns, onion-like carbon, carbon black, and graphite as conductive additives is given in this work. The best performance is not triggered by the highest or lowest surface area, and not by highest or lowest heteroatom content, but by the best ability to homogenously distribute within the Sb matrix. The latter provides an optimum interaction between carbon and Sb and is best enabled by onion-like carbon. A remarkable rate performance is attained, electrode cracking caused by volume expansion is successfully prevented, and the homogeneity of the solid/electrolyte interphase is significantly improved as a result of it. With this composite electrode, a reversible capacity of 490 mA h g-1 at 0.1 A g-1 and even 300 mA g-1 at 8 A g-1 is obtained. Additionally, high stability with a capacity retention of 73% over 100 cycles is achieved at charge/discharge rates of 0.2 A g-1 This journal is © The Royal Society of Chemistry.
- ItemContinuous wet chemical synthesis of Mo(C,N,O)x as anode materials for Li-ion batteries(London [u.a.] : RSC, 2023) Abdirahman Mohamed, Mana; Arnold, Stefanie; Janka, Oliver; Quade, Antje; Schmauch, Jörg; Presser, Volker; Kickelbick, GuidoMolybdenum carbides, oxides, and mixed anionic carbide–nitride–oxides Mo(C,N,O)x are potential anode materials for lithium-ion batteries. Here we present the preparation of hybrid inorganic–organic precursors by a precipitation reaction of ammonium heptamolybdate ((NH4)6Mo7O24) with para-phenylenediamine in a continuous wet chemical process known as a microjet reactor. The mixing ratio of the two components has a crucial influence on the chemical composition of the obtained material. Pyrolysis of the precipitated precursor compounds preserved the size and morphology of the micro- to nanometer-sized starting materials. Changes in pyrolysis conditions such as temperature and time resulted in variations of the final compositions of the products, which consisted of mixtures of Mo(C,N,O)x, MoO2, Mo2C, Mo2N, and Mo. We optimized the reaction conditions to obtain carbide-rich phases. When evaluated as an anode material for application in lithium-ion battery half-cells, one of the optimized materials shows a remarkably high capacity of 933 mA h g−1 after 500 cycles. The maximum capacity is reached after an activation process caused by various conversion reactions with lithium.
- ItemUnraveling the Electrochemical Mechanism in Tin Oxide/MXene Nanocomposites as Highly Reversible Negative Electrodes for Lithium-Ion Batteries(Weinheim : Wiley-VCH, 2023) Gentile, Antonio; Arnold, Stefanie; Ferrara, Chiara; Marchionna, Stefano; Tang, Yushu; Maibach, Julia; Kübel, Christian; Presser, Volker; Ruffo, RiccardoLithium-ion batteries are constantly developing as the demands for power and energy storage increase. One promising approach to designing high-performance lithium-ion batteries is using conversion/alloying materials, such as SnO2. This class of materials does, in fact, present excellent performance and ease of preparation; however, it suffers from mechanical instabilities during cycling that impair its use. One way to overcome these problems is to prepare composites with bi-dimensional materials that stabilize them. Thus, over the past 10 years, two-dimensional materials with excellent transport properties (graphene, MXenes) have been developed that can be used synergistically with conversion materials to exploit both advantages. In this work, a 50/50 (by mass) SnO2/Ti3C2Tz nanocomposite is prepared and optimized as a negative electrode for lithium-ion batteries. The nanocomposite delivers over 500 mAh g−1 for 700 cycles at 0.1 A g−1 and demonstrates excellent rate capability, with 340 mAh g−1 at 8 A g−1. These results are due to the synergistic behavior of the two components of the nanocomposite, as demonstrated by ex situ chemical, structural, and morphological analyses. This knowledge allows, for the first time, to formulate a reaction mechanism with lithium-ions that provides partial reversibility of the conversion reaction with the formation of SnO.