Porous Graphene-like Carbon from Fast Catalytic Decomposition of Biomass for Energy Storage Applications

A novel carbon material made of porous graphene-like nanosheets was synthesized from biomass resources by a simple catalytic graphitization process using nickel as a catalyst for applications in electrodes for energy storage devices. A recycled fiberboard precursor was impregnated with saturated nickel nitrate followed by high-temperature pyrolysis. The highly exothermic combustion of in situ formed nitrocellulose produces the expansion of the cellulose fibers and the reorganization of the carbon structure into a three-dimensional (3D) porous assembly of thin carbon nanosheets. After acid washing, nickel particles are fully removed, leaving nanosized holes in the wrinkled graphene-like sheets. These nanoholes confer the resulting carbon material with ≈75% capacitance retention, when applied as a supercapacitor electrode in aqueous media at a specific current of 100 A·g–1 compared to the capacitance reached at 20 mA·g–1, and ≈35% capacity retention, when applied as a negative electrode for lithium-ion battery cells at a specific current of 3720 mA·g–1 compared to the specific capacity at 37.2 mA·g–1. These findings suggest a novel way for synthesizing 3D nanocarbon networks from a cellulosic precursor requiring low temperatures and being amenable to large-scale production while using a sustainable starting precursor such as recycled fiberwood.Spanish Government Agency Ministerio de Economí a y Competitividad (MINECO) (grant number MAT2016-76526-R)

Digitale Teilhabe

Das Themenheft Digitale Teilhabe beschäftigt sich zentral mit den Potentialen der Nutzung der neuen Informations- und Kommunikationstechnologien durch benachteiligte Menschen. Im Leitartikel wird der Versuch unternommen, mögliche theoretische Anknüpfungspunkte und Forschungsfragen für weitere Studien- und Forschungsarbeiten in dem noch jungen Themenfeld der Digitalen Teilhabe zu identifizieren. Hierzu wird zunächst das zugrunde liegende Verständnis von Behinderung/Benachteiligung diskutiert und inklusive (Medien-)Bildung als Teil der Persönlichkeitsbildung skizziert. In verschiedenen Diskursen bzw. Disziplinen werden dann theoretische Anknüpfungspunkte für weitere Forschungsarbeiten benannt. Die Idee für das Themenheft ist im Rahmen des Projekts "Begleitforschung im PIKSL-Labor" des Zentrums für Planung und Evaluation Sozialer Dienste der Uni Siegen (ZPE) entstanden. Das PIKSL-Projekt zielt darauf ab, Menschen mit Behinderungen moderne Kommunikationstechnologien zugänglich zu machen, um ihnen Teilhabemöglichkeiten zu erleichtern und zugleich die personale Abhängigkeit von professioneller Unterstützung zu reduzieren. Der inter- und transdisziplinäre Ansatz von PIKSL wird durch die Vielfalt der Artikel in dem Heft deutlich: Digitale Teilhabe wird nicht alleine aus (medien-)pädagogischer bzw. sozialwissenschaftlicher Perspektive betrachtet. Die Besonderheit liegt in der Kooperation unterschiedlicher Disziplinen wie Soziale Arbeit, Kunst und Webdesign

Sozialmanagement - Professionalisierungsschub für die Soziale Arbeit oder feindliche Übernahme durch die BWL?

Der Begriff ‚Sozialmanagement‘ weckt auf den ersten Blick Assoziationen zu den klassischen Tugenden eines ehrbaren Kaufmannes. Doch selbst wenn sich innerhalb der Praxis Sozialer Arbeit an der einen oder anderen Stelle zutreffende Beispiele für solch einen Handlungstypus ausfindig machen lassen, verdeutlicht der Begriff ‚Sozialmanagement‘ vielmehr die folgende Entwicklung bzw. kann dafür als charakteristisch angesehen werden: „Wirtschaftlichkeit, d.h. die Beachtung ökonomischer Kriterien, Kosten-Nutzen-Abgleich u.ä, hat sich in den letzten Jahren zu einem zentralen Thema Sozialer Arbeit entwickelt“ (Lange 2000, S. 74)

Synthesis and Comparative Investigation of Silicon Transition Metal Silicide Composite Anodes for Lithium Ion Batteries

A significant increase in energy density of lithium ion batteries (LIBs) can be achieved by using high‐capacity, silicon (Si)‐based negative electrode materials. Several challenges arise from the enormous volumetric changes of Si during lithiation/delithiation, such as disintegration/pulverization of the active material and the electrode as well as ongoing electrolyte decomposition, leading to rapid capacity fading. Here, we synthesize and comparatively investigate three different porous transition metal‐Si‐carbon composite materials that are composed of an active Si phase and the corresponding inactive metal‐silicide phases. In this material design, the inactive phases, as well as the pores serve as a buffer to attenuate the previously mentioned detrimental effects. The synthesized materials are studied with respect to their structural and surface properties and are characterized electrochemically regarding their rate performance, and long‐term charge/discharge cycling stability. Thereby, the composite materials show a promising rate capability and a high specific capacity. Their low initial Coulombic efficiency, due to the porous structure, can be partially compensated by pre‐lithiation. This is demonstrated by the application of the synthesized materials in a LIB full‐cell set‐up vs. NMC‐111 cathodes, where the amount of lithium is confined due to anode/cathode capacity balancing

Hydrothermal-derived carbon as a stabilizing matrix for improved cycling performance of silicon-based anodes for lithium-ion full cells

In this work, silicon/carbon composites are synthesized by forming an amorphous carbon matrix around silicon nanoparticles (Si-NPs) in a hydrothermal process. The intention of this material design is to combine the beneficial properties of carbon and Si, i.e., an improved specific/volumetric capacity and capacity retention compared to the single materials when applied as a negative electrode in lithium-ion batteries (LIBs). This work focuses on the influence of the Si content (up to 20 wt %) on the electrochemical performance, on the morphology and structure of the composite materials, as well as the resilience of the hydrothermal carbon against the volumetric changes of Si, in order to examine the opportunities and limitations of the applied matrix approach. Compared to a physical mixture of Si-NPs and the pure carbon matrix, the synthesized composites show a strong improvement in long-term cycling performance (capacity retention after 103 cycles: ≈55% (20 wt % Si composite) and ≈75% (10 wt % Si composite)), indicating that a homogeneous embedding of Si into the amorphous carbon matrix has a highly beneficial effect. The most promising Si/C composite is also studied in a LIB full cell vs a NMC-111 cathode; such a configuration is very seldom reported in the literature. More specifically, the influence of electrochemical prelithiation on the cycling performance in this full cell set-up is studied and compared to non-prelithiated full cells. While prelithiation is able to remarkably enhance the initial capacity of the full cell by ≈18 mAh g−1, this effect diminishes with continued cycling and only a slightly enhanced capacity of ≈5 mAh g−1 is maintained after 150 cycles

Identification of Li x Sn Phase Transitions During Lithiation of Tin Nanoparticle-Based Negative Electrodes from Ex Situ 119 Sn MAS NMR and Operando 7 Li NMR and XRD

The lithiation mechanism of tin nanoparticle-based negative electrodes is reported and systematically studied via operando 7Li nuclear magnetic resonance (NMR) and X-ray diffraction (XRD) combined with ex situ 119Sn magic-angle spinning (MAS) NMR. Besides the formation of the Sn-rich phases Li2Sn5 and LiSn, also the Li-richer phase Li7Sn3 is observed in good agreement with the structural evolution of the binary Li–Sn phase diagram. However, the structural investigations using ex situ 119Sn MAS NMR clearly reveal the formation of a disordered LixSn phase with increasing lithiation, possessing the structural fingerprints of Li7Sn3 with no long-range order and a body-centered cubic (bcc) packing of Sn (from XRD). Thus, in contrast to previous studies relying on 7Li NMR only, the formation of any of the Li-rich bulk crystalline Li–Sn phases, Li13Sn5, Li5Sn2, Li7Sn2, and Li17Sn4, could not be confirmed from 119Sn MAS NMR, showing that these Li–Sn phases are not formed under electrochemical operation. From a more general point of view, our approach using ex situ 119Sn MAS NMR demonstrates the possibilities of using the heavier framework ions as reporters of the local structural environments in negative electrodes. This relies on the sensitivity of the isotropic 119Sn shift with respect to the first and second atomic coordination environments, which provides a powerful source of complementary structural information to the typically performed operando 7Li NMR and XRD measurements

An electrochemical evaluation of nitrogen-doped carbons as anodes for lithium ion batteries

New anode materials beyond graphite are needed to improve the performance of lithium ion batteries (LIBs). Chemical doping with nitrogen has emerged as a simple strategy for enhancing lithium storage in carbon-based anodes. While specific capacity and rate capability are improved by doping, little is known about other key electrochemical properties relevant to practical applications. This work presents a systematic evaluation of electrochemical characteristics of nitrogen-doped carbons derived from a biomass source and urea powder as anodes in LIB half- and full-cells. Results show that doped carbons suffer from a continuous loss in capacity upon cycling that is more severe for higher nitrogen contents. Nitrogen negatively impacts the voltage and energy efficiencies at low charge/discharge current densities. However, as the charge/discharge rate increases, the voltage and energy efficiencies of the doped carbons outperform the non-doped ones. We provide insights towards a fundamental understanding of the requirements needed for practical applications and reveal drawbacks to be overcome by novel doped carbon-based anode materials in LIB applications. With this work, we also want to encourage other researchers to evaluate electrochemical characteristics besides capacity and cycling stability which are mandatory to assess the practicality of novel materials

Lithiation Mechanism and Improved Electrochemical Performance of TiSnSb-Based Negative Electrodes for Lithium-Ion Batteries

Lithium alloying materials are promising candidates to replace the current intercalation-type graphite negative electrode materials in lithium-ion batteries (LIBs) due to their high specific capacity and relatively low cost. Here, we investigate the electrochemical performance of TiSnSb regarding its charge/discharge cycling stability as a negative electrode material in LIB cells. To assess a more practical performance with respect to a limited active lithium content in LIB full-cells, we evaluate the impact of pre-lithiation for TiSnSb with respect to the cycling stability in a NCM111||TiSnSb cell setup. The observation of the individual electrode potentials reveals comprehensive insights into the ongoing cell chemistry, showing that clear performance improvements can be achieved via pre-lithiation. Furthermore, the lithiation mechanism of TiSnSb is systematically studied via ex situ7Li magic-angle spinning (MAS) nuclear magnetic resonance (NMR), ex situ X-ray diffraction, and static ex situ119Sn wideband uniform rate smooth truncation Carr–Purcell Meiboom–Gill (CPMG) WCPMG NMR experiments. For comprehensive references regarding the isotropic 7Li shift of the Li–Sb intermetallic phases, all thermodynamically stable Li–Sb intermetallics of the binary Li–Sb systems have been synthesized and subsequently characterized by 7Li MAS NMR. Combined, our measurements for lithiated TiSnSb do not give any evidence for the formation of Li–Sn and Li–Sb intermetallics related to crystalline bulk phases (Li7Sn3, Li7Sn2, Li3Sb, and Li2Sb) as has been previously reported. In contrast, unique insights obtained from static ex situ119Sn WCPMG NMR and ex situ XRD measurements reveal the formation of ternary Li–Sb–Sn species during lithiation, which can be assigned to the intermetallic phase Li2.8SbSn0.2. Additionally, the 7Li MAS NMR measurements combined with the observed discharge capacity reveal a second Li species, which we assign to an amorphous Li–Sn phase

Solvent Co-intercalation into Few-layered Ti 3 C 2 T x MXenes in Lithium Ion Batteries Induced by Acidic or Basic Post-treatment

MXenes, as an emerging class of 2D materials, display distinctive physical and chemical properties, which are highly suitable for high-power battery applications, such as lithium ion batteries (LIBs). Ti3C2Tx (Tx = O, OH, F, Cl) is one of the most investigated MXenes to this day; however, most scientific research studies only focus on the design of multilayered or monolayer MXenes. Here, we present a comprehensive study on the synthesis of few-layered Ti3C2Tx materials and their use in LIB cells, in particular for high-rate applications. The synthesized Ti3C2Tx MXenes are characterized via complementary XRD, Raman spectroscopy, XPS, EDX, SEM, TGA, and nitrogen adsorption techniques to clarify the structural and chemical changes, especially regarding the surface groups and intercalated cations/water molecules. The structural changes are correlated with respect to the acidic and basic post-treatment of Ti3C2Tx. Furthermore, the detected alterations are put into an electrochemical perspective via galvanostatic and potentiostatic investigations to study the pseudocapacitive behavior of few-layered Ti3C2Tx, exhibiting a stable capacity of 155 mAh g–1 for 1000 cycles at 5 A g–1. The acidic treatment of Ti3C2Tx synthesized via the in situ formation of HF through LiF/HCl is able to increase the initial capacity in comparison to the pristine or basic treatment. To gain further insights into the structural changes occurring during (de)lithiation, in situ XRD is applied for LIB cells in a voltage range from 0.01 to 3 V to give fundamental mechanistic insights into the structural changes occurring during the first cycles. Thereby, the increased initial capacity observed for acidic-treated MXenes can be explained by the reduced co-intercalation of solvent molecules