Failure mechanisms associated with silicon‐based anodes are limiting the implementation of high‐capacity lithium‐ion batteries. Understanding the aging mechanism that deteriorates the anode ...performance and introducing novel‐architectured composites offer new possibilities for improving the functionality of the electrodes. Here, the characterization of nano‐architectured composite anode composed of active amorphous silicon domains (a‐Si, 20 nm) and crystalline iron disilicide (c‐FeSi2, 5–15 nm) alloyed particles dispersed in a graphite matrix is reported. This unique hierarchical architecture yields long‐term mechanical, structural, and cycling stability. Using advanced electron microscopy techniques, the nanoscale morphology and chemical evolution of the active particles upon lithiation/delithiation are investigated. Due to the volumetric variations of Si during lithiation/delithiation, the morphology of the a‐Si/c‐FeSi2 alloy evolves from a core‐shell to a tree‐branch type structure, wherein the continuous network of the active a‐Si remains intact yielding capacity retention of 70% after 700 cycles. The root cause of electrode polarization, initial capacity fading, and electrode swelling is discussed and has profound implications for the development of stable lithium‐ion batteries.
Underlying aging mechanisms of nano‐architectured a‐Si/c‐FeSi2 alloy/graphite composites are investigated by combining advanced electron microscopy and spectroscopy methods upon (de)lithiation. Exploiting the nanoscale morphology, chemical evolution of the alloy particles, and the SEI components unravels mechanisms involved in the aging process. The nanoscale organization of the alloy particles encodes higher structural stability, leading to a capacity‐retention of 70%.
The streptophyte green algal class Zygnematophyceae is the immediate sister lineage to land plants. Their special form of sexual reproduction via conjugation might have played a key role during ...terrestrialization. Thus, studying Zygnematophyceae and conjugation is crucial for understanding the conquest of land. Moreover, sexual reproduction features are important for species determination. We present a phylogenetic analysis of a field‐sampled Zygnema strain and analyze its conjugation process and zygospore morphology, both at the micro‐ and nanoscale, including 3D‐reconstructions of the zygospore architecture. Vegetative filament size (26.18 ± 1.07 μm) and reproductive features allowed morphological determination of Zygnema vaginatum, which was combined with molecular analyses based on rbcL sequencing. Transmission electron microscopy (TEM) depicted a thin cell wall in young zygospores, while mature cells exhibited a tripartite wall, including a massive and sculptured mesospore. During development, cytological reorganizations were visualized by focused ion beam scanning electron microscopy (FIB‐SEM). Pyrenoids were reorganized, and the gyroid cubic central thylakoid membranes, as well as the surrounding starch granules, degraded (starch granule volume: 3.58 ± 2.35 μm3 in young cells; 0.68 ± 0.74 μm3 at an intermediate stage of zygospore maturation). Additionally, lipid droplets (LDs) changed drastically in shape and abundance during zygospore maturation (LD/cell volume: 11.77% in young cells; 8.79% in intermediate cells, 19.45% in old cells). In summary, we provide the first TEM images and 3D‐reconstructions of Zygnema zygospores, giving insights into the physiological processes involved in their maturation. These observations help to understand mechanisms that facilitated the transition from water to land in Zygnematophyceae.
Abstract
Thiophosphate solid electrolytes (Li
3
PS
4
, hereafter denoted LPS) have the advantage of presenting a reasonable ionic conductivity at room temperature (≈ 0.3 mS cm
−1
) and an easy ...manufacturing, meaning that they can be sintered at room temperature. Unfortunately, during cycling, several chemo‐mechanical degradations quite often attributed to the electrochemical activities occur, but they could also be linked to the sintering process. To date, a fundamental understanding of room‐temperature sintering and its impact on the microstructure, the ionic conductivity, and the link between electrochemistry and structure/morphology remains imprecise. In this study, a comprehensive study of homemade amorphous 75% Li
2
S – 25% P
2
S
5
(Li
3
PS
4
) is presented, investigating the influence of pressure and time of room temperature sintering. Focused ion beam‐scanning electron microscopy coupled to electrochemical techniques such as electrochemical impedance spectroscopy, Li plating/ stripping and coupled to structural techniques such as wide‐angle X‐ray scattering are used to establish the link between structure, morphology, and electrochemical properties. It is demonstrated that the room temperature sintering of solid electrolytes is not that trivial and that the commonly accepted rule “less porosity = better ionic conductivity” is not always true and that many additional parameters should be considered to properly sinter the solid electrolyte.
Eukaryotic phytoplankton have a small global biomass but play major roles in primary production and climate. Despite improved understanding of phytoplankton diversity and evolution, we largely ignore ...the cellular bases of their environmental plasticity. By comparative 3D morphometric analysis across seven distant phytoplankton taxa, we observe constant volume occupancy by the main organelles and preserved volumetric ratios between plastids and mitochondria. We hypothesise that phytoplankton subcellular topology is modulated by energy-management constraints. Consistent with this, shifting the diatom Phaeodactylum from low to high light enhances photosynthesis and respiration, increases cell-volume occupancy by mitochondria and the plastid CO
-fixing pyrenoid, and boosts plastid-mitochondria contacts. Changes in organelle architectures and interactions also accompany Nannochloropsis acclimation to different trophic lifestyles, along with respiratory and photosynthetic responses. By revealing evolutionarily-conserved topologies of energy-managing organelles, and their role in phytoplankton acclimation, this work deciphers phytoplankton responses at subcellular scales.
Silicon (Si) is the most promising anode candidate for the next generation of lithium-ion batteries but difficult to cycle due to its poor electronic conductivity and large volume change during ...cycling. Nanostructured Si-based materials allow high loading and cycling stability but remain a challenge for process and engineering. We prepare a Si nanowires-grown-on-graphite one-pot composite (Gt–SiNW) via a simple and scalable route. The uniform distribution of SiNW and the graphite flakes alignment prevent electrode pulverization and accommodate volume expansion during cycling, resulting in very low electrode swelling. Our designed nanoarchitecture delivers outstanding electrochemical performance with a capacity retention of 87% after 250 cycles at 2C rate with an industrial electrode density of 1.6 g cm–3. Full cells with NMC-622 cathode display a capacity retention of 70% over 300 cycles. This work provides insights into the fruitful engineering of active composites at the nano- and microscales to design efficient Si-rich anodes.
Display omitted
•The increasing use of Ag nanoparticles is raising safety concerns for Human.•AgNPs are subject to various transformations before and after absorption in mammals.•A gap exists between ...in vitro and in vivo studies leading to discrepancies.•Cutting-edge imaging methods and speciation analysis provide clues for in vivo study.
Silver nanoparticles (AgNPs) are exponentially used in various consumer products including medical devices. This production leads to an increasing human exposure to silver in different forms. Indeed, AgNPs are subject to various transformations in aqueous aerobic conditions that trigger the production of Ag(I) species. The main environmental transformation produces the non-toxic species silver sulfide. Transformations occurring in mammals are more diverse and mainly depend on the interaction of AgNPs with thiol, chloride and proteins. Any of these species have a different impact on AgNPs and induces AgNP dissolution into Ag(I) species, aggregation and/or stabilization. The transformations occurring also depend on the exposure route. The main one is dietary but medical exposure is also growing with the massive use of nanosilver as biocide in medical devices. For the former, AgNP modifications and Ag distribution has been extensively studied using in vitro and in vivo models, while data related to medical use of nanosilver are scarce. However, most of the in vitro and in vivo data often remain inconsistent. In this review, we describe both in vitro, in cellulo and in vivo data about AgNP transformations, silver speciation and biodistribution. We try to reconcile all these data and describe the latest methods for the future studies of AgNP fate in mammals.
Photosynthesis is a unique process that allows independent colonization of the land by plants and of the oceans by phytoplankton. Although the photosynthesis process is well understood in plants, we ...are still unlocking the mechanisms evolved by phytoplankton to achieve extremely efficient photosynthesis. Here, we combine biochemical, structural and in vivo physiological studies to unravel the structure of the plastid in diatoms, prominent marine eukaryotes. Biochemical and immunolocalization analyses reveal segregation of photosynthetic complexes in the loosely stacked thylakoid membranes typical of diatoms. Separation of photosystems within subdomains minimizes their physical contacts, as required for improved light utilization. Chloroplast 3D reconstruction and in vivo spectroscopy show that these subdomains are interconnected, ensuring fast equilibration of electron carriers for efficient optimum photosynthesis. Thus, diatoms and plants have converged towards a similar functional distribution of the photosystems although via different thylakoid architectures, which likely evolved independently in the land and the ocean.
Bacterial spores owe their incredible resistance capacities to molecular structures that protect the cell content from external aggressions. Among the determinants of resistance are the quaternary ...structure of the chromosome and an extracellular shell made of proteinaceous layers (the coat), the assembly of which remains poorly understood. Here, in situ cryo-electron tomography on lamellae generated by cryo-focused ion beam micromachining provides insights into the ultrastructural organization of Bacillus subtilis sporangia. The reconstructed tomograms reveal that early during sporulation, the chromosome in the forespore adopts a toroidal structure harboring 5.5-nm thick fibers. At the same stage, coat proteins at the surface of the forespore form a stack of amorphous or structured layers with distinct electron density, dimensions and organization. By analyzing mutant strains using cryo-electron tomography and transmission electron microscopy on resin sections, we distinguish seven nascent coat regions with different molecular properties, and propose a model for the contribution of coat morphogenetic proteins.
In the quest for high-capacity Li-ion batteries, moving from classical intercalation reactions such as those occurring at graphite-based electrodes to alloying reactions is a promising alternative. ...Among active materials which form alloys upon lithiation, silicon is a good candidate thanks to its high theoretical capacity, although it shows limited cyclability due to significant aging effects. In comparison, germanium presents improved Li-ion conduction and mechanical properties. Mixing silicon and germanium, as in Si1−xGex alloys, is an attractive strategy for combining the best advantages of both elements. In this study, we report a combined operando X-ray diffraction (XRD) and electrochemical investigation of the influence of the germanium content on the (de)lithiation processes in crystalline Si1−xGex nanoparticle-based anodes during the first charge/discharge cycle. The alloyed particles, which show pronounced heterogeneities in composition, evidence a sequential amorphization of the different c-Si1−xGex phases depending on their Ge content, where the lithiation potential decreases upon increasing the silicon content, following Vegard's law-type of behavior. Operando XRD and galvanostatic cycling investigation of the highly lithiated crystalline phase Li15(Si1−xGex)4 evidence a narrow domain of existence with a composition close to x = 1. This study brings essential knowledge on the (de)lithiation mechanisms at play in Si1−xGex alloys, which is critical for mastering these promising materials that combine the best properties of silicon and germanium, with the possibility to tune their composition to tailor (de)lithiation properties and trade off performance and cycle life.
PDF
