9 Search Results

The silicon solid electrolyte interphase (SEI) faces cyclical cracking and reconstruction due to the ∼350% volume expansion. Understanding the SEI dynamic morphology and chemistry evolution from delithiated to lithiated states is thereby paramount to engineering a stable Si anode. Fluoroethylene carbonate (FEC) is a preferred additive with widely demonstrated enhancement of the Si cycling. Thus, insights into the dynamics of the FEC-SEI may provide hints toward engineering the Si interface. Herein, complementary ATR-FTIR, AFM, tip IR, and XPS probing reveal the presence of an elastomeric polycarbonate-like matrix in the FEC-generated SEI which is absent from the FEC-free SEI. Adding FECmore » to the baseline 1 M LiPF ₆ in EC:EMC (1:1) electrolyte promotes formation of a thinner and more conformal SEI, and subdues morphology and chemistry changes between consecutive half-cycles. From AFM, morphological stabilization of the FEC-SEI occurs earlier. Furthermore, conventional SEI biproducts such as Li ₂ CO ₃ and LiEDC appear in reduced quantities in the FEC-SEI implying a reduced quantity of Li-consuming species. The thin polymeric FEC-SEI enables deeper (de)lithiation of silicon. In conclusion, the enhanced mechanical compliance, chemical invariance, and reduced Li inventory consumption of the FEC-SEI are logically the key features underlying the Si cycling enhancement by FEC.« less

The hydrogen sorption properties of single-phase bcc (TiVNb)_100–xCr_x alloys (x = 0–35) are reported. All alloys absorb hydrogen quickly at 25 °C, forming fcc hydrides with storage capacity depending on the Cr content. Here, a thermodynamic destabilization of the fcc hydride is observed with increasing Cr concentration, which agrees well with previous compositional machine learning models for metal hydride thermodynamics. The steric effect or repulsive interactions between Cr–H might be responsible for this behavior. The cycling performances of the TiVNbCr alloy show an initial decrease in capacity, which cannot be explained by a structural change. Pair distribution function analysis ofmore » the total X-ray scattering on the first and last cycled hydrides demonstrated an average random fcc structure without lattice distortion at short-range order. If the as-cast alloy contains a very low density of defects, the first hydrogen absorption introduces dislocations and vacancies that cumulate into small vacancy clusters, as revealed by positron annihilation spectroscopy. Finally, the main reason for the capacity drop seems to be due to dislocations formed during cycling, while the presence of vacancy clusters might be related to the lattice relaxation. Having identified the major contribution to the capacity loss, compositional modifications to the TiVNbCr system can now be explored that minimize defect formation and maximize material cycling performance.« less

Lithium-ion battery safety and durability by nature are dependent on electrochemical and mechanical coupling. Interdisciplinary efforts are required to understand and quantify coupling behaviors. Here we design and conduct mechanically constrained charge and discharge characterizations with efforts supported by multiphysics modeling to unravel the coupling mechanisms of solid-liquid electrode-electrolyte and solid-solid active materials in lithium-ion batteries. We demonstrate that a lithium-ion battery cell under mechanical constraint exhibits a higher voltage during charging and a shorter charging time because of increased electrolyte resistance and decreased diffusivity caused by decreased electrode porosity. The reaction force response of the cell is a combinedmore » result of the cell structural response mechanically and lithium-ion intercalation/de-intercalation-induced volume variation electrochemically. Under mechanical constraint, cell capacity is significantly reduced in fast-charge scenarios; however, it can be recovered by a constant-voltage charge protocol. The results highlight the promise of multiphysics approaches to unravel the electrochemical-mechanical coupling mechanisms to direct battery system design and management.« less

Lithium sulfur (Li-S) batteries have the potential to outperform the current lithium ion batteries and transform the technology of the future. However, dissolution, diffusion, and shuttling of the dissolved polysulfides result in parasitic reactions and substantial capacity loss. To provide a better understanding of the shuttling process, a 1D porous electrode mathematical model has been developed in this paper. An approximation method is used to account for the shuttling-induced capacity loss by adding an extra source/sink term in the material balance equations for the species involved in the parasitic reactions. Shuttling constants used in the source terms can be determinedmore » by fitting the model predictions to the experimental measurements. Here, the results showed that by including the approximation method, the model was able to predict the active material loss and the continuous decrease of volume fractions of Li₂S on the cathode surface. The model sheds light on the capacity loss mechanism occurring inside the cell as a result of the shuttling of polysulfides.« less

Electrochemical water splitting is of prime importance to green energy technology. Particularly, the reaction at the anode side, namely the oxygen evolution reaction (OER), requires a high overpotential associated with O—O bond formation, which dominates the energy-efficiency of the whole process. Activating the anionic redox chemistry of oxygen in metal oxides, which involves the formation of superoxo/peroxo-like (O₂)^n–, commonly occurs in most highly active catalysts during the OER process. Here, a highly active catalyst is designed: electrochemically delithiated LiNiO₂, which facilitates the formation of superoxo/peroxo-like (O₂)^n– species, i.e., NiOO*, for enhancing OER activity. The OER-induced surface reconstruction builds an adaptivemore » heterojunction, where NiOOH grows on delithiated LiNiO₂ (delithiated-LiNiO₂/NiOOH). At this junction, the lithium vacancies within the delithiated LiNiO₂ optimize the electronic structure of the surface NiOOH to form stable NiOO* species, which enables better OER activity. This finding provides new insight for designing highly active catalysts with stable superoxo-like/peroxo-like (O₂)^n– for water oxidation.« less

Carbon-containing organic matter (OM) is constantly synthesized from atmospheric carbon dioxide (CO₂) by primary producing flora in Earth’s biosphere. The fate of this OM—i.e., how long it persists in the environment before being recycled back to atmospheric CO₂ by heterotrophic microbes and fauna—is highly variable, and largely dependent on the diversity of environmental conditions it is exposed to both at its origin and during transport to distant locations. This dynamic cycling of carbon, energy, and matter between the atmosphere and biosphere occurs within and across all types of terrestrial, aquatic, and marine ecosystems. While the underlying biological functions and chemicalmore » reactions related to carbon fixation and decomposition are generally common across ecosystems, the disciplines of terrestrial and aquatic biogeochemistry have historically pursued this topic along separate paths with differing strengths and weaknesses. Although this continues today, several focus areas have recently brought more cross-fertilization between these disciplines. One such focus area where terrestrial and aquatic communities have begun converging is the study of interactive effects on OM decomposition that occur when OM of different origins and reactivities mix. This line of research has embraced the necessity to consider reactivity within the context of the past history and present state of OM in all of its highly diverse forms. Interactive effects on OM cycling were first explored about 100 years ago in the context of soil humus mineralization and have since been termed priming effects. Priming can be defined as the enhancement of recalcitrant (stable) OM breakdown via microbial decay with the addition of a more labile (less-stable) OM source. Priming can involve dissolved and/or particulate OM, in some cases accompanied by nutrients, and results in more efficient decay/consumption of stable OM material than would have occurred otherwise in the absence of the less-stable OM. While much of the work on this topic began in terrestrial systems, aquatic researchers have followed suit and gained momentum in the last decade. Observations of priming in aquatic environments are becoming more widespread, but little consensus has been reached on their role, perhaps because we lack the mechanistic understanding to accurately predict when and where priming effects should occur. The motivation for the collection of studies summarized below is to progress towards a common language, set of experimental approaches, and perspective on the role of priming effects in both terrestrial and aquatic ecosystems.« less

Abstract Here, we examine how marine microbial communities respond when dissolved organic matter (DOM) is mobilized from coastal wetlands. Biological transformations of this DOM may increase in the presence of reactive substrates, such as algal‐derived DOM (ADOM) in the coastal zone—a process known as priming. We performed laboratory experiments examining transformations of DOM derived from coastal wetland peat (PDOM) with and without the presence ADOM. Associated shifts in microbial community composition and functional gene abundance were measured to evaluate mechanisms of priming effects. ADOM presence stimulated CO ₂ production when compared to the seawater control, which was further enhanced inmore » the copresence of PDOM. DOM characterization showed a substantial difference in features present at the end of the incubation when PDOM was present with and without ADOM, while metagenomic sequencing indicated shifts in microbial community composition and identified 23 unique functional genes associated with pathways for the breakdown of aromatic compounds.« less

Evidence for microbial Fe redox cycling was documented in a circumneutral pH groundwater seep near Bloomington, Indiana. Geochemical and microbiological analyses were conducted at two sites, a semi-consolidated microbial mat and a floating puffball structure. In situ voltammetric microelectrode measurements revealed steep opposing gradients of O₂ and Fe(II) at both sites, similar to other groundwater seep and sedimentary environments known to support microbial Fe redox cycling. The puffball structure showed an abrupt increase in dissolved Fe(II) just at its surface (~5 cm depth), suggesting an internal Fe(II) source coupled to active Fe(III) reduction. Most probable number enumerations detected microaerophilic Fe(II)-oxidizingmore » bacteria (FeOB) and dissimilatory Fe(III)-reducing bacteria (FeRB) at densities of 10² to 10⁵ cells mL^-1 in samples from both sites. In vitro Fe(III) reduction experiments revealed the potential for immediate reduction (no lag period) of native Fe(III) oxides. Conventional full-length 16S rRNA gene clone libraries were compared with high throughput barcode sequencing of the V1, V4, or V6 variable regions of 16S rRNA genes in order to evaluate the extent to which new sequencing approaches could provide enhanced insight into the composition of Fe redox cycling microbial community structure.The composition of the clone libraries suggested a lithotroph-dominated microbial community centered around taxa related to known FeOB (e.g., Gallionella, Sideroxydans, Aquabacterium). Sequences related to recognized FeRB (e.g., Rhodoferax, Aeromonas, Geobacter, Desulfovibrio) were also well-represented. Overall, sequences related to known FeOB and FeRB accounted for 88 and 59% of total clone sequences in the mat and puffball libraries, respectively. Taxa identified in the barcode libraries showed partial overlap with the clone libraries, but were not always consistent across different variable regions and sequencing platforms. However, the barcode libraries provided confirmation of key clone library results (e.g., the predominance of Betaproteobacteria) and an expanded view of lithotrophic microbial community composition.« less