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The chemical interactions in Fe–HfH2 metal matrix composites (MMCs) are studied across multiple length scales to elucidate the decomposition of the parent phases and corresponding reaction zone physics during direct current sintering. Fe–HfH2 composites were synthesized with increasing as-mixed hydride contents of Fe–25% HfH2, Fe–40% HfH2, Fe–55% HfH2, and Fe–70% HfH2 (all in vol. %) to demonstrate the ability to achieve sintered MMCs with target hydride contents. Samples were probed across multiple length scales through a multi-modal workflow employing x-ray diffraction, scanning electron microscopy and segmentation analysis, and synchrotron techniques including hard x-ray fluorescence mapping and nanoprobe x-ray absorption near-edge structure measurements. Under the selected sintering temperature and pressure conditions, hydrogen evolution is seen to evolve through parallel paths: thermal decomposition from during the transformation of HfH2 to HfHx<2 and through subsequent reaction with the Fe matrix leading to intermetallic phase formation. Specifically, HfFe and HfFe2 intermetallic formation accelerates the release of hydrogen with a subsequent HfO2 phase forming at grain boundaries. For this MMC, the consumption or loss of hydrogen can be considerable in compacts with initial hydride loading of 25%–40% HfH2 approaching 83% hydrogen loss for the lower volume fraction composites. Increasing the volume fraction of HfH2 to 70% enhanced the retained hydrogen content to 53% and attributed to the reduced interfacial area intrinsic to the increased HfH2 loading in this MMC. [ABSTRACT FROM AUTHOR]

Herein charge storage and transport properties are elucidated and cell degradation mechanisms of rechargeable aqueous Zn|α‐MoO3 batteries in three electrolyte systems (3 m ZnSO4, 3 m ZnCl2, and 30 m ZnCl2 [12.5 m] water‐in‐salt (WIS)) are distinguished by a combination of in situ X‐ray diffraction (XRD), in situ X‐ray absorption spectroscopy (XAS), operando optoelectrochemistry, and operando energy dispersive X‐ray diffraction (EDXRD). In conventional concentration 3 m electrolytes, in situ XRD and XAS, as well as ex situ scanning transmission electron microscopy data collectively support Zn2+ as the primary charge carrier. In addition, these systems are susceptible to cathode dissolution, Zn corrosion coupled with the hydrogen evolution reaction, and the resultant formation of basic zinc salt phases. The multi‐modal in situ and operando experimental analyses validate facile H+ intercalation and extraction in concentrated 30 m ZnCl2 WIS electrolyte. Via operando EDXRD, reaction front and charge transport limitation during discharge and charge in the viscous WIS electrolyte are spatially tracked. This work provides new insight into the stability and degradation mechanisms of aqueous zinc batteries during static storage and upon dynamic cycling, and highlights the utility of in situ and operando techniques in understanding the superior stability of WIS electrolytes. [ABSTRACT FROM AUTHOR]

Modulation of electron/ion transport in electrodes through the appropriate mesoscale electrode structural design is essential to achieving effective utilization of nanoscale electroactive materials. Herein, nanosheet MoS2+x/carbon [one-dimensional (1D) carbon nanotube (CNT) or two-dimensional (2D) graphene nanoplatelet (GNP)] heterostructures are prepared via a simple, one-step hydrothermal method, resulting in high-loading (16.2–21.0 mg/cm2) binder-free three-dimensional (3D) porous electrodes. In lithium-based batteries, an anionic S22––S2– redox system is demonstrated based on combined structural characterization using X-ray photoelectron spectroscopy, Raman spectroscopy, and in situ synchrotron-based X-ray absorption spectroscopy to elucidate the electrochemical behavior of the Mo and S centers. MoS2+x-GNP electrodes delivered 177 mAh/g (2.9 mAh/cm2) in the first cycle and 78 mAh/g (1.3 mAh/cm2) after 100 cycles at a current of 3.2 mA/cm2, representing high capacities despite such a high material loading for a sulfur-equivalent system, with 44% capacity retention and good rate capability. Conversely, the MoS2+x-CNT heterostructure displayed lower capacity and more capacity fade at all rates, attributed to aggregation of the active and carbonaceous materials in these electrodes and poor access to MoS2+x edge sites, as visualized via 3D Raman mapping and electron microscopy. The significantly improved capacity retention of the MoS2+x-GNP system is attributed to the (i) morphology because the arrangement of the 2D MoS2+x nanosheets on the GNP substrate allows for edge sites with excess sulfur to be exposed, (ii) increased stability of the structure during cycling, and (iii) homogeneous dispersion of the active and carbonaceous materials, resulting in good electrical contact. [ABSTRACT FROM AUTHOR]

The phase distribution of lithiated LVO in thick (∼500 μm) porous electrodes (TPEs) designed to facilitate both ion and electron transport was determined using synchrotron-based operando energy dispersive X-ray diffraction (EDXRD). Probing 3 positions in the TPE while cycling at a 1C rate revealed a homogeneous phase transition across the thickness of the electrode at the 1st and 95th cycles. Continuum modelling indicated uniform lithiation across the TPE in agreement with the EDXRD results and ascribed decreasing accessible active material to be the cause of loss in delivered capacity between the 1st and 95th cycles. The model was supported by the observation of significant particle fracture by SEM consistent with loss of electrical contact. Overall, the combination of operando EDXRD, continuum modeling, and ex situ measurements enabled a deeper understanding of lithium vanadium oxide transport properties under high rate extended cycling within a thick highly porous electrode architecture. [ABSTRACT FROM AUTHOR]

One of the inherent challenges with Li–S batteries is polysulfide dissolution, in which soluble polysulfide species can contribute to the active material loss from the cathode and undergo shuttling reactions inhibiting the ability to effectively charge the battery. Prior theoretical studies have proposed the possible benefit of defective 2 D MoS2 materials as polysulfide trapping agents. Herein the synthesis and thorough characterization of hydrothermally prepared MoS2 nanosheets that vary in layer number, morphology, lateral size, and defect content are reported. The materials were incorporated into composite sulfur‐based cathodes and studied in Li–S batteries with environmentally benign ether‐based electrolytes. Through directed synthesis of the MoS2 additive, the relationship between synthetically induced defects in 2 D MoS2 materials and resultant electrochemistry was elucidated and described. [ABSTRACT FROM AUTHOR]

mime-subtype="jpeg" mimetype="image" xlink:href="S2159685919000429_figAb" xmlns:xlink="http://www.w3.org/1999/xlink" /> Solid state batteries are an emerging alternative to traditional liquid electrolyte cells that provide potential for safe and high-energy density power sources. This report describes a self-forming, solid state battery based on the Li/I2 couple using an LiI-rich LiI(3-hydroxypropionitrile)2 electrolyte (LiI–LiI(HPN)2). As the negative and positive active materials are generated in situ, the solid electrolyte–current collector interfaces play a critical role in determining the electrochemical response of the battery. Herein, we report the investigation of solid electrolyte–current collector interfaces with a self-forming LiI–LiI(HPN)2 solid electrolyte and the role of varying interface design in reducing resistance during cycling. [ABSTRACT FROM AUTHOR]

Crystallite size reduction is a strategy utilized to increase deliverable capacity by decreasing the path length for lithium ion diffusion. However, reduction in crystallite size may also exacerbate unfavorable reactions within a battery limiting cycle life. Here, differences in capacity retention are observed for silver containing α-MnO2 (silver hollandite, AgHol), with two crystallite sizes. Under 30 mA/g discharge, the smaller crystallite size material (AgHol-S, 5 nm) delivers 266 mAh/g initial capacity with 91% capacity decrease from cycles 2-50. In contrast, the larger crystallite size material (AgHol-L, 14 nm) has an initial capacity of 129 mAh/g and only 9% decrease from cycles 2-50. A second electrochemical test was conducted using a capacity limit rather than a voltage limit. Under those test conditions, the structural distortion for the two materials observed by X-ray absorption spectroscopy (XAS) was similar, yet the terminal voltage decrease was more significant for the small crystallite sized sample. Determination ofMn dissolution revealed Mn solubility 5.4X higher for AgHol-S than AgHol-L with accompanying higher Mn deposition on the negative electrode and increased cell impedance. This study provides quantitative determination of capacity fade as related to structural distortion and transition metal dissolution as related to crystallite size. [ABSTRACT FROM AUTHOR]

A series of V-substituted α-MnO 2 (K x Mn 8- y V y O 16 · n H 2 O, y = 0, 0.2, 0.34, 0.75) samples were successfully synthesized without crystalline or amorphous impurities, as evidenced by X-ray diffraction (XRD) and Raman spectroscopy. Transmission electron microscopy (TEM) revealed a morphological evolution from nanorods to nanoplatelets as V-substitution increased, while electron-energy loss spectroscopy (EELS) confirmed uniform distribution of vanadium within the materials. Rietveld refinement of synchrotron XRD showed an increase in bond lengths and a larger range of bond angles with increasing V-substitution. X-ray absorption spectroscopy (XAS) of the as-prepared materials revealed the V valence to be >4+ and the Mn valence to decrease with increasing V content. Upon electrochemical lithiation, increasing amounts of V were found to preserve the Mn-Mn edge relationship at higher depths of discharge, indicating enhanced structural stability. Electrochemical testing showed the y = 0.75 V-substituted sample to deliver the highest capacity and capacity retention after 50 cycles. The experimental findings were consistent with the predictions of density functional theory (DFT), where the V centers impart structural stability to the manganese oxide framework upon lithiation. The enhanced electrochemistry of the y = 0.75 V-substituted sample is also attributed to its smaller crystallite size in the form of a nanoplatelet morphology, which promotes facile ion access via reduced Li-ion diffusion path lengths.

The phase distribution of lithiated LVO in thick (∼500 μm) porous electrodes (TPEs) designed to facilitate both ion and electron transport was determined using synchrotron-based operando energy dispersive X-ray diffraction (EDXRD). Probing 3 positions in the TPE while cycling at a 1C rate revealed a homogeneous phase transition across the thickness of the electrode at the 1st and 95th cycles. Continuum modelling indicated uniform lithiation across the TPE in agreement with the EDXRD results and ascribed decreasing accessible active material to be the cause of loss in delivered capacity between the 1st and 95th cycles. The model was supported by the observation of significant particle fracture by SEM consistent with loss of electrical contact. Overall, the combination of operando EDXRD, continuum modeling, and ex situ measurements enabled a deeper understanding of lithium vanadium oxide transport properties under high rate extended cycling within a thick highly porous electrode architecture.

One of the inherent challenges with Li-S batteries is polysulfide dissolution, in which soluble polysulfide species can contribute to the active material loss from the cathode and undergo shuttling reactions inhibiting the ability to effectively charge the battery. Prior theoretical studies have proposed the possible benefit of defective 2 D MoS 2 materials as polysulfide trapping agents. Herein the synthesis and thorough characterization of hydrothermally prepared MoS 2 nanosheets that vary in layer number, morphology, lateral size, and defect content are reported. The materials were incorporated into composite sulfur-based cathodes and studied in Li-S batteries with environmentally benign ether-based electrolytes. Through directed synthesis of the MoS 2 additive, the relationship between synthetically induced defects in 2 D MoS 2 materials and resultant electrochemistry was elucidated and described., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Fe 3 O 4 nanoparticles (NPs) with an average size of 8-10 nm have been successfully functionalized with various surface-treatment agents to serve as model systems for probing surface chemistry-dependent electrochemistry of the resulting electrodes. The surface-treatment agents used for the functionalization of Fe 3 O 4 anode materials were systematically varied to include aromatic or aliphatic structures: 4-mercaptobenzoic acid, benzoic acid (BA), 3-mercaptopropionic acid, and propionic acid (PA). Both structural and electrochemical characterizations have been used to systematically correlate the electrode functionality with the corresponding surface chemistry. Surface treatment with ligands led to better Fe 3 O 4 dispersion, especially with the aromatic ligands. Electrochemistry was impacted where the PA- and BA-treated Fe 3 O 4 systems without the -SH group demonstrated a higher rate capability than their thiol-containing counterparts and the pristine Fe 3 O 4 . Specifically, the PA system delivered the highest capacity and cycling stability among all samples tested. Notably, the aromatic BA system outperformed the aliphatic PA counterpart during extended cycling under high current density, due to the improved charge transfer and ion transport kinetics as well as better dispersion of Fe 3 O 4 NPs, induced by the conjugated system. Our surface engineering of the Fe 3 O 4 electrode presented herein, highlights the importance of modifying the structure and chemistry of surface-treatment agents as a plausible means of enhancing the interfacial charge transfer within metal oxide composite electrodes without hampering the resulting tap density of the resulting electrode.