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Abstract: Batteries with inorganic solid-state electrolytes (ISSE) are attracting notable interest for next-generation systems implementing Lithium (Li) metal anodes, in view of achieving higher energy densities combined with superior safety. Notwithstanding extensive research and development work, this technology is not yet ready for industrial implementation, one of the key challenges being the stability of ISSEs, chiefly at the anodic interface. This work attacks this issue for the specific case of the LAGP/Li (Lithium Aluminium Germanium Phosphate/Lithium) interface with a micro-spectroscopic approach centred on post mortem Scanning Transmission X-ray Microscopy (STXM) of intact LMO/LAGP/Li thin-film batteries, microfabricated in discharged state. Pristine and cycled cells were mapped to pinpoint morphochemical changes, induced by electrochemical ageing. The evidenced shape changes, corresponding to mechanical damaging of the solid/solid electrodic interfaces correlate with LAGP decomposition at the anode, leading to reduction of Ge, whereas the chemical state at the cathodic interface is preserved. Thanks to its submicron spacial resolution, the STXM at the Ge L-edge and O K-edge spectra allowed to assess the highly localized nature of the chemical transformation of LAGP and its correlation with the formation of Li outgrowth features.

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Abstract: The Piauí laterite (NE Brazil) was initially evaluated for Ni but also contains economic concentrations of Co. Our investigations aimed to characterise the Co enrichment within the deposit; by understanding the mineralogy we can better design mineral processing to target Co recovery. The laterite is heterogeneous on the mineralogical and lithological scale differing from the classic schematic profiles of nickel laterites, and while there is a clear transition from saprolite to more ferruginous units, the deposit also contains lateral and vertical variations that are associated with both the original intrusive complex and also the nature of fluid flow, redox cycling and fluctuating groundwater tables. The deposit is well described by the following six mineralogical and geochemical units: SAPFE, a clay bearing ferruginous saprolite; SAPSILFE, a silica dominated ferruginous saprolite; SAPMG, a green magnesium rich chlorite dominated saprolite; SAPAL, a white-green high aluminium, low magnesium saprolite; saprock, a serpentine and chlorite dominated saprolite and the serpentinite protolith. Not all of these units are ‘ore bearing’. Ni is concentrated in a range of nickeliferous phyllosilicates (0.1–25 wt%) including serpentines, talc and pimelite, goethite (up to 9 wt%), magnetite (2.8–14 wt%) and Mn oxy-hydroxides (0.35–19 wt%). Lower levels of Ni are present in ilmenites, chromites, chlorite and distinct small horizons of nickeliferous silica (up to 3 wt% Ni). With respect to Co, the only significant chemical correlation is with Mn, and Mn oxy-hydroxides contain up to 14 wt% Co. Cobalt is only present in goethite when Mn is also present, and these goethite grains contain an average of 0.19 wt% Co (up to a maximum of 0.65 wt%). The other main Co bearing minerals are magnetite (0.41–1.89 wt%), chlorite (up to 0.45 wt%) and ilmenite (up to 0.35 wt%). Chemically there are three types of Mn oxy-hydroxide, asbolane, asbolane-lithiophorite intermediates and romanechite. Spatially resolved X-ray absorption spectroscopy analysis suggests that the Co is present primarily as octahedrally bound Co3+ substituted directly into the MnO6 layers of the asbolane-lithiophorite intermediates. However significant levels of Co2+ are evident within the asbolane-lithiophorite intermediates, structurally bound along with Ni in the interlayer between successive MnO6 layers. The laterite microbial community contains prokaryotes and few fungi, with the highest abundance and diversity closest to ground level. Microorganisms capable of metal redox cycling were identified to be present, but microcosm experiments of different horizons within the deposit demonstrated that stimulated biogeochemical cycling did not contribute to Co mobilisation. Correlations between Co and Mn are likely to be a relic of parent rock weathering rather than due to biogeochemical processes; a conclusion that agrees well with the mineralogical associations.

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Abstract: Sustainability, environmental and safety concerns raised by the increasing demand of batteries are driving research towards post-lithium technologies. Rechargeable Zn batteries are strong candidates, but still not practically viable, owing to the extensively studied, but poorly understood unstable behavior of Zn metal upon discharge-charge cycling. This limiting factor warrants more fundamental investigations and the present report provides the lacking molecular-level information on the Zn-based compounds forming at the electrode/electrolyte interface as a result of electrochemical cyclic in weakly acidic aqueous electrolyte. The results are obtained using ex situ X-ray absorption spectromicroscopy maps, modelled mathematically and complemented with cyclic voltammetry, symmetric-cell tests and electron microscopy. We have identified the role of the zincate precipitation resulting from local alkalinization during recharge, combined with additional zincate formation and decomposition to zinc oxide during discharge. The mathematical model allowed a transparent interpretation of morphochemical changes observed. The synergy of these processes leads to electrochemical localization effects, resulting in the formation of a complexly structured and low conductive ZnO-based template, that might play a role in driving shape changes.

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Abstract: The corrosion control of WC-Co type hardmetals is steadily gaining momentum for novel crucial applications in the Oil & Gas and food industries. The corrosion rate of the Co-based binder, and the extent to which coupling to WC speeds it up, are strongly influenced by alloying. In this paper, we investigate the impact of Cr on the corrosion-product film formation of Co- and CoNi based hardmetal binders in acidic, neutral and alkaline aqueous solutions. We centred our study on the role of Cr in driving the distribution of oxidized Co and Ni at the micrometre scale, thanks to synchrotron-based soft-X ray microspectroscopy. We have investigated morphochemical distributions for the following grades: Co96Cr4, Co48Ni48Cr4, Co50Cr50. Chemical-state mapping has been complemented by electrochemical measurements and metallographic observations. Amounts of Cr and Ni of ca. 50% notably increase the corrosion resistance in all ambients, with a stronger beneficial effect of the former element. 4% addition of Cr results in slight positive effects, with the exception of the CoNi system in alkaline ambient, that, together with Co50Cr50, outperforms the other grades. In all investigated alloy-ambient combinations, a continuous oxidized metal film grows, onto which micrometric island form of shape and dimensions that depend on the specific grade and aggressive conditions. Quantitative descriptors of chemical-state maps and their theoretical interpretation in terms of electrochemical phase-formation by oxy-hydroxide precipitation, allow to correlate the island patterns with the degree of pseudopassivation.

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Abstract: Iron (Fe) limits primary productivity and nitrogen fixation in large regions of the world’s oceans. Hydrothermal supply of Fe to the global deep ocean is extensive; however, most of the previous work has focused on examining high temperature, acidic, focused flow on ridge axes that create “black smoker” plumes. The contribution of other types of venting to the global ocean Fe cycle has received little attention. To thoroughly understand hydrothermal Fe sources to the ocean, different types of vent site must be compared. To examine the role of more diffuse, higher pH sources of venting, a hydrothermal plume above the Von Damm vent field (VDVF) was sampled for Total dissolvable Fe (unfiltered, TDFe), dissolved Fe (<0.2 μm, dFe) and soluble Fe (<0.02 μm, sFe). Plume particles sampled in situ were characterized using scanning electron microscopy and soft X-ray spectromicroscopy. The VDVF vents emit visibly clear fluids with particulate Fe (TDFe-dFe, >0.2 μm) concentrations up to 196 nmol kg–1 comparable to concentrations measured in black smoker plumes on the Mid-Atlantic Ridge. Colloidal Fe (cFe) and sFe increased as a fraction of TDFe with decreasing TDFe concentration. This increase in the percentage of sFe and cFe within the plume cannot be explained by settling of particulates or mixing with background seawater. The creation of new cFe and sFe within the plume from the breakdown of pFe is required to close the Fe budget. We suggest that the proportional increase in cFe and sFe reflects the entrainment, breakdown and recycling of Fe bearing organic particulates near the vents. Fe plume profiles from the VDVF differ significantly from previous studies of “black smoker” vents where formation of new pFe in the plume decreases the amount of cFe. Formation and removal of Fe-rich colloids and particles will control the amount and physico-chemical composition of dFe supplied to the deep ocean from hydrothermal systems. This study highlights the differences in the stabilization of hydrothermal Fe from an off-axis diffuse source compared to black smokers. Off-axis diffuse venting represent a potentially significant and previously overlooked Fe source to the ocean due to the difficulties in detecting and locating such sites.