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The chemical compatibility of metallic materials with thermal transfer/storage media, which often involves aggressive working conditions (i.e., high-temperature, corrosive environments), challenges the safe operations advanced and sustainable energy-related infrastructures. Here, we report the corrosion-oxidation behaviors three multi-component alloys (MCAs) when exposed to a corrosive heavy-liquid metal condition (i.e., molten at 650 degrees C with 10-6 wt% oxygen dissolved). The two compositions, Al0.36Cr0.67FeNi0.98 (HAl11) Al0.27Cr0.71FeNi1.16Nb0.17 (HAl8Nb), show excellent corrosion-resistance via passivating a protective oxide on the alloy surface. Further characterizations of the oxide layers differentiate their corrosion-oxidation mechanisms: a protective Al2O3 oxide layer (with Cr and Fe segregation outmost) formed on HAl11 and a duplex oxide layer (outward growth of FeCr2O4/Cr2O3 layer plus inward growth of an Al2O3 layer) with internal oxidation HAl8Nb. Adding Nb improved the corrosion-oxidation resistance ("Nb-doping effect") by enhancing the outward diffusion of metallic elements and promoting the rapid establishment of an alumina scale. Besides, the presence of AlNbO4, which was predicted by thermodynamics calculation, lying between the spinel and Al2O3 formation, was also confirmed by experimental observations. Our findings advance the mechanistic understanding of MCAs' performances in extreme conditions and provide novel strategies for designing corrosion-resistant alloys geting aggressive application environments.

Two different types of electrolytes (co-solvent and multi-salt) are tested for use in high voltage LiNi_0.5Mn_1.5O₄||Si/graphite full cells and compared against a carbonate-based standard LiPF₆ containing electrolyte (baseline). Ex situ postmortem XPS analysis on both anodes and cathodes over the life span of the cells reveals a continuously growing SEI and CEI for the baseline electrolyte. The cells cycled in the co-solvent electrolyte exhibited a relatively thick and long-term stable CEI (on LNMO), while a slowly growing SEI was determined to form on the Si/graphite. The multi-salt electrolyte offers more inorganic-rich SEI/CEI while also forming the thinnest SEI/CEI observed in this study. Cross-talk is identified in the baseline electrolyte cell, where Si is detected on the cathode, and Mn is detected on the anode. Both the multi-salt and co-solvent electrolytes are observed to substantially reduce this cross-talk, where the co-solvent is found to be the most effective. In addition, Al corrosion is detected for the multi-salt electrolyte mainly at its end-of-life stage, where Al can be found on both the anode and cathode. Although the co-solvent electrolyte offers superior interface properties in terms of the limitation of cross-talk, the multi-salt electrolyte offers the best overall performance, suggesting that interface thickness plays a superior role compared to cross-talk. Together with their electrochemical cycling performance, the results suggest that multi-salt electrolyte provides a better long-term passivation of the electrodes for high-voltage cells.

Spinel LiNi_0.5Mn_1.5O₄ as one of the high-energy positive electrode materials for next generation Li-ion batteries has attracted significant interest due to its economic and environmental advantages. However, the sensitivity of this type of material upon short to long term ambient storage conditions and the impact on the electrochemical performances remains poorly explored. Nevertheless, this remains an important aspect for practical large-scale synthesis, storage and utilization. Herein, we study and compare the evolution of surface chemistry, bulk crystal structure and elemental content evolution and distribution of LiNi_0.5Mn_1.5O₄ using a variety of characterization techniques including XPS and STEM-EDS-EELS, as well as electrochemical analysis. We show that Mn species dominate the outer surface (0–5 nm), while Ni and Li are preferentially located further away and in the bulk. The studied LiNi_0.5Mn_1.5O₄ material is found to be stable, with minor changes in surface or bulk characteristics detected, even after 12 months of storage under ambient air conditions. The low surface reactivity to air also accounts for the minor changes to the electrochemical performance of the air-exposed LiNi_0.5Mn_1.5O₄, compared to the pristine material. This study provides guidance for the appropriate storage, handling and processing of this high-performance cathode material.

Four types of MAX-phase coating samples (Cr2AlC, V2AlC, Ti2AlC, and Ti3AlC2), synthesized via physical vapor deposition and post-annealing of elemental multilayer films, have been investigated toward their potential corrosion protection in 10(-6) wt% oxygen-containing molten Pb for 3200 h at 600 degrees C. Three MAX-phase coatings (Cr2AlC, Ti2AlC, and Ti3AlC2) are corrosion resistant against the molten Pb, via formation of a protective oxide layer. Specifically, various oxide scales formed on each sample: an Al2O3 scale, containing a low amount of Cr2O3 was formed in case of the Cr2AlC coating; a mixed Al2O3 and TiO2 oxide scale was observed for both Ti2AlC and Ti3AlC2 coatings. A more complex mixed oxide layer consisting of VO2, V4O7, and Pb-3(VO4)(2) phases is formed on the V2AlC coating, while the MAX-phase coating was almost entirely consumed. According to their corrosion performance against oxygen containing molten Pb, the order of corrosion resistance is: Cr2AlC > Ti2AlC > Ti3AlC2 > V2AlC.