Extending the low-temperature operation of sodium metal batteries combining linear and cyclic ether-based electrolyte solutions.

Nonaqueous sodium-based batteries are ideal candidates for the next generation of electrochemical energy storage devices. However, despite the promising performance at ambient temperature, their low-temperature (e.g., < 0 °C) operation is detrimentally affected by the increase in the electrolyte resistance and solid electrolyte interphase (SEI) instability. Here, to circumvent these issues, we propose specific electrolyte formulations comprising linear and cyclic ether-based solvents and sodium trifluoromethanesulfonate salt that are thermally stable down to -150 °C and enable the formation of a stable SEI at low temperatures. When tested in the Na||Na coin cell configuration, the low-temperature electrolytes enable long-term cycling down to -80 °C. Via ex situ physicochemical (e.g., X-ray photoelectron spectroscopy, cryogenic transmission electron microscopy and atomic force microscopy) electrode measurements and density functional theory calculations, we investigate the mechanisms responsible for efficient low-temperature electrochemical performance. We also report the assembly and testing between -20 °C and -60 °C of full Na||Na3V2(PO4)3 coin cells. The cell tested at -40 °C shows an initial discharge capacity of 68 mAh g-1 with a capacity retention of approximately 94% after 100 cycles at 22 mA g-1.

Programming Semiconductor Nanowire Composition with Sub-100 nm Resolution via the Geode Process.

We demonstrate the vapor-liquid-solid growth of single-crystalline i-Si, i-Si/n-Si, and SixGe1-x/SiyGe1-y nanowires via the Geode process. By enabling nanowire growth on the large internal surface area of a microcapsule powder, the Geode process improves the scalability of semiconductor nanowire manufacturing while maintaining nanoscale programmability. Here, we show that heat and mass transport limitations introduced by the microcapsule wall are negligible, enabling the same degree of compositional control for nanowires grown inside microcapsules and on conventional flat substrates. Efficient heat and mass transport also minimize the structural variations of nanowires grown in microcapsules with different diameters and wall thicknesses. Nanowires containing at least 16 segments and segment lengths below 75 nm are demonstrated.

Melting, Crystallization, and Alloying Dynamics in Nanoscale Bismuth Telluride.

It is critical to understand the transformation mechanisms in layered metal chalcogenides to enable controlled synthesis and processing. Here, we develop an alumina encapsulation layer-based in situ transmission electron microscopy (TEM) setup that enables the investigation of melting, crystallization, and alloying of nanoscale bismuth telluride platelets while limiting sublimation in the high-vacuum TEM environment. Heating alumina-encapsulated platelets to 700 °C in situ resulted in melting that initiated at edge planes and proceeded via the movement of a sharp interface. The encapsulated melt was then cooled to induce solidification, with individual nuclei growing to form single crystals with the same basal plane orientation as the original platelet and nonequilibrium crystal shapes imposed by the encapsulation layer. Finally, heating platelets in the presence of antimony caused alloying and lattice strain, along with heterogeneous phase formation. These findings provide new insight into important transformation processes in layered metal chalcogenide materials.

Linking void and interphase evolution to electrochemistry in solid-state batteries using operando X-ray tomography.

Despite progress in solid-state battery engineering, our understanding of the chemo-mechanical phenomena that govern electrochemical behaviour and stability at solid-solid interfaces remains limited compared to at solid-liquid interfaces. Here, we use operando synchrotron X-ray computed microtomography to investigate the evolution of lithium/solid-state electrolyte interfaces during battery cycling, revealing how the complex interplay among void formation, interphase growth and volumetric changes determines cell behaviour. Void formation during lithium stripping is directly visualized in symmetric cells, and the loss of contact that drives current constriction at the interface between lithium and the solid-state electrolyte (Li10SnP2S12) is quantified and found to be the primary cause of cell failure. The interphase is found to be redox-active upon charge, and global volume changes occur owing to partial molar volume mismatches at either electrode. These results provide insight into how chemo-mechanical phenomena can affect cell performance, thus facilitating the development of solid-state batteries.

Distinct Nanoscale Interphases and Morphology of Lithium Metal Electrodes Operating at Low Temperatures.

While Li-ion batteries are known to fail at temperatures below -20 °C, very little is known regarding the low-temperature behavior of next-generation high-capacity electrode materials. The lithium metal anode is of particular interest for high-energy battery chemistries, but improved understanding of and control over its electrochemical and nanoscale interfacial behavior in diverse conditions is necessary. Here, we investigate lithium deposition/stripping, morphology evolution, and solid-electrolyte interphase (SEI) structure and properties down to -80 °C using an ether-based electrolyte (DOL/DME). As temperature is reduced, we find that the morphology of deposited lithium is significantly altered. Furthermore, cryogenic transmission electron microscopy coupled with vacuum-transfer X-ray photoelectron spectroscopy reveal that the SEI exhibits different structure, chemistry, thickness, and conductive properties at lower temperatures. These results show that Li is promising for batteries operating under extreme conditions, and the distinct nanoscale evolution of Li electrodes at different temperatures must be considered when designing high-energy batteries.

Low-Temperature Pack Aluminization Process on Pipeline Steel To Inhibit Asphaltene Deposition.

Asphaltene deposition in petroleum refineries is known to be problematic as it reduces efficiency and may lead to structural failure or production downtime. Though several successful approaches have been utilized to limit deposition through the addition of dispersants and inhibitors to petroleum, these methods require constant intervention and are often expensive. In this study, we demonstrate an innovative technique to engineer the surface chemistry of pipeline steels to inhibit asphaltene deposition. Pack aluminization, a standard industrial-scale chemical vapor deposition process, is employed at a low temperature of 600 °C to aluminize API 5L X65 high strength pipe steel substrates. The results showed deposit-free steel surfaces after high-pressure and high-temperature fouling experiments. The improvement is attributed to the formation of an aluminide intermetallic phase of Fe2Al5, which changes the native oxide chemistry to favor alumina over hematite. The continuous passivating oxide scale, acting as a protective barrier, mitigates asphaltene deposition and sulfidic corrosion. Because this process is based on alloying the surface of the steel and is not a coating with a weakly adhered interface, it is not prone to delamination, and it can be re-formed when damaged within the aluminized region. The combination of low-cost processing and improved antifouling characteristics makes surface chemistry modification of steel a promising preventative approach against asphaltene deposition.