Laser powder bed fusion additive manufacturing is an emerging 3D printing technique for the fabrication of advanced metal components. Widespread adoption of it and similar additive technologies is hampered by poor understanding of laser-metal interactions under such extreme thermal regimes. Here, we elucidate the mechanism of pore formation and liquid-solid interface dynamics during typical laser powder bed fusion conditions using in situ X-ray imaging and multi-physics simulations. Pores are revealed to form during changes in laser scan velocity due to the rapid formation then collapse of deep keyhole depressions in the surface which traps inert shielding gas in the solidifying metal. We develop a universal mitigation strategy which eliminates this pore formation process and improves the geometric quality of melt tracks. Our results provide insight into the physics of laser-metal interaction and demonstrate the potential for science-based approaches to improve confidence in components produced by laser powder bed fusion.

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Advances in the design of materials for energy storage and conversion (i.e., "energy materials") increasingly rely on understanding the dependence of a material's performance and longevity on three-dimensional characteristics of its microstructure. Three-dimensional imaging techniques permit the direct measurement of microstructural properties that significantly influence material function and durability, such as interface area, tortuosity, triple phase boundary length and local curvature. Furthermore, digital representations of imaged microstructures offer realistic domains for modeling. This article reviews state-of-the-art methods, across a spectrum of length scales ranging from atomic to micron, for three-dimensional microstructural imaging of energy materials. The review concludes with an assessment of the continuing role of three-dimensional imaging in the development of novel materials for energy applications.

In situ X-ray-based measurements of the laser powder bed fusion (LPBF) additive manufacturing process produce unique data for model validation and improved process understanding. Synchrotron X-ray imaging and diffraction provide high resolution, bulk sensitive information with sufficient sampling rates to probe melt pool dynamics as well as phase and microstructure evolution. Here, we describe a laboratory-scale LPBF test bed designed to accommodate diffraction and imaging experiments at a synchrotron X-ray source during LPBF operation. We also present experimental results using Ti-6Al-4V, a widely used aerospace alloy, as a model system. Both imaging and diffraction experiments were carried out at the Stanford Synchrotron Radiation Lightsource. Melt pool dynamics were imaged at frame rates up to 4 kHz with a ∼1.1 μm effective pixel size and revealed the formation of keyhole pores along the melt track due to vapor recoil forces. Diffraction experiments at sampling rates of 1 kHz captured phase evolution and lattice contraction during the rapid cooling present in LPBF within a ∼50 × 100 μm area. We also discuss the utility of these measurements for model validation and process improvement.

Anion exchange membranes (AEMs) are being developed for potential use in fuel cell systems which include portable power applications. In a fuel cell, these membranes transport hydroxide ions from the cathode to the anode. If carbon dioxide is present, carbonate and bicarbonate ions can form, displacing the hydroxide ions. Among the challenges this presents, the carbonate and bicarbonate are less mobile than the hydroxide and therefore the ionic conductivity of the membrane suffers. A procedure is outlined to take data from a permeation based water flux experiment and determine diffusion coefficients and the ionic conductivity of the membrane. The water-membrane diffusion coefficients can be measured from a water flux experiment. Using principles from kinetic theory, the water-membrane diffusion coefficient can be converted to an appropriate ion-membrane diffusion coefficient. Finally, an equation derived from the dusty fluid model can be used to calculate the ionic conductivity of the membrane in different counter ion forms. The calculated ionic conductivities have been shown to agree well with reported values for proton and anion exchange membranes.Anion exchange membrane fuel cells (AEMFCs) have received increased attention in recent years. The AEMFC typically operates at low temperatures, below 80 • C, and can utilize alcohol fuels; making it of possible appeal for portable power applications. Operating in a high pH environment allows for favorable alcohol oxidation kinetics and the ability to use non-platinum oxygen reduction catalysts. 1,2 Despite recent improvements, there are still several challenges confronting the technology. The low hydroxide ionic conductivity of the AEM and the formation of carbonate and bicarbonate species which further reduce the membrane's ionic conductivity are two such challenges that are examined in this study. 3,4 Current AEMs often use a polymer hydrocarbon backbone with benzyl-trimethylammonium fixed side chain groups. This cation is a strong base (pK b ≈ 1) which allows for reasonable dissolution of the hydroxide ions (OH − ) from the membrane and easy transport through the membrane. 5 The polymer backbone can range from several polymers including poly(ethylene-co-tetrafluoroethylene) (ETFE), poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP), polypropylene, and polysulphone. 6-10 In one study, a fully hydrated AEM with an ETFE backbone was reported to have an ionic conductivity of roughly 30 mS/cm at 30 • C. When comparing this to Nafion 115 proton exchange membrane (PEM), which has a similar IEC, the PEM has a much higher ionic conductivity around 90 mS/cm. 7 If carbon dioxide (CO 2 ) is present, then the formation of carbonate (CO 3 −2 ) and bicarbonate (HCO 3 − ) ions can affect the membrane in several ways. One effect is the decrease in pH, which might actually work to increase the stability of the membrane. 6 However, the same ion exchange process also reduces the ionic conductivity of the membrane. This happens because the carbonate species displace the hydroxide ...

We report on the design of a battery electrode architecture in which ion and electronic transport pathways are contiguous and span the entire volume of a thick, nonplanar electrode. It is shown that for a range of active materials conductivities, the length scale for electronic transport in such an architecture can be tuned by simple manipulations of the electrode design to enable good access to the active material. The benefits of such electrodes for basic science research and practical lithium metal batteries are demonstrated in low-N:P ratio cells in which a conventional (300−800 μm) Li foil is successfully cycled with LiCoO 2 cathodes with high areal capacities (10−28 mAh/cm 2 ).

Lithium-metal deposition on graphite anodes limits the cycle life and negatively impacts safety of the current state of the art Li-ion batteries. Herein, deliberate interfacial modification of graphite electrodes via direct current (DC) magnetron sputtering of nanoscale layers of Cu and Ni is employed to increase the overpotential for Li deposition and suppress Li plating under high rate charge conditions. Due to their nanoscale, the deposited surface films have minimal impact (∼0.16% decrease) on cell level theoretical energy density. Interfacial properties of the anodes are thoroughly characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and spatially resolved mapping X-ray absorption near edge structure (XANES) spectroscopy. The spectroscopic measurements indicate that the Cu and Ni coatings form oxide upon exposure to an ambient environment, but they are reduced within the electrochemical cell and remain in a metallic state. Li plating is quantified by X-ray diffraction and associated electrochemistry measurements revealing that the surface treatment effectively reduces the quantity of the plated Li metal by ∼50% compared to untreated electrodes. These results establish an effective method using interfacial modification to achieve deliberate control of Li-metal deposition overpotential and reduction of lithium plating on graphite.