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Summary Room-temperature sodium-sulfur batteries have significant potential for large-scale applications due to the low cost and high energy density of both sulfur and sodium. Nevertheless, the insulating nature of sulfur and the shuttle effect are impeding their practical application. Here we report that dispersed single-atom Fe sites anchored on a nitrogen-doped carbon matrix present an atomic-level strategy for the development of sulfur hosts. The electronic structure of sulfur is modified by the atomically dispersed Fe-N4 sites, which can transfer the electron to sulfur, thereby enhancing its reactivity. The S@Fe1-NMC cathode delivers a high reversible capacity of 1,650 mAh g−1 initially and 540 mAh g−1 after 500 cycles at 100 mA g−1. A dual function mechanism is observed on S-Fe-N4 sites, which can activate the polysulfides by weakening the S-S bonds and accelerate Na+ diffusion into Na-poor regions to engender a high driving force for Na2Sx decomposition, thus inhibiting the shuttle effect.

The intermetallic Cu6Sn5 is ubiquitous in electronic interconnects where research has focused on controlling the size and distribution of this phase for improved performance. Cu6Sn5 also finds application as an anode material for advanced lithium-ion batteries. Cu6Sn5 anodes can be fabricated via an in-situ growth method involving the reaction between molten Sn and the Cu current collector. This manufacturing route offers some advantages over traditional anode fabrication however the process is slow, limiting its practical application. In this work we show the addition of 6 wt% Ni to the Cu current collector greatly accelerates the growth of (Cu,Ni)6Sn5 in Cu-xNi/Sn solid-melt couples, leading to a growth rate of up to 50x faster, reducing the processing time above 200 °C to less than 10 min. This research studies the dynamics of the formation of (Cu,Ni)6Sn5 between Cu-xNi alloys and liquid Sn through real-time observation using synchrotron X-ray imaging. The (Cu,Ni)6Sn5 growth dynamics are characterised, and the growth kinetics are analysed. Subsequently, the mechanism of the accelerated growth is investigated with electron backscatter diffraction and transmission electron microscopy. The results show the accelerated growth is due to the formation of η-(Cu,Ni)6Sn5 grains with two distinct Ni concentration ranges, leading to finer grains and spalling, which in turn facilitates the diffusion of Sn, enhancing the η-(Cu,Ni)6Sn5 formation kinetics.

The thermodynamic condition for phase formation in the Al–Si–Ti system is crucial for understanding the reason behind deteriorations of grain refinement and castability of Al–Si–Ti alloys. Seven Al–Si–Ti alloys annealed between 550 and 650 °C were used to clarify the inconsistencies of phase equilibria in the Al–Si rich region. The existences of τ1 (Zr3Al4Si5-type tetragonal), τ2 (ZrSi2-type orthogonal) and the three-phase equilibrium of τ1 + α-Al + Si were confirmed. Combined with a critical review of literature data, a CALPHAD-type thermodynamic description was developed for the phase equilibria in the Al–Si rich region of the Al–Si–Ti system between 550 and 900 °C. Meanwhile, edge-to-edge matching analysis according to the crystal structures of τ1 and τ2 shows that their nucleation efficacies for α-Al are both weaker than that of Ti(Al,Si)3. From the calculated phase equilibrium of L + τ2 + Ti(Al,Si)3 at 727 °C and the local equilibrium principle, τ2 would form on the surface of TiAl3 particle and deteriorate its grain refinement efficiency for α-Al. From the calculated liquidus projection, Ti(Al,Si)3 is the primary phase within 0–10.3 wt.% Si and 0.08–0.30 wt.% Ti. To avoid the formation of τ1 and τ2 for retaining good grain refinement efficiency and castability, a Ti/Si threshold was determined by thermodynamic calculations. Keywords: Aluminum alloys, Phase diagram, CALPHAD, Grain refinement, Ti/Si threshold

The directional coefficient of thermal expansion (CTE) of intermetallics in electronic interconnections is a key thermophysical property that is required for microstructure-level modelling of solder joint reliability. Here, CTE ellipsoids are measured for key solder intermetallics using synchrotron x-ray diffraction (XRD). The role of the crystal structure used for refinement on the CTE shape and temperature dependence is investigated. The results are used to discuss the βSn-IMC orientation relationships (ORs) that minimise the in-plane CTE mismatch on IMC growth facets, which are measured with electron backscatter diffraction (EBSD) in solder joints on Cu and Ni substrates. The CTE mismatch in fully-intermetallic joints is discussed, and the relationship between the directional CTE of monoclinic and hexagonal polymorphs of Cu6Sn5 is explored.