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Ag-carbon composite interlayers have been reported to enable Li-free (anodeless) cycling of solid-state batteries. Here, we report structural changes in the Ag-graphite interlayer, showing that on charge, Li intercalates electrochemically into graphite, subsequently reacting chemically with Ag to form Li-Ag alloys. Discharge is not the reverse of charge but rather passes through Li-deficient Li-Ag phases. At higher charging rates, Li intercalation into graphite outpaces the chemical reactions with Ag, delaying the formation of the Li-Ag phases and resulting in more Li metal deposition at the current collector. At and above 2.5 mA·cm−2, Li dendrites are not suppressed. Ag nanoparticles do not suppress dendrites more effectively than does an interlayer of graphite alone. Instead, Ag in the carbon interlayer results in more homogeneous Li and Li-Ag formation on the current collector during charge.

We investigate using a reconfigurable metamaterial structure based on high permittivity dielectric elements in a flexible origami framework to control the electromagnetic response of a suspended patch antenna. Origami-inspired dielectric structures are fabricated by additive manufacturing of origami elements using an ABS-30 vol% BaTiO3 filament (permittivity ∼11 ). The printed millimeter-scale elements are then assembled into an origami structure using flexible polymer hinges. Alternatively, dielectric origami structures are also achieved using a flexible, polymer-only origami lattice pre-fabricated by stereolithography into which shaped high dielectric elements (permittivity ∼18 ) of ABS-60 vol% CaTiO3, manufactured by field assisted sintering, are inserted. The various dielectric origami designs are inserted into the air gap between a suspended patch antenna and a ground plane, designed to operate at a resonant frequency of 1 GHz. The presence of the dielectric origami modifies the antenna resonant frequency and tunablity is then achieved through different configurations of the dielectric origami, actuated by hand or mechanically. Tunability arises because varying the configuration, and overall density, of the dielectric origami varies its effective permittivity and thus the patch resonant frequency. The dielectric origami structures provide a tunable range up to ∼14% , in good agreement with numerical simulations. Simulations are also used to show how broader tunability could be achieved easily, for example, by optimizing the size of the dielectric elements. Overall, the results using these preliminary dielectric origami structures, enabled by combining advanced manufacturing techniques, suggest that the approach offers a wide design space with the potential to realise novel antenna functionality and flexibility.

To match the high capacity of metallic anodes, all-solid-state batteries require high energy density, long-lasting composite cathodes such as Ni-Mn-Co (NMC)-based lithium oxides mixed with a solid-state electrolyte (SSE). However in practice, cathode capacity typically fades due to NMC cracking and increasing NMC/SSE interface debonding because of NMC pulverization, which is only partially mitigated by the application of a high cell pressure during cycling. Using smart processing protocols, we report a single-crystal particulate LiNi0.83Mn0.06Co0.11O2 and Li6PS5Cl SSE composite cathode with outstanding discharge capacity of 210 mA h g-1 at 30 °C. A first cycle coulombic efficiency of >85, and >99% thereafter, was achieved despite a 5.5% volume change during cycling. A near-practical discharge capacity at a high areal capacity of 8.7 mA h cm-2 was obtained using an asymmetric anode/cathode cycling pressure of only 2.5 MPa/0.2 MPa.

Growth in the Li-ion battery market continues to accelerate, driven by increasing need for economic energy storage in the electric vehicle market. Electrode manufacture is the first main step in production and in an industry dominated by slurry casting, much of the manufacturing process is based on trial and error, know-how and individual expertise. Advancing manufacturing science that underpins Li-ion battery electrode production is critical to adding value to the electrode manufacturing value chain. Overcome the current barriers in the electrode manufacturing requires advances in material innovation, manufacturing technology, in-line process metrology and data analytics to improve cell performance, quality, safety and process sustainability. In this roadmap we present where fundamental research can impact advances in each stage of the electrode manufacturing process from materials synthesis to electrode calendering. We also highlight the role of new process technology such as dry processing and advanced electrode design supported through electrode level, physics-based modelling. To compliment this, the progresses in data driven models of full manufacturing processes is reviewed. For all the processes we describe, there is a growing need process metrology, not only to aid fundamental understanding but also to enable true feedback control of the manufacturing process. It is our hope this roadmap will contribute to this rapidly growing space and provide guidance and inspiration to academia and industry.

Commercial Li-ion cell electrodes comprise a random mix of the constituent materials largely unchanged for more than three decades. During fast charge/discharge, electrode-scale Li-ion concentration gradients develop, along with a spatially heterogeneous distribution of overpotential, utilization and degradation of active material, which ultimately restricts the range of realizable energy-power combinations. We expand energy-power characteristics and reduce cell degradation rate using electrodes that are compositionally graded at the microscale to homogenize active material utilization. Trapezoidal-graded composition LiFePO4 cathodes, enabled by a layer-by-layer deposition technique, are compared with conventional electrodes: at an energy density of 500 Wh L−1 the best graded electrode design increased power density from approximately 100 W L−1 to 630 W L−1, while at a power density of 300 W L−1, the energy density increased from approximately 420 Wh L−1 to 600 Wh L−1. The results highlight the potential for new manufacturing approaches and electrode designs to provide performance enhancements for existing and future Li ion battery chemistries.

Hot tears are detrimental defects forming during the final stage of solidification when the remaining liquid loses the capacity to compensate for liquid to solid volume shrinkage. Although a mature semi-quantitative description of hot tearing has been developed, little is known about the dynamic evolution of hot tears as experimental studies have been conducted mostly post-solidification or in semi-static in-situ conditions. Here, we present a methodology to investigate the evolution of hot tears with high spatial and temporal resolution using synchrotron-based X-ray radiography. We develop a novel hot tear detection and tracking algorithm for quantification of hot tear density, area fraction and merging from the analysis of radiographic sequences of the solidification of thin metal samples. The methodology is demonstrated for an Al-5wt%Cu alloy and examples of the results and new insights that can be achieved are described.

The energy transition is one of the main challenges of our society and therefore a major driver for the scientific community. To ensure a smart transition to a sustainable future energy scenario different technologies such as energy harvesting using solar cells or windmills and chemical storage in batteries, super-capacitors or hydrogen have to be developed and ultimately deployed. New fabrication approaches based on additive manufacturing and the digitalization of the industrial processes increase the potential to achieve highly efficient and smart technologies required to increase the competitiveness of clean energy technologies against fossil fuels. In this frame, the present roadmap highlights the tremendous potential of 3D printing as a new route to fully automate the manufacturing of energy devices designed as digital files. This article gives numerous guidelines to maximize the performance and efficiency of the next generation of 3D printed devices for the energy transition while reducing the waste of critical raw materials. In particular, the paper is focused on the current status, present challenges and the expected and required advances of 3D printing for the fabrication of the most relevant energy technologies such as fuel cells and electrolysers, batteries, solar cells, super-capacitors, thermoelectric generators, chemical reactors and turbomachinery.

Lithium-ion battery electrodes are on course to benefit from current research in structure re-engineering to allow for the implementation of thicker electrodes. Increasing the thickness of a battery electrode enables significant improvements in gravimetric energy density while simultaneously reducing manufacturing costs. Both metrics are critical if the transition to sustainable transport systems is to be fully realized commercially. However, significant barriers exist that prevent the use of such microstructures: performance issues, manufacturing challenges, and scalability all remain open areas of research. In this Perspective, we discuss the challenges in adapting current manufacturing processes for thick electrodes and the opportunities that pore engineering presents in order to design thicker and better electrodes while simultaneously considering long-term performance and scalability.

Hybrid solid-state batteries using a bilayer of ceramic and solid polymer electrolytes may offer advantages over using a single type of solid electrolyte alone. However, the impedance to Li+ transport across interfaces between different electrolytes can be high. It is important to determine the resistance to Li+ transport across these heteroionic interfaces, as well as to understand the underlying causes of these resistances; in particular, whether chemical interphase formation contributes to giving high resistances, as in the case of ceramic/liquid electrolyte interfaces. In this work, two ceramic electrolytes, Li3PS4 (LPS) and Li6.5La3Zr1.5Ta0.5O12 (LLZTO), were interfaced with the solid polymer electrolyte PEO10:LiTFSI and the interfacial resistances were determined by impedance spectroscopy. The LLZTO/polymer interfacial resistance was found to be prohibitively high but, in contrast, a low resistance was observed at the LPS/polymer interface that became negligible at a moderately elevated temperature of 50 °C. Chemical characterization of the two interfaces was carried out, using depth-profiled X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry, to determine whether the interfacial resistance was correlated with the formation of an interphase. Interestingly, no interphase was observed at the higher resistance LLZTO/polymer interface, whereas LPS was observed to react with the polymer electrolyte to form an interphase.

Synchrotron x-rays are a powerful tool to probe real-time changes in the microstructure of materials as they respond to an external stimulus, such as phase transformations that take place in response to a change in temperature. X-ray imaging techniques include radiography and tomography, and have been steadily improved over the last decades so that they can now resolve micrometer-scale or even finer structural changes in bulk specimens over time scales of a second or less. Under certain conditions, these imaging approaches can also give spatially resolved chemical information. In this article, we focus on the liquid to solid transformation of metallic alloys and the temporal and spatial resolution of the accompanying segregation of alloying elements. The solidification of alloys provides an excellent case study for x-ray imaging because it is usually accompanied by the progressive, preferential segregation of one or more of the alloying elements to either the solid or the liquid, and gives rise to surprisingly complex chemical segregation patterns. We describe chemical mapping investigations of binary and quasi-binary alloys using radiography and tomography, and recent developments in x-ray fluorescence imaging that offer the prospect of a more general, multielement mapping technique. Future developments for synchrotron-based chemical mapping are also considered.

We explore the impact of origami structure meta-materials on electromagnetic devices. Here two modular origami-inspired dielectric structures were fabricated by 3D printing with the ability to shift the resonant frequency of patch antennas operating at approximately 1 GHz. Tunablity was achieved by deploying different dielectric origami configurations that were actuated to control the degree of folding or compression when placed on top of a standard patch antenna. The measured effects of the dielectric origami structure is to provide a 2% range of tunability of the antenna resonance frequency, with simulations showing a similar trend as experiments. The demonstration of active tuning by actuation of dielectric origami may find application in future antenna and telecommunication systems.

Primary grain refinement using inoculant additions and intermetallic compound (IMC) phase selection are critical aspects in the solidification of commercial aluminum alloys, controlling the final mechanical properties in service. Although there have been studies which suggest there are explicit interactions between the two phenomena, they have yet to be fully elucidated. Here, through study of intermetallic phase particles extracted from an inoculated casting, key features relating to the nucleation of different intermetallic phases via eutectic reactions are recognized and explained. In particular, rake-like IMCs are identified as initiation points for the deleterious $$\beta $$ β -AlFeSi IMC phase in a model 6xxx series Al alloy. A mechanism is proposed for how $${\text{TiB}}_{2}$$ TiB 2 inoculant particles, which are commonly used for primary phase refinement, play a role in enhancing the nucleation of intermetallic phases during eutectic reactions at the liquid/ $$\alpha $$ α -Al interface in the final stages of solidification. The implication of this mechanism is that, after the event of primary grain refinement, any unused $${\text{TiB}}_{2}$$ TiB 2 inoculant particles could be contributing to IMC formation thereby affecting the overall type, size, and distribution of intermetallic phases in the solidified alloy.

Heterogeneous, multi-layered electrodes based on high power Li4Ti5O12 interleaved with a smaller fraction of high capacity Si were fabricated using layer-by-layer spray printing, with the goal of achieving a balance of power and capacity for Li-ion storage technologies. The faradaic charge/discharge behavior of the multi-layered hybrid electrodes was investigated as a function of (i) the thickness of the discrete Si layer within the multi-layered electrode, and (ii) the location of the Si layer within the electrode: on the top of the Li4Ti5O12 (closest to the separator), between two layers of Li4Ti5O12 (sandwich configuration) or at the Li4Ti5O12 base (next to the current collector but furthest from the separator). The optimum arrangement of Si spray printed on Li4Ti5O12 offered outstanding electrochemical performance at high current densities of 4000 mA/g and after 500 cycles when in a full Li-ion battery configuration coupled with a spray printed LiFePO4 cathode. The optimized multi-layered electrode was reliably reproduced as a double-sided coating over large area current collectors (≥20 cm × 15 cm). Sprayed printed electrodes were also readily patterned in-plane as well as through-thickness, offering the prospect for selective additions of high capacity Si or other active or inactive electrode components at specific locations to provide new Li-ion battery performance characteristics.

LiFePO4(LFP) electrodes for Li-ion battery applications were prepared by spray printing. By optimising the substrate temperature, solvent ratio and electrode material concentration, a honeycomb pore structure was produced over a large area electrode. In a liquid electrolyte, the honeycomb structured LFP electrode showed improved cycling performance at high C-rate due to shortened pore pathways and improved Li mobility. In a solid-state configuration, a PEO(LITFSI)-Li1.5Al0.5Ge1.5(PO4)3(PEO-LAGP) based solid electrolyte was either spray printed on top of the LFP and/or interleaved within sub-layers of the LFP electrode, for both non-honeycomb and honeycomb pore morphologies. Cross-sectional scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) mapping combined with electrochemical impedance spectroscopy (EIS) testing showed that the honeycomb electrode with inter-leaved sub-layers of solid-state electrolyte improved interfacial contact between the electrode and electrolyte. When coupled with Li foil in a solid-state Li ion battery configuration, the honeycomb interleaved electrode also showed the best performance in terms of capacity and cycle stability at all testing temperatures, showing capability that exceeded previously reported performance.

Preserving high energy densities of batteries at fast charge and discharge rates at the cell-stack level is a critical challenge for applications such as electric vehicles. Current manufacturing methods usually produce lithium (Li) ion battery electrodes 4-based cathodes containing fast ion transport pathways and a pore structure gradient through the electrode thickness that promote high energy densities at fast rates. The electrodes exhibit 94 mA h g-1 at an ultra-high current density of 15 mA cm-2 (67% higher gravimetric energy density at the cell-stack level including inactive components) compared with 47 mA h g-1 for conventional electrodes containing random structures and the same materials. X-ray computed tomography and modeling are used to quantify the electrode structure within different sub-domains and along orthogonal directions, which directly rationalizes the excellent dynamic performance. The electrode microstructure design, manufacturing method and characterization tools will be of use for other energy storage and conversion devices that rely on fast directional mass transport.

To match the high capacity of metallic anodes, all-solid-state batteries (ASSBs) re- quire high energy density, long-lasting composite cathodes such as Ni-Mn-Co (NMC)- based lithium oxides mixed with a solid-state electrolyte (SSE). However in practice, cathode capacity typically fades due to NMC cracking and increasing NMC/SSE in- terface debonding because of NMC pulverization, which is only partially mitigated by the application of a high cell pressure during cycling. Using smart processing proto- cols we report a single crystal particulate LiNi0.83Mn0.06Co0.11O2 and Li6PS5Cl SSE composite cathode with outstanding discharge capacity of 210 mAh g−1 at 30 °C. A first cycle coulombic efficiency of >85%, and >99% thereafter, was achieved despite a 5.5% volume change during cycling. A near-practical discharge capacity at a high areal capacity of 8.7 mAh cm−2 was obtained using a novel asymmetric anode/cathode cycling pressure of only 2.5 MPa/0.2 MPa.

Discrete layering of high power Li4Ti5O12and high capacity SnO2in a through-thickness multi-layered composite electrode was achieved using a layer-by-layer spray printing approach in order to explore new capacity-power combinations for lithium ion based electrochemical energy storage. Electrochemical behavior of multi-layered electrodes was optimized as a function of the thickness of the discrete SnO2layer, in the range 2 to 6µm, interleaved between two layers of low volume expansion Li4Ti5O12. Three discrete layers of 2µm SnO2were then interleaved evenly between Li4Ti5O12layers to produce a “layer cake” negative electrode cross-section that offered remarkable rate capability when coupled with a spray printed LiFePO4positive electrode in a lithium ion battery arrangement. The multi-layered negative electrode was also coupled with a spray printed activated carbon positive electrode in a lithium ion capacitor configuration, providing significant improvements in energy density. The double-sided fabrication of the multi-layer electrode over a 20×20cm2current collector area suggested a possible hybrid electrochemical device that combines attributes of high capacity lithium ion batteries and high power lithium ion capacitors.

Extreme deformation of high-entropy alloys increases toughness by converting crystalline structures to amorphous zones., Ever-harsher service conditions in the future will call for materials with increasing ability to undergo deformation without sustaining damage while retaining high strength. Prime candidates for these conditions are certain high-entropy alloys (HEAs), which have extraordinary work-hardening ability and toughness. By subjecting the equiatomic CrMnFeCoNi HEA to severe plastic deformation through swaging followed by either quasi-static compression or dynamic deformation in shear, we observe a dense structure comprising stacking faults, twins, transformation from the face-centered cubic to the hexagonal close-packed structure, and, of particular note, amorphization. The coordinated propagation of stacking faults and twins along {111} planes generates high-deformation regions, which can reorganize into hexagonal packets; when the defect density in these regions reaches a critical level, they generate islands of amorphous material. These regions can have outstanding mechanical properties, which provide additional strengthening and/or toughening mechanisms to enhance the capability of these alloys to withstand extreme loading conditions.

Solid-state Li metal batteries (SSLMBs) combine improved safety and high specific energy that can surpass current Li ion batteries. However, the Li+ ion diffusivity in a composite cathode—a combination of active material and solid-state electrolyte (SSE)—is at least an order of magnitude lower than that of the SSE alone because of the highly tortuous ion transport pathways in the cathode. This lowers the realizable capacity and mandates relatively thin (30–300 μm) cathodes, and hence low overall energy storage. Here, a thick (600 μm) hybrid cathode comprising vertically aligned LiNi0.8Mn0.1Co0.1O2 (NMC811)-rich channels filled with a [LiTFSI+PEGMA+MePrPyl TFSI] polymer composite electrolyte is fabricated by an innovative directional freezing and polymerization method. X-ray micro-computed tomography, ion mobility simulations, and DC depolarization show that the cathode structure improves Li+ ion diffusivity in the cathode from 4.4 × 10−9 to 1.4 × 10−7 cm2 s−1. In a SSLMB full cell at 25 oC, the cathode provides gravimetric capacities of 199 and 120 mAh g−1, and ultra-high areal capacities of 16.7 and 10.1 mAh cm−2 at 0.05 and 1 C, respectively. The work demonstrates a scalable approach to realizing composite cathode structures with kinetically favorable ion transport characteristics in SSLMBs.

Bragg edge tomography was carried out on novel, ultra-thick, directional ice templated graphite electrodes for Li-ion battery cells to visualise the distribution of graphite and stable lithiation phases, namely LiC12 and LiC6. The four-dimensional Bragg edge, wavelength-resolved neutron tomography technique allowed the investigation of the crystallographic lithiation states and comparison with the electrode state of charge. The tomographic imaging technique provided insight into the crystallographic changes during de-/lithiation over the electrode thickness by mapping the attenuation curves and Bragg edge parameters with a spatial resolution of approximately 300 &micro, m. This feasibility study was performed on the IMAT beamline at the ISIS pulsed neutron spallation source, UK, and was the first time the 4D Bragg edge tomography method was applied to Li-ion battery electrodes. The utility of the technique was further enhanced by correlation with corresponding X-ray tomography data obtained at the Diamond Light Source, UK.

Oxide Dispersion Strengthened (ODS) steels are candidates for fuel cladding materials in sodium-cooled fast reactors and for structural materials in nuclear fusion power reactors. The effect yttrium-titanium-oxygen (Y-Ti-O) nano-oxide precipitates within ODS steels have on the micromechanical deformation mechanisms has been investigated. The aim is to assess the extent of any direct link between the Y-Ti-O dispersion and nanoindentation hardness, using electron backscatter diffraction, transmission electron microscopy (TEM), and atom probe tomography (APT) studies of a Fe-14Cr-3W-0.2Ti-0.25Y2O3(wt%) ODS steel at room temperature. Y-Ti-O nanoclusters had a non-uniform distribution and average number density that ranged from 5.8±0.1×1023to 1.3±0.1×1024m−3and Guinier radii ranging from 1.8±0.2nm to 2.1±0.2nm. Surprisingly, the local Y-Ti-O distribution did not correlate strongly with the nanohardness, indicating that the dominant hardening mechanisms was at best only weakly related to the Y-Ti-O distribution. Instead, scanning TEM and APT confirmed that the dominant hardening mechanism was due to the grain boundary refinement, and was further enhanced by tungsten enrichment to ~3.5 at.% at grain boundaries.

The formation of primary Fe-rich intermetallic compound crystals and the effect of TiB2 and TiC inoculation during solidification of a hypereutectic Al-Fe alloy has been investigated. Both horizontal, near isothermal conditions and vertical, directional thermal gradient conditions were studied using laboratory and synchrotron X-ray radiography. TiB2 and TiC inoculation enhanced formation of Fe-rich intermetallics under all experimental conditions. Near isothermal solidification resulted in the highest intermetallic number density and average formation rate, whilst increasing the thermal gradient reduced both. A model for intermetallic crystal formation is proposed to explain the effect of thermal gradient and cooling rate on the intermetallic number density and average formation rate.

Computer-aided design software and additive manufacturing provide flexibility for the direct fabrication of multi-material devices. This design and fabrication versatility has been investigated for the manufacture of dielectric spiral phase plates (SPP) that generate electromagnetic waves with helical wavefronts. Three types of SPPs designed to produce an orbital angular momentum (OAM) mode number l = |1| were additively manufactured using material extrusion and polyjet fabrication methods. The OAM mode characteristics of the transformed helical microwaves as a function of the SPP geometrical features were investigated experimentally in the 12–18 GHz frequency range. The SPPs were further combined with an additively manufactured dielectric lens that provided a marked improvement in OAM mode purity. Finally, multiplexing and de-multiplexing of two OAM modes were demonstrated successfully using an optimum SPP geometry and arrangement.

The faceted growth of primary Al13Fe4 intermetallic compounds was studied using in-situ X-ray radiography in a solidifying Al-3Fe alloy. Microscopic twins were frequently observed in the growing intermetallics and were confirmed by post-solidification electron backscatter diffraction. A twin plane re-entrant growth mechanism was suggested, where repeated formation of re-entrant corners facilitated crystal growth along a preferential direction, forming elongated plates. In contrast, for intermetallics where this preferential growth was constrained by surrounding crystals, formation of layered twins perpendicular to the preferential direction was promoted and led to lower aspect ratios, known to be less deleterious to tensile properties.

Magnesium diboride (MgB2) bulk superconductors may have practical applications as permanent magnets owing to their ability to trap larger fields than conventional ferromagnets and a transition temperature of 39 K that make them attractive for use in cryogen-free systems. Unlike the cuprate high temperature superconductors, grain boundaries in MgB2 act as pinning sites not weak links, and so show good current carrying ability in polycrystalline samples. This enables the materials to be processed using standard ceramic processing methods which are scalable to large diameters and mass production. The maximum trapped field in bulk superconductors scales with the critical current density (Jc ) of the material as well as the radius of the sample. To obtain the highest possible Jc values in MgB2 at high fields requires the bulk materials to be fully dense but fine-grained material, and possibly with a nano-scale distribution of non-superconducting impurity particles to further enhance pinning. Field assisted sintering technology (FAST) is a rapid process for obtaining dense ceramics from materials like MgB2 which are difficult to sinter with conventional pressure-less techniques. Rapid heat treatments are attractive both from a manufacturing point of view and because the total time that the sample is held at high temperature is short, limiting grain coarsening. In this paper, we report a systematic study of the influence of processing temperature on microstructure and superconducting properties of MgB2 bulks manufactured using FAST. We conclude that processing temperatures above 1000 °C are required to obtain materials that have sufficiently high electrical connectivity to generate large magnetic moments. However, the intrinsic (intragrain) Jc values in MgB2 are better in the samples processed at 900 °C owing to their finer scale microstructures and the MgB2 lattice being more defective.

Homogeneous electrode structures used in Li-ion batteries (LIB) lead to inhomogeneous active material utilization and gradients of overpotential and Li-ion concentration at the cell-scale, which are detrimental for both capacity retention at high charge-discharge rates and for battery life-time. To account for these gradients, we demonstrate that heterogenous electrode structures with engineered gradients in material distribution can improve LIB C-rate and long-term cycling performance when compared with conventional uniform electrodes in LiFePO4 || Li4Ti5O12 full-cell LIBs. An improvement in C-rate performance of > 120% and a capacity degradation rate reduced to

In the last two decades, X-ray imaging techniques have been used increasingly to study metal solidification in real-time as, thanks to advances in X-ray sources (synchrotron and laboratory-based) and detector technology, images can now be obtained with spatio-temporal resolutions sufficient to record key phenomena and extract quantitative information, primarily relating to crystal growth. This paper presents an overview of the research conducted at the University of Oxford over the last 6 years as a partner in the UK’s Future Liquid Metal Engineering (LiME) Manufacturing Hub. The focus is on in situ X-ray radiography to investigate the solidification of Al alloys, including the formation of primary α-Al crystals, and the formation and growth of secondary intermetallic phases. Technologically, the thrust is to understand how to control as-cast phases, structures and element distributions, particularly elements associated with recycling, as a means to facilitate greater recirculation of aluminium alloys. We first present studies on refinement of primary α-Al, including extrinsic grain refinement using inoculation and intrinsic refinement based on dendrite fragmentation. Second, we describe studies on intermetallic phase formation and growth, because intermetallic fraction, morphology and distribution are frequently a limiting factor of alloy mechanical properties and recyclability. Then we present some of the latest progress in studying liquid flow during solidification and associated hot tear formation. Finally, future research directions are described.

High-entropy alloys (HEAs), based on equiatomic or near-equiatomic mixture of usually four or more elements, have attracted considerable attention as there are indications that along with surprising microstructural simplicity of some alloys, they may also offer intriguing combinations of mechanical and other properties. Amongst these properties, there is growing interest in the irradiation response of HEAs and their potential to withstand the neutron bombardment environment of future civil nuclear power plants. One of the first proposed HEAs is face-centred cubic CrMnFeCoNi, also known as the Cantor alloy, and the irradiation response of the Cantor alloy and its sub-systems are the focus of this review. Using irradiation analogues (electrons, heavy ions and He) to neutron bombardment and considering simulations, advanced microstructural analysis and property measurement, the Cantor alloy and its derivatives are shown to exhibit encouraging irradiation resistance that, in many instances, is superior to more traditional dilute alloys of the same elements. The beneficial aspects are high phase stability and resistance to radiation-induced segregation, smaller size but higher number density of dislocation loops, significantly lower extent of swelling and improved resistance to He bubble growth. The future research directions for irradiation resistant HEAs are also suggested.

[Image: see text] Directional, micron-scale honeycomb pores in Li-ion battery electrodes were fabricated using a layer-by-layer, self-assembly approach based on spray-printing of carbon nanofibers. By controlling the drying behavior of each printed electrode layer through optimization of (i) the volume ratio of fugitive bisolvent carriers in the suspension and (ii) the substrate temperature during printing, self-assembled, honeycomb pore channels through the electrode were created spontaneously and reliably on current collector areas larger than 20 cm × 15 cm. The honeycomb pore structure promoted efficient Li-ion dynamics at high charge/discharge current densities. Incorporating an optimum fraction (2.5 wt %) of high-energy-density Si particulate into the honeycomb electrodes provided a 4-fold increase in deliverable discharge capacity at 8000 mA/g. The spray-printed, honeycomb pore electrodes were then investigated as negative electrodes coupled with similar spray-printed LiFePO(4) positive electrodes in a full Li-ion cell configuration, providing an approximately 50% improvement in rate capacity retention over half-cell configurations of identical electrodes at 4000 mA/g.

Carbon nanostructures are promising materials for electrochemical energy storage but their frequency response is usually poor, limiting their utilization in high-frequency applications. Here we demonstrate the growth of carbon nanostructures with different dopants of N, B, P/N, B/N, and Si, based on a scalable aerosol-assisted chemical vapor deposition process. The doped carbon nanostructures were directly grown on the conductive Ni substrates and exhibit an open and porous structure which is beneficial for fast ion transport and ion kinetics. Coin cells made of the doped carbon nanostructures demonstrate a frequency response as fast as 13,200 Hz at a phase angle of −45° and the smallest relaxation time constant of ∼77 μs. Together with a low equivalent series resistance and a large areal capacitance, the high-frequency supercapacitors based on doped carbon nanostructures could be promising in replacing traditional aluminium electrolytic capacitors for many high-frequency electronic devices.

Thick electrodes (>500 μm) that minimize the proportion of inactive components (current collectors, separators, etc.) are attractive for high energy density lithium ion battery (LIB) cell-stacks. However, the tortuous porosity inside the electrodes usually restricts the use of these more cost-effective thick electrodes, because lithium ion diffusion becomes restricted and capacity reduces to impractical levels. To overcome this problem, we manufacture 900 μm thick cathodes with aligned pore arrays in the predominant ion transport direction using a scalable ice templating technique without the need for post-processing sintering. The aligned porosity combined with a coral-like electrode structure exhibited high areal and gravimetric capacities (14 mA h cm−2 and 142 mA h g−1 at 0.1C) as well as a sustained rate capability at faster (dis)charge rates (e.g. 12 mA h cm−2 and 124 mA h g−1 at 1C) that outperformed the capacities (0.5 mA h cm−2 and 141 mA h g−1 at 0.1C) and rate capability (e.g. 0.4 mA h cm−2 and 103 mA h g−1 at 1C) of conventional LIB electrodes containing the same materials and with a random microstructure fabricated by standard slurry casting. X-ray tomography and numerical modelling were used to quantify and confirm the aligned porosity benefits, which were preserved after many cycles of operation, along with robust mechanical integrity of the electrodes.

The nucleation of primary Pt-rich intermetallic compound (IMC) crystals was studied in a model Al-Pt-Er alloy as an analogue to Al 13 Fe 4 that forms in commercial Al alloys. The Pt-rich IMCs provided strong X-ray absorption contrast that allowed earlier detection of formation events and the resolution of solute diffusion fields. Crystal formation behaviour was investigated during directional and isothermal solidification when the alloy was inoculated with TiB 2 particles at cooling rates of 0.1 Ks − 1 to 8 Ks − 1 using in situ synchrotron X-ray radiography. Different from previous studies that concerned disordered, solid solution phases such as α -Al dendrites, for the first time nucleation bursts of ordered compound crystals were observed, where the nucleation of the IMC crystals proceeded in distinct cascades (in the time domain) or waves (in the spatial domain), the magnitude of which increased with increasing cooling rate and particularly with decreasing thermal gradient in the melt. Comparing the crystal number density with the estimated number density of TiB 2 particles suggested that the IMC crystals nucleated only on the most potent TiB 2 particles, accounting for ∼ 0.5% of the total TiB 2 number density in the melt. The effect of the thermal gradient and cooling rate on the magnitude of the nucleation waves and the IMC number density was revealed in terms of the available undercooling in the liquid in front of an individual IMC and the solute depleted liquid fraction that arose from the interaction of an ensemble of IMC crystals.

A 2-D generalized Maxwell fish-eye lens has been fabricated with all-dielectric polymer/ceramic composite materials and evaluated numerically and experimentally. The graded refractive index profile of the lens was discretized into a concentric-ring structure and functioned as a two-way beam splitter. Epoxy composites, with a broad dielectric constant range that can be precisely controlled, were used to cast the lens using a low-cost manufacturing method that can readily accommodate different geometries. The lens was tested with a near-field microwave imaging system to demonstrate its capability of controlling waves at an operating frequency of 18 GHz. The measured results had some differences from the expected behavior, which are considered in detail and provided some insights into the practical manufacturing and measurement constraints for graded dielectric composites. Possible routes to increase the number of output beams are discussed.

Vertically-aligned crystalline silicon carbide nanowires (VASiCs) (1 mm long and 50–90 nm in diameter) were synthesised in gram scale using SiO 2 -infiltrated vertically-aligned multi-wall carbon nanotubes (VACNTs) and Si powder. In situ residual gas analysis was employed to study their formation and revealed CO to be the main by-product during synthesis. The in situ studies also showed that the formation of VASiCs begins at 1150 °C with the growth rate reaching a maximum at 1350 °C. A possible growth mechanism was established based on both, in situ and ex situ characterisation. The VASiCs have an estimated band gap of 2.15 eV, are photocatalytically active, and show strong light absorbance of up to 577 nm. Under UV–vis light (260–800 nm) as grown VASiCs could remove 90% Rhodamine B (RhB) within 30 min. Over period of 4 h under visible light (400–800 nm) more than 95% RhB was removed demonstrating their potential as visible-light-driven photocatalysts.

The rapid microstructural evolution of gas atomised Ni superalloy powder compacts over timescales of a few seconds was studied using a Gleeble 3500 thermomechanical simulator, finite element based numerical model and electron microscopy. The study found that the microstructural changes were governed by the characteristic temperatures of the alloy. At a temperature below the γ' solvus, the powders maintained dendritic structures. Above the γ' solvus temperature but in the solid-state, rapid grain spheroidisation and coarsening occurred, although the fine-scale microstructures were largely retained. Once the incipient melting temperature of the alloy was exceeded, microstructural change was rapid, and when the temperature was increased into the solid + liquid state, the powder compact partially melted and then re-solidified with no trace of the original structures, despite the fast timescales. The study reveals the relationship between short, severe thermal excursions and microstructural evolution in powder processed components, and gives guidance on the upper limit of temperature and time for powder-based processes if desirable fine-scale features of powders are to be preserved. Keywords: Ni superalloys, Rapid heating and cooling, Powder consolidation, Electron microscopy, Gleeble thermomechanical simulator, Finite element modelling

Additive manufacturing (AM) techniques are used increasingly for the direct fabrication of microwave devices, such as graded index lenses and dielectric resonator antennas, which have spatially-varying dielectric properties (i.e. relative permittivity) that are difficult to manufacture using traditional methods. However, there is no effective method to characterize the spatial distribution of permittivity within the printed component, either during manufacture or once the component is complete. Therefore it is not possible to confirm the extent to which the manufactured spatial distribution of permittivity meets the intended design. We report the integration of a novel split ring resonator (SRR) surface mapping technique directly into an AM process to make non-destructive in-line measurements of the local relative dielectric permittivity ( ϵ r ) within 3D objects as they are formed. We then reconstruct these data into 3D dielectric “images” of the printed component. Detailed insights into the dielectric imaging principle, data processing/analysis, as well as limitations and opportunities related to the technique are described. The work aims to accelerate the design-make-test cycle for advanced microwave devices, and suggests the possibility for real-time, closed-loop control of dielectric properties during AM.

Through-electrode thickness honeycomb architectures were layer-by-layer self-assembled directly through a scalable printing process for ultrapower hybrid lithium-ion capacitor applications. Initially, the electrochemical performance of the pore-array electrodes was investigated as a function of the active material type (graphene plates, carbon nanofibers, and activated carbon). Inactive components (conductive carbon and polymer binder) were then minimized to 5 wt %. Finally, an optimized activated carbon-based cathode was paired with a spray-printed Li4Ti5O12-based anode and a range of anode-to-cathode mass ratios in a lithium-ion capacitor arrangement were investigated. A 1:5 anode/cathode mass ratio provided an attractive energy density comparable with a Li4Ti5O12/LiFePO4 lithium-ion battery but with outstanding power capability that was an order of magnitude greater than typical for lithium-ion batteries. The pore-array electrode was reproduced over areas of 20 cm × 15 cm in a double-sided coated configuration, and the option for selectively patterning electrodes was also demonstrated.

A symmetric solid-state battery based on organic porous electrodes is fabricated using scalable spray-printing. The active electrode material is based on a textile dye (disperse blue 134 anthraquinone) and is capable of forming divalent cations and anions in oxidation and reduction processes. The resulting molecule can be used in both negative and positive electrode reactions. After spray printing an inter-connected pore honeycomb electrode, a solid-state electrolyte (σLi: × 10−4 S cm−1) based on a polymeric ionic liquid is spray-printed as a second layer and infiltrated through the porous electrodes. A symmetric all-organic battery is then formed with the addition of another identical set of electrode and electrolyte layers. Both density functional theory calculations and charge-discharge profiles show that the potentials for the negative and positive electrode reactions are amongst the lowest (≈2.0 V vs Li) and the highest (≈3.5 V vs Li), respectively, for quinone-type molecules. Over the C-rate range 0.2 to 5 C, the battery has a discharge cell voltage of more than 1 V even up to 250 charge-discharge cycles and capacities are in the range 50–80 mA h g−1 at 0.5 C.

The impact of multi-layered electrode microstructures on the dynamic capacitance of electrochemical double layer supercapacitors is investigated. An electrochemical model that describes ion diffusion and double layer dynamics across the layered electrodes is first developed and then matched to experimental data. With TiO2 particulate and carbon nanotube layered electrodes, two knee frequencies were observed in the real and imaginary capacitance plots in both experiment and model simulations. These two knee frequencies resulted in an increase in real capacitance at high frequencies (ω ≈ 100 − 102 rad s−1) but a reduction at lower frequencies (ω ≈ 10−2 rad s−1), with the response being largely insensitive to the relative layer thicknesses. The increased capacity at high frequencies was due to increased ion mobility across the electrodes caused by the layering, allowing diffusion limitations of identical homogeneous electrodes to be overcome. These results imply the suitability of layered electrodes for applications with highly dynamic charge profiles and/or relatively thick electrodes.

Additive manufacturing (AM) may offer a flexible, cost-effective approach to address conventional manufacturing limitations, such as time-consuming, high work-in-progress, multi-step assembly. In principle AM can also allow more novel geometric or even bespoke designs of structural and functional products. However, in terms of energy storage devices such as batteries and supercapacitors, the benefits of AM have not yet been explored to any significant extent. In this paper, a hybrid-AM system, combining low-cost fused filament fabrication (FFF) and direct ink writing (DIW) techniques, has been designed to fabricate supercapacitors (electro-chemical double layer capacitors, EDLCs) in a single, automated operation. The inherent flexibility of the AM process provided an opportunity to address restrictions in geometric form factor associated with conventional planar supercapacitor manufacturing approaches. Functioning, ring-shaped EDLC devices were manufactured in a single, multi-material operation comprising symmetric activated carbon electrodes in a 1 Μ potassium hydroxide (KOH) electrolyte hydrogel. Gravimetric and areal electrode capacitances were 116.4 ± 0.6 F g−1 and 599.2 ± 3.0 mF cm−2 at 10 mV s−1, with a columbic efficiency of 99.6 ± 0.4% in the as-printed condition. The work aims to accelerate progress towards monolithic integration of energy storage devices in product manufacture, offering an alternative fabrication process for applications with irregular volume/shape and mass-customization requirements.

Li-ion battery cathodes based on LiFePO4 are fabricated by a layer-by-layer spray printing method with a continuous through thickness gradient of active material, conductive carbon, and binder. Compared with cathodes with the more usual homogeneous distribution, but with the same average composition, both C-rate and capacity degradation performance of the graded electrodes are significantly improved. For example at 2C, graded cathodes with an optimized material distribution have 15% and 31% higher discharge capacities than sprayed uniform or conventional slurry cast uniform cathodes, and capacity degradation rates are 40–50% slower than uniform cathodes at 2C. The improved performance of graded electrodes is shown to derive from a lower charge transfer resistance and reduced polarization at high C-rates, which suggests a more spatially homogeneous distribution of over-potential that leads to a thinner solid electrolyte interphase formation during cycling and sustains improved C-rate and long-term cycling performance.

A spray printing manufacturing approach to lithium-ion batteries was investigated with a focus on minimizing inactive fractions and maximizing energy and power densities of printable electrodes. Using a lithium titanate based anode initially and comparing with conventional electrodes, the effects of conductivity enhancer and binder fractions, post-calendaring effects, different electrode manufacturing methods, conductivity enhancer types and electrode thicknesses were explored, and optimum electrode structures were identified. These insights were then applied to a lithium iron phosphate based cathode, and full spray printed lithium titanate/lithium iron phosphate cell configurations were investigated. Notably, the full-cell battery with a 1:1 capacity ratio of lithium titanate to lithium iron phosphate had a stable specific energy density of ∼300 Wh/kg and a power density of ∼2500 W/kg, showing the promise of layer-by-layer spray printing to realize fully the intrinsic properties of electrode materials in lithium-ion battery cells.

The efficiency of new artificial pinning centres have been investigated in NbTi using the oxide dispersion strengthening (ODS) concept more typically applied to steels and Ni-superalloys. NbTi alloys containing a dispersion of nanoscale Y2Ti2O7 particles have been successfully manufactured through a powder metallurgy route by mechanical alloying Nb, Ti and Y2O3 nanopowders using high energy ball milling and subsequent consolidation and annealing. The microstructure and superconducting properties of the NbTi-Y2O3 have been characterised after each processing step. After 40 h of ball milling, the Y2O3 particles are dissolved into the nanostructured NbTi matrix formed by mechanical alloying of Nb and Ti. On annealing at temperatures above 800 °C the dissolved Y and O react with Ti from the matrix, and fine Y2Ti2O7 particles (

This paper presents all-dielectric materials used to 3D print coupons with spatially varying dielectric permittivity and possessing high dielectric anisotropy. The coupons were directly printed through a dual-filament fused deposition modelling technique utilizing bespoke feedstock filament comprised a polymer-based micro-ceramic composite with controlled permittivity and loss. By designing the arrangement of both high and low permittivity filament materials in the printed coupons, the microwave operating frequency and magnitude of Mie-type resonances could be manipulated to provide metamaterial-like characteristics. Keywords: Additive manufacturing, Fusion deposition, Dielectric composites, Metamaterials

Mill scale, which is a waste product from the steel industry, abundantly available and comprising a mixture of iron oxides, has been converted into hollow and porous Fe2O3 micro-rods using a facile and scalable chemical treatment. The Fe2O3 morphology and structure was characterised by a range of electron microscopy and other techniques, and then sprayed into large area electrodes that were investigated for electrochemical supercapacitor and lithium ion battery applications. The Fe2O3 supercapacitor electrode delivered a specific capacitance of 346 F g−1 at 2 mV s−1 with 88% capacitance retention after 5000 cycles, while the battery electrode delivered an initial reversible specific capacity of 953 mA h g−1 at 0.1C, reducing to 933 mA h g−1 after 100 cycles and to 673 mA h g−1 at 5C. The Fe2O3 electrodes had similar or superior performance to more costly, small batches of laboratory synthesised Fe2O3 in both supercapacitor and battery applications, which was ascribed to the hollow and porous structure that facilitated ion mobility throughout the electrodes, a high surface area and excellent strain accommodation during lithiation and de-lithiation.