The Li-S battery has the potential to replace Li-ion batteries in high capacity and high gravimetric energy density applications, but certain technical challenges result in diminished cycle life and have hindered its commercialization. Lab-scale X-ray micro-tomography was performed on an elemental sulfur electrode and a miniaturized in-situ tomography Li-S cell, and the 3D visualization achieved with this technique provides a wealth of information, improving understanding of the evolution of morphological and microstructural parameters of the different phases. As X-ray imaging is inherently non-destructive, it enables these parameters to be observed in-situ as a function of cycle life and state of charge. The inherently anisotropic nature of active material dissolution, recrystallization and other degradation processes within the electrode necessitates a three-dimensional approach to enable their visualization and quantification, and X-ray tomography is a useful tool in informing the development of more optimal electrode designs.
The thermal conductivity of nitrogen-doped Ge 2 Sb 2 Te 5 (N-GST) was analyzed using Frequency Domain Thermoreflectance (FDTR). The thermal conductivity of amorphous N-GST (~0.15 W/m-K) was not found to change significantly as the nitrogen concentration was raised from 0 at% to ~6 at%, possibly due to the huge amount of phonon scattering in the disordered films. The thermal conductivity of crystalline N-GST films was found to increase initially with increasing N content, but then to decrease upon further N addition. X-ray diffraction spectra of N-GST films show increasing defect density that correlates with the decrease in thermal conductivity of the crystalline films at higher nitrogen content.
Abstract Vast quantities of powder leave production lines each day, often with strict control measures. For quality checks to provide the most value, they must be capable of screening individual particles in 3D and at high throughput. Conceptually, X‐ray computed tomography (CT) is capable of this; however, achieving lab‐based reconstructions of individual particles has, until now, relied upon scan‐times on the order of tens of hours, or even days, and although synchrotron facilities are potentially capable of faster scanning times, availability is limited, making in‐line product analysis impractical. This work describes a preparation method and high‐throughput scanning procedure for the 3D characterization of powder samples in minutes using nano‐CT by full‐filed transmission X‐ray microscopy with zone‐plate focusing optics. This is demonstrated on various particle morphologies from two next‐generation lithium‐ion battery cathodes: LiNi 0.8 Mn 0.1 Co 0.1 O 2 and LiNi 0.6 Mn 0.2 Co 0.2 O 2 ; namely, NMC811 and NMC622. Internal voids are detected which limit energy density and promote degradation, potentially impacting commercial application such as the drivable range of an electric vehicle.
Neuromorphic computing has emerged as a highly promising alternative to conventional computing. The key to constructing a large-scale neural network in hardware for neuromorphic computing is to develop artificial neurons with leaky integrate-and-fire behavior and artificial synapses with synaptic plasticity using nanodevices. So far, these two basic computing elements have been built in separate devices using different materials and technologies, which poses a significant challenge to system design and manufacturing. In this work, we designed a resistive device embedded with an innovative nano-vacuum gap between a bottom electrode and a mixed-ionic–electronic-conductor (MIEC) layer. Through redox reaction on the MIEC surface, metallic filaments dynamically grew within the nano-vacuum gap. The nano-vacuum gap provided an additional control factor for controlling the evolution dynamics of metallic filaments by tuning the electron tunneling efficiency, in analogy to a pseudo-three-terminal device, resulting in tunable switching behavior in various forms from volatile to nonvolatile switching in a single device. Our device demonstrated cross-functions, in particular, tunable neuronal firing and synaptic plasticity on demand, providing seamless integration for building large-scale artificial neural networks for neuromorphic computing.
X-ray computed tomography (CT) has emerged as a powerful tool for the 3D characterisation of materials. However, in order to obtain a useful tomogram, sufficient image quality should be achieved in the radiographs before reconstruction into a 3D dataset. The ratio of signal- and contrast-to-noise (SNR and CNR, respectively) quantify the image quality and are largely determined by the transmission and detection of photons that have undergone useful interactions with the sample. Theoretical transmission can be predicted if only a few variables are known: the material chemistry and penetrating thickness e.g. the particle diameter. This work discusses the calculations required to obtain transmission values for various Li(NiXMnYCoZ)O2 (NMC) lithium-ion battery cathodes. These calculations produce reference plots for quick assessment of beam parameters when designing an experiment. This is then extended to the theoretical material thicknesses for optimum image contrast. Finally, the theoretically predicted transmission is validated through comparison to experimentally determined values. These calculations are not exclusive to NMC, nor battery materials, but may be applied as a framework to calculate various sample transmissions and therefore may aid in the design and characterisation of numerous materials.
LiNixMnyCozO2 (NMC) electrodes typically consist of anisotropic single-crystal primary particles aggregated to form polycrystalline secondary particles. Electrodes composed of polycrystalline NMC particles have a comparatively high gravimetric capacity and good rate capabilities but do not perform as well as single crystal equivalents in terms of volumetric energy density and cycling stability. This has prompted research into well-dispersed single-crystalline NMC products as an alternative solution for high-energy-density batteries. Here, for the first time known to the authors, electrochemical acoustic time-of-flight (EA-ToF) spectroscopy has been shown to be effective in distinguishing between Li-ion batteries composed of either single-crystal NMC811 (SC-NMC811) or polycrystalline NMC811 (PC-NMC811) electrodes. Cells composed of PC-NMC811 electrodes had a higher degree of gas evolution compared to cells containing SC-NMC811 electrodes. Cells composed of PC-NMC811 electrodes also underwent larger changes in the acoustic signal's time-of-flight (ToF) during constant current cycling at a range of C-rates indicating expansion, fracture or dislocation of the reflective interfaces inside the cell. In addition, X-ray computed tomography (X-ray CT) has been used to confirm significant morphological differences between SC-NMC811 electrodes and PC-NMC811 electrodes including the electrode's particle size distribution (PSD) that is suggested to have an effect on acoustic signal interaction with these electrode interfaces.
In this work, tantalum oxide (TaOJ based ring contact Resistive Random Access Memory (RRAM) devices with varying TaO x thicknesses (5, 10 and 15 nm) were demonstrated and evaluated. TaO x layers were deposited using atomic layer deposition and were in contact with a Platinum (Pt) top electrode and Tantalum (Ta) sidewall electrode. RRAM devices with different TaO x thickness were compared to investigate the scaling capabilities for potential 3D RRAM application. It was found that as the TaO x thickness scaled to 5 nm, reasonable switching characteristics with less cycling variations were obtained which indicates that a thickness of 5 nm TaO x is capable of being implemented in sidewall RRAM geometries.
Rechargeable lithium-based batteries are one of the key enabling technologies driving the shift to renewable energy, and research into novel technologies has intensified to meet growing demands in applications requiring higher energy and power density. The mechanisms behind battery degradation can be investigated across multiple length-scales with X-ray imaging methods; at the nano-scale severe constraints are imposed on sample size in order to obtain adequate signal to noise. Here, we present a novel laser-milling technique to prepare geometrically optimal samples for X-ray nano-tomography. Advantages of this technique include significantly reduced sample preparation time, and a suitable geometry for mosaic acquisition, enabling a larger field of view to be captured at high spatial resolution, thus improving statistics. The geometry of the resulting electrode remains highly suitable for nano-tomography, and yet permits in situ and operando experiments to be carried out on standard electrode coatings, providing new insights into transient phenomena whilst closely mimicking standard electrochemical cells.
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