Transient Chemo-Mechanical Model of Lithium Stripping/Plating Impacted by External Pressure

Electronic devices have been advanced rapidly over the last few decades with improved performance through high-level integration. Lithium ion batteries (LIB), which is representative rechargeable energy storage system, is increasingly demanding to high-energy-density storage system for the stable operation of high performance devices like mobile, laptop, etc. In addition, a recent quantum leap in electronic vehicles (EVs) require to energy storage system with long cycling stability incomparable to previous electronic devices. To achieve high performances and long lifetime, the use of lithium metal is one of attractive anode for as LIBs, because Li metal has high theoretical specific capacity of 3860 mAh/g, low redox potential of -3.04V (verse the standard hydrogen electrode) and low gravimetric density of 0.59 g/cm3. Nevertheless, since Li metal anode has the lithiation-delithiation mechanism of the ‘hostless’ electrochemical plating/stripping unlike the conventional graphite anode, it is confronted with serious problems occurred from uncontrollable interfacial reaction between surface of lithium metal anode and electrolyte applying to traditional LIB system; that is (1) the uncontrollable formation of solid electrolyte interphase (SEI) layer limitless volume expansion of Li metal anode (2) the dendritic growth and isolation of Li interface derived from inhomogeneous deposition of Li+ ion flux (3) the Li surface fracture induced by heterogeneously plated Li+ ion. Through these process, repetitive formation of undesirable SEI layer at surface of Li anode make fresh electrolyte dissipation and concurrently the anode surface becomes more distorted. These side-phenomena strongly correlate with low coulombic efficiency and decreasing lifetime of lithium metal battery (LMB) system where lithium metal is used as anode. In this works, in a dimensional aspect, to solve such problem mentioned above through stabilizing of surface of lithium metal anode, we introduce Janus-faced protective layer (JPL) as gel polymer electrolyte. JPL was composed with dual layer of Ni (3~7μm) embedded poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) and bare PVdF-HFP through simple casting method. The process of preparing JPL membrane is so simple to instantly bring in existing roll-to-roll process, and it is also possible to make a low cost process considered relatively low nickel price. In terms of mechanical property, it is based on flexible polymer and shows the merit of being foldable enough to able origami. In addition, JPL play a role of protection of Li metal anode. JPL has two functionalities. The metal part of JPL directly contacted with anode, and this layer was frameworks for preventing irregular SEI layer formation through inward plating of Li ion, the polymer part is stable state enough to be used as a gel polymer electrolyte. When lithium metal anode is subjected to cycle-test while keeping in contact with the nickel side of JPL membrane, Scanning electron microscope (SEM) image showed that the surface of lithium metal anode was very clean without any fluctuation compared to the case where only polypropylene (PP) separator was used. (Figure. 1) Moreover, as shown in Figure 2., the LMB system applied JPL show high stability of tolerable overvoltage within 5mV, 15mV even at high-current of 10mA/cm2, 20mA/cm2, respectively, in Li//JPL/JPL//Li symmetric cell. These results are attributable to effective function of each layer as mentioned earlier. JPL consists of two layer, the tough and adhesive nature of PVdF-HFP prevents the polymer part from being damaged or torn by dendritic growth and simultaneously ensure that metal part functions as robust framework for SEI layer formation without escaped particle from the membrane. This frameworks induce the SEI layer, which can act as a resistive element, to grown in the metal part while surface of Li metal anode become get out of main subject from the SEI layer formation. By virtue of that property, JPL has not allow forming resistive elements on the surface of Li metal anode, preventing the voltage rising up due to the formation of resistive elements at surface, so tolerability of overvoltage with clean surface of anode is maintained. In conclusion, the model study of nickel micro-particle/PVdF-HFP composite suggests the straightforward direction of protective layer to apply lithium metal as anode in LIB system with alleviating the problem caused by the ‘hostless’ property of lithium metal anode. Thus, when JPL is introduced to a LIB system, it shows a fairly positive possibility for high performance Lithium metal battery. Figure 1

Lithium metal batteries are widely considered to be a next-generation battery technology due to their high energy density, fast charging capability, and potential to power a wide range of applications, from portable electronics to electric vehicles.Compared to conventional lithium-ion batteries, which use graphite as the anode material, lithium metal batteries have the potential to offer significantly higher energy density. This is because lithium metal has a much higher theoretical capacity than graphite, meaning it can store more energy per unit weight or volume. As a result, lithium metal batteries could potentially offer longer run times and smaller form factors than lithium-ion batteries, which are already widely used in consumer electronics and electric vehicles.In addition to their high energy density, lithium metal batteries also offer fast charging capabilities. This is because the lithium metal anode can be charged more quickly than the graphite anode used in conventional lithium-ion batteries. This could enable faster charging times for electric vehicles and other applications, reducing the time required for recharging and improving their overall usability.However, one of the major challenges with lithium metal batteries is dendrite growth, which can occur when lithium metal ions deposit unevenly on the surface of the anode during charging. These dendrites are needle-like structures that can penetrate the separator and cause short-circuits, leading to reduced battery performance and safety issues. As a result, much of the research on lithium metal batteries has focused on developing strategies to prevent dendrite growth, such as using coatings or electrolytes with additives that can stabilize the lithium metal anode.Despite these challenges, lithium metal batteries continue to be a promising next-generation battery technology. Researchers are working on improving their energy density, charging speed, and safety, and they are exploring a range of applications, from portable electronics to electric vehicles and grid-scale energy storage. If these challenges can be overcome, lithium metal batteries could revolutionize the energy storage industry and enable a wide range of new and exciting applications.To address this issue, we have explored the use of various coatings on the lithium metal anode to prevent dendrite growth. In this study, ordered mesoporous silica with different pore sizes and pore structures, such as SBA-15 and KIT-6, were used as coatings between the lithium metal anode and separator.SBA-15 and KIT-6 are two types of mesoporous silica materials that are widely used in various applications due to their unique properties. The synthesis of these materials involves the use of templates to control the pore size and structure.They are synthesized using a combination of a surfactant(pluronic P123 or cetyltrimethylammonium bromide;CTAB) as the template and tetraethyl orthosilicate(TEOS) as the silica source. The synthesis involves mixing a solution of surfactant and TEOS in acidic conditions, followed by aging and calcination steps. The resulting materials have a highly ordered hexagonal pore structure(SBA-15) and body-centered cubic pore structure(KIT-6) with a pore size ranging from 5 to 20 nm.By coating the surface of the lithium metal with a uniform pore structure material such as ordered mesoporous silica, dendrite growth can be suppressed and lithium deposition can occur more uniformly.The uniform pore structure material acts as a physical barrier to lithium ion diffusion and helps to control the deposition of lithium ions onto the surface of the lithium metal. When lithium ions are deposited onto the surface of the lithium metal, they can form a layer of lithium that can grow and become thick over time. If the lithium layer is too thick, it can become unstable and form dendrites. However, the uniform pore structure material can help to limit the thickness of the lithium layer and promote the deposition of lithium ions in a more uniform manner, thus reducing the likelihood of dendrite formation.Additionally, the uniform pore structure material can help to reduce the concentration of lithium ions at the surface of the lithium metal, which is another factor that can contribute to dendrite growth. By limiting the concentration of lithium ions at the surface, the uniform pore structure material can help to prevent the formation of high-concentration regions that can promote dendrite growth.Overall, the mechanism by which a uniform pore structure material can suppress dendrite growth involves controlling the deposition of lithium ions onto the surface of the lithium metal, limiting the thickness of the lithium layer, and reducing the concentration of lithium ions at the surface. These factors help to promote more uniform lithium deposition and prevent the formation of dendrites, leading to improved battery performance and safety.

A widely applicable strategy to convert fabrics into lithiophilic textile current collector for dendrite-free and high-rate capable lithium metal anode

The focus of this document is to record the learning and process development achieved by the completion of the Nano-Engineering of Detector Surfaces to Offer Unprecedented Imager Sensitivity to Soft X-rays and Low Energy Electrons LDRD. The goal of this effort was to study different silicon detector surface preparation methods such as ion implant parameters, and the addition of a quantum 2-layer superlattice. Enabling the preparation of the surface of silicon detectors (front side illuminated or bonded backside illuminated) increases the responsivity of the diode to shallowly absorbed photons. This increased sensitivity in turn allows for greater fidelity in imaging events that emit low soft X-rays or low energy electrons. Prior work has focused on passivating the surface of a silicon detectors with thin layers (tens of nm thick) of materials to reduce surface recombination sites. Measurements of visible light quantum efficiency, electron responsivity, and pulsed x-ray response indicate that detectors with a 2- layer superlattice enjoy a significant benefit over equivalent detectors using an ion implant at the illuminated surface. ACKNOWLEDGEMENTS The research described in this LDRD was carried out at Sandia National Laboratories, under a contract with the Department of Energy, and at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Supported by the Laboratory Directed Research and Development program at Sandia National Laboratories, a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525.

We study the use of nanoelectrode arrays (NEAs), consisting of billions/cm2 of ~ 75 nm diameter electrodes, for the electrochemical analysis of ionic halogen species in water. Such NEA sensors were previously demonstrated to detect part-per-billion (ppb) levels of Pb-ions in aqueous solutions without supporting electrolytes. Briefly, the individual electrodes in the NEA can be tailored with sufficient separation coupled with pore-depth control so that each experiences non-overlapping hemispherical diffusion zones within which the ionic flux of an analyte is independent of time. This geometry is well-suited for trace-level detection, as fast voltage sweeps result in a large and steady-state current density. With optimized design, the additive response from the plethora of nanoelectrodes leads to an orders-of-magnitude analytical advantage for electrochemical detection compared to conventional (mm) sized disc electrodes using sweep or pulse voltammetric techniques. NEAs are fabricated by anodizing RF-sputter deposited Al films on a substrate-of-choice, resulting in billions/cm2 tailored with controllable pore diameters. Each nanopore is partially filled via electrochemical plating with an appropriate working electrode material, such as Au, Pt or Ni. A thin W film is beneath the nanopore template for both processing assistance and to provide a backside electrical contact in parallel to every nanoelectrode. In the case that the NEA is recessed within the porous alumina, a thin conducting film can be added to the topside to function as a counter/pseudo-reference electrode. In some situations, the counter electrode can also serve as an ion collector, preconcentrating ionic species near the pore openings prior to beginning an electrochemical measurement. Using such NEA sensors, we will demonstrate trace detection levels for both Cl and I ionic species in water, and compare the limits-of-detection with conventional electrodes. In addition, we explore the possibility of using NEA sensors to detect halogens in the gas phase. By manipulating the NEA structure, the monitoring capability may be extended to gas phase detection of Cl2 or I2. Such gas-phase detection is possible by utilizing the natural humidity in air condensing on the nanopore walls above the recessed working electrodes. Indirect sensing of such gases occurs after they dissolve in the pore water to form electrochemically detectable halogen species. Notably, the electrochemical measurement is achieved with simple, condensed humidity as the sole ionically conducting phase, without the need for a supporting electrolyte. This is because the high resistivity of water† is mitigated by the short ionic path length: the net solution resistance is small because of the sub-micron distance separating the NEA electrodes from the counter/pseudo-reference electrode sputtered upon the surface of the opposite (open) end of the pore. †The conductivity of humidity levels we consider in this study range from 10-6 S/m (humidity from DI water) to 10-3-10-4 S/m (conductivity range of natural humidity across the USA as monitored by the National Atmospheric Deposition Program’s National Trend Network). This work is supported by the Laboratory Directed Research and Development program at Sandia National Laboratories. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Metallic lithium anode has long stood as the “holy grail” in the field of secondary batteries for its high theoretical specific capacity and low electrochemical potential. But its edge is blunted by the inherent uncontrolled lithium dendrite growth that can curtail the cycle life and raise safety concerns. In this work, a functional modification layer from a derivant of natural silk is developed to protect lithium anode via a facile automatic transfer route. Via offering abundant functional group sites, the Li‐ion flux on the anode surface is made uniform efficiently. The silk fibroin‐based modification layer also contributes to the in situ formation of a Li3N‐rich solid electrolyte interphase film on the lithium anode. Consequently, a high‐performance lithium metal anode with dendrite‐free morphology and significantly enhanced cycle stability is achieved: when paired with LiFePO4 cathodes, the full cell achieves a long‐term cycling stability of 3000 cycles at 5 C; when paired with sulfur cathodes (5 mgsulfur cm−2), a long lifespan for over 400 cycles at 1 C is achieved. This work offers a facile and practical approach for the interface modification of the high‐performance lithium anode and as well as provides a new perspective for the application of biomass‐based materials in advanced batteries.

Lithium metal anodes (LMAs) are critical for high-energy-density batteries such as Li-S and Li-O2 batteries. The spontaneously formed solid electrolyte interface on LMAs is fragile, which may not accommodate the cyclic Li plating/stripping. This usually will result in a low coulombic efficiency (CE), short cycle life, and potential safety hazards induced by the uncontrollable growth of lithium dendrites. In this study, we fabricate a Li alginate-based artificial SEI (ASEI) layer that is chemically stable and allows easy Li ion transport on the surface of LMAs, thus enabling the stable operation of lithium metal anodes. Compared to bare LMAs, the ASEI layer-protected LMAs exhibit a more stable Li plating/stripping behavior and present effective dendrite suppression. The symmetric Li∥Li cells with the ASEI layer-protected LMAs can stably run for 850 and 350 h at current densities of 0.5 and 1 mA cm-2, respectively. Additionally, the LiFePO4∥Li full cell with the ASEI layer-protected LMA exhibits a capacity retention of about 94.0% coupled with a CE of 99.6% after 1000 cycles at 4 C. We believe that this study of engineering an ASEI brings a new and promising approach to the stabilization of LMAs for high-performance lithium metal batteries.

Surface engineering of commercial Ni foams for stable Li metal anodes

In the field of semiconductor quantum dot spin qubits, there is growing interest in leveraging the unique properties of hole-carrier systems and their intrinsically strong spin-orbit coupling to engineer novel spin qubits. In contrast to the weak spin-orbit interaction found in Si, strong spin-orbit coupling in Ge may allow purely electrical spin control using the electric field component of a microwave drive signal applied to a confinement gate, without the need for additional components such as microwave stripline antennas or micromagnets. A crucial aspect in the search for alternative semiconductor qubit host materials is the need to maintain the advantages of existing platforms such as Si: low disorder, long coherence times, extensibility, and semiconductor foundry compatibility. Recent advances in semiconductor heterostructure growth have made available high quality, undoped Ge/SiGe quantum wells that can serve as hosts for hole spin qubits. These quantum wells consist of a pure strained Ge layer flanked by Ge-rich SiGe layers above and below, grown by reduced pressure chemical vapor deposition. Isotopic enrichment is possible if required. The heavy hole charge carriers are characterized by a small effective mass m* ~ 0.08m 0 (about 2.4x lighter than for electrons in Si), high mobility μ ≥ 1E5 cm2/Vs, and highly anisotropic g-factors. The small effective mass should allow relatively large and easily-coupled quantum dots. The next-nearest light hole band is theoretically predicted to be on the order of ~ 100 meV below the heavy hole band. The p-orbital character of the hole wavefunction may provide an advantage in minimizing contact hyperfine interactions with nonzero-spin lattice nuclei. There is both theoretical and experimental evidence of a cubic Rashba-type spin-orbit interaction in this material, whose large strength is manifest as a spin-orbit length on the order of 1 micrometer. An additional advantage over Si is that the two-dimensional band structure of Ge quantum wells does not feature valley states, which can present difficulties for qubit operations. Here, we will describe our ongoing efforts to prepare spin qubits in this platform, including development of gated device architectures, device tuning protocols, and charge-sensing capabilities. Initial work focused on single-layer gate layouts, in which lithographically-defined single and double quantum dots were demonstrated at dilution refrigerator temperatures. Charging energies of ~ 1.7 meV were observed. These devices featured a broad and shallow potential landscape, and only a small number of holes could be confined to a quantum dot. Although adjacent quantum dots could be coupled to one another, this coupling was not easily tuned using this gate design. These limitations in the confinement and control of quantum dots motivated the subsequent adoption of multilayer gate-stack architectures, similar to what has been demonstrated in Si. Our three-layer devices feature gate electrodes designed for accumulation of holes, local depletion to form quantum dots, and selective isolation/screening of electric fields. Device structures feature Ti/Pt gates, ALD oxide dielectrics, and implanted ohmic contacts. Symmetrically constructed devices comprise two gated channels for quantum dot confinement, one to be used as the quantum dot under study and the other operated as a local charge sensor. By monitoring the conductance of the charge sensor as the quantum dot is tuned, we can remotely determine the dot’s occupation number, in principle down to the last hole. Iterative cycles of device fabrication and measurement, combined with numerical modeling, have allowed continuous improvements to the device design. Early three-layer device designs suffered from poor isolation between the upper and lower mirror-symmetric device channels. Numerical modeling showed (and measurements have confirmed) that an additional isolation gate could allow improved autonomy of the two channels while maintaining their electrostatic coupling needed for charge sensing. Ongoing, simulation-informed work to fine-tune the device geometry, as well as efforts toward a qubit demonstration, will be discussed. This work was funded, in part, by the Laboratory Directed Research and Development Program and performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the US Department of Energy (DOE) Office of Science. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the US Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525. The views expressed in this article do not necessarily represent the views of the US Department of Energy or the United States Government. The work at NTU was supported by the Ministry of Science and Technology (107-2622-8-002-018-). Figure 1

SiC- and GaN-based power semiconductor devices have in the past few years enabled great improvements in the efficiency and power density of switching power converters. A wide variety of SiC devices (e.g. MOSFETs, JFETs, BJTs, thyristors, and PiN/Schottky/JBS/MPS diodes) are now available from a number of manufacturers, and the same is true for GaN HEMTs. Thus, while vertical GaN devices are not yet mature, new research in the field is increasingly turning to the “ultra” wide-bandgap (UWBG) semiconductors, including diamond, gallium oxide, and aluminum gallium nitride (AlGaN), due to the expected scaling of the critical electric field as the bandgap to the 2.0-2.5 power. Notably, AlGaN is an alloy system, so that heterostructures are available, and it is also a polar material, which enables polarization doping. Both of these benefits significantly expand the range of device architectures that may be considered, compared to materials that do not have these properties; this is especially significant for UWBG materials, all of which have energetically deep impurity dopants that do not fully ionize at room temperature. This talk will report on both vertical PiN diodes and lateral HEMTs composed of Al-rich Al x Ga1-x N (x ≥ 0.7, EG ≥ 5.2 eV) designed as prototype power switching devices. The talk will begin with an overview of the properties of AlGaN that motivate its application to power switching, as well as an analysis of conduction and switching loss mechanisms as a function of AlGaN bandgap for various device types (PiN diodes, Schottky diodes, etc.) These results will be compared to similar metrics for SiC, GaN, and UWBG materials other than AlGaN. The talk will then present results on several PiN diode structures. All of the structures to be presented have thick (5-8 mm) Al0.7Ga0.3N drift regions doped in the 1-3×1016 cm-3 range, and were grown on thick (1.3 mm) sapphire substrates; due to the insulating nature of the substrate, the cathode contact is to a heavily-doped n-layer on the front side of the wafer in a so-called “quasi-vertical” configuration. The diodes differ in the design of the p-type anode. Homojunction diodes suffer from low free carrier density in the p-Al0.7Ga0.3N due to the low fraction of Mg than is ionized in material of such a wide bandgap (EA > 400 meV). Thus, two alternate approaches to achieve appreciable hole density were examined: heterojunction diodes in with the anode is composed of Al0.3Ga0.7N, in which reasonable Mg activation can be achieved; and diodes utilizing anodes in which the composition is graded from Al0.7Ga0.3N down to GaN. In order to avoid premature edge and/or surface breakdown, all diodes studied utilized a junction termination extension formed by nitrogen implantation into the p-region. The talk will conclude with a presentation of a second class of device, which is a power switching HEMT utilizing an Al0.85Ga0.15N/Al0.70Ga0.30N heterostructure. This heterostructure, which as a 25 nm thick barrier, is characterized by a pinch-off voltage of -4.5 V, a channel mobility of 250 cm2/Vs, and a channel sheet charge density of 6×1012 cm-2. The key challenge for Al-rich HEMTs has been the formation of Ohmic source and drain contacts; the current density in previous HEMTs reported by our group has been limited by the quasi-rectifying nature of these contacts. The HEMTs in the present work utilize planar source and drain contacts, as opposed to the etched-and-regrown contacts that we have reported previously; for those previous contacts, the regrown material was heavily-doped n-type GaN. The planar contacts in this study are composed of a Ti/Al/Ni/Au stack deposited directly on the Al0.85Ga0.15N barrier. While the current-voltage characteristics of these contacts are still quasi-rectifying, they have enabled a current density of 46 mA/mm, which is more than ten times greater than that achieved in our previous-generation AlGaN-channel HEMT, which had comparable channel sheet resistance. An effective breakdown field of ~170 V/um was achieved in a field-plated device with 4 um gate-to-drain spacing. This effective breakdown field exceeds that typically reported for GaN-channel HEMTs (~100 V/um), demonstrating the potential of AlGaN-channel HEMTs for high-performance power switching devices. This work was supported by the Laboratory Directed Research and Development (LDRD) program at Sandia. Sandia National Laboratories is a multi-mission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Redox random access memory (ReRAM), also known as resistive or memristive switching memory, has had a dramatic increase in research activity in the past several years due to the prospect of sub-10nm scaling, high endurance, low switching energy, and high switching speeds (1), (2). In addition, it shows promise for specialized applications including radiation hardened memory for space (3) and as a computational element (4). There is particular interest in the nonvolatile, analog behavior of ReRAM devices for use in neuromorphic computing applications. Numerous implementations of brain-inspired systems have been suggested, typically utilizing the ReRAM as a synapse-like element in a classical perceptron network (4), (5). A particularly efficient method of utilizing analog memristor behavior employs a ReRAM crossbar matrix based “neuromorphic accelerator,” which trains and executes a multilayer back-propagation algorithm and provides significant improvement in energy per operation and enhanced throughput over traditional hardware (6). This accelerator makes use of the resistive switching cell as a finely tunable nonvolatile analog resistor. Although it is often thought that variability and noise do not significantly affect a neuromorphic system, the simulated accuracy of our algorithm is reduced 8-30% when realistic variability is introduced in the device model. Hence, we have undertaken an effort to characterize and model the analog behavior and fundamental origins of variability in ReRAM devices. CMOS compatible TiN/TaOx/Ta/TiN ReRAM cells have been developed as described in (7). Analog behavior of the ReRAM devices has been comprehensively characterized both using the typical I-V hysteresis loops, as well as a comprehensive characterization of response to pulses of different length and voltages; an example of this is given in Fig. 1. Significant variability is present in these measurements, which is consistent with other bipolar metal oxide ReRAM results presented in the literature (8). Both phenomenological and ab initio modeling efforts are being employed to provide a further understanding of the fundamental sources of noise and variation. An analytical model was developed, based on joule heating, which shows that TaOx ReRAM has two state variables: the conductivity and radius of the filament (9). Hence, each resistance state has a number of different configurations which rely on this internal state of the device. The amount of time at a given pulse voltage for a given resistance state to transition to another state is not set for a particular resistance, but also depends on the internal state of the device. Density functional theory (DFT) calculations were used to further understand the microscopic origin of switching in TaOx (10). A significant observation from this work is that the oxidation state of the oxygen vacancy (VO) is a key determining factor of the conductivity in these films. In particular the VO 0 state behaves similar to an ionized donor in a semiconductor. Results of our modeling efforts are being utilized both to create a circuit level model for the simulation of the neuromorphic accelerator, as well as to reduce the variability of TaOx ReRAM devices. This presentation will further discuss the results of these modeling efforts, comparison of theory to experiment, and application to our neuromorphic computing system.The authors gratefully acknowledge contributions from J.J. Yang, S. Lam, D. Henze, and R.S. Williams of HP Labs. This work partially funded by Sandia’s Laboratory Directed Research and Development (LDRD) Program. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.REFERENCES:1. International Technology Roadmap for Semiconductors (ITRS), 2013 Edition, available at www.itrs.net.2. M.J. Marinella and V. Zhirnov, in Emerging Nanoelectronic Devices, Ch. 13, eds. A. Chen, V. Zhirnov, J. Hutchby, Wiley, (2014).3. D.R. Hughart et al, Trans. Nuclear Sci. 99 1 (2013).4. J.J. Yang et al, Nat. Nano. 8, 13-24, (2013).5. B. Swaroop et al, Intl. Symposium on Circuits and Systems, (1998).6. B. Aimone et al, at Neural Inspired Computing Elements Workshop, (2014).7. A.J. Lohn et al, ECS Trans 58, 211-220, (2013).8. K. Prall et al, at 4th International Memory Workshop, (2012).9. P.R. Mickel et al., accepted for publication in Adv. Mater. (2014).10. R.J. Bondi et al., J. Appl. Phys, 114, 203701, (2013).

The rich history of scalable computing research owes much to a rapid rise in computing platform scale in terms of size and speed. As platforms evolve, so must algorithms and the software expressions of those algorithms. Unbridled growth in scale inevitably leads to complexity. This special issue grapples with two facets of this complexity: scalable execution and scalable development. The former results from efficient programming of novel hardware with increasing numbers of processing units (e.g., cores, processors, threads or processes). The latter results from efficient development of robust, flexible software with increasing numbers of programming units (e.g., procedures, classes, components or developers). The progression in the above two parenthetical lists goes from the lowest levels of abstraction (hardware) to the highest (people). This issue's theme encompasses this entire spectrum. The lead author of each article resides in the Scalable Computing Research and Development Department at Sandia National Laboratories in Livermore, CA. Their co-authors hail from other parts of Sandia, other national laboratories and academia. Their research sponsors include several programs within the Department of Energy's Office of Advanced Scientific Computing Research and its National Nuclear Security Administration, along with Sandia's Laboratory Directed Research and Development program and the Office ofmore » Naval Research. The breadth of interests of these authors and their customers reflects in the breadth of applications this issue covers. This article demonstrates how to obtain scalable execution on the increasingly dominant high-performance computing platform: a Linux cluster with multicore chips. The authors describe how deep memory hierarchies necessitate reducing communication overhead by using threads to exploit shared register and cache memory. On a matrix-matrix multiplication problem, they achieve up to 96% parallel efficiency with a three-part strategy: intra-node multithreading, non-blocking inter-node message passing, and a dedicated communications thread to facilitate concurrent communications and computations. On a quantum chemistry problem, they spawn multiple computation threads and communication threads on each node and use one-sided communications between nodes to minimize wait times. They reduce software complexity by evolving a multi-threaded factory pattern in C++ from a working, message-passing program in C.« less

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration. The National Nuclear Security Administration’s Sandia Field Office administers the Prime Contract and oversees contractor operations at Sandia National Laboratories, California. Activities at this multi-program engineering and science laboratory support the nuclear weapons stockpile program, energy and environmental research, homeland security, micro-and nanotechnologies, and basic science and engineering research. The U.S. Department of Energy’s National Nuclear Security Administration and its management and operating contractor are committed to safeguarding the environment, assessing sustainability practices, and ensuring the validity and accuracy of the monitoring data presented in this annual site environmental report. This report provides a summary of environmental monitoring of information and compliance activities that occurred at Sandia National Laboratories, California during calendar year 2023 unless noted otherwise. General site and environmental program information is also included. This report was prepared in accordance with DOE O 231.1B, Admin Change 1, Environment, Safety and Health Reporting.

Lithium sulfur (Li-S) batteries are a promising option for high energy density applications, such as electric vehicles and grid storage. In addition to a high theoretical specific energy, the Li-S system also boasts a lower cost and the use of relatively nontoxic, abundant materials compared to current lithium ion batteries. However, soluble, mobile polysulfide intermediates in the electrolyte lead to a polysulfide shuttling mechanism resulting in damage to the anode, loss of active material, and diminished cyclability. A better understanding of the polysulfide speciation as a function of depth of discharge is warranted to identify means to mitigate the polysulfide shuttle. In response, polysulfide speciation is examined, under relevant conditions, in an operational coin cell, at varying states of charge and position, using in situ confocal Raman microscopy. Specifically, a spectroscopic 2032 coin cell was designed for use in in situ experiments while maintaining a representative environment for discharge. The coin cell consisted of a carbon-sulfur cathode, lithium metal anode, and 1:1 1,2-dimethoxyethane to 1,3-dioxolane with 1M LiTFSI and 0.25M LiNO3electrolyte. To aid in comparison, polysulfide standards were synthesized and investigated using electrospray ionization-mass spectroscopy (ESI-MS). Raman and ESI-MS were utilized to map polysulfide speciation and relative abundances along the discharge curve. The electrolyte within the cell was probed as a function of position within the cell to determine the spatial distribution of differing polysulfide species. Challenges associated with performing Raman spectroscopy within this environment, to differentiate the varying polysulfide species in solution, were also investigated. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000. Figure 1

The wide applications of high‐capacity lithium metal anodes for lithium metal batteries are restricted by the uncontrollable lithium dendrite growth caused by the uneven lithium deposition and the infinite volume change of lithium anodes during the plating/stripping process. Herein, the composite ionic/electronic interlayer of Li2S/Mo is deposited on the surface of stainless steel mesh (SSM) by in situ electrochemical conversion reaction from MoS2 nanosheet arrays. The Li2S/Mo interlayer with high ionic conductivity can regulate uniform lithium‐ion flux and promote homogeneous lithium deposition without dendrite growth. The half cells with Li2S/Mo‐modified SSM current collector show stable cycling performance of more than 400 cycles at 1 and 1 mAh cm−2, with the average Coulombic efficiency higher than 96%. By coupling with LiFePO4 cathodes, the assembled full cells demonstrate improved cycling performance. This work provides a new idea for using metal sulfides as a lithiophilic interlayer to facilitate dendrite‐free lithium deposition.