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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Ultralight and fire-extinguishing current collectors for high-energy and high-safety lithium-ion batteries

Inactive components and safety hazards are two critical challenges in realizing high-energy lithium-ion batteries. Metal foil current collectors with high density are typically an integrated part of lithium-ion batteries yet deliver no capacity. Meanwhile, high-energy batteries can entail increased fire safety issues. Here we report a composite current collector design that simultaneously minimizes the ‘dead weight’ within the cell and improves fire safety. An ultralight polyimide-based current collector (9 μm thick, specific mass 1.54 mg cm-2) is prepared by sandwiching a polyimide embedded with triphenyl phosphate flame retardant between two superthin Cu layers (~500 nm). Compared to lithium-ion batteries assembled with the thinnest commercial metal foil current collectors (~6 µm), batteries equipped with our composite current collectors can realize a 16-26% improvement in specific energy and rapidly self-extinguish fires under extreme conditions such as short circuits and thermal runaway.

25 ENERGY STORAGE↗
DOE OSTI2016

Enhanced Electrical Resistivity and Properties via Ion Bombardment of Ferroelectric Thin Films

140 nm PbTiO 3 /20 nm SrRuO 3 thin-film heterostructures were grown on SrTiO 3 (001) single-crystal substrates via pulsed-laser deposition. In order to study the properties of these films, symmetric SrRuO 3 capacitor structures were fabricated using established techniques and dramatic differences were observed in the leakage characteristics of the heterostructures. The high-pressure O 2 and O 2 /Ar heterostructures reveal more than 2 orders of magnitude higher leakage current densities as compared to the low-pressure O 2 heterostructures. In turn, the high leakage current density of the heterostructures grown in high pressures precludes measurement of closed, saturated ferroelectric hysteresis loops, while nearly-square, fully saturated and closed hysteresis loops can be measured for the low-pressure O 2 heterostructures. The defects responsible for poor transport and ferroelectric properties in PbTiO 3 thin films are identified to be isolated point defects such as Pb 3+ centers and lead vacancies, which contribute to hole conduction. Introduction of bombardment-induced defects is shown to be an effective way to quench these trap states by turning them into deep lying defect complexes and clusters which, in turn, leads to a dramatic reduction of leakage current by up to 5 orders of magnitude and improvement of ferroelectric device performance.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Explaining an unusual electromigration behavior—A comprehensive experimental and theoretical analysis using finite element method

In metallic interconnects, it is generally assumed that electromigration (EM) failure location is independent of the applied electrical current and always occurs at the highest-current-density area. Our experiments show otherwise. We designed an Al interconnect that alters its failure location by only varying the applied current density. The failure occurs near the high for a current above 2 × 10 7 A/cm 2 , but at a location with 59% of the maximum for lower current densities. Thermoreflectance thermal imaging is employed to gather time-dependent high-resolution spatial temperature distributions of the Al interconnect during EM. More importantly, we propose a computationally inexpensive 2D finite element method that tracks EM evolution in time and matches well with the observations from different experimental conditions. A detailed analysis covering the major driving forces of EM is carried out to understand the complex physics behind EM. The atomic depletion rate contributed by each force is quantitatively studied. By examining the results from every tested experimental condition, the model reveals that the temperature gradient is the key reason causing atomic depletion near the failure location. Graphical illustrations and qualitative analysis are provided to intuitively show the key findings of our work.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2025

Excitation of whistler and slow-X waves by runaway electrons in a collisional plasma

Runaway electrons are known to provide robust ideal or collisionless kinetic drive for plasma wave instabilities in both the whistler and slow-X branches, via the anomalous Doppler-shifted cyclotron resonances. In a cold and dense post-thermal-quench plasma, collisional damping of the plasma waves can compete with the collisionless drive. Previous studies have found that, due to their higher wavelength and frequency, slow-X waves suffer stronger collisional damping than the whistlers, while the ideal growth rate of slow-X modes is higher. Here, we study runaway avalanche distributions that maintain the same eigen distribution and increase only in magnitude over time. The distributions are computed from the relativistic Fokker–Planck–Boltzmann solver, upon which a linear dispersion analysis is performed to search for the most unstable or least damped slow-X and whistler modes. Taking into account the effect of plasma density, plasma temperature, and effective charge number, we find that the slow-X modes tend to be excited before the whistlers in a runaway current ramp-up. Furthermore, even when the runaway current density is sufficiently high that both branches are excited, the most unstable slow-X mode has a much higher growth rate than the most unstable whistler mode. The qualitative and quantitative trends uncovered in the current study indicate that even though past experiments and modeling efforts have concentrated on whistler modes, there is a compelling case that slow-X modes should also be a key area of focus in the runaway self-mediation through wave instabilities.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Ta, Ti and Hf effects on Nb 3 Sn high-field performance: temperature-dependent dopant occupancy and failure of Kramer extrapolation

The increasing demand for improving the high-field (16-22 T) performance of Nb 3 Sn conductors requires a better understanding of the properties of modern wires much closer to irreversibility field, H Irr . In this study we investigated the impact of Ta, Ti and Hf doping on the high-field pinning properties, the upper critical field, H c2 , and H Irr . We found that the pinning force curves of commercial Ti and Ta doped wires at different temperatures do not scale and that the Kramer extrapolation, typically used by magnet designers to estimate high-field critical current density and magnet operational margins from lower field data, is not reliable and significantly overestimates the actual H Irr . In contrast, new laboratory scale conductors made with Nb-Ta-Hf alloy have improved high-field J c performance and, despite contributions by both grain boundary and point defect pinning mechanisms, have more predictable high-field behavior. Using Extended X-ray Absorption Fine Structure spectroscopy, EXAFS, we found that for the commercial Ta and Ti doped conductors, the Ta site occupancy in the A15 structure gradually changes with the heat treatment temperature whereas Ti is always located on the Nb site with clear consequences for H c2 . Finally, this work reveals the still limited understanding of what determines H c2 , H Irr and the high-field J c performance of Nb 3 Sn and the complexity of optimizing these conductors so that they can reach their full potential for high-field applications.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A Highly Porous Copper Electrocatalyst for Carbon Dioxide Reduction

Electrochemical reduction of carbon dioxide (CO 2 ) is an appealing approach toward tackling climate change associated with atmospheric CO 2 emissions. This approach uses CO 2 as the carbon feedstock to produce value-added chemicals, resulting in a carbon-neutral (or even carbon-negative) process for chemical production. Many efforts have been devoted to the development of CO 2 electrolysis devices that can be operated at industrially relevant rates; however, limited progress has been made, especially for valuable C 2+ products. Herein, we synthesized a nanoporous copper CO 2 reduction catalyst and integrated it into a microfluidic CO 2 flow cell electrolyzer. The CO 2 electrolyzer exhibited a current density of 653 mA/cm -2 with a C 2+ product selectivity of ~62% at an applied potential of -0.67 V (vs. reversible hydrogen electrode). Here, the highly porous electrode structure facilitated rapid gas transport across the electrode-electrolyte interface at high current densities. Further investigations on electrolyte effects revealed that the surface pH value was substantially different from the pH of bulk electrolyte, especially for non-buffering near-neutral electrolytes when operating at high currents.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Influence of Supporting Electrolyte on Hydroxide Exchange Membrane Water Electrolysis Performance: Anolyte

Hydroxide-exchange-membrane water electrolysis (HEMWE) is an emerging hydrogen-production pathway that combines many advantages of incumbent alkaline water electrolysis (AWE) and proton-exchange-membrane water electrolysis (PEMWE). Advancement in HEMWE has been accelerated with the development of stable and conductive hydroxide exchange membranes (HEMs) and a more comprehensive understanding of alkaline gas-evolving kinetics. However, performance and durability without supporting electrolytes (SELs) remain inferior to PEMWE and AWE and little is known about the role and impact of the SELs. This study investigates the effects of SELs used as anolyte solutions in HEMWEs including cation-type, anion-type, SEL conductivity and pH, presence of carbonates and increased cation/OH- ratios on cell voltage and stability. We report our findings that (i) cell potential and high-frequency resistance did not correlate with anolyte SEL conductivity, (ii) cation-type influences cell voltage at low current densities (<50 mA cm -2 ) as predicted by half-cell measurements, (iii) increased cation/OH- ratio causes increased overpotentials, and (iv) carbonates are exchanged in the HEM but removed via self-purging at high current density. Overall, this study concludes that concentrated KOH is still the best SEL.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

High performance ultraviolet photodetectors based on ZnO nanoflakes/PVK heterojunction

A high performance ultraviolet (UV) photodetector is receiving increasing attention due to its significant applications in fire warning, environmental monitoring, scientific research, astronomical observation, etc. The enhancement in performance of the UV photodetector has been impeded by lacking of a high-efficiency heterojunction in which UV photons can efficiently convert into charges. In this work, the high performance UV photodetectors have been realized by utilizing organic/inorganic heterojunctions based on a ZnO nanoflakes/poly (N-vinylcarbazole) hybrid. A transparent conducting polymer poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonate)-coated quartz substrate is employed as the anode in replacement of the commonly ITO-coated glass in order to harvest shorter UV light. The devices show a lower dark current density, with a high responsivity (R) of 7.27 × 10{sup 3 }A/W and a specific detectivity (D*) of 6.20 × 10{sup 13} cm Hz{sup 1/2}/W{sup −1} at 2 V bias voltage in ambient environment (1.30 mW/cm{sup 2} at λ = 365 nm), resulting in the enhancements in R and D* by 49% and one order of magnitude, respectively. The study sheds light on developing high-performance, large scale-array, flexible UV detectors using the solution processable method.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2023

Ultrahigh supercurrent density in a two-dimensional topological material

Ongoing advances in superconductors continue to revolutionize technology thanks to the increasingly versatile and robust availability of lossless supercurrents. In particular, high supercurrent density can lead to more efficient and compact power transmission lines, high-field magnets, as well as high-performance nanoscale radiation detectors and superconducting spintronics. In this work, we report the discovery of an unprecedentedly high superconducting critical current density (17 MA / cm 2 at 0 T and 7 MA / cm 2 at 8 T) in 1T'–WS 2 , exceeding those of all reported two-dimensional superconductors to date. 1T'–WS 2 features a strongly anisotropic (both in- and out-of-plane) superconducting state that violates the Pauli paramagnetic limit signaling the presence of unconventional superconductivity. Spectroscopic imaging of the vortices further substantiates the anisotropic nature of the superconducting state. More intriguingly, the normal state of 1T'–WS 2 carries topological properties. The band structure obtained via angle-resolved photoemission spectroscopy and first-principles calculations points to a Z 2 topological invariant. The concomitance of topology and superconductivity in 1T'–WS 2 establishes it as a topological superconductor candidate, which is promising for the development of quantum computing technology.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Tin-graphene tubes as anodes for lithium-ion batteries with high volumetric and gravimetric energy densities

Limited by the size of microelectronics, as well as the space of electrical vehicles, there are tremendous demands for lithium-ion batteries with high volumetric energy densities. Current lithium-ion batteries, however, adopt graphite-based anodes with low tap density and gravimetric capacity, resulting in poor volumetric performance metric. Here, by encapsulating nanoparticles of metallic tin in mechanically robust graphene tubes, we show tin anodes with high volumetric and gravimetric capacities, high rate performance, and long cycling life. Pairing with a commercial cathode material LiNi0.6Mn0.2Co0.2O2, full cells exhibit a gravimetric and volumetric energy density of 590 W h Kg-1 and 1,252 W h L-1 , respectively, the latter of which doubles that of the cell based on graphite anodes. This work provides an effective route towards lithium-ion batteries with high energy density for a broad range of applications.

25 ENERGY STORAGE↗
DOE OSTI2022

Scalable, Ultrathin, and High-Temperature-Resistant Solid Polymer Electrolytes for Energy-Dense Lithium Metal Batteries

We report all-solid-state batteries (ASSBs) demonstrate great promise, offering high energy density, good thermal stability, and safe operation compared with traditional Li-ion batteries. Among various solid-state electrolytes (SSEs), solid polymer electrolytes (SPEs) offer an attractive choice due to their thinness, low density, and good manufacturability. However, ultrathin SPEs that work with practical current densities or at high temperatures remain challenging, limiting applicable conditions of SPE-based batteries. Here, the authors report a novel scalable, ultrathin, and high-temperature-resistant SPE for ASSBs. This design includes an electrospun polyacrylonitrile (PAN) matrix and polyethylene oxide (PEO)/Li salt ionic conductor, which offers a stable LiF and Li 3 N containing SSE/Li interface. The unique interface—as well as the good mechanical strength—inhibits lithium dendrites and prevents short circuiting. As a result, symmetrical Li-Li cells deliver more than 300 h cyclability at 0.5 mA cm -2 . ASSBs fabricated with only 5 µm-thickness PAN-PEO/lithium bis(trifluoromethanesulfonyl)imide reach 300 cycles at 0.3 C rate at 60 °C. The excellent thermal stability of PAN also results in safer SPEs at high temperatures. The design extends battery operation up to temperatures of 120 and 150 °C, where it achieves 500 cycles at C/2 rate and 100 cycles at 2C rate, respectively.

25 ENERGY STORAGE↗
DOE OSTI2025

Stable cycling of high-mass loaded MnO 2 electrodes for sodium-ion batteries

Achieving cost-effective, sustainable solutions for large-scale energy storage are critical for advancing the global clean energy transition. In view of the challenges posed by limited lithium reserves, low-cost sodium-ion batteries (SIBs) have emerged as a promising direction, especially for grid-level energy storage. Among the various battery electrode materials, manganese dioxide (MnO 2 ) stands out as a favorable choice for such large-scale applications due to its earth abundance, cost-effectiveness, and non-toxic nature. Although MnO 2 is known as a pseudocapacitive material with superior cycling stability in aqueous electrolytes, its dissolution in non-aqueous electrolytes has restricted its use in long-lifetime batteries. In this study, we address two issues which have limited the use of MnO 2 electrodes in non-aqueous electrolytes. First, using electrochemical quartz crystal microbalance measurements in combination with other electrochemical methods, we demonstrate that diglyme (bis(2-methoxyethyl) ether) electrolyte can achieve stable cycling of electrodeposited ε-MnO 2 . These results enable us to tackle a second objective, that is increasing the mass loading of the MnO 2 electrode, since achieving high areal energy density is a significant factor in reducing manufacturing costs. Using 3D printed graphene aerogel (GA) as a scaffold, our studies show that the electrodeposited MnO 2 /GA electrodes possess scalable properties with mass loadings from 20 to 80 mg cm −2 . The resulting electrodes exhibit areal energy densities as high as 4.4 mA h cm −2 at a current density of 10 mA cm −2 . The high mass loaded MnO 2 electrodes were incorporated as a cathode in a SIB which used TiO 2 as the anode. The SIB device exhibited excellent performance with power densities in excess of 70 mW cm −2 . These studies highlight the promise of MnO 2 electrodes for use in a low-cost technology for large-scale energy storage.

25 ENERGY STORAGE↗
NASA NTRS2009

Radiation tests of highly scaled high density commercial nonvolatile NAND flash memories update 2009

Heavy ion single-event measurements on a variety of high density commercial NAND flash memories are reported. Three single event effect (SEE) phenomena are examined: single effect upsets (SEUs), single event functional interrupts (SEFIs), and catastrophic loss of ability to erase and program the device. Also, radiation results of multilevel flash technology are compared with results from single-level flash technology. These commercial high density memories appear to be much less susceptible to SEE and have better TID response compared to older generations of flash memories. The single-level devices are less sensitive to SEUs than multi-level devices. The charge pump in this study survived up to 600 krads. A new high current phenomenon in high density NAND flash memories is also discussed.

Nguyen, Duc N.↗
DOE OSTI2016

Durability of Polymer Electrolyte Membrane Fuel Cells Operated at Subfreezing Temperatures

The structure, composition, and interfaces of membrane electrode assemblies (MEA) and gas-diffusion layers (GDLs) have a significant effect on the performance of single-proton-exchange-membrane (PEM) fuel cells operated isothermally at subfreezing temperatures. During isothermal constant-current operation at subfreezing temperatures, water forming at the cathode initially hydrates the membrane, then forms ice in the catalyst layer and/or GDL. This ice formation results in a gradual decay in voltage. High-frequency resistance initially decreases due to an increase in membrane water content and then increases over time as the contact resistance increases. The water/ice holding capacity of a fuel cell decreases with decreasing subfreezing temperature (-10°C vs. -20°C vs. -30°C) and increasing current density (0.02 A cm -2 vs. 0.04 A cm -2 ). Ice formation monitored using in-situ high-resolution neutron radiography indicated that the ice was concentrated near the cathode catalyst layer at low operating temperatures (≈-20°C) and high current densities (0.04 A cm -2 ). Significant ice formation was also observed in the GDLs at higher subfreezing temperatures (≈-10°C) and lower current densities (0.02 A cm -2 ). These results are in good agreement with the long-term durability observations that show more severe degradation at lower temperatures (-20°C and -30°C).

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2022

Exploring implosion designs for increased compression on the National Ignition Facility using high density carbon ablators

It has long been recognized that high compression, and hence good confinement, is essential to achieving high yields in inertial confinement fusion implosions. In pursuit of multi-megajoule yields on the National Ignition Facility (NIF), a new campaign has begun aimed at testing the hypothesis that controlling hydrodynamic stability is key to achieving effective higher compression with the high density carbon ablators currently fielded on NIF. This campaign is built around a new implosion design, called SQ-n, that is derived from the uniquely stable Bigfoot design tested on NIF in 2016–2019. While very stable and with performance that was quite close to one-dimensional expectations, Bigfoot was a relatively high adiabat, and consequently lower compression design. The goal of SQ-n is then to evolve Bigfoot toward a higher compression design but without compromising its unique stability characteristics. Specifically, SQ-n adopts a ramped foot pulse shape to minimize early time Richtmyer–Meshkov instability growth and uses an ablator dopant distribution extending all of the way to the fuel–ablator interface that simulations suggest further reduces perturbation growth. In conclusion, this paper describes the design philosophy pursued with SQ-n, the results of instability modeling of the candidate design, and the experimental campaign planned to test these ideas in the near future.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

A graded catalytic–protective layer for an efficient and stable water-splitting photocathode

Achieving solar-to-hydrogen efficiencies above 15% is key for the commercial success of photoelectrochemical water splitting devices. While tandem cells can reach those efficiencies, increasing the catalytic activity and long-term stability remains a significant challenge. We show that annealing a bilayer of amorphous titanium dioxide (TiO x ) and molybdenum sulfide (MoS x ) deposited onto GaInP 2 results in a photocathode with high catalytic activity (current density of 11 mA/cm -2 at 0 V vs. the reversible hydrogen electrode under 1 sun illumination) and stability (retention of 80% of initial photocurrent density over a 20 h durability test) for the hydrogen evolution reaction. Microscopy and spectroscopy reveal that annealing results in a graded MoS x /MoO x /TiO 2 layer that retains much of the high catalytic activity of amorphous MoS x but with stability similar to crystalline MoS 2 . These findings demonstrate the potential of utilizing a hybridized, heterogeneous surface layer as a cost-effective catalytic and protective interface for solar hydrogen production.

14 SOLAR ENERGY↗