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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

A machine learning degradation model for electrochemical capacitors operated at high temperature

Electrochemical capacitors (ECs) have only recently been considered as an alternative power source for telemetry sensors of drilling equipment for geothermal or oil and gas exploration. The lifecycle analysis and modelling of ECs is underrepresented in literature in comparison to other storage devices e.g. Li-ion batteries. This paper investigates the degradation of ECs when cycled outside the manufacturer-specified operating temperature envelope and proposes a machine learning-based approach for modelling the degradation. Experimental results show that end of life, defined as a 30% decrease in capacitance, occurs at 1,000 cycles when the environmental temperature exceeds the maximum operating temperature by 30%. The life-cycle test data is then used as an input to a Gaussian process regression (GPR) algorithm to predict the capacitance fade trend. The GPR is validated on a total of nine commercial cells from two different manufacturers, achieving an average root mean squared percent error of less than 2% and a mean calibration score of 93% when referenced to a 95% confidence interval. The model can be utilized to determine the EC degradation rate at a range of operating temperature values.

42 ENGINEERING↗
DOE OSTI2023

In Situ Observation of Domain Wall Lateral Creeping in a Ferroelectric Capacitor

As a promising candidate for next-generation nonvolatile memory devices, ferroelectric oxide films exhibit many emergent phenomena with functional applications, making understanding polarization switching and domain evolution behaviors of fundamental importance. However, tracking domain wall motion in ferroelectric oxide films with high spatial resolution remains challenging. Here, in this study, an in situ biasing approach for direct atomic-scale observations of domain nucleation and sideways motion is presented. By accurately controlling the applied electric field, the lateral translational speed of the domain wall can decrease to less than 2.2 Å s −1 , which is observable with atomic resolution STEM imaging. In situ observations on a capacitor structured PbZr 0.1 Ti 0.9 O 3 /La 0.7 Sr 0.3 MnO 3 heterojunction demonstrate the unique creeping behavior of a domain wall under a critical electric field, with the atomic structure of the creeping domain wall revealed. Moreover, the evolution of the metastable domain wall forms an elongated morphology, which contains a large proportion of charged segments. Phase-field simulations unveil the competition between gradient, elastic, and electrostatic energies that decide this unique domain wall creeping and morphology variation. This work paves the way toward a complete fundamental understanding of domain wall physics and potential modulations of domain wall properties in real devices.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Electric Double-Layer Capacitor Based on an Ionic Clathrate Hydrate

Herein, we suggest a new approach to an electric double-layer capacitor (EDLC) that is based on a proton-conducting ionic clathrate hydrate (ICH). The ice-like structures of clathrate hydrates, which are comprised of host water molecules and guest ions, make them suitable for applications in EDLC electrolytes, owing to their high proton conductivities and thermal stabilities. The carbon materials in the ICH Me{sub 4}NOH[DOT OPERATOR]5H{sub 2}O show a high specific capacitance, reversible charge–discharge behavior, and a long cycle life. The ionic-hydrate complex provides the following advantages in comparison with conventional aqueous and polymer electrolytes: 1)The ICH does not cause leakage problems under normal EDLC operating conditions. 2)The hydrate material can be utilized itself, without requiring any pre-treatments or activation for proton conduction, thus shortening the preparation procedure of the EDLC. 3)The crystallization of the ICH makes it possible to tailor practical EDLC dimensions because of its fluidity as a liquid hydrate. 4)The hydrate solid electrolyte exhibits more-favorable electrochemical stability than aqueous and polymer electrolytes. Therefore, ICH materials are expected to find practical applications in versatile energy devices that incorporate electrochemical systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

PLZT Film Capacitors for Power Electronics and Energy Storage Applications

Ceramic film capacitors with high dielectric constant and high breakdown strength hold special promise for applications demanding high power density. By means of chemical solution deposition, we deposited ≈2-μm-thick films of lanthanum-doped lead zirconate titanate (PLZT) on LaNiO3-buffered Ni (LNO/Ni) foils and platinized silicon (PtSi) substrates. The dielectric properties and energy storage performance of the resulting samples were determined under a high level of applied electric field. X-ray diffraction stress analysis revealed that PLZT on LNO/Ni bears a compressive stress of ≈370 MPa while PLZT on PtSi endures a tensile stress of ≈250 MPa. Compressive stress was found to lead to heightened polarization, improved tunability, increased irreversible domain wall motion, and enhanced breakdown strength for PLZT deposited on the LNO/Ni as compared with the PtSi substrate. We observed a tunability of ≈55 and ≈40 % at room temperature under 100 kV/cm applied field, remanent polarization of ≈23.5 and ≈7.4 µC/cm^2, coercive electric field of ≈25.6 and ≈21.1 kV/cm, and dielectric breakdown strength of ≈2.6 and ≈1.5 MV/cm for PLZT deposited on LNO/Ni foils and PtSi substrates, respectively. A high recoverable energy density of ≈85 J/cm^3 and energy conversion efficiency of ≈65 % were measured on the PLZT film grown on LNO/Ni.

ceramic film capacitor↗
DOE OSTI2018

Effect of Thiourea on the Corrosion Behavior of Aluminum Anode Foil of Aluminum Electrolytic Capacitor

The specific capacitance is a key performing factor for the aluminum anode foil of aluminum electrolytic capacitor. In order to increase the specific capacitance, the effect of thiourea (TU) as corrosion inhibitor on the aluminum anode foil was investigated in this paper. Electrochemical impedance spectroscopy (EIS), polarization curves and weight loss measurements were used to investigate the effect of corrosion inhibitor TU added to nitric acid. EIS and inductance–capacitance–resistance (LCR) meter were also used to measure the specific capacitance of the aluminum anode foil, which was etched in nitric acid containing different contents of TU, and then formed in boric acid solution (100 g L{sup −1}) at 540 V. The results showed that the TU could be used as an inhibitor for Al in an acid solution. When the concentration of TU was 0.10%, the specific capacitance reached up to 0.661 μF cm{sup −2}, which increased by nearly 24% compared to that without TU. The data for the specific capacitance of Al anode foil corresponding to different TU concentrations obtained by EIS coincided well with the one obtained using LCR meter; thus, EIS could be effectively used for the preliminary selection of the type and ideal concentration of inhibitor.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Topological circuits of inductors and capacitors

Alternating current (ac) circuits can have electromagnetic edge modes protected by symmetries, analogous to topological band insulators or semimetals. How to make such a topological circuit? This paper illustrates a particular design idea by analyzing a series of topological circuits consisting purely of inductors (L) and capacitors (C) connected to each other by wires to form periodic lattices. All the examples are treated using a unifying approach based on Lagrangians and the dynamical H-matrix. First, the building blocks and permutation wiring are introduced using simple circuits in one dimension, the SSH transmission line and a braided ladder analogous to the ice-tray model also known as the π-flux ladder. Then, more general building blocks (loops and stars) and wiring schemes (m-shifts) are introduced. The key concepts of emergent pseudo-spin degrees of freedom and synthetic gauge fields are discussed, and the connection to quantum lattice Hamiltonians is clarified. A diagrammatic notation is introduced to simplify the design and presentation of more complicated circuits. These building blocks are then used to construct topological circuits in higher dimensions. The examples include the circuit analog of Haldane’s Chern insulator in two dimensions and quantum Hall insulator in four dimensions featuring finite second Chern numbers. The topological invariants and symmetry protection of the edge modes are discussed based on the H-matrix.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Confined seeds derived sodium titanate/graphene composite with synergistic storage ability toward high performance sodium ion capacitors

Sodium ion capacitors (SICs) are increasingly being focused, due to the feature of high energy/power densities derived from the integrated energy storage mechanisms, as well as the ubiquitous sodium sources. Practical anodes with exceptional rate capability can circumvent the kinetic mismatch with cathode, boosting energy/power metrics. Herein, a Na 2 Ti 7 O 15 nanowire/graphene anode is synthesized through an atomic layer deposition (ALD) seeding technique, by which the confined seeds enable Na 2 Ti 7 O 15 with ultra-high aspect ratio and interweaved structure with graphene nanosheets. The composite delivers a superior rate capability of 60 mAh g –1 at a high rate of 17.7 A g –1 , and an exceptional cyclic stability of 90% retention after 10 000 cycles even at 8.85 Ag –1 . It is demonstrated that the morphology, graphene platform, intrinsically low energy diffusion barrier of Na 2 Ti 7 O 15 , and associated reaction mechanism synergize the electron transport, sodium ion migration, and surface capacitive contribution, giving rise to such a decent electrochemical performance. The SICs deliver high energy/power densities (82.7 Wh kg –1 /97.5 W kg –1 , 25 kW kg –1 with 16 Wh kg –1 retained), proving a promise particularly at extremely fast charge/discharge condition. The proposed ALD seeding technique can be developed into a technical strategy for synthesizing high performance energy storage materials.

25 ENERGY STORAGE↗
DOE OSTI2021

Controlling MoO 2 and MoO 3 phases in MoO x /CNTs nanocomposites and their application to anode materials for lithium-ion batteries and capacitors

Molybdenum oxides (MoO 2 and MoO 3 ) are attractive anode materials for Li- and Na- ion batteries. Although there have been extensive studies on them individually, systematic and comparative studies are still lacking. Here, we demonstrate a facile and straightforward synthesis method to control the phase and oxidation state in the MoO x /CNTs nanocomposites via hydrothermal reaction followed by heat-treatment. By changing the gas atmosphere during the annealing process, well-dispersed MoO 2 /CNTs and MoO 3 /CNTs nanocomposites are formed without altering their overall morphology. This strategy enables us to investigate the true structure-property correlation of MoO x /CNTs nanocomposites by comparing the structure and electrochemical properties of MoO 2 /CNTs and MoO 3 /CNTs. When tested as anode materials for lithium-ion batteries, both HT-MoO 2&3 /CNTs electrodes show much-improved cycling stability and rate performance compared to the rod-shaped bulk MoO 3 electrode. In situ Mo K-edge x-ray absorption spectroscopy (XAS) has been further employed to compare and elucidate Li + storage mechanisms of both electrodes. When employed to the negative electrode of a high-power lithium-ion capacitor (LIC), the LIC full-cell composed of HT-MoO 3 /CNTs negative and activated carbon positive electrodes demonstrates impressive energy and power densities (~ 90 Wh kg –1 with 2000 W kg –1 ) and excellent cycling stability (96.8 % capacity retention after 300 cycles), revealing the versatility of the MoO x /CNTs electrodes in energy applications.

25 ENERGY STORAGE↗
DOE OSTI2022

Effect of oxide layer growth conditions on radiation detection performance of Ni/SiO 2 /epi-4H-SiC MOS capacitors

We report high resolution radiation detection has been demonstrated using Ni/SiO2/n-4H-SiC metal-oxidesemiconductor vertical capacitors fabricated using highly crystalline 4H-SiC epilayers. The oxide layers have been grown thermally using two different approaches: i) in-air, and ii) oxygen-ambience oxidation. The devices fabricated using the former method exhibited dark currents one order of magnitude higher than that in the latter. The observed difference has been attributed to the back-contact series resistance and capacitance. Regardless of the difference in the device parameters, detectors prepared using both of the methods exhibited very high energy resolutions of ≤ 0.5% for 5486 keV alpha particles emitted by an 241Am radioisotope. Capacitance mode deep level transient spectroscopic (DLTS) studies revealed similar type of electrically active defects along with Z1/2 and EH5 deep level defects in both the types of devices. The DLTS scans also revealed positive polarity peaks in these devices which indicate emission from minority carrier trap centers. The activation energy corresponding to the peak was found to be ~1.2 eV which has been assigned to HK3 defects responsible for hole trapping in 4H-SiC. The possibility of appearance of the positive peak due to non-negligible impedance of the back-contact has been ruled out based on the observation that the centroid of the observed peak did not change with detectors having different device parameters.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Mesoscale modeling of electric double layer capacitors with three-dimensional ordered structures

This paper presents general mathematical formulations for simulating electric double layer capacitors (EDLCs) with three-dimensional ordered structures. For the first time, a general set of boundary conditions was derived in order to account for the Stern layer without simulating it in the computational domain. These boundary conditions were valid for planar, cylindrical, and spherical electrode particles or pores. They made possible the simulations of EDLCs with complex geometries while rigorously accounting for both the Stern and diffuse layers. The model also simultaneously accounted not only for 3D electrode morphology but also for finite ion size and field-dependent electrolyte dielectric permittivity. It was used to faithfully simulate the complex structure of an EDLC electrode consisting of ordered bimodal mesoporous carbon featuring both macropores and mesopores. Areal and gravimetric capacitances were predicted based on non-solvated and solvated ion diameters. These two cases set the upper and lower bounds for the predicted capacitances. The capacitances predicted using non-solvated ion diameter were found to be in good agreement with experimental data reported in the literature. All surfaces contributed to the overall capacitance of EDLCs. The gravimetric capacitance of different bimodal carbons increased linearly with increasing specific surface area corresponding to constant areal capacitance.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2015

Reducing CO2 to dense nanoporous graphene by Mg/Zn for high power electrochemical capacitors

Converting CO2 to valuable materials is attractive. Herein, we report using simple metallothermic reactions to reduce atmospheric CO2 to dense nanoporous graphene. By using a Zn/Mg mixture as a reductant, the resulted nanoporous graphene exhibits highly desirable properties: high specific surface area of 1900 m2/g, a great conductivity of 1050 S/m and a tap density of 0.63 g/cm3, comparable to activated carbon. The nanoporous graphene contains a fine mesoporous structure constructed by curved few-layer graphene nanosheets. The unique property ensemble enables one of the best high-rate performances reported for electrochemical capacitors: a specific capacitance of ~170 F/g obtained at 2000 mV/s and 40 F/g at a frequency of 120 Hz. This simple fabricating strategy conceptually provides opportunities for materials scientists to design and prepare novel carbon materials with metallothermic reactions.

CO2 reduction↗
DOE OSTI2017

Collateral Advantages of a Gel Electrolyte for MnO 2 Nanowire Capacitors: Higher Voltage and Reduced Volume

Recently we demonstrated that symmetric, all Au@δ-MnO 2 core@shell nanowire capacitors can achieve cycle stability to 100 000 cycles and beyond in a poly(methyl methacrylate) (PMMA) gel electrolyte. Here we examine the limits of the PMMA gel to confer this extraordinary stability, in terms of the accessible maximum voltage, Vmax, and the thickness of the PMMA gel electrolyte layer. Two conclusions are (1) the PMMA gel permits the Vmax to be increased by 50% from 1.2 V to 1.8 V, allowing the specific energy to be increased 5–6 fold, and (2) the PMMA gel layer thickness can be reduced from 180 μm (previously) to 2 μm while simultaneously utilizing two layers of nanowires and patterning nanowires in each layer at 5× higher density. For this nanowire “sandwich” architecture, a net increase in volumetric capacity of 600× up to 500 mF/cm3 can be achieved while retaining cycle stability to 100 000 cycles.

25 ENERGY STORAGE↗
DOE OSTI2011

Reduction of leakage currents with nanocrystals embedded in an amorphous matrix in metal-insulator-metal capacitor stacks

CaTiO{sub 3} layers with varying thicknesses in metal-insulator-metal capacitor stacks were deposited at 550 deg. C using radio-frequency magnetron sputtering. The combination of electrical and transmission electron microscopy measurements allows a correlation of k-value and leakage current to the degree of crystallinity. Experiments show that higher crystallinity and, therefore, higher k-values lead to increasing leakage currents and change of conduction mechanisms. However, leakage currents are significantly reduced when crystallites are embedded in an amorphous matrix. Selective growth of these crystallites is owed to cube-on-cube nucleation of CaTiO{sub 3} on {l_brace}011{r_brace} Pt.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Analysis of carrier behavior in C60/P(VDF-TrFE) double-layer capacitor by using electric-field-induced optical second-harmonic generation measurement

By using displacement current measurement (DCM) and electric-field-induced optical second-harmonic generation (EFISHG) measurement, we studied the carrier behavior in the indium-tin oxide (ITO)/Poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE))/C60/Au(or Al) capacitors. Two DCM peaks appeared asymmetrically at around −35.5 V and +30.0 V in the dark. Correspondingly, the EFISHG response from the C60 layer was observed, but the peak positions were different with respect to DCM ones. The results show that the spontaneous polarization of the ferroelectric P(VDF-TrFE) polymeric layer directly affects the electric field in the C60 layer, and thus governs the carrier motion in this layer. As a result, the C60 layer serves like an insulator in the dark, while electrons and holes are captured and released at the interface in response to the turn-over of spontaneous polarization of ferroelectric layer. On the other hand, under white light illumination, C60 layer serves like a conductor due to the increase of photogenerated mobile carriers, and these carriers dominate the carrier motions therein. Our findings here will be helpful for analyzing carrier behaviors in organic electronic devices using ferroelectric polymers.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Static characterization of a soft elastomeric capacitor for non destructive evaluation applications

A large and flexible strain transducer consisting of a soft elastomeric capacitor (SEC) has been proposed by the authors. Arranged in a network setup, the sensing strategy offers tremendous potential at conducting non-destructive evaluation of large-scale surfaces. In prior work, the authors have demonstrated the performance of the sensor at tracking strain history, localizing cracks, and detecting vibration signatures. In this paper, we characterize the static performance of the proposed SEC. The characterization includes sensitivity of the signal, and temperature and humidity dependences. Tests are conducted on a simply supported aluminum beam subjected to bending as well as on a free standing sensor. The performance of the SEC is compared against off-the-shelf resistance-based strain gauges with resolution of 1 με. A sensitivity of 1190 pF/ε is obtained experimentally, in agreement with theory. Results also show the sensor linearity over the given level of strain, showing the promise of the SEC at monitoring of surface strain.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Misfit strain-temperature phase diagrams and domain stability of asymmetric ferroelectric capacitors: Thermodynamic calculation and phase-field simulation

Thermodynamic calculation and phase-field simulation have been conducted to investigate the misfit strain-temperature phase diagrams, dielectric property, and domain stability of asymmetric ferroelectric capacitors (FCs), with considering the effects of dissimilar screening properties and work function steps at the two interfaces. The distinct features of asymmetric FCs from their symmetric counterparts have been revealed and discussed. Polar states with nonzero out-of-plane polarization in parallel with the built-in field are found preferential to form in asymmetric FCs. Meanwhile, the built-in field breaks the degeneracy of states with out-of-plane polarization in anti-directions. This leads to the necessity of redefining phases according to the bistability of out-of-plane polarization. Moreover, the phase stability as well as the dielectric behavior can be significantly controlled by the properties of electrodes, misfit strain, and temperature. The phase-field simulation result also shows that polydomain instability would happen in asymmetric FCs as the equivalence of domain stability in anti-directions is destroyed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗