Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “ELECTRODE”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Infrared Microscopy as a Probe of Composition within a Model Biofuel Cell Electrode Prepared from Trametes versicolor Laccase

Abstract Infrared microscopy was applied in the study of laccase biofuel cell electrodes that demonstrated high current and power densities traceable to the use of a low equivalent weight (EW), short side chain (Aquivion) ionomer in the catalyst layer. The electrodes were prepared from a biocatalyst ink composed of orientation‐directing anthracene‐modified multi‐walled carbon nanotubes (An‐MWCNTs) in a dispersion of ionomer exchanged by hydrophobic cations. The ink was applied to an electronically conductive carbon felt support that was hot‐pressed to a Nafion‐NRE 212 (51 μm thickness) membrane, forming the framework for an air‐breathing biofuel cell cathode. Infrared microscopy sampling was performed with the use of a micro‐attenuated total reflection probe that enabled spectra to be recorded from ∼32 μm diameter circular spatial regions on the materials investigated. Sensitivity to deformation of the soft polymer membrane‐based materials was assessed through trial experiments on pure membrane samples before approaching the compositionally more complex biofuel cell electrodes. In studies of laccase cathodes, infrared spectral features of enzyme, buffer anions and surrounding An‐MWCNTs were identified. Heterogeneity in the spatial distribution of components and unexpected bands traceable to insoluble copper salts were detected. The results suggest directions for improving electrode activity and bring to light needs for advancing quantitative interpretations.

Liang, Ying↗
DOE OSTI2016

Silicon-based anodes for lithium-ion batteries: Effectiveness of materials synthesis and electrode preparation

Lithium-ion batteries are widely used throughout the world for portable electronic devices and mobile phones and show great potential for more demanding applications like electric vehicles. Unfortunately, lithium-ion batteries still lack the required level of energy storage to completely meet the demands of such applications as electric vehicles. Among advanced materials being studied, silicon nanoparticles have demonstrated great potential as an anode material to replace the commonly used graphite. Silicon has been shown to have a high theoretical gravimetric capacity, approximately 4200 mA h/g, compared to only 372 mA h/g for graphite. Though silicon nanoparticles have remarkably high capacity, they suffer from rapid degradation with each cycle due to electrode volume expansion of approximately 400% during lithiation, placing a large strain on the material. With each cycle that strain creates cracks in the electrode particles and causes them to break down into smaller particles, which create void spaces between the particles and lead to poor contact as reflected in poor conductivity. In this review, we discuss exciting new research on silicon-based anodes conducted during the past couple of years. Besides stressing the importance of well-designed nanostructures of Si, we focus on optimization of the Si electrode and resulting performance enhancement by properly selecting binders and synergistically integrating them with various carbon materials during electrode design and fabrication. Importantly, although each improvement strategy has its own advantage, appropriate combination of them will yield much higher anode performance. We summarize the core issues in developing the silicon anode and effective strategies in yielding more promising results. (C) 2016 Elsevier Ltd. All rights reserved.

Casimir, Anix↗
DOE OSTI2017

Quantitative Microstructure Characterization of a NMC Electrode

Performance of lithium-ion batteries (LIBs) is strongly influenced by the porous microstructure of their electrodes. In this work, 3D microstructures of calendared and un-calendared positive electrode LiNi1/3Mn1/3Co1/3O2 (NMC) have been investigated in order to extract relevant properties useful for battery modeling. Transport (volume fraction, connectivity, particle size and tortuosity) and electrochemical (specific surface area) properties have been calculated for the pore and the active material. Special attention has been paid to determine the size of the so-called representative volume element (RVE) required to be statistically representative of the heterogeneous medium. Several parameters have been calculated using a panel of different numerical methods in order to compare their results. Besides, the image level of detail has been evaluated (using original criteria based upon edge detection) to assess the overall data quality available for the study.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2019

Fast Charging of Li-Ion Cells: Part I. Using Li/Cu Reference Electrodes to Probe Individual Electrode Potentials

Increasing the charge rate of Li-ion cells over 1–2C (full charge in 30–60 min) would be highly desirable, but high currents flowing through the active materials push these cells to their endurance limits. In this article, we aim to understand how such high-current regimes affect electrochemical properties of the cells. Formation of Li metal deposits is a recognized hazard of high-rate charging, as Li plating can overtake lithium intercalation in the negative electrode. Here we demonstrate how microprobe Li/Cu reference electrodes can be used to characterize the graphite anode and layered oxide (NCM523) cathode during constant-current (≤ 6C) voltage-limited (4.39 V) charging of Li-ion cells. These reference electrodes are used to monitor the onset of Li plating conditions in situ during cell charging. As the current increases over 3C, the anode potentials decrease below -40 mV causing lithium nucleation. Surprisingly, this nucleation (at least, initially) does not result in capacity fade or a higher anode impedance even in strongly polarized cells, so it appears that the nascent Li nuclei are isolated from electrolyte by the pre-existing solid electrolyte interphase. Our study shows that microprobe reference electrodes are an important diagnostic tool to characterize full-cell behavior in the high-current regimes.

25 ENERGY STORAGE↗
DOE OSTI2023

Electrochemistry at Back-Gated, Ultrathin ZnO Electrodes: Field-Effect Modulation of Heterogeneous Electron Transfer Rate Constants by 30× with Enhanced Gate Capacitance

We report steady-state voltammetry of outer-sphere redox species at back-gated ultrathin ZnO working electrodes in order to determine electron transfer rate constants k ET as a function of independently-controlled gate bias, V G . We demonstrate that k ET can be modulated as much as 30-fold by application of V G ≤ 8 V. Key to this demonstration was integrating the ultrathin (5 nm) ZnO on a high dielectric constant (k) insulator, HfO 2 (30 nm), which was grown on a Pd metal gate. The high-k HfO 2 dramatically decreased the required V G values and increased the gate-induced charge in ZnO compared to previous studies. Importantly, the enhanced gating power of the Pd/HfO 2 /ZnO stack meant it was possible to observe a non-monotonic dependence of k ET on V G , which reflects the inherent density of redox acceptor states in solution. Furthermore, this work adds to the growing body of literature demonstrating that electrochemical kinetics (i.e., rate constants and overpotentials) at ultrathin working electrodes can be tuned by V G , independent of the conventional electrochemical working electrode potential.

36 MATERIALS SCIENCE↗
DOE OSTI2017

A Tunable 3D Nanostructured Conductive Gel Framework Electrode for High-Performance Lithium Ion Batteries

This study develops a tunable 3D nanostructured conductive gel framework as both binder and conductive framework for lithium ion batteries. A 3D nanostructured gel framework with continuous electron pathways can provide hierarchical pores for ion transport and form uniform coatings on each active particle against aggregation. The hybrid gel electrodes based on a polypyrrole gel framework and Fe3O4 nanoparticles as a model system in this study demonstrate the best rate performance, the highest achieved mass ratio of active materials, and the highest achieved specific capacities when considering total mass, compared to current literature. This 3D nanostructured gelbased framework represents a powerful platform for various electrochemically active materials to enable the next-generation high-energy batteries.

25 ENERGY STORAGE↗
DOE OSTI2017

Lithiation of multilayer Ni/NiO electrodes: criticality of nickel layer thicknesses on conversion reaction kinetics

X-ray reflectivity and transmission electron microscopy (TEM) were used to characterize the morphological changes in thin film electrodes with alternating Ni and NiO layers during lithiation as a function of the Ni buffer layer thickness. Complete lithiation of the active NiO layers occurs only when the thickness of the Ni/NiO bilayers are less than 75 Å – a threshold value that is determined by the sum of the Ni quantity in the Ni/NiO bilayer of the multilayer stack. Thicker Ni/NiO bilayers present a kinetic barrier for lithium ion diffusion inside the stack resulting in partial lithiation of the multilayer electrodes in which only the top NiO layer lithiates. Lithiation of NiO layers in a multilayer stack also leads to an interface-specific reaction that is observed to increase the thicknesses of adjacent Ni layers by 3–4 Å and is associated with the formation of a low-density Li 2 O layer, corresponding to an interfacially-driven phase separation of the NiO. Rate dependent cyclic voltammetry studies reveal a linear relation between the peak current and scan rate suggesting that the lithiation kinetics are controlled by charge transfer resistance at the liquid–solid interface.

25 ENERGY STORAGE↗
DOE OSTI2021

Effect of Pressurization on Solid Oxide Cell Oxygen Electrodes: the Role of PrO x Nanoparticle Infiltration

Pressurization of solid oxide cells improves performance by reducing electrode polarization resistance (R P ) and facilitates system integration with balance of plant components such as pressurized storage tanks. However, there are few reports on pressurization effects for electrodes designed for low-temperature operation and utilizing infiltrated catalysts. Here we report an electrochemical impedance spectroscopy study of high performing oxygen electrode materials, SrTi 0.3 Fe 0.63 Co 0.07 O 3-∂ (STFC) and PrO x infiltrated STFC, for oxygen partial pressures ($p$ $o$ 2 ) from 0.1 to 8 atm and temperatures from 550 to 650 °C. decreases more with pressurization for STFC:PrO x , fitting well to with an exponent n~0.3, compared to n~0.25 for STFC. The combination of PrO x infiltration and pressurization yields a substantial R P decrease, e.g., at 600 °C by ~7 times from 0.36 Ω cm 2 at $p$ $o$ 2 = 0.2 atm for STFC to 0.055 Ω cm 2 at $p$ $o$ 2 = 4 atm for STFC:PrO x . Here, a transmission-line-based circuit model impedance fit reveals that the significant oxygen surface reaction (R surf ) resistance contribution decreases substantially with PrO x infiltration; and its $p$ $o$ 2 dependence become more pronounced, with n increasing from ~0.25 to ~0.5. R surf for STFC:PrO x decreases so much at elevated $p$ $o$ 2 that the electrode/electrolyte interface resistance dominates.

25 ENERGY STORAGE↗
DOE OSTI2015

Effects of Particle Size, Electronic Connectivity, and Incoherent Nanoscale Domains on the Sequence of Lithiation in LiFePO 4 Porous Electrodes

High-resolution X-ray microscopy is used to investigate the sequence of lithiation in LiFePO 4 porous electrodes. For electrodes with homogeneous interparticle electronic connectivity via the carbon black network, the smaller particles lithiate first. For electrodes with heterogeneous connectivity, the better-connected particles preferentially lithiate. Correlative electron and X-ray microscopy also show the presence of incoherent nanodomains that lithiate as if they are separate particles.

36 MATERIALS SCIENCE↗