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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Two-dimensional modeling of the cathode sheath formation during the streamer-cathode interaction

In this paper, a computational simulation of the sheath formation during the streamer-surface interaction at atmospheric pressure is presented. A two-dimensional fluid model of a point-to-plane configuration is applied to investigate the evolution of the discharge in the vicinity of cathode plane. The effects of the surfaces on the properties of streamer have been studied for three cases, i.e., conductive surface with secondary electron emission (SEE), conductive surface without SEE, and dielectric surface. In all cases, we found that the axial propagation velocity of the streamer front decreases as the streamer arrives at the boundary of the cathode sheath. And the simulation results showed that the properties of the surface have a significant effect on the streamer. Besides the influences, the secondary emission coefficient and the relative permittivity on the streamer-surface interactions are also studied.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Surface degradation of Li{sub 1–x}Ni{sub 0.80}Co{sub 0.15}Al{sub 0.05}O{sub 2} cathodes: Correlating charge transfer impedance with surface phase transformations

The pronounced capacity fade in Ni-rich layered oxide lithium ion battery cathodes observed when cycling above 4.1 V (versus Li/Li{sup +}) is associated with a rise in impedance, which is thought to be due to either bulk structural fatigue or surface reactions with the electrolyte (or combination of both). Here, we examine the surface reactions at electrochemically stressed Li{sub 1–x}Ni{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2} binder-free powder electrodes with a combination of electrochemical impedance spectroscopy, spatially resolving electron microscopy, and spatially averaging X-ray spectroscopy techniques. We circumvent issues associated with cycling by holding our electrodes at high states of charge (4.1 V, 4.5 V, and 4.75 V) for extended periods and correlate charge-transfer impedance rises observed at high voltages with surface modifications retained in the discharged state (2.7 V). The surface modifications involve significant cation migration (and disorder) along with Ni and Co reduction, and can occur even in the absence of significant Li{sub 2}CO{sub 3} and LiF. These data provide evidence that surface oxygen loss at the highest levels of Li{sup +} extraction is driving the rise in impedance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Activity and Stability of (Pr 1-x Nd x ) 2 NiO 4 as Cathodes for Solid Oxide Fuel Cells: Part V. In Situ Studies of Phase Evolution

This study is to complement an early report (the manuscript is attached for review purpose) on the role of interlayer on activity and performance stability in praseodymium nickelates. The aforementioned report showed a remarkable 48% increase in power density while switching from common GDC interlayer to a new interlayer chemistry (PGCO). Furthermore, a stable long-term performance was linked with suppressed reaction between the cathode and PGCO interlayer. In this article, we report in situ studies of the phase evolution. The high energy XRD studies at a synchrotron source showed fully suppressed phase transition in praseodymium nickelates with PGCO interlayer, while the electrodes on the GDC interlayer undergo substantial phase transformation. Furthermore, in operando and post-test XRD analyses shown fully suppressed structural changes in electrodes operated in full cells at 750°C and 0.80 V for 500 hours. SEM-EDS analysis showed that the formation of PrO x at the cathode-interlayer interface may play a role in a decrease of mechanical integrity of the interfaces, due to thermal expansion mismatch, leading to a local stress between the two phases. Furthermore, phase evolution at a narrow interface may propagate toward the electrode bulk, leading to structural changes Q1 and performance degradation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Open‐Structured V 2 O 5 · n H 2 O Nanoflakes as Highly Reversible Cathode Material for Monovalent and Multivalent Intercalation Batteries

The high‐capacity cathode material V 2 O 5 · n H 2 O has attracted considerable attention for metal ion batteries due to the multielectron redox reaction during electrochemical processes. It has an expanded layer structure, which can host large ions or multivalent ions. However, structural instability and poor electronic and ionic conductivities greatly handicap its application. Here, in cell tests, self‐assembly V 2 O 5 · n H 2 O nanoflakes shows excellent electrochemical performance with either monovalent or multivalent cation intercalation. They are directly grown on a 3D conductive stainless steel mesh substrate via a simple and green hydrothermal method. Well‐layered nanoflakes are obtained after heat treatment at 300 °C (V 2 O 5 ·0.3H 2 O). Nanoflakes with ultrathin flower petals deliver a stable capacity of 250 mA h g −1 in a Li‐ion cell, 110 mA h g −1 in a Na‐ion cell, and 80 mA h g −1 in an Al‐ion cell in their respective potential ranges (2.0–4.0 V for Li and Na‐ion batteries and 0.1–2.5 V for Al‐ion battery) after 100 cycles.

Wang, Huali↗
DOE OSTI2015

Strong Lithium Polysulfide Chemisorption on Electroactive Sites of Nitrogen-Doped Carbon Composites For High-Performance Lithium–Sulfur Battery Cathodes

Despite the high theoretical capacity of lithium–sulfur batteries, their practical applications are severely hindered by a fast capacity decay, stemming from the dissolution and diffusion of lithium polysulfides in the electrolyte. A novel functional carbon composite (carbon-nanotube-interpenetrated mesoporous nitrogen-doped carbon spheres, MNCS/CNT), which can strongly adsorb lithium polysulfides, is now reported to act as a sulfur host. The nitrogen functional groups of this composite enable the effective trapping of lithium polysulfides on electroactive sites within the cathode, leading to a much improved electrochemical performance (1200 mAh g -1 after 200 cycles). The enhancement in adsorption can be attributed to the chemical bonding of lithium ions by nitrogen functional groups in the MNCS/CNT framework. Furthermore, the micrometer-sized spherical structure of the material yields a high areal capacity (ca. 6 mAh cm -2 ) with a high sulfur loading of approximately 5 mg cm -2 , which is ideal for practical applications of the lithium–sulfur batteries.

carbon materials↗
DOE OSTI2016

In situ electrochemical-electron spin resonance investigations of multi-electron redox reaction for organic radical cathodes

Organic radical batteries (ORBs) bearing robust radical polymers as energy storage species, are emerging promisingly with durable high energy and power characteristics by unique tunable redox properties. Here we report the development and application of in situ electrochemical-electron spin resonance (ESR) methodologies to identify the charge transfer mechanism of Poly(2,2,6,6- tetramethylpiperidinyloxy-4-yl methacrylate) (PTMA) based organic radical composite cathodes in the charge-discharge process of lithium half cells. The in situ experiments allow each electrochemical state to be associated with the chemical state (or environment) of the radical species upon the cell cycling. In situ ESR spectra of the composite cathode demonstrate a two-electron redox reaction of PTMA. Moreover, two different local environments of radical species are found in the composite electrode that includes both concentrated and isolated radicals. These two types of radicals show similarities during the redox reaction process while behave quite differently in the non-faradic reaction of ion sorption/desorption on the electrode surface.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2016

A facile cathode design combining Ni-rich layered oxides with Li-rich layered oxides for lithium-ion batteries

A facile synthesis method was developed to prepare xLi 2 MnO 3 ·(1-x)LiNi 0.7 Co 0.15 Mn 0.15 O 2 (x = 0, 0.03, 0.07, 0.10, 0.20, and 0.30 as molar ratio) cathode materials, combining the advantages of high specific capacity from Ni-rich layered phase and surface chemical stability from Li-rich layered phase. X-ray diffraction (XRD), high resolution transmission electron microscope (HRTEM) and electrochemical charge/discharge performance confirm the formation of a Li-rich layered phase with C2/m symmetry. Most importantly, high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) reveals a spatial relationship that Li-rich nano-domain islands are integrated into a conventional Ni-rich layered matrix (R$\bar{3}$m). This is the first time that Li-rich phase has been directly observed inside a particle at the nano-scale, when the overall composition of layered compounds (Li 1+δ Ni x Mn y M 1-x-y-δ O 2 , M refers to transition metal elements) is Ni-rich (x > 0.5) rather than Mn-rich (y > 0.5). Remarkably, xLi 2 MnO 3 ·(1-x)LiNi 0.7 Co 0.15 Mn 0.15 O 2 cathode with optimized x value shows superior electrochemical performance at C/3, i.e., 170 mA h g -1 with 90.3 % of capacity retention after 400 cycles at 25 °C and 164 mA h g -1 with 81.3 % capacity retention after 200 cycles at 55 °C.

25 ENERGY STORAGE↗
DOE OSTI2015

Design of surface protective layer of LiF/FeF 3 nanoparticles in Li-rich cathode for high-capacity Li-ion batteries

Advanced lithium-ion batteries for renewable energy storage applications have become a major research interest in recent years. Much better performance can be realized by improvements in the material surface design, especially for the cathode materials. Here, we present a new design for a surface protective layer formed via a facile aqueous solution process in which a nano-architectured layer of LiF/FeF 3 is epitaxially grown on bulk hierarchical Li-rich cathode Li[Li 0.2 Ni 0.2 Mn 0.6 ]O 2 . Coin cell tests of this material in the voltage range of 2–4.8 V indicated a high reversible capacity (260.1 mA h g -1 at 0.1 C), superior rate performance (129.9 mA h g -1 at 20 C), and excellent capacity retention. Differential scanning calorimetry showed good thermal stability. The enhanced capacity and cycling stability are attributed to the suppression of interfacial side reactions as well as the conversion reaction resulting from the introduction of LiF/FeF 3 as a surface protective layer.

Iron fluoride↗