Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “CATHODE”

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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

High-Voltage Performance of Ni-Rich NCA Cathodes: Linking Operating Voltage with Cathode Degradation

High-voltage Ni-rich cathodes have been studied as a possible way to achieve high energy density in Li-ion batteries. However, capacity fade due to structural changes at high voltages has limited their applications. In this study, we identify 4.5 V (vs. graphite) as the optimum upper cutoff voltage (UCV) for a Ni-rich NCA cathode [LiNi 0.8 Co 0.15 Al 0.05 O 2 ]. At this UCV, NCA delivers a 12 % increase in reversible capacity (when discharged to 2.5 V) and retains 92 % of its initial capacity after 100 cycles at 1C/-1C cycling when compared to 4.2 V as UCV. By increasing UCV to 4.7 V, the discharge capacity can be raised to >200 mAh/g. However, the rate of capacity fade is greater when compared to 4.5 V as UCV. This increased rate of capacity fade, at higher UCV, is related to irreversible lattice contractions that leads to structural rearrangement at charged states during high-voltage cycling. Lastly, our results show a change in transition metal oxidation states and an onset of structural ordering occurs when the UCV is 4.7 V.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Design of Graded Cathode Catalyst Layers with Various Ionomers for Fuel Cell Application

Proton exchange membrane fuel cells (PEMFCs) powered by green hydrogen (H2) have become a promising alternative to conventional hydrocarbon-fueled power generators. Despite technological advancements, further improvements in efficiency, durability, and low-cost production are required for the widespread adoption of PEMFCs. Though numerous approaches to improve PEMFC electrodes have been reported, most strategies utilize a single material set (e.g., one combination of catalyst and ionomer) to improve performance. Alternatively, anisotropic (graded) electrode structures with locally tunable properties may yield superior electrode performance due to improved ionic and gas phase transport. In this work, graded cathode catalyst layers (CCLs) incorporating different ionomers (Nafion D2020, Aquivion D79-25BS, and HOPI) were designed and prepared. Performance screening shows that some of these graded electrode structures have comparable performance to optimized single-ionomer electrode structures (D2020) suggesting some synergistic benefit. Additionally, we show that electrodes with lower equivalent weight (EW) D79 ionomer near the membrane and D2020 ionomer near the gas diffusion media outperformed electrodes with the inverted configuration. Finally, EIS analysis shows some graded ionomer structures (e.g. D79/D2020) have better than expected H+ conductivity, generally leading to better electrode performance. However, further optimization of ionomer content and catalyst ink formulations is needed to improve overall PEMFC performance.

DIRECT ENERGY CONVERSION↗
DOE OSTI2017

One-step hydrothermal synthesis and electrochemical performance of sodium-manganese-iron phosphate as cathode material for Li-ion batteries

The sodium-manganese-iron phosphate Na{sub 2}Mn{sub 1.5}Fe{sub 1.5}(PO{sub 4}){sub 3} (NMFP) with alluaudite structure was obtained by a one-step hydrothermal synthesis route. The physical properties and structure of this material were obtained through XRD and Mössbauer analyses. X-ray diffraction Rietveld refinements confirm a cationic distribution of Na{sup +} and presence of vacancies in A(2)’, Na{sup +} and small amounts of Mn{sup 2+} in A(1), Mn{sup 2+} in M(1), 0.5 Mn{sup 2+} and Fe cations (Mn{sup 2+},Fe{sup 2+} and Fe{sup 3+}) in M(2), leading to the structural formula Na{sub 2}Mn(Mn{sub 0.5}Fe{sub 1.5})(PO{sub 4}){sub 3}. The particles morphology was investigated by SEM. Several reactions with different hydrothermal reaction times were attempted to design a suitable synthesis protocol of NMFP compound. The time of reaction was varied from 6 to 48 h at 220 °C. The pure phase of NMFP particles was firstly obtained when the hydrothermal reaction of NMFP precursors mixture was maintained at 220 °C for 6 h. When the reaction time was increased from 6 to 12, 24 and 48 h, the dandelion structure was destroyed in favor of NMFP micro-rods. The combination of NMFP (NMFP-6H, NMFP-12H, NMFP-24H and NMFP-48H) structure refinement and Mössbauer characterizations shows that the increase of the reaction time leads to the progressive increment of Fe(III) and the decrease of the crystal size. The electrochemical tests indicated that NMFP is a 3 V sodium intercalating cathode. The comparison of the discharge capacity evolution of studied NMFP electrode materials at C/5 current density shows different capacities of 48, 40, 34 and 34 mA h g{sup −1} for NMFP-6H, NMFP-12H, NMFP-24H and NMFP-48H respectively. Interestingly, all samples show excellent capacity retention of about 99% during 50 cycles. - Graphical abstract: SEM micrographs (left) and evolution of the discharge on cycling with increasing rates from C/15 to 4 C (right) of NMFP material prepared by hydrothermal synthesis at 220 °C at indicated time. Display Omitted - Highlights: • One-step hydrothermal method was used to prepare sodium manganese iron phosphate NMFP. • 3D-NMFP dandelion sphere-like particles were obtained at 220 °C after 6 h. • Increasing reaction time leads to the enhancement of the crystallinity and crystal stabilility of NMFP. • The growth of the particle size and change of morphology are correlated to the reaction time. • EC performance of NMFP powders were greatly affected by the synthesis conditions.

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