13 research outputs found
Mechanical activation and thermodynamic destabilization of the lithium amide and lithium hydride system
No full textThe practical application of hydrogen storage in fuel cells for transportation purposes in hydrogen powered vehicles has been one of the major challenges. Complex metal hydrides have been considered as potential materials for practical on-board hydrogen storage applications because of their reversible storage and release of hydrogen, and moderately high gravimetric and volumetric hydrogen capacities. Within the last decade, the Li-N-H or (LiNH2+LiH) system has been investigated intensively as a candidate for practical on-board hydrogen storage. Despite of its reversible storage reaction with a theoretical capacity of 6.5 wt. % H2, there are two primary issues that prevent the utilization of this system for the on-board hydrogen storage: (1) the NH3 emission and (2) a relatively high operating temperature (∼280°C) for reversible hydrogen absorption and desorption at 1 bar of H2. ^ The NH3 emission results in hydrogen fuel contamination which can damage the PEM fuel cells and consequently degrade the hydrogen storage capacity. The utilization of the mechanical activation via the high-energy ball milling has been shown to be an effective way to address the NH 3 emission issue. This is due to the decrease in particle and crystallite size, increase in surface area, and better mixing of LiNH2 and LiH. The dehydriding reaction of the (LiNH2+LiH) mixture was also substantially enhanced by high-energy ball milling. The peak temperature for releasing large amounts of H2 from the mixture was reduced by ∼ 100°C via ball milling at room temperature for 180 min. ^ To lower the hydrogen absorption and desorption temperatures further and increase the H2 equilibrium pressure of the (LiNH2+LiH) system, the thermodynamic destabilization of the lithium amide through partial substitution of Li by Mg in lithium hydride has been pursued and confirmed that the (2LiNH 2+MgH2) mixture has a higher thermodynamic driving force for dehydrogenation than the (LiNH2+LiH) mixture, as reported by many other studies. This higher thermodynamic driving force results in a lower onset temperature for the dehydrogenation of the (2LiNH2+MgH 2) mixture than that of the (LiNH2+LiH) mixture. Furthermore, the isothermal hydriding and dehydriding cycling performance of the Li-Mg-N-H (1:2) system, starting with Li2MgN2H2 at 200°C has been examined in this study. This system exhibits a slow hydriding rate controlled by diffusion and a fast dehydriding rate that exhibits two distinct stages consisting of a very fast release at the beginning followed by a slow release. The hydriding and dehydriding reaction pathways during the cycling have been proposed.
Inorganic additives for passivation of high voltage cathode materials
No full textThe incorporation of additives designed to sacrificially react on the surface of cathode materials of lithium ion batteries has been investigated. Addition of low concentrations of inorganic additives including lithium bisoxalatoborate (LiBOB), lithium difluorooxalatoborate (LiBF2(C 2O4)), and tetramethoxy titanium (TMTi) to 1 M LiPF 6 in 1:1:1 EC/DEC/DMC improves the capacity retention of Li/Li 1.17Mn0.58Ni0.25O2 cells cycled to 4.9 V vs. Li. Surface analysis of the cathode materials (XPS and IR) suggests that structure of the cathode surface film is modified by the presence of the additives resulting in a decrease in detrimental electrolyte oxidation reactions on the cathode surface. © 2010 Elsevier B.V. All rights reserved
Cathode Solid Electrolyte Interphase Generation in Lithium-Ion Batteries with Electrolyte Additives
No full textThe incorporation of additives designed to sacrificially react on the surface of cathode materials of lithium ion batteries has been investigated. Addition of low concentrations of either organic (2,5-dihydrofuran (2,5-DHF) or γ-butyrolactone (GBL)) or inorganic additives (lithium bisoxalatoborate (LiBOB), lithium difluorooxalatoborate (LiBF2(C2O4)), tetramethoxytitanium (TMTi), and tetraethoxysilane (TEOS)) to 1 M LiPF6 in 1:1:1 EC/DEC/DMC improves the capacity retention of Li/ Li1.17Mn0.58Ni0.25O2 cells cycled to 4.9 V vs Li.</jats:p
Inhibition of electrolyte oxidation in lithium ion batteries with electrolyte additives
No full textThe incorporation of additives designed to sacrificially react on the surface of cathode materials of lithium ion batteries has been investigated. Addition of low concentrations of various additives to 1 M LiPF6 in 1:1:1 EC/DEC/DMC improves the capacity retention of Li/Li1.17Mn0.58Ni0.25O2 cells cycled to 4.9 V vs Li. Surface analysis of the cathode materials (XPS and IR) suggest that structure of the cathode surface film is modified by the presence of the additives resulting in a decrease in detrimental electrolyte oxidation reactions on the cathode surface. Film forming mechanisms and structures will be discussed
Low temperature milling of the LiNH(2) + LiH hydrogen storage system
No full textBall milling of the LiNH(2) + LiH storage system was performed at 20 degrees C, -40 degrees C, and -196 degrees C, and the resulting powders were analyzed using X-ray diffraction, scanning electron microscopy, nuclear magnetic resonance (NMR), specific surface area analysis, and kinetics cycling measurements. Ball milling at -40 degrees C showed no appreciable deviations from the 20 degrees C sample, but the -196 degrees C powder exhibited a significant increase in the hydrogen desorption kinetics. NMR analysis indicates that a possible explanation for the kinetics increase is the retention of internal defects generated during the milling process that are annealed at the collision site at higher milling temperatures. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All lights reservedclose181
Solid-State Hydrogen Storage: Storage Capacity, Thermodynamics, and Kinetics
No full textSolid-state reversible hydrogen storage systems hold great promise for on-board applications. The key criteria for a successful solid-state reversible storage material are high storage capacity, suitable thermodynamic properties, and fast hydriding and dehydriding kinetics. The LiNH(2) + LiH system has been utilized as an example system to illustrate these critical issues that are common among other solid-state reversible storage materials. The progress made in thermodynamic destabilization and kinetic enhancements via various approaches are emphasized. The implications of these advancements in the development of future solid-state reversible hydrogen storage materials are discussedclose9
Study the effects of mechanical activation on Li-N-H systems with H-1 and Li-6 solid-state NMR
No full textTo gain insight into the effects of mechanical activation (MA) on the hydrogen desorption of the lithium amide (LiNH2) and lithium hydride (LiH) mixture. LiNH2 and LiH + LiNH2 were mechanically activated by high-energy ball milling. The formed products were studied with in situ H-1 and Li-6 nuclear magic angle spinning (MAS) magnetic resonance (NMR) spectroscopy from ambient temperature to 180 degrees C. Up-field chemical shift was observed in Li-6 MAS NMR spectra with increased milling time, indicating that average local electronic structure around Li nuclei was modified during MA. H-1 MAS NMR was used to dynamically probe ammonia release from the activated LiNH2 at temperature as low as 50 degrees C. In the case of activated LiH + LiNH2 mixtures, the H-1 MAS NMR results implied that MA enhanced the dehydrogenation reaction of LiNH2 + LiH = Li2NH + H-2. (c) 2007 Elsevier B.V All rights reservedclose201
