1,720,976 research outputs found
Fitting of the Voltage-Li+ insertion curve of LiFePO4
No full textFitting of the voltage vs. insertion curves of the LiFePO4 electrode was based on theoretical expressions describing the Li+ diffusive process in a solid medium. The noninteracting gas model for the chemical potential of ions distributed in a solid matrix was taken into account, and the diffusion coefficient and the energy activation for the diffusion process were accordingly calculated. The polari- zation curves at various discharge stages were theoretically obtained, and a good agreement was found with the experimental data at all discharge rates. A mathematical relation describing the trend of the diffusion resistance vs. insertion degree was also developed
Effect of milling and doping on decomposition of NH3BH3 complex
No full textIn this work we considered three different samples: borane ammonia (BA) complex as received, ball milled BA and, finally, BA subjected to ball milling and doped with 1 mol% of hydrogen hexachloroplatinate hydrate. Their crystalline structure was described by XRD and morphology was investigated using SEM and EDS techniques. In order to describe samples behaviour in hydrogen release we plotted TGA curves and thermal decomposition tests were realized. We verified that ball milling increases the BA cristallinity and changes its morphology enhancing the amount of evolved gas. Both the milled and the doped samples show an increase of the pre-exponential factor in the Arrhenius equation. The activation energy remains almost unchanged for the doped sample and it increases for the milled one. As result it was found that the decomposition of 1 mol% doped sample could be provided by waste heat coming from a PEM fuel cell
Electrochemical Characterization of a Composite Polymer Electrolyte with Improved Lithium Metal Electrode Interfacial Properties
No full textIn the development of rechargeable lithium polymer batteries it is of paramount importance to control the passivation phenomena occurring at the lithium electrode interface. It is well estabilished that the type and the growth of the lithium passivation layer is unpredictably influenced by the presence of liquid components and/or impurities in the electrolyte. Therefore, one approach to improve the stability of the lithium interface is the use of liquid-free, highly pure electrolytes. The electrochemical properties of a composite polymer electrolyte obtained by hot pressing a mixture of polyethylene oxide (PEO), a lithium salt (lithium tetrafluoroborate, LiBF(4)) and a powdered ceramic additive (gamma-LiAlO(2)), will be presented and discussed. The electrochemical characterization included the determination of the ionic conductivity, the anodic break-down voltage and, most importantly, the stability of the lithium metal electrode interface and the lithium stripping-plating process efficiency. The main feature of this dry, true solid-state electrolyte is a very good compatibility with the lithium metal electrode, demonstrated by a very high lithium cycling efficiency, which approaches a value of 99%
Synthesis and characterization of amorphous hydrated FePO4 and its electrode performance in lithium batteries
No full textAmorphous iron(III) phosphate was synthesized by spontaneous precipitation from equimolar aqueous solutions of Fe(NH4)(2)(SO4)(2).6H(2)O and NH4H2PO4, using hydrogen peroxide as the oxidizing agent. The material was characterized by chemical analysis, thermogravimetrical analysis, differential thermoanalysis, X-ray powder diffraction, and scanning electron microscopy. The material was tested as a cathode in nonaqueous lithium cells. Galvanostatic intermittent titration technique was used to follow the lithium intercalation process. The effect of firing on the specific capacity was also tested. The material fired at 400degreesC showed the best electrochemical performance, delivering about 0.108 Ah g(-1) when cycled at C/10 rate. The capacity fade upon cycling was found as low as 0.075% per cycle. (C) 2002 The Electrochemical Society
A Versatile New Synthesis of Carbon-Rich LeFePo4 Enhaning Enhance Its Electrochemical Properties.
No full textLiFePO4/C composites were prepared by using organo-phosphonates as a source of iron, phosphorus and carbon. Fe[RPO3]·H2O (R = methyl or phenyl group) were decomposed in presence of Li2CO3 at high temperature and under nitrogen flux. During the high temperature synthesis the phosphonate is oxidized and reacting with lithium forms the electro-active material. The organic constituent of the precursor is oxidized to form carbon that interacting with the LiFePO4 surface, decrease the charge transfer resistance. The materials were characterized by chemical analysis, TG, DTA, X-ray powder diffraction and SEM. The LiFePO4/C composites were used to prepare electrodes for the electrochemical characterization. The material prepared starting from the phenyl-phosphonate showed impressive specific energy, specific power and capacity retention upon cycling The specific energy evaluated at C/10 rate was about 550 Wh kg-1. The specific power calculated at 30C rate was in excess at 14000 W kg-1 while the specific energy was about 28 % of the energy delivered at C/10. No capacity fading was observed upon cycling. The performance of LiFePO4 prepared with methyl-phosphonate as precursor was found to be slightly lower, probably due to the lower carbon content
Effect of milling and doping on decomposition of NH3BH3 complex
No full textsamples were heated at fixed temperature and the volume of the evolved gas recorded as a function of time. Milled and doped samples were
prepared by mechanical and mechanochemical reactions, respectively. Samples containing 1 and 2 mol% hydrogen hexachloroplatinate hydrate
were prepared. The materials were characterized by scanning electron microscopy (SEM) and X-ray diffractometry (XRD). Mechanical alloying
was effective to modify the crystallinity of the complex and to change the material morphology enhancing the amount of gas evolved. Both the
milled and the doped samples showed an increase of the pre-exponential factor in the Arrhenius equation. The activation energy decreased for the
doped sample, and it increased for the milled sample. As a result it was found that the decomposition of 1 mol% doped sample could be provided
by waste heat coming from polymer electrolyte membrane fuel cell.
© 2005 Elsevier B.V. All rights reserved
Synthesis and Characterization of Amorphous 3Fe2O3*2P2O5*10H2O and Its Electrode Performance in Lithium Batteries
No full textAmorphous 3Fe2O3*2P2O5*10H2O was prepared by oxidation of iron(II) phosphate, obtained by spontaneous precipitation from iron(II) and phosphate aqueous solution, by heating in air at 100°C. The material was characterized by thermal analysis, Mossbauer spectroscopy, X-ray power diffraction, and scanning electron micrograph analysis. the material, tested as cathode in a nonaqueous lithium cell, exhibited a specific capacity of about 140 mAh/g at a current density of 25 mA/g. The utization was reduced to about 76% by a tenfold increase of the discharge current. It shoved cyclability. More that 1000 cycles were performed at about 50 % of depth of discharge, with a capacity fade lower than 0.025%
- …
