410 research outputs found
Ionic liquids as safe electrolyte components for Li-metal and Li-ion batteries
No full textThis article reports the search for nonflammable, stable electrolytes based on ionic liquid (IL) compounds, able to effectively improve the needed safety and reliability of lithium batteries. The most significant results are reviewed with the aim of elucidating critical aspects governing the properties of IL electrolytes, including (1) transport properties affecting ionic conductivity and the cycling rate of battery systems, (2) electrochemical/chemical stability toward most conventional electrode materials, and (3) thermal properties determining the range of applicability. Both liquid and polymer electrolytes, adopting ILs as the main component or as an additive to standard electrolyte solutions, are considered. Very promising results, in terms of battery prototype performances in scaled-up configurations, demonstrate the validity of the use of ILs for practical applications. Even though further improvements are necessary, particularly at high current density operations in both lithium-metal and lithium-ion systems, the realization of safer, high-performance batteries based on IL electrolytes is certainly possible. It can be concluded that ILs represent a viable solution to disappointing compromises between energy density and acceptable safety features in lithium batteries
Aprotic ionic liquids as electrolyte components in protonic membranes
No full textIn this paper we describe the preparation and the properties of a series of aprotic ionic liquid-based, proton-conducting membranes. The ionic liquids (ILs) 1,2-dimethyl-3-n-propylimidazolium bis(trifluoromethanesulfonyl)imide and the 3-methyl-1-n-propylpyridinium bis(trifluoromethanesulfonyl)imide are used as the casting solvents of PVdF gel-type membranes; the proton conductivity is achieved by the addition of a superacid component, namely, trifluoromethanesulfonic acid (HTf) or N,N-bis(trifluoromethanesulfonyl)imide (HTFSI). The polymer electrolytes showed good thermal and electrochemical properties in the temperature range of interest for PEMFC applications. The strong coordination between the ILs and the HTFSI, which have the same anion, improves the thermal stability of this kind of membrane, but lowers the chemical properties and the conductivity, due to an increase in viscosity. HTf-added samples have an ionic conductivity of 2 x 10(-2) S cm(-1) at 100 degrees C, showing the best overall properties and making these membranes of interest applications in fuel cells
Removal of copper corrosion using in-situ and ex-situ film formed from hydrogels
No full textEco-friendly and non-harmful hydrogels were developed with the aim of corrosion removal from copper. The target for cleaning was prepared through electrochemical corrosion of copper sheets. X-ray diffraction analysis was performed to determine the corrosion products. Using the hydrogel, of which the composition was optimized, specifically one containing 15 wt% poly(vinyl alcohol) (PVA) with 10 wt% glycerol as well as one with 15 wt% sodium carboxymethyl cellulose, corrosion removal of the aforementioned target was carried out. For cleaning with in-situ films, the gels to which 7 wt% citric acid was added were applied and dried directly on the corroded copper, while ex-situ films were prepared by casting gel in a petri dish, drying, and immersing in 7 wt% citric acid solution and placed on the corroded copper. By peeling the films from the copper, corrosion removal was done. Deeper corrosion removal with a better area selectivity was achieved with in-situ films. In the case of PVA-based in-situ films, although the treatment influenced the deeper corrosion layer, the cuprite layer adjacent to the metallic copper was preserved. Infrared spectra of the in-situ PVA film formed on clean copper and corroded copper were compared to discuss the mechanisms of corrosion removal. Strategies for the corrosion removal with a high area selectivity using hydrogels are therefore proposed
Properties and fuel cell performance of a Nafion-based, sulfated zirconia-added, composite membrane
No full textThe effect of an acidic inorganic additive, i.e. Sulfated zirconia, on Nafion-based polymer electrolytes is evaluated by comparing the properties in terms of conductivity and fuel cell performance of a composite Sulfated zirconia-added Nafion membrane with those of an additive-free Nafion membrane. The peculiar surface properties of the selected filler promote a higher hydration level and a higher conductivity for the composite membrane under unsaturated conditions, i.e. at 20% RH. Tests on H-2-air fully humidified cells, monitored at 70 C and at atmospheric pressure, reveal small differences when passing from a plain Nafion to a composite Nafion/sulfated zirconia membrane as electrolyte. However, remarkably great improvements are observed for the composite membrane-based cell when the comparison tests are run at low relative humidity and high temperature, this Outlining the beneficial role of the Sulfated zirconia additive. (C) 2008 Elsevier B.V. All rights reserved
An Italian national project for the development of new microporous proton membranes for DMFC
No full textProton exchange membrane fuel cells (PEMFC) offer potential advantages of clean and efficient energy conversion systems for automobiles, portable applications and power generation. The main obstacles to a wide commercialisation of polymer electrolyte fuel cells are mostly related to the low proton conductivity at low relative humidity of the membranes, to their high methanol permeability and poor mechanical properties above 130°C. Accordingly, an intensive research is carried out throughout the world with the aim of developing new types of low-cost, highly-efficient proton membranes. To this goal is focused an Italian National Project granted by the Ministry of University and Research (MIUR) to the Department of Chemistry of the University of Rome "La Sapienza" who acts as a coordinator of a joint group involving 9 academic and university laboratories. The research has been addressed to: i) Nafion-modified membranes, ii) composite membranes based on ionomers different than Nafion and on a variety of suitable inorganic and/or organo-inorganic nano fillers; iii) Porous Teflon membranes filled with proton conductors of organo-inorganic type, and iv) Gel-type membranes formed by trapping acid liquid solutions into suitable polymer matrices; We report here in details the activities in progress in our laboratory aimed to the development of various type of composite, gel-type membranes. These membranes can be based on polymer blends, cross-linked polymers or polymer-ceramic composites [1-6]. Whatever the final matrix, it is desired to have a starting material showing a good film-forming capacity as well as high thermal and chemical stability. The results confirm that these membranes have improved thermal and electrochemical performance and tests in fuel cell prototypes demonstrate their practical value
Elettroliti avanzati, non fluorurati per batterie litio-ione
No full textL’attuale economia energetica mondiale basata sui combustibili fossili presenta una serie di fattori limitanti che generano una urgente richiesta di innovazione. Soluzioni valide al
problema sono sicuramente l’impiego di veicoli ad emissione zero, come veicoli elettrici o ibridi, e l’utilizzo di fonti di energia rinnovabili che però richiedono dei sistemi di stoccaggio
energetico molto efficaci. In questo contesto tra i sistemi di accumulo di energia le batterie a litio risultano avere ottime prestazioni in termini di densità energetica, efficienza e durata di
vita. Tuttavia problemi come la sicurezza, la stabilità, i costi e la reperibilità dei materiali ne limitano la diffusione su larga scala per questo tipo di applicazioni. Di conseguenza la
ricerca e lo sviluppo di questi dispositivi si focalizza sul miglioramento della chimica che caratterizza le loro componenti principali. L’obbiettivo di questo lavoro è quindi studiare il
comportamento di soluzioni elettrolitiche non convenzionali al fine di migliorare la stabilità e la sicurezza delle batterie litio-ione sostituendo i comuni sali di litio fluorurati con composti
della famiglia dei borani. L’interesse nei confronti di questa famiglia è dovuto al fatto che sono composti privi di fluoro, non tossici e risultano essere un’alternativa a basso costo del più
convenzionale litio esafluoro-fosfato (LiPF6).Tra questi è stato scelto il litio bis-ossalato-borato (LiBOB)
Mixtures of ionic liquid - Alkylcarbonates as electrolytes for safe lithium-ion batteries
No full textMixtures of alkylcarbonate electrolytes with an ionic liquid (IL) and a lithium salt have been studied in order to develop new electrolytes for lithium-ion cells with enhanced safety profiles. In this work the influence of the addition of N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Py14TFSI) on the electrochemical properties of commercial carbonate-based electrolytes, i.e. 1 M LiPF6 in EC:DMC (LP30) and in EC:DMC:DEC (LP71) is reported. Four new electrolyte compositions have been prepared and characterized. The addition of the ionic liquid in the electrolyte carbonate-based solution results in (i) an ionic conductivity comparable with that of the pristine IL-free carbonate-based electrolyte, (ii) the enlargement of the electrochemical stability window, and (iii) a large reduction of the self-extinguish time (SET) of the electrolyte mixture when exposed to a free flame. All the newly developed electrolytes have been tested in lithium cells versus LiFePO4 and Li4Ti5O12 electrodes: the cells show good performances in galvanostatic cycling. The best performing electrolyte i.e. LP30/Py14TFSI 70/30 wt/wt has been also successfully tested in a full Li-ion cell realized by coupling LiFePO4 and Li4Ti5O12 electrodes. (C) 2012 Elsevier B.V. All rights reserved
Coupled System of Modified Membrane and Modified Cathode for Efficient PEM-FC
No full textA coupled system formed by polyoxometalate (POM)-modified ultra-low Pt loading cathode and sulphated titania (S-TiO2)-doped Nafion membrane is evaluated in a proton exchange membrane (PEM) fuel cell (FC). Modification of fuel cell cathode is performed using Kegging-type polyoxometalate and low Pt loading, in order to enhance active area and mesoporosity [1]. Commercial Nafion is modified with superacidic sulphated titanium oxide nanoparticles, in order to improve the proton transfer and the hydration level in the membrane-electrode assembly (MEA) [2,3]. The cell performance is studied at different relative humidity with polarization dependence and electrochemical impedance spectroscopy at high and low current density. Analysis of cell performance shows that the catalytic and transport properties are improved, with respect to unmodified commercial materials, using the coupled system, despite the ultra- low Pt loading used, thanks to rich proton environment provided from both cathode and membrane
Preparation and Characterization of Nanocomposite Polymer Membranes Containing Functionalized SnO2 Additives
No full textIn the research of new nanocomposite proton-conducting membranes, SnO2 ceramic powders with surface functionalization have been synthesized and adopted as additives in Nafion-based polymer systems. Different synthetic routes have been explored to obtain suitable, nanometer-sized sulphated tin oxide particles. Structural and morphological characteristics, as well as surface and bulk properties of the obtained oxide powders, have been determined by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier Transform Infrared (FTIR) and Raman spectroscopies, N2 adsorption, and thermal gravimetric analysis (TGA). In addition, dynamic mechanical analysis (DMA), atomic force microscopy (AFM), thermal investigations, water uptake (WU) measurements, and ionic exchange capacity (IEC) tests have been used as characterization tools for the nanocomposite membranes. The nature of the tin oxide precursor, as well as the synthesis procedure, were found to play an important role in determining the morphology and the particle size distribution of the ceramic powder, this affecting the effective functionalization of the oxides. The incorporation of such particles, having sulphate groups on their surface, altered some peculiar properties of the resulting composite membrane, such as water content, thermo-mechanical, and morphological characteristics
Quasi-solid-state electrolytes - strategy towards stabilising Li|inorganic solid electrolyte interfaces in solid-state Li metal batteries
No full textSolid-state batteries (SSBs) based on inorganic solid electrolytes (ISEs) are considered promising candidates for enhancing the energy density and the safety of next-generation rechargeable lithium batteries. However, their practical application is frequently hampered by the high resistance arising at the Li metal anode/ISE interface. Herein, a review of the conventional solid-state electrolytes (SSEs) the recent research on quasi-solid-state battery (QSSB) approaches to overcome the issues of the state-of-the-art SSBs is reported. The feasibility of ionic liquid (IL)-based interlayers to improve ISE/Li metal wetting and enhance charge transfer at solid electrolyte interfaces with both positive and lithium metal electrodes is presented together with a novel generation of IL-containing quasi-solid-state-electrolytes (QSSEs), offering favourable features. The opportunities and challenges of QSSE for the development of high energy and high safety quasi-solid-state lithium metal batteries (QSSLMBs) are also discussed
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