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Advanced Materials for High-Performance Secondary Li and Mg Batteries
No full textIn order to obtain advanced energy storage systems with high energy density, the research activity here described, is focused on the study of electrolyte and cathodic materials for application in Lithium and Magnesium batteries. The materials are synthesized through inert atmosphere procedures and characterized with several techniques such as: Thermogravimetric Analyses (TGA), Differential Scanning Calorimetry (DSC), Vibrational spectroscopies (MIR, FIR, Raman), Solid state MAS-NMR, several electrochemical techniques (CV, CA, EIS) and Broadband Electrical Spectroscopy (BES). The results are used to study the interplay between the structure and the conduction mechanism of these materials. The most promising materials are then tested in prototype cells in order to evaluate their performance in operating devices.
As a general procedure, the electrolytes are synthesized with different concentrations of Li+ or Mg2+ charge carriers in order to evaluate the effect of the cation concentration on the thermal properties and conductivity of the materials. In addition, the complexation of the cations and its effect on the long-range charge transfer migration is carefully studied by Infrared and Raman spectroscopy. In the case of the cathodic materials the and their composition are modulated in order to study their effect on the lithium intercalation/deintercalation processes, efficiencies and on battery prototype performance.
The investigated materials comprise: a) an inorganic Solid-state Li-ion conductors, based on lithium-functionalized fluorinated titanium oxide NPs; b) a new class of single-ion conducting nanocomposite polymer electrolytes for Li batteries; and c) two electrolytes for Mg secondary batteries based on ILs and an innovative Mg salt. Moreover two studies about dielectric relaxation phenomena in 4a) Magnesium-polymer electrolytes and 4b) clay-based solid polymer electrolytes (SPEs) are presented which elucidate the interplay existent between molecular relazations in host polymer matrices and long range charge transfer processes. Concerning cathodic materials a family of high voltage multi-metal phosphate cathodic materials for secondary lithium batteries is proposed, studied and tested in button battery prototypes.
Firstly, a general introduction about the state of art of electrolytes and cathodes, with a particular attention on drawbacks and possible solution, which characterize these materials, is presented. Secondly, details about the synthesis and the characterizations of each class of materials is described in great details. Thirdly a concluding remark is provided.Al fine di ottenere sistemi di accumulo di energia elettrica sempre più performanti, l'attività di ricerca qui descritta, è focalizzata sullo studio di elettroliti e materiali catodici per applicazioni in batterie al litio e magnesio. I materiali vengono sintetizzati attraverso sintesi in atmosfera inerte e caratterizzati con diverse tecniche quali: analisi termogravimetrica (TGA), calorimetria a scansione differenziale (DSC), spettroscopie vibrazionali (FT-MIR, FT-FIR, Raman), NMR di stato solido, diverse tecniche elettrochimiche (voltammetria ciclica, cronoamperometria, impedenza elettrochimica) e spettroscopia elettrica a banda larga. I risultati sono utilizzati per studiare l'interazione tra la struttura e il meccanismo di conduzione di questi materiali. I materiali più promettenti sono testati in batterie a bottone prototipo tipo CR2032 per valutare la loro ciclabilità e stabilità su lungo periodo.
Come procedura generale, gli elettroliti vengono sintetizzati con differenti concentrazioni di portatori di carica tipo Mg2+ o Li+ per valutare l'effetto della concentrazione di cationi sulle proprietà termiche e sulla conducibilità dei materiali. Inoltre, la complessazione dei cationi e il suo effetto sul trasferimento di carica a lungo raggio sono studiati accuratamente tramite spettroscopia infrarossa e Raman. Nel caso dei materiali catodici la struttura e la composizione chimica di questi sistemi è modulata al fine di studiare il loro effetto sul processo di intercalazione/deinteracalazione dello ione litio, sull’efficienza e le prestastazioni dei prototipi di batteria a bottone tipo CR2032.
I materiali studiati comprendono: a) un conduttore inorganico di stato solido a singolo catione di litio basato su di un ossido di titanio fluorurato; b) una nuova classe di elettroliti nanocompositi polimerici per batterie al litio; e c) due elettroliti per batterie al magnesio basati su liquidi ionici e un sale innovativo di Mg. Inoltre, al fine di evidenziare le correlazioni esistenti tra le dinamiche dei rilassamenti molecolari degli elettroliti e i processi di trasferimento di carica a lungo raggio, sono stati effettuati due studi sui meccanismi di rilassamento dielettrico di: a) elettroliti polimerici al Mg; e b) elettroliti polimerici solidi a base di alluminio silicati (SPE). Infine viene proposta una nuova promettente famiglia di materiali catodici di cui si studiano le correlazioni tra struttura, morfologia e prestazioni in batterie secondare prototipo a bottone.
La tesi inizia con un’ introduzione generale sullo stato dell'arte degli elettroliti e dei catodi. Particolare attenzione è rivolta sugli svantaggi e sulle possibili future soluzioni. In secondo luogo, vengono descritti I n dettaglio la sintesi e caratterizzazione di ciascuna classe di materiali qui proposti. Quindi, si conclude evidenziando I risultati più salient ottenuti sui vari sistemi proposti
Magnesium Electrolyte Based on EMImBF4 and -[MgCl2]n for Secondary Magnesium Batteries
No full textthis report, a new magnesium ion electrolyte is proposed, based on δ-[MgCl2]n and ethylmethylimidazolium tetrafluoroborate (EMImBF4) ionic liquid. Anhydrous δ-[MgCl2]n was obtained by reacting metallic magnesium with n-chlorobutane in a strictly anhydrous atmosphere as described elsewhere. δ-[MgCl2]n consists of inorganic polymer chains where Mg atoms are bonded together by chloride bridges. The δ-[MgCl2]n chains show a high crystallographic disorder and reactivity toward Lewis bases. Twelve magnesiumconducting electrolytes with formula EMImBF4/(δ-[MgCl2]n)f with f ranging between 0 and 0.117 were prepared by dissolving directly δ-[MgCl2]n into EMImBF4; f is the molar ratio between δ-[MgCl2]n and EMImBF4. The metal concentration of the electrolytes was determined by ICP-AES. The correlation between structure, thermal properties and conduction mechanism of EMImBF4/(δ-[MgCl2]n)f was investigated by several techniques: (a) Medium- and Far-infrared spectroscopy, to reveal the structural features and interactions between the various components of each electrolyte; (b) Differential Scanning Calorimetry (DSC), to detect the thermal transitions; (c) Broadband Electric Spectroscopy (BES), to investigate the relaxation phenomena taking place in the materials and the conduction mechanism.
In addition, a detailed study of the mechanism of ion conduction in these electrolytes was carried out by BES in the 10E-2 Hz to 10 MHz and -150°C to 150°C frequency and temperature ranges, respectively. These studies were performed by analyzing the imaginary and real components of conductivity and permittivity spectra by suitable models
"Core-Shell" ORR Nano-Electrocatalysts Based on a PtNi Carbon Nitride "Shell" and Cu NP "Core"
No full textOne of the most severe bottlenecks in the operation of proton exchange membrane fuel cells (PEMFCs) is the sluggish kinetics of the Oxygen Reduction Reaction (ORR). Thus, suitable ORR Electrocatalysts are required in order to obtain PEMFCs able to yield a sufficiently high performance. State-of-the-art ORR electrocatalysts for application in PEMFCs are obtained by supporting Pt nanocrystals on active carbon supports characterized by a very large surface area. However, despite extensive investigations the performance of these electrocatalysts does not meet yet the strict requirements necessary for a large-scale application of PEMFC technology. A new preparation protocol has been proposed recently to obtain nano-electrocatalysts with a well-controlled chemical composition, based on the pyrolysis and activation of hybrid inorganic-organic precursors. The resulting carbon nitride nano- electrocatalysts thus prepared show an outstanding ORR performance both in “ex-situ” studies and in a single-cell configuration. In this work, a new family of multimetal carbon nitride nano-electrocatalysts is described. The materials are synthesized by pyrolysis of a hybrid inorganic-organic precursor including Pt and Ni atoms impregnating Cu nanoparticles acting as the support. The final ORR electrocatalysts are obtained after an extensive electrochemical dealloying activation process. The products are fully characterized before and after the activation processes. The chemical composition of the Electrocatalysts is determined by Inductively-Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) and microanalysis. The morphology is investigated by High-Resolution Scanning Electron Microscopy (HR-SEM) and High-Resolution Transmission Electron Microscopy (HR-TEM). The structure is probed by powder X-Ray Diffraction (XRD). The electrochemical performance of the electrocatalysts in the ORR is determined both by “ex-situ” measurements carried out by cyclic voltammetry with the rotating ring disk electrode (CV-TF-RRDE method) and by “in-situ” fuel cell studies in a PEM single-cell configuration.
Preliminary results indicate clearly that the proposed electrocatalysts show a remarkable ORR performance, which is significantly enhanced in comparison with the Pt/C reference both in terms of overpotential and selectivity in the 4-electron mechanism of the ORR
A new hybrid inorganic-organic nanocomposite electrolyte based on lithiated fluoride-functionalized titania plasticized with EMImTFSI ionic liquid
No full textLithiated Fluorinated TiO Nps Doped with Imidazolium ILs As Electrolytes for Lithium Batteries
No full textThe development of new materials for secondary batteries is nowadays one of the most active fields in the international scientific panorama.
The state of the art for liquid electrolytes in a lithium-ion cell is typically a mixture of organic carbonates such as ethylene carbonate (EC) or dimethyl carbonate (DMC). The mixture ratio varies depending upon the desired cell properties. These solvents contain solvated lithium ions. The latter are provided by lithium salts, most commonly lithium hexafluorophosphate (LiPF6). Despite the high conductivity of these electrolytes (conucibility >10-3 S•cm-1 at RT), important drawbacks are associated with the volatility and flammability of liquid solvents and the chemical instability of the LiPF6 salt. The latter undergoes hydrolysis in the presence of water traces, releasing fluoride anions.
Ionic liquids (ILs) are salts with melting temperatures lower than 100°C. When they are liquid at room temperature, ILs are classified as room temperature ILs (RTILs). Some typical properties of ILs are: a) a low volatility, a high thermal stability and a negligible flammability; b) a high ion density and conductivity; c) a wide electrochemical stability window; and d) a simple synthesis, carried out by choosing the cation and anion which best comply with the requirements of the intended application. These features make ILs very suitable as solvents in electrolytes for Li batteries.
Recently, a class of solid-state single-ion conducting materials based on lithiated fluorinated-TiO2 (LiFT) was proposed, which demonstrated its applicability as a nanofiller to obtain nanocomposite polymer electrolytes. LiFT consists of fluorinated anatase nanoparticles that are directly surface-functionalized with Li through an innovative one-step reaction with molten metallic lithium. The conductivity of LiFT is due to Li hopping processes between coordination sites present at the nanoparticle grain boundaries. These latter events take place in a very effective way.
The use of LiFT nanoparticles as the source of Li ions and ILs as the plasticizing agents allowed us to obtain innovative composite electrolytes for application in lithium batteries with a high thermal stability and conductivity. Indeed, the use of imidazolium ILs based on TFSI- and BF4- anions allowed us to investigate the different ability of these anions to coordinate and dissociate the Li cations present on the surface of LiFT nanoparticles. For these reasons it has to be highlighted that no conventional Li salts are used in the electrolytes here proposed.
In this report, composite electrolytes based on LiFT nanopowder, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMImTFSI) ILs are proposed. In details, LiFT nanopowder is doped with a known amount of both ILs to obtain two types of electrolytes with formula LiFT/EMImTFSI0.118 and LiFT/(EMImBF4)0.200. The resulting electrolytes contain around 25% wt of ILs and show a powder-like consistence.
The correlation between structure, thermal properties and conductivity mechanisms of the resulting LiFT/EMImTFSI0.118 and LiFT/(EMImBF4)0.200 electrolytes is investigated by a variety of techniques: (a) FT-MIR and FIR at different temperatures; (b) Differential Scanning Calorimetry (DSC); (c) Thermogravimetric Analysis (TGA); and (d) Broadband Electrical Spectroscopy (BES).
The materials are thermally stable up to 250°C and their conductivities at 30 and 130°C are, respectively, of 1.2x10-2 Scm-1 and 4.1x10-2 Scm-1 for LiFT/EMImTFSI0.118 and 1.7x10-3 Scm-1 and 1.7x10-2 Scm-1, for LiFT/(EMImBF4)0.200
Électrolytes halogénés caténés pour piles hybrides primaires et secondaires à base de métaux divalents et multivalents d’acide de lewis
No full textIodide-conducting plastic crystals based on N,N-dimethyl-2-(methylsilyloxy) ethanaminium cations (MESEAn+) for application in dye-sensitized solar cells
No full textThis report describes the synthesis and the properties of twelve iodide-conducting Plastic Crystal Electrolytes (PCEs) based on N,N-dimethyl-2-(methylsilyloxy) ethanaminium cations (MESEAn+) and I-/I3 - anions for application in dye-sensitized solar cells (DSSCs). The PCEs are obtained in three steps. In the first, the MESEAn+(Cl-)n precursor is prepared by reacting different chlorosilanes (CH3)4-n SiCln with 1 ≤ n ≤ 4 with N,N-dimethyl ethanolamine (DMEA). In the second step, the MESEAn+(I-)n PCEs are obtained by treating MESEAn+(Cl-)n with CH3I. In the final step, the MESEAn+(I-)n are doped with different aliquots of I2 to obtain blends of MESEAn+(I-)n and MESEAn+(I3 -)n PCEs bearing the active I-/I3 - redox couple. Twelve PCEs based on siloxane cations, with general formula {[MESEAn+(I3 -)n ]ρ%·[MESEAn+(I-)n ]100-ρ%} with 1 ≤ n ≤ 4 and 0 ≤ ρ% ≤ 8.3 are obtained. ρ% is the percentage of I3 - on the total anions included in the PCEs. The properties of the PCEs are investigated by vibrational spectroscopy (MIR FT-IR), high-resolution thermogravimetric analysis (HR-TGA), differential scanning calorimetry (DSC) and broadband electrical spectroscopy (BES) in order to study the correlations between the structural features, the conductivity and the composition of the proposed electrolytes. Results show that the PCEs with n = 3 and ρ% = 3.7 exhibit: (a) a melting temperature below 100 °C, which is typically observed in room-temperature ionic liquids; (b) a thermal stability up to 200 °C and (c) a conductivity of 0.8·10-4 S cm-1 at 50 °C
Interplay Between Vibrational Modes and Relaxations in Electrolytes for Secondary Magnesium Batteries Based on Haloaluminate Ionic Liquids
No full texthe search for electrolytes with enhanced performance is a crucial point for the development of efficient secondary Mg batteries. Early work on Mg deposition and stripping from Grignard-based non-aqueous solution were proposed in 1990 by Gregory et al., while the first example of polymer electrolytes comprising PEG400 and δ-MgCl2 was proposed in 1998. In the following years, electrolytes based on EthylMgBr and PEO, Grignard, and other organo-Mg7compounds were explored.
Among all proposed materials, Grignard and organo-Mg compounds, suffer from several drawbacks associated with their chemical stability in ethereal-based solvents, which are characterized by a high vapor pressure and flammability. On the contrary, Ionic Liquids (ILs) seem a very appealing class of materials for applications in Mg secondary batteries due to their: a) very low volatility, high thermal stability and non-flammability; b) high ion density and high conductivity; c) wide electrochemical stability window; and d) easiness of synthesis by evaluating the best cation and the anion for each application.
There are still several aspects that are not fully understood regarding the use of ILs in electrochemical devices. Indeed, the conductivity mechanisms, the formation of the solid-electrolyte interface (SEI) and long-term performance of these systems are still open questions. Nevertheless, from a fundamental point of view, understanding the interplay between the ILs relaxations and the charge carrier migration is crucial in order to clarify the effect of the ILs matrix on the conductivity mechanism of Mg2+ions.
Here we present a family of electrolytes based on 1-ethyl-3-methylimidazolium iodide, aluminium iodide, and δ-MgI28 with general formula [EMImI/(AlI3)m]/(δ-MgI2)n. The short-range structural features and the interactions in the electrolytes are elucidated by coupling Raman and Infrared (both in the medium and in the far infrared) spectroscopy with DFT calculations.
The detailed electrical response of the [EMImI/(AlI3)m]/(δ-MgI2)n materials in terms of polarization and relaxation events at temperatures higher and lower than the melting of EMImI/(AlI3)m are investigated by using Broadband Electrical Spectroscopy (BES). The results allow us to correlate the dielectric relaxation of the imidazolium cations with the overall long-range charge migrations, thus elucidating the interplay existing between conductivity and nanostructure of this new class of IL
Ab Initio Study and Vibrational Spectroscopy of Imidazolium Based Ionic Liquids with Dissolved δ-MgCl2
No full textIonic liquids (ILs) are liquid salts at room temperature having unusual properties as liquids. The most important properties of these electrolyte solutions are non-volatility and high ion conductivity which makes them a safe and advance choice for electrolyte solutions in energy devices. In general, ILs as the name implies, are comprised entirely of ions, usually organic cations and bulky anions. ILs are stable enough for ordinary use at temperatures of 200 to 300 ̊C. However, due to having organic cations their degradation begins at the weakest covalent bond. The chemical structure of ions can be tailored easily for the intended application. The structure and properties of these Coulomb systems are mainly determined by the type and strength of the intermolecular interactions between anions and cations. In particular, the subtle balance between Coulomb forces, hydrogen bonds (HBs) and dispersion forces is of great importance for understanding ILs.
Having these superior properties, ILs can be used as a good carrier for ion transport in batteries. Recently, imidazolium based ILs with δ-MgCl ions have been under investigations as new electrolytes for Mg-based batteries. These batteries show advantages over other competing types owing to the abundant source of Mg in the earth’s crust, better disposal and waste management. In addition, they have wide operation temperature range and their capacity loss over time is little.
The aim of this work is to use the results of first principles electronic structure calculations to study the structure of the new imidazolium based ILs with dissolved δ-MgCl . Although, there have been many studies on the imidazolium based ILs, but there is still a debate on whether the hydrogen bonding is responsible for the red shifted C–H stretching frequencies and downfield shifted C–H proton chemical shifts or not. Therefore, further studies on the structure and interactions of imidazolium based ILs especially in presence of δ-(MgCl ) are essential and helpful in optimal design of this new genre of electrolytes.
Differential scanning calorimetry on electrolytes composed of different amount of δ-MgCl dissolved in a homogeneous mixture of aluminum tri-chloride and 1-ethyl-3-methylimidazolium chloride (EMImCl) ionic liquid has been done. The results show that by varying δ-MgCl concentration at least two types of Mg complex depending on δ-MgCl concentration are formed. The IR spectrums show new peaks in the far infrared region by increasing the concentration of δ-MgCl indicating the formation of new bimetallic complexes. Also, Experimental IR investigations on EMImBF /[δ-(MgCl ) ] indicate that by increasing f which is the concentration of δ-(MgCl ), the Clˉ interaction band at 3050 cm , typical of the hydrogen bonding network in EMImCl appears in the difference spectra. The comparison between the profiles of pristine IL and EMImBF /[δ-(MgCl ) ] show that Mg forms different complexes with BF ˉ anion. However, these new complexes are not known.
Electronic structure calculations were undertaken on the ethyl-methyl imidazolium cation in proximity to a number of different anions (Clˉ, AlCl ˉ, BF ˉ) using Hatree-Fock (HF), post HF, DFT, and Hybrid methods with different basis sets. The calculations were performed using Gaussian 09 suite of program.
Geometry optimizations were followed by frequency calculations to confirm the presence of each local minimum. Different initial structures have been searched for each system to determine the global minimum. Then the calculated IR spectrums are compared to the experimental spectrums and the least expensive method which is capable of describing the experimental spectrum is chosen for further calculations. Next calculations are performed on larger clusters of cations and anions which contains MgCl . The IR spectrums are compared to experimental spectrums and the assignments of vibrational modes are done by visualizing the vibrational frequencies of the calculated structures
Broadband Electric Spectroscopy of triethylammonium-methanesulfonate and triethylammonium-perfluorobutanesulfonate Ionic Liquids
No full textIn recent years Proton Exchange Membrane Fuel Cells (PEMFCs) have drawn considerable interest from both the scientific community and the industry due to: a) a high energy
conversion efficiency; b) a low environmental impact; and c) the possibility of applications ranging from portable electronics to the automotive sector. The heart of a PEMFC is its
proton exchange membrane (PEM). The most widely used PEMs consist of perfluorinated polymer electrolytes such as Nafion. These systems have drawbacks such as their low proton conductivity at temperatures higher than 90°C and at low relative humidity which severely limits their large-scale commerciol use. In order to overcome these limitations, PEMs
composed of perfluorinated ionomers doped with proton-conducting ionic liquids (PCILs) were recently proposed due to their high conductivity under anhydrous conditions, large
electrochemical stability window and good thermal stability.
Here, we report the investigation of triethylammonium-methanesulfonate (MST) and triethylammonium-perfluorobutanesulfonate (PFBuT) PCILs by techniques such as Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC) and Broadband Electric Spectroscopy (BES). These measurements allow us to investigate the relationship between the thermal behaviour and the proton conduction mechanism of this type of ionic liquid. The TGA/DSC results indicated that: a)ILs are thermally stable up to 200°C; b) MST shows a glass transition at -17°C and two endothermic transitions at 20 and 38°C; and c) PFBuT shows a glass transition at -20°C and two endothermic transitions at 17 and
61°C. The BES results reveal that at 120°C, MST and PFBuT showed conductivity values of 1.4x10-2 and 7.8x10-3 S·cm-1, respectively. These results make the ILs promising materials to
be used in the preparation of membrane for PEMFCs operating above 100°C
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