New electrolytes for high power Li-ion batteries:electrochemical stability, Li-ion insertion kinetics and corrosion inhibition properties

A new generation of high power Li-ion batteries that avoid carbon as anodic material replacing it with the spinel Li4Ti5O12 has been studied in this work. For these new Li-ion cells new electrolyte compositions can be considered. The main work of this thesis was focused on the electrolyte. Electrochemical techniques such as Cyclic Voltammetry and Amperometry were used to characterize the behaviour of electrolytes containing LiSO3CF3 or LiN(SO2CF3)2 (LiTFSI) or LiN(SO2C2F5)2 (LiBETI) salts. It was confirmed that LiTFSI determines a severe corrosion of the aluminium current collector at potential around 3.7 V (vs. Li). A protective effect induced by solvents having a cyano-group has been shown. The increase in repassivation potential (ER) observed with nitriles is in the range 0.4-0.5 V, and the value diminishes with increasing the temperature. Based on the experimental observations made and information collected from the literature, a mechanism to explain the inhibiting properties of nitriles was proposed. This was based on the assumption that aluminium undergoing corrosion have highly reactive intermediates, e.g. Al+, capable of reducing the electrolyte. The extension of the experiments to prototype Li-ion cells demonstrated that corrosion inhibiting properties combine with superior Li-ion insertion kinetics. Prototype Li-ion cells were made using Swagelok-type cells. Tests of Li4Ti5O12/LiCoO2 cells were performed for high charge rate and under extensive cycling. Charge/discharge curves showed that the new electrolytes offer properties suitable for high power batteries. Particularly, electrolytes containing LiTFSI salt were found to be compatible with LiCoO2 cathode materials on an aluminium current collector under cycling of up to 4.15 V (vs.Li.) at ambient temperature. Electrochemical stabilities of some solvents from the lactone and nitrile families were studied as well as kinetics. Substitutions in the α and γ positions of the γ-butyrolactone (γ-BL) were not successful in increasing the electrochemical stability of the γ-BL. UVvis spectra as well as HPLC analyses on electrolyzed γ-BL/LBF4 electrolytes suggested that the electrochemical decomposition of γ-BL involves a complex mechanism. Likely the reactions: occurs 'in parallel', 'in sequence' and exhibits 'feedback'. Electrochemical stability of some nitriles tested: only oxidipropionitrile exhibited a resistance to oxidation higher than γ-BL. All the electrolytes under investigation showed higher currents on glassy carbon than on tin oxide electrodes. LiMn1.5Ni0.4Ti0.1O4 electrode for high voltage Li-ion battery were also tested. The use of cyclic voltammetry in combination with nano-composite TiO2 electrodes proved suitable for kinetics evaluation. The nature of the salts as well as the solvents provided an effect on the Li-ion insertion kinetics. The observed differences were explained by means of a computational approach (MESP) relating its results to the "hard soft/acid base" concept

Non-corrosive electrolyte compositions containing perfluoroalkylsulfonyl imides for high power Li-ion batteries

The use of LiN(SO2CF3)2 as salt in lithium-ion secondary cells was considered to be a promising alternative to LiPF6 salt. However, in practice this salt has never been used in rechargeable batteries due to the severe corrosion it causes to the aluminium current collector. The spinel Li4Ti5O12 has been a focus of attention for the major battery manufacturers as an alternative material for anodes instead of graphite; for cells employing this material, new electrolyte compositions can be considered which solve the corrosion problem and allow the use of imide-type salts. This work reports electrochemical studies characterizing the corrosion of aluminium electrodes polarized at high voltages in aprotic solvents containing LiSO3CF3 (LiTf) or LiN(SO2CF3)2 (LiTFSI) or LiN(SO2C2F5)2 (LiBETI) salts. Despite the observation that in common battery solvents LiTFSI causes severe corrosion of the aluminium current collector at potential around 3.7 V (vs. Li), solvents having a cyano-group showed a repassivation potential (ER) around 4.15 V (vs. Li). Based on the experimental observations made and previous literature reports, a mechanism to explain the inhibiting properties of nitriles is proposed. The nitrile-based electrolytes allow the final usage of LiTFSI in commercial batteries using LiCO2 as cathodic material on aluminium current collectors. Keywords: Aluminium corrosion, Corrosion inhibition, Imide salts, LiTFSI, Nitriles, Li-ion batterie

Characterization of a Novel Packaged Hydrogel Wound Dressing by 2.35 T Magnetic Resonance Imaging

Hydrogel wound dressing makes easier the treatment of patients suffering from difficult wounds. A new process for the manufacturing of a sterile, packaged hydrogel wound dressing, based on an interpenetrating structure of calcium alginate, agar, and polyvinylpyrrolidone, was recently developed. The new formulation overtakes some previous technologies’ drawbacks expressing a better resistance to mechanical deformations compared to products on the market. In this work, the 2.35 T proton density, spin-lattice relaxation time, spin-spin relaxation time, phase-coherence relaxation, and water apparent diffusion coefficient analysis in the new hydrogel and several alternative formulations, including a commercial one (Neoheal®), are reported. Specifically, the combination of agar, acting as a thermolabile forming agent, with calcium alginate and γ irradiated polyvinylpyrrolidone, acting, respectively, as physical, and chemical crosslinking agents with an irreversible (temperature independent) effect, have been investigated. The new hydrogel formulation brings a qualitative improvement in its handling due to its increased mechanical stiffness when compared to the commercial hydrogel reference. This comes together with a reduced water content (100 vs. 112 for proton density in arbitrary units) and swelling capacity (88% vs. 124%) but with improved water mobility (1.42 vs. 1.34 × 10−3 mm2 s−1 for the apparent diffusion coefficient)

Comparison between tail suspension swing test and standard rotation test in revealing early motor behavioral changes and neurodegeneration in 6-OHDA hemiparkinsonian rats

The unilateral 6-hydroxydopamine (6-OHDA) model of Parkinson's disease (PD) is one of the most commonly used in rodents. The anatomical, metabolic, and behavioral changes that occur after severe and stable 6-OHDA lesions have been extensively studied. Here, we investigated whether early motor behavioral deficits can be observed in the first week after the injection of 6-OHDA into the right substantia nigra pars compacta (SNc), and if they were indicative of the severity of the dopaminergic (DAergic) lesion in the SNc and the striatum at different time-points (day 1, 3, 5, 7, 14, 21). With this aim, we used our newly modified tail suspension swing test (TSST), the standard rotation test (RT), and immunohistochemical staining for tyrosine hydroxylase (TH). The TSST, but not the standard RT, revealed a spontaneous motor bias for the 6-OHDA-lesioned rats from the day 1 post-surgery. Both tests detected the motor asymmetry induced by (single and repeated) apomorphine (APO) challenges that correlated, in the first week, with the DAergic neuronal degeneration. The described TSST is fast and easy to perform, and in the drug-free condition is useful for the functional assessment of early motor asymmetry appearing after the 6-OHDA-lesion in the SNc, without the confounding effect of APO challenges.peer-reviewe

A bright tetranuclear iridium(III) complex

A cyclic tetranuclear cyclometallated iridium(III) complex using cyanide anions as bridging ligands and displaying a tetrahedrally distorted square geometry has been obtained with high yield; photo- and electrochemical characterizations show that most interesting properties of mononuclear cyclometallated iridium complexes are retained in the tetranuclear assembly