1,720,974 research outputs found
Investigation of the reactivity of Li- and Na- alanates as conversion anodes for lithium ion batteries
Full text linkAs for borohydrides, the alanate family promises very interesting capacities due to the light molar weight of aluminum and the high hydrogen content of these complex hydrides. In fact, in view of a full conversion reaction in LiH and metal elements, they can theoretically achieve more than 1000 mAhg-1 exchanging at least 3 electrons for redox center. Furthermore, their thermal stability makes these compounds feasible candidates for practical applications (details are in chapter 3).
The interest in them has been supported from pioneering DFT calculation performed in our laboratory few years ago [25,26], with the task to theoretically demonstrate the feasibility of alanates conversion reaction and its exploitability for application in lithium ion batteries. Besides our investigations, also Trepovich et al. [24] recently reported the use of LiAlH4 and NaAlH4 as anodes in lithium cells, furnishing a reference for comparison of our results and conclusions.
This PhD thesis provides the experimental evidences of the electrochemical activity of sodium and lithium alanates in lithium cells. The focus is on the properties and reaction mechanism of tetrahydro-alluminates (LiAlH4 and NaAlH4). Beside them, further three hexa-alanates phases (Li3AlH6, Na3AlH6 and Li Na2AlH6) have been investigated. In fact, the electrochemical reaction mechanism is expected to involve the formation of these compounds in the intermediate steps. Therefore, their behavior in electrochemical cells have been used to delineate a full picture of the conversion mechanism of the corresponding tetrahydro-alluminates compounds.
The work has been structured in three sections. The first section is focused on lithium alanates (LiAlH4 and Li3AlH6). Chapter 4 reports the studies conducted on LiAlH4. After confirming the electrochemical activity of this compound, mechanochemical treatments have been used to improve its performance. It's well known that mechanical grinding causes the reduction of the particles and induces strains that could lead to a better diffusion of hydrogen and lithium by increasing the number of diffusion paths. Comparisons with pristine sample have been made to evaluate the effects of the performed treatments on the structure, morphology and electrochemical performance. The electrochemical reaction mechanism has been elucidated by ex-situ diffraction experiments on LiAlH4 based electrodes at different state of charge. The chapter ends with the study of the reactivity of LiAlH4 with the carbonate based electrolyte used for electrochemical tests. Chapter 5 provides the results for Li3AlH6. In this case, mechanochemistry has been used to synthesize the compound.
Second section describes the sodium alanates compounds (NaAlH4, Na3AlH6 and LiNa2AlH6). As already did for lithium alanates, mechanochemical treatments have been used both to activate the bare NaAlH4 (chapter 6) and to synthesize hexa-alanates phases (chapter 7). Then, for the obtained samples the chemical-physical and the electrochemical properties have been studied. Finally, in the chapter 8, the conversion reactions of the three phases have been described by in situ diffraction experiments during discharge/charge cycling. Further investigations have been addressed on NaAlH4, in view of the encouraging results obtained.
In conclusion, the last section is dedicated to the performance improvements of the alanates based electrodes. In fact, for all the samples poor cell efficiency and cyclability have been observed. This could be mainly ascribed to the big volumetric expansion observed with conversion reaction as well to the high reactivity of this materials with the common solvents used as electrolytes, due to the high reducing power of alanates. Two main strategies have been adopted to reduce these effects: the nanoconfinement in a nanoporous carbon matrix, as described in chapter 9 and the replacement of carbonates based electrolyte with an ionic liquid, as in chapter 10
Recent advances in liquid and polymer lithium-ion batteries
No full textNew types of electrode and electrolyte materials have been investigated and characterized in our laboratory. These include high capacity lithium-tin alloys, high-rate lithium titanium oxide and high conductivity gel-type, polymer electrolytes. The results obtained, collected in this article, demonstrate that these materials may be combined for the development of new types of liquid and polymer lithium-ion batteries having impressive features in terms of capacity, stability, high rates and, particularly, safety. Taking this into consideration, these batteries appear suitable power sources for electric or hybrid vehicles
The role of the interface of tin electrodes in lithium cells: An impedance study
No full textIn this work we investigate by impedance spectroscopy the characteristics of a film formed on the surface of Sn electrodes when cycled in a lithium cell. We show that this film is formed by electrolyte decomposition catalyzed by the tin surface and that its characteristics depend upon cycling rate as reported in the literature. By the infrared analysis we study the chemical characteristic of mentioned film. By reporting the cycling response of a complete lithium-ion battery using a Sn anode coupled with a LiNi0.5Mn1.5O4 cathode, we show that the interfacial film may indeed influence the response of the batteries using conventional, tin-based anodes. (C) 2007 Elsevier B.V. All rights reserved
Insights about the irreversible capacity of LiNi0.5Mn1.5O4 cathode materials in lithium batteries
No full textThe accumulation of irreversible capacity in the first cycle and upon cycling has been studied for LiNi0.5Mn1.5O4-based cathodes (LNMO), bare and coated with ZnO. Materials have been synthesized at 800 degrees C and characterized by X-ray diffraction and transmission electron microscopy (TEM). The precipitation of a continuous ZnO film on the surface of LNMO has been highlighted by TEM. Galvanostatic cycling at room temperature and at 60 degrees C, linear sweep voltammetry (LSV), impedance spectroscopy and TEM techniques have been used to investigate the materials and the irreversible capacity accumulation upon cycling. Our study confirms that continuous parasitic processes occur upon cycling beyond the first charge/discharge. Anodic LSV test shows that side oxidation processes start on the surface of a LNMO electrode at potential slightly above the Ni2+/Ni4+ redox couple. At the end of charge an uniform and continuous thin film (3-4 nm) forms of on the bare LNMO. This film likely modifies upon cycling and it is apparently unable to passivate the LNMO surface preventing further decompositions. On the contrary the material coated with ZnO shows rough surfaces without large morphological alteration upon charge and cycling. The ZnO coating confirms its ability to mitigate the irreversible charge consumption. (C) 2013 Elsevier Ltd. All rights reserved
Novel Lithium Ion Batteries Based on a Tin Anode and on Manganese Oxide Cathodes
No full textIn this paper we report two innovative lithium ion batteries formed by the combination of a nanosized tin anode and a LiNi(0.5)Mn(1.5)O(4) or a LiNi(0.33)Co(0.33)Mn(1.33)O(2) cathode. The batteries have a very stable cycling response at a high rate of I C with an excellent capacity delivery, i.e., 140 mAhg(-1) and 175 mAhG(-1), respectively. Estimated energy density values are of the order of 150 Whkg(-1) for both batteries
Advanced electrolyte and electrode materials for lithium polymer batteries
No full textThe most recent results obtained in our laboratory on the characterization of two classes of polymer electrolytes and of olivine-type lithium iron phosphate electrodes are reviewed and discussed, especially in view of their application in advanced lithium batteries. (C) 2003 Elsevier Science B.V. All rights reserved
Batteria Litio-Ione Polimerica con configurazione elettrochimica
No full textLa presente invenzione si riferisce al settore degli accumulatori (o batterie) litio-ione, in particolare a una batteria con configurazione elettrochimica innovativa, dove l’anodo (elettrodo negativo) è un composto del tipo M-C, dove M è scelto nel gruppo costituito da Sn, Sb, Si, Mg, Al o leghe tra loro e C è carbone amorfo; il catodo è un ossido del tipo LiM1M2O4, dove M1 e M2 sono scelti nel gruppo costituito da Mn, Ni, Fe, Co, Po combinazioni tra loro; l’elettrolita è una membrana gel a base di floruro di polivinilidene. Vantaggiosamente, la presente invenzione consente lo sviluppo di batterie litio-ione polimeriche innovative con prestazioni superiori rispetto alle attuale in termini di sicurezza, costo, energia specifica e durata operativa
A New Type of Lithium-ion Battery Based on Tin Electroplated Negative Electrodes
No full textThis work describes the preparation and the characterization of various samples of metallic Sn electroplated on a cupper foil under different current and time regimes. These samples have been characterized by XRD and SEM and tested as negative electrodes in a cell using lithium foil as the counter electrode. The best electrode has been cycled with a capacity in the order of 990 mAhg(-1), i.e. approaching 100 % of theoretical capacity at 1 equivalent Li alloying. This electrode was also tested under a limited capacity regime (400 mAhg(-1)) showing an interesting cycle life. Finally, the electrode was used as anode in a lithium-ion cell with LiNi(0.5)Mn(1.5)O(4) as cathode. This cell performed well at high rate (1C rate), delivering high capacity and excellent charge-discharge efficiency for a limited amount of cycles
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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