1,720,988 research outputs found
Synthesis and characterization of advanced materials for Li-ion batteries :\ud 1. Si/RGO nanocomposite anodes.\ud 2. V2O5 gel cathodes.
No full textLithium-ion batteries represent the state-of-the-art of electrochemical energy storage. However, with the advance of microelectronic technology for portable devices and the progressive introduction into the automotive market of Electrical Vehicles (EVs.), a breakthrough in Li-ion materials is needed to overcome known issues related to cost, higher energy densities, safety and cycle life. Moreover, steps forward are also needed from a sustainability point of view, in order to reduce both costs and environmental impact during battery manufacturing.\ud
On the anode side, research in next-generation materials, capable of replacing the industry-standard graphite, are now underway. In this PhD thesis, a novel high capacity Silicon/Reduced Graphene Oxide (Si/RGO) nanocomposite has been synthesized, thoroughly characterized and evaluated under an electrochemical point of view. The electrode preparation has been optimized using an alternative binder and eco-friendly solvent like ethanol. The composite shows a good stability and capacity retention over prolonged cycling.\ud
On the cathode side, next-generation materials should have higher capacities in order to increase the energy density of the future batteries. In this PhD thesis, Vanadium Pentoxide (V2O5) - has been studied both in its amorphous (aerogel) and crystalline form as next generation Li-ion cathode materials. Also in this case materials were prepared, characterized and electrochemically tested. A green and eco-friendly approach during electrode processing was used also in this case.\ud
The data resulting from this PhD thesis were subject of the following publications and proceedings of congresses:\ud
- F. Maroni, R. Raccichini, A. Birrozzi, G. Carbonari, R. Tossici, F. Croce, R. Marassi, F. Nobili Graphene/silicon nanocomposite anode with enhanced electrochemical stability for lithium-ion battery applications, J. Power Sources, 2014; Vol. 269; 873 – 882. doi:10.1016/j.jpowsour.2014.07.064\ud
- A. Moretti, F. Maroni, F. Nobili, S. Passerini, V2O5 electrodes with extended cycling ability and improved rate performance using polyacrylic acid as binder, J. Power Sources, 2014, In Press. doi : 10.1016/j.jpowsour.2014.09.150\ud
- A. Moretti, F. Maroni, I. Osada, F. Nobili, S. Passerini, V2O5 aerogel as a versatile cathode material for lithium and sodium batteries, ChemElectroChem, 2014, In Press.\ud
- F. Nobili, F. Maroni, R. Raccichini, R. Tossici, R. Marassi, A Silicon/Graphene Composite Anode for High-Efficiency Lithium Batteries, 17th International Meeting on Lithium Batteries, June 10/14 2014, Cernobbio (CO) Italy, Abstract #361.\ud
- F. Nobili, F. Maroni, R. Raccichini, R. Tossici, R. Marassi, Graphene/Silicon nanocomposite anode with enhanced electrochemical stability for Li-ion battery applications, Green Lion European Project Workshop, October 28-29 2014, Ulm, Germany Abstract #20.\ud
- Si/RGO nanocomposite development was carried out within the ENEA project “Ricerca di materiali anodici per batterie litio ione operanti in elettroliti organici convenzionali di più elevata energia rispetto a quelle sul mercato” and reported in the following documents:\ud
- R. Marassi, F. Nobili, R. Tossici, M. Marinaro, A. Birrozzi, R. Raccichini, RdS 2012\ud
- A. Birrozzi, F. Maroni, G. Carbonari, R. Tossici, F. Nobili, R. Marassi, RdS 201
Sol-Gel Synthesis of Iron-Manganese Mixed Oxide as Superior and Eco-Friendly Anode for Lithium-Ion Batteries
No full textLithium-ion batteries (LIBs) are the perfect balance between portability, low cost and good performances. Considering the anodic side, graphite is the most used active material 1, which despite its wide use, and a specific capacity of 372 mAhg-1, has been included in the European Commission list of critical raw materials that have to be replaced in the future. For this reason, a great deal of effort has been devoted to investigate a relatively new class of materials emerged in this last few years, showing a different reactivity from traditional insertion materials, the so-called conversion materials. Among these, transition metal oxides (TMOs), can reach extremely high capacity values, up to five times higher than graphite 2. Despite this, they have evidenced several drawbacks: short cyclic life, a large first cycle irreversible capacity, and a relevant volume variation during cycling. In this work, an Iron-Manganese mixed oxide was synthesized by Sol-Gel method and tested as anode for Li-ion batteries. In order to address the aforementioned drawbacks, and improve the mechanical stability of the electrodes, improved binders with superior mechanical properties 3, such as Polyacrylic Acid (PAA) and Sodium-Carboxymethyl Cellulose (Na-CMC), and an environmentally friendly electrode processing using ethanol or H2O as solvents, were evaluated. The experimental data shown superior performance with respect to the standard Polyvinylidene Fluoride system, which makes use of the expensive and toxic N-Methyl-2-pyrrolidone (NMP) solvent.
References:
1 Scrosati, B.; Garche, J.; Journal of Power Sources 2010, 195, 2419-2430.
2 Cabana, J.; Monconduit, L.; Larcher, D.; Palacìn M.R.; Advanced Material 2010, 22, 170-192.
3 Magasinski, A.; Zdyrko, B.; Kovalenko, I.; Hertzberg, B.; Burtovyy, R.; Huebner, C.F.; Fuller, T.F.; Luzinov, I.; Yushin, G.; ACS Applied Materials & Interfaces 2010, 2, 3004-3010
Development of an UV-Visible spectroelectrochemical method to correlate State of Charge (SOC) and Open Circuit Voltage (OCV) in a Vanadium-Vanadium Redox Flow Battery
No full textVanadium-Vanadium Redox Flow Battery (VRFB) is a type of Redox Flow Battery (RFB) which uses the redox couples VO2+/VO2+ (cathode side) and V3+/V2+ (anode side) in a concentrated solution of H2SO4, with a cell voltage of 1.26 V at room temperature [1-2]. Since vanadium ions show different colours depending on their oxidation state, the UV-Vis spectroscopy is a useful technique to study all the systems which involve them. Due to the high concentration both of the vanadium ions and of sulphuric acid, the number of the species and their equilibriums vary with the operative conditions and the cell’s State of Charge. This produces deviations from linearity in the absorbance vs. concentration diagram and as consequence it is very difficult choose a specific wavelength which has a linear trend with the concentration of defined species. In this context, a model to correlate the State of Charge (SOC) and the Open Circuit Voltage (OCV) by employing both the electrochemical and the spectral techniques have been developed. In a typical experiment a certain amount of charge has been applied to the cell, then the current flow is interrupted to register both the OCV and the spectrum in equilibrium conditions. The sequence is repeated for the required number of times to charge/discharge the cell completely. From the obtained results, it is possible to assume that a more accurate correlation among OCV, Absorbance and SOC should be achievable, being known pure species spectra, applying methods of Pattern Recognition to the entire spectrum [3].
References:
1) Z. Yang, J. Zhang, M. C. W. Kintner-Meyer, X. Lu, D. Choi, J. P. Lemmon, J. Liu, Chem. Rev., 2011, 111, 3577-3613.
2) S. Hamelet, T. Tzedakis, J.-B. Leriche, S. Sailler, D. Larcher, P.-L. Taberna, P. Simon, J.-M. Tarascon, Journal of The Electrochemical Society, 2012, 159 (8), A1360-A1367.
3) A. Herrero, S. Zamponi, R. Marassi, P. Conti, M.C. Ortiz, L.A. Sarabia, Chemometrics and Intelligent Laboratory Systems, 2002, 61, 63-74
Graphene/silicon nanocomposite anode with enhanced electrochemical stability for lithium-ion battery applications
No full textA graphene/silicon nanocomposite has been synthesized using a green approach during both synthesis and electrode processing. It has been characterized and tested as anode active material for lithium-ion batteries. The synthesis was performed by dispersing silicon nanoparticles in a carbonaceous matrix, obtained by a dual step reduction process of a previously functionalized graphene oxide substrate which avoids the formation of aggregates of Si particles and partially buffers the huge volume variations associated with Li/Si alloying processes. The graphene oxide matrix functionalization was achieved using low-molecular weight polyacrylic acid and a low-cost and eco-friendly solvent like ethylene glycol. As concerns electrode processing, composite anodes were prepared using high-molecular PolyAcrylic Acid as green binder and using ethanol as non- toxic and cheap solvent, thus avoiding the standard PVDF/NMP system which is, on the other hand, toxic and highly expensive. Furthermore, Vinylene Carbonate (VC) was used as electrolyte additive. Long cycling performance was evaluated at a current of 500 mAg-1 : after 100 cycles the anode showed a discharge capacity retention of about 80%. Analyzing the impedance spectra of the tested cells, the beneficial effect of the VC additive was showed in terms of lower SEI resistance in the long term
A Silicon/Graphene Composite Anode for High-Efficiency Lithium Batteries
No full textComposite anodes based on Si and reduced graphene oxide (RGO) have been prepared using commercial Si nanopowder, graphene oxide (GO) and polyacrilic acid (PAA) as starting materials. A double reduction step, consisting in microwave irradiation at mild power followed by thermal annealing in reducing atmosphere, yielded the composite powder made of Si:reduced graphene oxide (RGO) in the approximate mass ratio 30:70. The charge/discharge properties of the anode materials are determined by the homogeneous dispersion of Si grains between RGO nanosheets, that act as structural buffer for volume changes related to Li-Si reversible alloying and as improved electrical conductor. Electrodes have been prepared using high-molecular weight PAA as binder, which promises better mechanical stability towards silicon volume changes. The electrochemical behavior of the composite anode material has been characterized by galvanostatic cyclations and electrochemical impedance spectroscopy, using LiPF61M in EC:DMC 1:1 electrolyte, also modified by the addition of 5% vinylene carbonate (VC).
Several anodes have been investigated, consistently delivering reversible capacities higher than 1000 mAhg-
1, with a mechanism that, after initial lithiation of crystalline Si, mainly involves reversible Li-Si alloying/dealloying between amorphous a-Li and a-LixSi phases. Particularly, when cycled in VC-modified
electrolyte the anode exhibits a remarkable cycle life, resulting in a residual capacity of more than 900 mAhg-
1 after 60 cycles at 500 mAg-1 and efficiency values close to unity. Several factors concur in determining this behavior, namely: (i) the efficient Si dispersion in RGO carbonaceous matrix; (ii) the good mechanical properties of PAA binder; (iii) the formation of a stabilized SEI by VC additive in the electrolyte
Ricerca di Sistema Elettrico. Materiali anodici avanzati per batterie al litio a base di leghe diverse
No full textNel presente rapporto sono contenuti i recenti sviluppi dell’attività di ricerca effettuata presso l’Unità di Ricerca UNICAM su anodi compositi a base di grafene (RGO, reduced graphene oxide) e Si, SnO2, leghe Sn- Sb, nell’ambito del programma “Ricerca di Sistema Elettrico” finanziato dall’Accordo di Programma Ministero dello Sviluppo Economico – ENEA.
I recenti sviluppi riguardano: (1) ottimizzazione delle prestazioni e della stabilità di anodi compositi Si/RGO mediante studio su vari tipi di legante acido poliacrilico (PAA) e utilizzo di elettrolita addizionato di vinilen carbonato (VC) reperibile commercialmente; (2) caratterizzazione elettrochimica a correnti superiori a quelle testate finora (fino a 1Ag-1); (2) miglioramento dell’efficienza di anodi compositi SnO2/RGO mediante ottimizzazione del contenuto di SnO2 nel materiale attivo; (3) ottimizzazione delle prestazioni e dell’efficienza a correnti elevate (500 mAg-1) mediante utilizzo di legante PAA ed elettrolita addizionato di VC.
La composizione, la struttura e la morfologia dei materiali attivi sono state caratterizzate mediante analisi termica, spettroscopia IR, diffrazione di raggi X, mentre le caratterizzazioni elettrochimiche sono state effettuate mediante cicli galvanostatici di carica/scarica.
I risultati ottenuti mostrano come per tutti gli anodi compositi in esame è possibile ottenere una capacità superiore a quella degli anodi ‘convenzionali’ a base di grafite, mentre la composizione e la morfologia dei materiali compositi hanno un effetto cruciale nel determinarne le prestazioni elettrochimiche, in particolare l’efficienza e la stabilità alla ciclazione ad elevate correnti
Buffering volume changes of Si nanocomposite anodes
No full textThe massive development of Li-ion technology has allowed for massive spreading of portable electronics, as well as for a progressive development of electrical vehicles (EV) with higher driving range. Despite this, the ever-increasing demand in energy density requests for a breakthrough in Li-storage materials. In this context, anode materials alternative to conventional graphite, with improved capacity, have been investigated for several years. Among these, Si plays a special role because of its extremely high theoretical capacity (4200 mAh g-1 corresponding to the formation of a Li22Si4 alloy). Nevertheless, the volume changes of about 300% associated with the alloying/dealloying processes represent a severe limitation to the electrode reversibility, so that actions aimed at counteracting this drawback are needed for the development of durable Si anodes.
The electrochemical behaviour of nanocomposite materials, based on commercial Si powder of about 100 nm size in which the volume changes are buffered by dispersing matrixes such as reduced graphene oxide (RGO) or transition metal oxides, is here presented. The electrodes and cells performances, in terms of specific capacity and durability, are optimized by the use of tailored binders and electrolyte formulations. A rationale of the improved behaviour is explored by applying several morphological, structural and electrochemical investigation techniques, with a special focus on electrode/electrolyte interfacial properties.
References:
1. M.N. Obrovac, L. Chistensen, Electrochem. Solid State Lett. 7 (2004) A93.
2. F. Maroni, R. Raccichini, A. Birrozzi, G. Carbonari, R. Tossici, F. Croce, R. Marassi, F. Nobili, J. Power Sources 269 (2014) 873
A lithium-ion battery based on LiFePO4 and silicon/reduced graphene oxide nanocomposite
Full text linkIn this paper, the preparation and chemical–physical characterization of a composite material made of silicon nanoparticles (nSi) and reduced graphene oxide (RGO) for using as an anode for lithium-ion batteries are report- ed. The nSi/RGO composite was synthesized by microwave irradiation followed by a thermal treatment under reducing atmosphere of a mixture of nSi and graphene oxide, and characterized by XRD, SEM, and TGA. The nano- structured material was used to prepare an electrode, and its electrochemical performance was evaluated in a lithium cell by galvanostatic cycles at various charge rates. The electrode was then coupled with a LiFePO4 cathode to fabricate a full lithium-ion battery cell and the cell performance evaluated as a function of the discharge rate and cycle number
V2O5 electrodes with extended cycling ability and improved rate performance using polyacrylic acid as binder
No full textIn this work the electrochemical characterization of V2O5 electrodes, prepared using polyacrylic acid (PAA) as binder, is presented. The obtained electrodes display stable high capacity values (250 mAh g-1) when cycled at low rates (44 mA g-1), and a reversible capacity of 90 mAh g-1 is obtained at high specific current (3A g-1). The PAA-based electrodes possess an excellent cycling ability with a capacity retention of 94 % after 100 cycles. The present study demonstrate the possibility to overcome the dramatic capacity fading of V2O5 by a simple approach, permitting to obtain electrochemical performance similar to those of more complicated nano-architectures via the use of a greener electrode manufacturing process
Electrospun Carbon / CuxO Nanocomposite material as Sustainable and High Performance Anode for Lithium-Ion Batteries
Full text linkThe increase in energy density of the next generation of battery materials to meet the new challenges of the electrical vehicles era calls for innovative and easily scalable materials with sustainable processes. An innovative CuxO/C nanocomposite material, characterized by a highly conductive 3D-framework, with CuxO/Cu-metal contiguous nanodomains is prepared by electrospinning. The electrode processing is made using a polyacrylic acid binder. The nanocomposite has been fully characterized and the electrochemical performance shows high specific capacity values over 450 galvanostatic cycles at 500 mAg-1 specific current with capacity retention values over 80 %. In addition, the composite shows remarkable high rate performance and highly stable interface, which has been studied by impedance spectroscopy
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