1,354,284 research outputs found
Dynamic transition of dendrite orientation in the spinodal decomposition of viscous binary mixtures under a thermal gradient.
No full textIn this study, spinodal decomposition of a very viscous regular binary mixture bounded within two walls cooled at different temperatures is simulated by using the diffuse interface model. Under a temperature gradient, phase separation starts from the cooler wall forming dendritic structures growing anisotropically with time. Two remarkably different dynamics are identified depending on whether heat propagates slower or faster than mass. For small thermal conductivity (i.e., small Lewis number), dendrites grow parallelly to the temperature gradient, keeping such an alignment until the steady-state. On the other hand, for large Lewis number, during the early stages phase separation proceeds within stripes oriented along iso-temperature lines, i.e., with dendrites aligned perpendicularly to the temperature gradient, which, however, gradually shift their orientation parallel to the temperature gradient as the steady-state is approached. Such a dynamic transition of dendrite orientation upon a temperature gradient when heat propagates faster than mass is found to hold also for non-equimolar mixtures and for different species thermal conductivities. These results shed light on the dynamics of phase separation in constrained systems and anisotropic conditions
Direct recycling of spent lithium-ion batteries for the recovery of cathode active material by solid-state relithiation
No full text1.Introduction – The transition to electric vehicles has become a pressing need to move toward thedecarbonization of the transport sector. Nevertheless, this shift will generate a significant volume of spentlithium-ion batteries (LIBs), necessitating effective recycling strategies. Existing large-scale recyclingmethods, such as pyrometallurgy and hydrometallurgy, allow to reintegrate valuable materials back intothe supply chain, especially critical raw materials [1]. Currently, there is a growing interest in directrecycling, which emerges as a promising technique due to low energy consumption, regenerating thecathode material without destroying its original crystal structure. In this work, an experimental procedurefor direct recycling of spent cathode material has been investigated by solid-state relithiation.
2.Experimental – A spent lithium-nickel-manganese-cobalt oxide LiNi0.5Mn0.3Co0.2O2 (NMC) batterywas first discharged and disassembled. Pretreatment steps included dissolution with triethyl phosphate at120 °C to remove the binder, separation of aluminum and copper foils, and thermal treatment at 720 °Cfor carbon black and graphite removal. Relithiation was carried out by solid-state mixing of the recoveredspent cathode powder with lithium carbonate (Li2CO3) and sintering in air. Different lithium carbonateexcess (10-30 %) and different sintering temperatures (800-900 °C) were investigated. The obtainedpowders were characterized by X-ray diffraction (XRD), Scanning Electron Microscope (SEM) analysis,and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES).
3.Results and Discussion – XRD analysis was conducted to investigate the crystalline structure of therecycled cathode materials, and it was compared with the pristine and spent NMC. XRD patternsconfirmed that NMC structure is maintained and homogeneous without impurities (Image 1). Thecalculated intensity ratio I(003)/I(101) of each sample is reported in Table I. Values greater than 1.2confirmed the good layered structure and low Li+/Ni+ cation mixing of all recycled NMC. The Li molarfractions, fLi, calculated as the ratio of Li and transition metal elements (Ni, Co, Mn) by ICP-OESanalysis, are reported in Table I. The results evidenced that 10 % Li excess at 900 °C is not sufficient forthe complete Li stoichiometry recovery in the cathode material; while, using 30 % Li excess with athermal treatment at 800 °C led to a Li fraction of 1.005, thus compensating the Li loss in the spentbattery. The SEM analysis of lithiated samples showed that the applied treatment allows to obtainparticles with the same dimension and morphology as the pristine NMC.
4.Conclusions – This work presented the results of an experimental investigation for the direct recyclingof LIBs spent cathode material. Characterization of recycled NMC demonstrated the successfulregeneration of chemical composition and crystalline structure, obtaining comparable morphology andparticles dimension when using 30 % excess of lithium and sintering at 800 °C.
5.References
[1]D. Latini, M. Vaccari, M. Lagnoni, M. Orefice, F. Mathieux, J. Huisman, L. Tognotti, A. Bertei, J.Power Sources, 546, (2022) p. 231979
Modellazione multiscala di celle a combustibile ad ossidi solidi: dalla microstruttura alle prestazioni
No full textIn questo studio si presenta un approccio modellistico integrato per la simulazione di celle a combustibile ad ossidi solidi (SOFC). La modellazione copre in primis gli aspetti microstrutturali degli elettrodi porosi compositi costituenti la cella, le cui proprietà effettive di trasporto e reazione sono predette con la teoria di percolazione e/o con la ricostruzione numerica della microstruttura in funzione di composizione, distribuzione granulometrica delle polveri e condizioni di sinterizzazione. Le proprietà effettive costituiscono i parametri dei modelli di trasporto e reazione all'interno della cella, basati su bilanci di massa e carica, che permettono di ottenere la distribuzione delle variabili di campo e l'efficienza energetica del sistema. L'accoppiamento della modellazione microstrutturale con quella di trasporto e reazione permette di correlare i due livelli di scala cosicché i modelli tra loro integrati sono utilizzati come strumento interpretativo dei dati sperimentali e come strumento per l'ottimizzazione di prestazione e design.In this study an integrated modelling framework for the simulation of solid oxide fuel cells (SOFC) is presented. The modelling firstly covers the microstructural aspects of porous composite electrodes which constitute the cell, whose effective transport and reaction properties are predicted by means of percolation theory and/or numerical reconstruction of the microstructure as a function of composition, particle size distribution and sintering conditions. The effective properties are parameters of the models of transport and reaction within the cell, based on mass and charge conservation balances, which allow to obtain the field variables distribution and the energetic efficiency of the system. Coupling the microstructural modelling with the transport and reaction modelling enables the correlation of the two different scale levels, so that the integrated models are used as interpretative tool of experimental data as well as design tool for optimize the performance
Norellia bertei Rondani 1866
No full text<i>Norellia bertei</i> Rondani, 1866 <p>ORIGINAL DESCRIPTION: 1866b: 16 (key), 17 (description) [1867b: 100 (key), 101 (description)].</p> <p> TYPE LOCALITY: “ <i>in Apennino parmensi</i> [Parmese Apennines (Italy)]”.</p> <p> TYPE MATERIAL: 1 ♀, syntype (completely covered with mold) (MZUF: Box 27): <i>Norellia</i> Desv. / <i>bertei</i> Rond., Apenn. [= Apennines] / 1421.</p> <p> CURRENT STATUS: junior synonym of <i>Norellia alpestris</i> Schiner, 1864 (Gorodkov 1986: 12); junior synonym of <i>Norellisoma alpestre</i> (Schiner, 1864) (Šifner 2003: 24).</p> <p> REMARKS: Rondani (1866b: 17) described <i>Norellia bertei</i> from just the female sex, without specifying the exact number of specimens, but giving a single measurement of length: “ <i>Foeminam tantum observavi a Doct. Bertéo … captam</i> [I observed only the female collected by. Dr. Bertè]”. We found one female syntype in this study. Rondani published the species first in a separate (1866b) and then in the journal version (1867b).</p>Published as part of <i>Sforzi, Alessandra & Sommaggio, Daniele, 2021, Catalog of the Diptera types described by Camillo Rondani, pp. 1-438 in Zootaxa 4989 (1)</i> on page 214, DOI: 10.11646/zootaxa.4989.1.1, <a href="http://zenodo.org/record/4980621">http://zenodo.org/record/4980621</a>
Morphology and electrochemical activity of SOFC composite cathodes: II. Mathematical modelling
No full textThis paper presents a mathematical model of mass and charge transport and electrochemical reaction in porous composite cathodes for application in solid oxide fuel cells. The model describes a porous composite cathode as a continuum, and characterises charge and mass transfer and electrochemical kinetics using effective parameters (i.e. conductivity, diffusivity, exchange current) related to morphology and material properties by percolation theory. The model accounts for the distribution of morphological properties (i.e. porosity, tortuosity, density of contacts among particles) along cathode thickness, as experimentally observed on scanning electron microscope images of LSM/YSZ cathodes of varying thickness. This feature allows the model to reproduce the dependence of polarisation resistance on thickness, as determined by impedance spectroscopy on LSM/YSZ cathodes of varying thickness. Polarisation resistance in these cathodes is almost constant for thin cathodes (up to 10 A mu m thickness), it sharply decreases for intermediate thickness, to reach a minimum value for about 50 A mu m thickness, then it slightly increases in thicker cathodes
Microstructural modelling for prediction of effective properties in porous SOFC electrodes
No full textA modelling framework for the prediction of effective properties in porous SOFC electrodes is presented. The model consists of: i) a packing algorithm to numerically reconstruct the microstructure, and ii) a Monte Carlo method to calculate the effective transport properties. This modelling technique improves the accuracy of the prediction of effective properties beyond percolation theory estimates. In addition, the numerical reconstruction does not rely on existing samples and complex instrumentations (for example, X-ray tomography, FIB-SEM analyses) required by other reconstruction methods.
The packing algorithm enables to numerically generate a representative sample of the electrode microstructure with the desired particle size distribution, composition and porosity. Sintering phenomena are simulated by increasing the overlap among the particles, pore-former particles are accounted for during the packing generation [1]. The model is capable to simulate packings of spherical particles as well as of agglomerates of spheres.
The reconstructed samples are then analyzed with a Monte Carlo method [2]. Random walk simulations are used to determine the transport properties in gas and solid phase, such as the effective diffusivity and the effective electric conductivity. Other geometric quantities can be evaluated, such as the pore size distribution, the surface area exposed to the gas phase, the three-phase boundary length.
In this study, effective properties as a function of porosity and particle size for random packings of spherical particles are calculated. The results are compared with independent experimental data, revealing a good agreement for both gas and solid phase properties. Effective properties of agglomerates of particles are also presented and compared with the results obtained for spherical particles. The comparison highlights that particle agglomeration significantly increases the mean pore size while reducing the effective gas diffusivity and the specific surface area exposed to gas phase (Figure 1).
The presented modelling technique can be used to improve SOFC electrode design and to support the interpretation of experimental data
Dynamic transition of dendrite orientation in the diffusive spinodal decomposition of binary mixtures under a thermal gradient
No full textWhile the spinodal decomposition of mixtures in unbounded systems has been largely investigated, little is known about phase separation constrained within a slab. In this study, spinodal decomposition of a very viscous regular binary mixture bounded within two walls cooled at different temperatures is simulated by using the diffuse interface model in 2D. Under a temperature gradient, phase separation starts from the cooler wall forming dendritic structures growing anisotropically with time. Two remarkably different dynamics are identified depending on whether heat propagates slower or faster than mass. For small thermal conductivity (i.e., small Lewis number), dendrites grow parallelly to the temperature gradient, keeping such an alignment until the steady-state. On the other hand, for large Lewis number, during the early stages phase separation proceeds within stripes oriented along iso-temperature lines, i.e., with dendrites aligned perpendicularly to the temperature gradient, which, however, gradually shift their orientation parallel to the temperature gradient as the steady-state is approached. Such a dynamic transition of dendrite orientation upon a temperature gradient when heat propagates faster than mass is found to hold also for non-equimolar mixtures and for different species thermal conductivities. These results shed light on the dynamics of phase separation in constrained systems and anisotropic conditions
Phase-separating Active Materials in Lithium-ion Batteries: Implications for Fast-charging and Material Characterisation
No full textSome active materials used in lithium-ion battery (LIB) electrodes undergo phase separation into Li-rich and Li-poor phases upon lithium intercalation. Typical examples include LiFePO4 (LFP) at the cathode and graphite at the anode. While phase separation enables useful features, such as a constant equilibrium potential as a function of state-of-charge, such behaviour poses challenges during material characterisation and for high-rate operation.
This study provides a perspective of phase separation in LIB active materials by combining non-equilibrium thermodynamics principles [1] with in-operando techniques [2]. The results show that classical techniques used to estimate solid-state diffusion coefficients, such as the galvanostatic intermittent titration technique (GITT) [3], must be revisited for this class of materials. In fact, although the rapid equilibration of the interface between Li-rich and Li-poor phases within a particle leads to a quick voltage relaxation, the solid-state diffusivity can be significantly lower than what this fast dynamics may suggest. This has significant implications on the distribution of lithium within secondary particles because, upon fast lithiation, the Li-rich phase grows at the particle surface and prevents further lithiation. This is especially critical for graphite anodes, since the Li-rich phase (also known as stage I) at the particle surface is the primary cause for the plating of metallic lithium outside the particle, as quantified in in-operando experiments [2]. Nevertheless, experiments also show that Li plating is not irreversible and part of the plated lithium can be stripped and back-intercalated in graphite when the current is interrupted. This discovery opens opportunities for alternative fast-charging protocols as long as the particle size distribution is well controlled to prevent excessive plating on small particles. On the other hand, experimental characterisation and simulation of a disordered carbon, which does not undergo phase separation, reveal an effectively faster solid-state diffusion and a more significant resistance to lithium plating even at high C-rate [4], thus enabling for a comprehensive comparison between solid-solution and phase-separating active materials when it comes to characterisation and fast-charging capabilities.
References
[1] 10.1021/ar300145c. Bazant, M.Z. Theory of Chemical Kinetics and Charge Transfer Based on Nonequilibrium Thermodynamics. Acc. Chem. Res. 2013, 46, 1144-1160
[2] 10.1038/s41467-023-40574-6. Lu, X.; Lagnoni, M.; Bertei, A.; Das, S.; Owen, R.E.; Li, Q.; O'Regan, K.; Wade, A.; Finegan, D.P.; Kendrick, E.; Bazant, M.Z.; Brett, D.J.L.; Shearing, P.R. Multiscale Dynamics of Charging and Plating in Graphite Electrodes Coupling Operando Microscopy and Phase-field Modelling. Nat. Commun. 2023, 14, 5127
[3] 10.1149/1.2133112. Weppner, W.; Huggins, R.A. Determination of the Kinetic Parameters of Mixed-Conducting Electrodes and Application to the System Li3Sb. J. Electrochem. Soc. 1977, 124, 1569-1578
[4] 10.1021/acsaem.3c01280. Ahn, S.; Lagnoni, M.; Yuan, Y.; Ogarev, A.; Vavrinyuk, E.; Voynov, G.; Barrett, E.; Pelli, A.; Atrashchenko, A.; Platonov, A.; Gurevich, S.; Gorokhov, M.; Rupasov, D.; Robertson, A.W.; House, R.A.; Johnson, L.R.; Bertei, A.; Chernyshov, D.V. Chemical Origins of a Fast-Charge Performance in Disordered Carbon Anodes. ACS Appl. Energy Mater. 2023, 6, 8455-8465
Acknowledgements
This study received funding from the National Recovery and Resilience Plan, Mission 4 Component 2 Investment 1.3 - Call for tender No. 1561 of 11.10.2022 of Ministero dell’Università e della Ricerca, according to attachment E of Decree No. 1561/2022, Project title “Network 4 Energy Sustainable Transition – NEST”, CUP I53C22001450006; funded by the European Union–NextGenerationEU. This paper reflects only the authors’ views and opinions; neither the European Union nor the European Commission can be considered responsible for them
A comparative study and an extended theory of percolation for random packings of rigid spheres
No full textA new method for the prediction of coordination numbers in random packings of rigid spherical particles is presented, consisting of improvements of basic relationships of percolation theory for the determination of numbers of contacts, percolation thresholds and probability of connection in binary mixtures and their extension to multicomponent and polydisperse mixtures. The proposed model is critically compared with previous percolation theories, showing a satisfactory agreement with experimental data and computer simulations of random packings over a wide range of particle sizes and compositions for both binary and multicomponent/polydisperse mixtures. (C) 2011 Elsevier B.V. All rights reserved
Physically-based impedance simulation to decouple convoluted transport and reaction phenomena in SOFC cathodes
No full textA mechanistic model, based on mass and charge conservation equations [1], is presented for the physically-based simulation of impedance spectra in composite solid oxide fuel cell cathodes, taking into account the complex interaction between transport and reaction phenomena. The impedance simulation, which reproduces the same procedure used in laboratory frequency response analyzers, allows the de-convolution of distinct elementary processes and the identification of a specific double layer chemical capacitance, describing the possible accumulation of adsorbed species and reaction intermediates at the interface between electron-conducting and ion-conducting particles. The satisfactory agreement of simulated spectra with experimental data for different operating conditions and electrode thicknesses reveals that the model is capable to reproduce the transient behavior of composite electrodes by relying on only one fitted parameter. Model simulations show that mass-transfer processes within the electrode produce a resistive contribution in the impedance spectra related to the effect of the local oxygen partial pressure on the reaction kinetics. In addition, the pores act as a buffer for molecular oxygen, leading to a capacitive contribution in the frequency range 10^2-10^4Hz, more pronounced at high current densities
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