Preparación de materiales grafíticos: aplicación como ánodos en baterías de ión-litio

Tesis doctoral presentada en el Departamento de Química Orgánica e Inorgánica de la Universidad de Oviedo. 2011. Tutora de la tesis: María Esther García DíazLithium-ion batteries are versatile, high performance and low cost energy storage systems. These batteries have turned into fundamental components for most of the portable electronic devices. The inherent attractive for lithium-ion batteries is the use of intercalation electrodes which can insert lithium ions in a reversible way inside their structure. Lithium-ion batteries use carbon materials, mainly, synthetic graphite as anode. The Final Objective of this Thesis is to use graphitic materials prepared from different precursors (anthracites, unburned carbon concentrates from coal combustion fly ashes and carbon nanofibers obtained in the catalytic decomposition of methane to produce hydrogen) as anodes in lithium-ion batteries. The graphitic materials were prepared by heating the precursors in the temperature interval 1800-2900 ºC. The materials were then characterized by determining their structural (degree of structural order and orientation of the graphitic domains), electrical (conductivity) and textural (surface area and porosity) properties. Subsequently, the performance of these graphitic materials as anodes in the lithium-ion batteries was evaluated by means the electrochemical parameters (reversible and irreversible capacity, ciclability and efficiency). Moreover, the relation between these parameters and the materials properties was also studied. Finally, a comparative study of electrochemical properties of the graphitic materials prepared in this work and those of synthetic graphites which are currently been employed as anodic materials for commercial lithium-ion batteries was carried out. In terms of reversible capacity, ciclability, irreversible capacity and efficiency of cycle, the battery performance by using as working electrodes the graphitic materials obtained from the unburned carbon concentrates and the carbon nanofibers, and the synthetic graphites of reference are absolutely comparable. Therefore, the application of these graphitic materials as anodes in lithium-ion batteries appears feasible. An increase of the battery reversible capacity with the structural order of the materials was observed, thus being an important factor to optimize these energy storage systems. However, for materials with a high degree of crystallinity, other no structural factors such as morphology and particle size, were also found to influence on the reversible capacity finally provided by the battery. Generally, the battery cyclability with the graphitic materials prepared is excellent; in addition, it was found to be independent of the materials structural order. After the SEI (Solid Electrolyte Interface) formation, lithium ions intercalation/deintercalation into the graphene layers occurs in almost a reversible way whenever the material porosity was below a specific value. An increase of the degree of structural order of the material lead to an improvement of the battery cycling efficiency, thus increasing the initial efficiency value and lowering the cycle number at which the efficiency reaches ~ 100 %. This effect is directly related with the decreasing of the material porosity.Las baterías de ión-litio son sistemas de almacenamiento de energía de alto rendimiento, bajo coste y versátiles que se utilizan en múltiples aparatos portátiles. El atractivo inherente a una batería de ión-litio es la utilización de electrodos de intercalación que son capaces de insertar de forma reversible iones litio dentro de su estructura. Estas baterías utilizan como ánodos materiales de carbono, generalmente, grafitos sintéticos. El Objetivo Final de esta Tesis Doctoral es utilizar materiales grafíticos preparados a partir de diferentes precursores (antracitas, concentrados de inquemados de cenizas volantes procedentes de la combustión de carbón y nanofibras de carbono generadas en la descomposición catalítica de gas metano para la producción de hidrógeno) como ánodos en baterías de ión-litio. Todos ellos fueron grafitizados en el intervalo de temperaturas 1800-2900 ºC. Los materiales grafíticos preparados fueron caracterizados, determinándose sus propiedades estructurales (grado de orden estructural y de orientación de los microcristales), texturales (área superficial y porosidad) y eléctricas (conductividad), todas ellas relacionadas con su comportamiento como ánodo en las baterías de ión-litio que se evaluó en función de los parámetros electroquímicos de la batería (capacidad reversible e irreversible, ciclabilidad y eficacia). Además, se estudió la relación entre dichos parámetros y las propiedades de los materiales. Finalmente, se llevó a cabo un estudio comparativo de las propiedades electroquímicas de los materiales grafíticos con las correspondientes a grafitos sintéticos que están siendo utilizados como ánodos en baterías de ión-litio comerciales. Las prestaciones de las baterías, en cuanto a capacidad reversible, ciclabilidad, capacidad irreversible y eficacia del ciclado, empleando como electrodos de trabajo materiales grafíticos preparados a partir de los concentrados de inquemados de cenizas volantes y de las nanofibras de carbono, y grafitos sintéticos de referencia que se usan en la manufactura de dichas baterías son totalmente comparables. Por tanto, la utilización de estos materiales grafíticos como ánodos en las baterías de ión-litio es, en principio, viable. La capacidad reversible de la batería tiende a aumentar con el orden estructural del material siendo por tanto un factor determinante para la optimización de estos sistemas de almacenamiento de energía eléctrica. Sin embargo, cuando se emplean materiales grafíticos con elevado grado de desarrollo de la estructura cristalina, otros factores no estructurales, tales como la morfología y el tamaño de partícula también influyen en la capacidad reversible suministrada por la batería. En general, la ciclabilidad de las baterías con los materiales preparados a partir de los diferentes precursores es excelente, con independencia del grado de orden estructural del material considerado. Una vez formada la capa pasivante, la intercalación/desintercalación de los iones litio en este tipo de materiales grafíticos transcurre de forma casi totalmente reversible, siempre que la porosidad se mantenga por debajo de unos límites. La eficacia del ciclado de la batería mejora al aumentar el grado de orden estructural del material, tanto por lo que respecta al valor inicial como al número de ciclo al cual dicha eficacia alcanza ~ 100 %, lo cual está directamente relacionado con la disminución de la porosidad.Peer reviewe

Is single layer graphene a promising anode for sodium-ion batteries?

In an attempt to find an adequate carbon material to achieve a successful reversible adsorption of Na+ ions, single layer graphene, is experimentally investigated in this work, for the first time, as anode for sodium-ion batteries. To this end, single layer graphene that was grown on copper foil by chemical vapor deposition was subjected to extended galvanostatic cycling and to cyclic voltammetry in the potential range of 0-2.8 V versus Na/Na+. Regardless of the current density and electrolyte formulation used, the amount of Na+ ions adsorbed/desorbed reversibly per surface area (specific reversible cell capacity) was very modest and comparable to that obtained with bare copper electrodes of reference, thus suggesting that the reversible capacity of the single layer graphene electrode is mostly due to the electrochemical response of the copper substrate. These experimental results clearly agree with recent theoretical calculations showing that the adsorption of Na+ ions on the surface of single layer graphene is energetically unfavourable unless that surface includes significant defects density.Financial support from IBERDROLA FOUNDATION (www.fundacioniberdrola.org, Projects 2014-2015) and the Spanish Ministry of Economy and Competitiveness MINECO (under Projects ENE2011-28318-CO-02 and ENE2014-52189-C2-2-R) is gratefully acknowledged. A. Ramos and N. Cuesta, respectively, thank the Spanish Research Council for Scientific Research (CSIC) for a JAE-Doc contract, co-funded by the European Social Fund (ESF), and the Spanish Ministry of Economy and Competitiveness (MINECO) for a pre-doctoral grant (BES-2012-052711).Peer reviewe

Assessment of graphitized coal ash char concentrates as a potential synthetic graphite source

Coal ash char concentrates from four countries (Portugal, Poland, Romania, and South Africa) were prepared, characterised, and graphitized under the scope of the Charphite project (Third ERA-MIN Joint Call (2015) on the Sustainable Supply of Raw Materials in Europe). Coal ash chars may be a secondary raw material to produce synthetic graphite and could be an alternative to natural graphite, which is a commodity with a high supply risk. The char concentrates and the graphitized material derived from the char concentrates were characterised using proximate analysis, X-ray fluorescence, X-ray diffraction (structural), Raman microspectroscopy, solid-state nuclear magnetic resonance, scanning electron microscopy, and petrographic analyses to determine if the graphitization of the char was successful, and which char properties enhanced or hindered graphitization. Char concentrates with a lower proportion of anisotropic particles and a higher proportion of mixed porous particles showed greater degrees of graphitization. It is curious to see that embedded Al2O3 minerals, such as glass and clay, influenced graphitization, as they most likely acted as catalysts for crystal growth in the basal direction. However, the graphitized samples, as a whole, do not compare well against a reference natural graphite sample despite some particles in select char concentrates appearing to be graphitized following graphitization.Fil: Badenhorst, Charlotte. University Of Johannesburg; SudáfricaFil: Santos, Cláudia. Universidad de Porto; PortugalFil: Lazaro Martinez, Juan Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Metabolismo del Fármaco. Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Metabolismo del Fármaco; ArgentinaFil: Bialecka, Barbara. Central Mining Institute; PoloniaFil: Cruceru, Mihai. University Constantin Brancusi of Targu Jiu; RumaniaFil: Guedes, Alexandra. Universidad de Porto; PortugalFil: Guimarâes, Renato. Universidad de Porto; PortugalFil: Moreira, Karen. Universidad de Porto; PortugalFil: Predeanu, Georgeta. University Politehnica Of Bucharest; RumaniaFil: Suárez-Ruíz, Isabel. Consejo Superior de Investigaciones Científicas; EspañaFil: Cameán, Ignacio. Consejo Superior de Investigaciones Científicas; EspañaFil: Valentim, Bruno. Universidad de Porto; PortugalFil: Wagner, Nicola. University Of Johannesburg; Sudáfric

Comportamiento como ánodos en baterías de ión-litio de materiales grafíticos preparados a partir de antracitas y concentrados de inquemados de cenizas volantes procedentes de la combustión de carbón

[EN] The electrochemical performance as anodes for lithium-ion batteries of graphite-like materials that were prepared from anthracites and unburned carbon concentrates from coal combustion fly ashes by high temperature treatment was investigated by galvanostatic cycling of lithium test cells. Some of the materials prepared have provided reversible capacities up to ~ 310 mA h g-1 after 50 discharge/ charge cycles. These values are similar to those of oil-derived graphite (petroleum coke being the main precursor) which is currently used as anodic material in commercial lithium-ion batteries.[ES] En este trabajo se ha estudiado la aplicación como ánodos en baterías de ión-litio de materiales grafíticos que habían sido previamente preparados mediante tratamiento térmico a alta temperatura de antracitas y concentrados de inquemados de cenizas volantes procedentes de la combustión de carbón; para ello, se llevaron a cabo ciclados galvanostáticos de baterías de litio tipo test. Algunos de los materiales preparados proporcionaron capacidades reversibles de ~ 310 mA h g-1 después de 50 ciclos, siendo estos valores comparables a los correspondientes a grafitos sintéticos (preparados principalmente a partir de coque de petróleo) que en la actualidad son utilizados como ánodo en baterías de ión-litio comerciales. Los valores máximos de capacidad reversible fueron obtenidos para aquellos materiales con mayor grado de orden estructural, el cual ha sido evaluado mediante Difracción de Rayos-X y Espectroscopía Raman. En este sentido, se calcularon correlaciones lineales razonablemente buenas entre la capacidad reversible y los parámetros estructurales de los materiales grafíticos. Además, todos los materiales preparados mostraron excelentes retenciones de la capacidad de carga a lo largo del ciclado, así como valores de capacidad irreversible mínimos. Otros factores no estructurales, tales como la morfología irregular de las partículas de estos materiales también influyeron muy positivamente en las prestaciones de los ánodos de las baterías, por lo que su utilización para esta aplicación, parece, en principio, factible.Financial support from the Spanish MICINN and MINECO (under Projects MAT2004-01094, ENE2008-06516 and ENE2011-28318) and PCTI of Asturias (under Project PC07-014) is gratefully acknowledged.Peer reviewe

Materiales grafíticos preparados a partir de inquemados de cenizas volantes : aplicación como ánodos en baterías de ión-litio

2 páginas, 3 figuras.-- Comunicación oral presentada a la X Reunión del Grupo Español del Carbón en Mayo del 2010.Peer reviewe

Silicon/Biogas-Derived Carbon Nanofibers Composites for Anodes of Lithium-Ion Batteries

© 2020 by the authors.The electrochemical performance of novel nano-silicon/biogas-derived carbon nanofibers composites (nSi/BCNFs) as anodes in lithium-ion batteries was investigated, focusing on composition and galvanostatic cycling conditions. The optimization of these variables contributes to reduce the stress associated with silicon lithiation/delithiation by accommodating/controlling the volume changes, thus preventing anode degradation and therefore improving its performance regarding capacity and stability. Specific capacities up to 520 mAh g−1 with coulombic efficiency > 95% and 94% of capacity retention are achieved for nSi/BCNFs anodes at electric current density of 100/200 mA g−1 and low cutoff voltage of 80 mV. Among the BCNFs, those no-graphitized with fishbone microstructure, which have a great number of active sites to interact with nSi particles, are the best carbon matrices. Specifically, a nSi:BCNFs 1:1 weight ratio in the composite is the optimal, since it allows a compromise between a suitable specific capacity, which is higher than that of graphitic materials currently commercialized for LIBs, and an acceptable capacity retention along cycling. Low cutoff voltage in the 80–100 mV range is the most suitable for the cycling of nSi/BCNFs anodes because it avoids formation of the highest lithiated phase (Li15Si4) and therefore the complete silicon lithiation, which leads to electrode damageThis research was funded by Spanish Ministries of Economy and Competitiveness MINECO (Project ENE2014-52189-C2-2-R) and Science, Innovation and Universities (Project RTI2018-094286-A-100), and Asturian Regional Government (GRUPIN 2018, Ref. IDI/2018/000234).Peer reviewe

Sustainable graphitic carbon materials from biogas as anodes for sodium-ion batteries

Novel graphitic materials of renewable origin, biogas-derived carbon nanofibers (BCNFs), are investigated as anodes for sodium-ion batteries in a glyme-based electrolyte. These materials show a unique combination of electrochemical properties, including suitable capacity (∼100 mAh g), high rate capability, excellent cycle stability and coulombic efficiency as well as long cycle life (∼6000 cycles up to 7.5 A g) which make them adequate candidates for this application. The sodiation of BCNFs occurs through different combinations of diffusion-controlled intercalation and capacitive intercalation processes. Overall, the quantitative contribution of the capacitive current to the total stored sodium in BCNF electrodes is noteworthy (28-71%), which account for their ultrahigh rate performance, comparable to that of supercapacitors, because of the improvement of the transportability of the Na ions through the graphene layers.Financial support from the Spanish Ministry of Economy and Competitiveness MINECO (Project ENE2014-52189-C2-2-R) and Iberdrola Spain Foundation (www.fundacioniberdrola.org, Project 2016-2017) is gratefully acknowledged. I. Cameán and J. Rodríguez-García, respectively, thank funding from Fundación General CSIC (Programa ComFuturo) and from MINECO for a Ph.D. fellowship (FPI BES 2015-071293) to develop the work

Optical parameters and microstructural properties of Solid Bitumens of high reflectance (Impsonites). Reflections on their use as an indicator of organic maturity

Six solid bitumen samples from Paja Formation (Cretaceous of Colombia) were optically, chemically and structurally characterized using bulk chemistry, reflectance indicating surface (RIS), micro-Raman and X-ray diffraction (XRD) parameters. The volatile matter and carbon contents and high random reflectance (Ro%) placed these solid bitumens in the category of cata-impsonites according to Jacob's classification. RIS axes (R, R and R) form almost a sphere, and consequently, the anisotropy (Ram or bireflectance values) of these materials is very weak, comparatively to other carbonaceous materials (coals) of similar degree of evolution. The weak anisotropy character of the solid bitumen is related to the absence of pressure in the system, which did not promote the orientation of the basic structural units (BSUs) in a three-dimensional arrangement. The degree of ordering evaluated by Raman parameters, such as full width at half maximum (FWHM) of the D1 and G bands, and XRD parameters, including d and crystallite sizes Lc and La, showed that the solid bitumens of the Paja Formation have a low structural order equivalent to high-rank coals, specifically anthracites B (3.0% ≤ Ro 4.0%). The discrepancy between high reflectance and low degree of structural order can explain why some of the equations used to estimate equivalent vitrinite reflectance (Ro eq. Vite) from solid bitumens do not work universally. Taking in consideration several equations available in the literature, Jacob's equation (Jacob, 1989) was the one that fitted the Ro eq. Vite values in the range of 3.0% to 4.0%, which parallels with the degree of structural order obtained for the solid bitumens. Consequently, Jacob's equation can now be extended to solid bitumen in the range of cata-impsonites

On the PF6− anion intercalation in graphite from sodium salt-based electrolytes containing different mixtures of organic carbonates

The intercalation of PF6− anions in graphite from various sodium salt-based electrolytes with organic carbonate mixtures as solvents is investigated. The purpose was to optimize the electrochemical performance of the graphite as cathode in terms of specific capacity, capacity stability, and coulombic efficiency to be coupled in the future with a hard carbon-based anode in a full sodium dual-ion battery. To this end, a detailed study was made of the influence of applied current density, upper cut-off voltage (UCOV), and electrolyte—in terms of both salt concentration and solvent mixture—on the intercalation/de-intercalation of PF6− anions in the graphite cathode. Low (37.2 mA g−1) and high (372.0 mA g−1) currents, UCOVs from 4.8 to 5.2 V, electrolytes with NaPF6 salt concentrations in the range of 0.2–1.2M and EC:DEC, EC:DMC and EC:EMC solvent mixtures were studied. The best graphite cathode performance was attained in 1.2MNaPF6/EC:EMC electrolyte at the highest current density of 372.0 mA g−1 and for the potential range between 2.9 and 5.0 V vs. Na/Na+. In these conditions, a discharge capacity of 79 mAh g−1 after 1000 cycles with a coulombic efficiency of 99 % and a remarkable capacity retention throughout cycling were determined.Financial support from the Spanish Ministry of Science, Innovation and Universities (Project RTI2018-094286-A-I00) and Asturias Regional Government (GRUPIN 2018, IDI/2018/000234) is gratefully acknowledged. I. Cameán thanks the funding from Fundación General CSIC (Programa ComFuturo, II Edition) to develop the work.Peer reviewe

Silicon/biogas-derived carbon nanofibers composites: a promising anode material for lithium-ion batteries

Introduction Silicon appears to be a promising anode material for increasing both the energy density and power of lithium-ion batteries due to, mainly, the high theoretical specific capacity, the relatively low working potential and the abundance in earth crust. However, the lithiation/delithiation of Si causes successive volume changes of this material leading to the fracture of the particles and the consequent poor reversibility and cycling stability of the electrode. Among different strategies which are being developed to avoid the Si-electrode degradation, this work has focused on: (i) the preparation of Si-based composites by adding a matrix (specifically carbon materials) which can help to buffer the volume changes and (ii) the limitation of the lower cut-off voltage (LCOV) which leads to a better control of these changes. Results and discussion Among different carbon matrices studied in this work, free-metal carbon nanofibers obtained from the catalytic decomposition of biogas (BCNFs) result the most suitable ones. Thus, the fishbone microstructure of these carbon nanofilaments, having a great number of active sites to interact with the Si particles, buffer the volume changes associated with the silicon lithiation/delithiation, preventing the electrode degradation. Specifically, an nSi:BCNFs 1:1 weight ratio in the active composite is the optimal. On the other hand, the limitation of the LCOV in the 80-100 mV range avoids the formation of the highest lithiated phase which leads to electrode degradation. Both strategies allow achieving a compromise between the specific capacity, which is greater than that of graphitic materials currently used in LIBs, and acceptable capacity retention along galvanostatic cycling. Thus, electrodes formed by 80 % of the nSi/BCNFs composite, including a 10 % of carbon black (CB), and 20 % of sodium carboxymethyl cellulose (NaCMC) as active material and binder, respectively, has been prepared in this work by a simple, fast and easily industrial-scaling process, achieving specific capacities up to ~ 520 mAh g-1 after 30 cycles with coulombic efficiency > 95 % and ~ 94 % of capacity retention along cycling at an electric current density of 100/200 mA g-1 and a LCOV of 80 mV