Materiales anódicos alternativos para el desarrollo de baterías de ión-litio sostenibles

Tesis doctoral presentada en el Departamento de Energía de la Universidad de Oviedo, 2016.[EN] Lithium-ion batteries are the most attractive and feasible alternative for the development of massive electrical energy storage systems to allow the implementation of renewable energy sources as well as the electric vehicle. Nevertheless, it is necessary to identify new eco-friendly electrode materials (active materials, conductive additives and binders) capable of improving the performance of the batteries without increasing the cost. Therefore, the Main Objective of this Thesis is to develop efficient anodes for lithium-ion batteries which increase the energy and power as well as the useful life of these devices, reducing the environmental impact associated with their manufacture, use and subsequent recycling. To achieve this goal, the work is organized in three activities that are related to the Specific Objectives set out. In a first activity, graphitic nanomaterials (graphite nanofibers) were prepared by heat treatment at high temperatures of carbon nanofibers produced in the catalytic decomposition of biogas, a renewable energy source. Graphite nanofibers with a highly-developed three-dimensional structure were used as anode active material for lithium-ion batteries. The electrochemical performance of these nanomaterials is comparable, or even superior at high-density currents, to that of oil-derived micrometric graphite, which is used on a large scale for lithium-ion batteries. The nanometric particle size reduces the diffusion time of the Li+ ions along the intercalation/deintercalation processes, allowing faster charge/discharge rates, thus making these graphite nanofibers potential candidates for anodes of high-power lithium-ion batteries. Afterwards, a series of hydrocolloids, more specifically, natural, safe and biodegradable biopolymers, among them sodium carboxymethyl cellulose, sodium alginate, xanthan gum and guar gum, were employed as an alternative to polyvinylidene difluoride, synthetic fluorinated polymer commonly used as binder in anodes for lithium-ion batteries. From the electrochemical studies at different current rates and binder concentrations it can be concluded that the electrochemical performance of the synthetic graphite anodes with hydrocolloids with a linear structure or with the fluorinated polymer are comparable, proving the viability of the named for this application. Furthermore, the required amount of hydrocolloid for a proper electrode performance is smaller, which together with their lower prices and the possibility of using water instead of an organic solvent, would reduce costs as well as the environmental impact caused by these devices.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

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

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

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

Graphitic biogas-derived nanofibers as cathodes for sodium dual-ion batteries: Intercalation of PF6− anions

The electrochemical intercalation of PF6− anions into graphitic nanomaterials of renewable origin with different degrees of structural order to be subsequently used as cathodes for sodium dual-ion batteries is herein investigated for the first time. Overall, the electrochemical performance of the biogas-derived carbon nanofibers depends on their graphitic structure, specifically on crystallite height which was found to be the determining parameter for the scope of electrochemical intercalation of PF6− anions into these nanomaterials.Financial support from Spanish Ministry of Science and Innovation (RTI2018-094286-A-100) and Asturias Government (IDI/2018/000234) is gratefully acknowledged. I. Cameán thanks funding from FGCSIC (Programa ComFuturo).Peer reviewe

Graphitized biogas-derived carbon nanofibers as anodes for lithium-ion batteries

The electrochemical performance as potential anodes for lithium-ion batteries of graphitized biogas-derived carbon nanofibers (BCNFs) is investigated by galvanostatic cycling versus Li/Li+ at different electrical current densities. These graphitic nanomaterials have been prepared by high temperature treatment of carbon nanofibers produced in the catalytic decomposition of biogas. At low current density, they deliver specific capacities comparable to that of oil-derived micrometric graphite, the capacity retention values being mostly in the range 70-80% and cycling efficiency ∼ 100%. A clear tendency of the anode capacity to increase alongside the BCNFs crystal thickness was observed. Besides the degree of graphitic tri-dimensional structural order, the presence of loops between the adjacent edges planes on the graphene layers, the mesopore volume and the active surface area of the graphitized BCNFs were found to influence on battery reversible capacity, capacity retention along cycling and irreversible capacity. Furthermore, provided that the development of the crystalline structure is comparable, the graphitized BCNFs studied show better electrochemical rate performance than micrometric graphite. Therefore, this result can be associated with the nanometric particle size as well as the larger surface area of the BCNFs which, respectively, reduces the diffusion time of the lithium ions for the intercalation/de-intercalation processes, i.e. faster charge-discharge rate, and increases the contact area at the anode active material/electrolyte interface which may improve the Li+ ions access, i.e. charge transfer reaction.Financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) under Projects ENE2011-28318-CO3-02 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 MINECO for a Ph.D. grant (BES-2012-052711) to develop the work.Peer reviewe

Estudio del mecanismo de intercalación electroquímica del anión PF6- en electrodos de grafito

Fundación General CSIC (Programa ComFuturo), Ministerio de Ciencia e Innovación en conjunto con la Unión Europea NextGeneration (Proyecto PID2020-113001RB-I00 MCIN/AEI- 10.13039/501100011033) y Principado de Asturias (Proyecto AYUD/2021/50921) por la financiación del trabajo.Peer reviewe

Exploring the application of carbon xerogels as anodes for sodium-ion batteries

Carbon xerogels (CXs) with the same chemical composition and BET surface area but different pore sizes (10–200 nm), which had been easily produced in large amounts via a cost-effective microwave-based process, are investigated as anodes for sodium-ion batteries (SIBs). The role of textural properties of CXs in the process of sodium ions storage was evaluated. The most suitable anode for SIBs was CX-100 with a pore size of 100 nm, the largest micropore volume and the lowest external surface area (Sext), which gives an idea of the most accessible surface of the material, along with relatively high open porosity. Larger pore sizes facilitate electrolyte penetration, thus improving Na+ ions diffusion inside the electrode, while microporosity is crucial in increasing electrode capacity since Na+ ions storage on CXs is mainly due to absorption on the surface and in structural defects (i.e., microporosity). Moreover, lowering Sext leads to a decrease in the Na+ ions used in the formation of the SEI layer and irreversibly absorbed during initial cycles, therefore improving electrode performance. In summary, an optimal combination of textural properties, including pore structure and Sext, should be considered in order to effectively design CXs for SIBs.Financial support from the Spanish Ministry of Science, Innovation and Universities (Project RTI2018-094286-A-100) and Asturias Regional Government (GRUPIN 2018, Ref. IDI/2018/000234) is gratefully acknowledged. I. Cameán is grateful for funding from the Fundación General CSIC (Programa ComFuturo, II Edition).Peer reviewe