Study of carbons as matrices for lithium batteries

Tres de los grandes desafíos a los que se enfrenta la sociedad son el cambio climático, la creciente demanda de energía y la búsqueda del desarrollo sostenible. La Asamblea General de las Naciones Unidas estableció los Objetivos de Desarrollo Sostenible (ODS) en la Agenda 2030 para marcar el camino hacia la transición ecológica que deben seguir los países firmantes. Este proceso inevitablemente incluye la reducción del consumo de combustibles fósiles y su reemplazo por energías renovables. Sin embargo, este tipo de energías presentan la desventaja de una producción discontinua al depender de fenómenos atmosféricos (luz solar, viento, mareas, etc.). Para permitir un abastecimiento continuo de energía empleando fuentes renovables es necesario contar con sistemas de almacenamiento energético avanzados. Las baterías son sistemas de almacenamiento electroquímicos donde la electricidad producida se utiliza para llevar a cabo una reacción química no espontánea, y cuando se requiera electricidad se producirá la reacción espontánea transformando la energía química en eléctrica. Estos dispositivos constan fundamentalmente de tres componentes: cátodo, ánodo y electrolito. El desarrollo de estos componentes para cualquier tecnología de baterías es fundamental a la hora de avanzar en sistemas de almacenamiento que apoyen la consecución de los retos marcados en los ODS. La presente Tesis Doctoral pretende colaborar en los objetivos 7, 12 y 13 de los ODS mediante la síntesis de nuevos carbones que puedan emplearse como cátodos y ánodos en baterías de litio y que además presenten prestaciones superiores a los actualmente comercializados. Así mismo, se ha propuesto la síntesis de carbones a partir de biomasa residual, lo que supone una revalorización de subproductos de la industria agroalimentaria, aumentando la sostenibilidad de este tipo de dispositivos y potenciando la economía circular asociada al sector energético. La presente Tesis Doctoral titulada “Estudio de carbones como matrices para baterías de litio”, dirigida por los doctores D. Álvaro Caballero Amores y Dña. Almudena Benítez de la Torre, se encuadra en la línea de investigación “Materiales Avanzados para Baterías Recargables” del grupo FQM-175 “Química Inorgánica”, desarrollada en el Departamento de Química Inorgánica e Ingeniería Química de la Universidad de Córdoba. Fundamentalmente, esta memoria se ha elaborado gracias a la ayuda predoctoral para la formación de profesorado universitario (FPU) con referencia FPU16/03718 concedida por el Ministerio de Universidades (Gobierno de España). Así mismo, los trabajos de investigación se han llevado a cabo gracias a la financiación de los Proyectos Nacionales de I+D+i (i) MAT2014-55907-R “Grafeno como base de baterías avanzadas Li/S y Na/S para almacenamiento de energías renovables en redes eléctricas inteligentes” y (ii) MAT2017-87541-R “Avances en la tecnología de baterías litio-azufre: rendimiento, seguridad y sostenibilidad”. Los materiales sintetizados en esta Tesis Doctoral se han evaluado en dos tipos de tecnologías, las baterías de litio-ion (LIB) y litio-azufre (Li- S). Una exposición más detalla de la situación actual, así como del funcionamiento de las baterías basadas en litio se recoge en el capítulo 1. En resumen, el plan de trabajo seguido en todas las investigaciones ha sido: (i) análisis del estado del arte, para conocer los últimos avances en la temática y la tendencia seguida en otros grupos de investigación, (ii) síntesis de carbones, procurando un equilibrio entre las propiedades adquiridas por el material y la sostenibilidad del proceso de preparación, (iii) síntesis de la mezcla o composite carbón-azufre, sólo en caso de emplear ese material como cátodo en baterías Li-S, (iv) caracterización integral de los materiales, incluyendo un análisis estructural, morfológico, textural, composicional y de estabilidad térmica, (v) preparación de electrodos y ensamblaje de las celdas electroquímicas (baterías de litioion o litio-azufre), y finalmente, (vi) caracterización electroquímica, mediante la realización de medidas galvanostásticas de carga y descarga, voltamperometrías cíclicas (CV) y espectroscopía de impedancia electroquímica (EIS). A colación de lo anterior, una descripción pormenorizada de los materiales y métodos de síntesis empleados, así como de las técnicas de caracterización utilizadas se detalla en el capítulo 3. Por su parte, el capítulo 4 recoge los resultados y la discusión de los mismo obtenidos en los distintos trabajos de investigación desarrollados durante esta Tesis Doctoral. En este sentido, este capítulo se divide en cinco secciones en función del material sintetizado y la tecnología empleada. Inicialmente se recogen los trabajos sobre carbones obtenidos a partir de reactivos comerciales mediante diferentes métodos de preparación: (i) carbones grafénicos utilizados como ánodos en baterías Li-ión y (ii) carbón derivado de MOF utilizado como cátodo en una batería semi-líquida Li-S. Los siguientes apartados han sido dedicados a la optimización y revalorización de un carbón derivado de biomasa: (iii) en primer lugar, dos carbones obtenidos a partir de hueso de cereza preparados con distintos agentes activantes (KOH y H3PO4) han sido testeados como ánodos en baterías Li-ion, posteriormente (iv) se probaron estos carbones en baterías Li-S; y, por último, (v) seleccionando el mejor de estos carbones, se optimizó la configuración de la celda y la proporción de azufre incorporada en el composite con el propósito de aumentar la seguridad de la batería Li-S y lograr mejores prestaciones en esta tecnología.Three of the great challenges society faces are climate change, the growing demand for energy and the search for sustainable development. The United Nations General Assembly established the Sustainable Development Goals (SDG) in the 2030 Agenda to mark the path towards the ecological transition that the signatory countries must follow. This process inevitably includes reducing the consumption of fossil fuels and replacing them with renewable energy. However, this type of energy has the disadvantage of discontinuous production as it depends on atmospheric phenomena (sunlight, wind, tides, etc.). To allow a continuous supply of energy using renewable sources, it is necessary to have advanced energy storage systems. Batteries are electrochemical storage systems where the electricity produced is used to carry out a non-spontaneous chemical reaction, and when electricity is required, the spontaneous reaction will occur, transforming chemical energy into electricity. These devices basically consist of three components: cathode, anode and electrolyte. The development of these components for any battery technology is essential when advancing in storage systems that support the achievement of the challenges set out in the SDGs. This Doctoral Thesis aims to collaborate in goals 7, 12 and 13 of the SDGs through the synthesis of new carbons that can be used as cathodes and anodes in lithium batteries and that also present superior performance to those currently marketed. Likewise, the synthesis of carbons from residual biomass has been proposed, which implies a revaluation of by-products of the agri-food industry, increasing the sustainability of this type of device and promoting the circular economy associated with the energy sector. This Doctoral Thesis titled "Study of carbons as matrices for lithium batteries", directed by doctors D. Álvaro Caballero Amores and Ms. Almudena Benítez de la Torre, falls within the line of research "Advanced Materials for Rechargeable Batteries" of the group FQM-175 "Inorganic Chemistry", developed in the Department of Inorganic Chemistry and Chemical Engineering of the University of Córdoba. Fundamentally, this report has been prepared thanks to the predoctoral grant for university teacher training (FPU) with reference FPU16/03718 granted by the Ministry of Universities (Government of Spain). Likewise, the research work has been carried out thanks to the financing of the National R+D+i Projects (i) MAT2014-55907-R “Graphene as a base for advanced Li/S and Na/S batteries for storage of renewable energies in smart electrical networks” and (ii) MAT2017-87541-R “Advances in lithium-sulfur battery technology: performance, safety and sustainability”. The materials synthesized in this Doctoral Thesis have been evaluated in two types of technologies, lithium-ion batteries (LIB) and lithium-sulfur (Li-S). A more detailed exposition of the current situation, as well as the operation of lithium-based batteries, is included in chapter 1. In summary, the work plan followed in all the investigations has been: (i) analysis of the state of the art, to find out about the latest advances in the subject and the trend followed in other research groups, (ii) synthesis of carbons, seeking a balance between the properties acquired by the material and the sustainability of the preparation process, (iii) synthesis of the mixture or carbon-sulfur composite, only if this material is used as a cathode in Li-S batteries, (iv) comprehensive characterization of the materials, including a structural, morphological, textural, compositional, and thermal stability analysis, (v) preparation of electrodes and assembly of electrochemical cells (lithium-ion or lithium-sulfur batteries), and finally, (vi) electrochemical characterization, by performing galvanostatic charge measurement and discharge, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). In light of the above, a detailed description of the materials and synthesis methods used, as well as the characterization techniques used, is detailed in chapter 3. On the other hand, chapter 4 collects the results and the discussion of the results obtained in the different research works developed during this Doctoral Thesis. In this sense, this chapter is divided into five sections depending on the synthesized material and the technology used. Initially, the works on carbons obtained from commercial reagents by different preparation methods are collected: (i) graphenic carbons used as anodes in Li-ion batteries and (ii) carbon derived from MOF used as cathode in a semi-liquid Li-ion battery -S. The following sections have been dedicated to the optimization and revaluation of a carbon derived from biomass: (iii) firstly, two carbons obtained from cherry pits prepared with different activating agents (KOH and H3PO4) have been tested as anodes in Li-ion batteries, later (iv) these carbons were tested in Li-S batteries; and, finally, (v) by selecting the best of these carbons, the cell configuration and the proportion of sulfur incorporated into the composite were optimized with the purpose of increasing the safety of the Li-S battery and achieving better performance in this technology

Síntesis y caracterización de grafenos tridimensionales. Aplicación como electrodos en baterías Litio-Azufre

Premio extraordinario de Trabajo Fin de Máster curso 2015-2016. QuímicaEl trabajo se ha centrado en el estudio de diferentes grafenos con morfología tridimensional y su capacidad de alojar azufre en sus cavidades con el objetivo de examinar sus propiedades en baterías Li/S. Para ello, se sintetizaron hidrogeles a partir de óxido grafítico mediante tratamiento hidrotermal. Para favorecer el crecimiento en 3D se usaron como aditivos sacarosa (para mitigar la tendencia de las láminas a empaquetarse) y el agente surfactante dodecil sulfato sódico (SDS) (para favorecer la unión entre el óxido grafítico y la sacarosa). Tras el tratamiento hidrotermal, los grafenos se calcinaron a 900 ºC en atmósfera de N2. Los grafenos obtenidos se caracterizaron mediante diferentes técnicas: difracción de rayos X, espectroscopía Raman, microscopía electrónica de barrido, espectroscopía de fotoelectrones de rayos X, análisis termogravimétrico y medidas de adsorción/desorción de N2. Para su estudio como componentes del cátodo de la batería Li/S, la impregnación de los grafenos con S se realizó “in situ” utilizando una disolución de tiosulfato de sodio en medio ácido como fuente del elemento. Las propiedades electroquímicas de las celdas se estudiaron mediante voltametría cíclica y cronopotenciometría. Solo los grafenos calcinados dieron buenas propiedades electroquímicas reflejadas en la liberación de altas capacidades específicas y una respuesta satisfactoria a altas densidades de corriente.The work has been focused on the study of different graphenes with three dimensional morphology and its ability to insert sulfur up in their cavities in order to examine their properties in Li/S batteries. For this aim, hydrogels were synthesized by hydrothermal treatment of graphitic oxide. To enhance the 3D growth we used as additives sucrose (to mitigate the tendency of the sheets to be restacked) and sodium dodecyl sulfate (SDS), a surfactant agent (to promote the link between the graphitic oxide and sucrose). After the hydrothermal treatment, the graphenes were calcined at 900ºC under a N2 atmosphere. The 3D graphenes obtained were characterized by different techniques: X-ray diffraction, Raman spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis and N2 adsorption/desorption measurements. For the study of these graphenes as cathode components of Li/S battery, the graphene impregnation with sulfur was carried out “in situ” using a solution of sodium thiosulfate in an acid medium as source of the element. The electrochemical properties of the cells were studied by cyclic voltammetry and chronopontentiometry. Only the calcined graphene gave good electrochemical properties, reflected in the release of high specific capacity and a satisfactory response at high current densities

Biomass-derived carbon/γ-MnO2 nanorods/S composites prepared by facile procedures with improved performance for Li/S batteries

The promising prospects of the Li/S battery, due to its theoretical energy density of about 2500 Wh kg─1, are severely limited by two main weaknesses: the poor conductivity of S and the solubility of the polysulphides in the electrolyte. A combination of carbon and transition metal oxides is the best option for mitigating both of these shortcomings simultaneously. In this work, we use hydrothermally-tailored γ-MnO2 nanorods combined with an activated biomass-derived carbon, which is an inexpensive material and easy to prepare. This strategy was also followed for a AC/MnO2/S composite, a preparation of which was made by grinding; this is the simplest method for practical applications. More complex procedures for the formation of in situ hydrothermal MnO2 nanorods gave similar results to those obtained from grinding. Compared with the AC/S composite, the presence of MnO2 markedly increased the delivered capacity and improved the cycling stability at both low (0.1 C) and high (1 C) currents. This behaviour results from a combination of two main effects: firstly, the MnO2 nanorods increase the electrical conductivity of the electrode, and secondly, the small particle size of the oxide can enhance the chemisorption properties and facilitate a redox reaction with polysulphides, more efficiently blocking their dissolution in the electrolyte

Lithium–Oxygen Battery Exploiting Highly Concentrated Glyme-Based Electrolytes

Concentrated solutions of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium nitrate (LiNO3) salts in either diethylene-glycol dimethyl-ether (DEGDME) or triethylene-glycol dimethyl-ether (TREGDME) are herein characterized in terms of chemical and electrochemical properties in view of possible applications as the electrolyte in lithium–oxygen batteries. X-ray photoelectron spectroscopy at the lithium metal surface upon prolonged storage in lithium cells reveals the complex composition and nature of the solid electrolyte interphase (SEI) formed through the reduction of the solutions, while thermogravimetric analysis shows a stability depending on the glyme chain length. The applicability of the solutions in the lithium metal cell is investigated by means of electrochemical impedance spectroscopy (EIS), chronoamperometry, galvanostatic cycling, and voltammetry, which reveal high conductivity and lithium transference number as well as a wide electrochemical stability window of both electrolytes. However, a challenging issue ascribed to the more pronounced evaporation of the electrolyte based on DEGDME with respect to TREGDME actually limits the application of the former in the Li/O2 battery. Hence, EIS measurements reveal a very fast increase in the impedance of cells using the DEGDME-based electrolyte upon prolonged exposure to the oxygen atmosphere, which leads to a performance decay of the corresponding Li/O2 battery. Instead, cells using the TREGDME-based electrolyte reveal remarkable interphase stability and much more enhanced response with specific capacity ranging from 500 to 1000 mA h g–1 referred to the carbon mass in the positive electrode, with an associated maximum practical energy density of 450 W h kg–1. These results suggest the glyme volatility as a determining factor for allowing the use of the electrolyte media in a Li/O2 cell. Therefore, electrolytes using a glyme with sufficiently high boiling point, such as TREGDME, which is further increased by the relevant presence of salts including a lithium protecting sacrificial one (LiNO3), can allow the application of the solutions in a safe and high-performance lithium–oxygen battery

A Stable High-Capacity Lithium-Ion Battery Using a Biomass-Derived Sulfur-Carbon Cathode and Lithiated Silicon Anode

A full lithium-ion-sulfur cell with a remarkable cycle life was achieved by combining an environmentally sustainable biomass-derived sulfur-carbon cathode and a pre-lithiated silicon oxide anode. X-ray diffraction, Raman spectroscopy, energy dispersive spectroscopy, and thermogravimetry of the cathode evidenced the disordered nature of the carbon matrix in which sulfur was uniformly distributed with a weight content as high as 75 %, while scanning and transmission electron microscopy revealed the micrometric morphology of the composite. The sulfur-carbon electrode in the lithium half-cell exhibited a maximum capacity higher than 1200 mAh gS−1, reversible electrochemical process, limited electrode/electrolyte interphase resistance, and a rate capability up to C/2. The material showed a capacity decay of about 40 % with respect to the steady-state value over 100 cycles, likely due to the reaction with the lithium metal of dissolved polysulfides or impurities including P detected in the carbon precursor. Therefore, the replacement of the lithium metal with a less challenging anode was suggested, and the sulfur-carbon composite was subsequently investigated in the full lithium-ion-sulfur battery employing a Li-alloying silicon oxide anode. The full-cell revealed an initial capacity as high as 1200 mAh gS−1, a retention increased to more than 79 % for 100 galvanostatic cycles, and 56 % over 500 cycles. The data reported herein well indicated the reliability of energy storage devices with extended cycle life employing high-energy, green, and safe electrode materials

Highly graphitized carbon nanosheets with embedded Ni nanocrystals as anode for Li-ion batteries

A C/Ni composite was prepared via thermal decomposition of a nickel oleate complex at 700 °C, yielding disperse Ni nanocrystals with an average size of 20 nm, encapsulated by carbon nanosheets as deduced from transmission electron microscopy (TEM) images and confirmed from X-ray photoelectron spectroscopy (XPS). Furthermore, the X-ray diffraction pattern revealed a good ordering of the carbon layers, forced by the Ni encapsulation to adopt a bending structure. Considering the close interaction between the graphitized framework and the metallic nanoparticles we have studied the properties of the composite as an anode for Li-ion batteries. Compared with other nanostructured synthetic carbons, this carbon composite has a low voltage hysteresis and a modest irreversible capacity value, properties that play a significant role in its behaviour as electrodes in full cell configuration. At moderate rate values, 0.25 C, the electrode delivers an average capacity value around 723 mAh·g−1 on cycling, among the highest values so far reported for this carbon type. At higher rate values, 1 C, the average capacity values delivered by the cell on cycling decrease, around 205 mAh·g−1, but it maintains good capacity retention, a coulombic efficiency close to 100% after the first cycles and recovery of the capacity values when the rate is restored from 3 to 0.1 C

Porous Cr2O3@C composite derived from metal organic framework in efficient semi-liquid lithium-sulfur battery

Embargado hasta 15/11/2022A carbon composite including Cr2O3 (Cr2O3@C) and benefitting of a metal organic framework (MOF) precursor is herein synthesized, and originally employed in a semi-liquid lithium-sulfur cell using a catholyte solution formed by Li2S8 polysulfide, conducting lithium salt and film forming additive dissolved in diethylene glycol dimethyl ether (DEGDME). The adopted cell configuration may actually allow the porous structure of the MOF derivative to efficiently enable the lithium/sulfur electrochemical process. Thus, structure, chemical composition, morphology and porosity of the composite are investigated by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and N2 adsorption/desorption isotherms, respectively. The data reveal a mesoporous material consisting of aggregated nanometric particles (<100 nm) with relatively high BET surface area (170 m2 g−1), uniform element distribution, and a carbon content of about 13 wt%. Cyclic voltammetry of the Cr2O3@C in semi-liquid lithium sulfur cell using the catholyte solution shows a reversible reaction with fast kinetics and Li-diffusion coefficient ranging from about 3 × 10−8 cm2 s−1 at 2.4 V vs. Li+/Li, to 1 × 10−8 cm2 s−1 at 2 V vs. Li+/Li. Furthermore, electrochemical impedance spectroscopy reveals a very stable interphase with an impedance below 5 Ω after an activation process promoted by cycling. The semi-liquid Li/S cell operates with remarkable stability and efficiency approaching 100%, delivers a capacity ranging from 900 mAh g−1 at C/10 rate to 780 mAh g−1 at C/3 rate, and performs over 100 charge/discharge cycles with very modest capacity decay

Alternative lithium-ion battery using biomass-derived carbons as environmentally sustainable anode

Embargado hasta 01/08/2022Disordered carbons derived from biomass are herein efficiently used as an alternative anode in lithium-ion battery. Carbon precursor obtained from cherry pit is activated by using either KOH or H3PO4, to increase the specific surface area and enable porosity. Structure, morphology and chemical characteristics of the activated carbons are investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetry (TG), Raman spectroscopy, nitrogen and mercury porosimetry. The electrodes are studied in lithium half-cell by galvanostatic cycling, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). The study evidences substantial effect of chemical activation on the carbon morphology, electrode resistance, and electrochemical performance. The materials reveal the typical profile of disordered carbon with initial irreversibility vanishing during cycles. Carbons activated by H3PO4 show higher capacity at the lower C-rates, while those activated by KOH reveal improved reversible capacity at the high currents, with efficiency approaching 100% upon initial cycles, and reversible capacity exceeding 175 mAh g−1. Therefore, the carbons and LiFePO4 cathode are combined in lithium-ion cells delivering 160 mAh g−1 at 2.8 V, with a retention exceeding 95% upon 200 cycles at C/3 rate. Hence, the carbons are suggested as environmentally sustainable anode for Li-ion battery