Studies of Lithium-Oxygen Battery Electrodes by Energy- Dependent Full-Field Transmission Soft X-Ray Microscopy

Energy‐dependent full‐field transmission soft X‐ray microscopy is a powerful technique that provides chemical information with spatial resolution at the nanoscale. Oxygen K‐level transitions can be optimally detected, and we used this technique to study the discharge products of lithium‐oxygen batteries, where this element undergoes a complex chemistry, involving at least three different oxidation states and formation of nanostructured deposits. We unambiguously demonstrated the presence of significant amounts of superoxide forming a composite with peroxide, and secondary products such as carbonates or hydroxide. In this chapter, we describe the technique from the fundamental to the observation of discharged electrodes to illustrate how this tool can help obtaining a more comprehensive view of the phenomena taking place in metal air batteries and any system involving nanomaterials with a complex chemistry

Chapter Studies of Lithium-Oxygen Battery Electrodes by Energy- Dependent Full-Field Transmission Soft X-Ray Microscopy

The employment of printing techniques as cost-effective methods to fabricate low cost, flexible, disposable and sustainable solar cells is intimately dependent on the substrate properties and the adequate electronic devices to be powered by them. Among such devices, there is currently a growing interest in the development of user-oriented and multipurpose systems for intelligent packaging or on-site medical diagnostics, which would greatly benefit from printable solar cells as their energy source for autonomous operation

Facile preparation of glycine-based mesoporous graphitic carbons with embedded cobalt nanoparticles

This research was supported by the Spanish Ministry of Science and Innovation, through the "Severo Ochoa" Programme for Centers of Excellence in R&D (CEX2019-000917-S), the projects MAT2017-91404-EXP, RTI2018-096273-B-I00, RTI2018-3097753-B-I00, with FEDER co-funding, the CSIC program for the Spanish Recovery, Transformation and Resilience Plan "Plataforma Temática Interdisciplinar Transición Energética Sostenible+ (PTI-TRANSENER +)" funded by the Recovery and Resilience Facility of the European Union, established by the Regulation (EU) 2020/2094. The authors also acknowledge the Generalitat de Catalunya (2017SGR1687). W.W. gratefully acknowledges the support from the China Scholarship Council (CSC No.:201808340076). This work has been performed within the framework of the doctoral program in materials science of UAB (W. W.).A simple route has been developed for the preparation of mesoporous graphitic carbons with embedded cobalt nanoparticles just using glycine as a nitrogen source, cobalt nitrate and distilled water. After heating the mixture to 300 °C under magnetic stirring, a dry solid product was obtained, which was then carbonized at 900 ºC under argon atmosphere. Changing the glycine/Co molar ratio allowed controlling the size of the cobalt particles and their dispersion in the carbon matrix, the porosity of the carbon and its graphitic character. The carbon-metal composites obtained were tested as oxygen cathodes in Li-O batteries. Cells assembled exhibited a full discharge capacity up to 2.19 mAh cm at a current of 0.05 mA cm and over 39 cycles at a cutoff capacity of 0.5 mAh cm. This work provides a green, feasible and simple way to prepare mesoporous graphitic carbons with embedded cobalt nanoparticles without involving templates

Hydrocarbonization. Does It Worth to Be Called a Pretreatment?

In this work, we aim to evaluate the potential of hydrothermal carbonization (also known as wet pyrolysis) as a pretreatment, by evaluating the changes induced in the raw material (cellulose) under varying experimental conditions. Hydrocarbonization processes were performed under different temperature, time and biomass/water ratios following a response surface methodology. The hydrochars obtained were characterized in terms of proximate analysis, behavior towards pyrolysis and combustion, heating value and surface textural and chemical features. The presence of typical hydrocarbonization reactions (dehydration, hydrolysis, decarboxylation, decarbonylation, recondensation, etc.) was only possible if a limit temperature (200°C) was used. Under these conditions, proximate analyses changed, the surface chemistry was modified, and the formation of a second lignite-type solid fraction was observed

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

Combined Influence of Meso- and Macroporosity of Soft-Hard Templated Carbon Electrodes on the Performance of Li-O2 Cells with Different Configurations

Li-O2 batteries can offer large discharge capacities, but this depends on the morphology of the discharged Li2O2, which in turn is strongly affected by the nanostructured carbon used as support in the air cathode. However, the relation with the textural parameters is complex. To investigate the combined effect of channels of different sizes, meso-macroporous carbons with similar mesopore volume but different pore size distribution were prepared from the polymerization of resorcinol-formaldehyde (RF) in the presence of surfactants and micro-CaCO3 particles. The carbon materials were used as active materials of air cathodes flooded by ionic liquid-based electrolytes in Li-O2 cells with two different configurations, one with a static electrolyte and the other with a stirred electrolyte, which favor a film-like and large particle deposition, respectively. The presence of large pores enhances the discharge capacity with both mechanisms. Conversely, with respect to the reversible capacity, the trend depends on the cell configuration, with macroporosity favoring better performance with static, but poorer with stirred electrolytes. However, all mesoporous carbons demonstrated larger reversible capacity than a purely macroporous electrode made of carbon black. These results indicate that in addition to pore volume, a proper arrangement of large and small pores is important for discharge capacity, while an extended interface can enhance reversibility in Li–O2 battery cathodes

Combined Influence of Meso- and Macroporosity of Soft-Hard Templated Carbon Electrodes on the Performance of Li-O₂ Cells with Different Configurations

Li-O2 batteries can offer large discharge capacities, but this depends on the morphology of the discharged Li2O2, which in turn is strongly affected by the nanostructured carbon used as support in the air cathode. However, the relation with the textural parameters is complex. To investigate the combined effect of channels of different sizes, meso-macroporous carbons with similar mesopore volume but different pore size distribution were prepared from the polymerization of resorcinol-formaldehyde (RF) in the presence of surfactants and micro-CaCO3 particles. The carbon materials were used as active materials of air cathodes flooded by ionic liquid-based electrolytes in Li-O2 cells with two different configurations, one with a static electrolyte and the other with a stirred electrolyte, which favor a film-like and large particle deposition, respectively. The presence of large pores enhances the discharge capacity with both mechanisms. Conversely, with respect to the reversible capacity, the trend depends on the cell configuration, with macroporosity favoring better performance with static, but poorer with stirred electrolytes. However, all mesoporous carbons demonstrated larger reversible capacity than a purely macroporous electrode made of carbon black. These results indicate that in addition to pore volume, a proper arrangement of large and small pores is important for discharge capacity, while an extended interface can enhance reversibility in Li−O2 battery cathodes

Simple method to relate experimental pore size distribution and discharge capacity in cathodes for Li/O2 batteries

We analyze in detail the relationship between pore size distribution and discharge capacity for cathodes in ionic liquid-based Li/O2 batteries at room temperature (RT) and 60 °C. We used several porous carbons with similar composition and apparent surface area but with pore distribution peaks in different points of the meso/macroporous region. The porous structure of carbons caused a significant influence on the discharge specific capacity. However, no obvious correlations between specific capacity and surface area or total pore volumes were observed. Carbons with high mesopore volumes and a predominant pore size of 20-40 nm exhibited the highest specific capacities. When temperature rises from room temperature to 60 °C, discharge capacity increases by a factor higher than two, with the smallest pores providing the highest increases. A model is introduced to empirically correlate capacity with pore size distribution. This model assumes that during electrochemical discharge the pore walls are uniformly coated in their thickness but that pores below a threshold size value do not participate at all to the capacity. Our model can account for the effects of pore size distribution using a discharge layer thickness of a few nanometers and with threshold values of excluded pore sizes, of 12 nm at RT and 10 nm at 60 °C. The model also allowed the estimation of the penetration depth of the discharge reaction on the electrode thickness and indicates that its increase is the main factor justifying the increase of capacity when temperature is increased.Work funded by the European Commission in the Seventh Framework Programme FP7-2010-GC-ELECTROCHEMICAL STORAGE, under contract no. 265971 “Lithium-Air Batteries with split Oxygen Harvesting and Redox processes (LABOHR)”, and by the Spanish Government under contracts MAT2012-39199-C02-01 and MAT2012-39199-C02-02. M.O.-M. acknowledges CSIC for a JAE-DOC research contract cofinanced by the European Social Fund. P.P. acknowledges a FPI-UCM fellowship (BE45/10)

Chapter Studies of Lithium-Oxygen Battery Electrodes by Energy- Dependent Full-Field Transmission Soft X-Ray Microscopy

The employment of printing techniques as cost-effective methods to fabricate low cost, flexible, disposable and sustainable solar cells is intimately dependent on the substrate properties and the adequate electronic devices to be powered by them. Among such devices, there is currently a growing interest in the development of user-oriented and multipurpose systems for intelligent packaging or on-site medical diagnostics, which would greatly benefit from printable solar cells as their energy source for autonomous operation

Facile preparation of glycine-based mesoporous graphitic carbons with embedded cobalt nanoparticles

Part of a collection: Composites & nanocompositesA simple route has been developed for the preparation of mesoporous graphitic carbons with embedded cobalt nanoparticles just using glycine as a nitrogen source, cobalt nitrate and distilled water. After heating the mixture to 300 °C under magnetic stirring, a dry solid product was obtained, which was then carbonized at 900 ºC under argon atmosphere. Changing the glycine/Co molar ratio allowed controlling the size of the cobalt particles and their dispersion in the carbon matrix, the porosity of the carbon and its graphitic character. The carbon–metal composites obtained were tested as oxygen cathodes in Li–O batteries. Cells assembled exhibited a full discharge capacity up to 2.19 mAh cm at a current of 0.05 mA cm and over 39 cycles at a cutoff capacity of 0.5 mAh cm. This work provides a green, feasible and simple way to prepare mesoporous graphitic carbons with embedded cobalt nanoparticles without involving templates. Graphical abstract: [Figure not available: see fulltext.].This research was supported by the Spanish Ministry of Science and Innovation, through the “Severo Ochoa” Programme for Centers of Excellence in R&D (CEX2019-000917-S), the projects MAT2017-91404-EXP, RTI2018-096273-B-I00, RTI2018-3097753-B-I00, with FEDER co-funding, the CSIC program for the Spanish Recovery, Transformation and Resilience Plan “Plataforma Temática Interdisciplinar Transición Energética Sostenible+ (PTI-TRANSENER +)” funded by the Recovery and Resilience Facility of the European Union, established by the Regulation (EU) 2020/2094. The authors also acknowledge the Generalitat de Catalunya (2017SGR1687). W.W. gratefully acknowledges the support from the China Scholarship Council (CSC No.:201808340076). This work has been performed within the framework of the doctoral program in materials science of UAB (W. W.)