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International audience; Hard carbon (HC) materials are commonly used as anode materials in Na-ion batteries. In most of the cases, their electrochemical performance is correlated only to their physicochemical properties, and the impact of the electrode additives (binders–conductive agent) and electrolyte is often neglected. In this work, a systematic study is performed to understand the role of electrode/electrolyte engineering on HC initial Coulombic efficiency (iCE), specific capacity, and cycle stability. Four HCs obtained by pyrolysis of several biopolymers, i.e., cellulose (HC-Cell), chitosan (HC-Chs), chitin (HC-Cht), and lignin (HC-Lig), are used. The binder was found to have an important impact on the electrochemical performance, with PVDF resulting in better performance than CMC. The carbon black additive had no significant impact on CMC-based electrochemical performance while it boosted the electrochemical performance of PVDF-based electrodes. For an optimized formulation (PVDF/carbon black), the best HC performance in NaPF6 in 1 EC:DEC was delivered by HC-Cell (83% iCE, 332 mAh g–1 at C/10, and 97% retention). This was attributed to its large graphene interlayer space, high purity, and low surface area. HC-Cht and HC-Chs exhibited similar good electrochemical performance (∼280 mAh g–1) whereas the use of HC-Lig resulted in low iCE and capacity fading overcycling due to the high level of impurities in its structure. This could be overcome by changing the electrolyte salt, by using NaClO4 (76% retention) instead of NaPF6 (52% retention). Based on the obtained results, the electrochemical performance could be correlated with the HC physicochemical properties and binder/conductive additive. It could be demonstrated that careful electrode engineering combined with proper electrolyte selection and tuned HC properties allowed all investigated materials achieving reasonable iCE (up to 83%), high specific capacity (∼280 to 332 mAh g–1), and high-capacity retention (72–97% after 50 cycles).

The model activated carbon spheres (ACSs) were optimized to be used as negative electrode in asymmetric electrochemical capacitors (ECs). A microporous commercial activated carbon was used as positive electrode. Carbon spheres (CSs) were synthesized by precipitation polymerization at room temperature followed by pyrolysis and activation. By enhancing the carbon:KOH ratio from 1:2 to 1:4, an increase in the specific surface area from 380 m2 g−1 to 2835 m2 g−1 (1:4) was achieved along with an increase in pore volume/size. Consequently, the electrochemical performance in the aqueous electrolyte was improved. After activation, low-temperature-pyrolyzed polymer spheres (400 °C) result in random-like particles with macroporous structure, while intermediate- and high-temperature-pyrolyzed materials (550 °C and 700 °C) lead to partially and totally conserved spheres. The interaction between the electrode material and electrolyte is important and is related to the texture, morphology, and surface chemistry of ACS. In 1 mol L−1 H2SO4, capacitance and rate handling are mostly affected by electrode morphology and wettability with the electrolyte. In 1 mol L−1 Li2SO4 electrolyte solution, texture and surface chemistry of the electrode material are crucial to obtain high-performance EC. Regardless of morphology, poor wetting properties of synthesized materials were found in Li2SO4, compared to the H2SO4 solution., Journal of Power Sources, 542, ISSN:0378-7753, ISSN:1873-2755

Char and Carbon Materials Derived from Biomass: Production, Characterization and Applications provides an overview of biomass char production methods (pyrolysis, hydrothermal carbonization, etc.), along with the characterization techniques typically used (Scanning Electronic Microscopy, X-Ray Fluorescence, Nitrogen adsorption, etc.) In addition, the book includes a discussion of the various properties of biomass chars and their suitable recovery processes, concluding with a demonstration of applications. As biomass can be converted to energy, biofuels and bioproducts via thermochemical conversion processes, such as combustion, pyrolysis and gasification, this book is ideal for professionals in energy production and storage fields, as well as professionals in waste treatment, gas treatment, and more.

Char and Carbon Materials Derived from Biomass: Production, Characterization and Applicationsprovides an overview of biomass char production methods (pyrolysis, hydrothermal carbonization, etc.), along with the characterization techniques typically used (Scanning Electronic Microscopy, X-Ray Fluorescence, Nitrogen adsorption, etc.) In addition, the book includes a discussion of the various properties of biomass chars and their suitable recovery processes, concluding with a demonstration of applications. As biomass can be converted to energy, biofuels and bioproducts via thermochemical conversion processes, such as combustion, pyrolysis and gasification, this book is ideal for professionals in energy production and storage fields, as well as professionals in waste treatment, gas treatment, and more.

Hard carbons (HCs) prepared from renewable precursors are promising cost-effective electrode-material candidates for the application in Na-ion battery. Usually these materials are derived from cellulose. Here, however, we demonstrate that other polysaccharides, such as chitin and chitosan, can be as well up-and-coming parent materials of HCs. Despite structural similarities, thermal decomposition of these two biopolymers proceeds differently, contributing to the discrepancies in physicochemical properties of resulting HCs. Although chitin- and chitosan-derived HCs have comparable d-spacings and crystallite sizes, solid-state pyrolysis of the former biopolymer leads to micromesoporous material with significant specific surface area, while that of chitosan yields nonporous carbon. Despite that, both materials deliver similar initial specific charge of 280 mAh g–1 (at C/10 rate), and their electrochemical performance starts to diverge only upon longer cycling at higher rate. With time, inorganic contaminants present in chitosan-derived HC presumably delay the diffusion of Na ions to and within the electrode and slow the rate of electrochemical reactions, eventually triggering polarization buildup. Further optimization of the chitosan-derived HC through acid treatment enables unblocking some of the micropores and increasing the carbon content in this material, therefore enhancing its active surface area and suppressing continuous fading of the specific charge.

International audience; Rapid development of the technologies based on electric energy in the last decades have stimulated intensive research on efficient power sources. Electrochemical energy conversion and storage systems are based on Faradaic reactions (charge transfer) and electrostatic attraction of ions at the electrode/electrolyte interface. The latter might be an interesting solution for applications requiring moderate energy density, high power rates, and long cycle life. Electrochemical capacitors (ECs) store the charge in a physical manner, hence, their energy density is moderate. At the same time, the lack of electrochemical reactions ensures very high power and long cycle life compared to batteries. Activated carbons with their versatile properties (like specific surface area, well-developed and suitable porosity, heteroatoms in the graphene matrix) are the most popular materials in EC application. This chapter provides a comprehensive overview of the carbon-based materials recently developed, with special attention devoted to those obtained by biomass carbonization and activation. Electrochemical properties demonstrated by such carbons are discussed in respect to their physicochemical characteristics

International audience; Imaging techniques are increasingly used to study Li-ion batteries and, in particular, post-Li-ion batteries such as Li–S batteries, Na-ion batteries, and all-solid-state batteries. Results that appear impressive owing to good image design and reconstruction are frequently published in high-impact-factor journals; however, questions have arisen about the added value of such results and the information they reveal about reaction mechanisms occurring in batteries during operation and/or degradation. We present here a review of imaging techniques and the knowledge acquired from these techniques for three systems: Li–S batteries, Na-ion batteries, and all-solid-state batteries. There are always advantages and disadvantages associated with these techniques, but beam damage remains the bottleneck to characterization. This factor needs to be considered seriously in order to obtain valuable outcomes that will enable improvements of battery performance and lifetime.

In the on going quest towards lithium-battery chemistries beyond the lithium-ion technology, the lithium–sulfur system is emerging as one of the most promising candidates. The major outstanding challenge on the route to commercialization is controlling the so-called polysulfide shuttle, which is responsible for the poor cycling efficiency of the current generation of lithium–sulfur batteries. However, the mechanistic understanding of the reactions underlying the polysulfide shuttle is still incomplete. Here we report the direct observation of lithium polysulfides in a lithium–sulfur cell during operation by means of operando X-ray diffraction. We identify signatures of polysulfides adsorbed on the surface of a glass-fibre separator and monitor their evolution during cycling. Furthermore, we demonstrate that the adsorption of the polysulfides onto SiO2 can be harnessed for buffering the polysulfide redox shuttle. The use of fumed silica as an electrolyte additive therefore significantly improves the specific charge and Coulombic efficiency of lithium–sulfur batteries. The presence of polysulfides in Li–S batteries is highly relevant to the battery performance, but their formation and evolution during battery operation are not well understood. Here the authors design an operando X-ray diffraction experiment to reveal their reaction mechanisms.