A Lithium-Ion Battery using a 3 D-Array Nanostructured Graphene-Sulfur Cathode and a Silicon Oxide-Based Anode

Diffusional Features of a Lithium-Sulfur Battery Exploiting Highly Microporous Activated Carbon

Diffusion processes at the electrode/electrolyte interphase drives the performance of lithium-sulfur batteries, and activated carbon (AC) can remarkably vehicle ions and polysulfide species throughout the two-side liquid/solid region of the interphase. We reveal original findings such as the values of the diffusion coefficient at various states of charge of a Li-S battery using a highly porous AC, its notable dependence on the adopted techniques, and the correlation of the diffusion trend with the reaction mechanism. X-ray photoelectron spectroscopy (XPS) and X-ray energy dispersive spectroscopy (EDS) are used to identify in the carbon derived from bioresidues heteroatoms such as N, S, O and P, which can increase the polarity of the C framework. The transport properties are measured by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic intermittent titration technique (GITT). The study reveals Li⁺ -diffusion coefficient (D_Li ⁺ ) depending on the technique, and values correlated with the cell state of charge. EIS, CV, and GITT yield a D_Li ⁺ within 10^-7 -10^-8  cm²  s^-1 , 10^-8 -10^-9  cm²  s^-1 , and 10^-6 -10^-12  cm²  s^-1 , respectively, dropping down at the fully discharged state and increasing upon charge. GITT allows the evaluation of D_Li ⁺ during the process and evidences the formation of low-conducting media upon discharge. The sulfur composite delivers in a Li-cell a specific capacity ranging from 1300 mAh g^-1 at 0.1 C to 700 mAh g^-1 at 2C with a S loading of 2 mg cm^-2 , and from 1000 to 800 mAh g^-1 at 0.2C when the S loading is raised to 6 mg cm^-2 .

Synergy between highly dispersed Ni nanocrystals and graphitized carbon derived from a single source as a strategy for high performance Lithium-Sulfur batteries

Due to their higher energy density, lower prices, and more environmentally friendly active components, Li-S batteries will soon compete with the current Li-ion batteries. However, issues persist that hinder this implementation, such as the poor conductivity of S and sluggish kinetics due to the polysulfide shuttle, among others. Herein, Ni nanocrystals encapsulated in a C matrix are obtained by a novel strategy based on the thermal decomposition of a Ni oleate-oleic acid complex at low-to-moderate temperatures: 500 and 700 °C. The two C/Ni composites were employed as hosts in Li-S batteries. Although the C matrix is amorphous at 500 °C, it is highly graphitized at 700 °C. At this moderate temperature, the simultaneous generation of Ni nanocrystals and the carbon matrix enhances the catalytic activity of Ni toward the graphitization process, which is negligible if starting from a mixture of a Ni salt and carbon source, even when calcined at temperatures as high as 1000 °C. The electrode made from the C/Ni composite obtained at 700 °C exhibits a high reversible capacity and an enhanced rate capability, much better not only than the C/Ni composite obtained at 500 °C but than others based on amorphous C calcined at very high temperatures, around 1000 °C. These properties are attributed to an increase in the electrical conductivity parallel to the ordering of the layers. We believe this work provides a new strategy to design C-based composites capable of combining the formation of nanocrystalline phases and the control of the C structure with superior electrochemical properties for Li-S batteries.

SiOx Anode: From Fundamental Mechanism toward Industrial Application

Silicon monoxide (SiO) has been explored and confirmed as a promising anode material of lithium-ion batteries. Compared with pure silicon, SiO possesses a more stable microstructure which makes better comprehensive electrochemical properties. However, the lithiation mechanism remains in dispute, and problems such as poor cyclability, unsatisfactory electrical conductivity, and low initial Coulombic efficiency (ICE) need to be addressed. Additionally, more attention needs to be paid on the internal relationship between electrochemical performances and structures. In this review, the different preparation processes, the derived microstructure of the SiO_x , the corresponding lithiation mechanism, and electrochemical properties are summarized. Researches about disproportionation reaction which is regarded as a key point and other modifications are systematically introduced. Closely linked with structure, the advantages and disadvantages of various SiO_x anode materials are summarized and analyzed, and the possible directions toward the practical applications of SiO_x anode material are presented. In a word, from the preparation and reaction mechanism of the material to the modifications and future development, a complete and systematical review on SiO_x anode is presented.

New Insight into the Working Mechanism of Lithium-Sulfur Batteries under a Wide Temperature Range

Sweet potato-derived carbon with a unique solid core/porous layer core/shell structure is used as a conductive substrate for gradually immobilizing sulfur to construct a cathode for Li-S batteries. The first discharge specific capacity of the Li-S batteries with the C-10K@2S composite cathode at 0.1C is around 1645 mAh g^-1, which is very close to the theoretical specific capacity of active sulfur. Especially, after 175 cycles at 0.5C, the maintained specific discharge capacities of the C-10K@2S cathode at -20, 0, 25, and 40 °C are about 184.9, 687.2, 795.5, and 758.3 mAh g^-1, respectively, and the cathode is superior to most of the classical carbon form matrices. Working mechanisms of the cathodes under different temperatures are confirmed based on X-ray photoelectron spectroscopy (XPS) and in situ X-ray diffraction (XRD) characterizations. Distinctively, during the discharge stage, the widely proposed two-step cathodic reactions occur simultaneously rather than sequentially. In addition, the largely accelerated phase conversion efficiency of the cathode at a higher temperature (from room temperature to 40 °C) contributes to its enhanced charge/discharge specific capacity, while the byproduct Li₂S₂O₇ or Li₃N irreversibly formed during the cycles limits its application performance at 0 °C. These conclusions would be very significant and useful for designing cathodes for Li-S batteries with excellent wide working temperature performance.

Simple and Sustainable Preparation of Cathodes for Li-S Batteries: Regeneration of Granular Activated Carbon from the Odor Control System of a Wastewater Treatment Plant

To obtain a wide variety of green materials, numerous investigations have been undertaken on industrial waste that can act as sustainable resources. The use of hazardous wastes derived from wastewater treatment plants (WWTPs), especially the activated carbon used in odor control systems, is a highly abundant, scalable, and cost-effective strategy. The reuse of waste materials is a key aspect, especially for the sustainable development of emerging energy storage systems, such as lithium-sulfur (Li-S) batteries. Herein, granular active carbons from two WWTP treatment lines were regenerated in air at low temperature and utilized as the sulfur host with micro-/mesoporous framework. The resulting regenerated carbon and sulfur composites were employed as cathodes for Li-S cells. The SL-ACt3@S composite electrode with 60 wt% loaded sulfur exhibited a remarkable initial capacity of 1100 mAh g-1 at C/10 rate and higher than 800 mAh g-1 at C/2. Even at a rate of 1C, it maintained a high capacity of almost 700 mAh g-1 with a capacity retention of 85.4 % after 350 cycles, demonstrating a very low capacity fading of only 0.042 % per cycle. It is essential to note that the coulombic efficiency was always higher than 96 % during all the cycles. In this proposal, the only used source material was expired carbon from WWTP that was obtained with a simple and effective regeneration process. This "trash into treasure" strategy leads to a new way for using hazardous waste material as high-performance and environmentally safe electrodes for advanced Li-S batteries.

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.

Investigation on Fabrication of Reduced Graphene Oxide-Sulfur Composite Cathodes for Li-S Battery via Hydrothermal and Thermal Reduction Methods

Lithium-sulfur (Li-S) battery is considered one of the possible alternatives for next-generation high energy batteries. However, its practical applications are still facing great challenges because of poor electronic conductivity, large volume change, and polysulfides dissolution inducing “shuttle reaction” for the S cathode. Many strategies have been explored to alleviate the aforementioned concerns. The most common approach is to embed S into carbonaceous matrix for constructing C-S composite cathodes. Herein, we fabricate the C-S cathode reduced graphene oxide-S (rGO-S) composites via one step hydrothermal and in-situ thermal reduction methods. The structural features and electrochemical properties in Li-S cells of the two type rGO-S composites are studied systematically. The rGO-S composites prepared by one step hydrothermal method (rGO-S-HT) show relatively better comprehensive performance as compared with the ones by in-situ thermal reduction method (rGO-S-T). For instance, with a current density of 100 mA g⁻¹, the rGO-S-HT composite cathodes possess an initial capacity of 1290 mAh g⁻¹ and simultaneously exhibit stable cycling capability. In particular, as increasing the current density to 1.0 A g⁻¹, the rGO-S-HT cathode retains a reversible capacity of 582 mAh g⁻¹ even after 200 cycles. The enhanced electrochemical properties can be attributed to small S particles uniformly distributed on rGO sheets enabling to significantly improve the conductivity of S and effectively buffer large volume change during lithiation/delithiation.

Pistachio Shell-Derived Carbon Activated with Phosphoric Acid: A More Efficient Procedure to Improve the Performance of Li-S Batteries

A sustainable and low-cost lithium-sulfur (Li-S) battery was produced by reusing abundant waste from biomass as a raw material. Pistachio shell was the by-product from the agri-food industry chosen to obtain activated carbon with excellent textural properties, which acts as a conductive matrix for sulfur. Pistachio shell-derived carbon activated with phosphoric acid exhibits a high surface area (1345 m²·g^-1) and pore volume (0.67 cm³·g^-1), together with an interconnected system of micropores and mesopores that is capable of accommodating significant amounts of S and enhancing the charge carrier mobility of the electrochemical reaction. Moreover, preparation of the S composite was carried out by simple wet grinding of the components, eliminating the usual stage of S melting. The cell performance was very satisfactory, both in long-term cycling measurements and in rate capability tests. After the initial cycles required for cell stabilization, it maintained good capacity retention for the 300 cycles measured (the capacity loss was barely 0.85 mAh·g^-1 per cycle). In the rate capability test, the capacity released was around 650 mAh·g^-1 at 1C, a higher value than that supplied by other activated carbons from nut wastes.

Defect Control in the Synthesis of 2 D MoS2 Nanosheets: Polysulfide Trapping in Composite Sulfur Cathodes for Li-S Batteries

One of the inherent challenges with Li-S batteries is polysulfide dissolution, in which soluble polysulfide species can contribute to the active material loss from the cathode and undergo shuttling reactions inhibiting the ability to effectively charge the battery. Prior theoretical studies have proposed the possible benefit of defective 2 D MoS₂ materials as polysulfide trapping agents. Herein the synthesis and thorough characterization of hydrothermally prepared MoS₂ nanosheets that vary in layer number, morphology, lateral size, and defect content are reported. The materials were incorporated into composite sulfur-based cathodes and studied in Li-S batteries with environmentally benign ether-based electrolytes. Through directed synthesis of the MoS₂ additive, the relationship between synthetically induced defects in 2 D MoS₂ materials and resultant electrochemistry was elucidated and described.

MIL-88A Metal-Organic Framework as a Stable Sulfur-host Cathode for Long-cycle Li-S Batteries

Lithium-sulfur (Li-S) batteries have received enormous interest as a promising energy storage system to compete against limited, non-renewable, energy sources due to their high energy density, sustainability, and low cost. Among the main challenges of this technology, researchers are concentrating on reducing the well-known “shuttle effect” that generates the loss and corrosion of the active material during cycling. To tackle this issue, metal-organic frameworks (MOF) are considered excellent sulfur host materials to be part of the cathode in Li-S batteries, showing efficient confinement of undesirable polysulfides. In this study, MIL-88A, based on iron fumarate, was synthesised by a simple and fast ultrasonic-assisted probe method. Techniques such as X-ray diffraction (XRD), Raman spectroscopy, Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), and N₂ adsorption/desorption isotherms were used to characterise structural, morphological, and textural properties. The synthesis process led to MIL-88A particles with a central prismatic portion and pyramidal terminal portions, which exhibited a dual micro-mesoporous MOF system. The composite MIL-88A@S was prepared, by a typical melt-diffusion method at 155 °C, as a cathodic material for Li-S cells. MIL-88A@S electrodes were tested under several rates, exhibiting stable specific capacity values above 400 mAh g⁻¹ at 0.1 C (1C = 1675 mA g⁻¹). This polyhedral and porous MIL-88A was found to be an effective cathode material for long cycling in Li-S cells, retaining a reversible capacity above 300 mAh g⁻¹ at 0.5 C for more than 1000 cycles, and exhibiting excellent coulombic efficiency.

A Comparative Study of Particle Size Distribution of Graphene Nanosheets Synthesized by an Ultrasound-Assisted Method

Graphene-based materials are highly interesting in virtue of their excellent chemical, physical and mechanical properties that make them extremely useful as privileged materials in different industrial applications. Sonochemical methods allow the production of low-defect graphene materials, which are preferred for certain uses. Graphene nanosheets (GNS) have been prepared by exfoliation of a commercial micrographite (MG) using an ultrasound probe. Both materials were characterized by common techniques such as X-ray diffraction (XRD), Transmission Electronic Microscopy (TEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). All of them revealed the formation of exfoliated graphene nanosheets with similar surface characteristics to the pristine graphite but with a decreased crystallite size and number of layers. An exhaustive study of the particle size distribution was carried out by different analytical techniques such as dynamic light scattering (DLS), nanoparticle tracking analysis (NTA) and asymmetric flow field flow fractionation (AF4). The results provided by these techniques have been compared. NTA and AF4 gave higher resolution than DLS. AF4 has shown to be a precise analytical technique for the separation of GNS of different sizes.