Aluminum sulfur batteries with ionic liquid electrolytes are promising next-generation energy storage devices due to the high abundance of both aluminium and sulfur. However, very little understanding of the discharge mechanism is currently available, which hampers their development. Herein, a mathematical model that considers the complex electrochemical reduction of the sulfide species as well as the formation of the various polysulfides is developed to describe the discharge performance and the reversibility of Al-S cells at different current densities. The model is validated with experimental data obtained from Swagelok cells composed of Al metal anode, S@CNT cathode, and EMIMCl-AlCl3 ionic liquid electrolyte. The cells exhibited different discharge mechanisms and Al2S3 precipitation routes at the different current densities. The contact resistance between the composite electrode and the current collector was the main factor limiting the discharge performance at high current densities. The reversibility of the Al-S cells based on the formation of Al2S3 precipitates strongly depends on the operating current density. The developed model will serve as a tool for other researchers to enhance the electrochemical performance of aluminum sulfur batteries.

While lithium-sulfur batteries theoretically have both high gravimetric specific energy and volumetric energy density, only its specific energy has been experimentally demonstrated to surpass that of the state-of-the-art lithium-ion systems at cell level. One major reason for the unrealized energy density is the low capacity density of the highly porous sulfur/carbon composite as the positive electrode. In this work, mechanical compression at elevated temperature is demonstrated to be an effective method to increase the capacity density of the electrode by at least 90 % and moreover extends its cycle life. Distinct impacts of compression on the resistance profiles of electrodes with different thickness are investigated by tortuosity factors derived from both electrochemical impedance spectroscopy, X-ray computed tomography and kinetic analysis based on operando X-ray diffraction. The results highlights the importance of a homogeneous electrode structure highlight lithium-sulfur system.

Sulfur electrodes for lithium-sulfur batteries necessarily contain a conductive additive, typically carbon, to enable the electrochemical reactions, since sulfur and the discharge product, Li2S, are insulators. Consequently, the full passivation of carbon, by deposition of sulfur and/or Li2S, would necessarily produce the death of the battery. However, here we demonstrate that for high-performance lithium-sulfur batteries operated under lean electrolyte conditions (electrolyte to sulfur ratio of 6 mu L mg(S)(-1) in Li-S coin cells), the extent of passivation of carbon is not severe enough to limit performance. This is shown by performing impedance measurements of fully charged lithium-sulfur batteries, from which we demonstrate that we can evaluate the specific surface area of carbon, and we find that the capacity fade with cycling is not due to a decrease in the electrochemically active surface area of carbon. These results show that introducing a higher surface area carbon in the sulfur electrode formulation is not needed to prevent passivation, and that the focus of lithium-sulfur development should be directed towards other issues, such as mitigating undesirable reactions at the lithium electrode and achieving robust sulfur electrode structures enabling fast transport of electrolyte species and, thus, more homogeneous reactions. (c) 2021 Elsevier Ltd. All rights reserved.

The Al-S battery is a promising next-generation battery candidate due to high abundance of both aluminium and sulfur. However, the sluggish kinetics of the Al-S battery reactions produces very high overpotentials. Here, for the first time, it was demonstrated that the incorporation of redox mediators could dramatically improve the kinetics of Al-S batteries. On the example of iodide redox mediators, it was shown that the charging voltage of Al-S batteries could be decreased by about 0.23 V with as little as 2.3 wt% of redox mediator added as electrolyte additive. Control electrochemical measurements, without prior discharge of the battery, demonstrated that >97 % of the charge capacity was due to the desired oxidation of Al2S3 and polysulfides, and X-ray diffraction experiments confirmed the formation of sulfur as the final charge product. The beneficial role of redox mediators was demonstrated with cheap and environmentally friendly electrolytes made of urea and AlCl3. This work showed that dramatic performance improvements could be achieved with low concentration of electrolyte additives, and therefore, much further performance improvements could be sought by combining multiple additives.

Ø = 25 mmV1 mm specimen well). A piece of glass was used as a flat surface to elevate the electrode during measurements. The morphology and element distribution of raw materials and sulfur electrodes was studied using a JEOL JSM59 scanning electron microscope (15 kV) with an Oxford instruments energy-dispersive X-ray spectroscopy (EDS) attach-ment. Viscosity measurements were taken using a Cannon–Fenske viscometer tube (Sigma–Aldrich) and the experiment was recorded using a mobile phone camera (Samsung Galaxy S10 + ). The viscosity values were calculated from the time required for the electrolytes to flow between two marks in the viscometer, as estimated from the video.

The high abundance and low cost of aluminum and sulfur make the Al-S battery an attractive combination. However, significant improvements in performance are required, and increasing the thickness and sulfur content of the sulfur electrodes is critical for the development of batteries with competitive specific energies. This work concerns the development of sulfur electrodes with the highest sulfur content (60 wt %) reported to date for an Al-S battery system and a systematic study of the effect of the sulfur electrode thickness on battery performance. If low-cost electrolytes made from acetamide or urea are used, slow mass transport of the electrolyte species is identified as the main cause of the poor sulfur utilization when the electrode thickness is decreased, whereas complete sulfur utilization is achieved with a less viscous ionic liquid. In addition, the analysis of very thin electrodes reveals the occurrence of degradation reactions in the low-cost electrolytes. The new analysis method is ideal for evaluating the stability and mass transport limitations of novel electrolytes for Al-S batteries.

A new indium(III) antimony(V) sulfide, (H1.33tren)[In2.67Sb1.33S8]·tren, has been prepared solvothermally at 433 K. The compound crystallises in the tetragonal space group I-42d (lattice parameters, a=12.6248(5) and c=19.4387(18)Å at 150K) and contains adamantane-like T2 supertetrahedral units comprised of corner-sharing InS45− and SbS43− tetrahedra. The adamantane-like units are then linked through sulfur vertices to generate an open, 3-D framework structure containing large pores in which neutral, protonated tren (tris(2-aminoethylene)amine) molecules reside. The presence of the organic components was confirmed by solid-state 13C NMR (10kHz), combustion and thermogravimetric analysis. The band gap, obtained from UV–vis diffuse reflectance measurements, is 2.7(2)eV. Stirring with either water or alkali-metal salt solution leads to removal of the neutral tren molecules and an ~9% reduction in unit-cell volume on formation of (H1.33tren)[In2.67Sb1.33S8]·(H2O)4.

Radical cations of a soluble rigid tetrathienoacene are capable of forming stable π-dimer dications at ambient temperature when the short backbone becomes extended with conjugated thiophene-2-yl substituents in the α-positions. On the other hand, simple attachment of methyl groups on the α-carbon of the external thiophen-2-yl rings proved sufficient to inhibit the dimerization. Stable radical cations were also exclusively formed for tetrathienoacene derivatives end-capped with bulky TIPS and phenyl substituents.

Radical cations of a soluble rigid tetrathienoacene are capable of forming stable pi-dimer dications at ambient temperature when the short backbone becomes extended with conjugated thiophene-2-yl substituents in the alpha-positions. On the other hand, simple attachment of methyl groups on the alpha-carbon of the external thiophen-2-yl rings proved sufficient to inhibit the dimerization. Stable radical cations were also exclusively formed for tetrathienoacene derivatives end-capped with bulky TIPS and phenyl substituents.