Sulfur Dissolution Research Articles

Metal Sulfide Nanofiber Anodes for High Capacity Sodium Rechargeable Batteries

A considerable amount of effort has been devoted to developing innovative and economical energy storage systems, including methods that are optimized for application to large-scale energy storage systems such as smart grids and electric vehicles. Sodium ion batteries have been spotlighted recently owing to lower material costs, the abundance of sodium resources, and analogous electrochemical components with existing Li-ion battery systems. However, unlike Li-ion batteries, current studies on Na-ion batteries have often confronted problems related to the insufficient Na storage capacities of electrode materials, especially anode materials, originating from the larger ionic radius of Na compared with Li (e.g. Li+: 0.76 Å, Na+: 1.02 Å). Therefore, the development of high capacity anode materials that enable facile insertion/extraction of large Na ions is essential for high performance Na-ion batteries. In recent years, metal sulfides have been considered as functional electrode materials for diverse applications such as electronic devices, energy conversion and storage systems due to their unique electronic properties and structural characteristics, compared to metal oxides. Metal disulfides (MoS2 and WS2) have also shown their possibility as a high capacity anode material (>700 mAh/g) because of (i) the large slab space between their 2-D planes, (ii) their reversible conversion reaction characteristics (MS2 + 4Na+ + 4e- → 2 Na2S + M, M = Mo, W), and (iii) the higher conductivity of Na2S products (metal sulfides) compared to Na2O (metal oxides). Similarly, amorphous metal trisulfides (MS3, M = Mo, W) could be considered as high capacity anode materials due to the structural flexibility of their glassy phase and the excess sulfur as an active component (MS3 + 6Na+ + 6e- → 3Na2S + M). Moreover, the electronic conductivity of MS3 can be improved by excess sulfur in the trisulfide structure. However, Na battery performance of metal trisulfides has not been thoroughly introduced thus far. Moreover, an effective solution is required for the sulfur dissolution issue originating from soluble polysulfide intermediates during the Na2S formation/decomposition process, thereby losing sulfur components and consequently degrading capacity. To address complex concerns, designing hierarchical architecture of the metal sulfide strucutre with a functional coating layer can offer considerable improvement in sodium battery performance. Reducing the size-dimension to the nanoscale and tailoring their morphologies can also afford an increased number of reaction sites and reduced Na ion diffusion. In this presentation, we report a tailored synthetic strategy used to create heterogeneous metal sulfide (e.g. MoS2, WSx)/oxide core-shell nanofiber materials with hierachical features, and we evaluate them as potential anode materials for high performance Na-ion batteries. The sulfide nanofibers are successfully prepared by electrospinning and subsequent calcination in a reducing atmosphere. Conformal oxide coating is applied to prevent capacity degradation of the metal sulfide anodes originating from sulfur dissolution. [1] W.-H. Ryu, J.-W. Jung, K. Park, S.-J. Kim, I.-D. Kim, Nanoscale, 2014, 6, 10975-10981 [2] W.-H. Ryu, H. Wilson, S. Sohn, J. Li, X. Tong, E. Shaulsky, J. Schroers, M. Elimelech, A. D. Taylor, ACS Nano, 2016, 10, 3257–3266 [3] S.-J. Lim, D.-W. Han, D.-H. Nam, K.-S. Hong, J.-Y. Eom, W.-H. Ryu and H.-S. Kwon, J. Mater. Chem. A, 2014, 2, 19623-19632

Catecholamine Functionalized Reduced Graphene Oxide-Sulfur Composite As a Cathode Material for Lithium-Sulfur Batteries

Among various next generation rechargeable batteries, Lithium-Sulfur batteries have emerged as a potential candidate to replace Li-ion batteries because the former has high theoretical energy density of 2500 Wh/Kg, which is almost 7 times higher than that of the currently used Li-ion batteries. To address the low conductivity of sulfur and polysulfide dissolution in the sulfur cathode during discharge cycling, we propose the use of functionalized reduced graphene oxide-sulfur composite as a better candidate compared to graphene oxide-sulfur composite (GO/S) which has relatively lower conductivity. The reduced graphene oxide structure with simultaneous introduction of catecholamine functional groups will have the advantage of higher electrical conductivity along with a better ability to adsorb polysulfides through chemical interaction. Catecholamine functionalized reduced graphene oxide (c-rGO) was prepared starting from GO as a raw material, followed by sulfur infiltration (c-rGO/S) at 155°C with an intended sulfur content of 74-75%. To emphasize the importance of introducing catecholamine functional groups in rGO/S composite for polysulfide adsorption by chemical interaction, thermally reduced graphene oxide- sulfur composite (t-rGO/s) with no functional groups and bare GO/S composite was tested too. The use of c-rGO/S composite maintains the capacity to as high as 700 mAh/g after 100 cycles at 0.5C whereas the high electrical resistivity of oxidized graphene-sulfur composite lower the capacity to as low as 300 mAh/g after 100 cycles at 0.5C. Even with the higher electrical conductivity, the t-rGO/S composite delivered a discharge capacity of only 400 mAh/g at 0.5C after 100 cycles amid the absence of any polysulfide adsorbing functional groups like the one present in c-rGO/S composite. Moreover, the evidence of effective polysulfide adsorption by chemical interaction in c-rGO/S in comparison to GO/S has be shown by in-situ UV-Vis spectroscopy results. Keywords: Catecholamine, Graphene-oxide, Polysulfide adsorption, In-situ UV-Vis spectroscopy

Heterogeneous WSx/WO₃ Thorn-Bush Nanofiber Electrodes for Sodium-Ion Batteries.

Heterogeneous electrode materials with hierarchical architectures promise to enable considerable improvement in future energy storage devices. In this study, we report on a tailored synthetic strategy used to create heterogeneous tungsten sulfide/oxide core-shell nanofiber materials with vertically and randomly aligned thorn-bush features, and we evaluate them as potential anode materials for high-performance Na-ion batteries. The WSx (2 ≤ x ≤ 3, amorphous WS3 and crystalline WS2) nanofiber is successfully prepared by electrospinning and subsequent calcination in a reducing atmosphere. To prevent capacity degradation of the WSx anodes originating from sulfur dissolution, a facile post-thermal treatment in air is applied to form an oxide passivation surface. Interestingly, WO3 thorn bundles are randomly grown on the nanofiber stem, resulting from the surface conversion. We elucidate the evolving morphological and structural features of the nanofibers during post-thermal treatment. The heterogeneous thorn-bush nanofiber electrodes deliver a high second discharge capacity of 791 mAh g(-1) and improved cycle performance for 100 cycles compared to the pristine WSx nanofiber. We show that this hierarchical design is effective in reducing sulfur dissolution, as shown by cycling analysis with counter Na electrodes.

Sulfur Nanogranular Film-Coated Three-Dimensional Graphene Sponge-Based High Power Lithium Sulfur Battery.

To meet the requirements of both high energy and power density with cycle durability of modern EVs, we prepared a novel nanosulfur granular assembled film coated on the three-dimensional graphene sponge (3D-GS) composite as a high-performance active material for rechargeable lithium sulfur batteries. Instead of conventional graphene powder, three-dimensional rGO sponge (3D-rGO) is employed for the composite synthesis, resulting in a sulfur film directly in contact with the underlying graphene layer. This significantly improves the overall electrical conductivity, strategically addressing challenges of conventional composites of low sulfur utilization and dissolution of polysulfides. Additionally, the synthesis mechanism of 3D-GS is elucidated by XPS and DFT analyses, where replacement of hydroxyl group of 3D-rGO sponge by sulfur (S8) is found to be thermodynamically favorable. As expected, 3D-GS demonstrates outstanding discharge capacity of 1080 mAh g(-1) at a 0.1C rate, and 86.2% capacity retention even after 500 cycles at a 1.0C rate.

Effects of cell construction parameters on the performance of lithium/sulfur cells

Current lithium‐ion batteries are predicted to be unable to provide the specific energy required to meet the ever‐increasing demands of rapidly emerging technologies. Due to a high theoretical specific capacity of 1675 mAh/g, sulfur has gained much attention as a promising positive electrode material for high specific energy rechargeable batteries. Although the lithium/sulfur cell has been studied for many years and continues to receive much attention today as an alternative power source for zero‐emission vehicles and advanced electronic devices, the realization of this novel cell's promise as a commercial product has yet to be successful. The major problems with sulfur electrodes involve: (1) the dissolution of sulfur (as polysulfides) and the resulting diffusion of dissolved polysulfides and (2) the deposition of insulating products (including Li2S) on both the negative and the positive electrodes. These solid deposits can physically block the electrode reaction sites, thus passivating the electrode surfaces. Another important problem is the large volume change that occurs with the conversion of S to Li2S. It is important to understand that the performance of Li/S cells is hampered by linked chemical and mechanical degradations and both degradation mechanisms must be correctly alleviated in order to markedly improve current‐technology Li/S cells. In this study, improved cycling performance via the reactive functional groups on graphene oxide to successfully immobilize sulfur and lithium polysulfides during operation has been demonstrated. The use of a new electrolyte and binder leads to improved cell performance in terms of high‐rate capability (up to at least 2 C) and good reversibility (S ↔ Li2S), yielding at least 800 cycles have also been demonstrated. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2749–2756, 2015

In Situ Polymerized PAN-Assisted S/C Nanosphere with Enhanced High-Power Performance as Cathode for Lithium/Sulfur Batteries.

Carbonaceous and polymer materials are extensively employed as conductor and container to encapsulate sulfur particles and limit polysulfide dissolution. Even so, high-power performance is still far from satisfaction due to the expansion and collapse of the electrode materials during thousands of charge-discharge process. Herein, it is found that colloidal carbon sphere with high elastic coefficient can be utilized as a framework to load sulfur, which can trap soluble polysulfides species in the pores within the sphere and efficaciously improve the electronic conductivity of the cathode. After modified by polyaniline (PAN) through in situ polymerization, PAN-assisted S/C nanosphere (PSCs-73, with 73 wt % sulfur) effectively minimize polysulfide diffusion, enhance the electron transfer rate and overcome the problem of volume expansion. The fabricated PSCs-73 cell shows outstanding long high-power cycling capability over 2500 charge/discharge cycles with a capacity decay of 0.01% per cycle at 5 C. Substantially, this composite can drive 2.28 W white indicators of LED robustly after minutes of charging by three lithium batteries in series, showing a promising potential application in the future.

Alkali and alkaline earth metal chloride solutions influence sulfide mineral dissolution

Alkali and alkaline metal chlorides have been considered as inert electrolyte species with respect to sulfide mineral dissolution in the presence of oxidizing agents such as O2 and Fe3+. Under anoxic conditions in the laboratory or the field, as exist in most saline subsurface environments, the potential reactivity of alkali and alkaline metal chlorides with sulfide minerals has typically been ignored. Arsenopyrite (FeAsS(s)), galena (PbS(s)), and pyrite (FeS2(s)) are commonly encountered sulfide mineral phases, the dissolution of which affects many ecosystems. In this study, dissolution experiments with these minerals were conducted under anoxic conditions with 10mM solutions of NaCl, CaCl2, and MgCl2 at constant pH of 2.56. Results show that these electrolytes affect sulfide mineral dissolution under anoxic conditions, either increasing or decreasing the rate. The extent to which sulfide mineral dissolution is affected is small but measurable and depends on the anionic species in the mineral and cationic species in solution. Specifically, the dissolution of arsenic from arsenopyrite increased with an increase in cation activity in solution, while the dissolution of sulfur decreased with an increase in chloride ion activity. These results suggest that sulfide mineral dissolution under anoxic conditions is caused by an interaction of cations in solution with anions on the mineral surface, and inhibited by the presence of competing anions in solution.

Tailored Carbon Nanotubes for High-Performance Lithium-Sulfur Batteries

Significant effort has been invested into addressing critical problems of lithium-sulfur batteries since they are considered as the next generation energy storage material due to their high specific energy density and low cost.1 Critical problems still remain including poor cycle life and rate capability originated from the insulating nature of sulfur and polysulfide intermediate dissolution into the electrolyte.2 Despite the considerable success in alleviating the problems such as drastic capacity fading and poor rate capability, commercial application still has a long way to go, especially at high current rate conditions. Here, we report a noble carbon matrix for lithium-sulfur batteries based on a partially unzipped multi-walled carbon nanotube(MWCNT) with favorable properties for the improved lithium-sulfur batteries. Partially unzipped MWCNT has additional benefit in that it was prepared by facile and scalable way without use of toxic or expensive materials. In contrast to MWCNT and fully unzipped nanoribbon, partially unzipped MWCNT clearly exhibited a unique structure of coexistence of carbon nanotube and nanoribbon in one tube as illustrated in Figure 1. The experimental optimization results were fully discussed with TEM, SAED patterns, EDS mapping, RAMAN, XPS, BET isotherms and EIS characterizations. Partially unzipped MWCNT showed increased surface area and pore volume with preserved electron conductive pathway owing to opened inner pores of MWCNT. Newly developed the pores of partially unzipped MWCNT were decorated with oxygen containing functional groups and acted as a stable polysulfide reservoir as illustrated in Figure 2. The synergistic effect of unique pore structure and oxygen containing functional groups led to the improved electrochemical performance at a high current rate of 8375 mA g-1 (5 C). Partially unzipped MWCNT-sulfur composite delivered 688.5 mAh g-1 at the initial discharge and retained 544.2 mAh g-1 after 100 cycles at the high current rate of 5 C as given in Figure 3. Furthermore, to understand the mechanism of the improved electrochemical performance of partially unzipped MWCNT, Partially unzipped MWCNT-sulfur was studied utilizing the Monte Carlo (MC) simulations. This modelling explains why the polysulfide dissolution into the bulk electrolyte was alleviated thus led to the improved electrochemical performance. We believe that our work can provide insight to many researchers in that partially unzipped MWCNT opens up a new concept of exploiting MWCNT inner pores. Reference 1. Chung, W. J.; Griebel, J. J.; Kim, E. T.; Yoon, H.; Simmonds, A. G.; Ji, H. J.; Dirlam, P. T.; Glass, R. S.; Wie, J. J.; Nguyen, N. A. et al. The use of elemental sulfur as an alternative feedstock for polymeric materials. Nat. Chem. 2013, 5, 518-524. 2. Manthiram, A.; Fu, Y.;Su, Y.-S. Challenges and Prospects of Lithium-Sulfur Batteries. Acc. Chem. Res. 2012, 46, 1125-1134. Figure 1

An Advanced Lithium‐Ion Sulfur Battery for High Energy Storage

A lithium‐ion battery is reported using a sulfur–carbon composite cathode, a graphite anode, and a dimethoxyethane‐dioxolane‐lithium bis‐(trifluoromethanesulfonyl)imide (DOL‐DME‐LiTFSI) electrolyte advantageously added by lithium nitrate (LiNO3) and a selected polysulfide (Li2S8). The suppressed sulfur dissolution, due to the Li2S8 buffer action, as well as reduced shuttle reactions by the film‐forming properties of the LiNO3 positively affect the lithium‐ion cell behavior in terms of delivered capacity, coulombic efficiency, and cycle life. The lithium–sulfur cell shows a stable capacity of 750 mAh g−1 for over 200 cycles with an enhanced cycling efficiency. Furthermore, the full lithium‐ion sulfur battery using a graphite‐based anode shows a working voltage of about 2 V and delivers a stable capacity of 500 mAh g−1. The full cell has enhanced safety content, due to the replacement of the lithium metal anode by suitable intercalation electrode, and shows a theoretical energy density as high as 1000 Wh kg−1 at high current rate of 1 C. The remarkable safety level, low materials cost, and high practical energy density, expected to exceed 300 Wh kg−1, suggest the battery reported is a suitable energy storage system for future applications.

Novel Flexible Sulfur Wire Fabrics (FSF) for Lithium-Sulfur Batteries

Introduction Lithium sulfur and lithium-air batteries hold much promise for the future of batteries on account of their theoretical capacities of 2567 and 3505 Wh/kg respectively(1). The dissolution of sulfur through the formation of soluble polysulfides and the poor electronic conductivity of sulfur are however, major problems hindering Li-S battery progress (1-3). In addition, particle fracture and delamination as a result of repeated volumetric expansion and contraction have also been identified as factors responsible for poor long term performance(4, 5). In our previous work on lithium-sulfur batteries, we have shown the effectiveness of using a thin Li-ion conducting barrier layer in improving the cycling characteristics(6). In this work, we develop a unique strategy to directly prepare sulfur wire mattes (Figure 1) capable of being spun as yarn and thereupon being used directly in the form of ‘textile fabric batteries’. Using these wires, we generate two other morphologies to specifically tackle fade and conductivity issues existing in sulfur cathodes. This results in sulfur cathodes with high electronic conductivity, minimal volumetric expansion and improved rate capabilities and cyclability. In addition, the electrodes that we use in this study allow us to obtain high areal capacities. Figure 1 shows SEM and EDAX map of the same. Results of these studies will be presented and discussed. Captions Figure 1:(a) Scanning electron microscopy image of the sulfur wires (b) EDAX map indicating the Sulfur distribution.

The solubility of sulfur in hydrous basaltic melts

Experiments were performed to determine the sulfur solubilities of hydrous basalts from Vesuvius, Etna and Stromboli (Italy). The melts were equilibrated at 1050 and 1200°C with H2O and sulfur (added as pyrrhotite), and at pressures ranging from 250 to 2000bar. Most experiments were performed under oxidising conditions (NNO+2), and a few under reducing conditions (NNO−1), with melt water contents of 0.5–3.5wt.%. Sulfur contents in glasses were determined by electron microprobe and range from 860 up to 6700ppm. No compositional effect is found between the three alkali basaltic melts. The fugacities of S-bearing species were derived using an MRK equation of state applied to an O–H–S fluid, knowing H2 and H2O fugacities, and range from 50 up to 3000bar. A thermodynamic species-based model is derived from our results along with available data in the literature, assuming that sulfur dissolution results from the additive contributions of both H2S and SO2 dissolution reactions. Compared to similar models developed for silicic melts, basalt compositions requires the incorporation of an Fe term, which accounts for the strong association between Fe and S in silicate melts, and considers the elevated Fe content of mafic melts. The model shows that, at any fixed fS2, the sulfur solubility in hydrous basalt displays a pronounced minimum around NNO, the position of which depends on temperature. The minimum in sulfur solubility coincides with the redox range were the abundance of S2 in the fluid reaches its maximum compared to either H2S or SO2 species. Such a minimum in solubility is in agreement with experimental constraints at 1bar under carefully controlled fO2 and fS2. Calculated proportions of dissolved species in the melt depend on the prevailing fS2 and fO2, being in general agreement with available spectroscopic models. Calculations of gas saturation pressures, which classically consider only H2O and CO2 dissolved volatiles, are strongly affected by S-bearing species. At fO2 close to, or higher than, NNO+1, omission of sulfur species may result in underestimates of gas saturation pressures of 1kbar or more. The same happens at fO2 below NNO−1.

Model Membrane-Free Li-S Batteries for Enhanced Performance and Cycle Life.

The success of the rechargeable Li-S cell is limited in part by the dissolution of lithium-polysulfide in the electrolyte. Remarkably, it is found that removal of the conventional membrane separator in a Li-S cell improves sulfur utilization and cycling performance, whether the sulfur is initially contained in the cathode or electrolyte. An optimized cell design yields discharge capacities as high as 980 mA h g-1 after 100 cycles.

Polyphenylene Wrapped Sulfur/Multi-Walled Carbon Nano-Tubes via Spontaneous Grafting of Diazonium Salt for Improved Electrochemical Performance of Lithium-Sulfur Battery

A novel conducting polymer polyphenylene is used to in situ wrap the MWCNT-core/Sulfur-shell composite via the spontaneous polymerization reaction process of benzenediazonium tetrafluoroborate (ArN2+ BF4−). The porous conductive polymer skin layer effectively prevents the dissolution of active sulfur and facilitates the diffusion of lithium ion towards to reaction site, due to the shortened diffusion distance. Moreover, this resulting architecture structure, Polyphenylene/S/MWCNTs, can accommodate the large volumetric expansion of sulfur during lithiation procedure, improving the cycling stability and rate capability of lithium-sulfur batteries. It delivers an initial discharge capacity of 1491.3mAh/g at 0.1C, and the remaining capacity is 1015.6mAh/g after 75 cycles. The as-prepared material also exhibits an excellent rate capability and cyclability at 0.5C, 1C and 5C. Our experimental results manifest that this composite is a potential candidate as cathode material for high performance lithium-sulfur batteries in the future.

Effects of species concentration and external resistance on spatiotemporal dynamics during the electro-oxidation of sulfide ion on a platinum disk electrode

Sulfide and hydroxide ions, acting as negative and positive feedback species of the oscillatory electro-oxidation of sulfide on a platinum disk, respectively, strongly affected the spatiotemporal dynamics of the process. Oscillations with both hidden N-shaped and N-shaped negative differential resistances were enhanced in both amplitude and potential range with increasing sulfide ion concentration, but weakened with increasing hydroxide ion concentration. The patterns in the N-shaped negative differential resistance oscillatory region changed from local pulses to global synchronous oscillations of sulfur deposition and dissolution with increasing sulfide ion concentration. However, as the hydroxide ion concentration increased, both the patterns and oscillations were suppressed and the pulse width also decreased. External resistance was another factor that caused complex oscillations and a novel pattern formation that was observed to be alternating between local pulses and synchronous oscillations of sulfur deposition and dissolution. A detailed analysis of the reaction mechanism and a model simulation provided a reasonable explanation of these phenomena and the dynamic features. This investigation further promoted analysis of the complex spatiotemporal dynamics of the sulfide electro-oxidation system and enriched the experimental results available in electrochemical systems. This research was helpful in the prediction and control of pattern formation processing through adjustment of the positive and negative feedbacks as well as spatial couplings.

Li Ion-Sulfur Batteries with Glyme-Lithium Salt Solvate Ionic Liquid Electrolytes

We have reported that equimolar mixtures of certain Li salts and glymes (triglyme (G3) and tetraglyme (G4)) form molten complexes at ambient temperature, and behave like typical ionic liquids (ILs).1,2 In the mixtures, ligand glyme molecules strongly coordinate (or solvate) to Li+ ions to form complex cations, hence, this family is classified as “solvate” ILs. Because complexation of appropriate Li salts with appropriate glymes allows realizing ILs involving Li+ ions as single cationic species, lithium solvate ILs possess high Li+ ion conductivity and transference number. In addition, the dissolution of lithium polysulfides (Li2S m ), the discharge products of elemental sulfur, was suppressed in certain solvate ILs due to their extremely low coordinating nature. Owing to these remarkable properties, they are fascinating electrolytes for Li-sulfur batteries.3,4 Recently, we found that solvate IL electrolyte allows successful charge-discharge of graphite electrode. These results inspire us to develop low-cost and safe batteries without Li metal anode. In this study, the battery performance of the graphite-sulfur full cells with the solvate IL electrolytes was evaluated employing a lithiated graphite (LiC6) anode or a lithiated sulfur (lithium sulfide, Li2S) cathode as a lithium source. A LiC6 anode and a Li2S cathode were prepared by chemical and electrochemical methods. Using these electrodes, two kinds of full cells in both charge and discharge states were fabricated. Reversible charge-discharge of both full cells can be performed at 60 ºC, however, the capacities decrease as repeating cycles and the coulombic efficiency for these cells is substantially low compared to our previous results. This is because relatively high operation temperature facilitate dissolution of elemental sulfur and/or Li2S m , leading to loss of active materials and undesired side-reactions. To overcome these problems, solvate IL electrolytes were diluted by an appropriate solvent with low donor ability. As a result, a stable cycle operation with a discharge capacity of 700–800 mA h g−1 and a coulombic efficiency of 90–95 % at 30 ºC was achieved over 100 cycles (Figure 1), irrespective of starting charge-discharge states.

Role of Organosulfur Compounds in the Growth and Final Surface Chemistry of PbS Quantum Dots

This paper describes the mechanism by which reaction of sulfur with 1-octadecene (ODE) induces a change in the shape of PbS quantum dots (QDs), synthesized from the S/ODE precursor and lead(II) oleate, from cubic to hexapodal by altering the ligand chemistry of the growing QDs. 1H NMR and optical spectroscopies indicate that extended heating of sulfur and ODE at 180 °C produces a series of organosulfur compounds with optical transitions in the visible region and that the binding of organosulfur ligands to the growing QD induces a preferential growth at the ⟨100⟩ faces (over the ⟨111⟩ faces) and, therefore, a hexapodal geometry for the particles. The study shows that S/ODE can be made a more reliable precursor by reducing the temperature and duration of the sulfur dissolution step and that any metal sulfide QD synthesis using elemental sulfur heated to high temperatures should take steps to reduce the in situ yield of organosulfur byproducts by avoiding olefinic solvents.

Vine-like MoS2 anode materials self-assembled from 1-D nanofibers for high capacity sodium rechargeable batteries.

A tailored conversion-reaction anode material of 1-D MoS2 nanofibers with a vine-like shape composed of MoS2 nanoflakes delivers exceptionally high Na capacity and exhibits excellent rate properties. The improved cycleability of the MoS2 nanofiber electrode is achieved by a uniform TiO2 coating, which effectively minimized the sulfur dissolution.

Novel Heterostructures for Lithium-Sulfur Batteries

IntroductionLithium-ion batteries with their unique high voltage, high energy density chemistries have come to fruition decades of fundamental research conducted in electrochemical systems and materials. The development of a number of plug-in hybrid and fully electric vehicles (EV) using lithium-ion technology and their favorable market response is the harbinger of a long-awaited transition in automotive technology. Despite these advances, there is still a genuine need for increasing energy densities for the successful transition to EVs (1, 2). Advances in lithium-ion anode technology have made it possible to obtain ~1500 mAh/g anodes with superior cycle life (3-5). However, cathode research has been rather stymied in contrast on account of the challenges faced in designing stable, conductive materials with high capacities. Cathode capacities thus far have been limited to ~ 300 mAh/g in high voltage (1, 6) lithium manganese-nickel-cobalt oxide chemistries. Lithium sulfur and lithium-air batteries though well-known but challenging to execute, hold much more promise of matching anode capacities on account of their theoretical capacities of 2567 and 3505 Wh/kg respectively(2). The dissolution of sulfur through the formation of soluble polysulfides and the poor electronic conductivity of sulfur are however, major problems hindering Li-S batteries.It has previously been demonstrated that the use of highly conductive porous carbon matrix and carbon nanotubes can help circumvent these issues (7-10). In addition, the use of a carbon matte as a barrier layer to polysulfide transport has been demonstrated to be effective in retaining high capacity(11). There is however a need to translate this design into thick electrodes capable of delivering high overall electrode capacity. In this study, we coat pristine sulfur particles with carbon and an ionically conducting matrix using a simple chemical method. The thick electrodes were prepared using this procedure and were tested in 2025 coin cells with lithium counter/reference electrodes. We demonstrate excellent charge storage behavior of these composite electrodes at various charge-discharge rates. Extended cycling of these composite electrodes reveals much improved capacity retention. Figure 1 shows the electrochemical results of these different configurations. Results of these studies will be presented and discussed.

Sensitivity analysis of a mathematical model of lithium–sulfur cells: Part II: Precipitation reaction kinetics and sulfur content

A sensitivity analysis of a mathematical model of a lithium–sulfur (Li–S) battery was performed, focusing on the precipitation rate constants and sulfur content, by investigating the response of the model to the variation of these parameters over a wide mathematical range. The necessity of rapid dissolution of elemental sulfur and rapid precipitation of reduced sulfur is discussed in detail. The sensitivity analysis suggests modifying the reduction reaction steps of sulfur can improve the predictions of the model of Li–S battery. Furthermore, an upper limit on the sulfur content of the cathode exists to ensure optimal performance. Although the model provides valuable knowledge concerning Li–S batteries, a modification to the assumed five-step reduction of sulfur combined with the consideration of the insulating nature of the active material is required to improve the model.

Electrode Performance of Newly Developed Ni-W-S Deposited Alloy for Alkaline Water Electrolysis

Ni-W-S coatings were fabricated by electroplating. The bath denoted as “Ni-W-S No.1” was derived from a neutral pH bath for Ni-W alloy plating. Furthermore, sulfosalicylic acid was added as a stress reducer in order to prevent surface cracks. In the solution denoted as “Ni-W-S No.2” contains sodium tungstate, as a source of tungsten, sodium citrate. Plating solution denoted as “Ni-S” is same bath with Ni-W-S No.2 without sodium tungstate. Ni-W-S electrodes showed significantly excellent characteristics as a cathode for alkaline water electrolysis. Specifically, the Ni-W-S electrode in which sulfosalicylic acid was added as a stress reducer exhibited an excellent performance comparing to conventional Ni-S and Ni cathode. In order to obtain the performances of thus obtained electrode for alkaline water electrolysis, an electrode surface morphology was observed by SEM and the film composition was evaluated by EDX. In order to specify the crystal structure, XRD was employed. Furthermore, in order to evaluate the durability performance as a cathode for water electrolysis, sequential changes in electrode performance was investigated periodically using LSV while performing long-term electrolysis test for 48 hours. Furthermore the prevention of sulfur dissolution during cathodic polarization was monitored.