Rechargeable Lithium-sulfur Batteries Research Articles

Understanding the Anchoring Effect of Two-Dimensional Layered Materials for Lithium-Sulfur Batteries.

Although the rechargeable lithium-sulfur battery system has attracted significant attention due to its high theoretical specific energy, its implementation has been impeded by multiple challenges, especially the dissolution of intermediate lithium polysulfide (Li2Sn) species into the electrolyte. Introducing anchoring materials, which can induce strong binding interaction with Li2Sn species, has been demonstrated as an effective way to overcome this problem and achieve long-term cycling stability and high-rate performance. The interaction between Li2Sn species and anchoring materials should be studied at the atomic level in order to understand the mechanism behind the anchoring effect and to identify ideal anchoring materials to further improve the performance of Li-S batteries. Using first-principles approach with van der Waals interaction included, we systematically investigate the adsorption of Li2Sn species on various two-dimensional layered materials (oxides, sulfides, and chlorides) and study the detailed interaction and electronic structure, including binding strength, configuration distortion, and charge transfer. We gain insight into how van der Waals interaction and chemical binding contribute to the adsorption of Li2Sn species for anchoring materials with strong, medium, and weak interactions. We understand why the anchoring materials can avoid the detachment of Li2S as in carbon substrate, and we discover that too strong binding strength can cause decomposition of Li2Sn species.

Polymer-Modified Carbon Nanotube Paper As an Efficient Current Collector in Li-S Batteries

Introduction Rechargeable batteries with high energy densities are highly demanded in our daily life and many commercial applications. Lithium-ion batteries have been successfully in the rechargeable battery market, but their energy densities are limited by the capacity of electrodes, particularly the cathodes such as LiCoO2, LiMn2O4, and LiFePO4. To further increase the energy density of rechargeable lithium batteries, alternative cathodes with high specific capacities, such as sulfur with a theoretical capacity of 1,672 mAh/g, are highly needed.1 Sulfur is also an environmental friendly material, which is an abundant element on earth and can be widely used for the future battery applications. Several challenges impede the application of rechargeable lithium-sulfur (Li-S) batteries. For instance, the dissolution and loss of intermediate polysulfide materials between the repeating charge and discharge processes result in rapid reduction of capacity and poor cycle life. To improve the cycling performance, a variety of approaches have been developed showing promising improvements. However, new approaches are still needed which can not only further improve the battery performance but also inspire more interest in the battery community. Lithium/dissolved polysulfide batteries using binder-free carbon nanotube (CNT) paper as a current collector have shown highly reversible cyclability with unprecedented capacities.2 LiNO3 additive in the electrolyte can form a passivation layer on the surface of lithium metal anode, which can reduce the reduction of lithium polysulfide on the anode side. However, prolonged cycle life (>100 cycles) cannot be obtained which is partially due to the loss of active material from the cathode. To overcome this issue, the current collector should be able to “hold” lithium polysulfides from migrating. We present here a strategy to modify CNT paper by a functional polymer to enhance the “holding” property of the current collector, which can eliminate the use of LiNO3 additive in the lithium/dissolved polysulfide batteries and improve cycle life. Experimental Polyvinylpyrrolidone (PVP) was selected as the functional polymer, which has been confirmed to have high affinity with lithium polysulfides and lithium sulfide.3 A solution (0.15 wt.%) of PVP in ethanol was added to a disc of a commercial CNT paper. Ethanol was evaporated by heating to render PVP-modified CNT paper, as shown in Fig. 1. To fabricate half cells, 20 µL of 0.25 M Li2S6/1 M LiCF3SO3 in dimethoxy ethane (DME)/1,3-dioxolane (DOL) (1:1 v/v) was added in the PVP-modified CNT paper as the cathode. Additional blank electrolyte was added in between the lithium metal anode and Celgard® separator. Results and Discussion PVP can be dissolved in ethanol, which can be easily removed during the post-heating process. The solution penetration allows uniform distribution of PVP in the CNT paper. After the modification process, PVP formed many small particles within the 3D CNT network and some thin films in the spaces among CNTs, as shown in Fig. 1. Without LiNO3 additive in the electrolyte, the cell can be discharged to 1.5 V without the reduction of LiNO3 at low potential. The cells show typical two distinguishable discharge voltage plateaus and two overlapped charge plateaus, which are similar to those with LiNO3 additive in the electrolyte.2 Fig. 2 shows the voltage profile of the cell in the 1st, 2nd and 50th cycle after initial charge to 3.0 V. Without LiNO3, the cell can be completely discharged to 1.5 V without a voltage slope meaning negligible side reactions in the discharge. With the PVP coating, diffusion of lithium polysulfides out of the cathode is significantly slowed down, which can be evidenced from the improved cycle life as shown in Fig. 3. The cell without PVP modification shows a rapid capacity decrease from 1,100 mAh/g to 200 mAh/g over 35 cycles. In contrast, the cell with PVP-modified CNT current collector, the cell maintains an average discharge capacity of 900 mAh/g over 50 cycles. The Coulombic efficiency was maintained at 82%. This study demonstrates that PVP can be an efficient binder holding lithium polysulfides from diffusion, which can significantly improve the battery cycling performance. References A. Manthiram, Y.-Z. Fu, and Y.-S. Su, J. Phys. Chem. Lett. 4, 1295 (2013).Y.-Z. Fu, Y.-S. Su, and A. Manthiram, Angew. Chem. Int. Ed. 52, 6930 (2013).Z.W. Seh, Q. Zhang, W. Li, G. Zheng, H. Yao, and Yi Cui, Chem. Sci. 4, 3673 (2013). Figure 1

Effect of Metal Nanoparticles on the Polysulfide Conversion Reactions in Rechargeable Li-Sulfur Batteries

Rechargeable lithium-sulfur (Li-S) batteries have emerged as the most promising electrochemical energy storage systems due to their high energy density, wide range of temperature operation, cost effectiveness, and eco-friendly in nature. Nevertheless, the drawbacks associated with the Li-S batteries such as insulating nature of sulfur species, corrosive nature of predeposited polysulfides at electrodes during discharge-charge processes, and formation of thick SEI layer still need to be circumvented. One of the promising ways to alleviate these problems is to use highly porous, conductive, and active species which can improve the kinetics of polysulfide conversion reactions and diffusion processes. In this context, we have investigated electronically conductive species incorporated graphene, specifically Metal/graphene hybrids (metal = Pt, Ni, and Co) as cathode in Li-S batteries and performed systematic studies to understand the electrochemical behavior of polysulfides during discharge-charge processes. Metal/graphene hybrids were prepared through wet chemical routes and employed them as electrodes for the conversion of polysulfides in Li-S batteries. Structural and morphological techniques depicted phase purity of the materials and well-dispersed metallic nanocrystallites with an average size of 5 nm on the graphene sheets. Electrochemical studies were carried out by assembling Li/sulfur cells inside glove box using a porous metal/graphene as electrodes cathode, 0.6M Li2S8-1M LiTFSI in TEGDME as electrolyte, and metallic lithium as anode. Galvanostatic discharge-charge tests indicated a two-fold increment in the Li-S battery performance with metal/graphene compared to pure graphene. A high discharge capacity of 750 mAh/g at C-rates of C/10 has been observed with Pt/graphene. The studies on metal/graphene based Li-S battery revealed pivotal role of metallic nanoparticles in enhancing the polysulfide conversion processes. # - Corresponding Author - leela.arava@wayne.edu

Activated Li2s As a High-Performance Cathode for Rechargeable Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are considered to be a promising alternative to lithium-ion (Li-ion) batteries as the next-generation rechargeable battery system. Despite significant progress in recent years, degradation of the lithium-metal anode remains a persistent challenge for Li-S batteries, resulting in safety concern for Li-S batteries and hindering their practical utility. One possible strategy to circumvent the problems associated with using metallic lithium is to use alternative, lithium-free anodes coupled with a lithium-containing sulfur-based cathode. Accordingly, Li2S has attracted much attention as a prospective cathode material. However, Li2S is highly insulating; either intricate synthesis to produce small Li2S particles or a high initial charging-cut-off voltage to activate Li2S bulk particles is required. However, these traditional methods invariably lead to increased manufacturing cost and/or instabilities in the ether-based electrolytes in Li-S batteries. We demonstrate here that the Li2S bulk particles can be effectively activated through surface interaction with P2S5. Furthermore, the effective activation and the facilitated oxidation of Li2S into polysulfides are believed to be due to the formation of shallow sulfur- and phosphorus-containing species at the surface of Li2S particle. In contrast to the pristine Li2S, the P2S5-activated Li2S cathodes demonstrate lower initial charging voltage plateaus. Furthermore, the lowest charging voltage plateau appears when the molar ratio between Li2S and P2S5 is 7:1, resulting in an activation of ~ 80 % of the theoretical capacity of Li2S below 3.0 V (Figure 1a). Considering that Li2S or P2S5 alone lacks electrochemical activity before charging above 3.0 V, we believe the accessible charge capacity below 3.0 V is attributed to the interaction between P2S5 and Li2S, leading to Li2S activation. However, further increase in the concentration of P2S5 produces a gradual increase in the charging voltage plateau, likely due to the increased cell resistance. Scanning electron microscopy images reveal that the typical Li2S particles are micron-sized spheres when the molar ratio between Li2S and P2S5 is higher than 5:1. Core-shell-like morphology appears when the molar ratio between Li2S and P2S5 is 5:1. In addition, X-ray photoelectron spectroscopy and Raman spectroscopy results confirm the formation of sulfur- and phosphorus-containing species at the activated Li2S surface. Especially, when the molar ratio between Li2S and P2S5 is 10:1, S 2p 3/2 peaks center at 159.8, 161.0, and 162.6 eV. The 159.8 eV peak is a characteristic peak of Li2S. The 159.8 eV Li2S peak is still present when the Li2S: P2S5 ratio is 7:1, but disappears when the ratio reaches 5:1, suggesting the formation of a thick surface layer. Reversible discharge capacities of ~ 800 mAh g (Li2S)–1 are obtained and the capacity retention is as high as 83 % after 80 cycles (Figure 1b). Coulombic efficiency remains near 100 % upon long-term cycling. This is in contrast to the pristine Li2S that delivers limited reactivity and inferior capacity due to the incomplete oxidation reaction. The superior cycling performance of the activated Li2S is due to the enhanced surface charge transfer reducing the electrochemically inaccessible Li2S and ensuring cathode conductivity. This facile activation enables the direct use of Li2S bulk particles as high-capacity cathode materials for Li-S batteries, significantly decreasing the manufacturing cost of Li-S batteries. We believe this strategy is of great significance for the safe and effective use of Li2S as a cathode material, and is a promising step toward the low-cost fabrication of metallic lithium-free Li-S batteries. Figure 1

Li2s Nanocrystals Confined in Free-Standing CNT Paper for High Performance Rechargeable Li-S Batteries

Introduction High energy density rechargeable batteries are greatly demanded owing to the increasing use of electric vehicles and portable electronics. Lithium-sulfur (Li-S) batteries, with a high theoretical specific capacity of sulfur (i.e., ∼1,672 mAh g-1), are considered to be one of the most promising substitutes to Li-ion batteries.1 Despite sulfur cathode material has many benefits (e.g., low cost, abundance, and high energy), Li-containing anodes (usually Li metal) are required which is a long-term safety concern. Lithium sulfide (Li2S), the fully lithiated state of sulfur with a theoretical capacity of 1,166 mAh g-1, is a more desirable cathode material compared to sulfur as it can allow the use of lithium-free anodes such as Si, Sn, Sb, or metal oxides.2,3 However, a large overpotential (∼1 V) was identified on the initial charge of bulky Li2S particles due to the insulating and low lithium ion diffusivity nature.4 Although significant improvements have been achieved by using some electrolyte additives,5-7new and scalable methods are still needed. Herein, we present a facile and scalable infiltration method to resolve this issue by adding a Li2S solution into a commercial, binder-free, self-standing carbon nanotube (CNT) paper as current collector followed by drying. Li2S nanocrystals are formed in the conductive CNT network, leading to a negligible overpotential in the first charge. Experimental As represented in Fig. 1, Li2S powder was first dissolved in anhydrous ethanol to form a uniform solution. 7 Then the Li2S solution was added into a piece of CNT paper, followed by drying inside an Argon-filled glove box (<0.1 ppm of H2O). Afterwards, a half cell was prepared by adding a certain amount of electrolyte (1 M LiCF3SO3 and 0.1 M LiNO3 in dimethoxy ethane (DME)/1,3-dioxolane (DOL) (1:1 v/v)) into the Li2S-CNT electrode, followed by a Celgard 2400 separator, additional electrolyte, and lithium metal anode. Finally the cells were crimped for electrochemical evaluation. Results and Discussion Li2S particles were deposited and confined in the nanoporous structure of the CNT paper to form Li2S nanocrystals after ethanol was removed, as shown in Fig. 1. The Li2S loading can be precisely controlled by tuning the concentration and volume of solution added to the paper. The as-prepared cell has an open circuit voltage (OCV) of ~2.16 V, which is much lower than that (2.28 V) of the cell with micro-sized Li2S particles.2 As shown in Fig. 2, the cell can be charged at a voltage below 2.5 V with negligible overpotential in the first charge which is similar to the following charge. Comparing to other Li2S cathodes reported,5-7 the Li2S-CNT electrode prepared by the infiltration method shows the lowest overpotential. The nanocrystals of Li2S formed in the CNT network contribute to the exceptional performance in the first charge. The cycling performance is shown in Fig. 3. The cell exhibits an initial discharge capacity of 727 mAh g-1with a capacity retention of 77% after 50 cycles at C/10 rate. The Coulombic efficiency is 82% in the first cycle and maintains at 98% on average in the following cycles. In summary, Li2S nanocrystals formed in the nanoscaled CNT network by the infiltration method show an unprecedented low overpotential in the first charge and a good cycle life with high efficiency. References A. Manthiram, Y.-Z. Fu, S.-H. Chung, C.-X. Zu, Y.-S. Su, Chem. Rev. , DOI: 10.1021/cr500062v (2014).Y.-Z. Fu, Y.-S. Su, A. Manthiram, Adv. Energy Mater. 4, 1300655 (2014).Y.-Z. Fu, C.-X. Zu, and A. Manthiram, J. Am. Chem. Soc. 135, 18044 (2013).Y. Yang, G. Y. Zheng, S. Misra, J. Nelson, M. F. Toney, Y. Cui, J. Am. Chem. Soc. 134, 15387 (2012).S. Meini, R. Elazari, A. Rosenman,A. Garsuch, D. Aurbach, J. Phys. Chem. Lett. 5, 915 (2014).C.-X. Zu, M. Klein, A. Manthiram, J. Phys. Chem. Lett. 5, 3986 (2014).F. Wu, J. T. Lee, et al., Adv. Mater., DOI: 10.1002/adma.201404194 (2014). Figure 1

Polysulfide transport through separators measured by a linear voltage sweep method

Shuttle of polysulfide from the sulfur cathode to lithium metal anode in rechargeable lithium–sulfur batteries is a critical issue hindering cycling efficiency and life. Several approaches have been developed to minimize it including polysulfide-blocking separators; there is a need for measuring polysulfide transport through separators. We here show a linear voltage sweep method to measure anodic (oxidization) current of polysulfide crossed separators, which can be used as a quantitative measurement of the polysulfide transport. The electrochemical oxidation of polysulfide is diffusion controlled. The electrical charge in Coulombs produced by the oxidation of polysulfide is linearly related to the concentration of polysulfide within a certain range (≤0.5 M). Separators with a high porosity (large pore size) show high anodic currents, resulting in fast capacity degradation and low Coulombic efficiencies in Li–S cells. These results demonstrate this method can be used to correlate the polysulfide transport through separators with the separator structure and battery performance, therefore provide guidance for developing new separators for lithium–sulfur batteries.

Effects of sulfur loading on the corrosion behaviors of metal lithium anode in lithium–sulfur batteries

The corrosion behaviors in rechargeable lithium–sulfur batteries come from the reactions between polysulfides and metal lithium anode, and they are significantly influenced by the sulfur loading. While there are limited papers reported on the effects of sulfur loading on the corrosion behaviors. In this paper, the effects have been investigated systematically. The corrosion films consisted of insulating lithium ion conductors are loose and porous, so that the corrosive reactions cannot be hindered. The thickness of the corrosion layers, consequently, increased along with increasing sulfur loading or cycle times. For instance, the thickness of corrosion layers after 50 cycles was 98μm in the cell with 5mg sulfur while it reached up to 518μm when the loading increased to 15mg. The continuous deposition of corrosion products gave rise to low active materials utilization and poor cycling performance.

Template growth of porous graphene microspheres on layered double oxide catalysts and their applications in lithium–sulfur batteries

The wise integration of individual two-dimensional graphene nanosheets into three-dimensional (3D) macroscopic architectures is essential for full exploration of their potential applications in electrochemical energy storage. Graphene microspheres (GMSs) with hierarchical porous architectures and high 3D electrical conductivities are highly expected to be the host carbon to accommodate sulfur cathode for lithium–sulfur batteries. Herein we reported the direct synthesis of GMSs assembled by 3D interconnected graphene with hierarchical pores by template chemical vapor deposition (CVD) on layered double oxide (LDO) microspheres. The LDO templates were derived from conformally calcined layered double hydroxide microspheres produced by spray drying. After methane-CVD, graphene was catalytically grown on LDO templates. Subsequent routine chemical etching of the LDO templates enabled as-obtained GMSs with a large diameter of ca. 11μm and a high surface area of 1275m2g−1. The GMS was employed as carbon scaffold to accommodate sulfur for rechargeable lithium–sulfur batteries. An initial areal discharge capacity of 2.67mAhcm−2 was obtained at a current density of 0.83mAcm−2 on flexible GMS paper electrode with an areal sulfur loading of 2.5mgcm−2.

Two-step synthesis of sulfur/graphene composite cathode for rechargeable lithium sulfur batteries

Sulfur/graphene composites with different sulfur contents were prepared by two-step synthesis, where graphene was regarded as a carrier of sulfur active substance. The surface structure and crystal form of the composites obtained were characterized and compared by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was found that sulfur was partially coated by graphene. The graphene folds provided more nano-pores and electron transport channels for sulfur. From TGA results, the sulfur contents of the sulfur/graphene composites measured were about 42.32 wt%, 54.94 wt%, and 65.23 wt%. Electrochemical tests demonstrated that sulfur/graphene composite (x=54.94 wt%) cathode exhibited better capacity retention (40.13%) compared with the pure cathode (20.46%), where an initial discharge capacity was up to 1 500 mAh·g−1 and it remained about 600 mAh·g−1 after 30 cycles. Furthermore, the electrochemical reaction mechanism and the state of reaction interface for Li/S battery were analyzed by cyclic voltammogram and AC-impedance spectra. The results indicated that the sulfur/graphene composite with a sulfur content of 54.94 wt%, based on a two-step synthesis, contributed to improving electrochemical properties of lithium/sulfur battery

One-step synthesis of an urchin-like sulfur/polyaniline nano-composite as a promising cathode material for high-capacity rechargeable lithium–sulfur batteries

Urchine-like sulfur/polyaniline nano-composite has been synthesized by a soft and facile approach. This novel composite could be directly utilized as the cathode material for Li–S battery and display high specific capacity and good cycle stability.

Sulfur–carbon yolk–shell particle based 3D interconnected nanostructures as cathodes for rechargeable lithium–sulfur batteries

A novel 3D interconnected S@C yolk–shell nanostructure from mild oxidation of ZnS@C accommodates S volume expansion upon lithiation in Li–S batteries, giving high capacity with good cycling performance.

A revolution in electrodes: recent progress in rechargeable lithium-sulfur batteries.

As a promising candidate for future batteries, the lithium-sulfur battery is gaining increasing interest due to its high capacity and energy density. However, over the years, lithium-sulfur batteries have been plagued by fading capacities and the low Coulombic efficiency derived from its unique electrochemical behavior, which involves solid-liquid transition reactions. Moreover, lithium-sulfur batteries employ metallic lithium as the anode, which engenders safety vulnerability of the battery. The electrodes play a pivotal role in the performance of lithium-sulfur batteries. A leap forward in progress of lithium-sulfur batteries is always accompanied by a revolution in the electrode technology. In this review, recent progress in rechargeable lithium-sulfur batteries is summarized in accordance with the evolution of the electrodes, including the diversified cathode design and burgeoning metallic-lithium-free anodes. Although the way toward application has still many challenges associated, recent progress in lithium-sulfur battery technology still paints an encouraging picture of a revolution in rechargeable batteries.

Sulfur@metal cotton with superior cycling stability as cathode materials for rechargeable lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries have great potential for some high energy applications such as electric vehicles and smart grids due to the high capacity, natural abundance, low cost and environmental friendliness of sulfur. In this work, we use the metal cotton to absorb sulfur firmly as cathode material for Li–S batteries. The as-designed sulfur@metal cotton (S@MC) composite shows a good cycling stability and rate capability. The capacity is retained at 480mAhg−1 at 0.1C after 200 cycles. Furthermore, for higher rates, the S@MC cathode material also exhibits stable capacity during different periods.

Biomass-derived Activated Carbon for Rechargeable Lithium-Sulfur Batteries

High-surface-area activated carbon (HSAAC) was synthesized by carbonizing coconut shells and subsequently activating the material with KOH. The as-prepared HSAAC had a mostly microporous structure (with small mesoporous inclusions) and exhibited a high specific surface area of 2258.7 m2g-1 and an average pore size of 2.246 nm. Sulfur was then loaded into the activated carbon (AC), and this S/HSAAC (62 wt%) was used as a cathode for Li-S batteries. These batteries delivered an initial discharge capacity of 1233 mAhg-1 at a current density of 200 mAg-1. Due to the strong absorption force of the micropores and a high pore volume, the cells retained 929 mAhg-1 with 80% capacity retention of the initial discharge after 100 cycles. Considering its low cost and ability to be produced at a large-scale, biomass-derived HSAAC is a promising electrode material that may advance high-energy rechargeable lithium-sulfur batteries toward use in practical applications.

Activated Li2S as a High-Performance Cathode for Rechargeable Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries with a high theoretical energy density of ∼2500 Wh kg(-1) are considered as one promising rechargeable battery chemistry for next-generation energy storage. However, lithium-metal anode degradation remains a persistent problem causing safety concerns for Li-S batteries, hindering their practical utility. One possible strategy to circumvent the aforementioned problems is to use alternative, high-capacity, lithium-free anodes (e.g., Si, Sn, carbon) and a Li2S cathode. However, a large potential barrier was identified on the initial charge of insulating bulk Li2S particles, limiting the cell performance. In this work, the bulk Li2S particles were effectively activated with an electrolyte containing P2S5, resulting in a lowered initial charging voltage plateau. This permits the direct use of commercially available bulk Li2S particles as a high-capacity cathode for room-temperature, rechargeable Li-S batteries, significantly lowering the manufacturing cost of Li-S cells.

Improved capacity retention of low cost sulfur cathodes enabled by a novel starch binder derived from food

Rechargeable lithium sulfur batteries are attracting great attention in recent years due to their high theoretical energy density, but they still suffer from poor cycle performance and other drawbacks. Up to now, most researchers have focused on the design of the state of the art S-containing composites or new and complex electrode architectures to improve their electrochemical performances. However, simple and low cost sulfur cathodes usually exhibit poor cycle performances. Here, we propose gelatinized starch, a natural biological macromolecule from the food industry as a binder for low cost sulfur cathodes to improve their capacity retention. Compared with PVDF, the starch binder is able to reduce the polarization of the sulfur cathode and enhance its capacity retention. The sulfur cathode with the starch binder exhibits a specific capacity retention of ∼90% at 0.2 C after 200 cycles, which corresponds to a small capacity decay of 0.05% per cycle. It is believed that these improvements result from the high stability of the starch binder in a liquid electrolyte, which can stabilize the structure of the cathode and reduce the irreversible accumulation of the discharge products.

Large-scale synthesis of ordered mesoporous carbon fiber and its application as cathode material for lithium–sulfur batteries

A novel type of one-dimensional ordered mesoporous carbon fiber has been prepared via the electrospinning technique by using resol as the carbon source and triblock copolymer Pluronic F127 as the template. Sulfur is then encapsulated in this ordered mesoporous carbon fibers by a simple thermal treatment. The interwoven fibrous nanostructure has favorably mechanical stability and can provide an effective conductive network for sulfur and polysulfides during cycling. The ordered mesopores can also restrain the diffusion of long-chain polysulfides. The resulting ordered mesoporous carbon fiber sulfur (OMCF-S) composite with 63% S exhibits high reversible capacity, good capacity retention and enhanced rate capacity when used as cathode in rechargeable lithium–sulfur batteries. The resulting OMCF-S electrode maintains a stable discharge capacity of 690mAh/g at 0.3C, even after 300cycles.

Enhanced electrochemical performance by wrapping graphene on carbon nanotube/sulfur composites for rechargeable lithium–sulfur batteries

A novel graphene-wrapped carbon nanotube/sulfur structure was designed to improve the electrochemical performance of the lithium–sulfur (Li–S) batteries. Owing to the introduction of the reduced graphene oxide (rGO) with the aim to restrain the polysulfide anions diffusion phenomenon, increase the overall electronic conductivity of the electrode and accommodate volume expansion between the delithiated S and lithiated Li2S phases, the resulted graphene-wrapped carbon nanotube/sulfur (S/CNT@rGO) composite makes the cycling performance of the Li–S batteries better than that without rGO. The S/CNT@rGO composite showed an initial discharge capacity of ~1299mAhg−1 at 0.2C rate. After 100 cycles of charge/discharge, the S/CNT@rGO composite retained a high specific capacity of ~670mAhg−1, much higher than that without rGO (<150mAhg−1). The results show that the graphene-wrapped carbon nanotube/sulfur composite could be a promising cathode material for high-rate performance Li–S batteries.

Binary sulfone/ether-based electrolytes for rechargeable lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are a promising electrochemical system because they exhibit high theoretical capacity of 1672 mAh g−1. However, widespread use of these batteries has been hindered by the poor conductivity and high dissolution rate of the active materials as well as by the high reactivity of the lithium electrodes. In this study, we investigated the effects of the choice of electrolyte on the electrochemical performance of Li-S batteries. We studied a number of cyclic and acyclic sulfone-based electrolytes and found that the physical and electrochemical properties of the sulfone-based electrolytes, which could be varied by varying their composition, had an effect on the solubility of S8 in the electrolytes. It was observed that, in contrast to the electrolyte based on 1,2-dimethoxyethane, the one based on a mixture of tetramethylene sulfone/1,2-dimethoxyethane dissolved S8 (or Li2Sm) to a lower degree and resulted in stable electrochemical performance in Li-S batteries. Thus, the chemical reactivity of the solvent used for the electrolyte should be taken into consideration along with the physical properties of the active materials when designing Li-S batteries.

Rechargeable lithium-sulfur batteries.

Rechargeable lithium-sulfur batteries.