Cycle Life Of Lithium-sulfur Batteries Research Articles

Quasi-Solid-State Electrolyte Induced by Metallic MoS2 for Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are a promising high-energy-density technology for next-generation energy storage but suffer from an inadequate lifespan. The poor cycle life of Li-S batteries stems from their commonly adopted catholyte-mediated operating mechanism, where the shuttling of dissolved polysulfides results in active material loss on the sulfur cathode and surface corrosion on the lithium anode. Here, we report in situ formation of a quasi-solid-state electrolyte (QSSE) on the metallic 1T phase molybdenum disulfide (MoS2) host that extends the lifetime of Li-S batteries. We find that the metallic 1T phase MoS2 host is able to initiate the ring-opening polymerization of 1,3-dioxolane (DOL), forming an integrated QSSE inside batteries. Nuclear magnetic resonance analysis reveals that the QSSE consists of ∼13% liquid DOL in a solid polymer matrix. The QSSE efficiently mediates sulfur redox reactions through dissolution-conversion chemistry while simultaneously suppressing polysulfide shuttling. Therefore, while ensuring high sulfur utilization, it avoids degradation of both electrodes, as well as the concomitant electrolyte consumption, leading to enhanced cycling stability. Under a practical lean electrolyte condition (electrolyte-to-sulfur ratio = 2 μL mg-1), Li-S pouch cell batteries with the QSSE demonstrate a capacity retention of 80.7% after 200 cycles, much superior to conventional liquid electrolyte cells that fail within 70 cycles. The QSSE also enables Li-S pouch cell batteries to operate across a wider temperature range (5 to 45 °C), together with improved safety under mechanical damage.

Life cycle assessment of lithium-sulfur batteries with carbon nanotube hosts: Insights from lab experiments

Lithium‑sulfur (Li-S) batteries are candidates for next-generation batteries. It can be produced sustainably using sulfur instead of controversial cathode minerals like cobalt. However, Li-S batteries must improve their energy density and cycle life at their current state of development. Hosting the sulfur on carbon nanotubes (CNT) is a potential solution. This study investigated the environmental performance of a CNT-based Li-S battery based on original experiment data. The CNT in the batteries functioned as binders, conductive fillers, and current collectors, reducing auxiliary materials and simplifying manufacturing processes. We conducted a cradle-to-gate life cycle assessment (LCA) to clarify the environmental performance. We showed that the global warming potential (GWP) of the Li-S battery pack in a conventional battery structure was 105 kg CO2e/kWh. By partially substituting current collectors, increasing lithium anode efficiency, and reducing solvent usage, we could achieve 87, 82, and 78 kg CO2e, respectively. The lowest GWP of Li-S battery was 20 % lower when compared to a graphite‑nickel manganese cobalt oxides (NMC) battery. In addition, the other environmental indicators, including human toxicity, ecotoxicity, and acidification, were 26 % to 79 % lower, showing no major environmental burden shift. One exception was the mineral resource depletion, which was 2 % higher because lithium metal, instead of synthetic graphite, was used as a high-capacity anode pair. This study also found that modifying the cathode production process by using a less energy-intensive filtration before evaporating the remaining solvent could significantly reduce the energy required, thus mitigating the previously identified environmental hotspot. Our finding highlighted that a prospective LCA collaborating with battery experimentalists could lead to novel discoveries for environmentally sustainable battery production. Overall, we showed that Li-S batteries are environmentally preferred at the production stage, as supported by advanced experiments. Further research into improving the cycle life of Li-S batteries is crucial when considering the use stage to reduce the environmental impact per functional unit of energy delivered over the battery lifetime.

The Role of Functionalized Conducting Polymer Binders in Improving Power Density and Cycle Life of Lithium-Sulfur Batteries

Lithium-Sulfur batteries are promising as the next-generation of low-cost, high-energy rechargeable batteries. However, the commercialization of this battery has been limited by poor rate capability and cycle life. To improve the performance of Li-S cells, we have investigated the role of two n-dopable conducting polymers, N2200 and N2200-OE, as binders for the sulfur cathode. The electron and ion transport properties of these polymer binders, along with their strong affinity for polysulfides, results in significantly enhanced performance compared to cells with the traditional insulating PVDF binder. The role of these conducting polymer binders in enhancing the performance of the cells is analyzed using impedance spectroscopy, shuttle current measurements, conductivity measurements, UV–vis spectroscopy, GIWAXS studies and post-cycling analysis of the anodes. The conducting polymer binders reduce the cell impedance by a factor of four leading to a marked improvement in rate capability. The shuttling of the polysulfides and the formation of insoluble sulfides at the anode is curtailed by the interaction of the polysulfides with the backbone of the polymer binders, leading to an impressive capacity retention of 82% after 500 cycles. These studies demonstrate the benefit of tailored polymer binders at the sulfur electrode in addressing the limitations of lithium-sulfur batteries.

Mn2O3 Incorporated Carbonized Bacterial Cellulose As Sulfur Host for Lithium-Sulfur Batteries

Early development and commercialization of lithium-ion batteries (LIBs) have enabled the portable electronic devices and powered the world. However, the ever-increasing demand for higher energy batteries have led to the quest for further improvement. Lithium-sulfur batteries (LSBs), with lithium anode and sulfur-based composite as cathode, have high theoretical specific energy of 2600 W h kg-1 (around 10 folds higher than LIBs system). Moreover, sulfur is produced as a by-product from petroleum refineries making research in LSBs more lucrative. However, there are a few critical challenges which restrict the commercialization of LSBs. First, insulating nature of sulfur (5 × 10-30 S cm-1) and lithium sulfide (Li2S, 10-13 S cm-1) impedes the electronic conductivity which results in low utilization of active sulfur. Secondly, the dissolution and diffusion of long-chain lithium polysulfides in electrolyte to lithium anode under concentration gradient causes series of severe issues such as loss of active sulfur, pulverization of lithium anode. Thirdly, the volume change during lithiation (up to 80%) results in degradation of cathode.To tackle aforementioned issues, we have utilized Mn2O3 incorporated carbonized bacterial cellulose (Mn2O3@CBC) as sulfur host for LSB. A facile melt-diffusion approach was adopted to encapsulate sulfur into Mn2O3@CBC matrix. The material was characterized using various physicochemical techniques - X-ray diffraction spectroscopy, Raman spectroscopy, Thermal gravimetric analysis, and Surface area analyzer. The Mn2O3@CBC system developed in this work offers the following benefits: (a) interconnected carbon nanofiber assembly which helps in fast diffusion of Li-ion and electrons; (b) porous morphology to accommodate volume change and to act as a reservoir for long-chain lithium polysulfides accumulation; (c) Mn2O3 as long-chain lithium polysulfide binding site and catalyst for conversion of long-chain lithium polysulfides to short-chain lithium polysulfides.To investigate the electrochemical property of the material, the performance is compared to bare sulfur and sulfur incorporated carbonized bacterial cellulose (S-CBC). Various electrochemical characterization such as cyclic voltammograms, galvanostatic charge-discharge, rate capability, long-term cycling was performed to investigate the performance of the materials. The material (S-Mn2O3@CBC) exhibited initial reversible capacity of 1150 mA h g-1 at 0.1C and retained 254.4 mA h g-1 at the extremely high current rate of 15C which is far ahead than the bare sulfur and S-CBC. Furthermore, the cycle life of LSB with low and high-sulfur loading was performed to further establish the advantage of using Mn2O3 as electro catalyst. Moreover, first-principles calculation was carried out to understand the functional mechanism for interaction of Mn2O3@CBC and intermediate lithium polysulfides. The excellent electrochemical performance substantiates that the S-Mn2O3@CBC is a good choice for cathode for LSBs. Figure 1

In situ Construction of Robust Biphasic Surface Layers on Lithium Metal for Lithium-Sulfide Batteries with Long Cycle Life.

Lithium-sulfur (Li-S) batteries have potential in high energy density battery systems. However, intermediates of lithium polysulfides (LiPSs) can easily shuttle to the Li anode and react with Li metal to deplete the active materials and cause rapid failure of the battery. A facile solution pretreatment method for Li anodes involving a solution of metal fluorides/dimethylsulfoxide was developed to construct robust biphasic surface layers (BSLs) in situ. The BSLs consist of lithiophilic alloy (Lix M) and LiF phases on Li metal, which inhibit the shuttle effect and increase the cycle life of Li-S batteries. The BSLs allow Li+ transport and they inhibit dendrite growth and shield the Li anodes from corrosive reaction with LiPSs. Li-S batteries containing BSLs-Li anodes demonstrate excellent cycling over 1000 cycles at 1 C and simultaneously maintain a high coulombic efficiency of 98.2 %. Based on our experimental and theoretical results, we propose a strategy for inhibition of the shuttle effect that produces high stability Li-S batteries.

Revealing the working mechanism of a multi-functional block copolymer binder for lithium-sulfur batteries

The lithium-sulfur (Li-S) battery is one of the most promising substitutes for current energy storage systems because of its low cost, high theoretical capacity, and high energy density. However, the high solubility of intermediate products (i.e., lithium polysulfides) and the resultant shuttle effect lead to rapidly fading capacity and a low coulombic efficiency, which hinder the practical application of Li-S batteries. In this study, block copolymers are constructed with both an ethylene oxide unit and a styrene unit and then used as binders for Li-S batteries. Electrochemical performance improvements are attributed to the synergistic effects contributed by the different units of the block copolymer. The ethylene oxide unit traps polysulfide, which bonds strongly with the intermediate lithium polysulfide, and enhances the transport of lithium ions to reach high capacity. Meanwhile, the styrene unit maintains cathode integrity by improving the mechanical properties and elasticity of the constructed block copolymer to accommodate the large volume changes. By enabling multiple functions via different units in the polymer chain, high sulfur utilization is achieved, polysulfide diffusion is confined, and the shuttle effect is suppressed during the cycle life of Li-S batteries, as revealed by operando ultraviolet–visible spectroscopy and S K-edge X-ray absorption spectroscopy.

Effect of Swelling in Electrolyte Polymer Binder Positive Electrode on the Characteristics of Lithium-Sulfur Batteries

Lithium-sulfur (Li–S) batteries attract great attention of researchers due to their high theoretical energy density (2600 W∙h∙kg-1) and economic efficiency compared to state-of-art lithium-ion batteries [1]. The depth of the electrochemical reduction of sulfur and the cycle life of lithium-sulfur batteries are determined by the amount of electrolyte retained in the positive electrode [2]. In turn, the amount of electrolyte in the positive electrode is determined by its porosity and the ability of binders to swell in the electrolyte. Therefore, polymer binders used in the positive electrode can significantly affect the characteristics of lithium-sulfur batteries. The aim of the work was to study the effect of the swelling of polymer binders of the positive electrode in the electrolyte solution on the characteristics of lithium-sulfur batteries. The sulfur electrodes, with the composition of 70 wt.% Sulfur (99.5%, Russia), 10 wt.% multi-walled carbon nanotubes (Sigma Aldrich) and 20 wt% binder was the object of study. Polymeric binders were PEO (ММ 4∙106), PVDF-HFP (ММ 3∙105), LA-132. Lithium-sulfur cells were assembled as described in [3]. Electrolyte was1M LiCF3SO3 in sulfolane. Sulfolane is promising solvent for lithium–sulfur batteries. Electrolyte solutions based on sulfolane have high chemical and electrochemical stability [4], and moderate conductivity [5]. Sulfolane has a high flash point (166°C) [6]. Lithium trifluoromethanesulfonate was chosen as a support salt since electrolytes based on it have good scattering ability and provide lithium–sulfur cells with the smallest capacity depletion compared to electrolyte systems based on other salts [4]. Studies have shown that all investigated sulfur electrodes had good elasticity, mechanical strength and adhesion. Swelling of the electrode layer of sulfur electrodes was estimated by weight method at room temperature (23-25 °C) as follows. Pre-weighted sulfur electrodes were placed into the electrolyte solution for 48 hours. Then the sulfur electrodes were removed from the electrolyte, the excess of electrolyte was removed from the surface of the electrodes by a filter paper, and weighed. The mass of the electrolyte sorbed by the sulfur electrode was calculated as the difference in the masses of the sulfur electrodes after and before their storage into the electrolyte solution. It is established that the composition of the polymer binder has a significant effect on the swelling of the positive electrode in the electrolyte (Table). Sulfur electrodes containing PEO as a polymer binder can soak up to 2.8 µL/mAh(S). Sulfur electrodes containing PVDF-HFP and LA-132 can soak 1.5 and 1.1 µL/mAh(S), respectively. The discharge voltage profiles of lithium-sulfur cells with sulfur electrodes containing various polymeric binders differ significantly (Figure). The shape of the discharge voltage profile of lithium-sulfur cells, with the polymer binder PEO, is traditional: there are two voltage plateau: high voltage and low voltage. And in the case of polymer binders LA132 and PVDF-HFP, the discharge capacity corresponding to the end of the high-voltage stage is significantly lower than for cells with PEO binder, and the low-voltage plateau is almost indistinguishable. The difference in the swelling of sulfur electrodes containing various polymeric binders in the electrolyte solution explains the differences in the characteristics of the lithium-sulfur cells. This work was performed as part of a Government Order to Ufa Institute of Chemistry of the Russian Academy of Sciences by the Ministry of Science and Higher Education of the Russian Federation (Theme No. AAAA-A17-117011910031-7) Russia and was also financially supported by the Russian Science Foundation (project No 17-73-20115).

Simple but Highly-Efficient Polysulfide Trapping Strategy for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) battery, as an attractive alternative to the state-of-the-art Li-ion battery by the merits of high energy density and abundant material sources, is expected to meet the urgent demand of next-generation electric vehicles. However, several challenges severely hinder its application process, including low conductivity of elemental sulfur and lithium sulfide, large volume expansion upon discharge, and unfavorable redox shuttle due to the soluble polysulfides (PSs). In order to increase sulfur utilization and cycle stability of the Li-S batteries, a variety of strategies on modifying sulfur cathode have been attempted, e.g. development of sulfur-carbon composite, introduction of extra surface coating and novel electrode component, etc. It is worthy to note that many studies involving PS’ trapping material/structure always brought about significant improvement of cell performance. This is because that the active species loss and shuttle side effect were reduced. Recently our research group has reported the good chemical affinity of polyacrylamide (PAM) to PSs, coming from the strong binding of the amide group in the PAM with Li-S• species. Therefore, the polymer was successfully used in the surface coating on either sulfur cathode or porous separator [1, 2]. Poly(acrylic acid) (PAA), another water-soluble polymer, also can act as a favorable PS blocking layer because the COOH groups in the long chain can form strong hydrogen bonds with the PS anions [3]. This research demonstrates a simple but highly-efficient PS trapping strategy that employs PAA and PAM as a functional binder and additive for sulfur cathode, respectively. The synergistic action of these two distinctive agents contributes to higher reversible capacity and longer cycle life of Li-S batteries compared to conventional electrode. The mechanism of trapping PSs in the artificially-designed cathode framework was discussed, and the enhancement of hydrophilic nature of the cathode to the liquid electrolyte was also considered. It needs to be emphasized that the novel cathode can be easily fabricated on a large-scale without any additional procedures. Fig. 1 Comparison of cycle performance of PAM/PAA-contained cathode and conventional sulfur cathode Reference: [1] T. Li, Y. Yuan, B. Hong, et al, Electrochim. Acta, 2017, 244, 192-198 [2] H. Lu, J. Wang, T. Li, et al, J Solid State Electrochem., 2018, 22, 953-958 [3] S. Zhang, D. Tran, Z Zhang, J. Mater. Chem. A, 2014, 2, 18288-18292 Acknowledgment: This work was financially supported by National Natural Science Foundation of China (No.51704222, 51604221 and 51574191), Natural Science Basic Research Plan in Shaanxi Province of China (No.2016JQ5040), and Special Scientific Research Program of Education Department of Shaanxi in China (No.17JK0427). Figure 1

Towards online tracking of the shuttle effect in lithium sulfur batteries using differential thermal voltammetry

Abstract Lithium sulfur (Li-S) batteries are an important next generation high energy density battery technology. However, the phenomenon known as the polysulfide shuttle causes accelerated degradation, reduced Coulombic efficiency and increased heat generation, particularly towards the end of charge. The real-time detection of the onset of shuttle during charge would improve the safety and increase cycle life of Li-S batteries in real applications. In this study, we demonstrate that the Differential Thermal Voltammetry (DTV) technique can be used for tracking shuttle during Li-S charging. By combining voltage and temperature measurements, DTV is shown to be sensitive to the magnitude of shuttle. We demonstrate significant differences in the DTV curves for Li-S cells charged at different currents and temperatures. Quantitative interpretations of the experimental DTV curves are performed through a thermally-coupled zero-dimensional Li-S model. The DTV technique, together with the model, is a promising tool for real-time detection of shuttle in applications, to inform control algorithms for deciding the end of charging, thus preventing excessive degradation and charge inefficiency.

Communication—Trace Montmorillonite Electrolyte Additive Producing Stable Lithium-Sulfur Batteries

In this paper, montmorillonite is used as an electrolyte additive to enhance the discharge and cycling performance of lithium-sulfur (Li-S) batteries. It is demonstrated that montmorillonite participates in the formation of a protective layer on the surface of lithium anode, which can effectively suppress shuttle effect and overcharge, leading to great enhancement of the cycle life of Li-S batteries. Even at a high current density of 1600 mA g−1 after 300 cycles, a high reversible capacity of 351 mAh g−1, as well as high coulombic efficiency, can still be obtained.

SnO2/Reduced Graphene Oxide Interlayer Mitigating the Shuttle Effect of Li-S Batteries.

The short cycle life of lithium-sulfur batteries (LSBs) plagues its practical application. In this study, a uniform SnO2/reduced graphene oxide (denoted as SnO2/rGO) composite is successfully designed onto the commercial polypropylene separator for use of interlayer of LSBs to decrease the charge-transfer resistance and trap the soluble lithium polysulfides (LPSs). As a result, the assembled devices using the separator modified with the functional interlayer (SnO2/rGO) exhibit improved cycle performance; for instance, over 200 cycles at 1C, the discharge capacity of the cells reaches 734 mAh g-1. The cells also display high rate capability, with the average discharge capacity of 541.9 mAh g-1 at 5C. Additionally, the mechanism of anchoring behavior of the SnO2/rGO interlayer was systematically investigated using density functional theory calculations. The results demonstrate that the improved performance is related to the ability of SnO2/rGO to effectively absorb S8 cluster and LPS. The strong Li-O/Sn-S/O-S bonds and tight chemical adsorption between LPS and SnO2 mitigate the shuttle effect of LSBs. This study demonstrates that engineering the functional interlayer of metal oxide and carbon materials in LSBs may be an easy way to improve their rate capacity and cycling life.

In-situ synthesis of carbon@Ti4O7 non-woven fabric as a multi-functional interlayer for excellent lithium-sulfur battery

Lithium-sulfur (LiS) batteries are promising rechargeable batteries because of their low cost, environment-friendly and high energy density. Numerous bi-functional interlayers have been used for enhancing the cycle life of LiS batteries based on novel cell configuration. Most interlayers, however, are conductive carbon materials, which that have weak interactions with polysulfides, and this resulting in fast capacity losing over long-term cycling. Herein, for the first time, carbon@Ti4O7 composite nanofibers (C@Ti4O7 CNFs) have been successfully synthesized using in situ synthetic method. The C@Ti4O7 CNFs interlayer cells have excellent electrochemical performances due to the good restriction of diffused polysulfide, the uniform distribution of final discharge products (sulfides) and the improved conductivity of the whole cathode in charge/discharge process. An initial capacity of 1046 mAh g−1 at 2 C is achieved, with a fade rate of only 0.09% per cycle over 500 cycles, and it finally keeps a capacity of 560 mAh g−1. Even with a high rate of 4 C, the cells still exhibited a favorable specific capacity of 860 mAh g−1 after 25 cycles, and it returns back to a high specific capacity more than 1000 mAh g−1 when the rate is reduced to 0.5 C, and this showing indicated good reversibility.

Symmetric Lithium Sulfide – Sulfur Cells: A Method to Study Degradation Mechanisms of Cathode, Separator and Electrolyte Concepts for Lithium-Sulfur Batteries

Novel cathode, electrolyte and separator concepts are expected to improve the capacity retention and cycle life of lithium-sulfur batteries by avoiding the dissolution of polysulfide-intermediates into the electrolyte or preventing their diffusion to and reaction with the lithium metal anode. However, their intrinsic evaluation is obscured by ill-defined degradation mechanisms of the lithium counter electrode due to electrolyte and polysulfide consumption during reformation of the solid electrolyte interface. Herein, we introduce symmetric lithium sulfide – sulfur cells to study the “cathode" specific degradation mechanisms of the cathode/electrolyte/separator-system in order to differentiate cathode-, separator, and electrolyte and lithium metal anode degradation. Two identical carbon/sulfur-composite cathodes, either of them one at first lithiated versus lithium, are assembled in a coin cell versus each other. The virtue of this test cell design is demonstrated evaluating prime shuttle-suppression concepts, namely a Nafion-coated polyolefin separator and a sparingly polysulfide-solvating electrolyte. We conclude that symmetric lithium sulfide – sulfur cells provide a valuable methodology to analyze the intrinsic capacity decay and cycle life of cathodes for lithium-sulfur cells with limited solvation and/or blocking of polysulfides, and it is an essential strategy to distinguish cathode from lithium anode degradation.

Long term stability of Li-S batteries using high concentration lithium nitrate electrolytes

The lithium-sulfur (Li-S) battery is a very promising candidate for the next generation of energy storage systems required for electrical vehicles and grid energy storage applications due to its very high theoretical specific energy (2500Whkg−1). However, low Coulombic efficiency (CE) during repeated Li metal plating/stripping has severely limited the practical application of rechargeable Li-S batteries. In this work, a new electrolyte system based on a high concentration of LiNO3 in diglyme (G2) solvent is developed which enables an exceptionally high CE for Li metal plating/stripping and thus high stability of the Li anode in the sulfur-containing electrolyte. The tailoring of electrolyte properties for the Li anode has proven to be a highly successful strategy for improving the capacity retention and cycle life of Li-S batteries. This electrolyte provides a CE of greater than 99% for over 200 cycles of Li plating/stripping. In contrast, the Li anode cycles for less than 35 cycles (with a high CE) in the state-of-the-art 1M LiTFSI + 0.3M LiNO3 in 1,3-dioxolane:1,2-dimethoxyethane (DOL:DME) electrolyte under the same conditions. The stable Li anode enabled by the new electrolyte may accelerate the applications of high energy density Li-S batteries in both electrical vehicles and large-scale grid energy storage markets.

Effects of Sulfur Loading and Mesoporous Carbon Properties on the Electrochemical Performances of Li-S Batteries

Energy storage devices with high energy density and low cost are highly demanding since the existing state-of-the-art Li-ion battery systems have intrinsic limitations in energy and price. Thus, lithium-sulfur (Li-S) batteries have attracted a great attention because sulfur is abundant and it has high theoretical capacity (1672 mAh g-1) and energy density (2600 Wh kg-1) when coupled with metallic lithium anode [1]. However, it is still challenging to device Li-S batteries offering a long-term cycling stability at a high level of sulfur loading due to the dissolution of polysulfides (Li2Sx, 4<x<8) into the electrolyte and their shuttle effect causing poor capacity retention and low coulombic efficiency [2]. Recently, many important technological breakthroughs have been reported to suppress the polysulfides shuttle effects, which potentially leads to long cycle life of Li-S batteries [3]. Nonetheless, the loading level of sulfur has to be much increased for the Li-S batteries to go beyond current LIBs in energy density. In this aspect, a rational design of sulfur cathode is still regarded as one of the most important measures in mitigating the polysulfides shuttle problems. In this study, we employed mesoporous carbons (MCs) and N-doped mesoporous carbon (N-MC) as the sulfur host materials. The MCs were prepared by a sol-gel process in an acidic aqueous mixture of commercial colloidal silica (20nm in diameter) as the template and sucrose as the carbon source [4]. The ratio of colloidal silica/sucrose was varied to obtain MCs with different textual properties. The N-MC was prepared by aniline polymerization in MC dispersion with ammonium persulfate as the initiator followed by carbonization of resulting composite product. The sulfur loading level of S/MCs and S/N-MC was varied in the range of 35-80 wt%, which corresponds to the sulfur loading density of 0.6~4 mg/cm2. We also studied the effects of sulfur loading methods (melt-impregnation in a flow or a closed system) and the use of a conductive separator (CS) on the electrochemical performances of Li-S batteries. The CS was prepared by direct coating of a flake-type graphite on a polypropylene (PP) membrane (Cellgard 2400). The electrochemical tests were conducted using CR203 coin-type cells with Li foil as the counter electrode. The working electrode was prepared by casting a paste that consisted of the active material, conductive additive and PVdF binder with a mass ratio of 7:1:2 or 8:1:1 onto a Al foil current collector. 1.0 M LiTFSI in 1,2-dioxolane(DOL)/1,2-dimethoxyethane(DME) containing 0.1 or 0.4M LiNO3 was used as the electrolyte. The cells were cycled in a cut-off voltage range of 1.5-3.0V Li+/Li. The MC-1(SBET = 1213 m2/g, Vpore = 2.75 cm3/g) is highly porous with pore size distribution in the range of 10-30 nm as shown in the TEM image in Fig. 1a. As compared in Fig. 1b and 1c, flake-type graphite are evenly coated onto the surface of porous PP membrane. The reversible capacities of various Li-S batteries at 0.5C are compared in Fig. 1d as a function of sulfur content. In overall, the reversible capacity was decreased with sulfur content. However, the reversible capacity was improved with strategic approaches depicted in Fig. 1d; (1) S/MC-1 showed much higher capacity than S/MC-2 (SBET = 887 m2/g, Vpore = 1.55 cm3/g ), (2) S/N-MC-1 showed much enhanced capacity compared to S/MC-1 at high sulfur content, and (3) the use of CS exhibited further improvement in the reversible capacity. As shown in Fig. 1e, an electrode of S/MC-1 (S = 65.7wt%) assembled with CS exhibited an excellent cycling stability at 0.5C up to 300 cycles. [1] P. G. Bruce, S. A. Freunberger, L. J. Hardwick, J.-M. Tarascon, Nat. Mater., 11, 19–29 (2012). [2] Y. Diao, K. Xie, S. Xiong, X. Hong, J. Power Sources, 235, 181 –186. (2013). [3] A. Rosenman, E. Markevich, G. Salitra, D. Aurbach, A. Garsuch, and F. F. Chesneau, Adv. Energy Mater., DOI: 10.1002/aenm.201500212 (2015). [4] H. I. Lee, G. D. Stucky, J. H. Kim, C. Pak, H. Chang, and J. M. Kim, Adv. Mater., 23, 2357-2361 (2011). Fig.1. (a) TEM image of MC-1 (Inset shows pore size distribution of MCs), SEM images of (b) PP membrane and (c) conductive separator, (d) reversible capacities (after 50 cycles at 0.5C) of various samples as a function of sulfur content, and (e) cycling performance of S/MC-1 assembled with CS. Figure 1

Improved Lithium-Sulfur Cell with a Thin Barrier Membrane

The development of a high cycle life rechargeable lithium-sulfur battery is of substantial interest due to its high theoretical specific capacity of 1675 mAh/g and energy density of 2600 Wh/kg. These properties combined with the low cost and abundance of sulfur are attractive for practical and high performance lithium-sulfur batteries. However, the realization of these lithium-sulfur batteries have been limited by performance issues relating to their poor cycle life and low energy efficiency. The typical lithium-sulfur cell loses 20-50% of its initial capacity within 100 cycles due to a parasitic reaction known as the polysulfide shuttle. The polysulfide shuttle originates from the inherent solubility of the higher order polysulfides, S8 2-, S6 2-, and S4 2-, at the positive electrode. These polysulfides are capable of shuttling between the positive sulfur electrode and negative lithium electrode. When a polysulfide species contacts the negative electrode, it will be reduced to a lower order polysulfide species. If reduced to another soluble species such as S6 2- or S4 2-, it will shuttle back to the positive electrode where it must be reoxidized, resulting in charging inefficiency. If reduced to an insoluble species such as S2 2- or S2-, it will precipitate, resulting in irreversible capacity loss. Therefore, inhibiting the polysulfide shuttle is necessary to improving the energy efficiency and cycle life of lithium-sulfur batteries. We herein present a method of inhibiting the polysulfide shuttle through use of a thin barrier membrane. The thin barrier membrane is non-porous and capable of conducting lithium ions. The non-porosity of the membrane allows for physical exclusion of polysulfide species from the lithium electrode while the ionic conductivity allows for transport of lithium ions necessary for charge and discharge processes. In a cell configuration, the thin barrier membrane is sandwiched between two porous separators to maintain electronic isolation and inserted between the sulfur and lithium electrode. We have studied the effect of the thin barrier membrane in 2032-type coin cells consisting of sulfur-carbon composite positive electrodes, lithium foil negative electrodes, and 1 M LiTFSI electrolyte. The performance of the membrane was compared to cells of similar construction without the membrane and also to cells with 0.25 M lithium nitrate, the state-of-the-art polysulfide shuttle inhibiting additive. We have analyzed the performance of all cells using galvanostatic cycling, electrochemical impedance spectroscopy, and direct shuttle current measurements.1 We have found that the thin barrier membrane improves the energy efficiency and cycle life of lithium-sulfur cells by suppressing the polysulfide shuttle.

Enhancement of cycle performance of Li-S batteries by redistribution of sulfur.

A practically available strategy is employed to improve the cycle life of lithium-sulfur batteries. The simple process of activation cycling at the polysulfide dissolution region leads to the partial dissolution of polysulfides and the redistribution of sulfur on the electrode. After 50 cycles, the modified activation-cycled sulfur cathode exhibits a capacity that is roughly double that of a cathode without activation cycling.

Effect of Initial Sulfur Morphology on Capacity and Cycle-Life of Lithium-Sulfur Batteries

not Available.