Li/S

Introduction As the demand for energy is harshly increasing nowadays, great effort has been devoted to developing various advanced energy-storage technologies with high energy density, long-term cyclability, and inexpensive costs. The lithium-ion battery technology has been the mainstream option for the portable energy supply for the past decades. However, the commercial lithium-ion battery has limited cathode capacity and energy density of about 170 mAh g-1 and 600 Wh kg-1, as well as the high costs of $10,000 per ton. To further increase the cathode capacity and lower the fabrication costs, sulfur, with a high theoretical capacity of 1,675 mAh g-1, a high theoretical energy density of 2,600 Wh kg-1 in lithium-sulfur batteries, and a cheap price of $150 per ton, has been chosen to become new cathode materials. Thus, lithium–sulfur battery, as an alternative branch of lithium-ion batteries, is a potential technology to solve the problems in portable energy supply.In lithium–sulfur system, multiple redox reactions occur during different steps of charge and discharge reactions. In the discharge process, the solid-state sulfur (S8) will be reduced to form liquid-state lithium polysulfides (Li2Sx, 4 ≤ x ≤ 8) and solid-state lithium sulfides (Li2S2/Li2S). The lithium sulfides will be charged back to solid-state sulfur. These reactions in charge and discharge processes repeat during cycling. Three key factors, the sulfur loading, the sulfur content, and the electrolyte-to-sulfur ratio, have been thoroughly researched for developing high-performance lithium–sulfur batteries in the past two decades. To commercialize the lithium–sulfur battery technology, limits on these three factors have been set, which are a sulfur loading of 5 mg cm-2 and above, a sulfur content of 65 wt% and above, and an electrolyte-to-sulfur ratio of 10 μL mg-1 and below. However, due to the complex reaction steps in lithium–sulfur system, these three factors are conflicted or cannot be achieved simultaneously in most of the research cases. Results and Discussion Here, in our presentation, we report a high-loading polysulfide cathode, achieving both high sulfur content and low electrolyte-to-sulfur ratio at the same time. A non-nanoporous carbon nanotube/nanofiber (CNT/CNF) is adopted as the electrode substrate to accommodate the active material, liquid polysulfide catholyte, forming a polysulfide cathode with a high sulfur loading of 8.64 mg cm-2, a high sulfur content of 68 wt%, and low electrolyte-to-sulfur ratios of 4–7 μL mg-1. With such a cathode design, the lithium-sulfur cell attain high discharge capacities of 630–870 mAh g-1 and 580–631 mAh g-1 at C/10 and C/5 cycling rates, which corresponds to the high energy densities of 10.5–11.5 and 11.4–15.7 mWh cm-2. In addition to the high electrochemical utilization, our lean-electrolyte lithium-sulfur cells demonstrate a long-term cyclability of 200 cycles.As a result, we further investigate the possible failure mechanism for a high-loading polysulfide cathode operating in a lean-electrolyte cell under a semi-dry electrolyte condition. The extended cycling test is performed to explore the discharge and charge efficiency as well as the lithiation and delithiation mechanisms. Two cycling rates, C/10 and C/5, are applied for comparison. It reveals that due to the semi-dry electrolyte condition, the decomposition of the polysulfide catholyte occurs during extended cycles. The overcharge issue is thus occurred as a result of the rapid consumption of electrolyte, and leads to slow ion diffusion, decreased Coulombic efficiency, and irreversible capacity loss. Additionally, the decayed cycling performances are more easily observed at the slow C/10 cycling rate than at the fast C/5 cycling rate. Conclusion In summary, according to the excellent cycling performances of our cell design with a high-loading cathode, high sulfur content, and lean electrolyte addition, we might be very close to overcome the three limiting factors for commercialization of lithium–sulfur battery technology. Moreover, the failure analysis of our lean-electrolyte lithium-sulfur cell demonstrates the main challenges in developing a lean-electrolyte lithium–sulfur cell. The attainment of a high and stable Coulombic efficiency as well as the fast electrolyte consumption during regular cycling rate would challenge the development of lean-electrolyte lithium-sulfur cell with more practical cell design parameters.

<p indent="0mm">With the rapid development of electronic transportation and portable electronics, commercial lithium-ion batteries would be unsatisfactory to meet the needs of future markets owing to the relatively low energy density. Seeking a reliable substitution system is becoming imperative. Lithium-sulfur (Li-S) battery has been recognized as a cutting-edge energy storage system because of its high theoretical capacity (1672 mAh g^–1) and cost-effectiveness of sulfur resources. Nevertheless, the severe shuttle effect and sluggish reaction kinetics significantly restrict its further commercialization. In the developing history of Li-S batteries, physical confinement and chemical adsorption have often been employed to achieve the anchoring of polysulfides. However, these strategies are still difficult to fully solve the problems of slow reaction kinetics and poor cycle performance. Recent years have witnessed the introduction of heterogeneous electrocatalysts into the Li-S system, which readily meets with great success in suppressing the shuttle effect and elevating the reaction kinetics. In this review, we introduce the basic reaction of Li-S battery and point out the main challenges in its current development stage, followed by summarizing the effects of electrocatalysts. Firstly, the polar electrocatalyst is able to effectively adsorb polysulfide and inhibit its diffusion in the electrolyte. Secondly, the electrocatalyst can effectively promote the conversion of polysulfide and improve the utilization rate of sulfur species. Thirdly, the uniform distribution of active sites in the electrocatalyst also contributes to the uniform deposition of short-chain polysulfides. In addition, the concepts and comparisons of homogeneous and heterogeneous electrocatalysts are presented, manifesting the essential significance of heterogeneous electrocatalysts in Li-S system. Homogeneous electrocatalysts usually refer to small soluble organic molecules with the same phase state as soluble polysulfides in the reaction system. Homogeneous electrocatalysts have more specific catalytic sites, whilst heterogeneous electrocatalysts have more diverse morphologies and higher possibility of multi-site synergistic catalysis. Then the common regulation strategies for heterogeneous electrocatalysts are classified, including vacancy regulation, doping regulation, heterostructure modulation, size control, and phase modulation. In further contexts, the underlying mechanisms of different regulation strategies for promoting polysulfide conversion are discussed. The introduction of heterogeneous electrocatalysts can effectively promote the reaction kinetics and improve their electrochemical performance. However, there are still many obstacles waiting to be solved in the practicability of Li-S batteries. For instance, there is a lack of highly selective and stable electrocatalysts. The identification of real catalytic sites in the electrocatalysts still remains unclear. Moreover, Li-S batteries have poor performance under lean electrolyte and low lithium consumption. In view of these issues, future development strategy is put forward from four aspects, encompassing material exploration, precise synthesis, characterization methods and practical application, aiming to bridge the gap between the reality and ideal in working Li-S batteries.

Engineering rare earth metal Ce-N coordination as catalyst for high redox kinetics in lithium-sulfur batteries

Quasi-solid-state sulfur cathode with ultralean electrolyte via in situ polymerization

Lithium-sulfur batteries are among the most promising low-cost, high-energy-density storage devices. However, the inability to host a sufficient amount of sulfur in the cathode while maintaining good electrochemical stability under a lean electrolyte condition has limited the progress. The main cause of these challenges is the sensitivity of the sulfur cathode to the cell-design parameters (i.e., the amount of sulfur and electrolyte) and the experimental testing conditions (i.e., cycling rates and analysis duration). Here, a hot-pressing method is presented that effectively encapsulates a high amount of sulfur in the cathode within only 5 s, resulting in high sulfur loading and content of, respectively, 10 mg cm-2 and 65 wt%. The hot-pressed sulfur (HPS) cathodes exhibit superior dynamic and static electrochemical performance under a broad cycling-rate (C/20-1C rates) and low electrolyte/sulfur ratio (6 µL mg-1 ) conditions. The dynamic cell stability is demonstrated by high gravimetric and areal capacities of, respectively, 415-730 mAh g-1 and 7-12 mAh cm-2 at C/20-1C rates with a high capacity retention of over 70% after 200 cycles. The static cell stability is demonstrated by excellent shelf life with low self-discharge and stable cycle life on storing for over one year.

Lithium sulfur (Li-S) battery is a promising alternative technology of lithium ion batteries. However, due to the complicity of the chemistry in Li-S batteries, the mechanism is not well understood. In addition, the co-existence of soluble species and insoluble species limits the application of other characterization techniques. The sensitivity and element selectivity make NMR spectroscopy a powerful tool to study the changes in local chemical environment and speciation process in Li-S batteries. In this study, in situ 7Li NMR spectroscopy was employed where plastic pouch cells were assembled and cycled in the magnet while NMR spectra were acquired simultaneously. Method to quantitatively study entire lithium inventory in a Li-S battery is developed and implemented, and the cell design is optimized for electrochemical performance and spectroscopic resolution. This methodology can be readily extended to Li-S batteries with other electrolytes where the speciation process can be tracked and analyzed. The development of electrolyte will also benefit greatly from the detailed understanding of the Li-S battery speciation process as well as the additive development. [1] See, et. al., J. Am. Chem. Soc., 2014, 136 (46), pp 16368–16377 [2] Xiao, et. al., Nano Lett., 2015, 15, 3309-3316

Lithium-sulfur (Li-S) batteries face critical challenges including sluggish polysulfide redox kinetics and the shuttle effect. This study presents a novel self-supporting carbon nanofibers decorated with Ti_xCr_1-xN solid-solution nanoparticles (CNFs@TCN) as Li₂S₆ host for lithium-sulfur (Li-S) batteries. By leveraging electrospinning and high-temperature nitridation reaction, we engineered a flexible electrode with tunable Ti/Cr ratios. Density functional theory (DFT) calculations and experimental analysis reveal that the TCN solid-solution phase optimizes electronic structure via Cr substitution, enhancing polysulfide adsorption and catalytic conversion kinetics. The CNFs@TCN-1/2 cathode (Ti:Cr&nbsp;= 1:2) exhibits exceptional performance of high initial capacity (1359 mAh g^-1), ultralow capacity decay (0.012% per cycle at 2 C), and remarkable rate capability (803 mAh g^-1 at 3 C). Under high sulfur loading (6.12 mg cm^-2) and lean electrolyte (E/S ratio=9.3 μL mg^-1), it delivers an areal capacity of 4.87 mAh cm^-2. This work demonstrates atomic-level d-band engineering of bimetallic nitrides as a powerful strategy to suppress shuttle effects and boost sulfur redox kinetics in practical Li-S batteries.

An effective strategy to tackle the twin crises of global deforestation and fossil fuel depletion is to recycle bio-mass materials for energy storage devices. Batteries have been proven to be the most effective electrochemical energy conversion and storage devices. As the most widely used battery system, lithium-ion (Li-ion) batteries have served our daily life and changed the world extensively in the past two decades. However, the potential of Li-ion battery system is approaching its limit and unable to fulfill diverse requirements. Among all possible candidates, lithium sulfur (Li-S) battery chemistry is considered to be one of the most promising next-generation, high energy density battery chemistries. The theoretical gravimetric capacity of this reaction is 1675 mAh g-1, and with the expected average voltage during discharge, the maximum energy density can be 2600 mWh g-1. However, how to build high-capacity and long-life span Li-S batteries via accessible and scalable methods is still questionable. Here we report a unique and innovative solution to capitalize on a currently overlooked resource to produce high-performance lithium-sulfur (Li-S) batteries from recycled paper. Common paper hardboard was peeled into long stripes and integrated with graphene oxide (GO) sheets by a capillary absorption method. The paper/GO hybrid was then activated at high temperature, forming activated paper carbon (APC)/graphene scaffold. The capillary absorbed GO sheets were homogeneously coated on the APC fibers and shrined geometrically during heating, forming nano sized bulges and pores, which remarkably improved sulfur loading and cathode conductivity. The recycled paper derived graphene Li-S battery exhibited superior life span of 620 cycles with an excellent capacity retention rate of 60.5%. More importantly, the APC/graphene/S stayed integral without pulverization even after such long cycling, indicating excellent mechanical robustness of cathode material. Since the malfunction of the battery can be ascribed to the anode, an activated paper carbon (APC) interlayer was sandwiched between the Li anode and the separator to suppress the degradation of Li anode by protecting the Li from unfavorable reactions, stretching the battery lifespan up to 980 cycles with a capacitance retention rate of 52.3% and improved rate ability. The capillary adsorption method and the porous anode interlayer configuration should find more applications in other porous bio-mass materials for energy storage devices. Figure 1

High Coulombic efficiency cathode with nitryl grafted sulfur for Li-S battery

For solving the drawbacks of low conductivity and the shuttle effect in a sulfur cathode, various nonpolar carbon and polar metal compounds with strong chemical absorption ability are applied as sulfur host materials for lithium-sulfur (Li-S) batteries. Nevertheless, previous research simply attributed the performance improvement of sulfur cathodes to the chemical adsorption ability of polar metal compounds toward lithium polysulfides (LPS), while a deep understanding of the enhanced electrochemical performance in these various sulfur hosts, especially at the molecular levels, is still unclear. Herein, for a mechanistic understanding of superior metal phosphide host in Li-S battery chemistry, an integrated phosphide-based host of CF/FeP@C (carbon cloth with grown FeP@C nanotube arrays) is chosen as the model, and this binder-free cathode can exclude interference from the binder and conductive additives. With a systematic electrochemical investigation of the loading sulfur in such oxide- and phosphide-based hosts (CF/Fe3O4@C and CF/FeP@C), it is found that CF/FeP@C@S shows much superior Li-S performances. The greatly enhanced performance of CF/FeP@C@S suggests that FeP can well suppress the shuttle effect of LPS and accelerate their transformation during the charge-discharge process. The first-principles calculations reveal the performance variations of Fe3O4 and FeP in Li-S batteries mainly because the shifts of the p band of the FeP could accelerate the interfacial electronics transfer dynamics by increasing the electronic concentration in the Fermi level of adsorbed Li2S4. The current work sheds light on the promising design of superior Li-S batteries from both theoretical and experimental aspects.

Lithium-sulfur (Li-S) batteries are considered as one of the most potential next-generation rechargeable batteries due to their high theoretical energy density. However, some critical issues, such as low capacity, poor cycling stability, and safety concerns, must be solved before Li-S batteries can be used practically. During the past decade, tremendous efforts have been devoted to the design and synthesis of electrode materials. Benefiting from their tunable structural parameters, hollow porous carbon materials (HPCM) remarkably enhance the performances of both sulfur cathodes and lithium anodes, promoting the development of high-performance Li-S batteries. Here, together with the templated synthesis of HPCM, recent progresses of Li-S batteries based on HPCM are reviewed. Several important issues in Li-S batteries, including sulfur loading, polysulfide entrapping, and Li metal protection, are discussed, followed by a summary on recent research on HPCM-based sulfur cathodes, modified separators, and lithium anodes. After the discussion on emerging technical obstacles toward high-energy Li-S batteries, prospects for the future directions of HPCM research in the field of Li-S batteries are also proposed.

Lithium-sulfur (Li-S) batteries have been intensively investigated as a next-generation rechargeable battery due to their high energy density of 2600 W·h kg(-1) and low cost. However, the systemic issues of Li-S batteries, such as the polysulfide shuttling effect and low Coulombic efficiency, hinder the practical use in commercial rechargeable batteries. The introduction of a conductive interlayer between the sulfur cathode and separator is a promising approach that has shown the dramatic improvements in Li-S batteries. The previous interlayer work mainly focused on the physical confinement of polysulfides within the cathode part, without considering the further entrapment of the dissolved polysulfides. Here, we designed an ultrathin poly(acrylic acid) coated single-walled carbon nanotube (PAA-SWNT) film as a synergic functional interlayer to address the issues mentioned above. The designed interlayer not only lowers the charge transfer resistance by the support of the upper current collector but also localizes the dissolved polysulfides within the cathode part by the aid of a physical blocking and chemical bonding. With the synergic combination of PAA and SWNT, the sulfur cathode with a PAA-SWNT interlayer maintained higher capacity retention over 200 cycles and achieved better rate retention than the sulfur cathode with a SWNT interlayer. The proposed approach of combining a functional polymer and conductive support material can provide an optimiztic strategy to overcome the fundamental challenges underlying in Li-S batteries.

Sulfur electrode tolerance and polysulfide conversion promoted by the supramolecular binder with rare-earth catalysis in lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are promising candidates for energy storage systems that can achieve high energy density.1 However, reducing the electrolyte volume in Li-S full batteries is generally unsatisfactory due to limited electrochemical reaction of Li-S. Also, the challenges of shuttle effect and sluggish sulfur conversion reaction impede towards practical application.2 Herein, I propose a practical-level lithium-sulfur battery system by introducing a method to promote the lithium-sulfur conversion reaction and suppressed polysulfide dissolution.A noteworthy designed with NiCo / NiCoO2 nanoparticles anchored in CNTs-embedded self-standing carbon structure is manufactured as host for sulfur. Through experimental techniques and first-principle calculation, the functions of NiCo/NiCoO2 nanoparticles in carbon structure are performed as follow; (ⅰ) NiCo/NiCoO2 affords polysulfide scavenging and chemisorption ability, suppressing the shuttle effect. (ⅱ) NiCo/NiCoO2 is an efficient polysulfide mediator by giving a electrocatalytic site for the Li-S redox reaction, promoting conversion kinetics and reversibility. (ⅲ) The high conductivity of host structure and sufficient porosity in carbon structure exhibit considerable improvement in the transfer of lithium ions and electrons in Li-S batteries. Even with high sulfur loading, the nanostructured NiCo/NiCoO2 enable to have stable cycling performance with lean electrolyte using a graphite anode in full-cell batteries, showing potential as a practical battery. A. Manthiram, Y. Fu, S.-H Chung, C Zu, Y.-S Su. Rechargeable Lithium–Sulfur Batteries. Chem Rev. 23 (2014)11751-11787.D. Bresser, S. Passerini, B. Scrosati. Recent progress and remaining challenges in sulfur-based lithium secondary batteries – a review. Chem Commun. 49 (2013)10545-10562.

The limitations encountered by insertion-compound cathodes for offering lithium batteries with an enhanced energy density at an affordable cost allow the conversion-reaction cathodes to garner significant attention. With no restrictions in maintaining their initial structure during discharge and charge, a high-capacity sulfur cathode in the lithium-sulfur battery enables a complete two-electron conversion reaction per atom and therefore provides an order of magnitude higher theoretical capacity (1,672 mA h g-1) than the currently used insertion-compound cathodes. Additionally, sulfur is inexpensive and environmentally benign. However, as a promising post lithium-ion battery technology, lithium-sulfur battery cathodes suffer from the insulating nature of sulfur and the irreversible migration of polysulfides within the cells. These challenges restrict the development of a lithium-sulfur battery cathode featuring high electrochemical efficiency and stability with a sufficient sulfur loading and content of above 4.0 mg cm-2 and 65 wt.%, respectively, in a cell with a reasonable low electrolyte-to-sulfur ratio of less than 10.0 uL mg-1.Here, we present innovations on electrode design enabling lithium-sulfur batteries to operate excellently with a high amount of sulfur (i.e., 14.4 mg cm-2 and 70 wt.%) and a low electrolyte-to-sulfur ratio of 4.0 uL mg-1. The cathode substrate is prepared by carbonized electrospinning nanofibers having 20 wt.%, 40 wt.%, and 100wt.% polyacrylonitrile mixing with Nafion as the sacrificial polymer. With a high content of the sacrificial Nafion, the carbonized nanofibers (e.g., 020CNF resulted from 20 wt.% polyacrylonitrile and 80 wt.% sacrificial polymer) generate a higher specific surface area of up to 640 m2 g-1 with 150 m2 g-1 contributed from micropores. Although a high surface area and micropores of the electrode substrate benefit the polysulfide retention, our experimental and analytical results prove that the majority of the electrolyte added in the cell is initially absorbed by this highly porous cathode substrate. This explains why a high amount of electrolyte is needed in the lithium-sulfur research, which causes a low energy density. This also expounds why our high-loading cathodes with a low amount of electrolyte either dry out in a short cycle life nor cannot get sufficient charges transferred via the electrolyte, resulting in a poor cell performance. On the other hand, the carbonized electrospinning nanofiber with no sacrificial polymer (i.e., 100CNF) possesses a relatively low specific surface area of 130 m2 g-1 and no micropores. Benefiting from a unique electrode-design criterion, the limited surface area ameliorates the fast consumption of electrolyte, while still blocking the fast polysulfide diffusion.As a result of the electrode design, the cells with the 100CNF substrate output a stable discharge capacity and Coulombic efficiency of above 650 mA h g-1 and 98%, respectively, for 100 cycles. Such excellent electrochemical efficiency and stability demonstrate a high capacity retention of 98% with a high areal capacity and energy density of 10 mA h cm-2 and 20 mW h cm-2, respectively, in a cell with a low electrolyte-to-sulfur ratio of only 4 uL mg-1. In conclusion, the electrochemical enhancements and engineering designs of the cathode substrates with limited nanopores make them advanced cathode designs for the development of high-loading/content sulfur cathodes in high-energy-density lithium-sulfur batteries.