A Design of Lean-Electrolyte Lithium-Sulfur Cells

Developing lithium-sulfur cells with a high-loading cathode at a lean-electrolyte condition is the key to bringing the lithium-sulfur technology into the energy-storage market. However, it has proven to be extremely challenging to develop a cell that simultaneously satisfies the abovementioned metrics while also displaying high electrochemical efficiency and stability. Here, we present a concept of constructing a conductive cathode substrate with a low surface area and optimized nanoporosity (i.e., limited micropores in the porous matrix) that enables achieving a high sulfur loading of 13 mg cm-2 and a high sulfur content of 75 wt % with an extremely low electrolyte/sulfur ratio of just 4.0 μL mg-1. The high-loading nanocomposite cathodes demonstrate high-areal capacities of 9.3 mA h cm-2, high energy densities of 18.6 mW h cm-2, and superior cyclability with excellent capacity retention of 85% after 200 cycles. These values are higher than the benchmarks set up for developing future commercial lithium-sulfur cells (i.e., areal capacity of >2-4 mA h cm-2, energy density of >8-13 mW h cm-2, and a long cycle life of 200 cycles with a capacity retention of 80%). The cathode design further exhibits high-rate capability from C/20 to 1 C rates and great potential to attain ultrahigh sulfur loading and a content of 17 mg cm-2 and 80 wt %. The key nanostructural feature that enables realizing fast-charge transport is the low surface area and limited microporosity that avoid the fast consumption of the electrolyte during cell cycling.

The lithium–sulfur battery is a promising next‐generation rechargeable battery system which promises to be less expensive and potentially fivefold more energy dense than current Li‐ion technologies. This can only be achieved by improving the sulfur utilization in thick, high areal loading cathodes while minimizing capacity fading to realize high practical energy densities and long cycle‐life. This study reports a simple method to fabricate a high capacity, high loading cathode with one of the highest cycle‐stabilities reported. It is demonstrated that sulfur sols formed by crashing dissolved elemental sulfur into water are trapped between graphene oxide sheets when flocculated with polyethyleneimine. Low temperature, hydrothermal treatment produces a conductive, partially covalent composite exhibiting outstanding cycle‐stability. Using this method, sulfur can be uniformly distributed at fractions as high as 75.7 wt%. Electrodes with high areal sulfur loadings (up to ≈5.4 mg cm−2), prepared using these composites, lead to projected high cell level practical energy densities of 400 Wh kg−1. The electrodes demonstrate negligible capacity loss over 250 cycles at 0.15 C and only 0.028% capacity loss per cycle over 810 cycles at 0.75 C. Eventual capacity fading is found to be linked to degradation of lithium‐metal anode suggesting that the cathode material remains stable over even more extended cycling.

Lithium Sulfur (Li-S) battery is generally considered as a promising technology where high energy density is required at different applications. Over the past decade, there has been an ever increasing volume of Li-S academic research spanning materials development, fundamental understanding and modelling, and application-based control algorithm development. In this study, the Li-S battery technology, its advantages and limitations from the fundamental perspective are firstly discussed. In the second part of this study, state-of-the-art Li-S cell modelling and state estimation techniques are reviewed with a focus on practical applications. The existing studies on Li-S cell equivalent-circuit-network modelling and state estimation techniques are then discussed. A number of challenges in control of Li-S battery are also explained such as the flat open-circuit-voltage curve and high sensitivity of Li-S cell’s behavior to temperature variation. In the last part of this study, current and future applications of Li-S battery are mentioned.

Advanced energy-storage technologies are urgently needed to satisfy the energy demands of the society. Sulfur is an appealing candidate for high energy-density batteries, owing to its high theoretical capacity (1,675 mA h g-1), natural abundance, and low cost.1-3 However, the rapid capacity degradation, low Coulombic efficiency, and short cycle life originating from polysulfide dissolution and migration remain challenging for the practical application of lithium-sulfur (Li-S) batteries.4, 5 Our previous reports have demonstrated that configuring interlayers between the separator and the sulfur cathode is an effective and convenient strategy to alleviate the shuttle effect.6 However, most of those interlayers are fabricated by vacuum-filtration method, which makes those polar materials easily stack together and thus form a very thick interlayer. Therefore, on the one hand, the transport of lithium ions will be limited by the thick polar interlayers, which is not desirable for fast insertion/de-insertion of Li ions and high rate capacity. On the other hand, the stacked thick interlayers, as an inactive material, will decrease the overall cell energy density. To address such issues, we present here a novel Co9S8 nanowall array with vertical hollow naoarchitecture as an efficient barrier for lithium polysulfides (LiPS) in Li-S batteries.7 We present well-aligned, hollow Co9S8 arrays in-situ grown on a Celgard (Co9S8-Celgard) separator as an efficient polysulfide barrier for high-performance Li-S cells without any significant increase in the weight and volume (Fig. 1a). This novel concept/strategy of designing a multifunctional separator via in-situ grown polar and conductive materials (Co9S8 hollow arrays) on a commercial separator dramatically suppresses the shuttle effect of LiPSs and significantly improves the electrochemical performance of Li-S cells. Due to its well-designed structure, in-situ growth/transformation, and the polarity and high conductivity of Co9S8, the Li-S cell with the Co9S8-Celgard separator not only effectively blocks the LiPSs even with pure sulfur cathodes with a high sulfur loading (5.6 mg cm-2), but also delivers excellent specific capacity, outstanding rate capability, and remarkable cycling stability for an impressive number of 1,000 cycles (Fig. 1b - d). In essence, the novel design and in-situ growth of MOF-derived multifunctional Co9S8 layers are crucial to suppress the severe polysulfide diffusion and alleviate the shuttle effect of LiPSs. We believe that this approach would promote greatly the development of modified separators, particularly the design and synthesis of multifunctional separators. Fig. 1 (a) Schematic illustration of the synthesis process of Co9S8-Celgard. (b) Rate performances at various cycling rates with the Celgard, MOF-Celgard, and Co9S8-Celgard separators. (c) Cycling performances of Li-S cells with high sulfur-loading cathodes with Co9S8-Celgard separators. (d) Long-term cycling performances of the Li-S cells with the Co9S8-Celgard separators at 1C rate for 1,000 cycles. REFERENCES 1 J. He, Y. Chen, W. Lv, K. Wen, C. Xu, W. Zhang, Y. Li, W. Qin, W. He, ACS Nano 2016, 10, 10981. 2 J. He, L. Luo, Y. Chen, A. Manthiram, Adv. Mater. 2017, 29, 1702707. 3 F. Wu, J. T. Lee, N. Nitta, H. Kim, O. Borodin, G. Yushin, Adv. Mater. 2015, 27, 101. 4 G. Zhou, S. Pei, L. Li, D. Wang, S. Wang, K. Huang, L. Yin, F. Li, H. Cheng, Adv. Mater. 2014, 26, 625. 5 J. He, Y. Chen, P. Li, F. Fu, Z. Wang, W. Zhang, J. Mater. Chem. A 2015, 3, 18605. 6 Y. Su, A. Manthiram, Nat. Commun. 2012, 3, 1166. 7 J. He, Y. Chen, A. Manthiram, Energ. Environ. Sci. 2018, 11, 2560. Figure 1

Lithium–sulfur batteries are among the most promising energy‐storage devices because of their high charge‐storage capacity, low cost, and the wide availability of sulfur. Thus, it is essential to develop the potential of lithium–sulfur cells as a next‐generation rechargeable energy‐storage technology and transition them into practical battery systems. However, the design of high‐energy‐density lithium–sulfur batteries with long‐term stability has encountered significant challenges due to the intrinsic materials characteristics (e.g. insulating nature of sulfur, irreversible polysulfide relocation, volume change of sulfur, lithium anode degradation, low electrolyte stability, and electrode degradation). Over the past 20 years, efforts to improve the battery performance and chemistry have resulted in new scientific insights, indicating that the electrochemical performance of lithium–sulfur system and its intrinsic materials challenges are further aggravated by several extrinsic technical conditions, including the cell‐fabrication parameters (e.g. the amount of sulfur, electrolyte, and lithium metal used) and the cell‐testing conditions (e.g. operating voltage window, testing temperature, and cycle rates). In order to successfully bring the lithium–sulfur battery technology to the market, we need to focus on developing high‐loading sulfur cathodes under lean electrolyte and controlled excess lithium conditions. However, it has proven extremely challenging to develop a cell that simultaneously satisfies these metrics while also displaying acceptable high electrochemical efficiency and stability. To understand these issues, the fundamental conversion battery chemistry and issues associated with lithium–sulfur system, particularly in terms of the intrinsic materials characteristics and extrinsic technical conditions are discussed in this article.

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

Lithium-sulfur batteries remain a promising next-generation renewable energy storage device due to their high theoretical energy density over the current commercial lithium-ion battery technology. However, to have any practical viability toward reaching the theoretical value, high-loading cathodes with sufficient sulfur content and specifically the effect of nonconductive binders must be investigated. We consider the limitations of conventional binders for high-loading, high-thickness cathodes by integrating a bifunctional binder with a linear polyethylene chain and maleate-capped ends. The linear polymer allows for flexibility within the high-loading cathode whereas the maleate ends improve the polysulfide trapping ability with carbon-sulfur binding. With the strong polysulfide immobilization ability due to the nucleophilic binding, the binder achieves high sulfur loadings of 12 mg cm-2 with a high sulfur content of 80 wt %. The work serves as a proof of concept for exploring the incorporation of polymeric materials into sulfur cathodes to realize practical viability.

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.

<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.

Lithium-sulfur (Li-S) batteries are promising energy-storage systems, offering up to five-fold increase in energy density as compared with present state-of-the-art Li-ion batteries thus potentially serving as a means to meet the growing demand for safe, environmentally friendly, high-energy density applications. For commercial batteries, cathodes with a high sulfur (active material) loading (> 2 mg/cm2) will be essential. Most reports on engineered cathode materials for Li-S batteries, however, are based upon low sulfur loadings (typically ~1 mg/cm2), which are impractical and often give misleading results about performance characteristics. It is unknown how such cathodes behave under high sulfur loading conditions. The binder is perhaps the most critical material for achieving a high sulfur loading. We have recently used polyamidoamine (PAMAM) dendrimers with differing surface chemistries as functional binders in Li-S cells with SuperP/S as the cathode material. Without any special efforts to engineer the cathode, we were able to obtain very favorable cycling stability and electrolyte wetting. This was attributed to the high density of the surface functional groups on the dendrimers which results in a larger number of possible binder-S/carbon interactions, and high curvature of the binder and high porosity which allows the sulfur particles to be more extensively exposed to the electrolyte (thus enhancing wetting). In addition, the binding between the large number of oxygen atoms on the dendrimers and the polysulfides, along with the greater number of interior pores, aids in preventing the dissolution of the polysulfides in the organic electrolyte. Dendritic macromolecules are also much more polar than linear conventional polymer-based binder chains and have a uniform distribution of surface groups. This ensures better interfacial interactions between the functional groups and carbon/S particles, as well as better adhesion to the substrate. Alongwith the cathode, the electrolyte is another critical component of Li-S batteries as it regulates the polysulfide shuttle phenomena thus determining the rate capability, cycling stabilities and energy densities of the batteries. The safety of the battery is also governed to a large extent by the electrolyte. Here, we will discuss the fundamental characteristics of dendrimers as aqueous binders for sulfur cathodes and compare their performance with other aqueous, commonly used linear polymeric binders such as styrene butadiene rubber (SBR) and sodium carboxyl methyl cellulose (CMC). Specifically, generation 4 PAMAM dendrimers with hydroxyl, 4-carbomethoxypyrrolidone, and sodium carboxylate surface functional groups served as promising, electrochemically stable binders for high sulfur loadings (~3-4 mg/cm2) with high initial cathode capacities (> 1000 mAh/g). In comparison to the use of a CMC-SBR binder, the electrodes with the dendrimer-based binders showed greatly improved performance. The CMC-SBR binder-based electrodes failed at high C-rates (0.2C) after 40 cycles, whereas the electrodes with the dendrimer-based binders had a capacity retention of >85% for more than 100 cycles. A detailed physicochemical characterization of the electrodes will be presented to substantiate the superior dendrimer-carbon/S interactions. We will also discuss our recently developed lithium aluminum germanium phosphate (LAGP) based solid-polymer-liquid hybrid electrolyte-separator system in conjunction with the above promising cathode materials for Li-S batteries. The hybrid separator showed (i) higher liquid electrolyte uptake, (ii) higher room T ionic conductivity, (iii) lower interfacial resistance with lithium, and (iv) lower cell voltage polarization during lithium cycling at high current density of 1.3 mA/cm2 at room temperature. The enhanced performance is attributed to higher liquid uptake, LAGP-assisted faster ion conduction and dendrite prevention. It is anticipated that by using novel dendrimer chemistries for electrode assembly, and hybrid electrolyte systems, this research will lead to the development and commercialization of high energy density, safe and long-cycle life Li-S batteries. Figure 1

While lithium-ion (Li-ion) batteries offer tremendous performance advantages over their battery predecessors (e.g., nickel-cadmium, lead-acid), they are approaching an asymptotic limit in specific energy (~250 Wh/kg at cell level) and do not adequately address next generation space platform requirements (e.g., by NASA [1]). As a result, there has been intense research and development (R&D) on higher specific energy batteries that have been coined beyond Li-ion. Rechargeable lithium-sulfur (Li-S) battery is a particularly attractive beyond Li-ion battery chemistry because it offers a high theoretical specific energy of 2500 Wh/kg (at materials level) [2] and a demonstrated practical specific energy >300 Wh/kg (at cell level) [3], making it a promising battery chemistry for future space applications that demand higher specific energy in batteries.Currently, no commercial Li-S battery exists due to several significant technical challenges that have thus far prevented the realization of the Li-S chemistry’s tremendous performance potential. These technical challenges include: (i) Low practical energy yield and significant capacity loss with cycling, due to lithium polysulfide formation/dissolution/migration during discharge [4]. (ii) High self-discharge rates and low Coulombic efficiency, due to redox shuttle reactions of the dissolved polysulfides. (iii) Safety concerns, mainly due to Li dendrite growth from the unprotected Li anodes [5].We will present our efforts in the development of a high energy density, long cycle life, long shelf life and enhanced reliability/safety Li-S battery technology, using a holistic and comprehensive approach to overcome technical challenges that hinder commercialization of Li-S batteries. In particular, we will demonstrate impact of various battery testing parameters, such as depth-of-discharge, charge/discharge current C-rate, on Li-S cell cycle performance and shelf life.Our investigation results showed that, using material engineered (active and inactive) cell components, the resultant Li-S cells demonstrated excellent cycle life performance, while achieving high specific capacities and energies when cycled under optimized battery testing schemes. The advanced Li-S battery technology has shown a great promise to achieve unprecedented specific energy/energy density and long-term cycle/shelf life stability for future space applications. References 2020 NASA Technology Taxonomy, https://www.nasa.gov/offices/oct/taxonomy/index.htmlZhang, Sheng S., Power Sources, 231, 153-162, 2013.Weibing Xing, # A02-0364, 238th Electrochemical Society Meeting (PRiME), Honolulu, HI, October 4-9, 2020.Besenhard JO. Handbook of Battery Materials. Wiley: New York; 1998.James R. Akridge, Battery Power Products & Technology, October 2001. Acknowledgement We would like to acknowledge financial support from NASA Glenn Research Center for this R&D work.

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

A lithium-sulfur (Li-S) battery has a high theoretical specific capacity (1675 mAh g-1 of elemental sulfur) and a high nominal energy density (2500 Wh kg-1 of cell weight), which offers the prospect of a significant energy density improvement compared to the mainstream lithium-ion batteries (150 Wh kg-1). However, the development of Li-S battery technology has been plagued by problems arising from the highly insulating nature of sulfur (5×10-30 S cm-1 at 25 °C), the high solubility of lithium polysulfides in the electrolyte and volumetric expansion of sulfur during lithiation. Here, we demonstrate the design and preparation of few-layer graphene (FLG) foam scaffold for sulfur loading to fabricate cathode structures for lithium-sulfur batteries. In this work, a free-standing FLG monolithic network foam was formed as a negative of a Ni metallic foam template by CVD followed by etching away of Ni. Then, a three-dimensional (3-D) cathode system for lithium sulfur (Li-S) batteries has been synthesised by loading sulfur on to this interconnected network of few-layered graphene (FLG) via a sulfur solution infiltration method. This cathode system did not require any additional binding agents, conductive additives or a separate metallic current collector thus decreasing the weight of the cathode by typically ~20-30 wt%. A Li-S battery with the sulfur/FLG foam cathode shows good electrochemical stability and high rate discharge capacity retention for up to 400 discharge/charge cycles at a high current density of 3200 mA g-1, which due to the FLG foam offers excellent electrical conductivity, an appropriate pore structure for containing the electro-active sulfur and facilitates rapid electron/ion transport. Even after 400 cycles the capacity decay is only ~0.064% per cycle relative to the early (e.g. the 5th cycle) discharge capacity, while yielding an average columbic efficiency of ~96.2%. To further understand the sulfur loading ability of FLG foam, the composites with high content (up to 72 wt %) were also investigated. The composite with high content of sulfur still presented good initial discharge capacity and good cycle stability after 200 cycles. Our results indicate the potential suitability of graphene foam for efficient and high-performance 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.

Carbon nanofibril composites with high sulfur loading fabricated from nanocellulose for high-performance lithium-sulfur batteries