Host For Lithium-sulfur Batteries Research Articles

Hollow spheres of Mo2C@C as synergistically confining sulfur host for superior Li–S battery cathode

Lithium–sulfur batteries (LSBs) have attracted much attention in the field of electrochemical energy storage due to their high energy density and low cost. However, the ‘shuttle effect’ of sulfur cathode, resulting in the poor cyclic performance of batteries, is a big barrier for the development of LSBs. To overcome this critical drawback, herein, a matrix of well-designed double carbon shells-encapsulated metallic Mo2C nanoparticles (Mo2C/C@C) is facilely achieved as an efficient sulfur host for high-performance LSBs. During the electrochemical process, the embedded polar and metallic Mo2C nanoparticles could effectively retard polysulfide migration. While for the carbon layers, they can not only act as conductive matrix but also promote the restriction for all sulfur species and maintain the structural stability simultaneously. Specially, the inner carbon layer is mainly for encapsulation and the outside one for surface-modification. As a result, such well-designed Mo2C/C@C–S cathode could effectively adsorb soluble polysulfides both from chemical and physical aspects, and well confines them inside the porous structure of Mo2C/C@C, thus achieving a high reversible capacity and superior cycling performance.

Hollow Carbon Nanospheres with Developed Porous Structure and Retained N Doping for Facilitated Electrochemical Energy Storage.

Development of highly porous carbons with abundant surface functionalities and well-defined nanostructure is of significance for many important electrochemical energy storage systems. However, porous carbons suffer from a compromise between porosity, doped functionality, and nanostructure that have thus far restricted their performances. Here, we report the design of highly porous, nitrogen-enriched hollow carbon nanospheres (PN-HCNs) by an interfacial copolymerization strategy followed by NH3-assisted carbonization, and further demonstrate their significance and effectiveness in enhancing the electrochemical performances. The PN-HCN simultaneously delivers a large surface area (1237 m2 g-1) and high N functionalities (6.25 atom %) with a remarkable efficiency of the surface area increase to N loss ratio enabled by NH3 treatment while inheriting the hollow nanospherical structure. Accordingly, owing to the enhanced surface area and retained N doping, the prepared PN-HCN demonstrates outstanding electrochemical performances as a cathode hostin lithium-sulfur batteries, including a near-to-theoretical capacity of 1620 mAh g-1, high rate capability and good cycling stability (789 mAh g-1 at 0.5C after 200 cycles). These results are superior to those of HCN without NH3 treatment. Also, PN-HCN exhibits superior capacitances (203 F g-1) and fast ion transport ability in supercapacitors. Our finding shows the simultaneous achievement of both highly porous structures and sufficient N functionalities for high-performance applications.

Synthesis of carbon coated Fe3O4 grown on graphene as effective sulfur-host materials for advanced lithium/sulfur battery

Lithium/sulfur battery (LSB) is considered as one of the most promising battery systems due to its high energy density of 2600 Wh kg−1. Nevertheless, the LSB suffers from some inherent problems that impede its practical application. To circumvent these problems, we grow carbon-coated ferroferric oxide (Fe3O4) nanoparticles on graphene (Fe3O4@C-G) as an effective sulfur host for LSB via a facile hydrothermal method followed by calcination. Highly conductive graphene is utilized to homogeneously deposit the carbon-coated Fe3O4 nanoparticles (Fe3O4@C), which enable rapid and steady long-distance electron transport. Moreover, the carbon coated particles of Fe3O4@C exhibit a developed micro-mesoporous structure, which not only provide space for sulfur loading to prepare a composite Sulfur/carbon-coated Fe3O4 nanoparticles on graphene (S/Fe3O4@C-G) cathode, but also provide channels for the interaction between Fe3O4 and lithium polysulfides. Furthermore, a strong chemical affinity of Fe3O4 nanoparticles coated by micro-mesoporous carbon layers towards polysulfides can be strengthened through the polar-polar interaction. Owning these advantages, the S/Fe3O4@C-G composite cathode deliver a high initial capacity of 1425 mAh g−1 at 0.2 C and maintain a capacity of 1102 mAh g−1 after 100 cycles.

Graphene/carbon aerogel for high areal capacity sulfur cathode of Li-S batteries

Lithium-sulfur batteries are promising high-energy-density devices for next-generation energy storage systems. One of the most challenging issues impeding their practical application is how to develop cost-effective thick sulfur cathode with fast kinetics. Carbon aerogels (CAs) show great potential as host for lithium-sulfur batteries, while the preparation of CAs usually requires special time-consuming drying techniques to retain their porous structure. In this work, we develop a facile method to tailor the flexible structure of the CAs by simply using NaCl, leading to a more stable porous structure that resists the collapse of pores during conventional drying process. High gravimetric and areal sulfur loading can be realized in the synthesized hierarchically porous carbon aerogel electrode. With 69 wt% and over 6 mg cm−2 sulfur loading on the cathode, the cell delivers an initial capacity of 1121 mA h g−1 and a reversible capacity of 797 mA h g−1 after 100 cycles under the current density of 0.2 C.

Silkworm Excrement Derived In‐situ Co‐doped Nanoporous Carbon as Confining Sulfur Host for Lithium Sulfur Batteries

AbstractLithium sulfur batteries (Li−S) are widely proposed as the next generation energy storage systems due to their super high energy density. However, one of the challenges remains in the “shuttle effects” of polysulfides, which hinders the practical application of Li−S. To address the above issue, herein, we propose an innovative design strategy of in‐situ co‐doped nanoporous carbon (ICPC) derived from silkworm excrement to achieve the strong chemical bonding and strict physical confinement of sulfur. As a result, the migration of polysulfides might be suppressed by the synergistic effects of physical and chemical interactions, which is helpful for the significant improvement of electrochemical performance. After 100 stable cyclic discharge‐charge tests at the current density of 0.2 C, the reversible capacity of the as obtained ICPC−S composite cathode still maintains around 500 mAh g−1, corresponding to 67% capacity retention. More importantly, high Coulombic efficiency of nearly 100% can be realized, suggesting the greatly avoided “shuttle effects”. Such a novel design of in‐situ co‐doped nanoporous carbon opens up new possibilities for high performance lithium sulfur batteries.

Hollow Carbon Spheres and Their Hybrid Nanomaterials in Electrochemical Energy Storage

AbstractElectrochemical energy storage is of extraordinary importance for fulfilling the utilization of renewable and sustainable energy sources. There is an increasing demand for energy storage devices with high energy and power densities, prolonged stability, safety, and low cost. In the past decade, numerous research efforts have been devoted to achieving these requirements, especially in the design of advanced electrode materials. Hollow carbon spheres (HCS) derived nanomaterials combining the advantages of 3D HCS and porous structures have been considered as alternative electrode materials for advanced energy storage applications, due to their unique features such as high surface‐to‐volume ratios, encapsulation capability, together with outstanding chemical and thermal stability. In this review, the authors first present a comprehensive overview of the synthetic strategies of HCS, and elucidate the design and synthesis of HCS‐derived nanomaterials including various types of HCS and their nanohybrids. Additionally, their significant roles as electrode materials for supercapacitors, lithium‐ion or sodium‐ion batteries, and sulfur hosts for lithium sulfur batteries are highlighted. Finally, current challenges in the synthesis of HCS and future directions in HCS‐derived nanomaterials for energy storage applications are proposed.

In situ grown α-Cos/Co heterostructures on nitrogen doped carbon polyhedra enabling the trapping and reaction-intensification of polysulfides towards high performance lithium sulfur batteries.

Lithium sulfur (Li-S) batteries are considered as one of the most promising next generation energy storage systems, whereas their intrinsic drawbacks impeded their practical implementation. Herein, a nitrogen doped porous carbon polyhedron coupled with a well distributed α-CoS/Co heterostructure mediator was designed and prepared as the sulfur cathode host for lithium sulfur batteries. The α-CoS/Co heterostructure on a nitrogen doped carbon polyhedron (NCP) not only provides a strong adsorption interaction towards soluble polysulfides, but more importantly, also promotes the fast conversion of polysulfides to insoluble products, chemically suppressing the shuttling of polysulfides through the simultaneous advantages of α-CoS and Co. As a result, the α-CoS/Co-NCP-S cathode exhibits high sulfur utilization with a 1611.4 mA h g-1 first discharge capacity and a well satisfactory redox cycling stability with a low capacity fade rate of 0.042% per cycle at 0.5 C for over 800 cycles. Moreover, the hybrid cathode delivers 860.2 mA h g-1 specific capacity for a high sulfur loading of 4.8 mg cm-2 with remarkable cycling performance.

Recent advances of polar transition-metal sulfides host materials for advanced lithium–sulfur batteries

Lithium sulfur batteries (LSBs) have been one of the most promising second batteries for energy storage. However, the commercialization of LSBs is still hindered by low sulfur utilization and poor cycling stability, resulting from shuttle effect and low redox kinetics of lithium polysulfides (LiPSs). Significant progress has been made over the years in enhancing the batteries performances and tap density with the transition-metal sulfides as sulfur host or additive in LSBs. In this review, we present the recent advances in the use of various nanostructured transition-metal sulfides applied in LSBs, and also focus on the interaction mechanisms of polar transition-metal sulfides with LiPSs and its catalysis for the redox of LiPSs. It may provide avenues for the application of transition-metal sulfides in LSBs. The challenges and perspectives of transition-metal sulfides are also addressed.

Porous nitrogen-doped carbon/MnO coaxial nanotubes as an efficient sulfur host for lithium sulfur batteries

As a promising candidate for next generation energy storage devices, lithium sulfur (Li-S) batteries still confront rapid capacity degradation and low rate capability. Herein, we report a well-architected porous nitrogen-doped carbon/MnO coaxial nanotubes (MnO@PNC) as an efficient sulfur host material. The host shows excellent electron conductivity, sufficient ion transport channels and strong adsorption capability for the polysulfides, resulting from the abundant nitrogen-doped sites and pores as well as MnO in the carbon shell of MnO@PNC. The MnO@PNC-S composite electrode with a sulfur content of 75 wt.% deliveries a specific capacity of 802 mAh·g–1 at a high rate of 5.0 C and outstanding cycling stability with a capacity retention of 82% after 520 cycles at 1.0 C.

Microporous Carbon Materials Derived From Sucrose as Sulfur Host for Lithium Sulfur Batteries

Lithium sulfur batteries have attracted increasing attention due to its high theoretical specific capacity (1675 mAh g−1) and high energy density (2600Wh kg−1)). However, to achieve the commercial application of lithium sulfur batteries, a cathode with excellent electrochemical performance is needed. Herein, we synthesized microporous carbon materials as sulfur host via a simple activation carbonization method. The MC/S delivered an excellent electrochemical performance. At 1 C rate, MC/S showed an initial discharge capacity of 899.5 mAh g−1, and maintained a capacity of 617.6 mAh g−1 after 150 cycles corresponding to a capacity decay rate of 0.208% per-cycle.

Carbon@titanium nitride dual shell nanospheres as multi-functional hosts for lithium sulfur batteries

Lithium-sulfur (Li-S) cells have received particular attention as a “post lithium ion” energy storage system. However, low sulfur utilization and poor redox kinetics are still key challenges to improving cycling efficiency. Herein, we develop a multi-functional polysulfide mediator based on carbon hollow nanospheres supported titanium nitride (C@TiN) dual-shell hollow nanospheres, in which the physical confinement, chemical adsorption, and catalysis for sulfur species conversion were successfully achieved simultaneously. As a result, C@TiN-S composites (approximately 70 wt% sulfur content) exhibit faster reaction kinetics and a higher polysulfide trap capability than that of C@TiO2-S composites when used as cathode materials in Li-S batteries. The C@TiN-S electrode delivers a reversible capacity of 453 mA h g−1, coupled with a high average Coulombic Efficiency (~ 99.0%). There is also limited capacitance decay (only 0.0033% per cycle), at a current density of 3 C, over 300 cycles. In particular, when the sulfur loading is increased to 4.2 mg cm−2, the C@TiN-S electrode can provide a high capacity of 820 mA h g−1 over 150 cycles at 0.2 C. DFT calculations reveal that the long-chain Li2S8 tend to break down into two shorter chain segments due to the strong interaction of TiN and LiPSs. Electrochemical analysis techniques indicate that TiN can effectively catalyze the reduction of polysulfide and the oxidation of Li2S during discharge and charge processes, respectively. Our work offers a new strategy to develop high-performance Li-S batteries based on multi-functional mediators.

Ultrafine and polar ZrO2-inlaid porous nitrogen-doped carbon nanofiber as efficient polysulfide absorbent for high-performance lithium-sulfur batteries with long lifespan

The limitations of low active material utilization, severe capacity fading and short lifespan, mainly resulting from the intermediate polysulfides shuttling, have been hampering the development and practical applications of the lithium-sulfur (Li-S) battery technology. To overcome these issues, a porous nitrogen-doped carbon nanofiber membrane containing ultrafine and polar ZrO2 (CNF@ZrO2) has been investigated as a promising polysulfide host in Li-S batteries. The CNF@ZrO2 interlayer not only serves as a high efficiency lithium polysulfide barrier to suppress the side reactions which is further demonstrated by molecular modeling studies, but also functions as an upper current collector which can enhance the polysulfide redox reactions. Thereby, Li-S batteries with high capacity, prolonged cycle life and stable reversible cyclability can be achieved. A negligible capacity fading rate of 0.039% per cycle over 500 cycles at 0.2 C is obtained. This work offers a facile and effective method of promoting Li-S batteries for practical applications.

In Situ Assembly of 2D Conductive Vanadium Disulfide with Graphene as a High‐Sulfur‐Loading Host for Lithium–Sulfur Batteries

AbstractLithium–sulfur (Li–S) batteries are deemed to be one of the most promising energy storage technologies because of their high energy density, low cost, and environmental benignancy. However, existing drawbacks including the shuttling of intermediate polysulfides, the insulating nature of sulfur, and the considerable volume change of sulfur cathode would otherwise result in the capacity fading and unstable cycling. To overcome these challenges, herein an in situ assembly route is presented to fabricate VS2/reduced graphene oxide nanosheets (G–VS2) as a sulfur host. Benefiting from the 2D conductive and polar VS2 interlayered within a graphene framework, the obtained G–VS2 hybrids can effectively suppress the polysulfide shuttling, facilitate the charge transport, and cushion the volume expansion throughout the synergistic effect of structural confinement and chemical anchoring. With these advantageous features, the obtained sulfur cathode (G–VS2/S) can deliver an outstanding rate capability (≈950 and 800 mAh g−1 at 1 and 2 C, respectively) and an impressive cycling stability at high rates (retaining ≈532 mAh g−1 after 300 cycles at 5 C). More significantly, it enables superior cycling performance of high‐sulfur‐loading cathodes (achieving an areal capacity of 5.1 mAh cm−2 at 0.2 C with a sulfur loading of 5 mg cm−2) even at high current densities.

Spherical Macroporous Carbon Nanotube Particles with Ultrahigh Sulfur Loading for Lithium-Sulfur Battery Cathodes.

A carbon host capable of effective and uniform sulfur loading is the key for lithium-sulfur batteries (LSBs). Despite the application of porous carbon materials of various morphologies, the carbon hosts capable of uniformly impregnating highly active sulfur is still challenging. To address this issue, we demonstrate a hierarchical pore-structured CNT particle host containing spherical macropores of several hundred nanometers. The macropore CNT particles (M-CNTPs) are prepared by drying the aerosol droplets in which CNTs and polymer particles are dispersed. The spherical macropore greatly improves the penetration of sulfur into the carbon host in the melt diffusion of sulfur. In addition, the formation of macropores greatly develops the volume of the micropore between CNT strands. As a result, we uniformly impregnate 70 wt % sulfur without sulfur residue. The S-M-CNTP cathode shows a highly reversible capacity of 1343 mA h g-1 at a current density of 0.2 C even at a high sulfur content of 70 wt %. Upon a 10-fold current density increase, a high capacity retention of 74% is observed. These cathodes have a higher sulfur content than those of conventional CNT hosts but nevertheless exhibit excellent performance. Our CNTPs and pore control technology will advance the commercialization of CNT hosts for LSBs.

Developing porous carbon with dihydrogen phosphate groups as sulfur host for high performance lithium sulfur batteries

Carbon matrix (CM) derived from biomass is low cost and easily mass produced, showing great potential as sulfur host for lithium sulfur batteries. In this paper we report on a dihydrogen phosphate modified CM (PCM-650) prepared from luffa sponge (luffa acutangula) by phosphoric acid treatment. The phosphoric acid not only increases the surface area of the PCM-650, but also introduces dihydrogen phosphate onto PCM-650 (2.28 at% P). Sulfur impregnated (63.6 wt%) PCM-650/S, in comparison with samples with less dihydrogen phosphate LPCM-650/S, shows a significant performance improvement. XPS analysis is conducted for sulfur at different stages, including sulfur (undischarged), polysulfides (discharge to 2.1 V) and short chain sulfides (discharge to 1.7 V). The results consistently show chemical shifts for S2p in PCM-650, suggesting an enhanced adsorption effect. Furthermore, density functional theory (DFT) calculations is used to clarify the molecular binding: carbon/sulfur (0.86 eV), carbon/Li2S (0.3 eV), CH3-O-PO3H2/sulfur (1.24 eV), and CH3-O-PO3H2/Li2S (1.81 eV). It shows that dihydrogen phosphate group can significantly enhance the binding with sulfur and sulfide, consistent with XPS results. Consequently a CM functionalised with dihydrogen phosphate shows great potential as the sulfur host in a Li-S battery.

Hierarchically Porous Carbon Derived from Peanut Shells for High-performance Lithium-sulfur Batteries

Lithium-sulfur (Li-S) batteries are considered to be a promising energy storage device because of their high theoretical energy density and relatively low cost. But low rate performance and poor cycle stability arising from the poor electronic conductivity and the shuttling of polysulfide intermediates hamper its practical application. In order to address these shortcomings, hierarchically porous carbon (HPC) derived from peanut shells is employed as a host to accommodate sulfur for the first time. As-prepared HPC possesses a hierarchically porous structure with a relatively high specific surface area of 1775.7 m2 g−1 and a large pore volume of 1.457 cm3 g−1. When as-prepared HPC was employed as cathode hosts for lithium-sulfur batteries, it was found that S/HPC composite displayed an excellent electrochemical performance. The initial discharge capacity of 1659.8 mA h g−1 is reached at 0.5 C and a reversible capacity of 815.7 mA h g−1 can be maintained after 100 cycles. Even if the current density increas...

Porous-Shell Vanadium Nitride Nanobubbles with Ultrahigh Areal Sulfur Loading for High-Capacity and Long-Life Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries hold great promise for the applications of high energy density storage. However, the performances of Li-S batteries are restricted by the low electrical conductivity of sulfur and shuttle effect of intermediate polysulfides. Moreover, the areal loading weights of sulfur in previous studies are usually low (around 1-3 mg cm-2) and thus cannot fulfill the requirement for practical deployment. Herein, we report that porous-shell vanadium nitride nanobubbles (VN-NBs) can serve as an efficient sulfur host in Li-S batteries, exhibiting remarkable electrochemical performances even with ultrahigh areal sulfur loading weights (5.4-6.8 mg cm-2). The large inner space of VN-NBs can afford a high sulfur content and accommodate the volume expansion, and the high electrical conductivity of VN-NBs ensures the effective utilization and fast redox kinetics of polysulfides. Moreover, VN-NBs present strong chemical affinity/adsorption with polysulfides and thus can efficiently suppress the shuttle effect via both capillary confinement and chemical binding, and promote the fast conversion of polysulfides. Benefiting from the above merits, the Li-S batteries based on sulfur-filled VN-NBs cathodes with 5.4 mg cm-2 sulfur exhibit impressively high areal/specific capacity (5.81 mAh cm-2), superior rate capability (632 mAh g-1 at 5.0 C), and long cycling stability.

Polymeric multilayer-modified manganese dioxide with hollow porous structure as sulfur host for lithium sulfur batteries

Lithium sulfur battery is promising as one of the next generation high performance electrochemical systems because of its high energy density and outstanding cost effectiveness. In this work, the hollow structured manganese dioxide modified by polymeric multilayers (PM) is proposed as the sulfur host for lithium sulfur batteries. In the polymeric multilayer-coated S@MnO2 cathode material (S@MnO2@PM), the MnO2 shell shows the capability in trapping the polysulfide intermediates and suppressing the shuttling caused by their dissolution into electrolyte, and the polymeric multilayers improves the Li+ ion transfer in the composites besides the trapping of polysulfides. The S@MnO2@PM composite exhibits good long-term cyclability due to the synergetic effect of polymeric multilayer and manganese dioxide with hollow porous structure, retaining a discharge capacity of 481 mAh·g−1 at 0.2 C after 1000 cycles. This demonstration indicates that polymeric multilayers coating on S@MnO2 facilitates the charge transfer and improves the cycling stability of lithium sulfur batteries.

Carbon Nitride-Based Hollow Sphere As Polysulfides-Shuttle Restricting Host for Lithium Sulfur Battery

Lithium sulfur battery is a promising candidate to replace the currently lithium ion battery due to the high theoretical specific capacity of sulfur cathode (1675 mA h g−1) and low cost. However, the development of sulfur cathode is hindered by the diffusion of highly soluble polysulfide intermediates formed during cycling and the poor electrical conductivity of sulfur, Li2S2 and Li2S. These issues lead to low Coulombic efficiency, fast capacity fading and low sulfur utilization. A variety of materials have been employed as sulfur matrixes in attempt to address the above mentioned issues, such as carbon materials, polymers and metal oxides. Recently, graphitic carbon nitride (g-C3N4), which possesses high nitrogen content, has been used as sulfur host. The abundant N atoms in g-C3N4 could retard diffusion of lithium polysulfides into electrolyte via the formation of Li-N chemical interaction between g-C3N4 and lithium polysulfides. However, g-C3N4 could hardly improve the sulfur utilization especially at high current density due to its intrinsically poor electrical conductivity (10−12-10−13 S cm−1). Herein, we successfully designed and synthesized a hollow carbon nitride-based sphere (HCNx) material with enhanced conductivity (10−2-10−3 S cm−1) via polymerization of ethylenediamine and carbon tetrachloride on silica spheres template and used it as sulfur host. The HCNx with nitrogen-enriched structure could not only retard diffusion of lithium polysulfides via the Li–N chemical interaction but also physically confine lithium polysulfides by its hollow structure and mesoporous shells. Furthermore, the enhanced electrical conductivity of HCNx improves the utilization of sulfur. The S/HCNx cathode exhibits a discharge capacity of 579 mAh g−1 after 500 cycles at 0.5C with a fade rate of 0.076% per cycle. When charging and discharging at 2 C, the S/HCNx cathode still exhibits a high reversible discharge capacity of 658 mAh g−1.

Chemical Bonding Hosts for Lithium-Sulfur Batteries

Chemical Bonding Hosts for Lithium-Sulfur Batteries