Adsorption Of Lithium Polysulfides Research Articles

Facile construction of porous carbon fibers from coal pitch for Li-S batteries

Coal pitch, an important by-product in the coal coking industry with a high output, is a low-cost and high-carbon yield precursor for the manufacturing of high-value carbon materials. Herein, N/O co-doped carbon fiber (CFCP), fabricated by electrospinning using pre-oxidized coal pitch as the precursor, was employed as the sulfur host for Li-S batteries. The presence of more pyrrolic N and graphic N in CFCP than carbon fiber made from polyacrylonitrile benefits the adsorption of lithium polysulfide and the battery’s life. Sulphur-CFCP cathode (S@CFCP) exhibited excellent specific capacity and cyclability, with a specific capacity of 701.1 mAh/g and a low capacity decay rate of 0.088% per cycle over 200 cycles at 2.0 C, respectively. The high ion diffusion rate, low charge transfer resistance, and effective conversion of lithium polysulfides enable the high electrochemical performance of S@CFCP.

Co3V2O8 composite carbon hollow spheres bidirectionally catalyze the conversion of lithium polysulfide to improve the capacity of lithium‐sulfur batteries

Although lithium‐sulfur batteries have a high theoretical energy density that is higher than lithium‐ion batteries, their development is limited by the slow kinetics of lithium polysulfide conversion. In this research, we utilize the excellent bidirectional catalysis and adsorption of lithium polysulfide by the bimetallic oxide Co3V2O8 composite carbon hollow sphere to address the kinetic obstacle of lithium‐sulfur battery. On the one hand, the carbon hollow sphere substrate provides a cavity that can hold a large amount of sulfur. On the other hand, it can limit the diffusion of lithium polysulfide by van der Waals forces. The combination of the above two points improves the capacity and stability of lithium‐sulfur batteries. It has a specific capacity of 1237.2 mAh g‐1 at 0.2 C current density and retains 603 mAh g‐1 after 100 cycles. At a high current density of 2 C, the specific capacity is 976.2 mAh g‐1. After 1000 cycles, it holds at 338.3 mAh g‐1, and the capacity retention rate per cycle is 99.89%. This work discovers the new potential of Co3V2O8 as an electrocatalyst and proposes a process that can widely prepare carbon materials with complex uniform distribution of electrocatalysts to achieve high specific capacity of lithium‐sulfur batteries.

Oxygen-defect-rich ZnV2O4/ZnO heterojunction as multifunctional separator to boost lithium polysulfide adsorption and conversion for superior lithium‑sulfur batteries

Lithium‑sulfur (Li-S) batteries have been recognized as one of the promising energy systems which can meet the large amounts of energy demanding. However, its practical application has been seriously hindered due to the instinct drawbacks such as low conductivity, large volume expansion and notorious “shuttle effect”. Herein, multi-structure lamellar flower-like zinc vanadate/zinc oxide heterojunction (CoNi@ZnV2O4/ZnO-N,C) with abundant oxygen vacancies, CoNi nanoalloys and N-doped carbon (C) layer has been successfully constructed. XPS and ex-situ XRD analysis reveal that the oxygen vacancies can replace lattice oxygen to adsorb lithium polysulfides (LPS), then stabilize the crystal structure. Additionally, with the synergistic catalysis of CoNi nanoalloys and N-doped C layer, the heterojunction can effectively accelerate the conversion of LPS and promote the precipitation of Li2S. When the lamellar flower-like heterojunction is applied as separator modifier, the “shuttle effect” of LPS can be effectively hindered, leading to synergistic enhancement of long cycle performance of Li-S batteries: the initial discharging capacities of 1468.9 and 1394.9 mAh g−1 can be obtained at 0.1 and 1C, respectively. After 1000 long-term cycles at 3C, the discharging capacity can be still maintained at 467.9 mAh g−1, with a capacity loss rate of 0.049 % per cycle, showing a stable high-rate performance.

Melamine Polymerization Promotes Compact Phosphorus/Carbon Composite for High-Performance and Safe Lithium Storage.

Phosphorus is regarded as a promising material for high-performance lithium-ion batteries (LIBs) due to its high theoretical capacity, appropriate lithiation potential, and low lithium-ion diffusion barrier. Phosphorus/carbon composites (PC) are engineered to serve as high-capacity high-rate anodes; the interaction between phosphorus and carbon, long-term capacity retention, and safety problems are important issues that must be well addressed simultaneously. Herein, an in situ polymerization approach to fabricate a poly-melamine-hybridized (pMA) phosphorus/carbon composite (pMA-PC) is employed. The pMA hybridization enhances the density and electrical conductivity of the PC, improves the structural integrity, and facilitates stable electron transfer within the pMA-PC composite. Moreover, the pMA-PC composite exhibits efficient adsorption of lithium polysulfides, enabling stable transport of Li+ ions. Therefore, the pMA-PC anode demonstrates a high specific charging capacity of 1,381mAhg-1 at 10Ag-1, and a great capacity retention of 86.7% at 1Ag-1 over 500 cycles. The synergistic effect of phosphorus and nitrogen further confers excellent flame retardant properties to the pMA-PC anode, including self-extinguishing in 2.5s, and a much lower combustion temperature than PC. The enhanced capacity and safety performance of pMA-PC show potential in future high-capacity and high-rate LIBs.

Ion/Electron Co-Conductive Triple-Phase Interface Enabling Fast Redox Reaction Kinetics in Lithium-Sulfur Batteries.

Lithium-sulfur batteries (LSBs) are promising next-generation energy storage systems because of their high energy densities and high theoretical specific capacities. However, most catalysts in the LSBs are based on carbon materials, which can only improve the conductivity and are unable to accelerate lithium-ion transport. Therefore, it would be worthwhile to develop a catalytic electrode exhibiting both ion and electron conductivity. Herein, a triple-phase interface using lithium lanthanum titanate/carbon (LLTO/C) nanofibers to construct ion/electron co-conductive materials was used to afford enhanced adsorption of lithium polysulfides (LiPSs), high conductivity, and fast ion transport in working LSBs. The triple-phase interface accelerates the kinetics of the soluble LiPSs and promotes uniform Li2S precipitation/dissolution. Additionally, the LLTO/C nanofibers decrease the reaction barrier of the LiPSs, significantly improving the conversion of LiPSs to Li2S and promoting rapid conversion. Specifically, the LLTO promotes ion transport owing to its high ionic conductivity, and the carbon enhances the conductivity to improve the utilization rate of sulfur. Therefore, the LSBs with LLTO/C functional separators deliver stable life cycles, high rates, and good electrocatalytic activities. This strategy is greatly important for designing ion/electron conductivity and interface engineering, providing novel insight for the development of the LSBs.

Could Commercially Available Aqueous Binders Allow for the Fabrication of Highly Loaded Sulfur Cathodes with a Stable Cycling Performance?

In this review, the application of five commercially available aqueous-based binders including sodium carboxyl methyl cellulose (CMC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyethylene oxide (PEO), and polyethyleneimine (PEI) as well as some representative custom (or purpose) synthesized functional binders used in lithium sulfur (Li-S) batteries is summarized based on the main evaluation criteria of cycling capacity, battery lifetime, and areal sulfur loading (and, consequently, energy density of the battery). CMC with SBR (styrene butadiene rubber) has been reported with promising results in highly loaded sulfur cathodes (>5 mg cm−2 sulfur loading). PVA and PEI were confirmed to provide an enhanced adsorption of lithium polysulfides due to the interaction with hydroxyl and amine groups. No competitive advantage in electrochemical performance was demonstrated through the use of PAA and PEO. Water-based binders modified with polysulfide-trapping functional groups have complex fabrication processes, which hinders their commercial application. In general, achieving a high capacity and long cycling stability for highly loaded sulfur cathodes using commercial aqueous-based binders remains a significant challenge. Additionally, the scalability of these reported sulfur cathodes, in terms of complexity, cost, and stable electrochemical cycling, should be evaluated through further battery testing, particularly targeting pouch cell performance.

Bidirectional enhancement of Li2S redox reaction by NiSe2/CoSe2-rGO heterostructured bi-functional catalysts

The high activity barriers of Li2S nucleation and deposition limit the redox reaction kinetics of lithium polysulfides (LiPSs), meanwhile, the significant shuttle effect of LiPSs hampers the advancement of Li-S batteries (LSBs). In this work, a NiSe2/CoSe2-rGO (NiSe2/CoSe2-G) sulfur host with bifunctional catalytic activity was prepared through a hard template method. Electrochemical experiment results confirm that the combination of NiSe2 and CoSe2 not only facilitates the bidirectional catalytic function during charge and discharge processes, but also increases the active sites toward LiPSs adsorption. Simultaneously, the highly conductive rGO network enhances the electronic conductivity of NiSe2/CoSe2-G/S and provides convenience for loading NiSe2/CoSe2 catalysts. Benefitting from the exceptional catalytic-adsorption capability of NiSe2/CoSe2 and the presence of rGO, the NiSe2/CoSe2-G/S electrode exhibits excellent electrochemical properties. At 1C, it demonstrates a low capacity attenuation of 0.087 % per cycle during 500 cycles. The electrode can maintain a discharge capacity of 927 mAh/g at a sulfur loading of 3.3 mg cm−2. The bidirectional catalytic activity of NiSe2/CoSe2-G offers a prospective approach to expedite the redox reactions of active S, meanwhile, this work also offers an ideal approach for designing efficient S hosts for LSBs.

A review of metal phosphides with catalytic effects in Li-S batteries: boosting the redox kinetics.

Lithium-sulfur batteries (Li-S batteries) are being widely studied as promising energy-storage solutions for the next generation owing to their excellent properties including high energy density, eco-friendliness, and low cost. Nevertheless, drawbacks, especially the severe "shuttle effect" and slow transformation of polysulfides, hinder the road to commercialization of Li-S batteries. The functional utilization of metal compounds in Li-S batteries has been verified, such as enhancing the conductivity, adsorption of lithium polysulfides (LPSs) and improving the kinetics of electrode processes. Benefiting from the outstanding catalytic capability and relatively good conductivity, metal phosphides have gradually received intense attention over the past few years. Consequently, significant progress has been achieved in the optimization of phosphides for Li-S batteries in recent years. This review introduces the application of metal phosphides in Li-S batteries from the aspects of their own characteristics, material structure design, and material interface control. The aim of this review is to enhance the understanding of the operational mechanism of metal phosphides and provide guidance for the development of Li-S batteries.

A Facile Molten Salt Method for Diverse TiC/C Hybrid as Effective Polysulfide Confinement toward Stable Lithium–Sulfur Batteries

Traditional carbon materials suffer from weak adsorption of lithium polysulfides and excessive consumption of electrolyte. A simple and feasible molten salt method is applied for constructing an active nanocrystalline TiC shell on the surface of porous carbon. The highly active TiC nanoshells endow the core–shell composite with efficient chemical–physical synergistic adsorption, which can effectively confine and convert polysulfides, thereby improving the electrochemical performance of lithium–sulfur batteries. The lithium–sulfur batteries assembled with modified separator deliver a high initial discharge specific capacity of 1396 mAh g−1 at a discharge rate of 0.5 C and a high capacity retention of 747.1 mAh g−1 after 500 cycles, with a high coulombic efficiency of 98% during cycling. Besides, this molten salt method can be applied to modify the porous carbon materials of various composite sulfur cathodes such as graphene, carbon nanotubes, and 3D nonwoven carbon fabrics.

Reinforcing the Adsorption and Conversion of Polysulfides in Li-S Battery by Incorporating Molybdenum into MnS/MnO Nanorods.

The Sabatier principle suggests that an excessive adsorption of lithium polysulfides (LiPSs) by metal compounds may hinder their conversion in the absence of a conversion module. Therefore, it is imperative to establish a synergetic effect mechanism between "strong adsorption" and "rapid conversion" for LiPSs. To achieve this coexistence, a molybdenum-doped MnS/MnO@C porous structure is designed as a multifunctional coating on the polypropylene (PP) separator. The incorporation of MnS/MnO@C enhances the adsorption capacity towards LiPSs, while molybdenum facilitates subsequent conversion. Benefiting from the synergistic effect of each component and its large specific surface area, the cell with Mo-doped MnS/MnO@C coating achieves smooth adsorption-diffusion-conversion processes and exhibits an appreciable rate performance with outstanding cycling stability. Even when sulfur loading increases to 9.68 mg cm-2 , the modified battery delivers an excellent initial areal capacity of 11.69 mAh cm-2 and maintains 6.97 mAh cm-2 after 50 cycles at 0.1 C. This study presents a promising approach to simultaneously accomplish "strong adsorption" and "rapid conversion" of polysulfides, offering novel perspectives for devising dual-functional modified separators.

Recent advances in copper-based materials for robust lithium polysulfides adsorption and catalytic conversion

Lithium–sulfur (Li–S) batteries are considered one of the most promising next-generation secondary batteries owing to their ultrahigh theoretical energy density. However, practical applications are hindered by the shuttle effect of soluble lithium polysulfides (LiPSs) and sluggish redox kinetics, which result in low active material utilization and poor cycling stability. Various copper-based materials have been used to inhibit the shuttle effect of LiPSs, owing to the strong anchoring effect caused by the lithiophilic/sulphilic sites and the accelerated conversion kinetics caused by excellent catalytic activity. This study briefly introduces the working principles of Li–S batteries, followed by a summary of the synthetic methods for copper-based materials. Moreover, the recent research progress in the utilization of various copper-based materials in cathodes and separators of Li–S batteries, including copper oxides, copper sulfides, copper phosphides, copper selenides, copper-based metal-organic frameworks (MOFs), and copper single-atom, are systematically summarized. Subsequently, three strategies to improve the electrochemical performance of copper-based materials through defect engineering, morphology regulation, and synergistic effect of different components are presented. Finally, our perspectives on the future development of copper-based materials are presented, highlighting the major challenges in the rational design and synthesis of high-performance Li–S batteries.

Uncovering the lithium-embedded behavior and catalytic mechanism of g-C3N4 as a sulfur host of lithium‑sulfur batteries in the initial discharge reaction

Due to its excellent anchoring properties to lithium polysulfide (LiPSs), g-C3N4 has been widely studied as anode material for lithium‑sulfur batteries (LSBs). g-C3N4 as the electrode material has an obvious irreversible capacity during the initial discharge progress. The mechanism of this irreversible reaction and its effect on the adsorption of LiPSs and cycling performance of g-C3N4 are not clear. Using first-principle calculations, founding that during the initial discharge progress, the binding energy of lithium to the heptazine ring is larger than the binding energy of lithium to sulfur resulting in this part of lithium entering the center of the heptazine ring and being unable to desorption form Li@g-C3N4, which is the main reason for the irreversible capacity. However, compared with g-C3N4, the conductivity of Li@g-C3N4 is enhanced and the diffusion of lithium atoms is facilitated not only by avoiding the strong interaction of other Li atoms with g-C3N4 because the vacancies have been filled. And the adsorption of LiPSs is also appropriately weakened, which can better maintain the structure integrity of the Li2S6 and Li2S8 molecules and lead to a lower reaction free energy during the discharge process.

Cations Mediate Lithium Polysulfide Adsorption in Metal–Organic Frameworks for Lithium–Sulfur Batteries

Cations Mediate Lithium Polysulfide Adsorption in Metal–Organic Frameworks for Lithium–Sulfur Batteries

Synergizing Spatial Confinement and Dual-Metal Catalysis to Boost Sulfur Kinetics in Lithium-Sulfur Batteries.

Sluggish kinetics and parasitic shuttling reactions severely impede lithium-sulfur (Li-S) battery operation; resolving these issues c ould enhance the capacity retention and cyclability of Li-S cells. Therefore, an effective strategy featuring core-shell-structured Co/Ni bimetal-doped metal-organic framework (MOF)/sulfur nanoparticles is reported herein for addressing these problems; this approach offers unprecedented spatial confinement and abundant catalytic sites by encapsulating sulfur within an ordered architecture. The protective shells exhibit long-term stability, ion screening, high lithium-polysulfide adsorption capability, and decent multistep catalytic conversion. Additionally, the delocalized electrons of the MOF endow the cathodes with superior electron/lithium-ion transfer ability. Via multiple physicochemical and theoretical analysis, the resulting synergistic interactions are proved to significantly promote interfacial charge-transfer kinetics, facilitate sulfur conversion dynamics, and inhibit shuttling. The assembled Li-S batteries deliver a stable, highly reversible capacity with marginal decay (0.075% per cycle) for 400 cycles at 0.2C, a pouch-cell areal capacity of 3.8 mAh cm-2 for 200 cycles under a high sulfur loading, as well as remarkably improved pouch-cell performance. This article is protected by copyright. All rights reserved.

Preparation and application of carbon nanotubes loaded atomic-level Ni–N4 catalyst for lithium-sulfur battery

Lithium-sulfur batteries (LSBs) are promising candidates as next-generation secondary batteries due to their advantages with respect to cost and energy density. However, their practical application is hindered by their slow kinetics and the shuttle behavior of soluble polysulfide ions. Herein, we successfully prepared a three-dimensional porous conductive catalyst material with an atomic-level Ni–N4 structure. The results showed that a strong adsorption of lithium polysulfides (LiPSs) by the Ni–N4 catalytic active sites and a strong catalytic effect on the conversion of LiPSs in the sulfur reduction reaction (SRR) as well as the lithium sulfide oxidation reaction (SOR) were achieved, effectively inhibiting the shuttle effect of polysulfide ions and promoting the sulfur cathode kinetics process. Thus, the LSBs exhibited an excellent performance with a specific capacity of 829.8 mAh g–1 and an average coulombic efficiency of 98.8 % after 420 cycles at a high rate of 1 C. Our work provides new insights and novel efforts to solve the shuttle effect in LSBs.

(Invited) Electrocatalysis and Surface Chemistry in Lithium Sulfur Batteries

This talk will focus on the application of electrocatalysis and surface/interface chemistry to solve the cycling stability problem of lithium sulfur batteries, which are a type of future high energy rechargeable battery that can deliver a few times more energy than the prevalent lithium ion batteries of the same mass. One critical problem is the adsorption of lithium polysulfides, the key reaction intermediates that control the electrochemical performance of the sulfur cathode. We find that 3d transition metal oxides effectively bind polysulfides via oxygen-lithium or metal-sulfur bonding, whereas metal phosphides and chalcogenides only do so with their oxidized surfaces. When the electrolyte/sulfur ratio is lowered for even higher energy density (lean electrolyte condition), we discover that catalysis is needed to overcome the potential limiting reaction barrier associated with the conversion of reaction intermediates. With this understanding, we have developed high capacity sulfur cathode materials achieving hundreds of stable charging-discharging cycles. This surface/interface chemistry approach also enables us to analyze the cycling behavior of the lithium/sodium metal anode and to develop electrode/electrolyte interphases for improving the charging-discharging efficiency and cycling stability, including lithium metal electrodes working with solid-state electrolyte.

Anchoring and catalyzing polysulfides by rGO/MoS2/C modified separator in lithium–sulfur batteries

Effective adsorption and catalysis are vital in developing high-efficient and stable lithium-sulfur (Li–S) batteries. Here, a coral-like porous composite containing molybdenum sulfide (rGO/MoS2/C) as interlayer on the separator to mitigate polysulfide shuttling. Since the rGO/MoS2/C composite exhibits promising electrolyte wetting properties with a large specific surface area, which can be fully utilized for the adsorption of lithium polysulfides (LiPSs). In addition, the molybdenum sulfide active site can effectively bind to and catalyze the conversion of LiPSs, further preventing the penetration of LiPSs. As a result, the assembled device shows excellent cycle stability with a low capacity decay of 0.022% per cycle over 1000 cycles (2.0C). In addition, the device still preserves a decent cycle ability even at low electrolyte and high sulfur loading conditions. This work presents a feasible strategy to anchor and accelerate the conversion of LiPSs by designing multifunctional transition metal sulfide composites with high adsorption properties and catalytic activity to achieve stable cycle of Li–S batteries.

Ordered porous metal oxide embedded dense carbon network design as high-performance interlayer for stable lithium-sulfur batteries

The design of multifunctional interlayer is important for the suppression of lithium polysulfides (LiPSs) shuttle effect in lithium-sulfur (Li-S) batteries. Herein, a multifunctional interlayer fabrication strategy is developed by depositing ordered porous metal oxide embedded with nitrogen-doped carbon nanotubes (NCNT) on the carbon nanofibers (CNFs) skeleton. In this design strategy, three-dimensional ordered macroporous N, Co-doped titanium oxides (N,Co-TiOx) is uniformly deposited on CNFs network, then in-situ growth of NCNT is implemented within the ordered porous oxides framework and CNFs, forming dense-structured adsorption/catalytic multifunctional interlayer (N,Co-TiOx/NCNT@CNFs). The ordered porous N,Co-TiOx together with the implemented NCNT not only provides an effective physical barrier for polysulfides diffusion, but also offers strong chemical interaction with LiPSs adsorption and promoted catalytic conversion kinetics. With these merits, the Li-S battery with N,Co-TiOx/NCNT@CNFs interlayer delivers an impressive rate capability of 638 mAh g-1 at a current density of 5 C. The cell also shows excellent cycling performance with a capacity decay of 0.033 % per cycle after 500 cycles at 1 C. More importantly, the Li-S pouch cells with N,Co-TiOx/NCNT@CNFs interlayer achieve a capacity of 806 mA h g−1 at sulfur loading of 4.0 mg cm−2 after 50 cycles at 0.1 C. This ordered porous metal oxide embedded dense carbon network design provides alternative strategy for the development of high-performance Li-S batteries interlayer.

Enhanced performance of lithium-sulfur battery cathode via composition optimization using modified MWCNTs as a conductive material and poly (acrylic acid) as a binder

Lithium–sulfur (Li–S) batteries are promising candidates for the next-generation energy storage devices for portable electronics and electric vehicles owing to their low-cost, high-energy density, and minimal environmental impact. However, low sulfur utilization and short life-cycle limit their performance and commercialization. Herein, Li–S battery cathodes were prepared by blending different proportions of active material sulfur (S) with modified multiwall carbon nanotubes (MWCNTs) as a conductive material, and poly (acrylic acid) (PAA) as a binder to optimize the electrode composition. Specially, we found that the oxidation of MWCNT improves not only their dispersion in water-based slurry during the electrode preparation but also improves the adsorption of lithium polysulfides during the electrochemical reaction. Cathode prepared with a 5:4:1 wt ratio of S: oxidized MWCNT: PAA shows the uniform dispersion of cathode slurry and exhibits the highest discharge capacity of ∼480 mA h g−1 when compared to other mixing ratios. This work demonstrates the feasibility of redox mediation to reinforce the electron accessibility with appropriately loaded sulfur on MWCNT.

Vanadium nitride/reduced graphene oxide composite interlayer with dual lithium-polysulfide adsorption effect for lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) have been developed as next-generation power sources owing to their high theoretical capacities and energy densities, cost effectiveness, and abundance. However, the low electrical conductivity of sulfur in the cathode and the dissolution of lithium polysulfides (LiPS) into the liquid electrolyte are challenging issues that deteriorate both capacity and energy density. Herein, a porous vanadium nitride and reduced graphene oxide (VN/rGO) composite is prepared as an LSB interlayer that enhances conversion and redox reactions and increases sulfur utilization. Polar VN in the VN/rGO interlayer chemically adsorbs LiPS while rGO provides excellent electrical conduction and a high specific surface area for the physical adsorption of LiPS. The dual LiPS adsorption effect of VN/rGO suppresses shuttle effect and enhances electrochemical performance, leading to specific capacities of 1025 and 693 mA h g−1 at 0.5 and 2 C, respectively, and a retention of 81 % at 0.5 C after 200 cycles.