Separator For Lithium-sulfur Batteries Research Articles

Tungsten phosphide on nitrogen and phosphorus-doped carbon as a functional membrane coating enabling robust lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) hold great potential as future energy storage technology, but their widespread application is hampered by the slow polysulfide conversion kinetics and the sulfur loss during cycling. In this study, we detail a one-step approach to growing tungsten phosphide (WP) nanoparticles on the surface of nitrogen and phosphorus co-doped carbon nanosheets (WP@NPC). We further demonstrate that this material provides outstanding performance as a multifunctional separator in LSBs, enabling higher sulfur utilization and exceptional rate performance. These excellent properties are associated with the abundance of lithium polysulfide (LiPS) adsorption and catalytic conversion sites and rapid ion transport capabilities. Experimental data and density functional theory calculations demonstrate tungsten to have a sulfophilic character while nitrogen and phosphorus provide lithiophilic sites that prevent the loss of LiPSs. Furthermore, WP regulates the LiPS catalytic conversion, accelerating the Li-S redox kinetics. As a result, LSBs containing a polypropylene separator coated with a WP@NPC layer show capacities close to 1500 mAh/g at 0.1C and coulombic efficiencies above 99.5 % at 3C. Batteries with high sulfur loading, 4.9 mg cm−2, are further produced to validate their superior cycling stability. Overall, this work demonstrates the use of multifunctional separators as an effective strategy to promote LSB performance.

Negatively charged hydrochar from Aesculus indica waste: A sustainable material for enhanced Li-S batteries performance

This study presents a negatively charged hydrochar from Aesculus indica waste, employing a microwave-assisted hydrothermal carbonization (HTC) method at very low temperatures (120∼200 °C). The research shows the utilization of these negatively-charged-oxygen-containing hydrochars in lithium-sulfur (Li-S) batteries effectively mitigates polysulfide shuttling through electrostatic repulsive forces and simultaneously facilitate uniform lithium-ion transportation, leading to substantial improvement in battery performance. Through detailed investigations into the HTC reaction mechanism, the concentration of the negatively charged oxygen functional groups is tunable by controlling the carbonization process, which could further improve the enhancement effects. Furthermore, negatively-charged-oxygen-containing hydrochars were utilized as modified separator in Li-S batteries to enhance the electrochemical performance. The batteries assembled with hydrochar modified separator, has an initial discharge capacity of 1216 mAh g−1 at 0.1 C, and after 200 cycles at 1 C, its reversible discharge capacity was still 800 mAh g−1 with more than 80 % capacity retention. This research not only provides an efficient method for the utilization of waste biomass, but also offers a new approach for the preparation of negatively charged carbon for lithium-sulfur batteries.

Nitrogen-doped carbon encapsulated trimetallic CoNiFe alloy nanoparticles decorated carbon nanotube hybrid composites modified separator for lithium‑sulfur batteries

The large-scale applications of lithium sulfur batteries have been limited by their rapid capacity loss, which can be attributed to the dissolution of polysulfide intermediates and subsequent irreversible shuttling effect. Several strategies have been attempted to the solve these problems by designing novel cell structure, including the modification of separator. Herein, a hybrid composite consisting of trimetallic CoNiFe alloy nanoparticles encapsulated with nitrogen doped carbon decorated carbon nanotubes (NC@CoNiFe/CNTs) was designed and coated on polypropylene (PP) separator for lithium sulfur batteries. The conductivity of mesoporous CNTs provide fast electronic transport and improve the sulfur utilization. The NC@CoNiFe nanoparticles can further adsorb the soluble polysulfides and serve as catalysts to promote the redox kinetics of polysulfides conversion. Benefiting from the synergism of physical confinement, chemical adsorption, and catalytic conversion, the lithium sulfur cell based NC@CoNiFe/CNTs-PP delivers excellent electrochemical performance at high sulfur loading. The lithium sulfur cell with NC@CoNiFe/CNTs-PP under 3.8 mg cm−2 sulfur loading exhibits a high initial capacity of 785.4 mAh g−1 at 0.5C and sustain a capacity of 572.4 mAh g−1 after 240 cycles, corresponding to a retention rate of 72.9 %. The cell with a high sulfur loading of 8.9 mg cm−2, it shows a discharge capacity of 8.89 mAh cm−2 and still maintains 7.24 mAh cm−2 over 100 cycles.

First-principles investigation of the catalytic mechanism of CeO2/KB composite separator in Li-S batteries

The CeO2/Ketjen Black (KB) composite separator has been shown to effectively reduce the shuttle effect and improve the reaction kinetics of lithium polysulfides (LiPSs) in lithium-sulfur (Li-S) batteries. A thorough investigation has been conducted using the Perdew-Burke-Ernzehof plus Hubbard U (PBE + U) calculations implemented within the Vienna ab initio simulation package (VASP). The focus has been on the catalytic mechanism of the separator, particularly the migration behavior of LiPSs and the conversion mechanism of Li2S2 → Li2S on CeO2 and KB surfaces. The study revealed that LiPSs have a strong preference for the CeO2 surface due to more potent adsorption energies. Moreover, it has been discovered that the subsequent migration and conversion processes of LiPSs are governed by the synergistic catalytic effect between CeO2 and KB. The rate-determining step in the overall catalytic process is the migration of Li2S2 on CeO2. These findings provide a deeper understanding of the catalytic mechanism and migration behavior of LiPSs, potentially guiding the development of advanced composite materials for Li-S batteries and facilitating the use of rare earth metal oxides for high energy storage and extended battery life.

Surface design for high ion flux separator in lithium-sulfur batteries

Addressing the shuttle effect is a critical challenge in realizing practical applications of lithium-sulfur batteries. One promising avenue refers to the surface modification of separators, transitioning them from closed to open structures. In the current investigation, a high ion flux separator was devised by means of MnO2 self-assembly onto a Porous Polypropylene (PP) separator, subsequently coupling it with biochar. The separator exhibited favorable ion and electronic conductivity. Moreover, it adeptly captured and transformed polysulfides into Li2S2/Li2S, cyclically curbing the mobility of Polysulfide lithium (LiPSs). In addition, this augmentation in the kinetic conversion of LiPSs during the electrochemical process translated into an impressive discharge specific capacity and area capacity of 939 mAh/g and 4 mAh cm−2, respectively. Moreover, this innovative design methodology provides an alternative avenue for future separator designs within lithium-sulfur batteries.

Catalyst for polysulfide conversion by Mo2C/MoO3 hybrids modified separator in lithium-sulfur batteries

The lithium-sulfur (Li–S) batteries have achieved important developments, but still suffer from some main intrinsic disadvantages, such as the dissolution and diffusion of the lithium polysulfides (LiPSs). In response, here we develop a Mo2C/MoO3 heterostructure as the interlayer to restrain the leakage and migration of LiPSs. Owing to its good conductivity and excellent electronic transport, this heterostructure can perform excellently as an ideal carrier for providing reduction reaction sites of LiPSs conversion, thus greatly improving the electrochemical properties of Mo2C/MoO3 for Li–S batteries. The resultant Mo2C/MoO3 electrodes can deliver a high specific capacity of 1346 mAh g−1 at 0.1C and long-term cycling stability (660 mAh g−1 after 800 cycles at 2C) with a low capacity decay rate of 0.05% per cycle, indicating high sulfur utilization and fast kinetic conversion of LiPSs and Li2S. When the sulfur loading is increased to 4.34 mg cm−2, the initial discharge capacity and areal capacity of the Mo2C/MoO3 electrode at 0.1C is still up to 1405 mAh g−1 and 6.1 mAh cm−2 with a coulombic efficiency of 99% in the first cycle, indicating faster LiPSs conversion. First-principle calculations reveal that the as-synthesized LiPSs species are selectively adsorbed on the MoO3 (001) and Mo2C (001) surface. This work provides an alternative strategy toward high-performance Li–S battery with high sulfur loading.

Polyaniline/rGO/S composite cathode with GO modified separator for lithium sulfur battery: A multipronged approach to tackle the shuttle effect

Lithium-sulphur batteries (LSBs) are a promising candidate for the next generation of high energy density, safe, green and affordable batteries but their practical utilization is hindered by several roadblocks including low cycle life, fast capacity fade, low sulfur utilization due to insulating nature of sulfur and “polysulfide shuttle”. This work employs multiple strategies to circumvent the aforementioned issues like utilizing (i) a reduced graphene oxide (rGO) conducting carbon framework for improving conductivity and mechanical stability of cathode, (ii) polyaniline conducting polymer with polar groups to restrain soluble lithium polysulfides (LiPS) by physisorption/chemisorption (iii) separator modification with graphene oxide to act as a second barrier layer to suppress LiPS migration and support the cathode current collector to enhance sulfur utilization. The combination of these strategies led to a LSB cell that exhibited high initial capacity, low capacity fade and improved lithium ion diffusion as well as lowered cell impedance. The synthesized cathode composite of PANI-rGO-sulfur (PGS) was characterized by several techniques like power x-ray diffraction, scanning electron microscopy, thermogravimetry etc. Electrochemical characterization of cells was performed by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic cycling. The coin cell delivered a superior initial capacity of 807 mAh/g at 100 mA/g current density. Upon cycling at a high current density of 1A/g it delivered a capacity of 478 mAh/g with excellent stability for 500 cycles and lower capacity fade of 0.02% per cycle.

Effect of Heterostructure-Modified Separator in Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries with high energy density and low cost are the most promising competitor in the next generation of new energy reserve devices. However, there are still many problems that hinder its commercialization, mainly including shuttle of soluble polysulfides, slow reaction kinetics, and growth of Li dendrites. In order to solve above issues, various explorations have been carried out for various configurations, such as electrodes, separators, and electrolytes. Among them, the separator in contact with both anode and cathode is in a particularly special position. Reasonable design-modified material of separator can solve above key problems. Heterostructure engineering as a promising modification method can combine characteristics of different materials to generate synergistic effect at heterogeneous interface that is conducive to Li-S electrochemical behavior. This review not only elaborates the role of heterostructure-modified separators in dealing with above problems, but also analyzes the improvement of wettability and thermal stability of separators by modification of heterostructure materials, systematically clarifies its advantages, and summarizes some related progress in recent years. Finally, future development direction of heterostructure-based separator in Li-S batteries is given.

Sulfonic acid functionalized covalent organic frameworks for lithium-sulfur battery separator and oxygen evolution electrocatalyst

Covalent organic frameworks (COFs) are considered as a class of potential candidates for energy storage and catalysis. In this work, a COF containing sulfonic groups was prepared to be a modified separator in lithium-sulfur batteries (LSBs). Benefiting from the charged sulfonic groups, the COF-SO3 cell exhibited higher ionic conductivity (1.83 mS⋅cm−1). Moreover, the modified COF-SO3 separator not only inhibited the shuttle of polysulfide but also promoted Li+ diffusion, thanks to the electrostatic interaction. The COF-SO3 cell also showed excellent electrochemical performance that the initial specific capacity of the battery was 890 mA h g−1 at 0.5 C and demonstrated 631 mA h g−1 after 200 cycles. In addition, COF-SO3 with satisfactory electrical conductivity was also used as an electrocatalyst toward oxygen evolution reaction (OER) via cation-exchange strategy. The electrocatalyst COF-SO3@FeNi possessed a low overpotential (350 mV at 10 mA cm−2) in an alkaline aqueous electrolyte. Furthermore, COF-SO3@FeNi exhibited exceptional stability, and the overpotential increased about 11 mV at a current density of 10 mA cm−2 after 1000 cycles. This work facilitates the application of versatile COFs in the electrochemistry field.

Improving performances of Lithium-Sulfur cells via regulating of VSe2 functional mediator with Doping-Defect engineering and Electrode-Separator integration strategy

The sluggish redox kinetics and the severe shuttle effect of soluble lithium polysulfides (LiPSs) are the main key issues which would hinder the development of lithium-sulfur (Li-S) batteries. In this work, a nickel-doped vanadium selenide in-situ grows on reduced graphene oxide(rGO) to form a two-dimensional (2D) composite Ni-VSe2/rGO by a simple solvothermal method. When it is used as a modified separator in Li-S batteries, the Ni-VSe2/rGO material with the doped defect and super-thin layered structure can greatly adsorb LiPSs and catalyze the conversion reaction of LiPSs, resulting in effectively reducing LiPSs diffusion and suppressing the shuttle effect. More importantly, the cathode-separator bonding body is first developed as a new strategy of electrode-separator integration in Li-S batteries, which not only could decrease the LiPSs dissolution and improve the catalysis performance of the functional separator as the upper current-collector, but also is good for the high sulfur loading and the low electrolyte/sulfur (E/S) ratio for high energy density Li-S batteries. When the Ni-VSe2/rGO-PP (polypropylene, Celgard 2400) modified separator is applied, the Li-S cell can retain 510.3 mA h g−1 capacity after 1190 cycles at 0.5C. In the electrode-separator integrated system, the Li-S cell can still maintain 552.9 mA h g−1 for 190 cycles at a sulfur loading 6.4 mg cm−2 and 4.9 mA h cm−2 for 100 cycles at a sulfur loading 7.0 mg cm−2. The experimental results indicate that both the doped defect engineering and the super-thin layered structure design might optimally be chosen to fabricate a new modified separator material, and especially, the electrode-separator integration strategy would open a practical way to promote the electrochemical behavior of Li-S batteries with high sulfur loading and low E/S ratio.

Mesoporous Carbon-Based Materials for Enhancing the Performance of Lithium-Sulfur Batteries.

The most promising energy storage devices are lithium-sulfur batteries (LSBs), which offer a high theoretical energy density that is five times greater than that of lithium-ion batteries. However, there are still significant barriers to the commercialization of LSBs, and mesoporous carbon-based materials (MCBMs) have attracted much attention in solving LSBs' problems, due to their large specific surface area (SSA), high electrical conductivity, and other unique advantages. The synthesis of MCBMs and their applications in the anodes, cathodes, separators, and "two-in-one" hosts of LSBs are reviewed in this study. Most interestingly, we establish a systematic correlation between the structural characteristics of MCBMs and their electrochemical properties, offering recommendations for improving performance by altering the characteristics. Finally, the challenges and opportunities of LSBs under current policies are also clarified. This review provides ideas for the design of cathodes, anodes, and separators for LSBs, which could have a positive impact on the performance enhancement and commercialization of LSBs. The commercialization of high energy density secondary batteries is of great importance for the achievement of carbon neutrality and to meet the world's expanding energy demand.

Proton-Induced Defect-Rich Vanadium Oxides as Reversible Polysulfide Conversion Sites for High-Performance Lithium Sulfur Batteries.

Lithium-sulfur (Li-S) batteries have attracted attention due to their high theoretical energy density, natural abundance, and low cost. However, the diffusion of polysulfides decreases the utilization and further degrades the battery's life. We have successfully fabricated a defect-rich layered sodium vanadium oxide with proton doping (HNVO) nanobelt and used it as the functional interface layer on the separator in Li-S batteries. Benefiting from the abundant defects of NVO and the catalytic activity of metal vanadium in the electrochemical process, the shuttle of polysulfides was greatly decreased by reversible chemical adsorption. Moreover, the extra graphene layer contributes to accelerating the charge carrier at high current densities. Therefore, a Li-S battery with G@HNVO delivers a high capacity of 1494.8 mAh g-1 at 0.2 C and a superior cycling stability over 700 cycles at 1 C. This work provides an effective strategy for designing the electrode/separator interface layer to achieve high-performance Li-S batteries.

Enhanced lithium polysulfide adsorption on an iron-oxide-modified separator for Li-S batteries.

Lithium-sulfur (Li-S) batteries are candidates for next-generation energy storage systems because of their low cost, high theoretical specific capacity and safety. However, the serious lithium polysulfide (LiPS) shuttle effect leads to a loss of reactive active substances and reduction of coulombic efficiency. In the current work, iron oxide (IO-700)-prepared by calcining a mixture of carbon spheres and ferric nitrate under an air atmosphere at 700 °C-was designed as a separator modifier to effectively adsorb LiPSs and accelerate the kinetics of the transformation of the intermediates, thereby inhibiting the shuttle effect. Li-S batteries including IO-700 showed long-term stability for 1000 cycles at 1C, with a capacity decay rate per cycle of only 0.0487%. A theoretical calculation indicated that, due to strongly polar active sites, Fe2O3 adsorbed LiPSs effectively to suppress the shuttle effect. This work has highlighted the importance for Li-S batteries of strongly polar active sites for anchoring LiPSs to inhibit the shuttle effect.

Design of spherical TiN/Nb4N5 heterostructure as bifunctional adsorption/catalytic material for lithium sulfur batteries

Lithium sulfur (Li-S) battery is the typical representative of the new generation secondary batteries, but its practical application is greatly hindered by the shuttle effect of lithium polysulfides (LiPSs) and sluggish electrochemical reaction kinetics. In this work, a spherical TiN/Nb 4 N 5 heterostructure is produced by nitridation of TiNb 2 O 7 microsphere and then used as an adsorption and catalytic material to fabricate modified polypropylene separator in Li-S batteries. Visual adsorption tests show that the TiN/Nb 4 N 5 heterostructure has better adsorption capacity of LiPSs than that of TiNb 2 O 7 microsphere precursor. The TiN/Nb 4 N 5 heterostructure also exhibits superior catalytic performance to accelerate the redox reaction kinetics of LiPSs conversion. The Li-S cell assembled with TiN/Nb 4 N 5 modified separator can deliver an initial discharge capacity of 917 mAh g -1 at 0.2 C, and a reversible capacity of 663.2 mAh g -1 after 200 cycles, higher than the cell assembled with TiNb 2 O 7 modified separator (555.4 mAh g -1 ) and pristine separator (385.1 mAh g -1 ). In short, this work provides a simple synthetic method to obtain a TiN/Nb 4 N 5 heterostructure with enhanced electrochemical performance of Li-S batteries. • TiN/Nb 4 N 5 heterostructure is synthesized by nitriding TiNb 2 O 7 microsphere; • TiN/Nb 4 N 5 heterostructure has strong adsorptive/catalytic conversion capability for polysulfides; • Li-S cell assembled with TiN/Nb 4 N 5 modified separator shows excellent electrochemical performance.

Designing polysulfides adsorption‐conversion on g‐C3N4‐based separator via doping heteroatoms boron and phosphorus toward high‐performance lithium‐sulfur batteries

AbstractThe notorious “shuttle effect” of lithium polysulfides (LiPSs) has suppressed the large‐scale commercial application of lithium‐sulfur batteries (LSBs). Also, the intrinsic advantages including inhibiting the shuttling‐circulation and promoting the conversion of LiPSs, on the separator are deemed as stimulating blocks on the exploitation of LSBs. Herein, guided by theoretical calculations, we have designed doping‐heteroatoms boron (B) and phosphorus (P) on graphitic carbon nitride (g‐C3N4), to suppress the “shuttle effect” of LiPSs and improve the battery cycling performance. Theoretical calculations show strong chemical bonding between Li atom and N substance of g‐C3N4, and corroborates synergistic mechanism of electron transfer and van der Waals interaction. The high adsorption energies with doping B/P atoms enable LiPSs adsorption on the separators inhibiting shuttle loss. As expected, the experiment data also demonstrate that superior electrochemical performance are achieved by utilizing B‐doped g‐C3N4 (BCN) separator. Incorporating the B‐doped g–C3N4 (BCN) separator in LSBs delivered an initial specific capacity of 1050 mAh g−1 at 1 C and 920 mAh g−1 at 2 C. Notably, it achieved a decay rate of 0.08% and 0.1% at 1 and 2 C, respectively, after 500 cycles. This study furthers our understanding of B/P doping separator enhancement and restraining LiPSs shuttling loss for an improved LSBs performance.

Modified separator engineering with 2D ultrathin Ni3B@rGO: Extraordinary electrochemical performance of the lithium-sulfur battery with enormous-sulfur-content cathode in low electrolyte/sulfur ratio

Compared to other batteries, a next-generation lithium-sulfur (Li-S) battery's specific capacity and energy density are relatively high. However, the actual electrochemical performance (particularly for the cell with a high cathode sulfur content and a lean electrolyte/sulfur ratio) falls well short of practical usage requirements. The ultrathin Ni 3 B@rGO-PP is designed in this study as a unique modified separator for Li-S cells. Because of its distinct electronic structure, the modified separator shows outstanding adsorption ability toward polysulfide through the boron element's active sites. Additionally, it has excellent electrocatalytic activity, significantly enhancing the performance of Li-S batteries. After the 100th cycle, the cell with 80 wt% sulfur content can retain 819 mA h g −1 under 0.2 C. Also, when the electrolyte/sulfur ratio is reduced to 15 µL mg −1 and 5 µL mg −1 , respectively, considerable capacity retention of 736.3 mA h g −1 and 615 mA h g −1 is achieved after the 100th cycle at 0.2 C. What's more, for the high sulfur loading (single-side up to 4.5 mg cm −2 ) cathode, the cell obtains a retention capacity of 578 mA h g −1 after the 200th cycle under 0.2 C. The surface engineering strategy with the Ni 3 B@rGO modified coating adopted in this work would open an efficient route to acquire the Li-S battery's outstanding electrochemical capability in the practical application situation. The boron element's active cites provide a unique electronic structure to the Ni 3 B@rGO coating layer, which effectively enhance the adsorption ability toward polysulfide, and further provide excellent electrocatalytic activity during the charging/discharging process, greatly improving the electrochemical performance of Li-S batteries. Thus, the Ni 3 B@rGO-PP exhibits long cycling stability even at a low E/S ratio, fast Li + transportation, and high ionic conductivity. • The Ni 3 B@rGO nanohybrid developed as a novel modified coating on the celgard separator in Li-S batteries. • The Ni3B@rGO-PP show outstanding adsorption ability to LiPSs through B active cites and enhances the cell conductivity. • The Ni 3 B@rGO-PP exhibits excellent anti-self-discharge, high ionic conductivity, and fast Li + transportation. • The Ni3B@rGO-PP presents promising electrochemical performances with a high-sulfur-content cathode (up to 83 wt%).

Flexible and free-standing bacterial cellulose derived cathode host and separator for lithium-sulfur batteries

This study demonstrates flexible, ultra-high rate, and long cycle life lithium‑sulfur batteries using bacterial cellulose (BC) derived cathode host as well as separator. The work also includes a new strategy to use active sulfur in the form of catholyte added directly to the electrolyte for improved sulfur utilization. The fabricated LiS cell with carbonized bacterial cellulose (CBC) as a cathode host and BC as a separator (CBC@BC) delivers an impressive capacity of 740 mAh g−1 at 1C. It retains a capacity of 310 mAh g−1 even at an ultra-high rate of 4C. To have commercial adoption of CBC@BC, we tested LiS cells with a high areal loading of 5 mg cm−2. The cell shows promising electrochemical performance for 500 cycles with a capacity retention of 82 %. Furthermore, first-principle calculations are performed to understand the interaction of soluble lithium-polysulfides with bacterial cellulose-derived material.

Composite cathodes and modified separators based on corn-silk-based porous carbon for high performance lithium–sulfur batteries

Corn by-products have been widely studied as a precursor of biomass carbon in energy storage systems. Without further doping or coating processes corn silk can achieve a high electrochemical performance when used as an anode of sodium and potassium ion batteries. Nonetheless, there is no report about corn silk used as a cathode for lithium-sulfur batteries. In this work, corn silk was made into porous carbon and used as sulfur scaffolds and modified materials for commercial separator in lithium-sulfur batteries. Corn silk possesses a natural pipe shape which grants the porous carbon a high specific surface area. With a simple dissolution crystallization method approximately 80% of the sulfur could be easily accommodated onto the porous carbon. The hierarchic pores not only limited the particle size of the sulfur to nanometers, but also buffered the volume expansion of sulfur and absorbed it tightly. Furthermore, with an ultralight porous carbon modified separator, significant improvement was achieved in the utilization of sulfur, cycling stability and alleviation of the polysulfide shuttling efficiently. The batteries delivered a specific capacity of 1290 mAh g-1 in the first discharge and 746 mAh g-1 after 100 cycles. The good electrochemical performance can be ascribed to the rational design of battery configuration.

Constructing Atomic Fe and N Co-doped Hollow Carbon Nanospheres with a Polymer Encapsulation Strategy for High-Performance Lithium-Sulfur Batteries with Accelerated Polysulfide Conversion.

As competitive next-generation rechargeable batteries, lithium-sulfur batteries (LSBs) suffer from the shuttle effect and the sluggish kinetics of intermediate polysulfides during charge and discharge processes, adversely affecting their electrochemical performances and actual applications. Herein, we demonstrate a polymer encapsulation strategy to synthesize atomic Fe and N co-doped hollow carbon nanospheres (Fe-NHC) with Fe-Nx sites for modifying commercial PP separator of LSBs to suppress the shuttle effect and promote the kinetics of intermediate polysulfides. Benefiting from the excellent structural design, the doped-N with positive charges could effectively adsorb negatively charged soluble polysulfides, help attract the soluble polysulfides to the Fe atoms and boost the catalytic transformation of the soluble polysulfides. Additionally, such a thin carbon shell could provide a short mass diffusion pathway and hence promote the adsorption and the catalytic conversion. Therefore, the battery with the Fe-NHC/PP separator delivers outstanding cycling and rate performances. At the large current density of 1 C, the specific capacity is 1079 mA h g-1 and maintains a low loss of 0.076 % per cycle within 500 cycles. Even at a harsh current density of 4 C, a high capacity of 824 mA h g-1 is still achieved, indicating the advantage of the Fe-NHC/PP separator in LSBs.

High absorption and fast polysulfides conversion of duel functional separator based on mesoporous-WC/rGO composite for lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) are next-generation energy storage devices owing to their high specific capacities and energy densities; however, critical problems remain unsolved, such as insulating sulfur as an active material and the dissolution of Li polysulfides into the liquid electrolyte during cycling, leading to low sulfur utilization, low rate performance, and rapidly decreasing capacity. Herein, we describe the synthesis of a nanocomposite structure comprising mesoporous tungsten carbide (meso-WC) and reduced graphene oxide (rGO) (meso-WC/rGO) and its application to an functional separator in LSBs. The resulting Li-S cell exhibits improved rate cycling performance: ~950 mAh g-1 at 1 C after 100 cycles. Moreover, even at a high sulfur loading of 3.0 mg cm-2, the Li-S cell with the meso-WC/rGO maintains enhanced performance, with a capacity of ~737 mAh·g-1 and a retention of 83% after 300 cycles. The Li-polysulfide shuttle effect was observed using H-type cells and adsorption tests. The enhanced performance results from suppression of the shuttle effect caused by the excellent adsorption of Li polysulfides, effective reuse of active materials, and promotion of the conversion reaction.