Insights into the aspect ratio effects of ordered mesoporous carbon on the electrochemical performance of sulfur cathode in lithium-sulfur batteries

Tailoring porous host materials, as an effective strategy for storing sulfur and restraining the shuttling of soluble polysulfides in electrolyte, is crucial in the design of high-performance lithium-sulfur (Li-S) batteries. However, for the widely studied conductive hosts such as mesoporous carbon, how the aspect ratio affects the confining ability to polysulfides, ion diffusion as well as the performances of Li-S batteries has been rarely studied. Herein, ordered mesoporous carbon (OMC) is chosen as a proof-of-concept prototype of sulfur host, and its aspect ratio is tuned from over ∼ 2 down to below ∼ 1.2 by using ordered mesoporous silica hard templates with variable length/width scales. The correlation between the aspect ratio of OMCs and the electrochemical performances of the corresponding sulfur-carbon cathodes are systematically studied with combined electrochemical measurements and microscopic characterizations. Moreover, the evolution of sulfur species in OMCs at different discharge states is scrutinized by small-angle X-ray scattering. This study gives insight into the aspect ratio effects of mesoporous host on battery performances of sulfur cathodes, providing guidelines for designing porous host materials for high-energy sulfur cathodes.

Enabling High-Performance Battery Electrodes by Surface-Structuring of Current Collectors and Crack Formation in Electrodes: A Proof-of-Concept

Today's society and economy demand high-performance energy storage systems with large battery capacities and super-fast charging. However, a common problematic consequence is the delamination of the mass loading (including, active materials, binder and conductive carbon) from the current collector at high C-rates and also after certain cycle tests. In this work, surface structuring of aluminum (Al) foils (as a current collector) is developed to overcome the aforementioned delamination process for sulfur (S)/carbon composite cathodes of Li-S batteries (LSBs). The structuring process allows a mechanical interlocking of the loaded mass with the structured current collector, thus increasing its electrode adhesion and its general stability. Through directed crack formation within the mass loading, this also allows an enhanced electrolyte wetting in deeper layers, which in turn improves ion transport at increased areal loadings. Moreover, the interfacial resistance of this composite is reduced leading to an improved battery performance. In addition, surface structuring improves the wettability of water-based pastes, eliminating the need for additional primer coatings and simplifying the electrode fabrication process. Compared to the cells made with untreated current collectors, the cells made with structured current collectors significantly improved rate capability and cycling stability with a capacity of over 1000mAhg-1. At the same time, the concept of mechanical interlocking offers the potential of transfer to other battery and supercapacitor electrodes.

Viologen-based ionic conjugated mesoporous polymer as the electron conveyer for efficient polysulfide trapping and conversion

The commercialization of lithium-sulfur (Li-S) batteries has been hindered by the shuttle effect and sluggish redox kinetics of lithium polysulfides (LiPSs). Herein, we reported a viologen-based ionic conjugated mesoporous polymer (TpV-Cl), which acts as the cathode host for modifying Li-S batteries. The viologen component serves as a reversible electron conveyer, leading to a comprehensive enhancement in the adsorption of polysulfides and improved conversion rate of polysulfides during the electrochemical process. As a result, the S@TpV-PS cathode exhibits outstanding cycling performance, achieving 300 cycles at 2.0 C (1 C = 1675 mA g-1) with low decay rate of 0.032% per cycle. Even at a high sulfur loading of 4.0 mg cm-2, S@TpV-PS shows excellent cycling stability with a Coulombic efficiency of up to 98%. These results highlight the significant potential of S@TpV-PS in developing high-performance Li-S batteries.

Tix+ in-situ intercalation and interlayer modification via titanium foil/vanadium ion solution interface of VO2.375 as sulfur-wrapped matrix enabling long-life lithium sulfur battery

Lithium sulfur battery (LSB) has great potential as a promising next-generation energy storage system owing to ultra-high theoretical specific capacity and energy density. However, the polysulfide shuttle effect and slow redox kinetics are recognized the most stumbling blocks on the way of commercializing LSB. On this account, for the first time, we use Tix+ in-situ intercalation strategy via titanium foil/vanadium ion (V5+) solution interface to modify the layer of vanadium oxide for long cycle LSB. The inserted Tix+ strengthens interlayer interaction and enhances lithium-ion mobility rate. Meanwhile, based on density functional theory (DFT) calculation, the mixed valence of V5+/V4+ in the vanadium oxide structure reduces the stress and strain of lithium-ion intercalation through the interlayer support of titanium ions (Tix+). Also, Tix+ refines the structural stability of the sulfur wrapped composite matrix so as to facilitate the LiPSs transformation, and improve the electrochemical performances. Consequently, the Ti-VO2.375/S cathode delivers a lower capacity decay of 0.037 % per cycle over 1500 cycles with a stable coulombic efficiency around 100 %.

Elevating Lithium-Sulfur Battery Durability through Samarium Oxide/Ketjen Black Modified Separator

Lithium-sulfur batteries have garnered significant attention as a promising next-generation battery technology due to their potential for high energy density. However, their practical application is hampered by slow reaction kinetics and the shuttle effect of lithium polysulfide intermediates. In this context, the authors introduce a pioneering solution in the form of a novel porous carbon nanostructure modified with samarium oxide, denoted as Sm2O3/KB. The material has a highly polar surface, allowing lithium polysulfide to be chemisorbed efficiently. The unsaturated sites provided by the oxygen vacancies of Sm2O3 promote Li2S nucleation, lowering the reaction energy barrier and accelerating Li2S dissolution. The porous structure of Ketjen Black provides a highly conductive channel for electron transport and effectively traps polysulfides. Meanwhile, the batteries with Sm2O3/KB/PP spacers exhibited remarkable electrochemical performances, including a low-capacity decay rate of only 0.046 % for 1000 cycles at 2 C and an excellent multiplicative performance of 624 mAh g-1 at 3 C. This work opens up a new avenue for the potential use of rare-earth-based materials in lithium-sulfur batteries.

Anion receptor and heavy metal-free redox mediator decorated separator for lithium-sulfur batteries

The adsorption-catalysis synergy for accelerated conversion of polysulfides is critical toward the electrochemical stability of lithium-sulfur battery (LSB). Herein, a non-metallic polymer network with anion receptor units, trifluoromethanesulfonyl (CF3SO2-) substituted aza-ether, was in-situ integrated on PE separator, working as an efficient host for anchoring lithium thiophosphates (LPS) as redox mediators and polysulfides through Lewis acid-base interaction. The anchored LPS on the modified PE separator displayed a robust chemical adsorption ability towards polysulfides through the formation of SS bond. Meanwhile, LPS decreased the energy barrier of Li2S nucleation and promoted redox reaction kinetics. The battery with LPS decorated separator revealed a long cycling lifespan with a per cycle decay of 0.056 % after 600 cycles, and a competitive initial capacity of 889.1 mAh/g when the of sulfur cathode increased to 3 mg cm-2. This work developed a new design strategy to promote the utilization of lithium phosphorus sulfide compounds in LSB.

Carbon Nanotube-encapsulated Chestnut Inner Shell O,N-doped Graded Porous Carbon as Stable and High-Sulfur Loading Electrode for Lithium-Sulfur Batteries

The shuttle effect of lithium-sulfur (Li-S) batteries and the poor conductivity of sulfur (S) and lithium polysulfide severely limit their practical applications. Currently, compounding carbon materials with S is one of the effective ways to solve this problem. Therefore, green, low-cost chestnut inner shell biochar (CISC) with graded porous structure was used as the S carrier in this experiment, and carbon nanotubes (CNTs) coating was employed as the S protective layer to improve the electrical conductivity and inhibit the shuttle effect. The results showed that the CISC prepared in this experiment had a relatively high specific surface area (1135.11 m2  g-1 ), and the S loading rate was as high as 65.72 %. The graded porous structure and high specific surface area of CISC can increase the loading rate of S and thus increase the battery capacity. Meanwhile, the naturally contained O and N elements can improve the chemisorption of S. The initial discharge capacity of the CISC@S/CNTs battery at 0.1 C is 967.3 mAh g-1 , and the capacity retention rate is 74.3 % after 500 cycles. The unique composite structure improves the battery's electrical conductivity, reduces the dissolution of polysulfides, and enhances the battery cycle stability.

Highly stable lithium sulfur batteries enhanced by flocculation and solidification of soluble polysulfides in routine ether electrolyte

Lithium-sulfur batteries (LSBs) are among the most promising next-generation high energy density energy-storage systems. However, practical application has been hindered by fundamental problems, especially shuttling by the higher-order polysulfides (PSs) and slow redox kinetics. Herein, a novel electrolyte-based strategy is proposed by adding an ultrasmall amount of the low-cost and commercially available cationic antistatic agent octadecyl dimethyl hydroxyethyl quaternary ammonium nitrate (SN) into a routine ether electrolyte. Due to the strong cation-anion interaction and bridge-bonding with SN, rapid flocculation of the soluble polysulfide intermediates into solid-state polysulfide-SN sediments is found, which significantly inhibited the adverse shuttling effect. Moreover, a catalytic effect was also demonstrated for conversion of the polysulfide-SN intermediates, which enhanced the redox kinetics of Li-S batteries. Encouragingly, for cells with only 0.1 % added SN, an initial specific capacity of 783.6 mAh/g and a retained specific capacity of 565.7 mAh/g were found at 2C after 200 cycles, which corresponded to an ultralow capacity decay rate of only 0.014 % per cycle. This work may provide a simple and promising regulation strategy for preparing highly stable Li-S batteries.

Activation of Bulk Li2S as Cathode Material for Lithium-Sulfur Batteries through Organochalcogenide-Based Redox Mediation Chemistry

Lithium sulfide (Li2S) is considered as a promising cathode material for sulfur-based batteries. However, its activation remains to be one of the key challenges against its commercialization. The extraction of Li+ from bulk Li2S has a high activation energy (Ea) barrier, which is fundamentally responsible for the initial large overpotential. Herein, a systematic investigation of accelerated bulk Li2S oxidation reaction kinetics was studied by using organochalcogenide-based redox mediators, in which phenyl ditelluride (PDTe) can significantly reduce the Ea of Li2S and lower the initial charge potential. Simultaneously, it can alleviate the polysulfides shuttling effect by covalently anchoring the soluble polysulfides and converting them into insoluble lithium phenyl tellusulfides (PhTe-SxLi, x > 1). This alters the redox pathway and accelerates the reaction kinetics of Li2S cathode. Consequently, the Li||Li2S-PDTe cell shows excellent rate capability and enhanced cycling stability. The Si||Li2S-PDTe full cell delivers a considerable capacity of 953.5 mAh g-1 at 0.2 C.

Two-birds with one stone: Improving both cathode and anode electrochemical performances via two-dimensional Te-CoTe2/rGO ultrathin nanosheets as sulfur hosts in lithium-sulfur batteries

A Te-doped CoTe₂ film could be grown in situ on reduced graphene oxide (rGO) to develop a Te-CoTe₂/rGO composite with an ultrathin layered structure, which has multiple protective effects on both the sulfur positive electrode and lithium negative electrode in lithium sulfur (Li-S) batteries. The Te-CoTe₂/rGO composite as a sulfur host not only shows a strong adsorbing ability for lithium polysulfides (LiPSs) but can also accelerate the conversion reaction of active material sulfur during the charging/discharging process. More importantly, this host can turn the shuttle effect from an unfavorable factor to a favorable factor, which could improve the electrochemical performance of the lithium anode with uniform lithium plating/stripping resulting from the intermediate polytellurosulfide species (Li₂Te_xS_y), which could be generated on the cathode surface via Te reacting with soluble Li₂S_n (4 ≤ n ≤ 8). As a result, the S@Te-CoTe₂/rGO cathode shows a discharge capacity of 970.0 mA h g^-1 in the first cycle at 1 C and retains a high capacity of 545.5 mA h g^-1 after 1000 cycles, corresponding to a low capacity decay rate of only 0.043% per cycle. In addition, in situ X-ray diffraction (XRD) and in situ Raman were used to explore the sulfur conversion process. This study not only demonstrates that a two-dimensional (2D) ultrathin Te-CoTe₂/rGO composite is successfully developed with multiple effects on Li-S batteries but also opens a new pathway for designing unique sulfur hosts to promote the electrochemical performance of Li-S batteries.

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.

Tin disulfide embedded on porous carbon spheres for accelerating polysulfide conversion kinetics toward lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are considered promising candidates for next-generation advanced energy storage systems due to their high theoretical capacity, low cost and environmental friendliness. However, the severe shuttle effect and weak redox reaction severely restrict the practical application of Li-S batteries. Herein, a functional catalytic material of tin disulfide on porous carbon spheres (SnS₂@CS) is designed as a sulfur host and separator modifier for lithium-sulfur batteries. SnS₂@CS with high electrical conductivity, high specific surface area and abundant active sites can not only effectively improve the electrochemical activity but also accelerate the capture/diffusion of polysulfides. Theoretical calculations and in situ Raman also demonstrate that SnS₂@CS can efficiently adsorb and catalyse the rapid conversion of polysulfides. Based on these advantages, the SnS₂@CS-based Li-S battery delivers an excellent reversible capacity of 868 mAh/g at 0.5C (capacity retention of 96 %), a high rate capability of 852 mAh/g at 2C, and a durable cycle life with an ultralow capacity decay rate of 0.029 % per cycle over 1000 cycles at 2C. This work combines the design of sulfur electrodes and the modification of separators, which provides an idea for practical applications of Li-S batteries in the future.

Single-walled carbon nanotube gutter layer supported ultrathin zwitterionic microporous polymer membrane for high-performance lithium-sulfur battery

Development of efficient lithium-sulfur (Li-S) battery requires the need to develop an appropriate functional separator that allows strong facilitation and transport of lithium ions together with limited passage of polysulfides. In this work, a multifunctional separator (TB-BAA/SWCNT/PP) is developed through spin coating of a novel zwitterionic microporous polymer (TB-BAA) on the gutter layer constructed from single-walled carbon nanotubes (SWCNT), where commercially available polypropylene (PP) separator is used to act as the mechanical support. SWCNT in this study serves as the first modification layer to decrease the size of the macropores in the PP separator, while the ultrathin TB-BAA top barrier layer with the presence of zwitterionic side chains allows the creation of confined ionic channels with both lithiophilic and sulfophilic groups. Due to the presence of available chemical interactions with lithium polysulfides, selective ion transport can be foreseen through such separator. In this regard, shuttle effect that is frequently encountered in Li-S battery can be suppressed effectively via implementing the as-obtained functional separator, resulting in the creation of credible and stable sulfur electrochemistry. The TB-BAA/SWCNT/PP-based Li-S battery has been investigated to possess high cycling ability (capacity fading per cycle of 0.055% over 500 cycles at 1 C) together with decent rate capability (736.6 mAh g^-1 at 3 C). In addition, a high areal capacity retention of 5.03 mAh cm^-2 after 50 cycles can be also obtained under raised sulfur loading (5.4 mg cm^-2).

A Novel EDOT/F Co-doped PMIA Nanofiber Membrane as Separator for High-Performance Lithium-Sulfur Battery

In this study, a novel fluorine-containing emulsion and 3, 4-ethylene dioxyethiophene (EDOT) co-doped poly-m-phenyleneisophthalamide (PMIA) nanofiber membrane (EDOT/F-PMIA)，as the separator of lithium-sulfur battery, was tactfully prepared via electrospinning. The multi-scale EDOT/F-PMIA nanofiber membrane can be served as the matrix to fabricate gel polymer electrolyte (GPE).Furthermore,under the influence of fluorine-containing emulsion and EDOT, the PMIA-based GPE possessed excellent thermostability, eminent mechanical property and well-distributed lithium-ions flux. Especially, the pore size of the nanofiber membrane decreased after adding the fluorine-containing emulsion and EDOT. And the element S and O in EDOT with lone pair electrons were capable of binding with the lithium polysulfides, which was conducive to inhibiting the "shuttle effect" of lithium polysulfides by combining the physical confinement and chemical binding.Therefore, the lithium-sulfur battery assembled with the EDOT/F-PMIA separator exhibited excellent electrochemical performance, which delivered a high initial capacity of 851.9 mAh g -1 and maintained a discharge capacity of 641.1 mAh g -1 after 200 cycles with a capacity retention rate of 75.2% at 0.5 C.

Zwitterionic covalent organic framework as a multifunctional sulfur host toward durable lithium-sulfur batteries

The shuttle effect and slow redox kinetics of sulfur cathode are the most significant technical challenges to the practical application of lithium-sulfur (Li-S) battery. Herein, a novel zwitterionic covalent organic framework (ZW-COF) wrapped onto carbon nanotubes (CNTs), labeled as ZW-COF@CNT, is developed by a reversible condensation reaction of 1,3,5-benzenetricarboxaldehyde (BTA) and 3,8-diamino-6-phenylphenanthridine (DPPD) with CNTs as a template and a subsequently-one-step post-synthetic grafting reaction with 1,3-propanesultone. The experimental results showed that, after loading active material sulfur, zwitterionic ZW-COF@CNT can effectively suppress the shuttle effect of the soluble lithium polysulfides (LiPSs) in Li-S batteries, and exhibits better cycling behavior than the as-developed neutral COF@CNT. Specifically, the as-obtained ZW-COF@CNT based sulfur cathode can maintain a discharge capacity of 944 mAh/g after 100 cycles, while that of COF@CNT based sulfur cathode drops to (665 mAh/g) after 100 cycles. Moreover, the ZW-COF@CNT based sulfur cathode delivers an attractive prolonged cycling behavior with a low capacity decay rate of 0.046 % per cycle at 1 C. This work sheds new light on rational selection and design of functionalized COFs based sulfur cathode in the Li-S battery.

Trade-off effect of 3d transition metal doped boron nitride on anchoring polysulfides towards application in lithium-sulfur battery

Sulfur cathodes in lithium-sulfur batteries (LSBs) suffer from the notorious "shuttle effect", low sulfur use ratio, and tardy transformation of lithium polysulfides (LiPSs), while using two-dimensional (2D) polar anchoring materials combined with single-atom catalysis is one of the promising methods to address these issues. Herein, the 3d transition metal (TM) doped 2D boron nitrides (BN), labeled as TM-BN, are studied for the anchoring and redox kinetics of LiPSs using first principles calculations. From the simulated results, the TM atom and adjacent N atoms are active adsorption sites for binding S atoms in LiPSs/S₈ and Li atoms in LiPSs, respectively. A negative d-band center closer to the Fermi level of TM-BN is key for enhancing the binding strength of TM-S and lowering the Li₂S decomposition energy barrier, while it deteriorates the activity of adjacent N atoms. Fortunately, the electrolyte environment has little effect on the superiority of the TM-BN for binding polysulfides/S₈, guaranteeing the sturdy anchor of polysulfides/S₈ in realistic conditions. The trade-off effect on the activities of TM and adjacent N atom sites in TM-BN for binding LiPSs highlights the excellence of Ti/V/Cr-BN as modification materials for LSB.

Prussian blue analogue/KB-derived Ni/Co/KB composite as a superior adsorption-catalysis separator modification material for Li-S batteries

Lithium‑sulfur batteries (LSBs) are gradually replacing conventional lithium-ion batteries (LIBs), credited to their high theoretical capacity, low cost, and non-toxicity. Nevertheless, the substantial capacity degradation caused by the polysulfide shuttling during charging and discharging has seriously hindered the commercialization of LSBs. Separator modification with functionalized carbon materials has been found to catalyze the breakdown of polysulfides, thereby improving the efficiency of LSBs. Herein, we synthesized Ni/Co-PBAs with KB structures to subsequently derive Ni/Co/KB composites by a carbonization process, which were later used as a modifier layer on the barrier in LSBs in order to effectively alleviate the shuttle problem. The capacity of the Ni/Co/KB composite decorated separator is found to be 1032 mAh/g at 0.5 C with a coulombic efficiency closer to 100%. In the long-term cycling capability evaluation, the initial cycle is approximately 802.9 mAh/g at 1 C, while capacity retention after 400 cycles is also 678.8 mAh/g, with a high-capacity retention rate of 84.5%. The potential of these composites as modifying materials for superior LSBs separators is verified by experimental and theoretical methods.

The Catalyst Design for Lithium-Sulfur Batteries: Roles and Routes

Lithium-sulfur battery is a promising candidate for next-generation high energy density batteries due to its ultrahigh theoretical energy density. However, it suffers from low sulfur utilization, fast capacity decay, and the notorious "shuttle effect" of lithium polysulfides (LiPSs) due to the sluggish reaction kinetics, which severely restrict its practical applications. Using the electrocatalyst can accelerate the redox reactions between sulfur, LiPSs and Li₂ S and suppress the shuttling of LiPSs, and thus, it is a promising strategy to solve the above problems, enabling the battery with high energy density and long cycling stability. In this personal account, we discuss the catalyst design for lithium-sulfur batteries according to the sulfur reduction reaction (SRR) and sulfur evolution reaction (SER) in the discharging and charging processes. The catalytic effects for each step in SRR and SER are highlighted and the homogenous catalysts, the selective catalysts, and the bidirectional catalysts are discussed, which can help guide the rational design of the catalysts and practical applications of lithium-sulfur batteries.

Mesoporous Ti4O7 nanosheets with high polar surface area for catalyzing separator to reduce the shuttle effect of soluble polysulfides in lithium-sulfur batteries

In the effort to accelerate adsorption and catalytic conversion of lithium polysulfides (Li-PSs) and suppress the shuttle effect of lithium-sulfur batteries (LSBs), the Ti 4 O 7 nanosheets/carbon material-modified separator is successfully fabricated to reducing soluble Li-PSs' crossover from cathode to anode. The catalyst of mesoporous Ti 4 O 7 nanosheets with O-Ti-O units synthesized at low temperature shows both excellent conductivity and high surface area. The modified separator can serve as a diffusion barrier of Li-PSs and catalyst for converting soluble low-chain sulfides into insoluble ones and then remarkably enhance the sulfur utilization and electrochemical performance of the LSB. This work provides a feasible avenue in both design and synthesis of mesoporous catalyst materials for suppressing the shuttle effect of lithium-sulfur batteries.

Design of advanced separators for high performance Li-S batteries using natural minerals with 1D to 3D microstructures

Lithium-sulfur (Li-S) batteries are of great interest due to their high energy density. However, polysulfides shuttle and low S loading severely impede their practical applications. Here, we report design of advanced separators for Li-S batteries using natural minerals with 1D to 3D microstructures. Four natural minerals with different microstructures including 1D halloysite nanotubes, 1D attapulgite nanorods, 2D Li⁺-montmorillonite (Mmt) nanosheets and 3D porous diatomite were used together with carbon black (CB) for preparation of the mineral/CB-Celgard separators. The Si-OH groups of the minerals act as Lewis acid sites, which could effectively absorb polysulfides by forming LiO and OS bonds with polysulfides. Among all the separators, the Mmt/CB-Celgard separator endowed the Li-S battery with the highest upper plateau discharge capacity (369 mA h g^-1), initial reversible capacity (1496 mA h g^-1 at 0.1 C), rate performance and cycling stability (666 mA h g^-1 after 500 cycles at 1.0 C with 0.046% capacity decay per cycle). The Mmt/CB-Celgard separator also enabled stable cycling of the Li-S battery with high S loading (8.3 mg cm^-2) cathode. This work will provide inspiration for future development of advanced separators for high-energy-density Li-S batteries.

Using sp2 N atom anchoring effect to prepare ultrafine vanadium nitride particles on porous nitrogen-doped carbon as cathode for lithium-sulfur battery

Porous carbon-supported transition metals and their compounds have attracted much attention as sulfur host materials for cathodes of lithium-sulfur batteries, due to their high chemisorption capacity and ability to catalyze the conversion of polysulfides. However, actual activity of these materials is not very high because of low specific surface areas of transition metal compounds synthesized at high temperatures. In this study, ultra-fine vanadium nitride particles with an average particle size of ca. 4 nm (VN/M/NC) are successfully grown on the surface of nitrogen-doped three-dimensional carbon using sp² nitrogen atoms, resulting from melamine pyrolysis in the presence of ammonium metavanadate, as anchor points to lock vanadium atoms in the VN/M/NC material. When used as a cathode for lithium-sulfur battery, VN/M/NC demonstrates initial discharge specific capacity of 1080 mAh g^-1 at 0.2 C, and retains a discharge capacity of 475 mAh g^-1 at a high rate of 2 C. With capacity attenuation of only 0.037% per cycle after 500 cycles at 1 C, the newly obtained VN/M/NC can be a promising cathode material for lithium-sulfur batteries.

Constructing MIL-101(Cr) membranes on carbon nanotube films as ion-selective interlayers for lithium-sulfur batteries

It is of significant importance to suppress the polysulfide shuttle effect for the commercial application of lithium-sulfur batteries. Herein, continuous MIL-101(Cr) membranes were successfully fabricated on carbon nanotube films utilizing a simple in-situ growth method, aiming at constructing interlayer materials for inhibiting the shuttle effect. Owing to the suitable pore aperture and super electrolyte wettability, the as-developed MIL-101(Cr) membrane can effectively inhibit the shuttle behaviour of polysulfides while allowing the fast transport of Li-ions simultaneously, working as an ionic sieve. Additionally, this MOFs membrane is also helpful in accelerating the polysulfide catalytic conversion. Therefore, the proposed interlayer delivers an extraordinary rate capability, showing a remarkable capacity of 661.9 mAh g-1 under 5 C. Meanwhile, it also exhibits a high initial capacity of 816.1 mAh g-1 at 1 C and an exceptional durability with an extremely low capacity fading of 0.046 % per cycle over 500 cycles.

Highly catalytically active CoSe2 supported on nitrogen-doped three dimensional porous carbon as a cathode for high-stability lithium-sulfur battery

Lithium-sulfur batteries, promising secondary energy storage devices, were mainly limited by its unsatisfactory cyclability owing to inefficient reversible conversion of sulfur and lithium sulfide on the cathode during the discharge/charging process. In this study, nitrogen-doped three-dimensional porous carbon material loaded with CoSe 2 nanoparticles (CoSe 2 -PNC) is developed as a cathode for lithium-sulfur battery application. A combination of CoSe 2 and nitrogen-doped porous carbon can efficiently improve the cathode activity and its conductivity, resulting in enhanced redox kinetics of the charge/discharge process. The obtained electrode exhibits a high discharge specific capacity of 1139.6 mAh g -1 at a current density of 0.2 C. After 100 cycles, its capacity remained at 865.7 mAh g -1 corresponding to a capacity retention of 75.97%. In a long-term cycling test, a discharge specific capacity of 546.7 mAh g -1 was observed after 300 cycles performed at a current density of 1 C.

Efficient capture and conversion of polysulfides by zinc protoporphyrin framework-embedded triple-layer nanofiber separator for advanced Li-S batteries

The practical application of Lithium-sulfur (Li-S) batteries is significantly inhibited by (i) the notable 'shuttle effect' of lithium polysulfides (LiPS), (ii) the corrosion of the lithium interface, and (iii) the sluggish redox reaction kinetics. The functional separator in the Li-S battery has the potential to provide the perfect solution to these problems. Herein a triple-layer multifunctional PVDF-based nanofiber separator, which contains GoTiN/PVDF layer on the top and bottom and ZnTPP/PVDF layer on the middle, is designed. The polarity and porous structure of this multifunctional separator can greatly improve the wettability of electrolytes and enhance the transportation of Li⁺. With the zinc-based porphyrin framework (ZnTPP) structure, this separator has a strong chemisorption and LiPS conversion ability, which greatly prevent the 'shuttle effect'. Consequently, the designed multilayer separator showed excellent electrochemical performance. As a result, the cell with GoTiN@ZnTPP@GoTiN nanofiber membrane displayed an initial discharge capacity of 1180 mAh/g with a benign capacity retention of 65.9% at 0.5C and high coulombic efficiency of more than 98.5% after 100 cycles. Even at 2C, it can still release a capacity of 798 mAh/g. Moreover, the remarkable capacity of 591 mAh/g could be achieved with a high sulfur load of 5.76 mg/cm² under a current density of 0.1C. Based on these merits, this novel and scalable multifunctional separator is a promising candidate to replace the conventional PP separator for advanced Li-S batteries to deal with various challenges.

Two-dimensional square metal organic framework as promising cathode material for lithium-sulfur battery with high theoretical energy density

Lithium-sulfur (Li-S) batteries are considered as new generation of energy storage which offer cost-effectiveness and high energy density. However, their commercialization is restricted due to a host of challenges associated with the cathode material which usually contains sulfur with several drawbacks, including a low electronic conductivity of sulfur, the 'shuttle effect', and a large volume expansion during discharge. Herein, a novel two-dimensional porphyrin-like square metal organic framework (MOF) was explored as a promising cathode material using first principles density function theory (DFT) assisted by genetic global search. The DFT results show that, among 7 kinds of transition-metal organic framework (TM-MOF), only V-MOF and Ru-MOF is found to possess considerable chemical interactions with S₈ and lithium polysulfides (LiPSs) in both vacuum and in electrolytic solvents, demonstrating distinguishable anchoring performance. The genetic global search and further DFT calculations indicate that the lithiation process on V-MOF exhibited a nearly constant open-circuit voltage of about 1.92 V to 1.95 V, and the theoretical energy density could reach up to 1469 Wh kg^-1 when lithiation of S₈ is considered on both sides of the substrate. The volume expansion of V-MOF during discharge is found to be about 34%, much smaller than 80% for solid sulfur. The band structure and density of states of V-MOF suggest metallic properties or a small band gap for bare surface or during the lithiation process. These results indicate that two-dimensional (2D) V-MOFs can serve as high-performance cathode material with distinguished anchoring performance to block polysulfide dissolution and thereby reduce the 'shuttle effect', and help attain ultra-high energy density. Our work points the way for designing and providing experimental realization of 2D layered materials applied in cathode with high energy density and stability.

An individual sandwich hybrid nanostructure of cobalt disulfide in-situ grown on N doped carbon layer wrapped on multi-walled carbon nanotubes for high-efficiency lithium sulfur batteries

Binding and trapping of lithium polysulfide (LPS) are being conceived as the most effective strategies to improve lithium-sulfur (Li-S) battery performance. Therefore, exploiting a simple but cost-effective approach for the absorption and conversion of LPS and the transfer of electrons and Li⁺ ions is of paramount importance. Herein, sandwich structure MWCNTs@N-doped-C@CoS₂ integrated with multiple nanostructures of zero-dimensional (0D) CoS₂ nanoparticles, 1D carbon nanotubes (CNTs), and 2D N-doped amorphous carbon layer was obtained, where MWCNTs was firstly uniformly attached with a polydopamine (PDA) of excellent adhesion, followed by hydrothermal method, the Co²⁺ nanoparticles were in-situ grown on the PDA by the formation of complex compound of Co²⁺ and N atoms in PDA, and then the CoS₂ nanoparticles were in-situ grown on CNTs in a point-surface contact way by a bridging of N-doped amorphous carbon layer derived from the carbonization of attached PDA after the vulcanization at 500 °C under Ar atmosphere. The multifunction synergism of absorption, conductivity, and the kinetics of LPS redox is significantly improved, consequently effectively suppressing the shuttle effect and tremendously increasing the utilization rate of active substance. For the Li-S battery assembled with MWCNTs@N-doped-C@CoS₂-modified separator, its rate capacity and cycling performance can be greatly enhanced. It can exhibit a high initial discharge capacity of 1590 mAh g^-1 at 0.1 C, a stable long-term cycling performance with a relatively low capacity decay of 0.07% per cycle during 500 cycles at 1 C, and a reversible capacity of 772 mAh g^-1 and a capacity decay of 0.04% per cycle during 250 cycles at 2 C. Even at a large current density of 4 C, an initial specific discharge capacity of 634 mAh g^-1 can still be delivered. With a high sulfur loading of 5.0 mg cm^-2, additionally, an outstanding cycling stability can also be well maintained at 685 mAh g^-1 at 0.1 C after 50 cycles. This work provides a novel and simple but effective strategy to develop such sandwich hybrid materials comprised of polar metal sulfides and conductive networks via an effective bridging to help realize durable and stable Li-S battery.

YF3/CoF3 co-doped 1D carbon nanofibers with dual functions of lithium polysulfudes adsorption and efficient catalytic activity as a cathode for high-performance Li-S batteries

Lithium-sulfur (Li-S) batteries have attracted extensive attention in the field of energy storage due to their high energy density and low cost. However, conundrums such as severe polarization, poor cyclic performance originating from shuttle effect of lithium polysulfides and sluggish sulfur redox kinetics are stumbling blocks for their practical application. Herein, a novel sulfur cathode integrating sulfur and polyvinylpyrrolidone(PVP)-derived N-doped porous carbon nanofibers (PCNFs) with embedded CoF₃ and YF₃ nanoparticles are designed and prepared though the electrostatic blowing technology and carbonization process. The unique flexible PCNFs with embedded polar CoF₃ and YF₃ nanoparticles not only offer enough voids for volume expansion to maintain the structural stability during the electrochemical process, but also promote the physical encapsulation and chemical entrapment of all sulfur species. Moreover, the uniform distribution of YF₃/CoF₃ nanoparticles also can expose more binding active sites to lithium polysulfide and present more catalytic sites to the greatest extent. Therefore, the assembled cells with the prepared cathode exhibited stable performances with an outstanding initial capacity of 1055.2 mAh g^-1 and an extended cycling stability of 0.029% per cycle during the 300 cycles at 0.5C. Even at a high sulfur loading of 2.1 mg cm^-2, The YF₃/CoF₃ doped-PCNFs exhibited a high discharge specific capacity of 1038 mAh g^-1, and the decay rate is also as low as 0.05% over 1000 cycles. This work shares a convenient and safe strategy for the synthesis of multi-dimension, dual-functional and stable superstructure electrode for advanced Li-S batteries.

A calcium fluoride composite reduction graphene oxide functional separator for lithium-sulfur batteries to inhibit polysulfide shuttling and mitigate lithium dendrites

Lithium-sulfur (Li-S) batteries have attracted tremendous attention as promising next-generation energy-storage systems due to their high specific capacity and high specific energy. However, the shuttle of polysulfides and the growth of Li dendrites severely obstruct the practical applications of these batteries. In this work, a functional separator is designed and fabricated in which nano-calcium fluoride (CaF₂) particles are embedded in reduced graphene oxide (rGO) and bladed on a PP separator. The density functional theory (DFT) calculations of the adsorption energy and bond length reveal that CaF₂ has a satisfying adsorption and catalytic effect on polysulfides (Li₂S_n). The factional separator could accelerate homogenous Li⁺ flow and retard the growth of Li dendrites. In addition, an initial specific capacity of 1504 mAh g^-1 at 0.05C is achieved, and it still retains a discharge capacity of 1050 mAh g^-1 over 100 cycles at 0.2C. Moreover, the capacity decay rate is only 0.06% per cycle over 420 cycles at a high current density of 0.5 C. The excellent performance could be attributed to the CaF₂@rGO modified separator not only accelerating the transmission of electrons but also effectively inhibiting the shuttling of polysulfides. This work provides a better method for attaining practical applications of high-performance lithium-sulfur batteries.

Siloxane based copolymer sulfur as binder-free cathode for advances lithium-sulfur batteries

One of the reasons why lithium-sulfur batteries have not yet been commercialized is a great attenuation of the capacity, although their theoretical capacity is ultrahigh. To alleviate this problem, we developed multifunctional organic matter, 3-aminopropyltriethoxysilane (APS), for preparing a uniform hybrid consists of silica 3D network skeleton and copolymerized sulfur nanoparticles (cpS). In this hybrid, abundant amidogen in APS induced polymerization with sulfur, which formed uniform copolymerized sulfur nanoparticles (nano sulfur), restraining the shuttle effect of polysulfides. Meanwhile, polycondensation APS not only acted as an efficiently binder, affording compact cathodes, but also formed a stable 3D silica structure to encapsulate sulfur nanoparticles, relieving the volume change of sulfur. Consequently, this binder-free cpS composite exhibited much enhanced electrochemical performances, including a high capacity of 1187.8 mAh·g^-1 at 0.1 C and a low capacity fading of 0.0654% per cycle for 500 cycles at 1 C. This study paved the way for high-energy-density batteries by simply applying a low-cost, environmentally-friendly, powerful network polymer cathode material.

High loading cotton cellulose-based aerogel self-standing electrode for Li-S batteries

Lithium-sulfur (Li-S) batteries have attracted considerable attention due to their high energy density (2600 Wh kg^-1). However, its commercialization is hindered seriously by the low loading and utilization rate of sulfur cathodes. Herein, we designed the cellulose-based graphene carbon composite aerogel (CCA) self-standing electrode to enhance the performance of Li-S batteries. The CCA contributes to the mass loading and utilization efficiency of sulfur, because of its unique physical structure: low density (0.018 g cm^-3), large specific surface area (657.85 m² g^-1), high porosity (96%), and remarkable electrolyte adsorption (42.25 times). Compared to Al (about 49%), the CCA displayed excellent sulfur use efficiency (86%) and could reach to high area capacity of 8.60 mAh cm^-2 with 9.11 mg S loading. Meanwhile, the CCA exhibits the excellent potential for pulse sensing applications due to its flexibility and superior sensitivity to electrical response signals.

All in one plasma process: From the preparation of S-C composite cathode to alleviation of polysulfide shuttle in Li-S batteries

Tremendous efforts have been made to improve the electrochemical performance of the lithium-sulfur batteries. However, challenges remain in achieving fast electronic and ionic transport while accommodate the significant cathode volumetric change. On the other hand, the severe capacity decay mainly attributed to polysulfide shuttle also hampers the practical applications. Here, we report a simple, low-cost, and eco-friendly method for the one-step preparation of a binder-free S-C composite cathode by plasma dissociation of CS₂ containing gases at room-temperature. The key issue of polysulfide shuttle effect in Li-S batteries is also effectively resolved just by the introduction of N₂ into the precursor gases. The electrode exhibits a high reversible capacity of ~600 mAh/g of the total hybrid of S + C at 100 mA/g after 100 cycles with an excellent initial coulombic efficiency of nearly 100%. The cells also demonstrate along cycle life and an extremely high capacity of ~306 mAh/g even after 300 cycles at 1 A/g with a high coulombic efficiency of about 100%. The proposed method will open the way for the plasma applications in facile preparation of Li-S batteries and the improvement of its electrochemical performance.

Polycarboxylate Functionalized Graphene/S Composite Cathodes and Modified Cathode-Facing Side Coated Separators for Advanced Lithium-Sulfur Batteries

Sulfur-hosting novel materials as a cathode for lithium-sulfur batteries are in the focus of many research to enhance the specific capacity and cycling stability. Herein, we developed composite cathodes consisting of polycarboxylate functionalized graphene (PC-FGF) doped with TiO₂ nanoparticles or poly1,5-diaminoanthraquinone (PDAAQ) and sulfur to enhance chemisorption property toward polysulfides. Additionally, PC-FGF/sulfur composite cathode functions as an efficient trapping site for polysulfides spices as well as contributes to facilitate electron and Li-ions movement toward or from the cathode. In the first experiment, the cell with sulfur incorporated TiO₂/PC-FGF cathode is assembled with three different cathode-facing side-coated glass fiber separators. At the second test, PDAAQ/PC-FGF cathode is assembled with the same separator materials as before.The best electrochemical performance observed was sulfur incorporated TiO₂/PC-FGF cathode with PDAAQ/PC-FGF-coated separator having a high discharge capacity of 1100 mAh g^- 1 at 0.5 C after 100 cycles. It is found that the combination of TiO₂/PC-FGF/sulfur cathode and PDAAQ/PC-FCF separator could serve as promising cathode and separator material due to high cycling stability and rate capability for advanced Li-S batteries.

Polyaniline-Coated Activated Carbon Aerogel/Sulfur Composite for High-performance Lithium-Sulfur Battery

An activated carbon aerogel (ACA-500) with high surface area (1765 m² g^-1), pore volume (2.04 cm³ g^-1), and hierarchical porous nanonetwork structure is prepared through direct activation of organic aerogel (RC-500) with a low potassium hydroxide ratio (1:1). Based on this substrate, a polyaniline (PANi)-coated activated carbon aerogel/sulfur (ACA-500-S@PANi) composite is prepared via a simple two-step procedure, including melt-infiltration of sublimed sulfur into ACA-500, followed by an in situ polymerization of aniline on the surface of ACA-500-S composite. The obtained ACA-500-S@PANi composite delivers a high reversible capacity up to 1208 mAh g^-1 at 0.2C and maintains 542 mAh g^-1 even at a high rate (3C). Furthermore, this composite exhibits a discharge capacity of 926 mAh g^-1 at the initial cycle and 615 mAh g^-1 after 700 cycles at 1C rate, revealing an extremely low capacity decay rate (0.48‰ per cycle). The excellent electrochemical performance of ACA-500-S@PANi can be attributed to the synergistic effect of hierarchical porous nanonetwork structure and PANi coating. Activated carbon aerogels with high surface area and unique three-dimensional (3D) interconnected hierarchical porous structure offer an efficient conductive network for sulfur, and a highly conductive PANi-coating layer further enhances conductivity of the electrode and prevents the dissolution of polysulfide species.

Metal/nanocarbon layer current collectors enhanced energy efficiency in lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries with intrinsic merits in high theoretical energy density are the most promising candidate as the next-generation power sources. The strategy to achieve a high utilization of active materials with high energy efficiency is strongly requested for practical applications with less energy loss during repeated cycling. In this contribution, a metal/nanocarbon layer current collector is proposed to enhance the redox reactions of polysulfides in a working Li-S cell. Such a concept is demonstrated by coating graphene-carbon nanotube hybrids (GNHs) on routine aluminum (Al) foil current collectors. The interfacial conductivity and adhesion between the current collector and active material are significantly enhanced. Such novel cell configuration with metal/nanocarbon layer current collectors affords abundant Li ions for rapid redox reactions with small overpotential. Consequently, the Li-S cells with nanostructured current collectors exhibit an initial discharge capacity of 1,113mAhg^-1 at 0.5C, which is ∼300mAhg^-1 higher than those without a GNH coating layer. The capacity retention is 73% for cells with GNH after 300 cycles. A reduced voltage hysteresis and a high energy efficiency of ca. 90% are therefore achieved. Moreover, the Al/GNH layer current collectors are easily implanted into current cell assembly process for energy storage devices based on complex multi-electron redox reactions (e.g., Li-S batteries, Li-O₂ batteries, fuel cells, and flow batteries).