Advanced Lithium Sulfur Batteries Research Articles

Highly electrocatalytic active amorphous Al2O3 in porous carbon assembled on carbon cloth as an independent multifunctional interlayer for advanced lithium-sulfur batteries

To realize practical applications of lithium-sulfur batteries, rational strategies have to be applied to overcome obstacles such as the shuttle effect and sluggish reaction kinetics of soluble long-chain lithium polysulfides (LPS). In this work, highly electrocatalytic active amorphous Al2O3 uniformly dispersed in porous carbon (Al2O3/C) anchored on carbon cloth (CC) was successfully fabricated. The resultant flexible Al2O3/C@CC was used as an independent interlayer for Li-S batteries, demonstrating strong physical confinement and chemical binding ability for LPS, as well as high catalytic activity for LPS conversion kinetics due to a synergistic effect of 3D conductive network, amorphous nature of Al2O3/C, porous structure and abundant active sites. The cells with such interlayer exhibit high specific capacity, superior cycling stability and rate capability, 903 mAh/g at 0.2C after 100 cycles and 810 mAh/g at 1.0C after 300 cycles can be achieved, moreover, 741 mAh/g can still be retained at a high rate of up to 5.0C. By contrast, Al-MOF grown on carbon cloth (Al-MOF@CC) exhibits limited performance improvement due to poor electrical conductivity, low structure stability, as well as limited ion diffusion rate and weak Lewis acid-base interactions due to lack of open channels.

Ultra-fine Co nanoparticles in-situ anchored on porous conductive nanosheets as efficient electrocatalysts for promoting sulfur redox reaction kinetics

Lithium-sulfur (Li-S) batteries are considered as one of the most promising energy storage devices due to their high theoretical energy density. However, the sluggish conversion kinetics and the polysulfides shuttling cause terrible capacity attenuation, impeding the practical developments. Herein, the Co/N co-doped mesoporous carbon nanosheet is developed after the pyrolysis of metal organic framework on graphene oxide layer, which is further explored as kinetics promotor towards advanced Li-S batteries. In this structure, the mesoporous carbon nanosheets with large specific surface area serve as the polysulfide trappers by physical constraint and the ultra-fine Co nanoparticles provide chemical adsorption and electrocatalytic capability for polysulfides, thus effectively suppressing the shuttle effect and accelerating the reaction kinetics. As a result, the Li-S batteries with modified kinetic modulation separators exhibit a high capacity of 585.3 mAh g−1 after 500 cycles at 1.0 C and excellent rate capability (511.2 mAh g−1 at 3 C).

Boosted Polysulfide Conversion by Co, Mn Bimetallic-Modulated Nitrogen–Carbon Material for Advanced Lithium–Sulfur Batteries

Lithium–sulfur batteries (LSBs) are regarded as one of the most promising future generation rechargeable battery energy storage devices due to their high theoretical specific capacity and energy density. However, the development of LSBs is largely influenced by the shuttle effect and slow kinetics of lithium polysulfides, which seriously hinder their commercial applications. Based on this, we propose a bimetallic modulating strategy to synthesize carbon tube embedded with Co and Mn bimetals anchored on a nitrogen-doped carbon nanosheet (Co/Mn-GC@N–C) function separator to catalytic polysulfide conversion and enhance the electrochemical performance. Co/Mn-GC@N–C possesses high electrical conductivity and large specific surface area, which can offer a lot of active sites for anchoring polysulfides, stimulating their redox reaction and quickening the electrode reaction kinetics. The comprehensive test results show that the cell with Co/Mn-GC@N–C exhibits a specific discharge capacity of 1215 mAh g–1 at 0.5C and a high Coulombic efficiency of 99.4% after 300 cycles; even the Co/Mn-GC@N–C cell with a high sulfur loading of 6.6 mg cm–2 shows a high area capacity of 5 mAh cm–2. Therefore, this bimetallic modulating strategy provides an option for the design of advanced high-performance lithium–sulfur battery separator materials.

Design and synthesis of novel pomegranate-like TiN@MXene microspheres as efficient sulfur hosts for advanced lithium sulfur batteries.

Lithium-sulfur (Li-S) batteries have the characteristics of low cost, environmental protection, and high theoretical energy density, and have broad application prospects in the new generation of electronic products. However, there are some problems that seriously hinder the Li-S batteries from going from the laboratory to the factory, such as poor stability caused by the large volume expansion of sulfur during charging and discharging, sluggish kinetics of the electrochemical reaction resulting from the low conductivity of the active materials, and loss of active materials arising from the dissolution and diffusion of the intermediate product lithium polysulfides (LiPSs). In this paper, the two-dimensional layered material MXene and TiN are firstly combined by spray drying method to prepare pomegranate-like TiN@MXene microspheres with both adsorption capacity and catalytic effect on LiPSs conversion. The interconnected skeleton composed of MXene not only solves the problem of easy stacking of MXene sheets but also ensures the uniform distribution of sulfur. Without affecting the excellent characteristics of MXene itself, the overall conductivity of the composite electrode material is improved. The TiN hollow nanospheres are coated with MXene layers to form a shell, catalyzing the adsorption of LiPSs and accelerating the transformation of high-order LiPSs to Li2S2/Li2S. As a result, the TiN@MXene cathode delivers a high initial discharge capacity of 1436 mA h g-1 at 0.1C, excellent rate performance of 636 mA h g-1 up to 3C, and an ultralong lifespan over 1000 cycles with a small capacity decay of 0.048% per cycle at the current density of 1.0C.

Novel bayberry-like functional separator coating as a physicochemical polysulfide barrier for advanced lithium–sulfur batteries

Polysulfide confinement mechanism in the ZSC cell.

Carbon nanotube-embedded hollow carbon nanofibers as efficient hosts for advanced lithium-sulfur batteries.

Lithium-sulfur (Li-S) batteries have attracted great research attention because of their high energy density and low cost. However, shuttling effects of polysulfides and insulation from elemental sulfur hinder their practical application. Herein, we report hollow carbon nanofibers filled with carbon nanotubes (denoted as HCNF/CNT) as host materials for sulfur to mitigate the shuttling behavior and improve the kinetics of insulative sulfur. The as-prepared HCNF/CNT with nano-conductive domains in the hollow carbon nanofibers enables high loading and efficient utilization of sulfur. Owing to their unique structural superiority, the sulfur-encapsulated HCNF/CNT cathode materials for Li-S batteries deliver excellent electrochemical performance, including high specific capacity of 1156 mA h g-1 at 0.2 C, good rate performance and cycling stability with a capacity retention of 77.2% after 200 cycles at 2 C. Such a unique structure can provide inspiration for the rational structural design of carbon materials as hosts for high performance Li-S batteries.

Oxygen defect-rich MnOOH nanorod as an effective modulator to boost polysulfide reaction kinetic for high-performance lithium sulfur battery

To boost the LiPSs conversion reaction for developing the high-performance lithium sulfur battery, the suitable catalyst of LiPSs redox is necessary. Herein, we designed the oxygen defect-rich MnOOH-3 nanorod as an effective modulator to regulate the LiPSs redox kinetics successfully. As a result, the derived CNT/MnOOH-3 film with successful LiPSs restriction/conversion and electron conductivity can be regarded as the superior interlayer for advanced lithium sulfur battery. After 250 cycles, the sulfur cathode with CNT/MnOOH-3 interlayer could deliver the discharge capacity of 736.9 mAh/g with a capacity retention ratio of 82.3%, which is higher than the cathodes with other interlayers. This result confirms that defect engineering is a promising strategy to prepare the potent catalytic additive for lithium sulfur battery.

Functional CNTs@EMIM+ -Br- Electrode Enabling Polysulfides Confining and Deposition Regulating for Solid-State Li-Sulfur Battery.

With an extremely high theoretical energy density, poly(ethylene oxide) (PEO)-based solid-state lithium-sulfur (Li-S) batteries are emerging as one of the most feasible and safest battery storage systems. However, the long-term cycling performance is severely impeded by polysulfides (Li2 Sn , n=4-8) shuttling and terrible electrode passivation from the electronic insulating Li2 S. Here, a novel cathode through chemically grafted 1-Ethyl-3-methylimidazolium bromide (EMIM+ -Br- ) to carbon nanotube (CNTs) for PEO-based Li-S batteries is reported (CNTs@EMIM-Br/S). Concretely, bi-functional mediator EMIM+ -Br- not only inhibits the polysulfides shuttling by strong chemical interactions via EMIM+ , but also facilitates the electrochemical kinetics for promoting the formation of 3D particulate Li2 S through high donor anion (Br- ). Satisfactorily, dual-function CNTs@EMIM-Br/S cathode exhibits high sulfur utilization with the capacity of up to 1298mAhg-1 , and keeps high capacity retention of 80.2% at 0.2C after 350 cycles, exceeding that of many reported PEO-based solid-state Li-S batteries. This work will open a new door for rationally designed architecture to enable the practical applications of advanced Li-S batteries.

Tuning the surface structure of CeO2 nanoparticles by chlorine-doped strategy to improve the polysulfide reaction kinetic for lithium sulfur battery

Boosting the reaction kinetics of sulfur cathode is a key strategy to develop the advanced lithium sulfur battery. Herein, we proposed a chlorine-modified strategy to regulate the LiPSs redox kinetics on CeO2 nanoparticle surface successfully. As a result, the derived CNT/CeO2-Cl composite with successful LiPSs restriction/conversion and electron conductivity can be regarded as the sulfur host material and the CNT/CeO2-Cl/S cathode exhibits superior electrochemical performance. Over 200 cycles, the CNT/CeO2-Cl/S could deliver the discharge capacity of 820.8 mAh/g with a capacity retention ratio of 82.9 %, which is higher than other cathodes. This result confirms the promising application foreground of CNT/CeO2-Cl for advanced lithium sulfur battery.

Scalable fabrication of Ni(OH)2/carbon/polypropylene separators for high-performance Li-S batteries

Lithium-sulfur (Li-S) batteries are one of the most promising energy storage systems due to their attractive features of high energy density, low cost, and environmental friendliness. However, the shuttle effect of lithium polysulfides stays an obstacle for the further advancement of Li-S batteries. Herein, a novel Ni(OH)2/carbon/ Polypropylene(Ni(OH)2/C/PP) separator was prepared and applied in Li-S batteries to alleviate the shuttle issue. The Ni(OH)2/C/PP separator was constructed through vacuum filtration coating a super thin layer of super P(0.007 mg cm–2) on the Celgard 2325 followed by decorating the carbon layer with Ni(OH)2 nanosheets film formed by a scalable gas-liquid diffusion method. Influence of Ni(OH)2/C on surface hydrophilicity, polysulfide permeability and catalytic effect on polysulfide conversion have been investigated. The results of contact angle, permeation test of Li2S6, XPS S2p spectra, symmetric Li2S6 cells, Li+ ion diffusion coefficient and Tafel slope confirmed that the Ni(OH)2/C/PP greatly improved the wettability for better penetration of electrolyte, lowered polysulfide permeability to retard its diffusion, and enhanced catalytic effect for the polysulfide conversion to boost the electrochemical kinetics. Thus, compared with the bare PP separator, the Ni(OH)2/C/PP separator enabled significantly increased capacity (1153 vs. 703 mAh g−1 at 0.2 C), greatly enhanced rate performance (816 vs. 381 mAh g−1 at 2 C) and satisfactory cyclability ( 0.10% decay rate after 500 cycles). This study provides a feasible separator modification approach for advanced Li-S batteries.

Cocklebur-like ZnSe-VO2@rGO nanostructures as host to boost the performance of lithium-sulfur batteries

Although lithium sulfur batteries (LSBs) have high theoretical capacity and energy density, low conductivity of sulfur and the discharge species (Li2S2, Li2S), the polysulfide shuttle and the large volume change hinder the commercialization of LSBs. To tackle the problem, we hydrothermally prepared a special cocklebur-like ZnSe-VO2@rGO nanostructure, in which graphene oxide (GO) is active in inducing thorn-like VO2 nanorods grown on carambola-like VO2 nanostructures. In this structure, the polar VO2 and ZnSe quantum dots (QDs) have strong chemical adsorption that can catalyze the polysulfide conversion and alleviate the shuttle effect; besides, the thorn-like VO2 nanorods act like numerous tentacles that capture polysulfides by increasing the contact area, and the reduced graphene oxide (rGO) nanosheets not only buffer the volume change, but also enhance the conductivity of the framework and improve the ion and electron transfer. Boosted by the synergetic effects of VO2, rGO and ZnSe QDs, the ZnSe-VO2@rGO/S cathode achieves a high specific capacity of 1026.1 mA h g−1 at 0.2 C and 712.3 mA h g−1 at 2 C. Good cyclic stability was obtained as well, with a high reversible capacity of 820 mA h g−1 and high retention of 89.1 % after cycling at 0.5 C for 150 cycles. Such outstanding performance indicated its good potential for use in advanced LSBs.

Electrostatic Potential-Induced Co-N4 Active Centers in a 2D Conductive Metal-Organic Framework for High-Performance Lithium-Sulfur Batteries.

The use of single-atom catalysts is a promising approach to solve the issues of polysulfide shuttle and sluggish conversion chemistry in lithium-sulfur (Li-S) batteries. However, a single-atom catalyst usually contains a low content of active centers because more metal ions lead to generation of aggregation or the formation of nonatomic catalysts. Herein, a 2D conductive metal-organic framework [Co3(HITP)2] with abundant and periodic Co-N4 centers was decorated on carbon fiber paper as a functional interlayer for advanced Li-S batteries. The Co3(HITP)2-decorated interlayer exhibits a chemical anchoring effect and facilitates conversion kinetics, thus effectively restraining the polysulfide shuttle effect. Density functional theory calculations demonstrate that the Co-N4 centers in Co3(HITP)2 feature more intense electron density and more negative electrostatic potential distribution than those in the carbon matrix as the single-atom catalyst, thereby promoting the electrochemical performance due to the lower reaction Gibbs free energies and decomposition energy barriers. As a result, the optimized batteries deliver a high rate capacity of over 400 mA h g-1 at 4 C current and a satisfying capacity decay rate of 0.028% per cycle over 1000 cycles at 1 C. The designed Co3(HITP)2-decorated interlayer was used to prepare one of the most advanced Li-S batteries with excellent performance (reversible capacity of 762 mA h g-1 and 79.6% capacity retention over 500 cycles) under high-temperature conditions, implying its great potential for practical applications.

Surface Defect Engineering of a Bimetallic Oxide Precatalyst Enables Kinetics-Enhanced Lithium-Sulfur Batteries.

Developing efficient electrocatalysts to accelerate the sluggish conversion of lithium polysulfides (LiPSs) is of paramount importance for improving the performances of lithium-sulfur (Li-S) batteries. However, a consensus has not yet been reached on the in situ evolution of the electrocatalysts as well as the real catalytic active sites. Herein, defective MnV2O6 (D-MVO) is designed as a precatalyst toward LiPSs' adsorption and conversion. We reveal that the introduction of surface V defects can effectively accelerate the in situ sulfurization of D-MVO during the electrochemical cycling process, which acts as the real electrocatalyst for LiPSs' retention and catalysis. The in situ-sulfurized D-MVO demonstrates much higher electrocatalytic activity than the defect-free MVO toward LiPSs' redox conversion. With these merits, the Li-S batteries with D-MVO separators achieve superior long-term cycling performance with a low decay rate of 0.056% per cycle after 1000 cycles at 1C. Even under an elevated sulfur loading of 5.5 mg cm-2, a high areal capacity of 4.21 mAh cm-2 is still retained after 50 cycles at 0.1C. This work deepens the cognition of the dynamic evolution of the electrocatalysts and provides a favorable strategy for designing efficient precatalysts for advanced Li-S batteries using defect engineering.

Tuning Li nucleation and growth via oxygen vacancy-enriched 3D flexible self-supporting protection layer of P-Mn3O4−x for advanced lithium-sulfur batteries

Lithium sulfur batteries have attracted much attention due to their high theoretical specific energy and environmental friendliness. However, the practical application is severely plagued by the cycling life issues resulting from the uncontrollable generation and growth of Li dendrites. Herein, an innovative 3D flexible self-supporting Li anode protection layer of P-Mn3O4−x is constructed via a facile solvothermal method followed by an annealing process. Benefiting from the rich oxygen vacancies coupled with the 3D flexible self-supporting skeleton, abundant lithiophilic sites and high ionic conductivity are obtained, which succeed in guiding Li+ homogeneous adsorption and redistribution, accelerating Li+ diffusion rate, inducing Li+ uniform deposition and nucleation. DFT calculations and experimental results conclusively demonstrate such a protection mechanism. Meanwhile, the effective anchoring and catalytic nature of polar P-Mn3O4−x can also be applied as an immobilization-diffusion-conversion host to improve polysulfides redox. Taking advantage of these merits, super-stable functions for Li symmetric cell matched with P-Mn3O4−x layer are achieved, which exhibits an ultralong lifespan of >5000 h with an ultralow overpotential of 20 mV, far lower than that of bare Li symmetric cell (overpotential of 800 mV only after 250 h) at high current densities of 5 mA cm−2 and high plating/stripping capacity of 10 mA h cm−2. Even in Li|P-Mn3O4−x||S full cell at 1 C, a high initial discharge specific capacity of 843.1 mA h g−1 is still delivered with ultralow capacity fading rate of 0.07% per cycle after 250 cycles, further confirming the synergistic regulation of P-Mn3O4−x for Li nucleation behavior. This work illustrates a sufficient guarantee of 3D protection layer coupled with oxygen vacancies in guiding Li diffusion and nucleation behavior and provides new guidance for promoting the development of advanced Li-S batteries.

Transition Metal−N/Graphene for advanced Lithium–Sulfur Batteries: A first principles study

Developing highly efficient anchoring materials with strong adsorption to lithium polysulfides to suppress ‘shuttling effect’ is crucial to address the short cycling life issue of lithium sulfur batteries. Herein, we systematically investigated transition metal, nitrogen co-doped graphene as host materials for sulfur cathode via first-principles study. The computation results reveal that TM2–NC materials have higher adsorption energy to lithium polysulfides than TM–NC materials. Fe2–NC is one of the most promising anchoring materials, where robust Fe–S and N–Li bonds ensure the stable adsorption of all LiPSs.

Nickel Cobalt Oxide Decorated Cerium Oxide Nanorods for Polysulfide Trapping and Catalytic Conversion in Advanced Lithium Sulfur Batteries

Lithium sulfur batteries (LSBs) are promising candidates for next-generation rechargeable batteries due to the active material sulfur being earth abundant, low cost and environmentally friendly element. But the most important feature of LSBs is that the theoretical capacity of sulfur is ~1645 mAh g-1 which is ~5 times higher than the conventional lithium-ion batteries. However, even with these valuable assets, LSB has not yet been commercialized due to the inherent problems of fast capacity loss resulting in low cycle lifetime. This capacity loss originates from the migration of dissolved sulfur discharge products in the electrolyte known as the notorious polysulfide shuttling effect.To deal with this issue, several research efforts have been made to trap the high order lithium polysulfides by a) physically encapsulation using high surface area carbonaceous materials and b) chemically binding the lithium polysulfides in its cathode host. Several materials are very popular to efficiently bind the lithium polysulfides such as transition metal oxides, nitrides, sulfides and have helped making significant advances to long cycle life lithium sulfur batteries. However, to make the transition to design next generation LSBs, there is a need for materials that can facilitate fast polysulfide conversion by catalytic reaction that will reduce the diffusion and agglomeration of polysulfides in the liquid organic electrolyte, resulting in high capacity and long cycle lifetime.With this strategy in mind, we have designed NiCoOx decorated on CeO2 nanorods support as cathode host material for LSBs to provide dual adsorption-catalysis synergy. The CeO2 nanorods with enriched surface defects can effectively bind the lithium polysulfides whereas the NiCoOx nanoclusters can provide highly efficient electrocatalytic sites to improve the conversion kinetics of elemental sulfur to high order lithium polysulfides to finally the lower order polysulfides. As a result, the derived LSBs exhibited excellent electrochemical performance with high capacity of 1236 mAh g-1 at 0.2C with a sulfur loading of 1.33 mg cm-2. Even with high sulfur loading 2.66 mg cm-2 the LSBs exhibits 755 mAh g-1 at 0.2C with a capacity decay of only 0.08% per cycle after 170 cycles. The battery also operates at the sulfur loading of 4 mg cm-2 and 5.33 mg cm-2 for more than 100 which is convincing considering commercialization of LSB. Key words: lithium sulfur batteries, lithium polysulfides, shuttle effect, cerium oxide, catalysis.

(Digital Presentation) A Design of Nickel/Sulfur Energy-Storage Materials for Electrochemical Lithium-Sulfur Cells

Introduction As one of the next-generation rechargeable battery technologies beyond the lithium-ion chemistry, the lithium-sulfur chemistry enables the low-cost sulfur cathode to generate a high theoretical capacity of 1,675 mAh g-1 (10 times higher capacity than those of lithium-ion battery cathode). It further exhibits a high theoretical energy density of 2,600 Wh kg-1 in lithium-sulfur batteries (2–3 times higher energy density than lithium-ion batteries). However, as reported in recent publications, the development is far from adequate with respect to the high-loading sulfur cathode with high active-material content in building advanced lithium-sulfur batteries with a high energy density. The material challenges result from the use of an insulating sulfur as the active material, which would generate lithium polysulfides that can easily diffuse out from the cathode. The high cathode resistance and fast loss of the active material lead to the poor electrochemical utilization and efficiency of lithium-sulfur battery cathodes. These negative impacts subsequent derive the additional electrochemical challenges. A high amount of conductive and porous substrates is added in the cathode to replace the active material, which results in the limited amount of sulfur in the cathode and further blocks the improvement of designing high-energy-density sulfur cathodes.To address the above-mentioned issues, the research progresses of high-performance sulfur cathodes aim to design functional host for sulfur cathodes with the use of carbon for high conductivity, polymers for high ionic transfer, porous materials for physical polysulfide retention, polar materials for chemical polysulfide adsorption, catalysts for high reaction kinetics, etc. However, metallic materials that naturally have high conductivity, strong polysulfide adsorption capability, and catalytic conversion ability, are rarely reported. This is because metals have the highest density as compared to the aforementioned host materials, which commonly causes an insufficient amount of active material in the cathode and therefore inhibits the design of metal-sulfur nanocomposite in sulfur cathodes.To explore the metal/sulfur nanocomposite as a new research trend in sulfur cathodes, we propose a design for a nickel/sulfur nanocomposite as a novel energy-storage material by the electroless nickel plating method, and discuss its applications in lithium–sulfur battery cathodes. The nickel/sulfur energy-storage material possesses metallic nickel on the surface of the insulating sulfur particles as a result of the reduction of nickel ions during autocatalytic plating. By controlling the synthesis and fabrications conditions, the nickel/sulfur energy-storage material attains adjustable high sulfur contents of 60–95 wt% and adjustable high sulfur loadings of 2–10 mg cm−2 in the resulting cathode. The high-loading cathode with the nickel/sulfur energy-storage material demonstrates high electrochemical utilization and stability, which attains a high areal capacity of 8.2 mA∙h cm−2, an energy density of 17.3 mW∙h cm−2, and a stable cyclability for 100 cycles. Results and Discussion Here, in our presentation, we discuss our novel method for the fabrication of nickel/sulfur energy-storage material as an advanced composite cathode material for exploring battery electrochemistry and battery engineering. We adopt a modified electroless-plating method to synthesize nickel/sulfur energy-storage materials characterized by adjustable high sulfur contents and promising cathode performance. The plated nickel coating provides the nickel/sulfur energy-storage materials with metallic conductivity and polysulfide adsorption ability, which addresses the two major issues of sulfur cathodes.[1,2] Therefore, the nickel/sulfur energy-storage material attains high sulfur contents in the cathode and exhibits a high charge-storage capacity of 1,362 mA∙h g−1 and an excellent cyclability for 100 cycles. Moreover, the nickel/sulfur energy-storage material enables high-loading sulfur cathodes with a sulfur loading of 10 mg cm−2, a high areal capacity of 8.2 mA∙h cm−2, and an energy density of 17.3 mW∙h cm−2. Conclusion In summary, the summary of our nickel/sulfur energy-storage materials presented in this presentation would demonstrate a light-weight metallic nickel coating technique for fast charge transfer and strong polysulfide retention in the sulfur nanocomposites composite sulfur cathode. Moreover, our systematic analysis of the nickel/sulfur energy-storage materials exhibits their achievements in attaining both high electrochemical designs of high sulfur content and loading as well as possessing high energy density and electrochemical stability. References C.-S. Cheng, S.-H. Chung, Chem. Eng. J. 2022, 429, 132257.C.-S. Cheng, S.-H. Chung, Batter. Supercaps 2022, 5, e202100323.

Melamine-Sacrificed Pyrolytic Synthesis of Spiderweb-like Nanocages Encapsulated with Catalytic Co Atoms as Cathode for Advanced Li-S Batteries

Due to the high theoretical capacity of 1675 mAh g−1 of sulfur, lithium-sulfur (Li-S) batteries can reach a high energy density of 2600 Wh kg−1, which has shown fascinating potential in recent decades. Herein, we report the spiderweb-like nanocage (Co/Mel) as a novel sulfur host with a melamine-sacrificed pyrolysis method. The incorporation of embedded cobalt nanoparticles (Co NPs) in the tips of carbon nanotubes (CNTs) can catalyze polysulfide transformation kinetics. In addition, the nanocages form a conductive three-dimensional spiderweb-like network that facilitates electrolytic penetration and electronic/ionic transportation. Moreover, the porous internal nano-cavities not only improve sulfur loading levels but also provide buffer space for volume expansion during charging and discharging. As a result, the hollow Co/Mel polyhedra with a high content of sulfur (75.5 wt%) displays outstanding electrochemical performance with an initial discharge-specific capacity of 1425.2 mAh g−1 at 0.1 C and a low decay rate of only 0.028% after 1000 cycles at 1 C.

Rational design of ultrathin Mo2C/C nanosheets decorated on mesoporous hollow carbon spheres as a multifunctional sulfur host for advanced Li-S batteries

Developing sulfur hosts with reasonable structure and effective catalyst is essential for lithium-sulfur (Li-S) batteries. Herein, a novel multifunctional sulfur host composed of hollow carbon spheres with mesoporous channels (MHCS) coupled with few ultrathin Mo2C/C nanosheets embedded with Mo2C nanocrystals ([email protected]2C/C) has been prepared via one-pot self-assembly and in-situ grown strategies. The Mo2C/C nanosheets with heterostructure can shorten the electron/ion transport path, and ultra-small Mo2C nanocrystals with abundant active sites contribute to enhancing chemical adsorption towards polysulfides and propel their conversion. Meanwhile, the MHCS facilitates physical adsorption towards polysulfides, effective sulfur/electrolyte permeation, fast electron/ion transportation, and sufficient buffering for volume change. Given these, the multifunctional [email protected]2C/C-S cathode demonstrates an initial specific capacity of 1316.8 mAh g−1 at 0.1 C and outstanding cycling stability with an average capacity decay rate of 0.045 % for 500 cycles at 0.5 C. Moreover, [email protected]2C/C-S cathode with high areal sulfur loading of 4.5 mg cm−2 can deliver a high initial discharge specific capacity of 797.4 mAh g−1, and a reversible capacity of 542.7 mAh g−1 after 500 cycles at 0.5 C. It is expected this work could provide a new perspective to the rational design of sulfur hosts for Li-S batteries with enhanced performance.

Efficient polysulfides trapping and redox enabled by Co/N-carbon implanted Li+-montmorillonite for advanced lithium-sulfur batteries

Li-S batteries are very promising next-generation energy storage systems due to their high theoretical capacity and energy density, but suffer from sluggish redox kinetics and serious polysulfides (PS) shuttle. Herein, Co/N-carbon implanted Li+-montmorillonite (Co/NC@Li-MMT) is designed to inhibit PS shuttle and maximize PS redox kinetics in Li-S battery. The Co/NC@Li-MMT 2D nanomaterial is fabricated by exfoliation of the Li-MMT nanosheets using melamine and Co(II)(acac)2, followed by one-step thermal reduction. The exfoliated Co/NC@Li-MMT with high Li+ and electrical conductivity can expose abundant active sites for efficient PS adsorption via Co-S and Si-S and Li bonds and for fast PS electrocatalytic conversion via Co and CoNC catalytic active sites. The Co/NC@Li-MMT modified PP (Co/NC@Li-MMT@PP) separator with a thin Co/NC@Li-MMT layer of 2.2 μm (0.3 mg cm−2 mass loading) features high Li+ conductivity, fast Li+ diffusion, superior electrolyte wettability as well as efficient PS trapping and fast PS redox kinetics as verified by various analytical techniques. Consequently, the Li-S battery with the Co/NC@Li-MMT@PP separator shows high initial capacity (1447 mAh/g), good rate performance, excellent cycling stability (0.027 % capacity fade per cycle at 1C over 300 cycles) and ultralow self-discharge.