Application Of Li-S Batteries Research Articles

Universal, minute-scale synthesis of transition metal compound nanocatalysts via graphene-microwave system for enhancing sulfur kinetics in lithium-sulfur batteries

The application of Li-S batteries on large scale is held back by the sluggish sulfur kinetics and low synthesis efficiency of sulfur host. In addition, the preparation of catalysts that promote polysulfide redox kinetics is complex and time-consuming, reducing the cost of raw materials in Li-S. Here, a universal synthetic strategy for rapid fabrication of sulfur cathode and metal compounds nanocatalysts is reported based on microwave heating of graphene. Heat-sensitive materials can achieve rapid heating due to graphene reaching 500 ℃ within 4 s via microwave irradiation. The MoP-MoS2/rGO catalyst demonstrated in this work was synthesized within 60 s. When used for catalysts for Li-S batteries whose graphene/sulfur cathodes were also synthesized by microwave heating, enhanced catalytic effect for sulfur redox reaction was verified via experimental and DFT theoretical results. Benefiting from fast redox reaction (MoP), smooth Li+ diffusion pathways (MoS2), and large conductive network (rGO), the assembled Li-S battery with MoP-MoS2/rGO-Add@CS displays a remarkable initial specific capacity, stable lithium anode and good cycle stability (in pouch cells) using this two-pronged strategy. The work provides a practical strategy for advanced Li-S batteries toward a wide range of applications.

Two-dimensional SnP3 monolayer for inhibiting the shuttle effect in lithium-sulfur batteries: A first-principles study

The problems of the shuttle effect and sluggish transformation kinetics of lithium polysulfides (LiPSs) severely inhibit the practical application of Li-S batteries. Exploring anchoring materials with catalytic properties is an effective way to overcome these obstacles. In this paper, the electrochemical performance of SnP3 monolayer as an anchoring material is explored by using first-principles calculations. SnP3 monolayer can effectively anchor soluble LiPSs under vacuum and solvent conditions, and provides abundant adsorption sites for anchoring multiple LiPSs. Importantly, the rate-limiting step has changed to the conversion of Li2S8 to Li2S6, suggesting that the monolayer can facilitate the conversion of LiPSs and inhibit their accumulation in the electrolyte. Furthermore, lower decomposition and diffusion barriers of Li2S effectively inhibit the volume expansion of Li-S batteries. Thus, SnP3 monolayer becomes a promising anchoring material with suitable catalytic properties. This work demonstrates the feasibility of SnP3 monolayer as an anchoring material and expands the membership of phosphide family for applications in the field of Li-S batteries.

In-situ constructing cathode protective film toward high performance of Li-S batteries at high sulfur loadings

Shuttle effect of lithium polysulfide (LiPSs) and low sulfur loadings encumber practical application of Li-S batteries. Sulfur cathode coating is a direct and effective strategy to alleviate the problem. However, it is difficult for the available ex-situ coating to suppress shuttle effect at high sulfur surface loading. In the present work, diphenylamine (DPA) is used as an electrolyte additive, which can undergo electropolymerization and form an in-situ PDPA film on sulfur cathode, thereby inhibiting LiPSs diffusion. More importantly, computations and experiments prove that DPA-LiPSs complexes are formed in the electrolyte, increasing the solubility of LiPSs and improving the conversion kinetics. Benefit from the above, the capacity of DPA battery reaches 1029.5 mAh g−1 with sulfur loading of 3 mg cm−2 at 1 C rate, and keeps 762.1 mAh g−1 after 1000 cycles. Excellent cycling performance is achieved even at a high sulfur loading of up to 7 mg cm−2. This work provides a new strategy for suppressing the LiPSs shuttle effect under high sulfur surface loadings.

Encapsulating Sulfur into a Gel-Derived Nitrogen-Doped Mesoporous and Microporous Carbon Sponge for High-Performance Lithium-Sulfur Batteries.

The practical application of Li-S batteries (LSBs) has long been impeded by the inefficient utilization of sulfur and slow kinetics. Utilizing conductive carbonaceous frameworks as a host scaffold presents an efficient and cost-effective approach to enhance sulfur utilization for redox reactions in LSBs. However, the interaction of pure carbon materials with lithium polysulfide intermediates (LiPSs) is limited to weak van der Waals forces. Hence, the development of an economical method for synthesizing heteroatom-doped carbon materials for sulfur fixation is of paramount importance. In this study, we introduce a hierarchical porous nitrogen-doped carbon sponge (NPCS) with an exceptionally high BET surface area of 3182.2 m2 g-1, achieved through a facile template-assisted polymerization method. The incorporation of inorganic salts, free radical polymerization, and deuteric freeze-drying techniques facilitates the formation of hierarchical pores within the NPCS. After sulfur fixation, the resulting S/NPCS electrode demonstrates remarkable electrochemical performance in LSBs. Specifically, it achieves an 80% sulfur utilization rate, maintains a high reversible specific capacity of 400 mA h g-1 even after 600 cycles at a demanding current density of 5.0 A g-1, and exhibits superior rate capability. It is believed that this work will inspire the rational design of cost-effective carbon-based electrodes for high-performance LSBs.

Preparing of N-P dual-doped auricularia auricula carbon host by yeast fermentation and its application in Li-S batteries

A nitrogen-phosphorus dual-doped auricularia auricula carbon (NP-AC) matrix was prepared through hydrothermal treatment using natural auricularia auricula as raw material and medium solution. Yeast was introduced and cultured by the auricularia auricula liquid medium. The NP-AC/S composite was prepared through further freeze-drying, carbonization, activation and compounding with sulfur procedures. The composition and microstructure of samples was characterized by X-ray diffraction (XRD), raman and X-ray photoelectron spectroscopy (XPS). The morphology was observed under scanning electron microscope (SEM) and transmission electron microscopy (TEM) method. The specific surface area was analyzed using nitrogen adsorption/desorption test. The weight ratio of sulfur was measured through thermogravimetric (TG) analysis. The original structure and composition of biomass were improved by yeast fermentation and the auricularia auricula block structure with low porosity was modified. The electrochemical performance of NP-AC/S composite in Li-S batteries was systematically explored. After 100 cycles at 0.2C current density, there was still nearly 1000 mAh g−1 reversible capacity, holding a capacity retention rate of more than 84 %. The cycle performance and rate performance were both far better than the ordinary activated carbon materials.

Enhanced polysulfide regulation of lithium-sulfur batteries by ZnS-SnO2 nano-heterostructures

Lithium–sulfur (Li–S) battery is recognized as the most promising next-generation energy storage system due to its high theoretical capacity and energy density. However, the shuttle effect of lithium polysulfides (LiPSs) and the sluggish electrochemical reaction kinetics severely hinder its practical application. In this study, a hierarchical porous carbon (HPC) conductive framework loaded with ZnS-SnO2 heterostructures (ZnS-SnO2/HPC) in situ was designed for application in Li-S batteries. The ZnS-SnO2/HPC combines the advantages of physical confinement, chemical anchoring, and rapid electron/ion migration to inhibit the shuttling of LiPSs while ensuring its rapid conversion, achieving effective regulation of the electrochemical behavior of LiPSs. The obtained lithium-sulfur battery has significantly improved electrochemical properties: high reversible capacity (868.2 mAh g−1 after 100 cycles at 0.2 C), excellent rate capacity (841.5 mAh g−1 at 3 C), and low self-discharge capacity loss (97% capacity retention after 5 days of standing). In addition, the synergistic effect also helps to improve the cycle stability, with a capacity fading rate of only 0.079% per cycle over 500 cycles at 1 C.

CAU-17 derived bismuth nanoparticles embedded in nitrogen doped carbon belts as catalyst layer on separator for high performance Li-S batteries

Sluggish polysulfide conversion (SPC) process combined with shuttling effect and poor electronic conductivity of sulfur become the main obstacles in hindering the commercial application of Li-S battery. In this study, to address these issues, CAU-17 derived bismuth nanoparticels embedded in nitrogen doped carbon belts is proposed as a catalyst layer on separator for high performance Li-S batteries. By incorporating the excellent electronic conductivity of bismuth metal nanoparticles, the abundant polar adsorption sites of nitrogen-doped carbon belts, and tailored adsorption space on such “metal-carbon hybrid architecture”, the promotion of the polysulfide nucleation as well as effective conversion efficiency in SPC process have been achieved. Density functional theory computation further confirms the enhanced adsorption energy of bismuth nanoparticles to dissolved polysulfides during SPC process. Benefitting from the unique architecture and rational catalytic design, the Li-S battery with bismuth nanoparticles embedded in nitrogen doped carbon belts modified separator possesses a high specific capacity of 1045 mAh g−1 at 0.2 C and maintains a satisfactory specific capacity of 612.8 mAh g−1 at 4.0 C. Simultaneously, the decent high-rate cycling stability is achieved after 500 cycles. This work deepens the understanding of designing a metallic-based electrocatalyst layer on separator for high performance Li-S battery.

Boosting Polysulfide Redox Kinetics by Temperature-Induced Metal-Insulator Transition Effect of Tungsten-Doped Vanadium Dioxide for High-Temperature Lithium-Sulfur Batteries.

The practical application of Li-S batteries is still severely restricted by poor cyclic performance caused by the intrinsic polysulfides shuttle effect, which is even more severe under the high-temperature condition owing to the inevitable increase of polysulfides' solubility and diffusion rate. Herein, tungsten-doped vanadium dioxide (W-VO2) micro-flowers are employed with first-order metal-insulator phase transition (MIT) property as a robust and multifunctional modification layer to hamper the shuttle effect and simultaneously improve the thermotolerance of the common separator. Tungsten doping significantly reduces the transition temperature from 68 to 35 °C of vanadium dioxide, which renders the W-VO2 easier to turn from the insulating monoclinic phase into the metallic rutile phase. The systematic experiments and theoretical analysis demonstrate that the temperature-induced in-suit MIT property endows the W-VO2 catalyst with strong chemisorption against polysulfides, low energy barrier for liquid-to-solid conversion, and outstanding diffusion kinetics of Li-ion under high temperatures. Benefiting from these advantages, the Li-S batteries with W-VO2 modified separator exhibit significantly improved rate and long-term cyclic performance under 50°C. Remarkably, even at an elevated temperature (80°C), they still exhibit superior electrochemical performance. This work opens a rewarding avenue to use phase-changing materials for high-temperature Li-S batteries.

Highly dispersed conductive and electrocatalytic mediators enabling rapid polysulfides conversion for lithium sulfur batteries

The practical application of Li-S batteries encounters hurdles in maintaining cycling durability and rate capability under realistic conditions. Electrostatic self-assembly stands as a captivating avenue for exploring new frontiers in nanoscale catalysis. Leveraging renewable bio-oil both as a carbon source and self-polymerization precursor, ultrafine Mo2C nanocrystals anchored on bio-oil-derived 3D hierarchical carbon matrix (Mo2C@BOC) are fabricated by a facile NaCl template-assisted electrostatic self-assembly and followed annealing procedure. Densely anchored ultrafine Mo2C nanocrystals, intertwined with highly conductive carbon nanosheets, unveil an enhanced exposure of catalytically active sites for lithium polysulfide immobilization, conversion, and supply amply nucleation sites to mediate the fast precipitation of Li2S2/Li2S. Attributed to these favorable features, Li-S cells based on the as-designed catalytic host attain satisfactory cyclability with a minimum capacity fading rate of 0.0144 % over 1000 cycles and excellent rate capability. Decent performance can be achieved even at a high sulfur loading of 8.0 mg cm−2 and a low electrolyte-to-sulfur ratio of 3.5 µL mg−1. This strategy for solving the shuttle effect under high sulfur loading provides a promising solution for the further development of high-performance Li-S batteries. This work provides a rational strategy for solving the shuttle effect under high sulfur loading and sheds light on the great potential of Mo2C@BOC for developing more practical Li-S batteries.

MoO2/t-C3N4 Heterogeneous Materials with Bidirectional Catalysis for the Rapid Conversion of S Species in Li-S Batteries.

Li-S batteries have drawn a lot of attention for their high theoretical specific capacity and significant economic benefits. However, the shuttle effect of polysulfides prevents them from being used widely. To tackle this difficulty, a heterogeneous structure based on tubular carbon nitride with evenly dispersed molybdenum dioxide nanoparticles (MoO2/t-C3N4) as the S host is constructed in this work. As a polar material with a large specific surface area, MoO2/t-C3N4 has a strong anchoring effect on polysulfide. Additionally, the heterogeneous material has excellent bidirectional catalytic ability for the redox process of S species based on the action of the built-in electric field formed by electron directional transfer. Not only does it improve the reaction kinetics of the redox process of the polysulfides but it also prevents polysulfides from accumulating on the surface of the modified material and deactivating it, further improving the utilization of the active material. Thus, MoO2/t-C3N4/S shows the high initial-discharge specific capacity of 812.7 mAh g-1 at the current density of 5C, and the Coulombic efficiency is maintained at more than 95% after 400 charge/discharge cycles. Moreover, MoO2/t-C3N4/S achieved a capacity retention of 89% after 100 cycles at the current density of 0.1C under the high S loading. Therefore, the research results of this work provide a trustworthy reference for the future commercial application of Li-S batteries.

Investigation of the Reaction Mechanism of All-Solid-State Lithium-Sulfur Batteries by Operando in Situ Raman Spectroscopy

In recent years, all-solid-state lithium-sulfur batteries (ASSLSBs) with sulfide-based solid electrolytes have become a leading energy storage system due to their high ionic conductivity, ultra-high energy density, high safety, and low cost. There have been many challenges with the practical applications of Li-S batteries, however, as a result of the sluggish redox kinetics of lithium polysulfide (LPS) and its shuttling effects. Single-atom catalysts (SACs) with atomically dispersed metal-based sites have proven to be promising electrocatalysts in Li-S batteries. To construct the ASSLSBs, we design and develop MoS2/SnS2 and Fe SACs with MoS2/SnS2 cathodes, Li5.4PS4.4Cl1.6 sulfide-based solid electrolytes, and Li-In anode. In the current study, in situ Raman spectroscopy is used to determine the LPS species in the sulfur cathode with SACs and without SACs during the ASSLSBs cycling. The aim is to understand the charge-discharge mechanism and the influence of SACs on the dissolution of sulfur and poly-sulfides. As compared to the MoS2/SnS2 cathode, the Fe@MoS2/SnS2 cathode exhibit the highest catalytic LPS conversion. In addition, the Fe@MoS2/SnS2 cathode delivers a high discharge capacity and long-cycling performance with high coulombic efficiency in ASSLSBs. In operando in situ Raman studies, SACs provide important new insights into the charge-discharge reaction mechanism for the next generation of ASSLSBs.

A multifunctional LaFeO3 nanocages modified separator for propelling polysulfides chemisorption and catalytic conversion in Li-S batteries

The sluggish reaction kinetics of sulfur and the shuttle effect of intermediate polysulfides are the thorny issues for the commercialization of Li-S batteries. Commercial polypropylene separators cannot prevent the shuttling of polysulfides due to their large porosity. Therefore, the development of a novel type of separator can efficiently prohibit the transmission of polysulfides, will be beneficial to the practical application of Li-S batteries. Herein, we report a commercial membrane modified with perovskite-type LaFeO3 nanocages to block the transportation of polysulfides. Researches show that the modified multifunctional separators can not only effectively inhibit the shuttle of polysulfides, but also accelerate the reaction kinetics between S and Li2S. The electrochemical performance is greatly improved, which can be mirrored in the rate performance: 689.3 mA h g−1at 4C, and cycling performance with the capacity decay rate of only 0.0585% per cycle for 1000 cycles at 1C. More significantly, the considerable electrochemical performance is still hold under the harsh condition of lean electrolyte.

High loading atomically distributed Fe asymmetrically coordinated with pyridinic and pyrrolic N on porous N-rich carbon matrix driving high performance of Li-S battery

The practical application of Li-S battery is severely hampered by the sluggish sulfur-related redox reaction (SROR) kinetics along with lithium polysulfides (LiPSs) shuttle effect, advanced single-atom catalyst (SAC) is pursued to improve the SROR conversion capability. Herein, a novel SAC possessing of high loading (3.02 wt%) atomically dispersed Fe five-coordinated with pyridinic and pyrrolic N anchored on porous N-rich (16.4 at.%) carbon matrix is obtained. The resultant Fe-N5/NC SAC has a high Brunauer-Emmett-Teller surface area of 523 m2 g−1. The unique asymmetrical Fe-N5 sites in Fe-N5/NC are identified by spherical aberration-corrected high-angle annular dark-field scanning transmission electron microscope, X-ray photoelectron spectroscope, synchrotron X-ray absorption spectroscopy, density functional theory calculation, etc. The experimental and theoretical results demonstrate that the Fe-N5/NC SAC not only exhibits strong adsorption for LiPSs, but also provides a significant electrocatalytic effect on the SROR in Li-S battery. A high initial capacity of 1519 mAh g−1 was obtained at a current density of 0.1 C for the Li-S battery based on the Fe-N5/NC modified separator. An ultralong life of 2000 cycles was achieved for the Li-S battery, which has good initial capacities of 1030 mAh g−1 and 883 mAh g−1 with low decay rates of 0.032% and 0.031% per cycles at 1 C and 2 C, respectively.

Spherical Sulfur-Infiltrated Carbon Cathode with a Tunable Poly(3,4-ethylenedioxythiophene) Layer for Lithium-Sulfur Batteries.

Li-S batteries have received significant attention owing to their high energy density, nontoxicity, low cost, and eco-friendliness. However, the dissolution of lithium polysulfide during the charge/discharge process and its extremely low electron conductivity hinder practical applications of Li-S batteries. Herein, we report a sulfur-infiltrated carbon cathode material with a spherical morphology and conductive polymer coating. The material was produced via a facile polymerization process that forms a robust nanostructured layer and physically prevents the dissolution of lithium polysulfide. The thin double layer composed of carbon and poly(3,4-ethylenedioxythiophene) provides sufficient space for sulfur storage and effectively prevents the elution of polysulfide during continuous cycling, thereby playing an essential role in increasing the sulfur utilization rate and significantly improving the electrochemical performance of the battery. Sulfur-infiltrated hollow carbon spheres with a conductive polymer layer demonstrate a stable cycle life and reduced internal resistance. The as-fabricated battery demonstrated an excellent capacity of 970 mA h g-1 at 0.5 C and a stable cycle performance, exhibiting ∼78% of the initial discharge capacity after 50 cycles. This study provides a promising approach to significantly improve the electrochemical performance of Li-S batteries and render them as valuable and safe energy devices for large-scale energy storage systems.

“Wane and wax” strategy: Enhanced evolution kinetics of liquid phase Li2S4 to Li2S via mutually embedded CNT sponge/Ni-porous carbon electrocatalysts

The lithium-sulfur battery (Li-S) has been considered a promising energy storage system, however, in the practical application of Li-S batteries, considerable challenges remain. One challenge is the low kinetics involved in the conversion of Li2S4 to Li2S. Here, we reveal that highly dispersed Ni nanoparticles play a unique role in the reduction of Li2S4. Ni-porous carbon (Ni-PC) decorated in situ on a free-standing carbon nanotube sponge (CNTS/Ni-PC) enriches the current response of liquid phase Li2S4 and Li2S2 around the cathode more than 8.1 and 5.7 times higher than that of the CNTS blank sample, respectively, greatly boosting the kinetics and decreasing the reaction overpotential of Li2S4 reduction (lower Tafel slope and larger current response). Thus, with the same total overpotential, more space is provided for the concentration difference overpotential, allowing the more soluble polysulfide intermediates farther away from the surface of the conductive materials to be reduced based on the “wane and wax” strategy, and significantly improving the sulfur utilization. Consequently, S@CNTS/Ni-PC delivers excellent rate performance (812.4 mAh·g−1 at 2C) and a remarkable areal capacity of 10.1 mAh·cm−2. This work provides a viable strategy for designing a target catalyst to enhance the conversion kinetics in the Li2S4 reduction process.

Scalable, flexible and fire-retardant janus membranes for simultaneously inhibiting dendrite growth and catalyzing polysulfide conversion in lithium-sulfur batteries

Shuttle effect of lithium polysulfides (LiPSs) and the problems arising from lithium dendrites impede the practical applications of Li-S batteries. Herein, a scalable and fire-retardant janus membrane (C@OPBI-CeO2//GF) with glass fiber membrane (GF) as substrate and hierarchically porous C@OPBI-CeO2 membrane as the cathode has been constructed. The cathode membrane with porous conductive networks can replace the conventional Al foil and significantly promote Li+ and electron transportation. Meanwhile, the doped CeO2 nanoparticles in the membrane can trap and catalyze LiPSs transformation. The interwoven GF membrane allows the uniform distribution of Li+ on Li plate by redistributing the Li+ flux. It also facilitates the rapid diffusion of Li+ and promotes the reversible Li plating and stripping processes against dendrite growth. Furthermore, the introduction of OPBI and GF improve the structural stability and high temperature resistance of the membrane which are of great significance to realize the commercial application of Li-S batteries. The batteries assembled with the janus membrane have a specific capacity of 620 mA h g − 1 after 550 cycles at a current density of 1 C, and still deliver a capacity of 720 mA h g − 1 after 100 cycles even at a high sulfur loading of 5 mg cm−2.

Electrochemical Reactivation of Dead Li2 S for Li-S Batteries in Non-Solvating Electrolytes.

The use of non-solvating, or as-called sparingly-solvating, electrolytes (NSEs), is regarded as one of the most promising solutions to the obstacles to the practical applications of Li-S batteries. However, it remains a puzzle that long-life Li-S batteries have rarely, if not never, been reported with NSEs, despite their good compatibility with Li anode. Here, we find the capacity decay of Li-S batteries in NSEs is mainly due to the accumulation of the dead Li2 S at the cathode side, rather than the degradation of the anodes or electrolytes. Based on this understanding, we propose an electrochemical strategy to reactivate the accumulated Li2 S and revive the dead Li-S batteries in NSEs. With such a facile approach, Li-S batteries with significantly improved cycling stability and accelerated dynamics are achieved with diglyme-, acetonitrile- and 1,2-dimethoxyethane-based NSEs. Our finding may rebuild the confidence in exploiting non-solvating Li-S batteries with practical competitiveness.

Scissor g-C3N4 for high-density loading of catalyst domains in mesoporous thin-layer conductive network for durable Li-S batteries

The application of Li-S batteries (LSBs) is hindered by the undesired shuttle effect that leads to the fast consumption of active materials. The separator modification by using the carbon matrix with embedded metal nitride as catalyst can ease the problem. However, the previous synthesis processes of metal nitride catalysts are difficult to achieve a balance between their high-density production, homogenous distribution and excellent electronic contact with conductive substrates. Herein, we propose a bond scissoring strategy based on g-C3N4 to prepare NbN catalyst domains with high-density loading uniformly embedded in mesoporous thin-layer conductive carbon network (NbN/C) for durable LSBs. The molten salt reaction process is favorable for the diffusion of Nb cations into a porous g-C3N4 precursor to break the C-N bond and immobilize the N element. The residual monolithic carbon framework with space confinement effect limits the irregular growth and stacking of NbN precipitates. The NbN catalytic domains exhibit a strong adsorption effect on lithium polysulfides (LiPSs) and accelerate their liquid-solid conversion reactions. The LSBs utilizing an NbN/C-modified separator show superior cycling and rate performance, with a high-capacity retention of 72.7% after 1,000 cycles under 2 C and a high areal capacity of ~7.08 mA h cm-2 under a high sulfur loading of 6.6 mg cm-2. This g-C3N4-assisted strategy opens a new gate for the design of an integrated catalysis-conduction network for high-performance LSBs.

Cobalt Nanocluster-Doped Carbon Micro-Spheres with Multilevel Porous Structure for High-Performance Lithium-Sulfur Batteries

Lithium-Sulfur batteries (Li-S batteries) have gained great interest in next-generation energy storage systems due to their high energy density and low-cost sulfur cathodes. There is, however, a serious obstacle in the commercial application of Li-S batteries due to the poor kinetics of the redox process at the sulfur cathode and the “shuttle effect” caused by lithium polysulfide (LiPSs). Herein, we report the synthesis of a sulfur cathode host material that can drastically inhibit the “shuttle effect” and catalyze the conversion of LiPSs by a simple electrostatic spray technique, namely, cobalt (Co) nanoclusters doped with N-containing porous carbon spheres (Co/N-PCSs). The results show that Co/N-PCSs has catalytic activity for the transformation of liquid LiPSs to solid Li2S and alleviates the notorious “shuttle effect.” This new sulfur cathode exhibits stable running for 300 cycles accompanied by a capacity of 650 mAh g−1 at a current density of 1 C, a capacity fading rate of 0.051% per cycle, and a Coulombic efficiency maintained at close to 100%. The results demonstrate that Co/N-PCSs offers the possibility of practical applications for high-performance Li-S batteries.

A tandem electrocatalyst with dense heterointerfaces enabling the stepwise conversion of polysulfide in lithium-sulfur batteries

The complicated sulfur phase transformation and diversity kinetics of lithium polysulfide intermediates hinder the practical applications of Li-S batteries. Herein, we report that Mo-Ni bimetal sulfide nanosheets with dense heterointerfaces and defects can decouple the complicated reactions into well-controlled multi-steps in tandem. Specifically, the MoS2 in Mo-Ni tandem catalyst is more effective in catalyzing the phase transformation from Li2S8 to Li2S4, while NiS2 delivers higher catalytic activity toward both the Li2S4 to Li2S conversion and the Li2S dissociation steps, as indicated by density functional theory calculations and comprehensive experiments. This integrated system tends to selectively propel the stepwise conversion of sulfur and thereby enhancing the battery performance. As a result, the sulfur loaded cathode delivers a high initial capacity of 1481 mAh g−1 at 0.2 C, and a low capacity decay rate of 0.0236% per cycle over 1000 cycles at 2 C. This study demonstrates the feasibility of using tandem catalysis for regulating the smooth solid-liquid-solid multiphase transformation of polysulfides.