High-performance Li-S Batteries Research Articles

Nano storage-boxes constructed by the vertical growth of MoS2 on graphene for high-performance Li-S batteries

In order to accelerate the reaction kinetics of lithium-sulfur batteries, the introduction of electro catalysis and proper structural control of the sulfur cathode is urgently needed. MoS2 nano sheets was selectively grown vertically (V-MoS2) on the microwave-reduced graphene (rGO) sheets through chemical coupling to construct a self-supporting sulfur cathode with a nano storage-box structure (V-MoS2 as the wall and rGO as the bottom). RGO, which has a high conductivity of 37 S cm−1, greatly accelerates the transfer of electrons from the active sites on the edge of the layer to the solution. The introduction of carbon tubes can connect the abundant pores in the foam and act as a long-range conductive path. The 2D-orthogonal-2D structure maximally exposes the edge active sites of MoS2, and together with graphene form a nano reactor of sulfur, intermediate lithium polysulfides and discharge product Li2S(2). The effective combination of the microstructure confinement of the nano storage-boxes and the efficient synchronous catalytic mechanism of V-MoS2 greatly improves the electrochemical performance of the lithium-sulfur batteries. As a result, the assembled lithium-sulfur battery displays a high initial discharge capacity of 1379 mAh g−1, good cycle stability (86% capacity retention after 500 cycles at 0.1C) and superior rate performance.

Functionalized Mo2B2 MBenes: Promising anchoring and electrocatalysis materials for Lithium-Sulfur battery

Applications of Li-S batteries are primarily hindered by shuttling effect, poor electronic conductivity of sulfur and inactive decomposition of low-order lithium polysulfide (LiPS). To solve these problems, the anchoring and electrocatalysis properties of two-dimensional transition metal boride (MBene) have been extensively studied to provide general design principles for enhanced electrochemical performance in Li-S batteries. Our results show that direct application of bare Mo2B2 MBene in Li-S battery gives rise to the decomposition of high-order LiPSs, which originates from the excessively strong binding strength between S atoms and surface Mo atoms. Then, we highlight that surface functionalization on Mo2B2 MBene possesses suitable anchoring performance to suppress the shuttling effect. Meanwhile, owing to the excellent electronic conductivity even after the adsorption of LiPS, the functionalized MBenes effectively stimulate the redox electrochemistry in Li-S battery. Finally, accompanied with omnidirectional fast diffusion of Li atom, the functionalized MBene exhibits superior electrocatalysis activity for Li2S decomposition with ultra-low diffusion (0.191 eV) and decomposition (0.441 eV) barriers, improving the capability and coulombic efficiency of Li-S batteries. Our findings pioneer the application of MBenes as anchoring and electrocatalysis materials for Li-S batteries and provide a developed insight on the design of high-performance Li-S battery cathodes.

Binder Free Three-Dimensional Hybrid Cathode for Stable and High-Performance Li-S Batteries

Lithium-sulfur batteries (LSBs) represent a promising energy storage technology with a potential for next-generation high-energy storage systems due to their high specific capacity, abundant resources, low cost, non-toxicity, and environmentally friendly characteristics. However, due to many critical limitations such as insulating nature of elemental sulfur, poor lithium polysulfide (LiPS) conversion kinetics, polysulfide shuttle effect resulting in capacity fading, and low cyclic stability, commercialization of LSBs are far from realization. One of the most essential strategy to mitigate the issues with LSBs is to prevent polysulfide shuttling thereby maximizing the sulfur utilization and enhance the overall Li-S battery performance. In this work, we develop a binder free three-dimensional hybrid cathode for Li-S battery using multiwall carbon nanotubes (CNTs) and molybdenum sulfide (MoS2) as a catalyst, collectively enhancing LiPS conversion and ion transport ability and hence increased energy density, both gravimetric and volumetric. Different uniform mixtures of CNTs, MoS2, and conductive carbon black are prepared and loaded with high sulfur loading of ~6 mg cm-2. Various electrochemical performance parameters influencing cathode performance with respect to both gravimetric and volumetric energy densities are studied. Parameters that help improve the overall battery performance are identified and discussed.

Multifunctional Trilayer Separator for High-Performance Lithium-Sulfur Batteries Under Extreme Conditions

Lithium-ion Batteries (LIBs) have transformed mankind's lives beyond imagination in the past few decades. They have found their use in a variety of applications such as defense, transportation, portable electronics, and space explorations. To keep up with the demand, stress is applied for discovering materials with higher capacity and energy densities. High capacity anodes like silicon, tin, antimony, carbon composites have been identified. However, limited cathode materials are available at disposal viz., LiCoO2, LiMnNiCoO2, LiFePO4, LiMn2O4. Most of these cathodes have capacities <250 mAh g-1, and thus LIBs cannot keep up with the ever-growing demand from the applications. The high-theoretical capacity chemistry of lithium-sulfur comes to the rescue. It is the lightest element to be used as a cathode, which has attractive properties such as capacity of 1672 mAh g-1, economical (~$50 per metric tonne), and abundance in nature. However, chemistry suffers from three critical issues viz., poor sulfur conductivity, polysulfide shuttling, and lithium dendrite growth. To tackle the insulative sulfur and polysulfide shuttling effect approaches such as coating sulfur with metal sulfide or oxides, mesoporous carbon, conductive polymers, inverse vulcanization have been applied. Unfortunately, these techniques lead to a reduction in the energy density of the system, involve complex fabrication steps or raw materials are expensive. On the issue of lithium metal dendrites growth, electrolytic additives, exotic electrode coatings, and special shutdown separators are used. The downside to all of these is that they impede cell performance or are uneconomical.Here we report, the use of a multifunctional trilayer separator in Li-S battery to tackle all three issues simultaneously. Modified separator acted as a barricade for polysulfide from shuttling by trapping them preferably due to the favorable interactions. The performance of Li-S cells with and without modified separator was compared for long term cycling and rate studies. It was found that cells with modified separator outperformed those with pristine separator. Modified separator cell exhibited capacities of 925, 833, 644, 480, 326, 260, and 220 mAh g-1 at 0.1C, 0.2C, 0.5C, 1C, 2C, 3C and 4C rates, respectively with 95% capacity retention. The choice of electrolyte affects battery performance drastically. However, using 1M LiTFSI in 1:1 (v/v) 1, 3-Dioxolane (DOL): 1, 2-Dimethoxyethane (DME) with additives, provided remarkable results at low and high-temperature ranges. At 0 ℃, the cell with the modified separator yielded about 350 mAh g-1 capacity at 0.5C over 200 cycles. The performance of the cells was stellar even at 50 ℃ with 500 mAh g-1 capacity at 0.5C rate after 100 cycles. Multiple module calorimetry provided the thermal heat signature to elucidate the safety features of the Li-S system with the modified separator and compared with the existing LIBs. High-performance Li-S batteries proposed here can be valuable to a variety of applications like defense, transportation, and space explorations, where drastic conditions affect the battery functionalities, in the times ahead.

Defective graphene coating-induced exposed interfaces on CoS nanosheets for high redox electrocatalysis in lithium-sulfur batteries

Herein, we propose the construction of sandwich-structured hosts filled with continuous 3D catalysis-conduction interfaces. The RG@CoS@C-C-RG@CoS@C architecture enables fast electron and Li+ diffusion, strong adsorption of S/Li2Sx and high-efficiency conversion on two-sided RG@CoS surfaces. With detailed experimental and theoretical characterization, we reveal that although the conformal graphene coating largely shields the catalytic activity and adsorbing ability of CoS nanosheets, the exposed interfaces of CoS at the defective sites of the graphene coating exhibit especially strong lithium polysulfide (LiPSs) anchoring and high conversion efficiency, with high-flux Li+ and electron transfer from the circumjacent graphene coating and the buried carbon nanofibers. Furthermore, the exposed interfaces exhibit an effective decrease in Li2S decomposition by releasing Li+ onto the circumjacent graphene surface with a low Li+ diffusion barrier and anchoring the remaining Li-S bond on the exposed CoS interface with a high adsorption energy. The unique structure consisting of catalytic CoS nanosheets, defective RG coating, and interwoven C fiber interlayers enables not only the coupling of Li+ diffusion and electron transfer but also efficient regulation of the polysulfide reaction, thereby producing a synergistic catalyzing effect on both LiPS conversion and Li2S decomposition. As a result, the batteries with RG@CoS@C membranes as interlayers exhibit stable cycle performance and reversible capacities of 629.2 mA h g−1 after 420 cycles at 2.0 C. The proposed strategy will contribute to guiding the design of novel composite materials for high-performance Li-S batteries.

High-performance Li-S batteries enabled by polysulfide-infiltrated free-standing 3D carbon cloth with CeO2 nanorods decoration

To achieve scale-up commercialization of Li-S batteries, parasitic shuttle effect, leading to low utilization of active material and fast capacity decay, has to be resolved effectively. Herein, we prepared CeO2 nanorods decorated interwoven 3-D carbon cloth via facile one-step hydrothermal reaction and Li2S6-containing polysulfide as starting material to successfully improve the electrochemical performance of Li-S battery. First, strong chemical interaction toward polysulfides was successfully constructed by polar CeO2 nanorods and numerous oxygen vacancies on their surface acting as efficient polysulfides anchoring sites significantly enhanced the utilization of active material sulfur. Second, interwoven freestanding carbon cloth can considerably enhance redox kinetics through a 3-D interconnected network with abundant long-range electron transfer channels and can significantly improve redox kinetics by easy accessibility to electrolyte and abundant ion transport pathways. Third, the utilization of Li2S6-containing catholyte leads to uniform distribution of active material and improves sulfur utilization. Benefiting from the aforementioned advantages, free-standing 3-D carbon cloth with CeO2 nanorods decoration combined with Li2S6-containing catholyte (CC@CeO2@Li2S6) electrode delivered an initial discharge capacity of 1311 mA h g−1 at 0.2C and approximately 95% of the initial discharge capacity was remained after 100 galvanostatic cycles, manifesting superior capacity retention with minimal capacity fading of 0.050% per cycle.

Facilitating redox kinetics of sulfur species by cobalt-nitrogen co-doped porous hollow carbon for high-performance Li-S battery

The shuttle effect of polysulfides is the main obstacle restricting the development of lithium-sulfur batteries. However, most efforts focused on physical adsorption and polar adsorption cannot fundamentally solve the problem of sluggish conversion of polysulfides, especially for high sulfur loading. Herein, a cobalt-nitrogen co-doped porous hollow carbon sphere (Co-CN) is synthesized in one step. The porous conductive carbon spheres can realize a rapid charge transfer, mitigate volume expansion during cycling and enhanced physical adsorption for polysulfides. Nitrogen and cobalt doping provide chemisorption and catalysis for the restriction and conversion of polysulfides. Furthermore, liquid Li2S8 polysulfide was used as sulfur source to guarantee high sulfur loading and fast redox kinetic. Benefiting from the triple effect of physical adsorption, chemical adsorption and catalysis, the Co-CN@Li2S8 cell with sulfur loading of 5.15 mg cm−2 delivers a high reversible initial capacity of 1499 mAhg−1 at 0.1C and 880.9 mAhg−1 after 100 cycles. More excitingly, the capacity decay rate was only 0.012% per cycle at 1C over 1000 cycles, indicating excellent long cycle stability. This work provides a facile and effective route for Co-CN as a sulfur host in lithium-sulfur battery.

A novel hierarchical porous carbon derived from durian shell as enhanced sulfur carrier for high performance Li-S batteries

Herein, this study reports a durian shell derived hierarchical porous carbon (DPC) material as the cathode precursor for lithium-sulfur batteries. The DPC with special pore feature is synthesized through carbonizing durian shell and activating by KOH, and then the sulfur is encapsulated into hierarchical porous carbon (DPC/S) successfully for the cathode material. The synthesis conditions of alkali/carbon ratio and activation temperature have important influence on the pore features of DPC and the electrochemical performance of DPC/S composites. When the activation temperature is 900 °C, the pore volume of 4DPC with the alkali/carbon ratio of 4 is 1.6 cm3 g−1 while the range of pore size distribution is 0.5–20 nm. At a current density of 0.5C, the discharge capacity of 4DPC-900/S reaches 604 mAh g−1 after 100 cycles. Not only the pore volume can influence on the electrochemical performance of DPC/S composites, but the pore size distribution plays an important role as well.

MoP QDs@graphene as highly efficient electrocatalyst for polysulfide conversion in Li-S batteries

The shuttle effect of lithium polysulfides (LiPSs) and sluggish redox conversion significantly hinder practical implementation of lithium-sulfur batteries (LSBs). To overcome these issues, herein, we present MoP quantum dots anchored N, P-doped graphene (MPQ@G) as a multifunctional LSB cathode. The N, P-doped graphene layers serve as a conductive skeleton to support the MoP QDs which can accelerate the electron transfer, physically hinder the polysulfide migration and thus enhance the electrochemical performance. More importantly, as a polar and conductive catalyst, MoP QDs provide catalytically active sites for the conversion of LiPSs. As a result, the LSBs with MPQ@G/S cathodes deliver an elevated initial capacity of 1220.2 mAh g−1 at 0.2 C and remain 98.9% after rate cycles, signifying its exceptional cycling stability. Moreover, it displays a large capacity of 681.2 mAh g−1 even at a high rate of 1 C. The Li-S pouch cell also presents high specific capacities and preeminent cycling stabilities, confirming its great potential for high-rate applications. Density functional theory calculations demonstrate the improved absorptivity and redox conversion reversibility of LiPSs. This work provides an efficient strategy to improve composite with highly adsorptive and catalytic properties for high-performance Li-S batteries.

Regulating the polysulfide redox kinetics for high-performance lithium-sulfur batteries through highly sulfiphilic FeWO4 nanorods

Owing to their high theoretical capacity, energy density, good environmental protection, and low cost, lithium-sulfur batteries are regarded as extremely promising next-generation energy storage equipment for electrical and portable devices. However, their practical application is mainly hindered by the polysulfide shuttle and the slow redox kinetic in the electrochemical process. In this study, we prepared FeWO4 nanorods by a simple hydrothermal method to enhance the electrochemical performance of lithium-sulfur batteries. The FeWO4 nanorods act as catchers and electrocatalyst for polysulfide in lithium sulfur batteries. These FeWO4 nanorods could efficiently adsorb polysulfide and enhance the conduction of Li ions, leading to inhibition of the polysulfide shuttle effect and enhancement of the electrochemical reaction kinetic for cycling stability and rate performance. Density functional theory calculation shows the existence of the high binding energy between FeWO4 nanorods and polysulfide, which can limit polysulfide to the surface of FeWO4 nanorods. Therefore, the Li-S batteries with FeWO4 nanorods not only provide an initial discharge capacity of 1318 mAh g−1 at the current of 0.8 mA with high coulombic efficiency of 97%, but also shows a capacity decay rate of 0.07% during 600 cycles at a current of 3.2 mA. With the above-mentioned dates, this work offers a promising new strategy to regulate the kinetic behaviors of polysulfide for high-performance Li-S batteries.

Regulating the electron filling state of d orbitals in Ta-based compounds for tunable lithium‑sulfur chemistry

Building the fundamental relation between the polysulfides adsorption on cathode additives and LiS chemistry kinetics is critical for the rational design of efficient and reliable LiS batteries. Herein, we reveal that LiS chemistry kinetics can be well regulated by manipulating the electron-filling state of d orbitals in Ta2O5. The prepared S@N-Ta2O5/rGO with moderate N contents delivers the lowest polarization for LiPSs conversion and the highest specific capacity of 1252.8 mAh g−1 at 0.2C. More importantly, the theoretical analysis unravel that the enhanced electrochemical performance is mainly originated from the orbital-induced adsorption modulation. This work could offer a powerful platform to manipulate the LiS chemistry by orbital engineering for high-performance LiS batteries.

Optimizing inner voids in yolk-shell TiO2 nanostructure for high-performance and ultralong-life lithium-sulfur batteries

The TiO 2 nanosheets constructed yolk-shell sulfur-TiO 2 (S@void@TiO 2 ) architecture with optimized inner voids demonstrates high-performance and ultralong-life for Li-S battery. • Designing TiO 2 nanosheets constructed yolk-shell TiO 2 (S@void@TiO 2 ) nanostructure for Li-S battery. • Verifying intense chemical interaction via the hybridization of Li 1 s, S 2p and O 2p orbitals in S@void@TiO 2. • Optimizing the inner voids for volume expansion to guarantee the cathode integrity. • Improving the electrolyte wettability and Li + kinetics in S@void@TiO 2. • Realizing high capacity and long cycle with a small capacity decay for Li-S battery. A TiO 2 nanosheets constructed yolk-shell architecture with tunable inner voids is designed and prepared as sulfur host for high-performance and ultralong-life Li-S battery. With the integration of TiO 2 nanosheets to form yolk-shell sulfur-TiO 2 (S@void@TiO 2 ) architecture with controllable inner voids, the S@void@TiO 2 composite with optimized inner voids provides sufficient contacting sites to improve the utilization of insulating sulfur and allows sulfur to freely expand without destroying the electrode. In particular, the density functional theory (DFT) calculations from molecular level reveal that the hybridization of Li 1s, S 2p and O 2p orbitals ensures the effective chemisorption between polysulfides and TiO 2 with long-term cycling stability. Consequently, the optimized S@void@TiO 2 electrode maintains a capacity of 766 mAhg −1 after 1000 cycles at 0.2C. Even at 2C for 400 cycles, the capacity still retains at 511 mAhg −1 , representing the best results of TiO 2 -based nanostructures for Li-S batteries. This work illustrates that carefully design novel yolk-shell structure is important to address the shortages of sulfur-based cathodes for advanced Li-S battery.

Fe-cation Doping in NiSe2 as an Effective Method of Electronic Structure Modulation towards High-Performance Lithium-Sulfur Batteries.

The commercialization of Li-S batteries is hindered by the shuttling of lithium polysulfides (LiPSs), the sluggish sulfur redox kinetics as well as the low sulfur utilization during charge/discharge processes. Herein, a free-standing cathode material was developed, based on Fe-doped NiSe2 nanosheets grown on activated carbon cloth substrates (Fe-NiSe2 /ACC) for high-performance Li-S batteries. Fe-doping in NiSe2 plays a key role in the electronic structure modulation of NiSe2 , enabling improved charge transfer with the adsorbed LiPSs molecules, stronger interactions with the active sulfur species and higher electrical conductivity. Effective promotion of the sulfur redox kinetics and enhanced sulfur utilization were achieved under high areal sulfur loadings. The stronger interactions with LiPSs together with the unique 3D structure of Fe-NiSe2 /ACC also induced the transformation of Li2 S2 /Li2 S growth from conventional 2D films to 3D particles, significantly eliminating the barriers of solid nucleation and growth during the phase transition of liquid LiPSs to solid Li2 S2 /Li2 S. With a high sulfur loading of 9.9 mg cm-2 , the Fe-NiSe2 /ACC cathode enabled a high area capacity of 9.14 mAh cm-2 with a low average decay of 0.11 % per cycle over 200 cycles at 0.1 C.

The Electrocatalyst based on LiVPO4F/CNT to enhance the electrochemical kinetics for high performance Li-S batteries

• The LVPF/CNT are used as the catalyst to enhance the redox kinetics in LSBs. • The in situ XRD reveals the catalytic process of LVPF/CNT in LSBs. • The reaction mechanism has been thoroughly explored by DFT. The preparation of functional separator has become an effective strategy to enhance the electrochemical performance of lithium-sulfur batteries (LSBs). Therefore, a functional separator suitable for LSBs has aroused great interest. In this work, we report a novel functional separator using LiVPO 4 F together with carbon nanotube (LVPF/CNT) as functional coating. The LVPF/CNT modified separator not only acts as a conductive layer to facilitate electron and lithium ion (Li + ) transport, but also provides chemisorption for lithium polysulfides (LiPSs) and improves the electrochemical kinetics of LSBs. Thus, the cell with LVPF/CNT modified separator delivers an excellent cycle life with the capacity of 578.5 mAh g −1 after 1000 cycles at 1.5C. An ultra-long cycle life (551 mAh g −1 after 350 cycles at 0.5C) and a high areal capacity of 5.58 mAh cm −2 are obtained at a high sulfur loading of 7 mg cm −2 . Moreover, the visualized transformation of the LiPSs in the tailor-made cell is also revealed by in situ XRD, while the density functional theory (DFT) simulated the principle of the interaction between the LVPF and LiPSs. This work provides a promising and insightful research to develop the progressive LSBs with functional separator.

Achieving high electrochemical performance Li-S batteries by the employment of Co3O4 nanospheres as sulfur hosts

Achieving high electrochemical performance Li-S batteries by the employment of Co3O4 nanospheres as sulfur hosts

Mesoporous 3D titanium dioxide embed carbon nanofibers with superior polysulfide adsorption ability for high electrochemical performance Li-S batteries

The rechargeable lithium-sulfur batteries are promising candidate for the energy storage applications due to their low cost and high energy density. However, the lithium-sulfur batteries show poor electrochemical performance, caused by the polysulfide dissolution and low electrical conductivities of the sulfur cathode. Herein, we develop a new strategy to solving these two issues by designing titanium dioxide embed carbon nanofibers/S (CNFs@TO/S) hybrid composites. In this unique hybrid structure, the mesoporous 3D carbon nanofibers could provide fast electron conduction paths and structural stability. The titanium dioxide could act as polysulfide absorber via chemical bond between TiO2 and polysulfide. Owing to these synthetic effect, the as-prepared CNFs@TO/S cathodes exhibit advanced electrochemical performances.

2D Zr-Fc metal-organic frameworks with highly efficient anchoring and catalytic conversion ability towards polysulfides for advanced Li-S battery

The practical viability of Li-S battery is largely hampered by undesirable shuttling behavior and sluggish conversion kinetics of polysulfides. Considering that, a multifunctional interlayer, prepared by weaving ferrocene-based two-dimensional (2D) metal-organic framework (Zr-Fc MOF) nanosheets and carbon nanotubes (CNT) via simple vacuum filtration, is proposed to achieve high-performance Li-S battery. Using a combination of in situ Raman spectroscopy, first-principles calculations and systematic electrochemical evaluation, we unveil that the Zr-Fc MOF, as a new polysulfides confinement agent, can not only restrain polysulfides shuttling via both electrostatic attraction and chemical anchoring capability, but also provide excellent electrocatalytic effect on polysulfides redox kinetics. The intertwined CNT throughout Zr-Fc MOF nanosheets facilitates electron conductivity as well as sufficient exposure of capturing and catalyzing active sites of Zr-Fc MOF. Accordingly, attributed to the synergistic entrapping-catalysis-conversion effect, we demonstrate that Li-S cell coupling with the as-prepared Zr-Fc MOF/CNT interlayer exhibits a dramatically enhanced rate performance and outstanding cyclability (1500 cycles at 1 C with ultralow capacity decay rate of 0.027% under sulfur loading of 4.11 mg cm−2). This work will inspire more intelligent 2D MOF materials simultaneously with highly efficient trapping and catalytic conversion of polysulfides for high-energy and long-life Li-S battery.

Graphene/MXene fibers-enveloped sulfur cathodes for high-performance Li-S batteries

Developing scalable and facile techniques to design and construct unique structures of cathodes with high performance is challenging for the practical Li-S batteries. In this work, highly effective and scalable cathodes based on curved graphene/MXene bi-nanosheets-constituted fibers is demonstrated for long-lifetime Li-S batteries. Wet-spinning is introduced to design and fabricate sulfur cathodes based on graphene/MXene hybrid fibers, in which sulfur is uniformly distributed and intimately enveloped between graphene and MXene nanosheets. The high chemical affinity towards polysulfides enabled by MXene is demonstrated by experiments and density functional theory (DFT) calculations. The assembled cells show high sulfur utilization (the discharge capacity of 1483.1 mAh g−1 at 0.1 C), high rate performance (733.3 mAh g−1 at 2 C) and excellent long cycle stability (0.043% per cycle decay at 1 C over 1000 cycles). Moreover, a reversible areal capacity of 5 mAh cm−2 is achieved under a high sulfur loading of 5.6 mg cm−2, revealing its great potential for practical applications. This study gives a valuable guidance to design advanced sulfur cathodes for high-performance Li-S batteries.

Modified Separator Based on mesoporous carbon/TiO2 composites as Advanced Polysulfide Adsorber for High Electrochemical Performance Li-S Batteries

Lithium-sulfur batteries have been drawn much attention for the researchers due to their high energy density low cost, and environmental friendliness. However, the severe polysulfide dissolution and poor electronic conductivity limit the actual electrochemical performance. Separator modification is considered as a promising method to enhance the electrochemical performance of lithium-sulfur batteries. Herein, we develop mesoporous carbon/TiO2 (MC/TO) composites as the modifying materials on the surface of the pure separator. The polar metal oxide TiO2 on the modified separator could adsorb the polysulfide while the mesoporous graphitic carbon could improve the electronic conductivity at the same time. Owing to the above merits, the lithium-sulfur batteries with MC/TO modified separator display excellent electrochemical performance with a capacity of 658 mAh g−1 at 2 C over 500 electrochemical cycles. This work provides a promising strategy to design modified separator which could inhibit the polysulfide dissolution and accelerate the sulfur redox kinetics, therefore obtaining high electrochemical performance Li-S batteries.

Simultaneous defect-engineered and thiol modified of MoO2 for improved catalytic activity in lithium-sulfur batteries: A study of synergistic polysulfide adsorption-conversion function

Rational design of nanostructure and proper interfacial engineering is of significant in pursuing high performance Li-S batteries. Here we report a strategy to fabricate reduced graphene oxide coated MoO2 with defect engineered and thiol modified nanotubes (H-S@MoO2/rGO) as highly stable host material for cathode in Li-S batteries. Thiourea was used as sulfur source and etching agent to construct the hollow architecture and realize thiol modification of MoO2 with the aid of ethanol. The modifying H-S@MoO2/rGO nanotubes offer improved affinity with LiPSs and accelerating the conversion kinetics from LiPSs to final Li2S. Oxygen vacancy remarkably reduce energy barrier and facilitating charge transfer, improving catalytic activity, regulating the deposition of Li2S on electrode surface. Furthermore, H-S@MoO2/rGO nanotubes offer enough interior capacity for high sulfur loading of 84 wt% (donate as S-S@MoO2/rGO), effectively confine sulfur through confinement effect. The simultaneous defect-engineered and thiol modified of MoO2 effectively cooperate the adsorption, diffusion and conversion of LiPSs in sulfur redox process, synergistically enable host material effective adsorption-conversion function for polysulfide. The developed S-S@MoO2/rGO cathodes exhibit excellent rate performance and superior reliability with a high specific capacity of 927 mAh g−1 and small capacity fading rate of 0.042% per cycle over 500 cycles at 0.1 Ag−1. This work shows a feasible and effective method to analyze the systematic kinetic and in-depth mechanism explanation of functional groups modifying metal oxide to guide the design of effective catalysts for practical application in lithium-sulfur batteries.