High Sulfur Loading Research Articles

Honeycomb-like porous carbon embedded ferrous sulfide nanoparticles as bifunctional separator modifier by forming sulfur bonds with polysulfides in advanced lithium-sulfur batteries

To develop practical and outstanding lithium-sulfur (Li-S) batteries, it is advisable to adsorb soluble polysulfides and catalyze insoluble Li2S2/Li2S. Herein, a ferrous sulfide decorated honeycomb-like porous carbon (FeS/HMPC) was synthesized by sulfuration strategy to act as a separator modifier in Li-S batteries. Owing to the positive migration of the Fe d-band center, the binding of FeS to polysulfides is dominated by the S bond (Fe-SLiPSs), which makes FeS have strong adsorption capacity for various types of polysulfides. Moreover, FeS shows the minimum energy path for the migration of typical polysulfide Li2S. In other words, it has the smallest diffusion barrier. Hence, the FeS/HMPC-PP not only realizes the efficient suppression of the shuttle effect but also catalyzes the redox reaction of polysulfides. Benefiting from the above advantages, the FeS/HMPC-PP based cells exhibit a high initial capacity of 1673 mAh g−1 at 0.2 C and a reversible capacity of 686.7 mAh g−1 at 3 C after 500 cycles. Moreover, the cell with a high sulfur loading of 2.4mg cm−2 demonstrates an ultra-low-capacity decay of 0.007% per cycle at 0.2 C. This work provides novel insights and promising candidates to act as a functional separator for Li-S batteries with long life and high-rate electrochemical performance.

Unlocking Liquid Sulfur Chemistry for Fast-Charging Lithium-Sulfur Batteries.

A recent study of liquid sulfur produced in an electrochemical cell has prompted further investigation into regulating Li-S oxidation chemistry. In this research, we examined the liquid-to-solid sulfur transition dynamics by visually observing the electrochemical generation of sulfur on a graphene-based substrate. We investigated the charging of polysulfides at various current densities and discovered a quantitative correlation between the size and number density of liquid sulfur droplets and the applied current. However, the areal capacities exhibited less sensitivity. This observation offers valuable insights for designing fast-charging sulfur cathodes. By incorporating liquid sulfur into Li-S batteries with a high sulfur loading of 4.2 mg cm-2, the capacity retention can reach ∼100%, even when increasing the rate from 0.1 to 3 C. This study contributes to a better understanding of the kinetics involved in the liquid-solid sulfur growth in Li-S chemistry and presents viable strategies for optimizing fast-charging operations.

Rationalizing the impact of oxygen vacancy on polysulfide conversion kinetics for highly efficient lithium-sulfur batteries

The “shuttle effect” of lithium polysulfides (LiPSs) is a huge challenge for practical use of high-energy-density lithium-sulfur (Li-S) batteries, and one of the main reasons is the sluggish kinetics of sulfur conversion. Metal oxides are able to expedite the sulfur electrochemistry, and the structural defects enhance the adsorption-conversion ability of metal oxides for polysulfides. However, a significant research gap still remains regarding the relationship between the oxygen vacancy concentration and the adsorptive-catalytic performance of metal oxides. Herein, we establish a correlation between oxygen vacancy concentration and adsorptive-catalytic properties by using tungsten oxide (WOx) as model catalysts. It is revealed that high-concentration oxygen vacancy is beneficial for enhancing the binding between tungsten oxide and LiPSs, reducing the energy barrier of Li2S decomposition, and promoting polysulfide conversion kinetics. Consequently, the Li-S batteries using the tungsten oxide with high-concentration oxygen vacancies deliver high initial discharge capacity of 1169 mA h g−1 at 0.2 C and 865 mA h g−1 at 2 C, low attenuation rate of 0.064% per cycle over 1100 cycles at 2 C. With a high sulfur area loading of 5.34 mg cm−2, the Li-S batteries still exhibit high initial gravimetric capacity of 982 mA h g−1 at 0.1 C and areal capacity of 5.92 mA h cm−2. This work promotes the feasibility of defect engineering on metal oxides as an effective mean to enhance the practicality of Li-S batteries.

Greenly growing carbon nanotubes on graphene for high-performance lithium–sulfur batteries

The expanding energy storage market in response to global decarbonization goals generates countless waste, causing severe environmental issues. To address this dilemma, end-of-life batteries must be upcycled for a second life. Here we report an all-green strategy for growing carbon nanotubes (CNTs) on graphene. The graphene was upcycled from end-of-life lithium-ion batteries and the CNTs were then grown directly on the graphene by pyrolyzing biomass as the carbon source and yeast as the catalyst. When being used in a lithium–sulfur battery cathode, the graphene provided a highly conductive network while the CNTs enabled high sulfur loading and volume buffering, rendering the battery with high capacity, high stability, and long lifespan. The CNT/graphene constructed battery exhibited longevity of over 1500 cycles with a capacity fading rate of 0.042% per cycle and a steady Coulombic efficiency of over 97%. The all-green CNT/graphene hybrids present new pathways to upcycling batteries to second life.

Cubic FeS2 enabling robust polysulfide adsorption and catalysis in lithium/sulfur batteries

Lithium/sulfur batteries are considered to have great prospects in advanced energy storage devices in the future. However, the shuttling of polysulfides in electrolytes and sluggish electrochemical kinetics of polysulfides hinder the development of lithium/sulfur batteries. To address these stumbling blocks, we introduced cubic pyrite FeS2 modification of Ketjen black@sulfur (FeS2/KB@S) composite that adsorb and provide sufficient sites with polysulfides interaction. The cubic pyrite FeS2 has a pivotal effect on the adsorption and catalysis performance of the polysulfides, which further accelerates the redox kinetics. Consequently, the FeS2/KB@S cathode with 3.1 mg/cm2 sulfur loading attained a high discharge capacity of 0.5 C current density and reversible capacity was 446 mAh/g after 500 cycles. Meanwhile, it also shows excellent rate capability and still maintains a high capacity of 508 mAh/g at 2 C current density. Even at high sulfur loading of 5.1 mg/cm2, the FeS2/KB@S electrode still delivers a high initial area capacity of 4.03 mAh/cm2 at 0.2 C. The cyclic and rate properties of FeS2/KB@S were greatly improved over that of KB@S. The results suggest the multifunction cubic pyrite FeS2 that anchors effectively and catalysis is beneficial to realize the goal of large-scale application for lithium/sulfur batteries.

One-pot preparation of structurally tunable mesoporous hollow carbon spheres and their application for lithium‑sulfur battery with high sulfur content

Hollow carbon nanomaterials as sulfur hosts have been investigated extensively for lithium‑sulfur (LiS) battery. Herein, we report the preparation of structurally tunable mesoporous hollow carbon spheres (MHCs) by a simple one-pot self-assembly method. The structural parameters (specific surface area, pore capacity, pore size, and cavity) of the MHCs were adjusted by varying the concentration of the reactants. Three representative MHCs were characterized in detail, and the reasons for their formation were explained. Among them, the optimized MHC features a high specific surface area (1547.9 m2 g−1), large pore capacity (2.04 cm3 g−1), moderate pore size (∼ 6 nm), and internal cavity (r2/r1 = 0.62), which can meet the requirements of high sulfur loading, good carbon/sulfur contact, sufficient buffer space, and fast electron/ion transport channels. Consequently, the optimized MHC@S cathode exhibited improved electrochemical properties (maintaining a capacity of 484.7 mAh g−1 after 500 cycles at 0.5C with a decay rate of 0.068 %) under the condition of high sulfur content of 90.02 wt% and the electrolyte/sulfur ratio of 10 μL mg−1. Moreover, the raw materials are cost-effective, and the process is simple to operate without requiring expensive equipment. This study provides a promising candidate for carbon-based materials as sulfur hosts in practical LiS battery.

Regulating the phase and catalytic activity of cobalt phosphide based on the morphological engineering of ZIF-67 to enhance the redox kinetics of polysulfides for high-performance lithium-sulfur batteries

Transition metal phosphides capture wide attention as electrocatalysts in lithium-sulfur (Li-S) batteries due to their unique electrocatalytic activity, and metal-organic framework (MOF) is well suited as precursor due to the inherent advantages such as structural/morphology diversity, tunable composition and distribution of internal elements. However, the relationship of the fabrication process, the phase and actual catalytic activity have been controversial. Herein, based on a facile morphological engineering of ZIF-67 (a classic MOF), three kinds of cobalt phosphide (polyhedron, cube and flake-like) are fabricated and different from traditional delicate strategies such as adopt surfactant and methanol to fabricate three-dimensional ZIF-67 (polyhedron or cube), two-dimensional flake ZIF-67 can be obtained just in aqueous solution without any agent. Besides, CoP/Co2P heterostructure is regularly induced although they are fabricated under the same condition, especially for flake cobalt phosphide. Furthermore, the flake cobalt phosphide exhibits improved redox reaction kinetics of polysulfides than that of other cobalt phosphides. After modifying commercial separator using the obtained flake cobalt phosphide, the Li-S battery exhibits a high initial capacity of 1253.6 mAh g−1 at 0.2 C and 858.7 mAh g−1 at 2 C. Meanwhile, the battery can also deliver a capacity of 1064.2 mAh g−1 even under a high sulfur loading of 4.0 mg cm−2. Furthermore, a capacity retention can reach 67.1% after 110 cycles. This work emphasizes the importance of morphology design of multifunctional catalysts for high performance Li-S battery.

Anchoring and catalyzing polysulfides by rGO/MoS2/C modified separator in lithium–sulfur batteries

Effective adsorption and catalysis are vital in developing high-efficient and stable lithium-sulfur (Li–S) batteries. Here, a coral-like porous composite containing molybdenum sulfide (rGO/MoS2/C) as interlayer on the separator to mitigate polysulfide shuttling. Since the rGO/MoS2/C composite exhibits promising electrolyte wetting properties with a large specific surface area, which can be fully utilized for the adsorption of lithium polysulfides (LiPSs). In addition, the molybdenum sulfide active site can effectively bind to and catalyze the conversion of LiPSs, further preventing the penetration of LiPSs. As a result, the assembled device shows excellent cycle stability with a low capacity decay of 0.022% per cycle over 1000 cycles (2.0C). In addition, the device still preserves a decent cycle ability even at low electrolyte and high sulfur loading conditions. This work presents a feasible strategy to anchor and accelerate the conversion of LiPSs by designing multifunctional transition metal sulfide composites with high adsorption properties and catalytic activity to achieve stable cycle of Li–S batteries.

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

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

Mott-Schottky MXene@WS2 Heterostructure: Structural and Thermodynamic Insights and Application in Ultra Stable Lithium-Sulfur Batteries.

Due to the "shuttle effect" and low conversion kinetics of polysulfides, the cycle stability of lithium sulfur (Li-S) battery is unsatisfactory, which hinders its practical application. The Mott-Schottky heterostructures for Li-S batteries not only provide more catalytic/adsorption active sites, but also facilitate electrons transport by a built-in electric field, which are both beneficial for polysulfides conversion and long-term cycle stability. Here, MXene@WS2 heterostructure was constructed by in-situ hydrothermal growth for separator modification. In-depth ultraviolet photoelectron spectroscopy and ultraviolet visible diffuse reflectance spectroscopy analysis reveals that there is an energy band difference between MXene and WS2 , confirming the heterostructure nature of MXene@WS2 . DFT calculations indicate that the Mott-Schottky MXene@WS2 heterostructure can effectively promote electron transfer, improve the multi-step cathodic reaction kinetics, and further enhance polysulfides conversion. The built-in electric field of the heterostructure plays an important role in reducing the energy barrier of polysulfides conversion. Thermodynamic studies reveal the best stability of MXene@WS2 during polysulfides adsorption. As a result, the Li-S battery with MXene@WS2 modified separator exhibits high specific capacity (1613.7 mAh g-1 at 0.1 C) and excellent cycling stability (2000 cycles with 0.0286 % decay per cycle at 2 C). Even at a high sulfur loading of 6.3 mg cm-2 , the specific capacity could be retained by 60.0 % after 240 cycles at 0.3 C. This work provides deep structural and thermodynamic insights into MXene@WS2 heterostructure and its promising prospect of application in high performance Li-S batteries.

High Crystallinity 2D π-d Conjugated Conductive Metal-Organic Framework forBoosting PolysulfideConversion in Lithium-Sulfur Batteries.

The catalytic performance of metal-organic frameworks (MOFs) in Li-S batteries is significantly hindered by unsuitable pore size, low conductivity, and large steric contact hindrance between the catalytic site and lithium polysulfide (LPSs). Herein, the smallest π-conjugated hexaaminobenzene (HAB) as linker and Ni(II) ions as skeletal node are in situ assembled into high crystallinity Ni-HAB 2D conductive MOFs with dense Ni-N4 units via dsp2 hybridization on the surface of carbon nanotube (CNT), fabricating Ni-HAB@CNT as separator modified layer in Li-S batteries. As-obtained unique π-d conjugated Ni-HAB nanostructure features ordered micropores with suitable pore size (≈8 Å) induced by HAB ligands, which can cooperate with dense Ni-N4 chemisorption sites to effectively suppress the shuttle effect. Meanwhile, the conversion kinetics of LPSs is significantly accelerated owing to the small steric contact hindrance and increased delocalized electron density endued by the planar tetracoordinate structure. Consequently, the Li-S battery with Ni-HAB@CNT modified separator achieves an areal capacity of 6.29 mAh cm-2 at high sulfur loading of 6.5mg cm-2 under electrolyte/sulfur ratio of 5µL mg-1 . Moreover, Li-S single-electrode pouch cells with modified separators deliver a high reversible capacity of 791 mAh g-1 after 50 cycles at 0.1 C with electrolyte/sulfur ratio of 6µL mg-1 .

Accelerated Multi-step Sulfur Redox Reactions in Lithium-Sulfur Batteries Enabled by Dual Defects in Metal-Organic Framework-based Catalysts.

The sluggish sulfur redox kinetics and shuttle effect of lithium polysulfides (LiPSs) are recognized as the main obstacles to the practical applications of the lithium-sulfur (Li-S) batteries. Accelerated conversion by catalysis can mitigate these issues, leading to enhanced Li-S performance. However, a catalyst with single active site cannot simultaneously accelerate multiple LiPSs conversion. Herein, we developed a novel dual-defect (missing linker and missing cluster defects) metal-organic framework (MOF) as a new type of catalyst to achieve synergistic catalysis for the multi-step conversion reaction of LiPSs. Electrochemical tests and first-principle density functional theory (DFT) calculations revealed that different defects can realize targeted acceleration of stepwise reaction kinetics for LiPSs. Specifically, the missing linker defects can selectively accelerate the conversion of S8 →Li2 S4 , while the missing cluster defects can catalyze the reaction of Li2 S4 →Li2 S, so as to effectively inhibit the shuttle effect. Hence, the Li-S battery with an electrolyte to sulfur (E/S) ratio of 8.9 mL g-1 delivers a capacity of 1087 mAh g-1 at 0.2 C after 100 cycles. Even at high sulfur loading of 12.9 mg cm-2 and E/S=3.9 mL g-1 , an areal capacity of 10.4 mAh cm-2 for 45 cycles can still be obtained.

Accelerated Multi‐step Sulfur Redox Reactions in Lithium‐Sulfur Batteries Enabled by Dual Defects in Metal‐Organic Framework‐based Catalysts

AbstractThe sluggish sulfur redox kinetics and shuttle effect of lithium polysulfides (LiPSs) are recognized as the main obstacles to the practical applications of the lithium‐sulfur (Li−S) batteries. Accelerated conversion by catalysis can mitigate these issues, leading to enhanced Li−S performance. However, a catalyst with single active site cannot simultaneously accelerate multiple LiPSs conversion. Herein, we developed a novel dual‐defect (missing linker and missing cluster defects) metal–organic framework (MOF) as a new type of catalyst to achieve synergistic catalysis for the multi‐step conversion reaction of LiPSs. Electrochemical tests and first‐principle density functional theory (DFT) calculations revealed that different defects can realize targeted acceleration of stepwise reaction kinetics for LiPSs. Specifically, the missing linker defects can selectively accelerate the conversion of S8→Li2S4, while the missing cluster defects can catalyze the reaction of Li2S4→Li2S, so as to effectively inhibit the shuttle effect. Hence, the Li−S battery with an electrolyte to sulfur (E/S) ratio of 8.9 mL g−1 delivers a capacity of 1087 mAh g−1 at 0.2 C after 100 cycles. Even at high sulfur loading of 12.9 mg cm−2 and E/S=3.9 mL g−1, an areal capacity of 10.4 mAh cm−2 for 45 cycles can still be obtained.

Carbon-coated nitrogen, vanadium co-doped MXene interlayer for enhanced polysulfide shuttling inhibition in lithium-sulfur batteries

Polysulfides (LiPSs) shuttling significantly impedes the real application of lithium-sulfur (Li–S) batteries. Herein, nitrogen (N), vanadium (V)-co-doped MXene with N-doped carbon coating layer (denoted as CNVM) is prepared and then used as the interlayer material between cathode and commercial separator to suppress the shuttle effect of LiPSs. The doped heteroatoms alter the structure of MXene, enhancing the adsorption ability by providing enormous chemisorption sites for LiPSs and also accelerating the electron transfer. Meanwhile, the N-doped carbon coating further improves the electrical conductivity and raises the chemical affinity to LiPSs. Finally, enhanced electrochemical reaction kinetics and accelerated polysulfide conversion are obtained. Thus, the as-assembled Li–S batteries using the CNVM interlayer display high discharge capacity of 1373 mAh g−1 at 0.1 C, outstanding rate performance of discharge capacity up to 723 mAh g−1 at 3 C, long cycling life, as well as low average capacity degradation of 0.075% per cycle. Also, the practical application of the multifunctional CNVM-based interlayer is further manifested by the stable electrochemical performance even under a high sulfur loading of 7.2 mg cm−2 and decent service states of the as-assembled pouch cells.

Growing Electrocatalytic Conjugated Microporous Polymers on Self-Standing Carbon Nanotube Films Promotes the Rate Capability of Li-S Batteries.

Lithium-sulfur (Li-S) batteries hold great promise for widespread application on account of their high theoretical energy density (2600Wh kg-1 ) and the advantages of sulfur. Practical use, however, is impeded by the shuttle effect of polysulfides along with sluggish cathode kinetics. it is reported that such deleterious issues can be overcome by using a composite film (denoted as V-CMP@MWNT) that consists of a conjugated microporous polymer (CMP) embedded with vanadium single-atom catalysts (V SACs) and a network of multi-walled carbon nanotubes (MWNTs). V-CMP@MWNT films are fabricated by first electropolymerizing a bidentate ligand designed to coordinate to V metals on self-standing MWNT films followed by treating the CMP with a solution containing V ions. Li-S cells containing a V-CMP@MWNT film as interlayer exhibit outstanding performance metrics including a high cycling stability (616mA h g-1 at 0.5 C after 1000 cycles) and rate capability (804mA h g-1 at 10 C). An extraordinary area-specific capacity of 13.2mA h cm-2 is also measured at a high sulfur loading of 12.2mg cm-2 . The underlying mechanism that enables the V SACs to promote cathode kinetics and suppress the shuttle effect is elucidated through a series of electrochemical and spectroscopic techniques.

Regulation of the pore structure of carbon nanosheets based electrocatalyst for efficient polysulfides phase conversions

The practical applications of lithium-sulfur (Li-S) batteries are hampered by the sluggish redox kinetics and polysulfides shuttle in the cyclic process, which leads to a series of problems including the loss of active materials and poor cycling efficiency. In this paper, the pore structures of carbon nanosheets based electrocatalysts were precisely controlled by regulating the content of water-soluble KCl template. The relationship between pore structures and Li-S electrochemical behavior was studied, which demonstrates a key influence of pore structure in polysulfides phase conversions. In the liquid-sloid redox reaction of polysulfides, the micropores and small mesopores (d < 20 nm) exhibited little impact, while the mesopores (d > 20 nm) and macropores played a decisive role. As a typical exhibition, the nickel-embedded carbon nanosheets (Ni-CNS) with a high content of large mesopores and macropores can aid Li-S batteries in exhibiting stable cycling performance (760.1 mAh g−1 at 1 C after 300 cycles) and superior rate capacity (847.8 mAh g−1 at 2 C). Furthermore, even with high sulfur loading (8 mg cm−2) and low electrolyte (E/S is around 6 µL mg−1), the high area capacity of 7.7 mAh cm−2 at 0.05 C could be achieved. This work can provide a guideline for the design of the pore structure of carbon-based electrocatalysts toward high-efficiency sulfur species redox reactions, and afford a general, controllable, and simple approach to constructing high performance Li-S batteries.

Design of ZnSe-CoSe heterostructure decorated in hollow N-doped carbon nanocage with generous adsorption and catalysis sites for the reversibly fast kinetics of polysulfide conversion

Although lithium-sulfur batteries (LiSBs) are regarded as one of the most promising candidates for the next-generation energy storage system, the actual industrial application is hindered by the sluggish solid–liquid phase conversion kinetics, severe shuttle effect, and low sulfur loadings. Herein, a zeolitic imidazolate framework (ZIF) derived heterogeneous ZnSe-CoSe nanoparticles encapsulated in hollow N-doped carbon nanocage (ZnSe-CoSe-HNC) was designed by etching with tannic acid as a multifunctional electrocatalyst to boost the polysulfide conversion kinetics in LiSBs. The hollow structure in ZIF ensures large inner voids for sulfur and buffering volume expansions. Abundant exposed ZnSe-CoSe heterogeneous interfaces serve as bifunctional adsorption-catalytic centers to accelerate the conversion kinetics and alleviate the shuttle effect. Together with the highly conductive framework, the ZnSe-CoSe-HNC/S cathode exhibits a high initial reversible capacity of 1305.3 mA h g−1 at 0.2 C, high-rate capability, and reliable cycling stability under high sulfur loading and lean electrolyte (maintaining at 745 mA h g−1 after 200 cycles with a high sulfur loading of 6.4 mg cm−2 and a low electrolyte/sulfur ratio of 6 μL mg−1). Theoretical calculations have demonstrated the heterostructures of ZnSe-CoSe offer higher binding energy to lithium polysulfides than that of ZnSe or CoSe, facilitating the electron transfer to lithium polysulfides. This work provides a novel heterostructure with superior catalytic ability and hollow conductive architecture, paving the way for the practical application of functional sulfur electrodes.

3D conductive molecular framework derived MnO2/N, P co-doped carbon as sulfur hosts for high-performance lithium‑sulfur batteries

The practical application of lithium-sulfur (LiS) batteries is impeded by the shuttle effect and slow redox reaction kinetics, resulting in rapid capacity decay and low Coulombic efficiency. Three dimensional (3D) carbon-based network structure is used as sulfur host due to its special properties, such as high porosity and high conductivity. In this work, 3D MnO2/N, P co-doped carbon (3D MnO2/NPC) composites were achieved via freeze-drying MnO2/polyaniline composite aerogel followed by carbonizing process. The strongly polar MnO2 skeleton can provide sufficient adsorption capacity to anchor polysulfide and the heteroatom-doped carbon can compensate for the poor conductivity of MnO2 to guarantee the participation of rapid electrochemical reactions. As a result, the MnO2/NPC/S cathode demonstrates an initial specific discharge capacity of 1189 mAh g−1 at 0.2 C and a high rate capability of 569.2 mAh g−1 at 5 C, as well as excellent long-term cycling performance with the capacity decay rate of 0.033 % per cycle for 1000 cycles at 1 C. Moreover, the cathode exhibits excellent cycling stability even at a high sulfur loading of 6 mg cm−2.

Two Birds with One Stone: Ammonium-Induced Carbon Nanotube Structure and Low-Crystalline Cobalt Nanoparticles Enabling High Performance of Lithium-Sulfur Batteries

The electrochemical performance of lithium–sulfur batteries (LiSBs) has been hampered by the slow redox kinetics and shuttle effect of lithium polysulfides (LiPSs), which require the rational design and synthesis of highly active electrocatalysts towards this reaction. Herein, worm-like N-doped porous carbon nanotube-supported low-crystalline Co nanoparticles (a-Co-NC@C) were derived from binary Zn–Co ZIF via a two-step thermal annealing method. Initial thermal annealing 950 °C in Ar + H2 atmosphere results in the carbonization of binary Zn–Co ZIF and the formation of high crystalline Co nanoparticles. Thermal annealing in ammonia atmosphere at 350 °C not only results in the reduced crystallinity of cobalt nanoparticles; it also promotes the growth of highly graphitized and heavily N-doped intertwined carbon nanotubes. The enlarged porous carbon nanotube structure offers accommodation for sulfur content, while the doped carbon and Co nanoparticles with reduced crystallinity facilitate the redox kinetics of LiPSs, improving the cycling stability, rate performance and capacity of LiSBs batteries. As a result, the a-Co-NC@C cathode displays a specific capacity of 559 mAh g−1 after 500 cycles at 1 C, and a specific capacity of 572 mAh g−1 at 3 C. It delivers a specific capacity of 579 mAh g−1 at high sulfur loading of a 2.55 mg cm−2 at 1 C after 400 cycles. This work highlights the importance of phase engineering of carbon matrix and transition metal nanoparticles in electrochemical performance of Li-S batteries.

Uniform loading of ultrathin MoS2 nanosheets on hollow carbon spheres with mesoporous walls as efficient sulfur hosts for promising lithium-sulfur batteries

The electrochemical performance of lithium-sulfur batteries (LSBs) can be improved by combining rational structural design with the high-efficient catalyst to construct sulfur host materials. The PVP-assisted hydrothermal method was used to synthesize a composite (HCSM@uMoS2) with ultrathin MoS2 nanosheets uniformly loaded on hollow carbon spheres with mesoporous walls (HCSM). The ultrathin MoS2 nanosheets containing 1T metal phase (uMoS2) improved the electrical conductivity of the material while exposing more active sites, enhanced the adsorption to polysulfide and improved the redox reaction kinetics for polysulfide, thus fully suppressing the shuttle effect. Together with the advantages of HCSM, the mesoporous walls and internal cavity can offer enough sulfur storage room and significantly buffer the volume expansion of sulfur species; the high specific surface area and abundant porosity favor electron/ion transfers. As a result, the HCSM@uMoS2-S electrode exhibited outstanding electrochemical performance (675.4 mAh g−1 retention capacity at 0.5 C for 500 cycles) even under the conditions of high areal sulfur loading (5.6 mg cm−2) and less electrolyte (E/S = 10 μL mg−1). This study provides a reference for building sulfur hosts for high-capacity, long-life, and practical LSBs.