Cathode Material For Lithium-sulfur Batteries Research Articles

Nitrogen sulfur dual-doped porous biochar fibers for high performance lithium-sulfur battery

Porous carbons have gained great attention for applications in lithium-sulfur (Li-S) batteries. However, achieving high specific surface area, hierarchical porosity, and abundant heteroatom-doping with facile approaches is still challenging. Herein, nitrogen, sulfur dual-doped hierarchical porous carbons (PBF@N@S) are obtained via a simple and sustainable activation process of cotton fibers. The as-prepared PBF@N@S exhibits a hierarchically interconnected network porous structure and large specific surface area. Meanwhile, abundant nitrogen, sulfur atoms are simultaneously doped in the carbons. These characteristics make the carbon favorable for hosting sulfur. The PBF@N@S sample with 50 wt% sulfur content (PBF@N@S-S-50%) delivers a high initial capacity with excellent cycling performance. Such high performance suggests that the PBF@N@S-S could be a promising cathode material for Li-S batteries.

Theoretical identification of the superior anchoring effect and electrochemical performance of Ti2CS2 by single atom Zn doping for lithium-sulfur batteries.

As one of the promising next-generation energy storage systems, lithium-sulfur (Li-S) batteries have been the subject of much recent attention. However, the polysulfide shuttle effect remains problematic owing to the dissolution of intermediate polysulfide species in the electrolyte and the sluggish reaction dynamics in Li-S batteries. To overcome these issues, this work reports an effective strategy for enhancing the electrochemical performance of Li-S batteries using single atom Zn doping on the S-terminated Ti2C MXenes (Ti2-xZnxCS2). Spin-polarized density functional theory (DFT) calculations were performed to elucidate the interactions of lithium polysulfides (LiPSs) and the Ti2-xZnxCS2 surface in terms of geometric and electronic properties, as well as the delithiation process of Li2S on the Ti2-xZnxCS2 surface. It is found that doping single atom Zn could induce a new Lewis acid-based sites, which could provide proper affinity toward LiPSs. Combined with the metallic character, a low Li diffusion barrier and high catalytic activity for the delithiation process of Li2S, makes Ti2-xZnxCS2 a promising cathode material for Li-S batteries. The results demonstrate the importance of surface chemistry and the electronic structure of MXenes in LiPSs' adsorption and catalysis capability. We believe that our findings provide insights into the recent experimental results and guidance for the preparation and practical application of MXenes in Li-S batteries.

Water Kefir Grains-Microbial Biomass Source for Carbonaceous Materials Used as Sulfur-Host Cathode in Li-S Batteries.

Nowadays, the use of biomass to produce cathode materials for lithium-sulfur (Li-S) batteries is an excellent alternative due to its numerous advantages. Generally, biomass-derived materials are abundant, and their production processes are environmentally friendly, inexpensive, safe, and easily scalable. Herein, a novel biomass-derived material was used as the cathode material in Li-S batteries. The synthesis of the new carbonaceous materials by simple carbonization and washing of water kefir grains, i.e., a mixed culture of micro-organisms, is reported. The carbonaceous materials were characterized morphologically, texturally and chemically by using scanning electron microscopy, N2 adsorption-desorption, thermogravimetric analysis, X-ray diffraction, and both Raman and X-ray photoelectron spectroscopy. After sulfur infiltration using the melt diffusion method, a high sulfur content of ~70% was achieved. Results demonstrated that the cell fitted with a cathode prepared following a washing step with distilled water after carbonization of the water kefir grains only, i.e., not subjected to any chemical activation, achieved good electrochemical performance at 0.1 C. The cell reached capacity values of 1019 and 500 mAh g-1 sulfur for the first cycle and after 200 cycles, respectively, at a high mass loading of 2.5 mgS cm-2. Finally, a mass loading study was carried out.

Integration of PDAAQ and Non-stoichiometric MgO as Host Cathode Materials for Lithium-Sulfur Batteries with Superior Cycle Stability: Density Functional Theory Calculations and Experimental Validations

Integration of PDAAQ and Non-stoichiometric MgO as Host Cathode Materials for Lithium-Sulfur Batteries with Superior Cycle Stability: Density Functional Theory Calculations and Experimental Validations

Environmentally friendly, non-glove box, closed-system and continuously massive production of lithium sulfide for battery applications

Lithium sulfide (Li2S) is an important material for lithium-sulfur batteries and solid-state batteries. However, its prohibitive price hinders the practical development of these technologies, reflecting multiple problems in existing production processes including high temperature/energy demands, greenhouse gas emissions, low yield, low purity and the use of air sensitive equipment. Herein we report the development of an environmentally friendly process for the scalable production of Li2S without need for a glove box. The net chemical process is the reaction between Li metal and hydrogen sulfide (H2S) with ethanol as the auxiliary solvent, which can in principle be recovered and recycled. The production capability reaches 1.0 kg_Li2S/day, 50–100 times greater than the largest scale reported in the literature. The material quality of the resulting Li2S is validated through its use as a cathode material in lithium-sulfur batteries, achieving essentially comparable performance with commercial Li2S. Moreover, additional value is provided by concomitant H2 production which is demonstrated through its use for the in-situ reduction of copper oxide. We believe that the process described by this work can be readily adapted to support the developments of advanced batteries.

Design of transition metal carbonitrides (MCNs) as promising anchoring and high catalytic performance materials for lithium-sulfur batteries

The challenges faced by the application of lithium-sulfur (Li-S) batteries with high specific capacity and high energy density include the shuttle effect, which reduces the rate of sulfur reduction reaction (SRR), the difficulty of decomposition of insoluble Li2S during charging, and poor conductivity during charging and discharging. Herein, the adsorption, catalytic and electrical properties of a new class of two-dimensional transition metal carbonitrides (MCNs) have been systematically investigated as candidate cathodes for Li-S batteries. Density functional theory (DFT) calculations combined with van der Waals (vdW) interaction analysis show that TiCN and VCN can effectively suppress the shuttle effect with different solvents. The analysis of the Gibbs free energy and Li2S decomposition energy barrier of the lithiation process show that TiCN and VCN can significantly accelerate the decomposition of Li2S and sulfur reduction reaction, and improves the battery cycle performance. Moreover, the quantum conductivity (G) and density of state (DOS) of the VCN cathode during the whole charge-discharge process indicate that the electrode always has good conductivity. Based on these advantages, VCN is considered as a potential high-performance cathode material for Li-S batteries. This research has a certain guiding effect on the application of two-dimensional (2D) carbon and nitrogen materials in Li-S batteries.

Sulfur/Polyacrylonitrile-Based N-Terminated Graphene Nanoribbon Cathodes for Li-S Batteries

Conductive sulfur/carbon copolymers with a high reversible capacity are promising alternative cathode materials for lithium-sulfur batteries. Here, the focus is set on nitrogen-terminated zigzag graphene nanoribbons (N-GNRs) resembling intermediate product of electrospun polyacrylonitrile (PAN)-based carbon nanofibers. In particular, the possibility of combining strong nitrogen-sulfur interactions, which has been recently shown to lead to a shuttle-free discharge mechanism, and superior electrical conductivity of graphene nanoribbons is explored in S/N-GNR copolymers. Structural and electronic properties of ${\mathrm{S}}_{x}/$N-GNR structures, $x=1,\dots{},8$, prior and during the discharge are studied using density-functional theory calculations along with ab initio molecular dynamics simulations. It is found that the GNR backbone assumes a rippled structures in all S/N-GNR structures considered here. The most favorable sulfur structures in S/N-GNR copolymers are found to consist of short sulfur chains with $x\ensuremath{\sim}4,5$. It is also observed that, similar to N-GNRs, S/N-GNR copolymers show a metallic behavior which is brought about by the conductive backbone. In addition, consecutive lithiation reactions are studied and product structures are obtained. It is demonstrated that a shuttle-free, solid-solid transformation could also be expected during the discharge of S/N-GNR copolymers, whereas the lithiated structures remain electrically conductive, irrespective of the discharge state. Therefore, the current study promotes the use of S/N-GNR copolymers as an alternative to other poorly conductive PAN-based S/C copolymer cathodes for lithium-sulfur batteries (such as S/cPAN), while largely mitigating lithium polysulfide formation.

Improvement of Sulfur Cathode Reversibility by Specific Chemical Lithium Pre-doping Method

1.IntoroductionRecently, lithium-ion batteries (LIBs) have been required in terms of a high energy density for large-scale applications such as power supplies for electric vehicles. Lithium-sulfur (Li-S) batteries are, therefore, expected as next generation batteries because of their high energy density.Sulfur is utilized as cathode material for Li-S batteries because of a high specific capacity. However, sulfur has a low electric conductivity and a risk of dissolution into an electrolyte during a charge-discharge process [1]. L. Nazar et al. applied activated carbon as substrate for sulfur to help electric conduction and prevent dissolution of sulfur [2]. The activated carbon allows Li-S batteries to show high specific capacity with high reversibility. Even if these problems are solved, however, Li-S batteries have a further problem of excessive initial irreversible capacity during the first discharge process. Li pre-doping is a useful technique to cancel the large irreversible capacity in actual LIBs. Abe et al. reported a chemical lithium pre-doping method for a graphite using lithium naphthalenide [3]. Studies have been reported on the use of such pre-doping to improve the performance of Li-S batteries, for instance, with a sulfur-Ketjenblack composite cathode [4]. In our previous study, we have applied that method to a sulfur cathode composed of microporous activated carbon and sulfur before cell assembly and developed a Li2S cathode that suppressed the initial irreversible capacity during the first discharge process. However, the Li2S cathode showed an unignorable initial irreversible capacity and poor cycle life [5].This work attempts to improve the reversible capacity of the Li2S cathode by a specialized chemical lithium pre-doping method. Our report would lead to the proposal of novel cathode and anode options in Li-S batteries. Method 2-1. Fabrication of lithium naphthalenide solutionAs Li metal and Li2S are both sensitive to moisture in air, all the following synthesis processes were carried out in an Ar-filled glove box. Lithium naphthalenide, a dark green solution was prepared by mixing an equal mol amount of Li metal with naphthalene in a cyclic ether solvent.2-2. Fabrication of Li2S-AC cathodesEach sulfur cathode was prepared by mixing the S-AC (a composite of microporous activated carbon and sulfur), acetylene black, carboxymethyl cellulose, and styrene butadiene rubber at a respective weight ratio of 93: 3: 2: 2 and coating the resulting aqueous slurry on a carbon paper.The 1M lithium naphthalenide solution was dropped on the sulfur cathode. After 20 min reaction, the cathode was rinsed several times with 2–dimethoxyethane (DME) to remove the residues of reagents. The cathode was then dried under reduced pressure for 12 h. After that, the resulting Li2S cathode was impregnated with a mixture of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) (VC: FEC = 1: 1 by weight). After 20 min impregnation, the cathode was dried under reduced pressure for 12 h.2-3. Assembling of cellsCells were assembled with the Li2S electrode and Li metal foil as an anode. Lithium bis(trifluorosulfonyl)imide (LiTFSI): tetraglyme (G4): 1,1,2,2–tetrafluoroethyl–2,2,3,3–tetrafluoropropyl ether (D2) at a respective ratio of 10: 8: 40 (by mol) was used as the electrolyte.3.Major results and discussionThe Li2S cathode without the VC/FEC impregnation showed an initial charge capacity of 1791 mAh g-1 and an initial discharge capacity of 1298 mAh g-1, indicating a large irreversible capacity. In contrast, the Li2S cathode with the VC/FEC impregnation showed 1446 mAh g-1 and 1422 mAh g-1, respectively. Thus, the impregnation with VC/FEC reduced the initial irreversible capacity and improved the initial charge capacity. According to these results, Li remaining in the sulfur cathode would be partially consumed to form a film by the impregnation with VC/FEC. In addition, the capacity retention of the Li2S cathode with and without the VC/FEC impregnation was 73 % and 64 % at the 30th cycle, respectively. This suggests that the Li2S cathode with the film leads to better cycle performance than that without the film.We will also report the results of surface composition analysis of the Li2S cathode with and without the VC/FEC impregnation by Hard X-ray Photoelectron Spectroscopy (HAXPES).

Synthesis of hollow S/FeS2@carbon nanotubes microspheres and their long-term cycling performances as cathode material for lithium-sulfur batteries

• The dissolution of lithium polysulfides is effectively alleviated. • CNTs improve the conductivity of S/FeS 2 @CNTs composites. • Low capacity decay rate of 0.024% per cycle for over 500 cycles is obtained. The lithium-sulfur batteries as a promising next-generation rechargeable battery are practically limited by their poor long-term cycling performance originating from the dissolution of lithium polysulfides. Combining physical and chemical interactions to trap lithium polysulfides is an effective way to improve the long-term cycling performance. Herein we have synthesized the hollow S/FeS 2 @Carbon nanotubes (S/FeS 2 @CNTs) microspheres by loading sulfur into FeS 2 @CNTs microspheres with carbon nanotubes entangling hollow FeS 2 microspheres. The hollow S/FeS 2 @CNTs microspheres working as cathode for lithium-sulfur batteries have delivered initial discharge capacity of 1245 mA h g −1 at 0.2 C. Particularly, the long-term cycling performance has been achieved that the capacity beyond 440.2 mA h g -1 can maintain for 500 cycles at 1 C, with a low capacity decay rate of 0.024 % per cycle. The significantly improved cycling performance of S/FeS 2 @CNTs can be attributed to the synergistic effects that the dissolution of lithium polysulfides diminishes by combining the physical interaction of CNTs with chemical absorption of FeS 2 , as well as the volume expansion of the cathode can be alleviated by the internal void space.

Suppressing Polysulfides Shuttling and Promoting Sulfur Utilization via Transition Metal and Nitrogen Co-Doping on Graphdiyne Cathodes of Lithium-Sulfur Batteries: A First-Principles Modeling

While lithium-sulfur (Li-S) batteries are considered the next-generation energy storage devices, several issues inhibit their commercialization, including poor conductivity, shuttling of lithium polysulfides (LiPSs), and sluggish decomposition of small LiPSs. Here, we illustrate through first-principles modeling that doping graphdiyne (GDY) with transition metal (Co, Fe) and nitrogen (TM-N) effectively suppresses the shuttle effect and enhances sulfur utilization by promoting dissociation of small LiPSs. We find that the TM-N doping provides additional electrons to the substrate, which could improve the redox activity of the substrates. The additional electrons also improve charge transfer between the substrate and adsorbate that enhances the LiPS adsorption. Electronic structure analysis reveals that the strong interactions originate from the formation of TM-S bonds and electrostatic attractions between Li and N. Such strong adsorptions prevail in the interaction between the LiPSs and electrolyte molecules; hence, the doped GDY could effectively prevent the dissolution of LiPSs and inhibit the shuttle effect. Moreover, the doped GDY substrates exhibit small barriers of Li–S and Li–N bond breaking that facilitate the decomposition of small LiPSs. This implies that TM-N-doped GDY promotes kinetics of LiPS transformation, which increases sulfur utilization and diminishes capacity fading upon charge–discharge cycles. From the computational viewpoints, the TM-N-doped GDY substrates are considered promising cathodes of Li-S batteries. This work serves as a useful guide to rationally design high-performance two-dimensional (2D) carbon-based cathode materials for Li-S batteries.

Increasing N active sites by in-situ growing conformal C3N4 layer in hierarchical porous carbon-based networks for fast Li+ transfer and polysulfide anchoring in lithium-sulfur batteries

Various challenges remain to be overcome in lithium-sulfur (Li-S) batteries, including the volume expansion and low conductivity of sulfur, the shuttle effect of lithium polysulfides and the sluggish redox reaction in the cell. Herein, we propose a multilayered conductive framework by the in situ growth of a conformal graphene-like C3N4 (GCN) coating on porous CNT@NC networks with carbon nanotubes (CNTs) as the core and N-doped carbon (NC) as the crosslinking shell. The abundant N in the GCN coating increased the surface N concentration of the framework from 14.38% to 18.77%, which enriched the active sites in the frameworks for the adsorption and catalysis conversion of LiPSs and Li2S with a low energy barrier. Furthermore, the scalable frameworks can provide an 85% porosity for a sufficient reaction interface and accommodate the volume expansion of sulfur. The synergistic effect between GCN and the highly conductive hierarchical structure can accelerate the transport of Li+ and electrons as well as the diffusion of electrolyte. Benefitting from the above advantages, the Al-free CNT@NC@GCN electrode exhibits a reversible capacity of 647.6 mAh g−1 after cycling for 450 cycles at 1C with a low capacity fading rate of 0.09% per cycle. This proposed facile strategy creates inspiring insights into the design of novel cathode materials for Li-S batteries.

Novel nitrogen-doped bamboo-structure carbon nanotubes as superior sulfur host for high-performance lithium-sulfur batteries

In this work, nitrogen-doped bamboo-structure carbon nanotubes (BCNTs) with large diameters (ranging from 50 nm to 300 nm), high specific surface area (437.41 m2·g−1) and thin tube wall (less than 8 carbon layers) were prepared as sulfur host for lithium-sulfur (Li-S) batteries. Sulfur nanoparticles (NPs) with diameters of 20–30 nm were in-situ synthesized on the surface of BCNTs by a facile ultrasonic treatment, which can enhance the binding ability between sulfur and carbon, and then improve the utilization of sulfur. It is found that the in-situ synthesized S@BCNTs composite cathode with a high sulfur content of 62.2 wt% exhibits an initial specific capacity of 1008.4 mAh·g−1 at a current density of 0.1 C, and can still maintain a capacity of 383.9 mAh·g−1 after 500 cycles. Careful composition and microstructure analyses reveal that these excellent electrochemical performance can be ascribed to the synergistic effect of conductive nitrogen doping (especially pyridinic-N and pyrrolic-N) and homogeneous sulfur coating on the surface of BCNTs, which contributes to accelerating electron transport, adsorbing polysulfides and alleviating the shuttle effect. As a result, the as-prepared nitrogen-doped BCNTs can be pretty promising cathode materials for Li-S batteries. This work can open up a new possibility for the design of stable Li-S cathodes for high-performance batteries.

Design of Novel Transition-Metal-Doped C6N2 with High-Efficiency Polysulfide Anchoring and Catalytic Performances toward Application in Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are highly expected because of their high theoretical specific capacity and energy density. However, its application still faces challenges, including the shuttle effect affecting the sulfur reduction reaction, the high decomposition energy barrier of Li2S during charging, the volume change of sulfur, and the poor conductivity during charging and discharging. Here, combined with density functional theory and particle swarm optimization algorithm for the nitrogen carbide monolayer structural search (CmN8-m, m = 1-8), the surprising discovery is that a single metal-atom-doped C6N2 monolayer could effectively accelerate the conversion of lithium polysulfide and anchor lithium polysulfide during discharging and decrease the decomposition energy barrier of Li2S during charging. This "anchoring and catalyzing" mechanism effectively reduces the shuttle effect and greatly improves the reaction kinetics. Among a series of metal atoms, Cr is the best doping element, and it exhibits suitable adsorption energy for polysulfides and the lowest decomposition energy barrier for Li2S. This work opens up a new way for the development of transition-metal-doped carbon-nitrogen materials with an excellent catalytic activity for lithium polysulfide as cathode materials for Li-S batteries.

Cubic pyrite nickel sulfide nanospheres decorated with Ketjen black@sulfur composite for promoting polysulfides redox kinetics in lithium-sulfur batteries

Lithium polysulfides shuttle effect and their sluggish redox kinetics have seriously affected the development of lithium-sulfur batteries. To solve these issues, we have designed cubic pyrite-structure NiS 2 nanospheres modification of Ketjen black@sulfur (NiS 2 /KB@S) composite as cathode materials for lithium-sulfur batteries. The NiS 2 nanospheres have a positive effect on the adsorption and catalysis performance of the lithium polysulfides, which further facilitates the redox kinetics. Consequently, the NiS 2 /KB@S cathode with 3.1 mg cm −2 sulfur loading attains a discharge capacity of 869 mAh g −1 at 0.5 C and reversible capacity is 461 mAh g −1 after 500 cycles. Even at high sulfur loading of 5.3 mg cm −2 , the NiS 2 /KB@S electrode still delivers a high initial area capacity of 4.82 mAh cm −2 at 0.2 C with capacity retention capacity of 3.74 mAh cm −2 after 120 cycles. The cyclic and rate properties of NiS 2 /KB@S are greatly improved over that of KB@S. The results suggest that multifunction cubic pyrite-structure NiS 2 nanospheres that anchors effectively and catalysis is beneficial to the large-scale application for lithium-sulfur batteries. • Pyrite NiS 2 nanospheres serve as an activation catalyst in Li/S batteries. • Kinetic analyses prove that NiS 2 accelerates the redox kinetics of polysulfides. • NiS 2 /KB@S cathode achieves better cycling performance than KB@S.

Ultralong cycle life enabled by in situ growth of CoMo1−xP/Mo heterostructure for lithium-sulfur batteries

Lithium-sulfur batteries (Li-S batteries) are considered as promising new-generation electrochemical energy storage devices due to their extremely high theoretical energy density (2600 Wh kg−1) and theoretical specific capacity (1675 mAh g−1). However, numerous problems such as poor conductivity and the shuttle effect during discharge–charge process limit the practical application of lithium-sulfur batteries. In this work, porous tubular CoMo1−xP/Mo constructed by in situ growth of metal Mo was designed as the sulfur host for lithium-sulfur batteries. The introduction of Mo modulated the electronic structure of CoMoP to improve the conductivity of cathode and facilitate the redox kinetics, as well as the CoMo1−xP/Mo heterostructure was beneficial to inhibit the shuttle effect through the interaction with lithium polysulfides, which improved cycling stability. As a result, CoMo1−xP/Mo/S cathode had a low-capacity decay rate of only 0.029% per cycle after 2000 cycles at 0.5 C. This work provided a new perspective for the further design of high-performance lithium-sulfur battery cathode materials.

Boron nitride wrapped N-doped carbon nanosheet as a host for advanced lithium-sulfur battery

Sandwich structure of boron nitride (BN) nanocrystals wrapped with uniform interconnected N-doped carbon nanosheets (N-CNs) is prepared as a lithium-sulfur battery cathode material to overcome the sluggish redox reaction and severe “shuttle effect” of lithium polysulfides (LiPSs). The BN@N-CNs-2/S presents outstanding rate capacity of 528 mAh g−1 at 2 A g−1, with extended cycle life and sluggish capacity decrease rate of 0.026% per cycle at 2 A g−1 for more than 1000 cycles. Such high performance is a result of the unique sandwich structure of BN nanocrystals evenly compounded on N-CNs, which leads to uniform distribution of active sulfur species and effectively alleviates volume expansion in the cycling process. The BN@N-CNs sandwich structure possesses the key advantages of high conductivity of N-CNs, strong chemisorption and catalytic effect for LiPSs, which is demonstrated by theoretical calculations and cyclic voltammetry curves of the symmetrical cells.

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

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

Preparation of macadamia nut shell porous carbon and its electrochemical performance as cathode material for lithium–sulfur batteries

Biomass carbon material as the sulfur storage matrix of lithium–sulfur batteries is one of the research hotspots. In this paper, the macadamia nut shells are used as the precursor to prepare porous carbon material. By exploring the effect of temperature on the microstructure and electrochemical performance of porous carbon materials during activation, it is found that the porous carbon material prepared under the activation condition of 900 °C has a developed pore structure, super high specific surface area (3552.7 m2•g−1), larger pore volume (2.2 cm3•g−1) and higher mesoporous content (23.85%). And the composite cathode material with the sulfur content of 70.1% has the highest specific capacity, and the initial discharge specific capacity for 0.2 C can reach 942.4 mAh•g−1. The composite material S/OCNT@OPC-1:1 obtained by compounding it with carbon nanotubes at a mass ratio of 1:1 has higher specific capacity, better rate performance and cycle performance. At 0.2 C, the initial discharge specific capacity is as high as 1252.6 mAh•g−1, and it remains at the level of 717.3 mAh•g−1 after 200 cycles. Even at 1 C, the specific capacity is still 984.3 mAh•g−1, and it remains at 690.9 mAh•g−1 after 200 cycles, and the capacity retention rate is 70.2%. Our work shows that the composite material obtained by combining low-cost biomass carbon materials and carbon nanotubes as the cathode material for lithium-sulfur batteries has obvious advantages.

Recent advances on graphene-based materials as cathode materials in lithium-sulfur batteries

Representing one of the advanced energy storage devices, lithium-sulfur batteries have a wide range of possible applications. While it serves as a promising energy storage system, it should adhere to multiple important criteria before a large-scale application can be realized. The novel uses of graphene can resolve the deficiencies of lithium-sulfur batteries. Graphene is an exceptional conductive material with excellent mechanical stability and is extremely flexible. Because of its large porosity value, it enables a high sulfur loading within its matrix and effectively encapsulates polysulfide. Graphene oxide, on the other hand, often exhibits a number of functional groups capable of chemically bonding to polysulfides, resulting in good capability for polysulfide entrapping. Physical containment of sulfur by graphene materials and its chemical interactions with sulfur can be further improved by designing 3D graphene-sulfur configurations through doping of functional groups or heteroatoms. This review article offers an insight into the strategies for achieving a high sulfur loading cathode with a long cycle life and high retention potential through sulfur containment and carbon host functionalization, for which this review focuses on the functionalization of graphene. Throughout these strategies, significant performance improvements can be achieved. • LSB as one of the promising alternatives for lithium-ion battery. • Discussion on solutions for key issues affecting the performance of LSB cathode. • Overview of the scientific and technological works in graphene-based LSB cathode. • Graphene with chemical and physical irregularities is more favorable as cathode.

Enhanced multiple anchoring and catalytic conversion of polysulfides by SnO2-decorated MoS2 hollow microspheres for high-performance lithium-sulfur batteries

Lithium-Sulfur (Li-S) batteries are very competitive in energy storage equipment due to their high theoretical capacity and low cost of raw materials. However, the serious polysulfide "shuttle effect", volume expansion effect and slow conversion reaction kinetics of Li−S batteries during the charge/discharge cycle process still need to be resolved urgently. Herein, we prepared a novel sulfur host of SnO2-decorated MoS2 hollow microspheres (SnO2-MoS2 HMSs). The unique hollow structure provides enough space to accommodate a large amount of sulfur and effectively adapts to its large volume expansion during charge and discharge process. On the other hand, the SnO2 nanoparticles that attached to the surface of the MoS2 nanosheets will accelerate the catalysis of MoS2 and enhance the bonding strength with the polysulfide intermediates through the S−Sn−O chemical bond, which further inhibits the shuttle effect. The newly synthesized SnO2-MoS2 HMSs cathode has achieved excellent electrochemical performance. The initial discharge specific capacity of 1326.4 mAh g−1 was obtained at 0.2 C, and after 100 cycles, the specific capacity of the SnO2-MoS2 HMSs/S cathode only decreased slightly to 1183.8 mAh g−1, its capacity retention rate reaching as high as 89.2%. We expect the newly synthesized hollow structured MoS2 with SnO2 decoration provides a new strategy for the construction of Li-S battery cathode materials.