Host Materials For Lithium-sulfur Batteries Research Articles

Recent advances in carbon-based sulfur host materials for lithium-sulfur batteries

Lithium-sulfur batteries (LSBs) have been brought into focus as the development direction of the next-generation power battery system due to their high energy density, eco-friendliness, and low cost, which has a broad application prospect in the field of energy storage. However, some problems are still unresolved in the sulfur cathode, e.g., poor electric conductivity, serious volume expansion of sulfur, shuttle effect caused by easy dissolution of lithium polysulfides in the electrolyte, and slow redox reaction kinetics of sulfur species. These issues lead to poor cycle stability and rate performance, making it hard to meet the requirement for LSBs in practical applications. Since the inherent nature of sulfur is the root cause of the above problems, reasonable design of functional sulfur hosts will be an effective way to break through the current bottlenecks of LSBs. The review covers the latest research progress on carbon-based sulfur host materials of LSBs, including structural design and functional optimization strategies, aiming to prepare multifunctional sulfur host materials by integrating physical confinement, chemical adsorption, and catalytic effect towards lithium polysulfides. The obstacles and future prospects of carbon-based sulfur hosts have also been brought forward, which provides in-depth guidance for practical application of LSBs.

Monolayer SrB8 as potential highly efficient electrocatalysts for lithium-sulfur batteries: First principle study

Lithium-sulfur batteries have extremely high theoretical specific capacity and energy density, but their commercial application has been hindered by the shuttle effect, poor cathode conductivity and sluggish reaction kinetics during charging and discharging. The proposed two-dimensional (2D) multifunctional sulfur host material is an effective strategy to solve the above problems. In this work, the anchoring and catalytic properties of SrB8 monolayer for S8 and Li2Sn (n = 1, 2, 4, 6, 8) were studied by means of density functional theory. The results show that SrB8 has moderate adsorption energy for lithium polysulfides (LiPSs), and can effectively prevent the dissolution of long-chain LiPSs into the electrolyte without destroying the integrity of the clusters. The metallic feature of the SrB8 monolayer is well preserved during the adsorption process, thus ensuring a high electric conductivity at the cathode. At the same time, the SrB8 monolayer has a lower decomposition barrier and diffusion barrier for Li2S molecules, which significantly improves the charge and discharge rate of lithium-sulfur batteries. The results show that SrB8 monolayer is a promising multifunctional host material for lithium-sulfur batteries.

Flower-like covalent organic frameworks as host materials for high-performance lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have emerged as a promising alternative energy storage system due to their high energy density and cost-effectiveness. However, practical applications of Li-S batteries are hindered by challenges such as the shuttle effect and sluggish redox kinetics. In this study, a three-dimensional (3D) flower-like diaminoanthraquinone (DAAQ)-covalent organic framework (COF) was developed, featuring nanorod-like petals and enriched with abundant N and O adsorption sites, serving as a host material for the sulfur cathode of Li-S batteries. Through a process of sulfur melting-diffusion, the resulting DAAQ-COF@S cathode material demonstrated a stable 3D cross-linked morphology with a hierarchical pore structure, maximizing the exposure of N/O adsorptive sites and facilitating rapid ion diffusion. This effectively inhibited the shuttling effect of lithium polysulfides (LiPSs) and enhanced rate performance. Consequently, DAAQ-COF@S cathodes exhibited a high initial discharge capacity of 1182.0 mAh g−1 at 0.1 C, with a capacity retention rate of 79.6% after 500 cycles at 2 C. Even at a high current density of 4 C, they maintained a high capacity of 616.8 mAh g−1, surpassing the majority of previously reported COF-based host materials for Li-S batteries. This work underscores the significance of COF micromorphology and advances the development of high-performance cathodes for Li-S batteries.

CeO2/Co heterostructure encapsulated in hollow necklace-like carbon fiber as an advanced host material for high-performance lithium-sulfur batteries

The shuttle effect of lithium polysulfides (LiPSs) and the sluggish reaction kinetics of LiPSs conversion pose serious challenges to the commercial feasibility of lithium-sulfur (Li-S) batteries. To address these obstacles, herein, we construct CeO2/Co heterostructures in hollow necklace-like carbon fibers (CeO2/Co-CNFs) as the cathode host material for Li-S batteries. The specific surface area of fibers is significantly enhanced by using a template, thereby promoting the utilization efficiency of sulfur. Meanwhile, CeO2/Co-CNFs show strong conductivity, effective adsorption to LiPSs, and robust catalytic activity for LiPSs conversion. As a result, the Li-S battery with CeO2/Co-CNFs displays 961 mAh g−1 at 0.2 C, with an 86 % capacity retention rate after 100 cycles. At 2.0 C current density, the composite cathode maintains an initial discharge capacity of 782 mAh g−1, with a mere 0.044 % capacity loss per cycle. Furthermore, in situations with limited electrolytes, high sulfur loading, and high areal mass loading, the composite cathode can provide a high areal capacity of 6.2 mg cm−2 over 100 cycles. This work provides a useful approach for investigating high-performance Li-S battery cathodes.

Chemical Interactions between Dissolved Polysulfides and Potential Catalytic Host Materials for Li-S Batteries.

Given that both elemental sulfur (S8) and lithium sulfide (Li2S) exhibit insulating properties, the involvement of conductive host materials becomes crucial for facilitating charge transfer in sulfur cathodes within lithium-sulfur (Li-S) batteries. Furthermore, there has been a recent surge in the exploration of host materials for sulfur cathodes to address the "polysulfide shuttle" effect. This effect arises from the formation of polysulfide species during the charge-discharge cycles of the Li-S batteries and can be mitigated through physical or chemical interactions with specific materials. To qualitatively and accurately assess the interactions between polysulfides and the potential host materials, this study utilized a well-established high-performance liquid chromatography method for polysulfide analysis. The objective was to monitor the changes in polysulfide solutions after contact with 44 different carbon and inorganic materials. Based on both qualitative and quantitative chromatographic results, it was determined that 20 out of the 44 materials exhibit significant interactions with polysulfides. The primary form of interaction observed is the irreversible disproportionation reaction with elemental sulfur being one of the resulting products.

Physical and Electrochemical Properties of Transition Metal Oxides with Hollow Structure As Sulfur Host Material for Lithium-Sulfur Batteries

INTRODUCTION Because of its high theoretical energy density, possibly low cost, and environmental friendliness, lithium-sulfur (Li-S) batteries have received a lot of interest. However, the principal disadvantage impeding the success of Li–S batteries lies in the severe leakage and migration of soluble lithium polysulfide intermediates out of cathodes upon cycling caused “shuttle effect”. The loss of active sulfur species incurs significant capacity decay and poor battery lifespans which has prevented it from commercial realization.Several researches have been conducted with an attempt to improve capacity of batteries while maintaining life of the Li-S cellใ including an introduction of nanostructured cathode host materials. Two main approaches have currently been explored a. chemical confinement and b. physical confinement to anchor the lithium poly-sulfide (LiPSs) reaction products durin the charging process. Transition metal oxides such as TiO2 and SnO2 has been studied with a potential material to anchor polysulfides via Lewis acid–base interactions and thus maybe able to chemically confine LiPSs within or on the transition metal oxide. Physical confinement may also be possible by trapping LiPSs within a transition metal oxide host structure e.g. hollow structure and thus help impedes polysulfide dissolution into the electrolyte. In this study, TiO2 and SnO2 are focused to understand the physical and electrochemical properties of sulfur host material with hollow structures. The in situ XAS is also conducted to understand the behavior of the dissolution and migration of long-chain LiPSs intermediates (Li2S x , 4 ≤ x ≤ 8) in the sulfur cathode upon discharge. EXPERIMENTAL The transition metal oxide, TiO2 and SnO2, were successfully synthesized by a templated method. The synthesis process involved four steps, preparation of SiO2 spheres, synthesis of SiO2@transition metal oxide core-shell structure by coating transition metal oxide shell on SiO2 and crystallization by calcination and etching the SiO2@transition metal oxide to form hollow transition metal oxide spheres. Structural properties of the synthesized samples were studied by X-ray diffraction (XRD) using Cu-Kα (λ=1.5418 Å) radiation. Particle morphologies and size of the resulting compounds were observed using a field emission scanning electron microscope. Composite electrodes for electrochemical studies were prepared by doctor blade coating of a slurry compound onto carbon-coated aluminium foil current-collectors. The transition metal oxide and sulfur composite, conductive carbon and PVDF binder were mixed in the ratio of 80:10:10 by weight. Electrochemical characterizations were performed by in 2032 coin cells and Galvanostatic charge-discharge cycling was done between 1.8-3.0 V at 0.1C using a MACCOR Series 4000 at room temperature. RESULTS AND DISCUSSIONS Based on the XRD results, single phase anatase TiO2 and tetragonal SnO2 were both successfully synthesized by the templated method. SEM images (Fig. 1a and 1b) demonstrate that TiO2 and SnO2 are generally spherical structures with nanometer scale dimensions ranging from 250-350 nm and 450-500 nm, respectively. The interior hollow region can be seen clearly in the images of broken spheres. The shelled surface of the synthesized powders is hierarchically made up of interconnected nanocrystals providing a possibly porous structure. Hence, the hierarchically porous and hollow structure has a large surface area for adsorbing the LiPSs distributed in the electrolyte.Fig. 1c shows the charge and discharge voltage profiles of SnO2 and sulfur composite electrode cathode in the first five cycles. Two discharge plateaus were clearly observed, which might be attributed to the two-step sulfur-lithium reaction process. The initial plateau, centered about 2.30 V, was commonly attributed to the reduction of the S8 ring and the formation of S8 2−. The second discharge plateau at 2.10 V was attributed to further reduction of the higher polysulfides (Li2S n , 4 ≤ n ≤ 8) to the lower polysulfides (Li2S n , n ≤ 3). There exhibited two plateaus in the charge process at about 2.25 and 2.35 V, respectively. Electrochemical performance in relations to capacity retention and the in situ XAS to understand the behavior of the dissolution and migration of LiPSs will be discussed in the meeting. Figure 1

Engineering bimetal phosphorus trisulfides heterointerface in semi-open frame structure for lithium-sulfur batteries

Monofunctional host materials of lithium-sulfur (Li-S) batteries are inadequate to simultaneously address the complex issues including “shuttle effect” and sluggish redox kinetics. Herein, iron and manganese bimetallic phosphorus trisulfide (Fe-MnP2S6) with heterointerfaces and a semi-open frame structure was synthesized as a multifunctional host material for Li-S batteries. Theoretical calculations suggest that due to the strong electronic coupling effect, electrons migrate from the MnPS3 layer to the FePS3 layer, accelerating charge and ion transfer on the surface of FePS3. The d-band center of metal atoms shifts towards the Fermi level through the introduction of Mn2P2S6, enhancing the interaction with polysulfides. Moreover, the frame exhibits excellent structural stability and physical limiting ability of sulfur. As a result, the cell with Fe-MnP2S6 delivers impressive electrochemical performance and redox kinetics, including a capacity of 1388 mAh/g at 0.2C, a rate performance of 850 mAh/g at 4C and a capacity attenuation rate of 0.028 % per cycle over 1,000 cycles at 1C. Through meticulous structural design and optimal composition adjustments, our work explores the mechanism of metal phosphorus trisulfides (MPS3) in Li-S batteries.

In-Operando Raman Study on the Use of 2D and Suboxide Titanium Host Materials for Lithium-Sulfur Batteries

While Lithium-Sulfur (Li-S) batteries have promised high capacities and low-cost material inputs, their potential has yet to be realized due to inherent issues with sulfur cathodes. In particular the polysulfide shuttle effect and sulfur’s intrinsic insulating properties stand in the way of a commercial battery, the demands of which include high sulfur loading and high cycling stability. Engineering the sulfur cathode, via the use of promising new materials has been an avenue of research pursued in the hopes of mitigating the shuttle effect via polysulfide entrapment and introducing more conductive materials.Of particular interest have been titanium oxide based materials which have shown polysulfide adsorption capabilities. However, the most common titanium oxide, anatase titanium (IV) oxide (TiO2) acts as an insulator, limiting its use in high sulfur loading batteries. Therefore, the use of more conductive titanium oxide materials is an attractive avenue of research. A previously reported freestanding titanium suboxide (TiO) carbon nanofiber cathode demonstrated excellent capacities (~790 mAh/g, ~2 mg/cm2). A rare lepidocrocite phase has also been observed via Raman spectroscopy in a newly discovered titanium carbide derived titanium oxide nanofilament (1D-NF). This material demonstrates properties that makes it attractive as a sulfur host material, having a high surface area of ~1700 m2/g, improved polysulfide reduction kinetics via the formation of polythionates, and polysulfide-cathode host interactions. The inclusion of these nanofilaments in sulfur cathodes yields capacities of ~800 mAh/g with ~1 mg/cm2 sulfur loading.The proposed mechanism via which these titanium oxide based materials function has never been investigated in-operando, and herein we conduct an in-operando Raman study to understand the behavior of these materials. Principally we will investigate the Eg band whose vibration can be moderated by the interaction of terminal sulfur atoms acting as Lewis bases and titanium atoms acting as Lewis acids, due to their vacant valance electrons. This interaction has been observed via postmortem XPS. The use of in-operando Raman allows us to uniquely observe transient behavior of the host material as well as the impact of crystal structure on polysulfide host interactions.

Nickel Oxide Decorated Halloysite Nanotubes as Sulfur Host Materials for Lithium-Sulfur Batteries.

Lithium-sulfur batteries with high energy density still confront many challenges, such as polysulfide dissolution, the large volume change of sulfur, and fast capacity fading in long-term cycling. Herein, a naturally abundant clay material, halloysite, is introduced as a sulfur host material in the cathode of Li-S batteries. Nickel oxide nanoparticles are embedded into the halloysite nanotubes (NiO@Halloysite) by hydrothermal and calcination treatment to improve the affinity of halloysite nanotubesto polysulfides. The NiO@Halloysite composite loaded with sulfur (S/NiO@Halloysite) is employed as the cathode of Li-S batteries, which combines the physical confinements of tubular halloysite particles and good chemical adsorption ability of NiO. The S/NiO@Halloysite electrode exhibits a high discharge capacity of 1205.47mAhg-1 at 0.1C. In addition, it demonstrates enhanced cycling stability, retaining ≈60% of initial capacity after 450 cycles at 0.5C. The synthesized NiO@Halloysite can provide a promising prospect and valuable insight into applying natural clay materials in Li-S batteries.

Rational design of Co3S4-CoN@N-doped carbon hollow spheres with polar S-Co-N bond as bifunctional host materials for lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have drawn much research attention as a contender for next-generation energy conversion systems because of their high capacity density and abundant raw materials. The large volume expansion and the insulating nature of sulfur and polysulfide shuttling issues limit future Li-S battery development. Herein, MOF-derived CoN nanoparticles embedded in an N-doped carbon layer are successfully constructed on the surface of the Co3S4 hollow sphere to form the Co3S4-CoN@NC heterostructure with strong S-Co-N bonds, which act as bifunctional host materials for Li-S batteries and show excellent adsorption and high-efficiency catalysis for lithium polysulfide (LiPSs). The hollow structure pre-stores a buffer space for the volume change of the electrode, limiting polysulfide dissolution. Furthermore, the carbon layer can improve the material's overall structural strength and electrical conductivity. Co3S4-CoN heterostructure with strong S-Co-N bonds can adsorb and accelerate the catalytic conversion of LiPSs. Co3S4-CoN@NC exhibits a high initial specific capacity of 1542.0 mAh g−1 at 0.1 C and a stable capacity of 872.6 mAh g−1 at 0.5 C after 100 cycles with a high Coulombic efficiency of nearly 100 %.

CoO embedded porous biomass-derived carbon as dual-functional host material for lithium-sulfur batteries

A new strategy is developed to fabricate sulfur electrode by infusing sulfur into a conductive biochar decorated with highly dispersed CoO nanoparticles. The loading of the CoO nanoparticles, as the active sites for reactions, is efficiently increased by using the microwave-assisted diffusion method. It is demonstrated that biochar can serve as an excellent conductive framework to effectively activate sulfur. Simultaneously, the CoO nanoparticles possessing excellent capability to adsorb polysulfides can remarkably alleviate the dissolution of polysulfides, and greatly enhance the conversion kinetics between the polysulfides and Li2S2/Li2S in the charge/discharge processes. The sulfur electrode dual-functionalized with biochar and CoO nanoparticles exhibits excellent electrochemical performance, including high initial discharge specific capacity of 930.5 mAh g−1 and low capacity decay rate of 0.069 % per cycle during 800 cycles at 1C rate. It is particularly interesting that the CoO nanoparticles distinctively enhance the Li+ diffusion during the charge process, endowing the material with excellent high-rate charging performance. This could be beneficial for the development of Li-S batteries with fast charging feature.

Conjugated Three-Dimensional High-Connected Covalent Organic Frameworks for Lithium-Sulfur Batteries.

Developing conjugated three-dimensional (3D) covalent organic frameworks (COFs) still remains an extremely difficult task due to the lack of enough conjugated 3D building blocks. Herein, condensation between an 8-connected pentiptycene-based D2h building block (DMOPTP) and 4-connected square-planar linkers affords two 3D COFs (named 3D-scu-COF-1 and 3D-scu-COF-2). A combination of the 3D homoaromatic conjugated structure of the former building block with the 2D conjugated structure of the latter linking units enables the π-electron delocalization over the whole frameworks of both COFs, endowing them with excellent conductivities of 3.2-3.5 × 10-5 S cm-1. In particular, the 3D rigid quadrangular prism shape of DMOPTP guides the formation of a twofold interpenetrated scu 3D topology and high-connected permanent porosity with a large Brunauer-Emmett-Teller (BET) surface area of 2340 and 1602 m2 g-1 for 3D-scu-COF-1 and 3D-scu-COF-2, respectively, ensuring effective small molecule storage and mass transport characteristics. This, in combination with their good charge transport properties, renders them promising sulfur host materials for lithium-sulfur batteries (LSBs) with high capacities (1035-1155 mA h g-1 at 0.2 C, 1 C = 1675 mA g-1), excellent rate capabilities (713-757 mA h g-1 at 5.0 C), and superior cycling stability (71-83% capacity retention at 2.0 C after 500 cycles), surpassing the most of organic LSB cathodes reported thus far.

Monolayer MSi2P4 (M = V, Nb, and Ta) as Highly Efficient Sulfur Host Materials for Lithium–Sulfur Batteries

Despite the high capacity and low cost of lithium-sulfur (Li-S) batteries, their commercialization is greatly blocked by multiple bottlenecks including the shuttle effect of lithium polysulfides (LiPSs), poor conductivity of sulfur, and sluggish reaction kinetics. Herein, we propose novel two-dimensional MSi2P4 (M = V, Nb, and Ta) monolayers as promising sulfur hosts to improve the Li-S battery performance. Our calculations show that MSi2P4 monolayers offer moderate binding strengths to the polysulfides, which are expected to effectively inhibit the LiPS shuttling and dissolution. Moreover, the conductive properties of the MSi2P4 systems are well maintained after LiPS adsorption, eliminating the insulating nature of sulfur species. Remarkably, MSi2P4 monolayers exhibit superior electrocatalytic activity for the sulfur reduction reaction and the Li2S decomposition reaction, which considerably lowers the energy barriers of LiPS conversions during discharge and charge, thus ensuring the fast redox kinetics and high sulfur utilization of Li-S batteries. This study pioneers the application of MSi2P4 monolayers as highly efficient sulfur host materials for Li-S batteries and affords insights for further development of advanced Li-S batteries.

Synthesis of 2-substituted-Pyrimidine-based porous aromatic frameworks via oxygen involved biginelli multicomponent polymerization: toward high performance Li–S batteries

Facile, general methods for the preparation of functionalized porous aromatic frameworks (PAFs) are necessary. Herein, we describe a new method for the one-step synthesis of functionalized pyrimidine-based PAFs via oxygen involved Biginelli multicomponent polymerization. As first application instance, we constructed a 2-amino-pyrimidine-based PAF (BPAF-1), and followed by employed it as a sulfur host material for lithium-sulfur batteries. Attributed to its 2-amino-pyrimidine structural superiorities, the BPAF-1/S composites demonstrate excellent electrochemical performance as cathode in lithium-sulfur batteries, such as good cyclability with a high capacity retention of 78.1% after 500 cycles and high rate capability up to 5C. Besides, it is convenient to bring various 2-substituted functional groups such as –OH, –SH, methyl, and phenyl functional groups to pyrimidine-based PAFs under similar conditions, which provided its wide applicability.

TiN porous ceramics with excellent electrochemical properties prepared by freeze-drying and in-situ nitridation reaction

Porous ceramics have attracted extensive attention because of their high porosity, low thermal conductivity, large specific surface area and good corrosion resistance. In this work, TiN porous ceramics with high porosity are successfully prepared via the combination of freeze-drying and in-situ nitridation reaction method using Ti powder and chitosan as raw materials. The influence of the solid content of Ti powder, the concentration of chitosan/acetic acid solution and the nitridation temperature on the morphologies and physical properties of as-prepared TiN porous ceramics are fully investigated. The sample with high porosity of 92.8% and low bulk density of 0.27 g/cm3 can be obtained through optimal parameters (the solid content of Ti powder is 9.6 wt%, the concentration of chitosan/acetic acid solution is 5 wt%, and the nitridation temperature is 1473 K). Particular emphasize is that the as-prepared TiN porous ceramics can be used as sulfur host material for lithium-sulfur batteries (LSBs). Good rate performance and cycle stability of TiN/S electrodes are achieved by electrochemical performance tests. The initial discharge capacity of TiN/S electrodes is 778 mAh g−1 at 0.5C, and the capacity retention rate is 94% after 200 cycles.

In situ conversion to construct fast ion transport and high catalytic cathode for high-sulfur loading with lean electrolyte lithium–sulfur battery

The difficulty of lithium ion transport and the slow redox reaction kinetics of polysulfide severely limit the performance of lithium-sulfur batteries under high sulfur loading and lean electrolyte conditions, thus hindering the practical process of lithium-sulfur batteries. Herein, FeF2 @rGO composites were used as sulfur host materials for lithium-sulfur batteries, which is in situ converted into LiF and FeS during the first discharging process, achieving rapid lithium ion transport and high catalytic activity simultaneously. The electrode delivered high discharge capacity and low capacity decay of 0.028% per cycle for 500 cycles. Even under elevated sulfur loading and lean electrolyte conditions, the electrode with FeF2 @rGO can exhibit high areal capacity of 12.3 mAh cm−2(12.7 mg cm−2 and 6 μL mg−1).

Rational Design of Co3s4-Con@N-Doped Carbon Hollow Spheres with Polar S-Co-N Bond as Bifunctional Host Materials for Lithium-Sulfur Batteries

Rational Design of Co3s4-Con@N-Doped Carbon Hollow Spheres with Polar S-Co-N Bond as Bifunctional Host Materials for Lithium-Sulfur Batteries

Graphene-wrapped microspheres decorated with nanoparticles as efficient cathode material for lithium-sulfur battery

• Graphene-wrapped microspheres decorated with metal nanoparticles was developed. • Cr-Ni-NDs@G is an efficient multifunctional sulfur host material for Li-S batteries. • The interaction and conversion kinetic of lithium polysulfide were studied. • The sulfur cathode exhibits high specific capacity and cycling performance. Lithium-sulfur (Li-S) battery is now a promising technology for energy storage. However, the commercialization of Li-S battery was hindered by the shuttle effect of lithium polysulfide and the slow reaction kinetics of sulfur. In this study, MIL-101(Cr) with graphene oxide was composited together through spray-drying. Then, a graphene microsphere composite consisted of three-dimensional conductive network decorated with Cr-Ni-based nanodots (Cr-Ni-NDs) was developed through a facile heat treatment. The microsphere composite was denoted as Cr-Ni-NDs@G, which offers a porous structure and high surface area to increase the accommodation and uniform distribution of sulfur in the cathode. Meanwhile, the three-dimensional conductive network embedded by Cr and Ni nanoparticle not only improved the transportation of electrons, but also act as the active site strengthening the adsorption of lithium polysulfide, promoting the catalytic transformation of lithium polysulfide to Li 2 S. Due to these complementary features, the S/Cr-Ni-NDs@G cathode exhibited a high initial specific capacity (1222.3 mAh·g −1 at 0.2C) and good rate performance (706 mAh·g −1 at 3.0C). In addition, after 500cycles at 1.0C, the faded rate of per cycle of the Li-S battery is only 0.059%. The result demonstrated that S/Cr-Ni-NDs@G composite can be a promising energy storage material in the development of Li-S batteries.

BC6N as a promising sulfur host material for lithium-sulfur batteries

Lithium-sulfur batteries (LSBs), which have six times the energy density of traditional lithium-ion batteries, are favorable candidates for the power system of next-generation electric vehicles, however, the sulfur cathode of lithium-sulfur batteries currently suffers from poor capacity retention and bad cycle performance. In this work, we study anchoring properties of B and N co-doped graphene by using density functional theory computations. Three doping configurations are considered and named as the adjacent (BC6NA), meta (BC6NM) and para (BC6NP) dopping, respectively. BC6NA has the best anchoring performance, as it has a strong absorption energy for the three clusters Li2S4 (1.20 eV), Li2S6 (1.51 eV) and Li2S8 (1.81 eV), while both BC6NM and BC6NP have a relatively worse anchoring performance due to their weak physical adsorption, especially for the Li2S4 cluster. Moreover, after adsorption the conductivity of the BC6NA is enhanced and the dissociation energy of the cluster is reduced, which further improve the performance of LSBs. This indicates that monolayer BC6NA is a promising sulfur host material for LSBs with a good anchoring performance.

Rational design of an Allyl-rich Triazine-based covalent organic framework host used as efficient cathode materials for Li-S batteries

To overcome the loss of soluble lithium polysulfides (LiPSs) generated during the discharge process of lithium-sulfur (Li-S) batteries, a lot of efforts have been devoted to the design of novel micro- or nano-structured host materials, aiming to trap soluble polysulfide within the network. Covalent organic framework (COF) as porous materials have been receiving a great deal of attention. Herein, an allyl-rich triazine covalent organic framework (ART-COF) synthesized by 5-(allyloxy) isophthalaldehyde and 4,4′,4″-(1,3,5-triazine-2,4,6-triyl) trianiline (TAPT) is used as cathode host material for Li-S batteries. Owning to the synergistic effect of physical force (through microporous channel) and chemical force (through C-S covalent bond and dipole–dipole interaction between nitrogen and lithium), the shuttle action of LiPSs to anode electrode can be effectively limited. ART-COF shows a high initial specific capacity of 1270 mAh g−1 which retains 1220 mAh g−1 after 100 charge–discharge cycles at 0.2C, and even at 1C it also demonstrates an initial specific capacity of 993 mAh g−1 which retains 818 mAh g−1 after 500 cycles with a low fading rate of 0.035% per cycle. This work represents a sustainable approach for developing highly stable and long-lived Li-S batteries.