The controversial lithium-sulfur (Li-S) batteries still have too many challenges to be commercially developed. The electrical conductivity of elemental sulfur is poor. Moreover, the shuttle effect caused by soluble polysulfides can reduce sulfur utilization and produce lithium dendrites at the anode. To address the above disadvantages, Bi2Se3@CoSe composite is in-situ synthesized on carbon nanotubes through one-step hydrothermal method and applied to the cathodes. The strong metallicity of Bi2Se3@CoSe composite improves the electrical conductivity. In comparison with pure metal selenides, the attached CoSe particles on lamellar Bi2Se3 surface increase the adsorption sites of lithium polysulfides to effectively alleviate the shuttle effect. Combined with these advantages, S/Bi2Se3@CoSe/CNTs cathode exhibits a long cycling stability. Over 700 cycles, the cathode shows a capacity decay rate of 0.049% per cycle at 0.5 C. In addition, the cathode shows high initial capacity (840.4 mAh g-1) with sulfur content of 2.31 mg cm-2 at 0.1 C. This study demonstrates the efficacy of Bi2Se3@CoSe composite in improving the conductivity of the sulfur cathodes and polysulfides chemisorption.

Lithium-sulfur batteries (LSBs) are one of the representatives of a new generation of high-performance batteries, due to their large theoretical specific discharge capacity, high energy density and low cost et al. However, shuttle effect and slow conversion kinetics of polysulfides (LiPSs) hinder the performance of LSBs. In order to mitigate shuttle effect, metal-organic frameworks are introduced. Carbon nanotubes (CNTs) is used as composite cathode, due to their high electrical conductivity. V-MOF/CNTs-derived hexagonal VC/CNTs nanosheets are successfully synthesized and used as the sulfur host. VC/CNTs nanosheet with mesoporous structure can provide a lot of active sites. VC nanosheets are uniformly distributed and interconnected with CNTs to form a conductive network structure. VC/CNTs has excellent chemical adsorption and catalytic properties on polysulfides, which can improve the redox reaction kinetics and the adsorption capability. Due to the synergistic effects, S/VC/CNTs has an excellent cycling stability. S/VC/CNTs shows a significant initial specific capacity of 1370 mAh g-1 at 0.1C. Capacity decay rate per cycle is about 0.037% After 500 cycles at 0.5C, the Coulomb efficiency is nearly to 100%. The results show that the introduction of VC/CNTs composites with special hexagonal structure can accelerate the catalytic electrochemical reaction, and the dissolution and diffusion of polysulfides are well controlled.

Lithium-sulfur batteries have gotten to be a hot inquire about subject due to their tall hypothetical particular capacity (1675 mAh center dot g(-1)) and energy density (2600 Wh center dot kg(-1)). Focal points such as plenteous sulfur assets, non-toxicity and natural invitingness moreover make lithium-sulfur batteries one of the foremost promising vitality capacity frameworks. In any case, the destitute electrical conductivity of sulfur, the "transporting" of polysulfide between anodes and the contrast in thickness between sulfur and its diminishment items are still issues that restrain its application. Related studies have appeared that transition metal selenides have great electrical conductivity. Based on their polar characteristics, transition metal selenides can accelerate the energy of redox responses, restrain shuttle effects, and improve the electrochemical properties of lithium-sulfur batteries. This paper mainly reviews the applications of transition metal selenides in lithium-sulfur battery cathode materials and separators, and presents a viewpoint on research direction and development of transition metal selenides in lithium-sulfur battery applications.

The controversial lithium-sulfur (Li-S) batteries have not been commercially developed due to the poor electrical conductivity of elemental sulfur and the shuttle effect caused by soluble polysulfides. To address the above disadvantages, Bi2Se3@CoSe composite is in-situ synthesized on carbon nanotubes through one-step hydrothermal method and applied to the cathodes. The strong metallicity of Bi2Se3@CoSe composite improves the electrical conductivity. In comparison with pure metal selenides, the attached CoSe particles on lamellar Bi2Se3 surface increase the adsorption sites of lithium polysulfides to effectively alleviate the shuttle effect. Combined with these advantages, S/Bi2Se3@CoSe/CNTs cathode exhibits a long cycling stability with capacity decay rate of 0.049% per cycle at 0.5 C after 700 cycles. In addition, the cathode shows high initial capacity (840.4 mAh g-1) with sulfur loading of 2.31 mg cm-2 at 0.1 C. This study demonstrates the efficacy of Bi2Se3@CoSe composite in improving the electrical conductivity of the sulfur cathodes and polysulfides chemisorption.

Introducing defects into two-dimensional materials can increase the ligand-unsaturated sites, thereby enhancing the redox catalysis of polysulphides. In this study, the selenium defects in the two-dimensional material VSe2 can effectively improve the electrochemical performance of lithium-sulfur batteries. Compared with VSe2, VSe2-x could strongly adsorb polysulfides, catalyze the conversion and accelerate the redox reactions of polysulfides. S/VSe2-x/CNTs cathode with an initial discharge specific capacity of 1457 mAh g-1 at 0.1 C current density and capacity decay rate per cycle of only 0.039% after 800 cycles at 0.5 C, showing excellent cycling stability. In addition, a high areal capacity of 4.35 mAh cm-2 and a reversible capacity of 4.106 mAh cm-2 after 100 cycles at 0.1 C can be achieved with the S/VSe2-x/CNTs cathode with a high areal sulfur loading of 4.5 mg cm-2. The results show that the shuttle effect is effectively suppressed by introducing defects in the two-dimensional transition metal dihalide compounds. Thus, the electrochemical performance of the sulfur electrode for lithium-sulfur batteries is improved. This work is expected to provide a new perspective for the rational design of sulfur host materials for high-performance lithium-sulfur batteries. (c) 2023 Elsevier B.V. All rights reserved.