Search

Summary: Lithium‐sulfur batteries (LSBs) have received numerous studies because of their advantages of high specific capacity, low cost of the sulfur element and so on. However, there are several obstacles restricting the commercial use of LSBs, including low conductance of sulfur, volume expansion effect of the positive sulfur electrode and serious shuttle effect of soluble lithium polysulfides. In this work, a composite of carbon nanotubes (CNTs) and hollow Co9S8 (CNTs/Co9S8) is synthesized via ZIF‐67 as a template and is applied on the surface of the PE separator for LSBs. Benefited from the excellent conductance of CNTs as well as the adsorption and catalysis properties of polar hollow Co9S8, the cell with the CNTs/Co9S8 composite functional separator delivered the discharge capacity of 977.6 and remained 456 mAh g−1 after 500 loops at a current density of 0.5 C, corresponding to a low attenuation rate of only 0.1% per cycle, as well as excellent rate properties. Even at high areal mass loading of active sulfur, LSBs exhibited excellent long‐term cycling stability at various current rates. In addition, the Li dendrites were remarkably restrained, which further enhanced the safety of batteries. This paper provides an effective and newfangled approach with modified separators coating composite materials of carbon species and structural sulfide to inhibit the shuttle of intermediate polysulfides and further enhance the utility of LSBs in the future. [ABSTRACT FROM AUTHOR]

Because of its high theoretical specific capacity, lithium-sulfur batteries are regarded as one of the most promising secondary batteries. However, there are still a series of problems, which seriously affect the commercial application of lithium-sulfur batteries. Therefore, a magnetic porous carbon material was developed in this work for the modification of lithium-sulfur battery separators, which may reduce the shuttle effect of polysulfides and increase its electrochemical performances. The solvothermal preparation of Ni-Zn bimetallic MOF precursors was followed by a high-temperature carbonization in nitrogen environment to sublimate Zn ions and produce porous structures, achieving Ni@C(Zn) composite. In order to improve the electrochemical performances of lithium-sulfur batteries, the Ni@C(Zn) composite was coated on one side of the polyethylene (PE) separator. Ni@C(Zn) composite displays good physisorption and chemisorption properties, and it can also operate as a secondary current collector to promote the usage of active materials as well as inhibiting shuttle effect of polysulfides. By using Ni@C(Zn) coated PE separator, the initial discharge specific capacity of lithium sulfur battery is as high as 1278.6 mAh g−1 at a current density of 0.05 C when the S cathode is loaded with 3 mg cm−2 active materials. Furthermore, the discharge specific capacity in the first cycle at 0.5 C is 749.4 mAh g−1, which remains at 461 mAh g−1 after 500 long cycles, and the capacity retention rate is as high as 61.5%. Even when the S loading is as high as 5 mg cm−2, it can still experience a stable cycle of 100 cycles at 0.2 C. • Ni@C(Zn) composite was derived by bimetallic Ni-Zn MOFs. • Ni@C(Zn) composite was used as separator modification layer of lithium sulfur battery. • larger specific surface area and higher porosity can better block the shuttle of polysulfides. • Ni@C(Zn) composites have good catalytic effect which can promote the redox conversion of polysulfides. [ABSTRACT FROM AUTHOR]

Lithium-sulfur batteries have the advantages of high specific capacity, high energy density, environmental friendliness, and low price, and have become one of the most promising new electrochemical technologies. However, during the charge-discharge reaction, the shuttle effect of the reaction intermediate polysulfides leads to a decrease in battery activity, which limits its development and commercialization. In this paper, we prepared a novel ZnO/N/Ketjen Black (KB) composite to act as a separator barrier to reduce the influence of polysulfides shuttle effects. A simple aqueous solution reaction was used to mix Zn(NO 3) 2 ∙6H 2 O with KB and ZIF-8/KB was obtained by adding dimethylimidazole, and then ZIF-8/KB precursor was carbonized at high temperature in inert gas atmosphere to obtain ZnO/N/KB composite. Finally, the prepared ZnO/N/KB composite was coated on commercial PE separator. Through the dual effects of adsorption and catalysis, the shuttle effect of polysulfides is sufficiently inhibited by the ZnO/N/KB layer, therefore the electrochemical performances of lithium-sulfur batteries are largely improved. The results show that when the sulfur cathode of Li-S battery contains 3 mg cm−2 active material, the specific discharge capacity can be as high as 1284.5 mAh g−1 at 0.05 C. Furthermore, at a higher rate of 0.5 C, the initial discharge specific capacity also reaches 868.3 mAh g−1. After 400 cycles of the charge/discharge process, it still remains 495.9 mAh g−1, which means a capacity retention rate of 57.1%. ZIF-8/KB composite was synthesized by simple aqueous solution reaction. ZnO/N/KB was obtained by further high-temperature carbonization and coated on one side of PE separator of lithium sulfur battery. KB provides excellent conductivity and physical adsorption capacity. ZIF-8 derived N species and ZnO nanoparticles improve the chemical adsorption capacity through chemical bonds. Therefore, the cycle performance and rate performance of lithium sulfur battery are greatly improved. [Display omitted] [ABSTRACT FROM AUTHOR]

• Co-N/KB composite is derived from ZIF67/KB precursor which is prepared by a facile water solution reaction. • Co-N/KB composite is coated on the PE separator of Li-S coin battery which served as the polysulfides barrier layer. • Co-N/KB barrier show both physical and chemical interactions with polysulfides based on its rich pore structure and Co-N active site doping. • Coin cells with sulfur areal density of 5 mg cm−2 can cycle with a high capacity retention 81.1% after 200 cycles. The commercialization of lithium sulfur battery is greatly impeded by the severe capacity decay induced by polysulfides shuttle during charge/discharge process. Herein, we propose a composite carbon material with Co-N doping and high conductivity for polysulfides barrier layer. ZIF67 and high conductivity Ketjen Black(KB) are combined by a facile water solution reaction at room temperature at first, afterwords the as-prepared ZIF67/KB precursor is calcined in nitrogen atmosphere to obtain a novel Co-N/KB nano structure. The Co-N/KB hybrid is then coated on the commercial PE separator to improve electrochemical properties of Li-S battery. The Co-N/KB coating layer apparently promote the redox kinetics and show chemisorption ability toward polysulfides. Furthermore, the coating layer with high conductivity can also be used as a second current collector to promote the electronic transmission, which will increase the use ratio of active substances and improve the cycle retention. By the use of Co-N/KB modified separator, the initial discharge capacity of sulfur cathode with a sulfur areal loading of 3 mg cm−2 reaches 888 mAh g−1 at 0.5 C and shows a slow capacity decay rate of 0.025%/cycle after 200 cycles. Even when the areal loading of active sulfur is added up to 5 mg cm−2, the battery can also show a stable cycle performance for more than 300 cycles. [ABSTRACT FROM AUTHOR]