Search

Lithium-sulfur batteries (LSBs) have attracted widespread attention because of their advantages such as high discharge capacity and high energy density. Although LSBs have good development potential, there are still many obstacles, such as poor conductivity, volume expansion etc., especially shuttle effect which seriously limit the application of LSBs. To restrain the shuttle effect, we proposed a novel Co 3 O 4 /ZnO dodecahedral heterojunction as a separator blocking layer which was derived form ZIF-67/ZIF-8 bimetallic MOF. Since the bimetallic oxide heterojunction contains more abundant oxygen vacancies, it has better adsorption and catalytic performances than monometallic oxides. Co 3 O 4 /ZnO coated on the PE separator can effectively block the lithium polysulfides (LiPSs) shuttle due to its good adsorption ability, furthermore, the catalytic effect will accelerate the reaction of LiPSs and improve the electrochemical performances. Consequently, the initial discharge specific capacity of the Co 3 O 4 /ZnO modified separator battery at 0.5 C rate reaches up to 875.5 mAh g−1 when the cathode sulfur areal density is 3 mg cm−2, and still keep 500.9 mAh g−1 after 400 long cycles. Even when the cathode sulfur areal density is 5 mg cm−2, it still shows good cycle stability. • Co 3 O 4 /ZnO dodecahedral heterojunction is derived from ZIF-67/ZIF-8 bimetallic MOF. • Co 3 O 4 /ZnO heterojunction is used as a separator coating material for Li-S battery. • Co 3 O 4 /ZnO heterojunction show excellent absorption and catalytic effect for polysulfides. [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]

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]

Due to the increasing demand of new energy vehicles and large-scale power grids for high energy density devices, lithium-sulfur batteries (LSBs) have attracted more and more researchers' attention stemming from their advantages of high theoretical specific capacity, low cost of active substances and environmental friendliness. However, there are still some intractable problems hindering the commercialization of LSBs, among which the most serious problem is "shuttle effect" of polysulfides. For the purpose of solving this problem, this paper prepared hollow structure molybdenum sulfide/cobalt sulfide mixed with amorphous carbon (MoS 2 /Co 9 S 8 /C) (HMCC) nanoparticles using ZIF-67 as the precursor and coated on the side of ordinary PE separator facing the positive electrode by a simple scraper coating process. The combination of MoS 2 and Co 9 S 8 bimetallic sulfides can not only adsorb and catalyze the rapid transformation of intermediates, but also effectively conduct lithium ions mainly because of the exposure of many active sites of layered MoS 2 in the outermost layer. In addition, a small amount of carbon inside can enhance electrical conductivity of the coating, increasing the utilization of active substances, and the stable hollow structure can act as a "transfer station", greatly inhibiting the large amount of polysulfides to run off. The dual advantages of structure and composition make the modified separator have excellent performance in different current densities. Reversible specific capacities of 930.4 mAh g−1 and 690.7 mAh g−1 are released at 0.5 C and 1 C, and capacity retention of 72 % and 64 % after 500 and 600 cycles, respectively. In addition, due to the rapid conduction of lithium ions, the growth of lithium dendrites is greatly inhibited, which maintains the high safety of the battery. This provides a new research direction for the application of other new bimetallic sulfides in the separator modification of LSBs. • A hollow bimetallic sulfide composite MoS 2 /Co 9 S 8 /C is derived from ZIF-67. • MoS 2 /Co 9 S 8 /C is used as a separator coating layer for lithium polysulfides. • The hollow MoS 2 /Co 9 S 8 /C show both physical confinement and catalytic effect on lithium polysulfides. [ABSTRACT FROM AUTHOR]