Synthesis And Application Of Co/Mo-Sulfide Composite Materials For Lithium-Sulfur Batteries

Compared with lithium batteries,lithium-sulfur batteries have more advantages,such as higher energy density,lower raw material prices,and more environmental protection.Therefore,the researchers believe that lithium-sulfur batteries can be used as new energy storage batteries in the future.However,before the formal commercial application of lithium-sulfur batteries,there are still several difficulties to be solved,including the low conductivity of sulfur,poor cycle stability,and poor rate performance.Although scientists have done a lot of work,these problems have not been really solved until now.This paper provides an overview of the current research progress of lithium-sulfur batteries,focuses on methods to functionalize separators/interlayers to improve battery cycling stability,and discusses the battery performance of different modified separator materials.On this basis,we start from the perspective of separator modification,aiming to composite with other metal-based materials by developing metal sulfide materials.In order to improve the performance of all aspects of the battery,we can better suppress the shuttle effect of polysulfides by applying a variety of composite materials.Our main research contents are as follows:First,we composite sulfide with phosphide to solve the shuttle effect of lithium-sulfur batteries through the synergistic effect of different materials.We partially vulcanized ZIF-67 to obtain Co S@ZIF-67 material,and then obtained Co₉S₈@CoP-CN material with spherical shell structure by first carbonization and then phosphating,and co-coated it with CNT on the PP separator.The material is surrounded by a Co₉S₈spherical shell containing nitrogen-doped carbon.After phosphating,the Co metal inside the material is phosphated to CoP.The synergistic effect of CoP and Co₉S₈enables the material to better adsorb and anchor polysulfides while accelerating the reaction kinetics of the battery reaction.Lithium-sulfur batteries employing the Co₉S₈@CoP-CN deliver an initial discharge capacity of 1356.4 m Ah g^-1 and retain capacity of 739.5 m Ah g^-1 after 500 cycles at 0.2 C with a capacity fading rate of 0.091%per cycle.Meanwhile,the material can maintain a specific capacity of 826 m Ah g^-1 at0.5 C.In addition,the Co₉S₈@CoP-CN material also exhibits excellent cycling stability and rate performance in Li-S batteries.Subsequently,we exploited the adsorption of polysulfides by metal oxides and sulfides to reduce polysulfide diffusion while increasing the reaction kinetics of chemical reactions.We prepared a separator-modified material with Mn₂Mo₃O₈supported on graphene and MoS₂ by a simple one-step hydrothermal reaction.The material was directly coated on the PP separator to obtain the modified separator.It can be seen from the test that the material is rich in oxygen defects,which is beneficial to improve the redox reaction kinetics of the battery reaction.Through electrochemical tests,we learned that rGO@MoS₂@Mn has certain catalytic properties for polysulfides.The initial discharge specific capacities of the material are 1339.5 m Ah g^-1,1093.4 m Ah g^-1,817.7 m Ah g^-1,664.6 m Ah g^-1 and 526.9 m Ah g^-1 at 0.1 C,0.2 C,0.5 C,1 C and 2C,respectively.Meanwhile,rGO@MoS₂@Mn can still maintain a specific capacity of679.1 m Ah g^-1 after 400 cycles at a rate of 0.5 C,and the decay efficiency per cycle is0.088%.Defects on graphene and various elements in the material help the material to adsorb and retain polysulfides on the positive side.At the same time,the oxygen defects on the material improve the reaction kinetics of the redox reaction and help the polysulfides to quickly react into simple substances.Sulfur and Li₂S/Li₂S₂ thus improve the performance of the battery and have certain practical application potential.