Preparation And Properties Of Cathode Materials For Lithium-sulfur Batteries

Today,with the emphasis on environmental protection and efficiency,all kinds of electronic equipment and new energy vehicles are developing rapidly.At the present stage,lithium ion batteries cannot gradually meet people’s needs due to their low energy density.Among the numerous cathode materials,sulfur cathode is expected to become the mainstream of the next generation of batteries due to its high theoretical specific capacity(1765 m Ah/g)and high energy density(2600 Wh/Kg)and the existence of a large amount of sulfur in nature,which is easy to obtain and cheap.However,in the current research,the shuttle effect and volume expansion of sulfur and the non-conductivity of sulfur hinder the industrialization of lithium-sulfur batteries.This thesis mainly starts from the design of cathode materials,aiming at preparing porous carbon materials with anchoring function and closely combining conductive carbon materials from the synthesis of nano-sulfur-coated cobalt materials,so as to suppress the problems of lithium-sulfur batteries to a certain extent and improve the electrochemical performance.This paper mainly from two aspects,one is the use of organic reaction synthesis of porous carbon,on this basis to explore its performance in lithium sulfur battery after further improvement,through metal oxide modified molecular sieve as a pore structure,through organic method "carbon plating" synthesis of functional porous carbon materials.Second,through the reaction in the inorganic solution directly in the carbon material inside and outside the hole formed nano hollow sulfur coated Co material,simplifying the cathode material synthesis steps and time.At the same time,the reaction rate of sulfur anode active substance was increased.The details are as follows:(1)Porous carbon materials with anchor properties were synthesized by using organic reaction synthesis and organic reaction coating Co3O4@MCM,and positive materials with different sulfur chain states were synthesized by controlling reaction temperature after mixing with sublimation sulfur.The electrochemical performance of the cathode prepared battery applied to the sulfur cathode was tested.It was found that the sulfur had stable charge-discharge performance at DPC@S,but there was a limitation of low sulfur load.The modified synthesis Co3O4@MDPC@S and AXOY@MCM@S(A:Zn,Mo,Cr,Mn)have high sulfur loading capacity.In the study on the properties of these cathode materials,Co3O4@MDPC@S material in the experimental synthesis method has a good performance in maintaining specific capacity.The initial specific capacity reaches 907.8 m Ah /g at 0.2 C current density,and remains close to 690 m Ah/g after about 300 cycles.(2)Hollow nano sulfur structures were prepared by solution method.Two new positive structures were prepared by composite Co and mesoporous material CNTs/Mxene.In this experiment,compared with the current preparation of sulfur anode,the process is simple and the heating time is short.It can effectively ensure the uniform distribution and loading of sulfur in mesoporous carbon.The electrochemical properties of HNS@Co@CNTs and HNS@Co@Mxene were tested.The first-lap discharge capacity of HNS@Co@CNTs was 980.3 m Ah/g and reduced to 690.5 m Ah/g after 300 cycles.HNS@Co@Mxene first cycle discharge capacity is802.3 m Ah/g,reduced to 409.8 m Ah/g after 400 cycles.The synthesis method of the two cathode materials used in this paper provides a new idea for the development of cathode materials for lithium-sulfur batteries,which is helpful to improve the performance of lithium-sulfur batteries.