Preparation And Properties Of Nitrogen-doped Porous Carbon-sulfur Solid State Batteries

With the advent of the 5G era,intelligent wearable devices and artificial intelligence are popular in people’s lives.Lithium-sulfur battery has attracted widespread attention due to its outstanding energy density and abundant raw materials,low cost and other advantages,and is considered to be the most potential new generation battery system at present.In order to solve the safety problems of traditional liquid batteries,the research and development of solid-state lithium-sulfur battery began to enter people’s vision.However,the commercial application of solid lithium-sulfur batteries is hindered by the problem that the positive sulfur electrode has poor conductivity and the polysulfide catalyzes the conversion,the lithium dendrites are easy to grow from the negative lithium electrode,and the ionic conductivity is low at room temperature due to the large impedance of solid electrolyte.In order to solve the above problems,this study conducted a comprehensive design from three aspects:the construction of conductive network of sulfur anode,the protection of lithium metal anode and the preparation of solid electrolyte.（1）A kind of nitrogen-doped carbon nanofiber active material was prepared by template method.The material has high graphitization degree,specific surface area of391.6 m²g^-1,abundant pore structure with an average pore size of 5.2 nm.It has obvious chemical adsorption and physical anchoring effect on polysulfide,which is convenient for complex loading of elemental sulfur.When the sulfur content is 62.9 wt%,the electrochemical performance of the material is the best.The specific capacity of the first cycle discharge is as high as 1480 m Ah g^-1at 0.1C.At 25℃and 0.5C current density,the capacity decay rate of each cycle is only 0.091%.（2）A The lithium anode is coated with a protective coating.The mixed protective coating of polyoxethane（PEO）and wax greatly improves the air stability of the lithium sheet,which can be fully exposed to air for 6 hours without oxidation.PEO provides the lithium ion transmission channel for the modified lithium sheet to ensure the normal operation of the negative electrode.It is found that the comprehensive performance of lithium metal anode is the best when the ratio of PEO to paraffin is 1:4.（3）A composite solid electrolyte with polyvinylidene fluoride（PVDF）as polymer matrix,nano-sized lithium aluminium titanophosphate（LATP）as inorganic filler and lithium perchlorate（Li Cl O₄）as lithium salt was prepared by solution casting method.The electrolyte has the advantages of good mechanical flexibility and stable electrochemical performance.At room temperature,the ionic conductivity is 8.07×10^-5S cm^-1,the lithium migration number is up to 0.77,and the electrochemical stability window is 4.56 V.The rate performance and cycle stability of the assembled high-safety solid-state lithium-sulfur battery have been significantly improved.The first charge and discharge specific capacity of 0.1C at 25℃can reach 799.78 m Ah g^-1,and the capacity decay rate of each cycle is only 0.132%under 0.2C long cycle.It proves the significance of this research and provides reference value for the research of a new generation of solid-state lithium-sulfur batteries.