Sulfur Carbon Cathode And Polyvinylidene Fluoride Composite Separator For Lithium-sulfur Battery

As the world's population continues to increase,the demand for energy from mankind has also been increasing.It is of great significance to vigorously develop sustainable energy.Lithium-sulfur battery is a new type of energy storage battery which uses sulfur-carbon material as positive electrode and has very high specific capacity(theoretical value of 1672 m Ah/g),low cost of sulfur,environment friendliness and little harm to the human body Lithium sulfur batteries have great prospects for development,in recent years has become a research hot spot,much attention.In this dissertation,a new type of membrane material was prepared by electrospinning to fabricate a nanofiber membrane for volume reduction caused by polysulfide shuttling.The new membrane material was applied to lithium-sulfur batteries to improve the cycling capacity and cycle performance.The paper also studied the relationship between the structure and properties of this new type of separator material.Specific work as follows:In order to better study the performance of the separator,the positive electrode material of lithium-sulfur battery has a great influence on the performance of the battery.First of all,in this paper,the positive electrode material has been studied.Several different carbon materials(CNF,SPC,CMK3 and Super P)respectively with sublimation of sulfur in the ball mill and heat treatment composite preparation of carbon-sulfur cathode material,and test and analysis.The results show that the S/CMK3 composites have better battery performance.The carbon materials with excellent electrical conductivity and specific surface area can not only improve the conductivity of sulfur,but also can adsorb S And provide space for the volume expansion of sulfur,thereby improving the cycle stability of the battery.In order to solve the problem of shuttle effect in lithium-sulfur batteries,a PVDF/ PSSLi/PVDF composite membrane with sandwich structure was designed in this paper.With the good film-forming structure and large interspace of electrostatic spinning PVDF fibers,we added SO32-group to modify the film which can block the polysulfide,and studied the composite membrane material and structure corresponding to their electrochemical performance in lithium-sulfur battery.In the meantime,the phase separation and electrochemical characterization of different membranes were carried out and compared.The influence of the separator on the lithium ion,sulfur ion and organic molecules in the electrolyte and the relationship between the parameters and the electrochemical performance were studied.The results show that the composite membrane has good mechanical properties and thermal stability.The modification of SO32-group and its compact structure can effectively inhibit the shuttle effect of polysulfide and improve the cycle stability of the battery.The PVDF/PSSLi/PVDF composite membrane had an initial capacity of 1194 m Ah/g and substantial capacity of 701.1 m Ah/g after 50 cycles,with an decay rate of 0.82% for each cycle.While the commercial membrane had an initial capacity of 984.5 m Ah/g and substantial capacity of 465.5 m Ah/g after 50 cycles,with a decay rate of 1.1% per cycle.It shows that the PVDF/ PSSLi PVDF composite membrane can block the shuttle effect of polysulfide ion and has better ion selectivity,which can improve the cycle stability of the battery in the application of lithium-sulfur battery.