The Research Of The Long Cycle Performance Of Lithium Sulfur Battery

Due to its high energy density,lithium-sulfur batteries has attracted a lot of attention in recent years.The theoretical capacity of sulfur is 1675mAh/g,and energy density of lithium-sulfur battery is 2600Wh/kg,which is higher than commercial lithium-ion batteries.Furthermore,Sulfur resources not only are very rich in nature,but also the price is cheap,and the sulfur element is environmentally friendly,so lithium-sulfur battery is expected to replace the commercial lithium-ion battery to become the next-generation high-energy battery,However,lithium-sulfur battery is still a lot of serious problems hindered its development.First,the conductivity of sulfur is particularly poor,resulting in low utilization of active substances.The second intermediate polysulfide easily dissolved in the electrolyte,resulting in"shuttle effect" and poor cycle stability.Third,during the lithium-sulfur battery cycle process,the sulfur element occurs the volume expansion effect and destabilizing the stability of the battery.These problems have limited the development and application of lithium-sulfur batteries.In this paper,the following research work is carried out to improve the cycling stability of lithium-sulfur battery,from the modified membrane,adding physical barrier sandwich and the preparation of modified graphene/sulfur cathode material.(1)We designed a crosslinking reaction on the surface of the polypropylene membrane induced by the oxygen plasma.During the plasma discharge process,the C-C and C-H bonds of the side chain methyl groups of polypropylene were broken under the plasma process,oxygen-containing functional groups will produce in the breakpoint position,such as-COOH,-OH and other oxygen-containing functional groups.The separator treated with oxygen plasma has a good electrolyte wettability.The reduced graphene/sulfur cathode material is assembled into a battery.During the cycle process,the electronegative oxygen-containing functional group can suppress the electronegative polysulfide to the cathode and enhance the cycle stability.(2)A nano-particle-deposited nitride interlayer was drived from LDH grown on the carbon paper.This nitride interlayer has better conductivity,and the structure of this nanoparticle could maintained the electrolyte well that improve the transmission ability of electrons.Nitride interlayer can capture and adsorb poly sulfides by physical or chemical interactions:metal nitrides and metal oxides are formed on the surface of metal oxides which will enhance the chemical stability,and the metal oxides can provide a polar surface.The polar surface has a strong adsorption with the polysulfide,thereby reducing the dissolution of polysulfide.An addition interlayer between the electrode and the separator provides a buffer layer for the volume expansion of the sulfur electrode.The cycling performance of sulfur electrodes with the nanoparticle-stacked metal nitride interlayer had an excellent cycle performance owing to the interactions between metal nitride and polysulfides.The battery delivered an initial capacity of 764.6 mAh/g and still possesses a capacity of 477.5 mAh/g with capacity retention of 62.4%after 800 cycles.(3)Graphene is one of the most widely used carbon materials in lithium-sulfur batteries system.Graphene has excellent electrical conductivity and extremely high atomic mobility.We designed a plasma etched,nitrogen-doped graphene as the sulfur loaded material in lithium-sulfur batteries system.After the plasma treatment,the loading amount of sulfur increase a lot,from 60%to 75%.Due to nitrogen doping,the ability to adsorb polysulfide of graphene is enhanced,cycle stability has been significantly improved.This method provides a novel method for designing a more durable lithium-sulfur battery.