Synthetization And Electrochemical Performance Of Cathode Materials For Lithium-sulfur Batteries

With the developments of economic and the progress of technology,the current energy storage systems are increasingly unable to meet the needs of the society,so it is imperative to research new types of energy storage systems.Lithium-sulfur batteries have drawn widespread attention due to their high energy density and other advantages,therefore they are known as one of the most promising new types of energy storage systems.The theoretic specific energy of the lithium-sulfur battery systems is up to 2600Wh Kg-1,ten times higher than the current lithium-ion battery.In addition,elemental sulfur has many advantages such as rich in natural,environmental friendly and so on.However,there are also many problems with lithium-sulfur batteries,such as the poor electrical conductivity of the active material(sulfur)in the cathode,volume expansion during the discharge-charge process,and a "shuttle efect" which leads to the fast capacity decay and the short life of the batteries resulting from the dissolution of intermediate products in the electrolyte during discharge-charge process.Therefore,for the cathode materials of lithium-sulfur batteries,the key to improving the performance is to improve the conductivity,suppress "shuttle effect" and relieve volume expansion.From researches,porous carbon has the advantages of large specific surface area,good conductivity and environmental friendliness.Acted as a cathode material of lithium-sulfur batteries when mixed with elemental sulfur,it can increase the conductivity of elemental sulfur and reduce the volume expansion during discharge-charge process.By forming chemical bonds with polysulfides,metal oxides can suppress the "shuttle effect" and improve the cycling performance of lithium-sulfur batteries.Therefore,in this paper,to study their electrochemical performance,porous carbon and metal oxides are used as carriers of sulfur.The main research content is as follows:1)The ZrO2 hollow sphere structure is synthesized by using SiO2 template.Then forming a carbon layer on the surface of ZrO2 hollow sphere by carbonized glucose,a uniform size ZrO2@C hollow sphere is obtained.And used as a sulfur carrier,ZrO2@C hollow sphere is applied to the cathode materials of lithium-sulfur batteries.in.The hollow sphere structure can relieve the volume expansion during discharge-charge process,it also can contain a large amount of elemental sulfur and then increase the sulfur loading(68%).The ZrO2 material can inhibit the dissolution of discharge intermediate(polysulfide)into the electrolyte by forming a chemical bond with it.The existence of the carbon layer increases the electrical conductivity of the system,provides a good electron transport path,and reduces the electrochemical impedance.After testing,the battery demonstrates good cycle performance:at a current density of 0.1 C,the initial discharge capacity is up to 1254.1 mAh g-1and a performance remaining of 580.7 mAhg-1 after 150 cycles.2)The porous carbon material is synthesized by using dithiosalicylic acid as a carbonizng precursor.After activated by 4M KOH solution,the product is used as a sulfur carrier in the cathode materials of lithium-sulfur batteries.The abundant mesoporous and microporous structure of the material increases the systemic sulur content,relieves the volume expansion,and inhibits the "shuttle effect".Moreover the good conductivity of the material provides a good channel for the transmission of electrons and lithium ions,accelerates the electrochemical reaction of the system Tested the material synthesized at different carbonizing temperatures,we can see that the material carbonized at 500? has the best electrochemical performance:the capacity maintains at 489.7 mAh g-1 after 100 cycles and remains 412.3 mAh g-1 after 500 cycles at a current density of 0.1 C.