Effects Of Surface Modification Of Separator And Cathode Materials On Performances Of Li-S Battery

With the development of electronic technology,portable communication devices and electric vehicles have put forward new requirements for new batteries,such as high specific energy,high safety,low cost,environmental friendliness and durability.Since the energy density of lithium-ion batteries has reached the theoretical limit,researchers have focused on lithium-sulfur batteries.Li-S battery is a secondary battery with sulfur or sulfide as the positive electrode and metallic lithium as the negative electrode.However,commercialization of batteries has encountered difficulties due to problems such as poor conductivity of sulfur and sulfides,low utilization of active materials,and shuttle effects.To solve these problems,the present experiments of the lithium-sulfur battery material mainly focus on the surface coating modification of cathode materials and separators.The thesis mainly includes:(1)In this experiment,a hard template method was used to prepare a mesoporous carbon with a layered structure as a conductive carrier of sulfur by using glucose as a precursor carbon source and nano-CaCO₃was decomposed into Ca O and CO₂by sintering.Three kinds of sulfur/mesoporou(S/AC)carbon cathode materials were prepared,and the relationships between the ratio of nano-CaCO₃template to glucose and the electrochemical performances of lithium-sulfur batteries were studied.The results show that the performance of lithium-sulfur battery S/MC2 with mesoporous carbon MC2 prepared by mass ratio CaCO₃:C₆H₁₂O₆=1:1.5 is the best.The first discharge specific capacity of the battery reached 1388mAhg^-1,and the specific discharge capacity was 883mAhg^-1at 0.5 C rate after 100 cycles.(2)Coated with AC and MoS₂on both sides of the battery-grade separator.The molybdenum disulfide(MoS₂)was first coated on the separator close to the lithium anode;then the activated carbon(AC)was coated on the other side near the sulfur cathode,labeled AC-MoS₂.Assembled Li-S batteries with separators coated by AC-MoS₂,MoS₂and uncoated separator show the initial discharged specific capacities of 1288mAhg^-1,1219mAhg^-1and 957mAhg^-1,and after 100 cycles those of 1109mAhg^-1,998mAhg^-1and 507mAhg^-1at 0.5 C rate,with the coulombic efficiency remains over 98%.(3)The positive electrode of lithium-sulfur battery is coated by physical vapor deposition magnetron sputtering technology to reduce the shuttle of intermediate products and achieve good cycle stability.Al₂O₃and TiO₂were deposited on a Al foil coated with sulfur/activated carbon(S/AC)by radio frequency sputtering.Some Al₂O₃and TiO₂particles could be embedded in the carbon pores,which inhibited the shuttle of polysulfide and improved the cycle stability of the battery.Both films also improve the performances of the batteries.The assembled battery which its cathode is sputtered with Al₂O₃film at 0.5 C,the first and 100th discharge specific capacities are1249mAhg^-1and 965mAhg^-1.The efficiency is greater than 97%.