| As the technology and economy grows,higher standard is raised up to meet the demand of people's life.Li-Sulfur battery has become a hotspot of research with the advantage of high theoretical specific capacity 1600 mAh g-1,high energy density 2500 Wh kg-1,abundant source of Sulfur and low cost.Although there is so many advantages,there is still a lot of problem in the research:poor conductivity leading to the low utilization of active materials,severe volume expanding during cycling leading to cathode structure destruction,and "shuttle effects" leading to low coulombic efficiency and loss of active materials.To solve these problems,researchers have paid a lot of effort in the cathode,anode,separator and electrolyte.To address these problem,a kind of N,S-doped macroporous carbon material was synthesized as supporter of Sulfur,and was used to suppress the "shuttle effect".This carbon material with N,S elements doped improve the polarity in surface,in order to get good wettability of polar and nonpolar solvent both to assure the efficiency of battery reaction.To characterize the absorption to polysulfide ion,UV-Vis,XPS was carried out to clarify the mechanism.After galvanostatic charge-discharge test,it was found that the cycling performance was increased.The initial discharge specific capacity was 1167 mAh g-1,while the specific capacity retained about 991 mAh g-1.Besides the rate performance was improved also,at the rate of 10 C,the specific capacity reaches 438 mAh g-1.Furthermore,the influence to the cycling performance of the ratio of polymerization was explored as well,which shows that when the Glucose:Thiourea =2:1,the cycling performance improved most.In order to decrease the damage of volume expanding and concerns about safety,a method about synthesis of Li2S/C material is reported.In the research above,hard template as nano CaCO3 was used to create uniform pores and tunnels in carbon materials.In this method,Li2SO4 crystals were used instead of nano CaCO3,which behaved not only as the template but also the precursor of Li2S crystals.After high temperature heating,Li2S can be synthesized in situ.SEM,TEM,HRTEM,XRD,TGA was taken to characterize the morphology and property of this Li2S/NS-MPC composite.In addition,the mechanism of initial charge process of Li2S was explored,and it was found that add sulfur as additive in cathode can decrease the overpotential effectively.After modifying with PBI-PEO on cathode,the specific capacity raised tremendously,almost equal to the specific capacity of sulfur cathode.The initial discharge capacity reaches 1082 mAh g-1 Li2S,equal to 1554 mAh g-1 S.After 300 cycles at the rate of 0.5 C,the specific capacity retain 565 mAh g-1 Li2S,equal to 811 mAh g-1 S.With the purpose of fulfilling the commercial use of Li-S battery,a fullcell with Li2S cathode and graphite anode was made,in which the anode should be prelithiated so as to decrease the loss of active materials.The initial discharge capacity of the fullcall reaches 565 mAh g-1,but its stabilization isn't good,after 100 cycles whose specific capacity was below 100 mAh g-1.Next more effort should be put in the exploration of the reason of capacity loss.These attempt of Li-S fullcell means a lot to the commercial use of Li-S battery. |
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