Preparation Of Modified Polymer Separators And Its Application In Lithium Sulfur Battery

The lithium-sulfur battery has aroused tremendous attention due to its high theoretical specific capacity,unique energy densities,low cost and co-friendly properties.However the lower conductivity of sulfur and the dissolution of polysulfide during the discharge process,have limited its practical application.The polymer separator is an important component part of lithium-sulfur battery,which plays an essential role in its performance.This paper designs three kinds of modified polymer separators with different structure.The morphology of the modified polymer separators were characterized by SEM,FTIR,XRD etc,then we use the modified separators to assemble button cell and test the cycle stability by charging and discharging at constant current.Moreover,we further study the relationship between structure and performance.The conductivity and electrochemical reaction have been improved by using acetylene black and Super P surface modification polymer separators.The first cycle capacity of acetylene black and Super modified separators were 858 mAh·g^-1and1198 mAh·g^-1 at a current density of 0.1C,but fade to 485 mAh·g^-1and 483 mAh·g^-1after 50 cycles.Although the utilization of positive active material has been improved,yet there is still an obviously capacity fading and the cycle stability remains to be improved.We further use polyporous diatomite/conductive agent composit to modify the separators,the structure of polyporous diatomite has improved the loan mass of conductive agent,which further improved the conductivity and electrochemical reaction,the fist cycle capacity of diatomite/acetylene black composit and diatomite/Super P composit were 1358 mAh·g^-1and 1246 mAh·g^-1 at a current density of 0.1C,after 50 cycles,respectively,while the capacity was kept in 699 mAh·g^-1 and 964mAh·g^-1.This surface modification enhanced the wettabbility and affility to electrolyte.The cycle stability has also been increased.Graphene oxide has been synthesized by Hummers method.The anodization degreed is very high which characterized by FTIR and XRD.Then we use this high anodization degreed GO to modify the polymer separator.On one hand,we obtained that the first cycle capacity was slighty lower than other reseach works,resulting from structure defection of GO,on the other hand,the capacity has been keeping at 802mAh·g^-1 after 50 cycles at a current density of 0.1C.The conservation rate of cycle capacity can reach as high as 82.3%.The results confirming that the layered-two-dimension material can significantly keep polysulfide between their layers,which restrain the dissolution of polysulfide of polysulfide in electrolyte,thus limiting shuttle effect.