Preparation And Modification Of Carbon Microspheres As Modified Materialsin Lithium-Sulfur Batteries Separators

With the development of technology,human beings have higher requirements for energy storage equipment.Especially in the development of new energy automobile batteries,the capacity of traditional lithium-ion batteries have reached the limit and cannot meet the demand of market.The lithium-sulfur battery,as a new type of secondary energy source,has attracted much attention due to environmental friendly and its high theoretical specific capacity.However,many problems in Li-S batteries have limited its commercial use,such as low utilization of active materials,volume expansion of positive electrode materials and the shuttle effect of polysulfides(LiPSs).In order to solve the above problems,we based on the synthesis of carbon microspheres,which were modified by two modification methods.Then the modified materials were coated on the surface of commercial polypropylene(PP)separators.Firstly,carbon microspheres were synthesized using dopamine as the nitrogen(N)source and carbon(C)source in this paper.The iron nitrate nonahydrate(Fe(NO3)3·9H2O)was selected as the iron source.The carbon microspheres impregnated with Fe(NO3)3·9H2O were doped Fe inside the carbon microspheres successfully.By comparing the microsphere morphology and performance of different doping ratios,specific process parameters are determined.The iron-nitrogen-doped carbon microspheres(Fe/N@MCS)were used to modify the separators.At a current density of 0.2 C,the initial discharge capacity was as high as 1398.3 mAh/g,and at a large current density of 0.5 C,the initial discharge capacity reached 922.4 mAh/g.Secondly,A layer of molybdenum disulfide(MoS2)was grown on the surface of the polydopamine microspheres by hydrothermal method.After carbonization,a petal-shaped molybdenum disulfide@carbon microspheres(MoS2@MCS)-was prepared successfully.The modified separators with MoS2@MCS composite material has good cycle life and stable Coulomb Efficiency.At a current density of 0.2 C,the initial discharge capacity reached 1187.3 mAh/g.After 200 cycles,the Coulomb Efficiency still remained above 98%,much higher than that of commercial separators.In addition,at a 3 C rate,the capacity of the MoS2@MCS modified separators is more than 5 times that of commercial separators.Finally,we use MoS2@MCS composite materials as modified materials to explore the different adhesives using on the PP separators.When the laboratory-made triblock copolymer is used as an adhesive,the modified separator retains its intact structure after circulation.And compared with traditional adhesives polyvinylidene fluoride(PVDF)and water-based polyacrylic acid(PAA),the laboratory-made triblock copolymer has more excellent cycle stability.