Preparation And Structural Properties Of Graphene-based Aerogel Composites

Owing to the good electrical conductivity,large specific surface area,low density and adjustable structure of graphene,it has been widely used in the application fields of lithium-sulfur(Li-S)battery and electromagnetic wave absorption.Using a three-dimensional(3D)mesoporous graphene as the host of elemental S can effectively increase the electronic conductivity of sulfur cathode and can significantly improve the electrochemical performance of Li-S batteries,by buffering the volume changes during cycling and by capturing the electrolyte-soluble intermediates of lithium polysulfide(Li2Sn,3?n?8).In addition,a certain amount of O-containing functional groups and residual defects in the graphene oxide or its reduced derivative(GO or rGO)can modify the relaxations of these functional groups' electronic dipole and defects polarization,facilitating the binding/complexing of rGO with metal ions to form the composites of metallic nanoparticles and rGO.In some sense,the composite of rGO and Co nanoparticles may further functionalize in modifying the redox kinetics of intermediate Li2Sn,while the nanocomposite of cobalt-nickel alloy(CoNi)and rGO could greatly decrease the mass density of the alloy and simultaneously modify its single loss mechanism.Herein,the syntheses and structural characterization of metallic cobalt or cobalt-nickel alloy containing graphene oxide-based composites are conducted at first.And then,the Co-containing composite of elemental N-doping reduced graphene oxide(Co/NrGO)is used as a multifunctional agent in lithium sulfur batteries,while the nanocomposite of CoNi alloy and reduced graphene oxide(CoNi/NrGO)is used as an additive in paraffin to assay its ability in electromagnetic wave adsorption.That is,this dissertation deals with two parts,being shown as below.(1)A 3D mesoporous composite of Co/NrGO and its manually grinding mixture with elemental S(Co/NrGO/S)are prepared and used as cathode-/separator-coated interlayers and working electrode in assembled Li-S cells,respectively.Nanostructured characteristics of high-conductivity Co/NrGO are expected to host the electrochemically re-cycled molecular S8,to entrap the electrolyte-soluble Li2Sn and then to catalyze its reversible conversion to electrolyte-insoluble S8/Li2S.Benefiting from the multifunction,the good cycling stability(1070 mAh g-1,the 100th cycle,0.2 C),high rate capability(835 mAh g-1,2.0 C)and excellent durability(905 mAh g-1,the 250th cycle,0.5/0.2 C)of Co/NrGO/S indicate an effective approach to constructing the 3D mesoporous architecture of Co/NrGO for high-performance Li-S batteries.(2)A combined method of initial solvothermal synthesis,subsequent impregnation and final thermal reduction is used to prepare the nanocomposites of CoNi alloy and N-doped reduced graphene oxide by varying the weight content of the alloy at first:CoNi/NrGO-1(5.7 wt%)CoNi/NrGO-2(8.3 wt%)and CoNi/NrGO-3(14.1 wt%).And then,by the homogeneously dispersing a CoNi/NrGO sample in solid-state paraffin,within the frequency region of 2-18 GHz microwave absorbing properties of this paraffin dispersion are conducted.The electromagnetic wave absorption performances of these paraffin dispersions comparatively give an optimal recipe:the best composite of CoNi/NrGO-2 with a filling amount of 9 wt%,the maximum reflection loss(RL)of-32.5 dB at 7.76 GHz with a matching dispersion thickness of 3.0 mm,the maximum absorption bandwidth(RL<-10 dB)of 3.67 GHz(from 14.20 to 17.67 GHz)at thickness?1.5 mm.Actually,when the paraffin dispersion thickness changes from 1.5 to 5.0 mm,the effective absorption bandwidth(RL<-10 dB)of CoNi/NrGO-2 could be tuned from 3.86 to 17.87 GHz correspondingly.In a word,the excellent microwave absorption performances of CoNi/NrGO-2 can be attributed not only to the complexing of CoNi nanoparticles(166.9 ± 1.3 nm in diameter)with rGO nanosheets(?6 nm in thickness)but also to a synergistic effect among the magnetic loss of CoNi,the dielectric loss of rGO and their interface interactions.