Li-storage Performance Of Graphene-based Hierarchical Porous Martix To Load Sulfur As Electrode Materials

Lithium-sulfur?Li-S?batteries have high energy density,however they are currently facing many challenges that inhibit their practical applications.For instance,“shuttle effect”of soluble lithium polysulfides?LiPS?intermediates between electrodes,poor electrical conductivity of sulfur and its lithiation conterpart Li2S,large volumetric variation during lithiation/delithiation of sulfur.To address these issues,in this thesis,we have designed graphene-based hierarchical porous matrix to load sulfur,in which graphene builds up conductive skeleton.Meanwhile,polar silica,g-C3N4 and doped nitrogen atoms have been used to inhibit shuttle effect of soluble LiPS.Herein,a variety of graphene-based hierarchical porous matrixs have been synthesized to load sulfur as electrode materials through liquid-phase mixing method and spray drying method.Their microstructure and composition have been investigated,and the electrochemical Li-storage performances have been evaluated.The main conclusions are as follows:?1?In hierarchical porous g-C3N4/r-GO architectures as light-weight sulfur hosts,the architectures with small pore volume induce some residual sulfur on the surface,resulting in poor cycling stability.The large pore volume is inappropriate for trapping LiPS because of high macropore density.The g-C3N4/r-GO/S electrode materials with appropriate micro/meso/macropores matching have the best electrochemical Li-storage performance.?2?The C3N4/r-GO/S electrode material delivers initial charge capacity of 837.7mAh g^–1 and maintains 589.6 mAh g^–1 after 100 cycles at current density of 2 C,exhibiting very good cycling performance.Even at 3.5 C(5.86 A g^–1),its reversible capacity can maintain 528.8 mAh g^-1,which is 55%of the capacity at 0.2 C.?3?SiO2 nanoparticles can effectively prevent agglometrtion of the graphene sheets and produce abundant pore structure in the nitrogen-doped reduced graphene oxide/SiO2 matrix?N-Fr-GO/SiO2?prepared by spray drying method.?4?The nitrogen-doped reduced graphene oxide/SiO2/S electrode material delivers discharge/charge capacities of 1144/1161.5 mAh g^–1 in the initial cycle at 0.2 C,which is higher than those of the undoped counterpart material.At a current density of1 C,the first-cycle charge capacity is 672.5 mAh g^–1,and the charge capacity can maintain 549 mAh g^–11 and after 100 cycles,correspondingly,the capacity retention is as high as 81.6%.