Preparation,characterization And Electrochemical Properties Of Metal Sulfurs And Carbon Nanocomposites

The electrode material is an important part of the battery system,and its electrochemical performances will directly affect the overall performances of batteries.New electrode materials not only need to have good comprehensive electrochemical performances,such as good cycle stability,high specific capacity and excellent rate performance,but also require low cost,wide availability,and can meet people’s increasing use requirements.Because of the high theoretical specific capacity and low cost,metal sulfides are widely studied as electrode materials in ion batteries.However,the practical application of metal sulfides in ion batteries is limited by the low conductivity,obvious volume effect and low utilization rate.In this paper,we prepared two new composite materials of metal sulfides and carbon materials with different design ideas according to the characteristics of different metal sulfides.The results show that these two ion batteries electrode materials exhibit good electrochemical characteristics in the process of lithium and sodium ions storage,respectively.The main research results are as follows:1.Composite（ZnS-CNTs）of etched multi-walled carbon nanotubes（H-O-CNTs）and ZnS nanoparticles was prepared and used as the anode material of lithium-ion battery.CNTs were etched in air to obtain rough surfaces with many defects,which could provide many adsorption sites for the growth of ZnS nanoparticles.The ZnS-CNTs composite exhibits high reversible capacity of 451.3 mAh/g after 1200 cycles at a high current density of 5 A/g,and superior rate capability（377.8 mAh/g at 8 A/g）.Interestingly,the ZnS-CNTs electrode exhibits the excellent specific capacity recovery phenomenon,resulting in an excellent stability during the long-term cycling.SEM images of the ZnS-CNTs electrode materials after different cycles show that the ZnS nanoparticles and CNTs gradually merged together with the increase of cycles,which not only effectively alleviates the structural damage caused by volume change of ZnS in the charge and discharge cycling,but also greatly increases the specific capacity due to the increase of its electrochemical reaction area..2.MoS₂/C composite materials are considered as an important electrode material in sodium-ion batteries.By effectively combining MoS₂ and carbon materials to fully utilize its advantages in sodium-ion storage is a challenging and significant topic.A novel MoS₂-C composite was designed by using cellulose nanocrystals（CNCs）as a low-cost green carbon source to combine with MoS₂.Through the hydrothermal reaction and subsequent pyrolysis process,the pre-carbonization of CNCs and the formation of MoS₂were synchronized.Finally,a 3D layered microspheres（200-250 nm）composed of ultra-thin Mo ₂-C nanosheets were synthesized successfully.It was found that ultra-thin MoS₂-C nanosheets consisted of CNCs-derived short-range ordered carbon and a few layers of MoS₂.A robust structure was provided by ultra-thin MoS₂-C nanosheets composed of MoS₂ and CNCs-derived carbon,which exhibits excellent cycling stability and excellent rate performance in sodium ion half-cell tests,and high first specific capacity（397.9 mAh/g）in full cell tests.This work provides an important and effective way to prepare MoS₂-C,which can be used in large-scale energy storage systems and have excellent electrochemical performance.