| Molybdenum disulfide(MoS2)is a two-dimensional layered material which is bonded by weak van der Waals force.Because of its large interlayer spacing,which is beneficial to the intercalation/deintercalation of ions,it is widely used in lithium-ion batteries and sodium-ion batteries.However,unlike lithium-ion batteries and sodium-ion batteries,the radius of zinc hydrate(Zn(H2O)6]2+)is as large as 0.404?0.43 nm,and the electrostatic interaction between Zn2+and MoS2 crystal structure is large,which leads to the slow diffusion kinetics of Zn2+in MoS2.In addition,MoS2 also has some issues,such as poor conductivity,poor hydrophilicity,agglomeration and volume expansion.In view of these issues,this thesis uses three methods to modify MoS2,and studies the effect of the modified methods on zinc storage performance of MoS2.The main research contents and results are as follows:(1)Study on the zinc storage performance and mechanism of hierarchical MoS2@CNTs hybridMoS2 nanosheets with large interlayer spacing were grown on the surface of carbon nanotubes by hydrothermal method with thiourea,sodium molybdate and carbon nanotubes as main raw materials.The composition,surface morphology and microstructure of the hybrid were characterized by X-ray diffraction,scanning electron microscopy,Raman spectroscopy and so on.The zinc storage performance and mechanism of the hybrid were studied by means of electrochemical test,density functional theory and molecular dynamics simulation.The results show that MoS2 nanosheets grow in situ along CNT surface to form a hierarchical structure,and the interlayer spacing of MoS2 is about 0.97 nm.Density functional theory calculations,molecular dynamics simulation,galvanostatic intermittent titration technique test and electrochemical impedance spectroscopy show that the expansion of interlayer spacing reduces the intercalation barrier of Zn2+,promoting the rapid diffusion of Zn2+,and the carbon nanotubes skeleton improves the charge transfer efficiency.In addition,the hierarchical structure effectively inhibits the agglomeration of MoS2 nanosheets,increases the specific surface area and increases the active sites of electrochemical reaction.At 0.1 A g-1,the MoS2@CNTs electrode displays a capacity of 180.0 mAh g-1.At 3.0 A g-1,the retention rate of specific capacity is 51.7%.In addition,the specific capacity of the MoS2@CNTs electrode is 111.7 mAh g-1 at 1.0 A g-1,and the retention rate is still 80.1%after 500 cycles(2)Study on the zinc storage performance and mechanism of MoS2/PANI hybridOleic acid was inserted into MoS2 interlayer by hydrothermal method with thiourea,sodium molybdate,oleic acid and sodium oleate as main raw materials.Then,polyaniline was inserted into MoS2 interlayer by the limiting domain reaction of oleic acid and aniline monomer and the in situ polymerization of aniline to form MoS2/PANI heterojunction.In order to explore the composition,surface morphology and microstructure of the hybrid,the X-ray diffraction,scanning electron microscopy,Raman spectroscopy and other tests were carried out.The zinc storage performance and mechanism of the hybrid were studied by combining electrochemical test and density functional theory.The results show that MoS2 layer and polyaniline layer overlap to form heterojunction,and the interlayer spacing of MoS2 is about 1.03 nm.The results of galvanostatic intermittent titration technique test show that the intercalation of polyaniline promotes the rapid diffusion of Zn2+.The results of density functional theory calculations show that the insertion of polyaniline layer effectively shields the electrostatic interaction between Zn2+and MoS2 crystal structure.Moreover,the insertion of polyaniline leads to the band gap between the guide band and valence band of MoS2/PANI hybrid much smaller than that of the original MoS2(1.18 eV vs.1.87 eV),which improves the charge transfer efficiency.In addition,polyaniline can also maintain the structural stability of the hybrid as interlayer support.MoS2/PANI hybrid electrode has a specific capacity of 181.6 mAh g-1 at 0.1 A g-1,and the specific capacity is still 83.2 mAh g-1 at 2.0 A g-1,which indicates that the MoS2/PANI hybrid has good rate performance.The initial specific capacity of MoS2/PANI electrode is 106.5 mAh g-1 at 1.0 A g-1.After 1000 cycles,the retention rate is still 86%,indicating that MoS2/PANI hybrid has good cycle stability.(3)Study on the zinc storage performance and mechanism of 1T-MoS2/rGO hybrid1T phase rich MoS2 nanosheets were grown on graphene by hydrothermal method with thioacetamide,molybdenum trioxychloride and graphene oxide as main raw materials.In order to explore the composition,surface morphology and microstructure of the hybrid,the X-ray diffraction,scanning electron microscopy,Raman spectroscopy and other tests were carried out.The zinc storage performance and mechanism of the hybrid were studied by electrochemical test.The results show that MoS2 nanosheets grow in situ on graphene,the content of 1T phase is about 86.6%,and the interlayer spacing is about 0.94 nm.The results of ex situ X-ray photoelectron spectroscopy and ex situ Raman spectroscopy show that graphene inhibits the transition of MoS2 from 1T phase to 2H phase during the cycling test,and provides a large number of active sites for the rapid diffusion of Zn2+ and electrons.In addition,the existence of graphene inhibits the agglomeration and volume expansion of MoS2 nanosheets,and improves the cycling stability.Due to the rapid difffusion of Zn2+and electrons,the polarization effect is reduced and the contribution rate of pseudocapacitance is significantly improved.At 0.1 A g-1,the 1T-MoS2/rGO electrode displays a capacity of 191.4 mAh g-1,and the retention rate is still 47.4%at 10.0 A g-1.In addition,at a high current density of 5.0 A g-1,the 1T-MoS2/rGO hybrid electrode has an initial specific capacity of 108.3 mAh g-1,and the retention rate is still 88%after 1000 cycles,demonstrating an excellent cycle stability and rate performance. |
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