Construction And Electrochemical Performance Of MoS₂-based Composite Materials

Lithium-ion batteries have been widely used due to their high energy density,long cycle life and environmental friendliness.Molybdenum disulfide(MoS2),a typical two-dimensional(2D)layered material,has been considered as a promising candidate for energy storage,especially for lithium ion batteries(LIBs)/sodium ion batteries(SIBs)system.Benefiting from the well-defined layered structure,MoS2 as active electrode materials exhibits a desirable theoretical specific capacity(670 mAh g-1),much higher than that of the commercial graphite anode materials(370 mAh g-1).However,the practical application of MoS2 is still hindered by the intrinsically low electronic conductivity as well as large volume variation during the charge/discharge process,resulting in poor cycling stability and inferior rate performance based on the conversion reaction mechanism.Thus,many research groups have been committed on constructing graphene/MoS2,aiming to improve the conductivity,stabilize the structure as well as reduce the volume change.In order to adapt to the development of electric vehicles,wind energy,solar energy and intelligent communication industries,the demand for high energy density energy storage systems is more urgent.Lithium-Sulfur(Li-S)Batteries have the potential to be the next-generation rechargeable lithium batteries because of their high theoretical specific capacity of 1675 mAh g-1 of the sulfur cathode and remarkable energy density of 2600Wh kg-1.Moreover,the natural abundance,low cost,and nontoxicity of sulfur should make Li-S batteries become commercially attractive compared to the conventional LIBs.However,there are still several challenges that need to be addressed before the technology become practical.The large volume variation of sulfur electrode during the discharge/charge process,the shutting effect caused by dissolution of intermediate lithium polysulfides(Li2Sn,n>3)into the electrolytes during the solid-liquid-solid transition process and the insulating nature of sulfur hindered the practical application of lithium-sulfur batteries.These issues bring about low Coulombic efficiency and rapid decline of capacity upon cycling.MoS2 has been demonstrated to have strong binding energies with Li2Sx,which benefit for capturing the dissolved LiPSs and accelerating the kinetics redox reaction.However,the poor intrinsic conductivity and limited exposure of edge sites for 2H-MoS2 render slow kinetics and unexploited active centers for LiPSs absorption.Compared to the 2H-phase MoS2,the metallic 1T-phase MoS2 allows more favorable electron transfer and strong interactions between positively charged S-vacancy(Vs)and negatively charged polysulfdes.The prepared MW-rGO/MoS2 composite material is used as the negative electrode for lithium/sodium ion battery,and TiN@1T-MoS2/S is used as the positive electrode material of lithium-sulfur battery.It exhibits excellent cycle performance and rate performance.The main research contents are as follows:In this work,we propose a facile and general"prereduction-microwave"strategy to repair the lattice defects of reduced graphene oxides composites just in a few seconds,particularly,which has been successfully carried out on r-GO/MoS2 composite previously synthesized through the hydrothermal method.This post repaired strategy not only can effectively improve the conductivity of graphene framework,but also well preserve the structural properties of graphene-based composites.Therefore,the optimized rGO/MoS2 composite achieves improved conductivity,good wettability,short ion diffusion length and excellent structural stability compared to the untreated rGO/MoS2 composite,which presents desirable capacity of 734 mAh g-1 for 200 cycles at 0.5 A g-1 and 335 mAh g-1 for 100 cycles at 1 A g-1 for lithium ion and sodium ion storage,respectively.This method will further promote the development of graphene-based materials for efficient energy storage and conversion.Herein,we design a new hybrid material of TiN@1T-MoS2 hollow sphere for Li-S batteries.The rational designed structure of TiN@1T-MoS2 hollow sphere has the following conspicuous merits for Li-S batteries:(1)the large void space of hollow TiN@1T-MoS2 sphere not only allows the higher content of sulfur,but also accommodates the large volumetric expansion of sulfur during lithiation;(2)the metallic electrical conductivity of 1T-MoS2 and TiN with enormous conductive paths benefits the charge transfer,leading to better high rate perfonnance;(3)the internal TiN sphere and the external MoS2 nanosheets grown on TiN sphere provides more accessible active sites for LiPSs absorption and contribute to fast reaction kinetics.TiN@1T-MoS2 hollow sphere with 82.5 wt%sulfur content deliver a high specific capacity of 798 mAh g-1 after 200 cycles at 0,5 C and 463 mAh g-1 after 800 cycles at 1C.