Construction And Electrochemical Performances Of MoS₂ Based Heterostructrued Materials

Electrochemical energy storage devices such as lithium ion battery with high capacity,excellent stability and low cost are urgently needed for settling the energy problem.The development of electrochemical energy storage devices based on the contruction of advanced electrode materials.Heterostructured electrode materials have been widely studied for their potential application in electrochemical energy storage becasue they exhibit superior ion storage capacity than that of individual component.What's more,their physical or chemical properties could be affected significantly by modulating the heterogeneous interface.However,the underlying mechanisms are not yet fully studied.In this work,we constructed nanoscale electrochemical energy storage device with MoS₂ nanosheet/MnO₂ nanowire heterostructure and designed two charge/discharge channels to study the effect of the heterogeneous interface on the energy storage performances.The present study thus provides important understanding of heterostructured electrode materials for electrochemical energy storage.In this work,the pure MnO₂ nanowires were synthesized via hydrothermal method.Then,the nanowires were transferred onto the silicon wafers?SiO₂/Si?by spin coating.The layered MoS₂ nanosheets were obtained by micromechanical exfoliation,followed by stacking the MoS₂ nanosheets on the MnO₂ nanowires to form MoS₂/MnO₂ heterostructure.The morphology and structure of the obtained samples were then studied.We constructured nanoscale electrochemical devices based on the MoS₂ nanosheets,MnO₂ nanowires and MoS₂/MnO₂ heterostructure to investigate the capacity,ion diffusion coefficient,and enegy storage mechanisms.The electrochemical performances were studied by connecting the working electrode to MoS₂ and MnO₂ sides of the MoS₂/MnO₂ heterostructure respectively.The intrinsic mechanism of the energy storage of the heterostuctrued material was investigated.The results are shown as follows:?1?MnO₂ nanowires were synthesized via hydrothermal method.The nanowires were transferred onto the silicon wafers by spin coasting.The MoS₂ nanosheets were obtained by micromechanical exfoliation.The MoS₂/MnO₂ heterostructure was fabricated by stacking the MoS₂ nanosheets on the MnO₂ nanowires.The morphology and stcutrue of these samples were characterized through SEM,XRD,RAMAN etc.?2?Nanoscale electrochemical devices based on the MoS₂ nanosheets,MnO₂nanowires and MoS₂/MnO₂ heterostructure were assemblied.The MoS₂ nanosheets deliveres an area capacity of 0.04 mAh cm^-2 at a scan rate of 20 mV s-1,in 6 mol L^-1KOH.At the same scan rate,the MoS₂/MnO₂ heterostructure exhibits an area capacity of 0.31 mAh cm^-2?the working electrode was connected to the MnO₂ side of the MoS₂/MnO₂ heterostructure?,which is 1.5 times higher than that of the working electrode was connected to the MoS₂ side of the MoS₂/MnO₂heterostructure.The ion diffusion coefficients of the MoS₂/MnO₂ heterostructure in different testing modes were further calculated.When the working electrode was connected to the MnO₂ side,the heterostructure demonstrated an optimal ion diffusion coefficient of 1.28×10^-5 cm² s^-1,which is almost 1.3 times as high as that measured under different testing mode?the working electrode was connected to the MoS₂ side of the MoS₂/MnO₂ heterostructure?.?3?In situ measurements of electron transport in the MoS₂/MnO₂heterostructure were carried out to detect the electron transport of the heterostcuture in charge/discharge processes.MoS₂/MnO₂ heterostructure shows a unidirectional conductivity under initial state.After discharging,the heterostucture shows a bidirectional conductivity,however it turn to unidirectional conductivity again after the charge process.We proposed that the different capacity and ion diffusion coefficients of the MoS₂/MnO₂ heterostructure under the two testing modes were due to the unidirectional conductivity in the heterogenous interface.