Regulation Of Interlayer Spacing In Molybdenum Disulfide And Their Supercapacitor Performance

In recent years,with the intensification of global warming and the increasing consumption of traditional fossil energy,this has caused serious environmental problems and energy crisis.In order to cope with these severe problems,there is an urgent need to develop renewable energy and its equipment.Recently,supercapacitors have been widely studied as energy conversion and storage devices with significant superiorities such as high power density,fast charging/discharging speed,long cycle-life,safety,reliability,and environmental friendliness.As a typical TMDs material with a graphene-like"sandwich"structure,MoS₂ has been widely studied in the field of supercapacitors.The interlayer spacing of MoS₂（0.615 nm）is much wider than that of graphene（0.335 nm）,and it can be further expanded,which results in MoS₂ being in a decoupled state.Based on the crystal structures and electronic properties of MoS₂,the performances of the electrochemical supercapacitor were improved by fine-tuning the interlayer spacing of MoS₂,and the mechanism of the supercapacitor performance improvement was analyzed.The details of this dissertation are summarized briefly as follows:1.The author proposed a small molecule direct embedding strategy to construct high-performance supercapacitors,and an ammonium thiocyanate intercalation MoS₂ microflowers material（E-MoS₂）was prepared by a one-pot hydrothermal method.This preparation strategy is achieved by directly embedding SCN^-and NH₄⁺,ionization products of ammonium thiocyanate,into the interlayers of MoS₂,which can be easily realized in the case of excess thiourea.The E-MoS₂ allows fast and stable charge transfer/diffusion and exposes more active sites to enhance its supercapacitor performance.It was confirmed by XRD,FT-IR,TGA and TEM that ammonium thiocyanate was inserted into the interlayer of MoS₂.It is known from experimental tests that the best supercapacitor performance can be obtained when the molybdenum-sulfur ratio of the synthesized sample is 1:10,and its specific capacity can reach 170 F g^-1 at a current density of 1 A g^-1.After 3000 cycles of testing at a charge/discharge current density of 2 A g^-1,the specific capacity of the sample is still 98.5 F g^-1,and the capacity retention rate is 70%,which showing that the materials has higher supercapacitor performance and higher stability.The improvement of its supercapacitor performance is due to the ammonium thiocyanate intercalation opening the MoS₂ interlayer spacing.This expansion can accelerate the diffusion of sodium ions,reduce the diffusion barrier of ion insertion and improve the interlayer conductivity,which is beneficial to supercapacitor for ion insertion/desertion process.The synthetic ammonium thiocyanate intercalation MoS₂ microflowers materials can simultaneously complete the isomeric conversion of thiourea,the intercalation of ammonium thiocyanate and the synthesis of MoS₂ through a one-pot hydrothermal synthesis,which simplifies the process steps and has a synthesis process Simple,low cost and other advantages.2.Through the strategy of lowering the reaction temperature of synthesizing MoS₂,an oxygen-doped MoS₂ microflowers（O-MoS₂）was synthesized.The O-MoS₂ allows fast and stable charge transfer/diffusion and exposes more active sites to enhance its supercapacitor performance.It was confirmed by XRD,Raman,FT-IR and EDS that oxygen doping successfully expanded the interlayer spacing of MoS₂.It is known from experimental tests that MoS₂-180 has obtained excellent supercapacitor performance,and its specific capacity reaches143.1 F g^-1 at a current density of 1 A g^-1.After 3000 cycles of testing at a charge/discharge current density of 2 A g^-1,the specific capacity of the sample is still 73.5 F g^-1,and the capacity retention rate is 69.3%,which showing that the material has higher supercapacitor performance and higher stability.The improvement of its supercapacitor performance is due to the oxygen doping opening the MoS₂ interlayer spacing.This expansion can accelerate the diffusion of sodium ions,reduce the diffusion barrier of ion insertion and improve the interlayer conductivity,which is beneficial to supercapacitor for ion insertion/desertion process.