Construction Of Transition Metal Sulfide Energy Storage Electrode And Enhancement Of Its Carrier Transport Performance

The increasing depletion of fossil energy and the massive release of harmful gases cannot meet the requirements of sustainable development.It is urgent to find an effective way to deal with the energy crisis.Lithium-ion batteries have high energy density,low self-discharge rate and long cycle time,and are one of the most widely used technologies in the field of energy storage.With the increasing demand for high-performance lithium-ion batteries,the performance of current commercial lithium-ion batteries is gradually unable to meet people’s needs.New anode materials with excellent lithium storage performance are one of the important ways to achieve high-performance lithium-ion batteries.Graphite is currently the most widely used anode material in commercialization,but its theoretical specific capacity is only 372m Ah g^-1.Therefore,the design and preparation of new anodes with high specific capacity,long cycle life,and better rate capacity are critical.The layered transition metal sulfide,due to its special two-dimensional layered structure,can promote the insertion and extraction of lithium ions,making it a type of anode material that has attracted much attention.Among them,molybdenum disulfide is widely studied because of its high theoretical specific capacity,abundant reserves and low cost.However,due to the low conductivity and changes in the chemical structure during the charge and discharge cycle,its rate performance and cycle stability are poor.In this paper,the controllable preparation of molybdenum disulfide and the optimization of lithium storage performance are carried out from three aspects:shape control,electrode structure design and heteroatom doping.First,a vertically oriented manganese doped molybdenum disulfide nanosheet composite electrode was synthesized on a carbon cloth substrate modified by a carbon nanowire array.The sample uses a carbon cloth modified with carbon nanowires as the substrate to greatly improve the overall conductivity of the composite electrode.The ultra-thin nanosheets can provide more space for lithium ion insertion and extraction,effectively alleviating the chemical structure of the charge and discharge process.Variety.Theoretical calculations confirmed that manganese doping reduced the diffusion barrier of lithium ions in molybdenum disulfide.Combined with AC impedance analysis,it was found that the diffusion coefficient of lithium ions in manganese doped molybdenum disulfide was significantly improved.At the same time,the single-layer manganese doped molybdenum disulfide electronic structure band gap is significantly narrowed,showing metal characteristics,indicating that its electronic conductivity is improved.As the negative electrode,it has an initial specific capacity of 1280 m Ah g^-1 at a current density of 0.1 A g^-1 and a specific capacity of 920 mAh g^-1 at a large current density of2 A g^-1.After 1000 cycles of charge and discharge at a current density of 1 A g^-1,the reversible capacity can still maintain 71%of the initial capacity,showing good cycle stability and rate performance.The results of theoretical calculations and electrochemical performance tests show that enhancing the carrier transport performance of molybdenum disulfide,that is,improving the intrinsic electronic conductivity and lithium ion diffusion coefficient of molybdenum disulfide is an effective way to improve the rate performance and cycle stability of molybdenum disulfide.Sexual strategy.Rhenium disulfide is a hot two-dimensional layered transition metal sulfide recently studied,which has extremely weak interlayer coupling energy and high theoretical specific capacity,and also has high catalytic hydrogen evolution activity.These characteristics provide the possibility for the application of rhenium disulfide in the field of lithium ion batteries and electrocatalytic hydrogen evolution.However,due to the semiconductor characteristics of rhenium disulfide itself,the lower conductivity hinders the improvement of the electrochemical performance of rhenium disulfide.In order to improve the conductivity of rhenium disulfide,we designed and prepared a composite electrode of molybdenum-doped rhenium disulfide nanosheets vertically grown on the carbon nanowire array in situ.According to the electrocatalytic hydrogen evolution test,this electrode exhibits a low overpotential of 101 m V at-10 m A cm^-2,a Tafel slope as low as 40 m V dec^-1,and has good stability.At the same time,as a negative electrode of lithium ion battery,it has a high specific capacity(1278 m Ah g^-1 at0.1 A g^-1)and good cycle stability and rate capacity(426 m Ah g^-1 at 5 A g^-1).Combining electrochemical experiments and theoretical calculations to explain the performance improvement brought about by molybdenum doping,it is confirmed that the semiconductor characteristics of rhenium disulfide can be changed by molybdenum doping,and the electronic structure of single-layer molybdenum doped rhenium disulfide narrows the band gap,showing Out of the metal characteristics,the electronic conductivity is significantly improved.At the same time,the diffusion energy barrier of lithium ions in molybdenum-doped rhenium disulfide is significantly reduced.On the other hand,after molybdenum-doped,the hydrogen adsorption free energy of the catalytically active site of rhenium disulfide is significantly reduced.