Preparation And Electrochemical Properties Of Transition Metal Chalcogenides

In recent years,transition metal chalcogenide compounds(TMC)have attracted much attention due to the low cost,high conductivity and high theoretical capacity.However,due to the repeated insertion and deinsertion of ions in the electrochemical reaction process,it is easy to lead to electrode fragmentation and agglomeration,resulting in slow ion diffusion kinetics,which seriously affects its electrochemical performance.By selecting appropriate templates,a series of TMCs with different structures were prepared via simple synthesis methods.At the same time,heterointerfaces,nitrogen doped carbon shell and oxygen doped were introduced into the TMC.The main contents of this paper are as follows:(1)Multi-yolk Zn Se/Co Se₂heterostructures confined in N-doped carbon hexahedron(denote as Zn Se/2(Co Se₂)@NC),have been prepared from precursor Zn Co₂-ZIF via a facile low-cost two-step method.The numerous void spaces can efficiently buffer the volume changes during the repeated insertion/deinsertion,and enhance the cycling performance.The abundant heterojunction interfaces between Zn Se and Co Se₂can create lattice mismatch and distortion,promoting the ions diffusion kinetics and producing outstanding pseudocapacitive effect,which can enhance the specific capacity and improve the rate performance.The prepared Zn Se/2(Co Se₂)@NC electrodes possess excellent lithium and sodium storage performance.The results show that Zn Se/2(Co Se₂)@NC electrodes exhibit a high specific discharge capacity(853.2 mAh g^-1)and a good initial coulomb efficiency(62.7%)at 0.1 A g^-1.Even at 1 A g^-1,Zn Se/2(Co Se₂)@NC electrodes remain the capacity of 394.2 mAh g^-1after 500 cycles.For LIBs,Zn Se/2(Co Se₂)@NC electrodes still display excellent reversible specific capacities of 1554.3 mAh g^-1after 100 cycles at 0.1 A g^-1,respectively.(2)The oxygen doped tubular-core-shell hierarchical structured Mo S₂(denote as OHT-Mo S₂@NC)was prepared by used rag as template via a hydrothermal method.Oxygen doping can reduce the band gap of Mo S₂and enhance the interlayer conductivity.At the same time,the tubular core-shell hierarchical structure can prevent the crushing and pulverization of Mo S₂during the cycle.In addition,after compounding with carbon,the structure stability of Mo S₂is further improved.Therefore,OHT-Mo S₂@NC electrodes exhibit superior electrochimcal performance.For sodium-ion batteries(SIBs),OHT-Mo S₂@NC electrodes show high capacity of802.3 mAh g^-1at 0.1 A g^-1after 100 cycles,long-time cycling performance with the capacity of 496.6 mAh g^-1and remarkable capacity retention of 95.2% over 500 cycles at 1 A g^-1.For lithium-ion batteries(LIBs)and potassium-ion batteries(PIBs),OHT-Mo S₂@NC still endows excellent reversible capacity of 1029.6 mAh g^-1and459.7 mAh g^-1at 0.1 A g^-1over 100 cycles,respectively.