Controllable Preparation And Sodium/potassium Storage Properties Of ZIFs-derived Cobalt Sulfide And Its Hybrid Materials

The progress of the industry cannot be achieved without the supply of energy but traditional fossil energy sources will pollute the environment.Therefore,in order to promote development while protecting the human living environment,green energy storage devices need to be developed.Lithium-ion batteries(LIBs)are sustainable secondary batteries with a wide range of applications that are currently well researched.However,the low content and uneven distribution of lithium in the earth's crust dramatically hinder the continuous development of LIBs.Therefore,people have focused their research on sodium and potassium,which have similar chemical properties to lithium and are hundreds of times more abundant in the earth's crust than lithium,and are more promising for research and application.However,since the ionic radii of sodium and potassium are larger than those of lithium,the conventional anode materials for LIBs are not necessarily suitable for sodium-ion batteries(SIBs)and potassium-ion batteries(PIBs),so novel anode materials need to be developed for SIBs and PIBs.Cobalt sulfides with high theoretical capacity have drawn research interest.However,its volume expansion during long-term charge and discharge tends to lead to structural collapse.Thus,it needs to be modified to accommodate the swelling effect and enhance the electrochemical performance.Zeolite imidazolate frameworks(ZIFs)have the advantages of high porosity,large specific surface area,and thermal stability,even leaving a highly conductive and solid matrix after annealing to accommodate the swelling effect.Given this,ZIFs are suitable as templates for the derivatization of cobalt sulfides.In this paper,ZIF-67 was employed as a template to derive cobalt sulfides embedded in the nitrogen-doped carbon and then were modified by ion-exchange reaction,vertical growth on the surface,or high-temperature calcination.Therefore,hetero-structured materials with high reversible capacity and cycle stability were designed by doping with cations or anions.The results achieved are as follows:(1)Materials with core-shell structure were designed by growing ZIF-8 on the surface of ZIF-67,and Co S₂/Sb₂S₃ nanoparticles with the heterogeneous structure were prepared by the ion-exchange method.Co S₂/Sb₂S₃@NC/CNT maintained 60%capacity retention at the current density of 0.5 A g^-1 after 200 cycles in SIBs,while the reversible specific capacity of 453.5m Ah g^-1 was maintained after 50 cycles at a current density of 0.2 A g^-1 in PIBs.Moreover,the results of the pseudocapacitance test,which showed that the pseudocapacitance contribution increased as the scan rate increased,indicated that the ion transport was accelerated,confirming that the three-dimensional double carbon framework made the conductivity improved.(2)The Co S₂/NC@VS₄ composites were constructed by growing nanoscale VS₄ particles on the surface of Co S₂ particles using a one-step hydrothermal method.The nanoscale VS₄particles significantly shortened the ion transport channels and enhanced the ion transfer rate,thus exhibiting excellent electrochemical properties.The material underwent cycling 700 times at a current density of 1.0 A g^-1 in SIBs and still maintained a reversible capacity of 307 m Ah g^-1.When it cycled 430 turns in PIBs and still provided a reversible capacity of 291 m Ah g^-1 at a current density of 1.0 A g^-1.The resistance before and after cycling was measured by AC impedance testing,and the results demonstrated that the resistance became smaller after cycling,providing evidence that the material had remarkable cycle stability.(3)The micron-sized ZIF-67 was created by varying the reaction solvent and time.Then high-temperature selenization and sulfidation were performed to obtain Se doped Co S₂ particles with a nitrogen-doped carbon framework.The Se doping was observed to effectively enhance the reversible specific capacity of the material by comparison with Co S₂ and Co Se₂ containing only a single anion.This is due to the fact that the Se atomic radius is larger than that of S.Its doping increases the crystal plane spacing and facilitates ion insertion into the material so that Co S_2-xSe_x/NC exhibits outstanding electrochemical properties.In SIBs,the reversible specific capacity of 390.5 m Ah g^-1 was achieved by 1500 cycles when placed at a current density of 5.0A g^-1,while in PIBs,the reversible capacity of 323.06 m Ah g^-1 was provided by 500 cycles when placed at a current density of 1.0 A g^-1.Moreover,the relationship between diffusion control and the charge was explored by the GITT test.The ion diffusion rate slowed down when a redox reaction occurred.The overall trend of ion diffusion rate decreased as the discharge potential decreased,and conversely,during charging,the overall trend of ion diffusion rate also decreased as the potential rose.