Surface And Interface Regulation Of ZIF-67 Derived Composite Host And Application In The Cathode Of LSBs

Due to its high theoretical specific capacity(1675 mA h g-1)and energy density(2600 Wh kg’1),the application of elemental sulfur as a cathode’s material has been promoted to a climax in recent years.However,the "shuttle effect" of polysulfides(LiPSs)and their slow reaction kinetics led to loss of active materials and capacity fading,which seriously affect the electrochemical performance of lithium sulfur batteries(LSBs).To address the above issues,this work starts from the preparation of multifunctional and stable sulfur cathodes,and constructs N doped carbon anchored CoV2O6/Co(V-Co/NC)and CoSe2/CoSe0.25S1.75(CS-CSS/NHC)heterogeneous nanoparticles as the host of sulfur.By utilizing the strong chemical adsorption of CoV2O6 and CoSe0.25S1.75 on LiPSs,the strong catalytic conversion of Co and CoSe2 on LiPSs,and the transport effect of polysulfide ions from the built-in electric field of CoV2O6←Co and CoSeo.25S1.75←CoSe2 at the interface,the "adsorption-diffusion-conversion" tandem catalytic process for polysulfides is achieved,thereby suppressing the shuttle effect of LiPSs.This,enhances the conversion kinetics of LiPSs,and ultimately improves the electrochemical performance of LSBs.The main research contents are as follows:(1)Co based metal organic skeleton ZIF-67 as a precursor is firstly immersed in vanadate solution to partially in-situ replace the imidazole skeleton with vanadate.Then,ZIF-67 derived V-Co/NC materials are constructed in situ through atmospheric calcination.The changes of the matrix structure and the synergistic effect among the components are studied after the addition of vanadium in the V-Co/NC host.On the one hand,the NC skeleton with a unique hollow structure constructs a three-dimensional interconnected conductive network,which can effectively buffer volume expansion,and accelerate the transmission ability of electric charges;On the other hand,the "adsorption-diffusion-conversion" effect of CoV2O6/Co nanoparticles on LiPSs accelerates the catalytic conversion of LiPSs.Due to the synergistic effect of structure and composition,the as-prepared V-Co/NC@S cathode achieves a specific discharge capacity of 791.25 mA h g-1 at 0.2 C,exhibiting good cycle stability and rate performance.(2)Using Co based metal organic skeleton ZIF-67 as a precursor,CS-CSS/NHC host materials are constructed in situ through synchronous selenization/sulfuration processes.The NHC framework inherits the characteristics of ZIF-67 polyhedron morphology and high porosity,enabling effective sulfur loading.The CoSe2/CoSe0.25S1.75 heterogeneous particles uniformly dispersed on a carbonaceous framework provide abundant active sites and chemically interact with LiPSs,achieving enhanced regulation of LiPSs from capture to transfer and conversion,avoiding the accumulation of LiPSs in the electrolyte,improving the utilization of active materials and the redox reaction kinetics of LiPSs.Based on the above results,CS-CSS/NHC@S cathode delivers a high initial capacity(1245.91 mA h g-1 at 0.1 C),long cycle stability(0.083%capacity attenuation per cycle for 300 cycles at 1 C),and excellent rate performance(623.92 mA h g-1 at 1 C).