Design And Electrochemical Performance Study Of MOF-Derived Adsorption-Catalysis Functional Materials For Lithium Sulfur Batteries

Lithium-sulfur battery with irreplaceable advantages:high theoretical energy density(2600Wh kg^-1),high theoretical specific capacity(1675m Ah g^-1),abundant raw material reserves,low price,and environment-friendly,have attracted wide attention,which is considered one of the most potential energy storage systems.However,the serious"shuttle effect",sluggish redox reaction kinetics,and significant volume changes in sulfur cathode during cycling seriously hinder the actual development of lithium-sulfur batteries.Metal-Organic Frameworks（MOF）exhibit a three-dimensional pore structure with a large surface area.The framework can maintain intact pores after annealing treatment which can effectively suppress shuttle effects.Therefore,this paper focuses on the construction of adsorption-catalysis functional materials for polysulfides based on MOF materials and studies the effects of crystal structure and heterostructure on the shuttle effect and reaction kinetics of polysulfides.The details are as follows:1.Crystalline CoP and amorphous CoP modified carbon nanotube networks were prepared based on Zeolitic Imidazolate Frameworks（ZIF）materials（c CoP@CNTs and a CoP@CNTs）,and the composite was used to modify separator for lithium-sulfur batteries to investigate the electrochemical performance.Compared to crystalline CoP,the defects and unsaturated dangling bonds in amorphous CoP can effectively accelerate the formation of energy barriers for Li₂S and provide a stronger adsorption capacity for polysulfides.Therefore,the cells delivered an initial reversible specific capacity of1227.9 m Ah g^-1 at 0.2 C,good rate performance of 795.9 m Ah g^-1 was also achieved at a high current density of 2.5 C.Furthermore,the cells maintain an extremely low cyclic performance attenuation rate of only 0.049%per cycle for 1000 cycles at 1 C.2.Zn Se-CoSe heterostructure modified nitrogen-doped hollow carbon nanostructures（Zn Se-CoSe HNC）derived from tannic acid etched bimetallic Zn Co-MOF as sulfur hosts for high-performance lithium-sulfur batteries.Zn Se-CoSe heterostructure can effectively promote the continuous conversion ofα-S₈-polysulfides-Li₂S towards Li₂S-polysulfides-β-S₈,and provide strong chemical adsorption ability for polysulfides.While the hollow structure can effectively alleviate the expansion of sulfur species and provide physical constraints to hinder the diffusion of polysulfides.Therefore,the Zn Se-CoSe HNC/S cathode exhibited a reversible specific capacity of973.9 m Ah g^-1 after 100 cycles at 0.2 C.Besides,the Zn Se-CoSe HNC/S cathode has exhibited excellent long-term cycle stability（average capacity decay rate of 0.044%at2 C per cycle）.Even at high sulfur loading of 6.4 mg cm^-2 and a low E/S of 6μL mg^-1,the cathode still delivered a high initial capacity of 906.2 m Ah g^-1 at 0.2 C.