Preparation Of MIL-101(Cr) Membrane Materials On Carbon Based And Its Application In Interlayer Of Lithium Sulfur Batteries

Lithium-sulfur（Li-S）batteries hold one of the most promising next-generation power storage devices,in view of this high theoretical specific capacity(1675 m Ah g^-1)and high energy density(2600 Wh kg^-1).However,there still remain some difficulties in the commercial process,which the non-conductivity of sulfur,the large volume variation of sulfur during the cycle,and the dissolution and diffusion of lithium polysulfide（Li PS）in the electrolyte.In particular,soluble lithium polysulfide can migrate through the separator to the anode side,causing shuttle effect.The shuttle effect of lithium polysulfide would lead to the irreversible loss of active substances and rapid capacity.The introduction of interlayer material between the cathode and the separator is one of the most studied strategies to solve the shuttle effect.Metal-organic framework（MOF）has attracted attention in the field of Li-S battery due to its large specific surface area,abundant active sites and excellent post-modification adjustability.In this paper,the stability of Cr-based MIL-101 materials are selected as the research object.MIL-101（Cr）membrane materials are designed and prepared on carbon cloth（CC）and carbon nanotube（CNT）thin film,respectively.Among them,MIL-101@CC interlayer exhibits excellent adsorption-catalytic properties of MIL-101（Cr）thin film.Further,continuous orientation MIL-101（Cr）membrane are successfully synthesized on the surface of CNT thin film by utilizing the membrane forming properties of MIL-101（Cr）.The prepared MIL-101（Cr）interlayer retained adsorption-catalytic properties and had selective sieves for the lithium polysulfide and Li ions,which further improved the electrochemical performance of lithium sulfur battery.The main research contents are as follows:（1）Highly oriented MIL-101（Cr）thin film（MIL-101@CC）are prepared on carbon cloth by in-suit secondary growth method.The interlayer possesses a unique hierarchical porous structure and fully exposed active sites,and the thin film structure increases the density of the active sites,allowing effective anchoring of Li PS through strong physical/chemical adsorption.MIL-101（Cr）thin film have Lewis acidic Cr（Ⅲ）centers,which are able to coordinate with Li PS through Lewis acid-base interactions.In addition,the interlayer material can promote the conversion of Li PS.Benefiting from these features,the interlayer material can effectively inhibit the shuttle effect and improve the electrochemical performance of Li-S battery.The initial specific capacity is 814 m Ah g^-1 under current density of 1 C,with the capacity decay of 0.039%;When the current density is up to 3 C,the specific capacity can still reach 635 m Ah g^-1.（2）Continuous MIL-101（Cr）films are prepared on CNT thin film by hydrothermal method.Owing to the suitable pore aperture and super electrolyte wettability,the MIL-101（Cr）membrane acts as an ionic sieve,that selectively inhibit Li PS while allowing rapid transport of lithium ions.Moreover,the interlayer material can also absorb and catalyze the catalytic conversion of Li PS.Therefore,the Li-S battery with MIL-101/CNT interlayer shows excellent cycle stability.The initial capacity is 816 m Ah g^-1,with the capacity decay of 0.046%.Meanwhile,the proposed interlayer shows a remarkable specific capacity of661.9 m Ah g^-1 under the high current density of 5 C.