Preparation And Electrochemical Performance Of Natural Clay Mineral Modified Separator For Lithium-sulfur Battery

Li-S battery is the most promising next generation secondary battery system due to the high theoretical specific capacity(1675 mA h g^-1)and theoretical specific energy(≈2600 W h kg^-1).However,the practical application of Li-S batteries is plagued by some issues such as low conductivity of sulfur,low sulfur loading of cathode materials and shuttle effect of polysulfides.Separator,an indispensable and important component of Li-S batteries,plays a key role in the electrochemical performance of Li-S batteries.Some recent studies have shown that the modification of separators is an effective method to solve the issues of Li-S batteries.Clay minerals are natural nanomaterials with various nanostructures,high specific surface area and low cost.Thus,for accelerating the commercial application of Li-S batteries,this paper mainly carried out the following work.（1）By the combination of natural illite/smectite clay（ISC）,carbon black（CB）and binder（PVDF）,the ISC/CB-Celgard separator was prepared via modification of the Celgard^@2400 separator on one side.The ISC/CB-Celgard separator shows super-electrolyte-philicity and good mechanical stability.The ISC has abundant-OH groups,which can quickly trap a lot of polysulfides by forming Li-O and S-O bonds with polysulfides.The ISC/CB layer can also inhibit polysulfides shuttle by physical shield.Moreover,the ISC/CB layer with good electrical conductivity could transfer electrons to reactivate the trapped polysulfides and then enhance S utilization.Consequently,the Li-S battery with the ISC/CB-Celgard separator shows high initial reversible capacity(1322 mA h g^-1)at 0.1 C and excellent cycle stability with low capacity decay rate（0.054%per cycle）during 500 cycles at 1.0 C.Furthermore,high areal capacity of 6.8mA h cm^-2 is achieved for the battery with the ISC/CB-Celgard separator and the self-supporting CNT/S cathode with high S loading(8.9 mg cm^-2)at 0.32 mA cm^-2.（2）In this chapter,four clay minerals with different microstructures including halloysite（Hal,nanotube）,attapulgite（Atp,nanorod）,montmorillonite（Mmt,nanosheet）and diatomite（Dao,3D porous）were used together with CB and PVDF for modifying the Celgard^@2400 separator.The Hal/CB-Celgard,Atp/CB-Celgard,Mmt/CB-Celgard and Dao/CB-Celgard separators were obtained.All the modified separators show excellent electrolyte wettability and high flexibility.However,clay minerals with different microstructures have different effects on the migration of ions and electrons in Li-S batteries,so the batteries with the separators showed different electrochemical performance.The Mmt/CB-Celgard separator outperforms the other modified separators in inhibiting polysulfides shuttle and enhancing electrochemical performance of Li-S battery.The performance of the other modified separators in enhancing electrochemical performance is in the order of Atp/CB-Celgard>Hal/CB-Celgard>Dao/CB-Celgard.The adsorption capacity and kinetics also indicate that the adsorption performance of the minerals with different microstructures for polysulfides is different from each other.Thus,the relationship between microstructure of the minerals and performance of the Li-S battery is reported.