Preparation And Electrochemical Performance Of Graphene Aerogel-based Cathode For Lithium-sulfur Battery

In recent years,the rapid development of the new energy vehicle industry has put forward higher request on the energy density of power battery.In the existing rechargeable battery systems,lithium-sulfur(Li-S)battery has attracted tremendous attention due to its ultra-high theoretical specific capacity(1675mAh/g)and specific energy(2600Wh/kg).On the other hand,due to the influences of some factors,such as low electrical conductivity of sulfur and high solubility of polysulfides,the commercialization of lithium-sulfur batteries is still facing many challenges.The research interests in lithium-sulfur batteries mainly include the cathode material,the electrolyte and the protection of anode,in which the preparation of novel composite cathode material is the hotspot of research.Starting from the shortage of lithium-sulfur batteries,this paper has prepared a sulfur/polymer/graphene aerogel composite cathode material using a no-slurry method,which combined the advantages of both carbon materials and polymers,further improving the performance of lithium-sulfur batteries and simplifying the preparation of cathode.The main contents of the paper are as follows:(1)Synthesizing a three-dimensional graphene aerogel(GA)bulk material using the two-step reduction and freeze-casting method,which has high porosity and high conductivity.By comparing the differences in the micromorphology and structure of the products under different reaction conditions,the effects of reduction time and pre-freezing condition on the performance of three-dimensional graphene aerogel were analyzed.Moreover,the mechanism of two-step reduction and freeze-casting method was summarized.(2)Preparing the polyvinylpyrrolidone-coated sulfur(PVP-S)particle through simple solution reaction and centrifuge precipitation method,which has smaller size,better dispersity and homogeneity than general sublimation sulfur.Meanwhile,the graphene aerogel was used as conductive matrix to prepare S/GA and PVP-S/GA composites respectively,and the comparative analysis has been made between the two composites through microtopography test,thermogravimetric analysis(TGA),X-ray diffraction(XRD)and Raman spectra,etc.And then the role of PVP in the solution reaction and its effects on the morphology and properties of the product were systematically studied.(3)Simple mechanical compression was applied on the PVP-S/GA and S/GA composites to prepare flexible sheet,which has been directly used as working electrode to fabricate button battery.The as prepared lithium-sulfur batteries have been studied and analyzed systemically through cyclic voltammetry(CV),charge/discharge test,rate discharge performance and electrochemical impedance(EIS)test,etc.The as prepared binder-free cathode in this paper enables an areal sulfur loading of about 2.8mg/cm~2,which delivers a high areal specific capacity of 3.34mAh/cm~2 at 0.1C.On the other hand,the PVP-S particles with unique coating structure can effectively suppress the dissolution of lithium polysulfides,further improving the stability and cycling life of lithium-sulfur batteries.