Preparation Of High-Porosity GO-PC Composite For Lithium-Sulfur Batteries

The ultrahigh theoretical specific capacity and energy density of lithium-sulfur batteries with nontoxicity and natural abundance of sulfur,have attracted much attention in recent years.However,the insulating nature of sulfur,large volumetric expansion during discharging and shuttle effect of polysulfide greatly limit the practical application of lithium-sulfur batteries.In view of the above problems,this research work designed and fabricated a high-porosity graphene oxide-porous carbon(GO-PC)composite with strong adsorption capacity for lithium polysulfide,and applied it in the construction of cathode and diaphragm modification,so as to improve the comprehensive performance of lithium-sulfur battery.The main research contents of this article are as follows:(1)With sodium chloride as template,the high-porosity and high-specific surface area GO-PC composite was fabricated by the process of ultrasonic blending,freeze drying and etching by deionized water,and as the host of sulfur cathode,it showed excellent kinetic performance.The internal abundent channel of GO-PC composite can not only be used as convenient path for the transmission of Li+ to accelerate the transmission rate,but also alleviate the issue of volume expansion,endowing the cathode with excellent rate capability.Using sodium chloride as template to create pores is non-toxic environmental protection,easy etching and low cost.GO is rich in oxygen-containing functional groups,and as matrix,it can effectively immobilize polysulfide and inhibit the dissolution and shuttle effect of polysulfide.Taking glucose as carbon source,the porous carbon was formed in situ by calcining process in the composite,which can effectively improve the conductivity of composite and make it unnecessary to add conductive agent during the preparing process of cathode plate.The experiment results presented that the GO-PC/S II composite with medium dosage of template has the most suitable hierarchical pore structure and shows excellent dynamic performance,rate capability(618.3 mAh g-1 at 2 C)and cycling performance over 300 cycles.At the rate of 0.5 C,the specific capacity of the first discharge reached 1242.7 mAh g-1,and it still remain 629.0 mAh g-1 after 150 cycles.At the rate of 1 C,the specific capacity of the first discharge was 1036.2 mAh g-1,and it still remain 500.6 mAh g-1 after 300 cycles.(2)By using electrostatic spinning technology,a layer of GO-PC/PVA fiber mesh was successfully deposited on one side of the battery diaphragm,and the diaphragm was modified to improve the comprehensive performance of the battery.High-porosity GO-PC composite and PVA were dissolved in deionized water by the method of heating,stirring and ultrasonic,respectively,and then they were proportionally configured into the precursor solution for electrostatic spinning.By controlling a single variable,the optimum preparation parameters of modified diaphragm were explored,and then modified diaphragm with suitable morphology was obtained.The adsorption effect of GO-PC composite on polysulfide is used to prevent it from passing through the diaphragm and inhibit the shuttle effect.Meanwhile,the fiber network structure of GO-PC/PVA thin layer will not block the transmission of Li+.In this work,carbon nanotube/sulfur(CNT/S)composite with properties of good electrical conductivity and light weight was used as cathode.The experiment results showed that the lithium-sulfur battery with modified diaphragm has overall higher discharge capacity and better cycling stability than that with common diaphragm.