The Preparation Of Sepiolite Composite Modified Separator And Its Application In Lithium-Sulfur Batteries

Lithium-sulfur batteries have received increasing attention because of their excellent theoretical specific capacity(1675 m Ah/g),high energy density(2600 Wh/kg)and low cost.However,the problems of the lithium-sulfur battery greatly limit its commercial application.As an indispensable part of the lithium-sulfur battery,the separator does not participate in the electrochemical reaction during the charging and discharging process directly.But the separator plays an important role in the electrochemical stability and safety of battery during the charging and discharging process.Currently,Celgard often uses commercial separators.However,the polyolefin membrane has a large pore size and poor thermal stability,which affect the life of the lithium-sulfur battery.Sepiolite has attracted the attention of researchers due to its strong adsorption,thermal stability and mechanical strength.In this paper,an experimental study based on composite materials of sepiolite is carried out.From the aspects of the pore size of the separator,the effect on polysulfide and thermal stable of the separator,respectly,the hydrothermal method and electrospinning technology are used to explore the effect of composite materials modified separator on the electrochemical performance of lithium-sulfur batteries.The research content of this paper mainly includes the following three aspects:(1)As a metal-organic frame material,HKUST-1 has an adjustable aperture,which can block the shuttle of polysulfide effectively.The composite material(H-Sep)of HKUST-1 and sepiolite was successfully prepared by the hydrothermal method,and was used as the modified separator by coating in this chapter.The battery assembled with the modified separator had the first discharge specific capacity of 1642 m Ah/g,which was better than that of battery with a commercial Celgard separator.However,after 100 cycles,the capacity deteriorated due to the unideal structural stability of HSep during cycling.The large porous frame of H-Sep composite material result in oversized pores,which can not hinder the shuttle of polysulfides effectively.(2)Using polyacrylonitrile(PAN)as the carbon source,the sepiolite carbon fiber composite was prepared by using sol-gel combined with electrospinning technology and high-temperature carbonization method(C-Sep).The effect of sepiolite carbon fiber modified separator on the electrochemical performance of lithium-sulfur batteries was studied.After 300 cycles,the reversible specific capacity of 416 m Ah/g was still maintained at 1 C current density,and the electrochemical performance of C-Sep was better than that of Celgard separators.(3)Based on the optimal ratio of polyacrylonitrile(PAN)and sepiolite in chapter four,the composite fiber membrane(polyacrylonitrile/sepiolite(E-PAN/Sep))was prepared by electrospinning combined wit rolling.The E-PAN/Sep composite fiber membrane had a discharge specific capacity of 1227 m Ah/g at 0.2 C current density,which was better than commercial Celgard separators.However,as the chargedischarge reaction progressed,the battery assembled with E-PAN/Sep fiber membrane appeared overcharge,which results in expired performance.By disassembled the battery,we found that the E-PAN/Sep composite fiber membrane inside the battery was torn.