Synthesis And Performance Of Interlayers And Gel Electrolyte For Lithium-sulfur Batteries

Lithium-sulfur?Li-S?battery is considered as one of the most promising next generation energy storage devices due to its high theoretical specific capacity?1675mAh/g?and theoretical energy density?2600 Wh/kg?.It has attracted wide attentions in the field of energy and materials.Compared with commercial lithium ion batteries,sulfur is much cheaper and more environmentally friendly.However,Li-S system has some drawbacks which need to be solved before commercialization,such as low electronic conductivity of sulfur,big volume change during charging and discharging and the shuttle effect of polysulfides.They all lead to severe irreversible capacity fading and poor rate performance.Applying an interlayer between cathode and separator is a simple way to impede shuttle effect by physical and chemical adsorption.Another method is applying gel electrolyte to fix liquid component so that the dissolution and migration of polysulfide are limited.Nevertheless,both two ways could not realize fast charging and discharging due to the lack of continuous high lithium ion conductive structure.Li-S batteries still can not meet the requirement of power batteries now,and it is important to enhance high rate performance in Li-S system.Lithium titanate?LTO?is commercialized material which has a high lithium ion conductivity.The Ti-O bond has strong interaction with polysulfide.Thus,LTO can be used in the design of interlayer to improve performance of Li-S batteries.In this paper,carbon nanofiber based interlayer was designed and its preparation method was developd.The LTO,SiO₂ and titanic oxide were used as active additives to combine with carbon nanofibers.It was found that the Li-S batteries with interlayers containing titanic oxide performed better than batteries using interlayers with inert additives.However,adding the LTO particles directly cannot improve battery performance effectively due to large size,poor dispersion and discontinuous structure of LTO.In the respect of synthesis method,comparing interlayers using SiO₂ particles with using TEOS precursor,uniform and fine particles synthesized by liquid phase could improve the performance of Li-S batteries.In addition,a fine LTO particle coated carbon nanofibers?LTO-CNF?was prepared by a sol-gel method.This material has both electronic conductive network and lithium ion pathways.The LTO shell provides a large quantity of adsorption sites,and it also has catalysis on electrochemical reaction of polysulfide.The composite could greatly promote high rate performance of Li-S batteries.The LTO-CNF interlayer performs best with a mass loading of 0.519 mg/cm².With such an interlayer,a capacity of 641.9 mAh/g was obtained at a high rate of 5 C.Last but not least,interlayers and gel polymer electrolyte?GPE?were applied in Li-S batteries together.Acrylate-based gel electrolyte was easily obtained and it is polymerized to form polymer with more double bonds for poly-arylate chemicals.The obtained GPE has a higher lithium ion transference number than liquid electrolyte.However,when interlayers and acrylate-based GPE were applied in the Li-S batteries simultaneously,huge polarization occurred and its electrochemical performance of Li-S batteries was not satisfactory.Further research on matching interlayers with GPE is needed.