Study On The Design And Catalytic Activity Of Functional Separator For High Performance Lithium-sulfur Battery

Due to the rapid development of the electric and hybrid vehicle industry,numerous issues such as range anxiety are emerging.The energy density of traditional lithium-ion batteries has reached the bottleneck,and it is urgent to find a new energy storage system to meet the needs of the current social development.Lithium-sulfur batteries(LSBs)are deemed to the most promising candidate for the next generation of energy storage systems because of their many advantages,such as low cost,eco-friendly,high specific capacity(1675 m Ah g^-1)and high energy density(2600 Wh kg^-1).However,many challenges,such as the insulation of sulfur and its sulfides,the large volume change during charge and discharge process,the“shuttle effect”of polysulfide and poor electrochemical kinetics,limit the further application of LSBs.In recent years,solving the issues of LSBs and preparing the LSBs with high stability and long cycle life have become the research focus in the field of energy storage.Compared to the design of sulfur hosts with complex process,the functional separator is considered to be a low-cost and efficient solution to solving the many issues of LSBs.In this dissertation,according to the inherent issues,research status and development prospects of LSBs,around the functional membrane design of LSBs and the performance characterization of catalysts,several research schemes for the preparation of high stability LSBs were proposed.Furthermore,the main research contents of this dissertation are as follows:(1)An efficient polysulfide trapper of a nitrogen and nickel-decorating amylum scaffold-coated(AC/Ni/N)separator for ultrahigh performance in LSBs.In this paper,using the chemical reaction between Ni Cl₂·6H₂O and starch under high temperature calcination,N/Ni co-doped pseudographite scaffold for functional separator was obtained with starch as carbon source,urea as N source,Ni Cl₂·6H₂O as Ni source.The AC/Ni/N can provide a rich multi-stage pore structure,which can not only promote the transport of electrons and lithium ions(Li⁺),but also inhibit the shuttle effect of polysulfide as physical barrier.Moreover,the uniform distribution of N atoms and Ni nanoparticles on the surface of the functional separator can provide numerous active sites for polysulfide chemisorption,which can inhibit the shuttle effect of polysulfide by chemisorption.More importantly,the Ni nanoparticles with high electrocatalytic activity can effectively promote the conversion of polysulfide and improve the internal electrochemical kinetics of the LSBs.Thanks to the above advantages,the cell with AC/Ni/N functional separator delivers excellent electrochemical stability(575 m Ah g^-1 at 1.5 C after 700 cycles)and rate performance(659 m Ah g^-1 at 2.5 C).Even with the sulfur loading of 7 mg cm^-2,the obtained cell also exhibits excellent reversible specific capacity(714 m Ah g^-1 at 0.1 C after 100cycles)and satisfactory cycle stability.Promoting polysulfide conversion by catalytic separator with Li Ni PO₄ and r GO(LNPO/r GO)hybrids for high performance LSBs.The LNPO nanoparticles obtained by high-temperature calcination were uniformly distributed on the surface of r GO by simple grinding and ultrasound to form LNPO/r GO hybrids with many active sites.The r GO conductive skeleton can promote the transport of electrons and Li⁺,and suppresses the shuttle effect of polysulfide by physical barrier.LNPO nanoparticles,as functional additives of LSBs,can not only chemically adsorb polysulfide,but also suppresses the shuttle effect of polysulfide.Moreover,it can effectively promote the transformation process of polysulfide and endow the LSBs with faster kinetic reaction.In addition,the cell with LNPO/r GO functional separator delivers the long cycling life(629 m Ah g^-1 at 1.5 C after 1400 cycles)and high areal specific capacity(4.2 m Ah cm^-2).(3)The electrocatalyst based on Li VPO₄F/CNT(LVPF/CNT)to enhance the electrochemical kinetics for high performance LSBs.Carbon nanotubes(CNT)are used as the conductive matrix,and LVPF nanoparticles are grown in situ in the void of the conductive network of CNT by two-step calcination.Compared with r GO,CNT can provide more favorable tubular channels for electron and Li⁺transport.LVPF itself has a number of active sites that can form chemical bonds with polysulfide,which has a strong adsorption effect on polysulfide.And LVPF can effectively improve the problem of poor electrochemical kinetics in the LSBs.Moreover,LVPF/CNT hybrids play an important role in the preparation of high energy density LSBs.The cell with LVPF/CNT functional separator exhibits Long cycling life and cycling stability(578.5 m Ah g^-1 at 1.5 C after 1000 cycles).Even the sulfur loading is 7 mg cm^-2,the obtained cell also maintains excellent cycling stability(551 m Ah g^-1 at 0.5 C after 350 cycles)and high areal specific capacity(5.58 m Ah cm^-2).In conclusion,in this dissertation,a variety of carbon-based functional additives for LSBs functional separator were prepared by high temperature calcination.On the one hand,these functional separators can suppress the shuttle effect of polysulfide through chemisorption to ensure the cycling stability of LSBs.On the other hand,it can promote the conversion of polysulfide and improve the electrochemical kinetics of LSBs.The functional separators prepared solve some common issues existing in LSBs,and provides a novel idea for the development of functional separator of LSBs.