Study On The Synthesis Of Functional Interlayer And Cathode Materials And Their Electrochemical Performance Of Lithium-sulfur Batteries

Energy availability is continually becoming more essential to rapid economic development globally.With a focus on the negative impacts of fossil fuels,an increased effort has been applied to the field of renewable energy.Since renewable energy sources are often intermittent in nature,storage technologies,such as batteries,are required to use them effectively.Lithium-sulfur?Li-S?batteries have attracted particular attention due to the high theoretical energy density and specific capacity.Additionally,sulfur is an environmentally friendly and low-cost material with abundant reserves^[1].However,Li-S batteries also show several serious defects,including poor conductivity(about 10^-30 S cm^-1 at 25°C),large volume expansion?about 80%?of sulfur as cathode,and shuttle effect of intermediate products?lithium polysulfides?during charge/discharge process.For the shuttle effect,the highly soluble polysulfide intermediates?Li₂S_x,x>3?can easily dissolve in the liquid electrolyte and pass through the separator,then are partly deposited on the surface of lithium anodes after being reduced to Li₂S or Li₂S₂,resulting in an irreversible active material loss,severe self-discharge,low columbic efficiency,increasing impedance and extensive capacity fading for Li-S cell during cyclic testing^[2].All these shortcomings hinder the fulfillment of its theoretical specific capacity and obstruct its practical application severely.Thus,the design of cathode host was a most direct and essential part for Li-S batteries'application.Meanwhile,to further utilize the dissolved polysulfides in the electrolyte,the developing of a functional interlayer between separator and cathode also becomes a hot topic in the research of Li-S battery.First,a hierarchical porous graphene bubble?PGB?was synthesized by using the template to incorporate with sulfur for enhanced electrochemical property.The synthesized PGB owns a porous structure with abundant mesopores which can restrict the dissolution of polysulfides,and the curved carbon layer can further protect the polysulfides from further shuttling.Thus,PGB can serve as a better host with much better electrochemical performance.Then,a ZnFe₂O₄@C composite was synthesized by simple steps.ZnFe₂O₄@C@S was obtained after incorporate ZnFe₂O₄@C composite with sulfur.The interaction between ZnFe₂O₄ and polysulfides improved the electrochemical performance of the lithium sulfur battery.A novel multi-functional interlayer?CP@CNF?composed of an outer cyclized-PAN network and inner carbon nanofiber skeleton based on dip-coating electrospun CNF film in PAN solution and subsequent thermal cyclization treatment was proposed to improve the electrochemical performance of Li-S battery.The CNF film skeleton with superior conductivity serves as a platform for sulfur reutilization while the conductive cyclized-PAN network processing abundant pyridinic nitrogen groups acts as the polar host to capture polysulfides and confine their dissolution and shuttling.The assembled Li-S batteries with CP@CNF interlayers exhibit enhanced cycle and rate performances.