Structural Design And Electrochemical Performance Of Cathode Materials For Lithium-sulfur Battery

The increasing energy demand and serious environmental pollution are two focuses of social concerns,which lead to the hot research of developing green renewable energy and electrochemical energy storage system.Lithium-sulfur battery has been considered as one of the most competitive electrochemical energy storage systems owing to its high theoretical capacity(1675 mAh g^-1)and energy density(2500 kW kg^-1).However,several inherent defects from sulfur cathodes are impeding the further commercialization of lithium-sulfur battery,including the insulation of sulfur and lithium sulfide,the “shuttle effect” caused by easy soluble polysulfide in the electrolyte,the volume expansion of sulfur cathodes during charge-discharge cycling and so on.To address these issues,this paper will improve the charge/discharge stability of sulfur cathode by investigating the structural design of sulfur cathode with carbon host and the modification of separator interlayer.The specific research contents are as follows:?1?The three dimensional reduced graphene oxide aerogel?GA?treated with three different reducing agents of hydrazine hydrate,ascorbic acid and hydroiodic acid was combined with sulfur as the cathode in lithium sulfur battery.The sulfur cathode with the hydroiodic acid-treated GA?I-GS?showed the better electrochemical performance.The initial discharge specific capacity was 1096 mAh g^-1,and the discharge specific capacity was 891 mAh g^-1with a capacity retention rate of 81% after 100 cycles at 0.5 C.?2?The manganese dioxide modified GA was coated on the separator?MG?,and the hydroiodic acid-treated GA and the untreated GA was combined with sulfur as a positive electrode material to assemble the lithium-sulfur battery with a novel structure.The modification of cathode structure?I-GS electrode?and separator?MG modified-separator?can significantly improve the cycle stability of the sulfur positive electrode.The initial discharge specific capacity was 1096 mAh g^-1,and the discharge specific capacity was 891 mAh g^-1with a capacity retention rate of 81% after 100 cycles at 0.5 C.?3?The porous carbon/metal oxide/polymer/sulfur composite was prepared as the cathode in lithium sulfur by using MnO₂ modified GA as the basic conductive framework and flexible polyvinyl alcohol and polyvinylpyrrolidone network as the second layer limiting network.The as-prepared electrode exhibited excellent electrochemical performance.It presented discharge capacities of 1492,1054,833,659 mAh g^-1at 0.1 C,0.2 C,0.5 C and 1 C,respectively.After a few stepwise cycles,the reversible capacity of the MGPP@S electrode could still retain 1036 and 812 mAh g^-1at 0.2 and 0.5 C,respectively.