Design And Synthesis Of Nanostructured Carbon And The Application In High-performance Lithium-sulfur Battery

Lithium sulfur battery with high specific energy density has attracted much attention.However,the poor conductivity of active material-sulfur,the shuttle effect caused by the loss of lithium polysulfide during the charging and discharging process,sulfur volume expansion??79%?,etc restrict the practical application of lithium sulfur battery.In this paper,aiming at how to disperse high load sulfur,alleviate the strain caused by the volume expansion of sulfur,and inhibit the loss of lithium polysulfide,an internal modification strategy to hollow carbon spheres is proposed to efficiently disperse sulfur or Li₂S,and confine the lithium polysulfide.Furthermore,the modified hollow carbon spheres are transferred into the three-dimensional carbon fiber free-standing membrane as high area density sulfur-loaded framework for Li-S battery cathode achieve high capacity,good rate performance and excellent cycle stability.The research contents are listed as follows:?1?The yolk-shell CNF@CS nanospheres were fabricated using spiny silica spheres as templates,and glucose and resorcinol/formaldehyde as carbon precursors.Exploring the influence of inner core structure and cavity size on lithium storage and the mechanism of synergistically confining polysulfides.The CNF@CS electrode loading80%sulfur exhibits high discharge capacity of 1201 m Ah g^-1at a low rate of 0.2C,and 584 m Ah g^-1and 502 m Ah g^-1even at high rates of 8C and10C,resperctively.The capacity was retented to 474.8 m Ah g^-1after 800cycles with a capacity decay of 0.05%per cycle.?2?The unique core carbon nanoflower was transferred into carbon fiber by electrospinning technology to form a three-dimensional carbon nanoflower@carbon fiber?CNF@CF?free-standing membrane,which was used as sulfur host for Li-S battery cathode.The relationship between key factors such as the structure of CNF@CF,the area density of sulfur loading,the amount of electrolyte,etc.and the performance of the battery or the effect of polysulfides confining were studied.The synergistic mechanism on physical-chemical multiple inhibiting polysulfides stemmed from cavity,carbon core and shell was revealed.As a result,the CNF@CF free-standing membrane electrode with a sulfur area density of1.5 mg cm^-2exhibits a high discharge capacity of 1245 m Ah g^-1at a current density of 0.2 C,and good cycle stability.When the area density of sulfur is enhanced to 13.4mg cm^-2,a capacity of 11.24 m Ah cm^-2was achieved,and maintained to 8.46 m Ah cm^-2after 100 cycles.