Preparation Of Metal Oxide/carbon/sulfur Composite And Its Application In Lithium Sulfur Batteries

In recent days,lithium ion batteries can't meet the need with the rapid development of electronic products and electric vehicles.It's urgent to develop a new energy system.Li-S batteries have rapidly grown attentions for next generation electrochemical energy storage system due to it's advantageous to greater theoretical energy density(2600 Wh kg-1),specific capacity(1675 mAh g-1),environmentally-friendly and cost-effective production.But before the commercialization of the batteries,there are many obstacles needed to be overcome,including the poor conductivity of sulfur(5×10-30 S cm-1 at 25?),shuttle effect of polysulfide,damages of lithium dendrites and volume expansion of sulfur(?80%)during charge-discharge process.To resolve those problems,we used polyacrylonitrile as sulfur host.(1)Preparation and electrochemical properties of carbon/sulfur/znic oxide compositesWe prepared carbon/sulfur/metal oxide composite materials to improve the electrochemical performance of the battery.Fristly,N-rich polyacrylonitrile-based mesoporous carbon nanofibers(CPAN)were obtained through electrospining and carbonization process.Then,sulfur was loaded into CPAN to obtain carbon/sulfur nanofibers(C/S).Finally,carbon/sulfur/zinc oxide composites(C/S/ZnO)were prepared by simple ball-milling method.C/S/ZnO composites were applied to lithium sulfur battery.ZnO can produce chemical bonds with polysulfides which can limit the dissolution of polysulfides and improve the utilization of active materials.The initial specific capacity of C/S/ZnO electrode was up to 876.06 mAh g-1 at 0.5 C and the capacity was retained as 740.33 mAh g-1 after 130 cycles,the average decay rate per revolution was as low as 0.06%.At a high ratio of 2 C,the initial specific capacity reached 678.69 mAh g-1,and the capacity remained at 81.64%after 100 cycles.(2)Preparation and electrochemical properties of carbon-magnesium oxide/sulfur@zinc oxide compositesIn addition,we prepared carbon-magnesium oxide@zinc oxide composites(C-MgO@ZnO)with core-shell structure by one-step doping and atomic layer deposition.The N-rich and MgO-doped carbon nanofibers were obtained by adding Mg(Ac)2 into spinning solution,the method simplifies the doping steps and makes the process easier to control.By wrapping the nanofibers with ALD technology,the layer is uniform and with same diameter.Finally,carbon-magnesium oxide/sulfur@zinc oxide composites(C-MgO/S@ZnO)were obtained by hot-melt method.The ZnO nanolayer can not only adsorb polysulfide to improve the capacity of lithium sulfur battery,but also restrict the volume expansion of cathode during charging and discharging process.At 0.5 C,the initial specific capacity of the electrode reached 1066.08 mAh g-1,and the capacity retention was 1004.91 mAh g-1 after 130 cycles,the average decay rate per revolution was only 0.04%.At a high rate of 2 C,the initial capacity reached 846.97 mAh g-1,the capacity remained at 95.98%after 100 cycles.The above results show that the C-MgO/S@ZnO exhibits excellent electrochemical performance in lithium sulfur batteries.