Synthesis Of Carbon Nanofiber By Electrospinning For Lithium-sulfur Batteries

With the time passing,great progress in the economy and the living styles makes the demand for energy rises sharply.Nowadays,clean energy has been vigorously developed because of the loss of fossil energy and the emergency of environmental protection.Thanks to high theoretical energy density(2600 Wh kg-1),which is five times of the traditional lithium-ion battery,rechargeable lithium sulfur battery is considered to be one of the most promising clean energy sources.Howe'ver,the drawbacks of lithium sulfur batteries such as insulating sulfur are limited for their application.The addition of conductive additive,such as carbon black,in insulating sulfur and dissolution of polysulfides intermediates cause irreversible loss of capacity.Herein,in order to improve the electrochemical performance,new types of cathode for lithium sulfur batteries are designed and developed.The main contents of the thesis are listed as below:1.The carbon nanofibers of PAN-CNT-GO have been prepared by electrostatic spinning technique.As for the cathode materials of lithium sulfur battery,the electrochemical properties were tested.As a result,the specific capacity was 240 mAh g-1 at 2 C after 200 cycles,which is 65.1%of initial capacity.The sample shows the good cycle stability.2.The carbon nanofibers of PAN-CNT and PAN-PVP have been prepared by electrostatic spinning technique.The morphology characterization showed that the carbon nanofibers became curved with the addition of CNT,and the surface roughness of the fibers was increased with the addition of PVP.The samples were used as the interlayer of lithium sulfur battery,while CMK-3 was used as cathode material.The initial capacity can reach to 1197 mAh g-1 at 2 C.Interestingly,the capacity can still maintain at 804 mAh g-1 after 100 cycles.As for the continuous charge and discharge test at different rates of 0.1 C,0.2 C,0.5 C,1 C,2 C and 5 C,the capacities are 1077 mAh g-1,889 mAh g-1,767 mAh g-1,694 mAh g-1,607 mAh g-1 and 423 mAh g-1 respectively.When the rate changes back to 0.1 C,the capacity can get back to 907 mAh g-1,indicating that the interlayer of PAN-PVP can significantly improve the stability of the batteries.3.a-MnO2 nanowires were synthesized by hydrothermal method and the one-dimensional linear structure was confirmed by morphological characterization.The electrochemical test results of ?-BMnO2 nanowires as the cathode show that the initial capacity is 797 mAh g-1 at 0.1 C,and the capacity can still get to 591 mAh g-1 after 25 cycles.