Preparation And Modification Of Porous Carbon/Sulfur Composites And Its Application In Lithium Sulfur Battery

Compared with traditional lithium ion batteries,lithium sulfur batteries have higher energy density and specific capacity,which fit the trends of people demands in future.The energy density of lithium sulfur battery is about 2600 kg-1 Wh in theory,and the theoretical specific capacity can reach 1673 m Ah g-1,which is higher than traditional lithium ion batteries.In addition,sulfur has the advantages of low cost,non-toxic,and no polluting.Because of the great advantages in various aspects,lithium sulfur batteries has become a promising energy storage material.Nevertheless,the insulating property and shuttle effect cause the poor cycle performance,which limited the commercial application of lithium sulfur battery.In this paper,we designed and prepared the phosphorus doped porous carbon / sulfur composite cathode material to improve the electrochemical performance of lithium sulfur battery.The main research contents and results are as follows:(1)Phosphorus-doped porous carbon was prepared through the method of high temperature carbonization with luffa fiber as carbon source and phosphoric acid as activating agent.The Phosphorus doped porous carbon has high specific capacity of 2230.033 m2 g-1 and large pore volume of 2.686 cm3 g-1.Phosphorus doped porous carbon / sulfur composite has great electrochemical properties with 60 wt% sulfur content.The first cycle discharging specific capacity could reach 1357 m Ah g-1 at 0.2 C rate and 1036 m Ah g-1 at 1 C rate.After 100 cycles the specific capacity still kept 852 m Ah g-1 at 0.2 C and 782 m Ah g-1 at 1 C.(2)Phosphorus-doped porous carbon was coated with PPy through the method of chemical oxidative polymerization.The phosphorus-doped porous carbon / sulfur composite coated with PPy,which was used as the cathode materials of lithium sulfur battery,has great electrochemical performance.The reversible specific capacity of lithium sulfur battery was more than 90 % of the initial specific capacity at 0.2 C and 0.5 C rates.The results show that phosphorus doping is helpful to improve the specific capacity,and the coating of PPy can improve the cycle performance of lithium sulfur battery.The lithium sulfur battery prepared with luffa fiber has such a good electrochemical performance that may promote the commercialization of lithium sulfur batteries.