The Study Of Application And Performance Of Metal Oxide As Additive In Lithium-sulfur Battery

The energy density of lithium-sulfur batteries are as high as 2600 Wh/kg,coupled with the natural abundance,environmental friendliness and low cost of sulfur,causing it as one of the most promising secondary battery systems.However,the commercialization of Li-S battery is greatly hinders by the low utilization rate of sulfur,severe capacity fading during the charge/discharge cycles,low rate performance,and serious self-discharge phenomenon.The mesoporous carbon has good conductivity,high pore volume,and large surface.The metal oxide can adsorb the polysulfide lithium and slow the shuttle effect.Therefore,in this study,the sulfur is combined with the mesoporous carbon;and then Co3O4 or Mg0.6N0.4O is added as additives.The structure and electrochemical properties of the composites were investigated.The main contents are as follows:As a carbon source,sucrose was mixed with nano-silicon dioxide to synthesize mesoporous carbon,which was a porous structure with an average pore size of about 10 nm,coupled with sulfur distributed evenly on the surface and in the pores of mesoporous carbon.Most of the sulfur was distributed in the mesoporous carbon with fine particles,and mesoporous carbon conducts as electron channel.The initial discharge capacity was 1327 mA·h/g at 0.1 C rate,and after 100 cycles,discharge capacity was 400 mA h/g.The capacity retention rate was 30%.The coulombic efficiency approximatively 95%,showing a good capacity stability.The Co3O4-MPC/S composite cathode materials were uniformly mixed by the solution-dipping method.According to the SEM images,Co3O4 and S were round particles,which attached to the skeleton of MPC.Co3O4,S were distributed uniformly in the MPC through by energy dispersive spectrometer(EDS).The initial discharge capacity was 1289 mA·h/g at 0.1 C rate,and after 100 cycles,discharge capacity was 580 mA·h/g.The capacity retention rate was 45%which was higher than those of MPC/S composites.It showed that distributed evenly Co3O4 can be adsorption of intermediate products of polysulffide lithium,inhibit the lithium sulfide dissolved in the electrolyte and migration,thereby reduced the shuttle effect on the battery performance,then suppress sulfur direct aggregation and deposition in the electrode surface;during charg process.As a result the battery capacity and cycle stability were improved.In this study,nanosized Mg0.6Ni0.4O particles were prepared by aself-propagating high temperature synthesis(SHS)method,and then mixed with MPC/S composites by ball milling to obtain Mg0.6Ni0.4O-MPC/S composites.TEM image displayed that Mg0.6Ni0.4O was spherical nanoparticles with a particle size about 40 nm.The initial discharge capacity was 1360 mA-h/g at 0.1 C rate,and discharge capacity was 695 mA-h/g after 100 cycles.The capacity retention rate was 51%,which showed that the addition of Mg0.6Ni0.4O could effectively adsorb sulfur and polysulfide,slow the shuttle effect.Thereby the electrochemical performance of the Li-S batteries,such as cycle stability and coulombic efficiency were improved.