Preparation And Properties Of Sandwich-type Cathode For Lithium-sulfur Batteries

With a high theoretical specific capacity of 1675 m Ah/g and a theoretical energy density of 2500 Wh/kg,the lithium sulfur battery is a highly promising high energy chemical power system in the next generation of electrochemical energy storage equipment.In addition,sulfur resources are abundant and environmentally friendly,and have great application prospects.However,lithium sulfur batteries are still facing serious practical problems in practical applications: the poor conductivity of sulfur as cathode material for lithium sulfur batteries requires a large amount of conductive agent;the polysulfide produced by intermediate reaction is easily soluble in electrolyte,resulting in the increase of internal resistance of batteries;volume expansion occurs in the process of electrode reaction,which leads to collapse and destruction of cathode material structure,and "shuttle effect" easily occurs,resulting in low utilization rate of active substances and low cycle life.These problems limit the development of the lithium sulfur battery and seriously hinder its application.In view of the above problems in the sulfur electrode,this paper uses magnetron sputtering method to directly sputter carbon particles onto the current collector aluminum foil for loading sulfur,and deposit a carbon film layer on the surface of the aluminum foil evenly and firmly.The vacuum tube furnace vapor-deposits sulfur on the surface of the carbon film layer to uniformly deposit sulfur on the carbon and tightly combines with carbon to prepare a carbon/sulfur composite positive electrode.In order to further improve the cycle stability and electrochemical performance of the lithium sulfur batteries,carbon was magnetron sputtered again on the surface of sulfur on the basis of carbon/sulfur composite cathode materials,so that carbon and sulfur were fully contacted and conductivity was increased.Carbon/sulfur/carbon sandwich lithium sulfur battery cathode plates were prepared.This process eliminates the use of binders and reduces the negative effects of the binder compared to conventional methods of coating the slurry.The cathode sheets of carbon/sulfur structure type and carbon/sulfur/carbon sandwich structure type lithium sulfur battery were prepared,and the cathode composite materials with different sputtering time were prepared.The results show that the carbon/sulfur structure is not conducive to ion transport and electron conduction,and the active material cannot be fully involved in the reaction,resulting in poor utilization of the active material.The first discharge specific capacities of the carbon/sulfur composite materials with sputtering time of 30 min,60 min and 90 min were 738.1 m Ah/g,857.7 m Ah/g and 782.2 m Ah/g.The carbon/sulfur/carbon sandwich composite material can fully integrate carbon and sulfur,and effectively improve the utilization rate of the active material.The first discharge specific capacities of carbon/sulfur/carbon composites with sputtering time of 30 min,60 min and 90 min were 972.6 m Ah/g,1240.8 m Ah/g and 1116.8 m Ah/g respectively,indicating that the sputtering time needs to be controlled properly and suitable sputtering time is beneficial to regulate the recombination between carbon and sulfur and improve the utilization of active materials.Carbon films with different morphologies and densities were prepared on the basis of carbon/sulfur/carbon structure by controlling different magnetron sputtering power.The results show that the first discharge specific capacity of the positive electrode material is 1072.9 m Ah/g at a sputtering power of 80 W,and the first discharge specific capacity of the positive electrode material with a sputtering power of 100 W reaches 1240.8 m Ah/g.When the sputtering power is increased to 120 W,the discharge specific capacity of the positive electrode material began to decrease to 1146.6 m Ah/g.Controlling reasonable sputtering power can adjust the structure and pore size distribution of carbon materials,facilitate the combination of carbon and sulfur,improve the utilization of sulfur,and make composite cathode materials have excellent comprehensive electrochemical performance.