The Application Research Of Coated CNTs With Phosphorus Doping Modification And Carbon Black Modified Functional Interlayer In Lithium Sulfur Batteries

Lithium ion battery,as a reusable energy conversion device,has been rapidly developed in recent years,and widely used in the fields of mobile phone,laptop,electric vehicles and so on.The traditional lithium ion battery can not meet the high energy density requirements for electric vehicles' long mileage and large-scale stationary energy storage equipment due to the low theoretical specific capacity and energy density.Lithium sulfur batteries with elemental sulfur serving as cathode active material,can exhibit a high theoretical capacity of 1675mAh/g and energy density of 2600 Wh/kg.In addition,sulfur is naturally abundant and cheap with low environmental impact.Consequently,lithium sulfur batteries become one of the most attractive candidates for the next generation of high-energy storage system.However,lithium sulfur batteries currently still exist many technical problems to be solved,including that the low conductivity of sulfur and its finally discharge products,polysulfide dissolution in liquid organic electrolyte and volumetric expansion of sulfur during the charge and discharge process.This paper summarized and analyzed the research progress and development of lithium sulfur batteries.To achieve the purpose that suppress the loss of the high solubility of intermediate lithium polysulfide generated during the charge and discharge process,improve the utilization of active materials and electroconductivity of the whole electrode,we modified the conductive carbon matrix and synthetized carbon nanotubes/sulfur composite materials with phosphorus doping modification and ketjen carbon black modified functional interlayer.(1)Carbon nanotubes/sulfur composite materials with phosphorus doping modification.Using commercial low-cost multi-wall carbon nanotubes as the basic matrix,phosphate as phosphorus source,glucose as the carbon coating layer source,we improve the morphology of composite materials by optimizing the experimental conditions.And then carbon nanotubes/sulfur composite materials with phosphorus doping modification were synthetized by thermal method with sulfur.The microspores' volume of the modified carbon tube increases,and phosphorus content in which is 1.61%.,and the composite materials with 68% sulfur show good cycle performance.The modified CPC-8/S and CPC-9/S composite samples reach their maximum discharge capacity of 615.8 mAh/g and 620.1 mAh/g and maintain 338 mAh/g and 349.4 mAh/g after 250 cycles respectively,their capacity decay rate were 0.192%/cycle and 0.189%/cycle,and the coulombic efficiency was close to 100% with better higher-rate performance.(2)Carbon black modified functional interlayer.With the commercialized black conductive agent severing as raw materials,the acid treatments are introduced to generate carboxyl functional groups,the dispersed ECP nanoparticles connect when ethylene glycol works as a bridging agent.finally,modified functional interlayer is prepared with three-dimensional conductive ability.The first discharge specific capacity of ECP-P is 940.3 mAh/g and the highest discharge specific capacity reaches 1535.8 mAh/g at 0.1C with the modified layer;The first discharge specific capacity gets 1240.9 mAh/g with a maximum discharge specific capacity of 1250.7 mAh/g,maitains 1108.7 mAh/g after 194 cycles at 0.5C,the capacity decay rate is 0.056%/cycle;The first discharge specific capacity is 867.6 mAh/g,and 761.4mAh/g after 250 cycles at 1C,and the capacity decay rate is 0.0049%/ cycle.