Preparation And Property Research Of The Composite Cathode Materials For Lithium-sulfur Battery

With the rapid development in the fields of advanced portable devices, electric vehicles, hybrid vehicles and smart grids and so on, rechargeable batteries with long life and high energy density have been in great demand. Sulfur is a promising cathode material, which has a theoretical specific capacity of about 1675 mAh g-1 and a theoretical specific energy of 2600 Wh kg-1. In addition, sulfur is of natural abundance, low cost and environmental friendliness. Both these advantages make lithium-sulfur batteries promising candidates as the next generation power sources. However, there still are a number of complex problems that need to be solved for the commercialization of lithium-sulfur batteries, including low Coulombic efficiency, low sulfur utilization and rapid capacity loss during repeated cycling. These problems are caused by the low electronic conductivity of sulfur and its discharge products, and the diffusion, shuttling effect, and side reactions of soluble poly sulfides produced during electrode reactions.In order to address these problems, we design and synthesize a novel porous carbon substrate by carrying out a very simple method. Sodium alginate is used as carbon source and annealed under argon atmosphere to obtain the hierarchically porous carbon (HPC). Then the sulfur powder is mixed with the as-prepared HPC and heated under argon protection before cooled to the room temperature, yielding the composite S/HPC. The sulfur cathode displays good electrochemical features. By employing a potentiostatic process at the end of charge, the reversibility of electrode reaction of sulfur is further improved. It shows admirable cycling and rate performances by delivering reversible capacities of 849.4 mAh g-1,673.4 mAh g"1 and 538 mAh g"1 after 50 cycles at 0.1 C,100 cycles at 0.5 C and 200 cycles at 1 C, respectively.Furthermore, we proposed to improve the performance of the sulfur cathode by introducing a built-in carbon nanotubes network inside a biomass-derived hierarchically porous carbon. The balanced structural design of the carbon substrate enables effective trapping of active sulfur within the cathode, while also provides a highly-efficient and robust pathway for electron transmission, contributing to an increased conductivity and structural integrity of the cathode. Further, by employing a potentiostatic process at the end of charge, the reversibility of electrode reaction of sulfur is improved, leading to optimized electrochemical performances. The sulfur cathode benefiting from our strategy delivers an initial discharge capacity of 1739 mAh g-1 and reaches a high initial Columbic efficiency of 87.6%, and maintains its efficiency to> 97.5% from the 2nd cycle. It also shows admirable cycling and rate performance by delivering reversible capacities of 1015 mAh g-1 and 622 mAh g-1 after 50 cycles at 0.1 C and 200 cycles at 1 C, respectively.