Research And Application Of High Specific Surface Area Carbon Materials In Lithium-sulfur Batteries

Rapid development of emerging fields such as electric vehicles and drones calls for ever-higher demands for lithium-ion battery performance.Lithium-sulfur battery is considered to be one of the most promising candidates among all new-generation energy storage systems due to its excellent theoretical specific capacity and energy density.However,scale-up application of Li-S battery is inhibited by serious issues including the insulation of elemental sulfur,low utilization rate of sulfur,shuttle effect during the charging and discharging processes and volume expansion.With the aim of overcoming aforementioned obstacles,starting from the design of sulfur-based cathode materials,we combine the outstanding catalytic activity of transition metals with the electrical conductivity of carbon support and successfully synthesized atomic-level dispersed transition metal carbon-based composite materials that have cost advantages and can be prepared on a large scale.Main research work is as follows:Co-N-C@KB,atomic cobalt-dispersed transition metal carbon-based composite material,was synthesized through a ligand-mediated approach.The material was composed of Ketjen Black(KB)that is rich in Co-N-C active sites and thus,Co-N-C@KB can be used for the elevation of battery performance.With Ketjen Black acting as a carbon support,a complex was prepared from oil bathing of transition metals with 2-2'-bipyridine material as an intermediate ligand,and then,Co-N-C@KB was obtained after the carbonization.The material combines the excellent electrical conductivity,high specific surface area of KB and ultra-high activity of Co-N-C loci,which is conducive to the fixation of elemental sulfur and the conversion of polysulfides,and thus improving the capacity and cycling performance of lithium-sulfur batteries.On the basis of this,Co-N-C@KB can be employed as cathode in Li-S battery to obtain an initial discharge capacity as high as 1442 m Ah g^-1,and the capacity retention rate after 300 cycles at 0.2 C rate was above 70%.We continue to explore a variety of transition metal(Fe,Ni,Co-Fe)systems on the basis of single metals.Corresponding atomic-level dispersed transition metal carbon-based composite materials were synthesized,and their physicochemical characterization and electrochemistry performance was tested.The result shows that Co-Fe-N-C@KB composite material exhibited a synergistic effect between Fe and Co metals,which can further optimize the rate performance and cycling performance of the battery,and the capacity retention rate reached 78%at a rate of 0.2 C.At the same time,this article also explores the preparation process of the soft packing battery.By large-scale preparation of transition metal carbon materials to replace commercial carbon materials,the performance of the battery has been greatly improved,and the discharge specific capacity attained 1042 m Ah g^-1.Therefore,carbon-based composite materials based on transition metals have great potential in the application of lithium-sulfur batteries.