Preparation And Electrochemical Properties Of Biomass Carbon Derived Sulfur Composite Cathode

The continuous development of electronic devices and electric vehicles places higher and higher demands on the performance of batteries.Lithium-sulfur batteries have received widespread attention due to their high energy density(about 2600 Wh kg^-1)and low cost.However,the electronic insulation properties of active material sulfur and discharge products Li₂S₂/Li₂S,as well as the dissolution and shuttle effect of lithium polysulfides,limit the large-scale application of lithium-sulfur batteries.In recent years,the composite of sulfur with porous carbon materials can significantly improve the cathode conductivity and suppress the shuttle effect.However,the non-polarity of pure carbon materials will rapidly decay in capacity after several cycles of the battery.If external heteroatoms are introduced,the preparation cost is often high,and the process is complicated and energy-intensive,which is not conducive to the development of the commercialization of lithium-sulfur batteries.In response to the above problems,this paper successfully prepared porous carbon materials with abundant heteroatoms and pore structures by carbonizing two kinds of plant materials that can be found everywhere in nature,serving as a sulfur-carrying framework to inhibit the dissolution and shuttling of lithium polysulfides and improve the utilization of active materials.rate and enhance battery performance.Specifically,the following research work has been carried out:（1）Using catkin-derived porous carbon as a conductive substrate,nickel phosphide（Ni₂P）was grown on the surface to serve as a sulfur-carrying framework.The hollow nanofibrous structure of biomass carbon can sterically confine the dissolution of lithium polysulfide,can provide abundant ion/electron paths to accelerate the reaction kinetics,and effectively buffer the volume expansion of the sulfur electrode during cycling.The supported Ni₂P can increase the thiophilic properties of the sulfur-supported framework and enhance the electrode reaction kinetics.Therefore,the initial discharge capacity of the battery can reach 1198 m Ah g^-1 at 0.1 C,763 m Ah g^-1 at 1 C,and the specific capacity still shows 586 m Ah g^-1after 800 cycles,and the capacity retention rate reaches 76.04%.（2）Using lignocellulose as biomass precursor to prepare nitrogen-rich porous carbon materials as sulfur hosts to stabilize sulfur electrodes.The abundant pore structure and uniform heteroatomic distribution of porous materials not only physically limit the diffusion of lithium polysulfides,but also increase the chemical interaction of the two,further suppressing the shuttle effect.Therefore,the discharge specific capacity of this cell is as high as 666.4 m Ah g^-1 at 1 C.After 100 cycles,the capacity retention rate is as high as 85.33%.