Study On The Performance Of Chitin Derived Carbon Based Materials For Lithium Sulfur Battery

Faced with increasing energy demand and severe environmental issues,it is urgent to develop a new generation of green and efficient energy storage systems.Although lithium-ion batteries are widely used,their lower energy density and lifespan are insufficient to meet the rapidly changing new energy industry.Therefore,it is necessary to develop a high energy density energy storage system to adapt to development.Lithium sulfur batteries have attracted much attention due to their high theoretical energy density,low cost,and environmentally friendly characteristics.However,due to issues such as poor conductivity of active substances and the shuttle effect of intermediate polysulfides,they have not been officially put into use.The selection of positive electrode materials is the key to solving many problems,among which electrochemical stable carbon materials are the focus of research.Based on the above ideas,this article uses low-cost chitin as a precursor to synthesize host carbon materials suitable for lithium-sulfur battery positive electrodes,and optimizes them into high-performance lithium-sulfur battery positive electrode materials with commercial value by changing their composition and morphology structure.The research content is as follows:（1）Using biological waste chitin as a precursor,dissolve it in potassium hydroxide/urea solution,and obtain porous carbon fiber materials with multiple morphologies through heat treatment as positive electrode materials for lithium-sulfur batteries.The use of biomaterials as precursors allows nitrogen and oxygen elements to enter porous carbon fiber materials through in-situ doping.By alkali activation,a large number of micropores,mesopores,and macropores were distributed.In the preparation of porous carbon fibers with different morphologies,the highest specific surface area is 2105.17 m2g^-1.Formed by combining with sulfur CNHPCF-1（chitin-derived nitrogen-doped hierarchical porous carbon fiber-1）The electrode has good electrochemical performance.When tested at a current density of 0.2 C,the discharge specific capacity reached 1368.80 m Ah g^-1,which is close to the theoretical value.Even in the cyclic test with a load of 6.08mg cm^-2,the capacity of 5.2 m Ah cm^-2can still be maintained after 100 cycles.Analysis shows that a large number of micropores in CNHPCF-1 can limit the shuttle of polysulfides,and the conductive network formed by a reasonable spatial structure accelerates electron transport,improving the conversion efficiency and sulfur utilization efficiency of polysulfides.（2）By adding compounds to the dissolved chitin solution,a porous carbon material WC-WO₃-NPC（nitrogen doped porous carbon loaded with WC-WO₃heterostructure）doped with dual phase heterostructure was prepared as the positive electrode material for lithium-sulfur batteries.The two-phase metal particles doped by this method are evenly distributed and well embedded in the porous carbon,which not only does not limit the porous structure to play a role,but also provides a large number of active sites for catalytic conversion of polysulfides.Under the combined action of biphasic heterostructure and porous network structure,the synthesized WC-WO₃-NPC@S It has excellent electrochemical stability.In the long cycle test with different current densities at0.2 C（200 cycles）and 2 C（200 cycles）,the capacity retention rate after the cycle is over 90%.Through analysis of relevant detection results,it is shown that WC acts as a catalytic particle to accelerate the catalytic conversion of polysulfides during the reaction process of lithium sulfur batteries,while WO₃acts as an adsorption center to effectively limit polysulfides,and the biphasic particles play a significant role in synergy with each other.