Preparation Of Porous Carbon-based Materials By Template Method And Its Application In New Energy Storage Devices

LIBs are widely used in electronic devices,new energy vehicles and large-scale power grids due to their high energy density and environmental friendliness.Meanwhile,SIBs and LSBs are considered as a very promising new battery system that can replace or complement LIBs in specific application scenarios due to their abundant resources,low cost,similar preparation,and assembly processes to LIBs.The electrode material is the most important component to determine the performance of the battery,the traditional LIBs and the SIBs anode materials are graphite and hard carbon,respectively.Bi-based materials have a high theoretical specific capacity and show great potential for LIBs/SIBs,but their reaction process causes large volume expansion,which affects the cycling performance of the battery.Due to its excellent mechanical properties,good electrical conductivity,and chemical stability of porous carbon materials,their use as carriers for Bi-based materials can effectively buffer volume expansion and exhibit specific capacity and cyclic stability that far exceed those of conventional carbon materials.Also,when porous carbon material is used as a carrier for sulfur cathode,it can effectively mitigate the volume expansion and shuttle effect of sulfur and improve the utilization of sulfur,which in turn improves the capacity and cycling performance of LSBs.As a method to effectively control the synthesis of pore structure,the template method opens up a new research field for the preparation of new porous carbon materials and has a wide range of applications in the field of energy storage.In this paper,porous carbon materials are investigated to improve the cycling stability of Bi-based anode materials and sulfur cathode materials.Self-supported thin films and powdered porous carbon materials are prepared by electrospinning and electrostatic spraying techniques using Bi₂S₃ nanorods and PTFE as templates for the pore structure and their effects on the electrochemical performance is investigated for use on of LIBs,SIBs,and LSBs.The main work can be summarized as follows:（1）Bi/Bi₂O₃（m）-CNFs with longitudinal pore structure are successfully synthesized by electrospinning technique and subsequent pre-oxidation high-temperature heat treatment using Bi₂S₃ nanorods as a template.The synthesized Bi/Bi₂O₃（m）-CNFs achieve three functional strategies together to improve the cycling stability of the anode.Its internal longitudinal pore structure can effectively improve the mechanical properties of the electrode material;N and S co-doped carbon materials increase the mechanical properties and electrical conductivity of electrode materials;the Li₂O formed during the discharge of Bi₂O₃ can effectively buffer the volume expansion during the discharge process,which improves the cycling stability of the Bi-based anode material.Electrochemical performance testing reveals that the synthesized Bi/Bi₂O₃（0.2 g）-CNFs possess the best electrochemical lithium storage performance.The Bi/Bi₂O₃（0.2 g）-CNFs composite has a high initial discharge specific capacity of 806 m Ah g^-1 at 0.1 A g^-1 and can be stably cycled for 1000 cycles.（2）Based on the above studies,Bi₂O₃ longitudinal porous carbon nanofiber（Bi₂O₃@C-NFs）sodium storage materials with better cycling performance by changing the heating time,and the synthesis mechanism of Bi₂O₃ is studied.It is found that after increasing the heating time to 4 h at600℃,all the Bi is converted to Bi₂O₃.Some of the Bi₂O₃ nanoparticles diffuse into the carbon nanofibers and are uniformly distributed throughout the fibers.Benefitting from its unique structure and composition,Bi₂O₃@C-NFs self-supporting anode show excellent cycling performance(211 m Ah g^-1 after 2000 cycles at 5 A g^-1).（3）To further improve the specific surface area and buffer volume expansion of electrode materials,porous carbon spheres（PCSs）with higher specific surface area are formed in-situ using PVP as the carbon precursor and PTFE emulsion as the template by electrostatic spraying combining with one-step carbonization,and they are used in the anode of LSBs.The PCSs are synthesized by modulating the solvent percentage under fixed PVP to PTFE mass ratio（PVP:PTFE=1:3）and heating conditions.The results show that pure porous carbon sphere structure can be formed when the solvent ratio reaches 60%.The Co and N co-doped PCSs with uniformly distributes through-body porous structure and high specific surface area of 212 m~2 g^-1 are formed by adding trace amounts of Co（NO₃）₂ and subject to high temperature treatment.Because of its unique porous structure and large specific surface,it can be used as a carrier for monomeric S.Moreover,Co and N elements can also increase the adsorption performance of carbon materials on polysulfides.After compounding with S as the cathode material for LSBs,and it still has a discharge capacity of 650 m Ah g^-1 after 300 cycles at a current density of 1 C.