Preparation Of Nanomaterials Based On Polymer-derived Ceramic Approach And Research On Electromagnetic Wave Absorption/Lithium-ion Storage Performance

Polymer-derived ceramic approach(PDC approach)utilizes the excellent processing and molding properties of organic polymer precursors to prepare ceramics and carbon materials through the steps of processing,crosslinking,and pyrolysis.However,in the process of organic-inorganic conversion,precursor nanoparticles involve complex pyrolysis reactions.In addition,due to the large surface area and the large number of non-bonding electrons on the surface of nanoparticles,the activity of nanoparticles is high,and the interaction between particles is easy to occur in the pyrolysis process,resulting in the formation of bulk ceramics.So,there are few reports on the preparation of core-shell nanoparticles by PDC approach.In this paper,pitch was used as isolating agent and Co-containing polycarbosilane sol particles were used as raw materials.Carbon coated Co-containing ceramic nanoparticles were prepared by cross-linking and pyrolysis of PDC approach.Co-containing ceramic nanoparticles with porous core-shell structure can be obtained by removing carbon,and hollow porous carbon materials can be prepared by etching silicide.The results are as follows:Carbon coated Co-containing ceramic nanoparticles were decarbonized by air at 500℃ to prepare Co-containing ceramic nanoparticles with porous core-shell structure.The in-situ formation of mesopores on the shell,microstructural and phase evolution of resulting nanoparticles were investigated by means of XRD,TEM,XPS,Raman spectroscopy and BET method.The excellent electromagnetic wave absorption properties of ceramic nanoparticles can be attributed to the unique core-shell structure,complex phase composition in the shell and in-situ formed mesopores.By adjusting the decarbonization time,the obtained nanoparticles-paraffin composites possess properties as follows:In the X-band(8.2-12.4 GHz),the minimum reflection coefficient(RCmin)reaches-60.9 dB and the widest effective absorption bandwidth(EAB)is 3.50 GHz.By adjusting the matching thickness,the EAB amounts 15.5 GHz(from 2.5 to 18 GHz).Carbon coated Co-containing ceramic nanoparticles were etched in HF solution to remove the silicide in the materials,and pitch-derived carbon with hollow porous structure was obtained.By adjusting the pyrolysis temperature,the microstructure evolution of pitch-derived carbon was explored,and its electrochemical performance as anode material for lithium-ion battery was studied.The result showed that the maximum specific surface area(210.06 m2/g)was obtained at 1200℃.The design of hollow porous structure is beneficial to improve the lithium-ion and electron transport performance,and improve the cycle stability of the battery.When the pyrolysis temperature is 1200 ℃,the synthesized pitch-derived carbon maintains a reversible discharge capacity of 559.0 mAh/g after 450 cycles at a current density of 1C,and the coulombic efficiency per cycle is>99.2%,showing excellent lithium-ion storage performance.