Preparation And Li-storage Performance Of Hierarchically Porous Carbon Aerogels

Carbon aerogel?CA?is a new nanoporous carbon material with high porosity,high specific surface area,low density and controllable pore size distribution,and has been widely used in chemical industry,environmental treatment,drug sustained delivery and release,electro-adsorption,supercapacitors,fuel cells,catalysts carriers,thermal insulation materials,especially in the field of anode materials for lithium ion batteries.However,the pore structure of carbon aerogel is relatively single,and the proportion of surface active sites is low,which is not conducive to the transportation of lithium ions and not efficient for the reaction of electrodes.Meanwhile,the process of supercritical drying in the preparation process of CA is complex and costly,which greatly limits CAs'application in the cathode materials of lithium ion batteries.Based on the research of carbon aerogels and anode materials for lithium ion batteries,this work focuses on the preparation and Li-storage properties of hierarchically porous carbon aerogels.Carbon aerogels with controllable microstructure were prepared by atmospheric drying and high-temperature carbonization,and the pore forming technology was used to achieve hierarchical porous structure in carbon aerogels.With hierarchically porous carbon aerogels as substrates,the transition metal oxide nanoparticles were loaded to prepare composite materials,and the lithium storage performances were analyzed.The construction of hierarchical porous structure,the loading of transition metal oxide nanoparticles and atmospheric drying technology will build the foundation for carbon aerogels using as anode materials in lithium ion batteries.The research contents and results are as follows:?1?Preparation optimization of carbon aerogels with atmospheric drying method.Carbon aerogels were prepared by organic condensation gelation method combined with atmospheric drying and high temperature carbonization process under different catalytic conditions,with resorcinol and formaldehyde as precursors and water as solvent.In the preparation process catalyzed by sodium carbonate,the porosity and pore size distribution can be controlled by changing the molar ratio of resorcinol/formaldehyde?R/F?and the amount of solvent water.The amount of catalyst?resorcinol/catalyst,R/C molar ratio?affects the gelation time and the strength of gelation skeletons.When the molar ratio of R/F is 1:2,R/C is 500,the precursor mass fraction is 30 wt%and suitable carbonization conditions(heating rate of 1 ^oC·min^-1,carbonization temperature of 900 ^oC and time of 1 h),the as-prepared CA has homogeneous microstructure with high pore volume(0.571 cm³·g^-1)and high BET specific surface area(749.84 m²·g^-1).In the preparation process catalyzed by hydrochloric acid,the prepared carbon aerogels show different pore structure characteristics with micro-macropores,compared with the ones catalyzed by sodium carbonate.?2?Preparation and lithium storage properties of hierarchical porous carbon aerogels.Pore forming process was carried in CA by adding polyethylene oxide?PEO?with different molecular weight in sodium carbonate catalytic and hydrochloric acid catalytic systems.???In the sodium carbonate catalyzed system,the addition of PEG2000 can significantly reduce the apparent density of carbon aerogels and form a three-dimensional continuous skeleton structure.The as-prepared CAs show a higher reversible specific capacity and a slightly reduced cycling stability.???In the hydrochloric acid catalyzed system,the addition of PEG 2000 has a significant regulatory effect on the pore structure of the carbon aerogels.Withe the increase of PEG2000,the pore size of the carbon aerogels gradually expands,some micropores transform into mesoporous to construct micro-meso-macro hierarchically porous structure.The decrease of micropores leads to the reduction of BET special surface area.The specific capacity of resultant carbon aerogels with hierarchical porous structures decrease,while showing high cycling stability.?3?Preparation and lithium storage properties of transition metal oxide nanoparticles loaded carbon aerogel composites.MnO₂/Mn₂O₃@CA and Ni/NiO@CA composite materials were prepared respectively on the basis of hierarchical porous carbon aerogels by means of liquid synthetic method combined with heat treatment,and the lithium storage properties were analyzed.After loading,the framework of carbon aerogels is etched into mesoporous structure of different sizes and the transition metal oxide nanoparticles distribute uniformly in CA.The as-prepared composites show a higher reversible specific capacity and good cycling stability in charge-discharge test at 0.2 C,resulting from the active sites provided by a large number of mesoporous structures and high specific capacity of transition metal oxide nanoparticles.