Preparation Of Hierarchical Structure Materials And Applications In Energy Storage Devices

The hierarchical structural materials consisted of low-dimensional materials have become a hot topic in the field of nanotechnology.They possess large surface area and high porosity.The hierarchical structure can reduce the agglomeration of the active material and make it expose more active sites.In addition,this structure can not only maintain the high theoretical capacity of lithium/sodium storage of the active material itself,but also alleviate its volume expansion during charging and discharging process.At present,the hierarchical structural nanomaterials have been widely developed and applied in lithium/sodium ion batteries,lithium sulfur batteries,supercapacitors and other energy storage devices.In this thesis,the hierarchical structural materials have been synthesized by spray drying,hydrothermal method,freeze-drying method and they have been applied in energy storage devices,obtaining excellent electrochemical performance.The main research contents are as follows:?1?A hierarchical 3D honeycomb-like rGO anchored with SnS₂ quantum dot?3D SnS₂ QDs/rGO?was prepared via spray-drying and sulfuration.SnS₂ QDs were uniformly distributed into rGO layers.The 3D honeycomb-like rGO structure can enhance the conductivity,restrain the aggregation and buffer the volume expansion of SnS₂ QDs.As a result,the 3D SnS₂ QDs/rGO composite electrode possesses a high capacity and long cycling stability?862 mAh/g for LIBs at 0.1 A/g after 200 cycles,233 mAh/g for SIBs at0.5 A/g after 200 cycles?.?2?GO nanosheets,PS nanospheres?act as sacrificed template?,Iron?III?chloride hexahydrate and sodium hypophosphite were used to prepare the hierarchical 3D porous rGO anchored with FeP particle composite?3D FeP/rGO?via spray-drying and phosphorization.Then the 3D FeP/rGO was mixed with sulfur to get the 3D FeP/rGO-S?FPGS?composite.Subsequently,a modified separator was synthesized by vacuum filtration the 3D FeP/rGO composite on commercial separator,which act as an interlayer applied in LSBs.The FeP particle act as a catalyst to accelerate polysulfide conversion in the LSBs redox reactions.The 3D FeP/rGO modified separator?FPGI?can serve as physical barrier to suppress the migration of polysulfide.The rGO structure can enhance the conductivity of the electrode material.As a result,the cell with FPGS-FPGI delivers a high reversible capacity 925 mAh/g after 500 cycles at a current density of 0.5 C.?3?The carbon spheres,prepared by hydrothermal method,were mixed with Tin chloride pentahydrate by surface-layer-adsorption.Then,the sample was preprocessed and coated with a certain thickness of TiO₂.Subquently,the hierarchical Sn/C@TiO₂/TiN composite was obtained by annealing the above sample in NH₃ atmosphere under certain nitridation time.The double conductivity of carbon spheres and TiN could improve the electrical conductivity of the materials.Carbon layer and TiN layer could be used as dual limiting layer to confine the volume change of Sn particles during Na⁺insertion/extraction processes.The electrochemical test results showed that the electrode material possessed a rapid redox reaction kinetics and it could deliver a capacity of 232 mAh/g at 0.5 A/g after200 cycles.