Lithium-Ion Battery Performance,Gas And Humidity Sensing Properties Based On Multi-functional Complexes And Oxide Nanostructure

Metal organic frameworks?MOFs?not only exhibit high specific surface area and good pore structure,but also possess a variety of unsaturated metal active sites.So they have great potential in electrochemistry,catalysis,optics,sensors,and ion exchange applications etc.In addition,metal oxide materials have the advantages of multifarious morphology,unique physical and chemical properties,they are supposed to be used in a wider range applications such as lithium-ion battery and sensors.In this dissertation,the mainly contents are as follows:Firstly,based on the ligand thiazolidine 2,4-dicaboxlic acid?H₂L?,single crystal and micro-nano crystal of Co-containing MOFs were synthesized.MOFs micro crystals achieved a high reversible specific capacity of 913 mAh·g^-1 at the current density of 100 mA·g^-1,which was nearly four times higher than that of the CoL-MOFs single crystal.Co L-MOFs micro-nano crystal also showed good rate performance at different current density.Finally,the mechanism of charge and discharge of the Co L-MOFs material was carried out;it was found that the Co²⁺and ligand were all changed under different states of charge and discharge through XRD,FTIR and XPS studies.So we can inference that Li⁺maybe not only react with Co²⁺,but also insert into the organic ligand.The CoL-MOFs single crystal and micro-nano crystal were also applied to the humidity sensor.The humidity response value of CoL-MOFs single crystal material was very low,which almost can be ignored.However,CoL-MOFs micro-nano crystal material revealed a higher response to humidity.At 100 Hz,the impedance change was four magnitudes in the range of 12-97%RH.What's more,it also showed short response and recovery time,good reproducibility and stability.Since the Co L-MOFs crystal was a size and morphology dependent material,which significantly affected the electrochemical and humidity sensing properties.Secondly,the ultrathin SnO₂ nanosheets were synthesized by a hydrothermal method.The SnO₂ nanosheet sensor displayed obvious response to 200 ppm formaldehyde vapor at the optimum operation temperature of 200?,and the corresponding response value was217.3?about eight times higher than that of commercial SnO₂ powders?.In order to further improve the gas sensing performance.0.2%mol Au was loaded on the surface of SnO_2.The studies indicated that the optimum operation temperature decreased to 130?,the response increased to 523.6 for 200 ppm formaldehyde,and the response and recovery time was 50 and52 s,respectively.The enhanced gas-sensing properties were owing to the quantum size effect,exposed active surfaces,and Au decoration,leading to Au-SnO₂ schottky junction and catalysis of the gas reaction.Also,porous ZnO nanosheets were synthesized,which exhibited great rate capacity performance under different current density.The reversible specific capacity was 290.2mAh·g^-1 after 200 laps of charge and discharge cycle under the 100 mA·g^-1current density.Compared with the commercial ZnO powders,the electrochemical performance was significantly improved.The transmission of Li⁺was promoted by the unique porous nanosheet structure.The innovation of this paper is,on the one hand,facile synthesis of the three-dimensional Co L-MOFs micro crystal based on the ligand thiazolidine 2,4-dicaboxlic acid?H₂L?through a precipitation method.As a lithium-ion battery anode material,it showed a high reversible specific capacity.At the same time,it,as the wet materials,also showed excellent moisture sensing performance.On the other hand,ultrathin SnO₂ and porous ZnO nanosheets were synthesized by a hydrothermal method.What's more,Au decorated SnO₂ demonstrated more outstanding gas sensing properties and great selectivity to HCHO.As negative electrode material of lithium-ion battery,the electrochemical performance of porous ZnO nanosheets was much higher than that of commercial ZnO powders.