Functional Nanomaterials For The Anode Of Renewable Energies

In the process of human social modernization,energy plays an indispensable role.The depletion of traditional fossil energies and air-pollution caused by the burning of fossil fuels,force all the scientific workers to pay an attention to the development and utilization of renewable energies gradually.The technologies of energy conversion and storage play an important part in the utilization of renewable energies,especially for the unsustainable energies.However,restricted by the shortcomings of traditional materials,less exposed active surface and slower diffusion,the performances of energy conversion and storage devices are far from the satisfication of human beings' demands.Functional nanomaterials have incomparable advantages over traditional materials,and can improve the performances of energy conversion and storage devices significantly.In this dissertion,we focus on the synthesis and applications of functional nanomaterials as anodes of dye-sensitized solar cells and rechargeable lithium-ion batteries for renewable energy conversion and storage mainly.Dye-sensitized solar cells(DSSCs)have attracted much attention due to the numerous advantages,such as ease of fabrication,long service life and low cost.In addition,DSSCs can use plastics as the alternative bases to make the cells lighter,and can take advantage of the multicolored dyes to ensure the cells colorful.Therefore,DSSCs are widely regarded to be qualified for the replacement of commercial silicon solar cells in the future market.Functional nanomaterials provide new strategies and methods in promoting the photoelectric conversion efficiency(PCE)of DSSCs,in the same time,we discusse the effects of fuctional nanomaterials on enhancing the light-harvesting efficiency in the anode of DSSCs in this dissertion,the main research contents and results are summed up as follows:We have synthesized the structure of rutile titanium dioxide clusters(RTCs)with hydrothermal method,and applied them as the light scattering layer of DSSCs' anode materials.The RTCs have splendid light scattering properties,and can improve the ultilization efficiency of sunlight effectively.When compared with the commercial P25 anode materials,the RTCs obtain a PCE of 7.68%,increasing by 17%than that of P25 electrodes.The better PCE of RTCs is not only ascribed to their excellent scattering properties,but also to the fast electronic transmission paths offered by their fundamental constitutional unit,single crystal nano-spindles.However,not all the nano-spindles are closely linked,in order to solve this problem,we post-treat the RTCs with organic colloids to generate titanium dioxide nanoparticles between the blank of RTCs,employing the titanium dioxide nanoparticles as the bridge of electronic transmission between the blanks.When adding gold nanoparticles into the organic colloids,both the surface plasmon resonance effect of gold nanoparticles and the scattering effect of rutile titanium dioxide clusters promote the PCE of DSSCs up to 9.15%.Rechargeable lithium-ion batteries have already been commercialized because of a variety of advantages,such as high specific capacity,high voltage,long cycle life,no memory effect,and they have been widely applicated in many fields,such as conventional electronic products,military products,and the electric cars popular on the market at present.In order to meet the challenges of the market on the performance of rechargeable lithium-ion batteries,synthesizing new materials,especially functional nanomaterials with excellent properties,is very important for the long-term development of human society.In this dissertion,two types of functional nanomaterials have been synthesized and used in the anode of rechargeable lithium-ion batteries,the main research contents and results are summed up as follows:We have synthesized titanium dioxide ultra-thin nanosheets(Ti02-NS)with a hydrothermal method,and applied them in the anode of rechargeable lithium-ion batteries.Compared with traditional titanium dioxide nanoparticles(TiO2-NP),on one hand,the TiO2-NS are yield rich and easy to synthesize,on the other hand,they possess a high specific capacity of 220 mAh/g,which is increased by 15%than that of TiO2-NP.The main reason is that the ultra-thin nanosheet structure of TiO2-NS not only enlarges the contact area between the electrode and electrolyte,but also shortens the diffusion path of lithium ion and the transmission path of electron.Notably,the TiO2-NS have super excellent structural stability,the specific capacity can still maintain in the half of the maximum value after being cycled for 1000 times at a variety of current density,while the specific capacity of TiO2-NP almost decreases to 0 after being cycled for 400 times.To verify this conclusion,we post-mortem the cells after being cycles for 1000 times,and the HRTEM characterization results are consistent with the above-mentioned conclusion:although being pressured by lithium ion in the process of insertion and de-intercalation for so many times,the ultra-thin nanosheets structure can still hold its original morphology.As the market demand for power is higher and higher,the silicon anode material with high specific capacity has attracted more and more attention.However,the volume expansion of silicon in the cyclic process is so severe that the cycle performance is disastrous.In order to solve this problem,we wrap silicon nanoparticles into the carbon skeleton structure with an electrospinning method,and then the volume expansion of silicon has been controlled effectively.When applying this composite structure into the anode of rechargeable lithium-ion batteries,after being conducted on the electrochemical tests,the composite structure of silicon nanoparticles and carbon skeleton presents good cycle performance.The main reason is that,on one hand,the porous structure of carbon skeleton is conducive to the penetration of electrolyte;on the other hand,the carbon skeleton structure controls the volume expansion rate of silicon nanoparticles.