| There is a growing demand for energy with the development of economy,but the usage of the clear energy source such as solar,wind,tides and geothermal has been limited by the intermittent and geographical environment,thus,the energy should be stored,electrochemical energy storage has the advantages of economical,simple and efficient compared with other energy storage methods.Compared with the conventional metal-based electrode active material,organic active materials have become a research hotspot in recent years due to their wide range,low cost,safety,environmental friendly and regulable electrochemical properties.However,facing with such a large number of-organic molecular systems,how to design and screen the target molecules with excellent electrocheirucal properties economically and efficiently has become the key problem.The first principles calculation based on the density functional theory has the advantages of batch and efficient calculation of redox potential and other electrochemical properties,and the theoretical calculation results can be well coiisisteiit with the experimental results,so it has becone the preferred way to guide the design of molecular structure and predict molecular electrochemical properties.In this paper,the eleetrochemical properties of five kinds of nolecular systens have been calculated.The stability,redox potential,solubility and other electrochemical properties of quinone compounds,phenazine compounds(NSPZ),deep eutectic solvents(NMePh-LiTFSI?[ZnCl(acetamide)3]+),bipolar molecule(Fc-bipy+3)and metal organic complexes([Fe(bpy)3]2+)were introduced.The specific work includes the following five parts:1?In chapter two,various quinone derivatives have been investigated to determine the suitability for the application in organic RFBs.Moreover,the redox potential can be intermally regulated through the tuning of contribution from the ? and ? bonding contribution in the redox-active site.Furthennore,the binding geometry of some selected quinone derivatives with metal cations has been studied.Chemical bond composition analysis shows that the contribution from ?/? bond and oan coupling efficient detennines the redox potential of quinone derivatives.The contribution from? bond is more significant than that from the ? bond.DOS analysis further suggests that high redox potential can be realized in quinoneslvith small ?-?*and ?-?*energy gap,or with higher contribution ratio of a bonds in the top of VB.or in those with a bond in the top of VB not be crossed by ? bond.The binding energy calculation reveals that the Li+-ions prefer to bind with O atom of carbonyl groups?These studies provide an alternative strategy to identify and design of new quinone molecules with proper redox potential for electrical energy storage in organic RFBs.2?In chapter three and four,the work starts from the initial simplest configuration(NSPZ)of reduced phenazine and then the redox potential,stability and other electrochemical properties of various NSPZ derivatives after the modification of functional groups was calculated.By comprehensive comparison,the structure(DPPZ)with phenyl-containing functional groups replacing NSPZ showed the optimal electrochemical properties.Then,based on the stable DPPZ molecule,we calculated its redox reaction mechanism and selected the optimal electrolyte composition(LiTFSI).In tenns of application,we calculated the properties of oligomers and lithium salts respectively,the mechanism of poor solubility of oligomer or even insolubility of PZDB-Li2 salt was investigated.This work systematicly integrates the theoretical calculation methods of electrochemical properties in organic electrochemical energy storage area.From the structural optimization to the practical application,the theoretical calculation is in good agreement with the experimental test results,which saves the experimental time and cost,and provides a reference for the subsequent theoretical calculation of electrochemical properties of organic molecules.3?In chapter live,as an electrode active material,NMePh exhibit low redox potential and can form a deep eutectic solvents(DES)after mixed with LiTFSI.Theoretical calculation verified the mechanism of the DES is the coordination interaction between the oxygen atoms of carbonyl and lithium ions,which weakens the strong ionic bond between Li+ and TFSI-.The working principles of improving the stability,reducing the viscosity and enhancing the reversibility of the redox reaction through adding ureas were studied,the calculation result shows that the addition of urea can form stable Li+-O tetra-coordinated geometry,which decreased the mean interaction energy of systems and weakened the strong interaction between Li+ and redox active center O atoms.in addition,the optimal ratio of 2:1:3 was selected for the experiment.Finally,the stability of the geometric structure of NMePh molecules was verified by searching the reaction path.Furthermore,the formation mechanism,viscosity regulation through decrease the hydrogen bond interaction and redox reaction of zinc-based deep eutectic solvents were calculated.The calculation results can be well consistent with the experimental results and provides theoretical guidance for the experimental work.4?In chapter six,from the view of molecular design,bipolar molecular(Fc-bipy3+)has been designed and synthesized through combined the ferrocene and pyridine cation by alkyl chain which exhibit higher and lower redox potential,respectively.The theoretical calculation shows that the Fc-bipy3+ ean keep structure stability during the process of charging and discharging.With the modification of water-soluble quaternary ammonium salt,Fc-bipy3+ exhibit improved solubility and the solubility become better with the increase ot the charges,When the bipolar active molecules were applied for the redox flow battery,Fe-bipy3+ can exist in the sodium chloride solution stably.After 4000 cycles of charging and discharging,the capacity of the battery could remain 75%.The cycle performance of the battery in this work can be compared with the traditional redox flow battery.5?In chapter seven,from the view of molecular structure design,netal complexes can be formed through combined the transition metal iron ion and two organic ligands(bpy,phen).After theoretical calculation,the redox active center of[Fe(bpy)3]3+ and[Fe(phen)3]3+ focus on the metal iron ion,and metal iron ions exhibit low spin configuration(t2g6/5),the six coordination of iron ionc can protect the active center from side reaction with electrolyte.The calculation of the solvation free energy indicates that the solubility of+3 is greater than that of+2,which indicates that no precipitation will occur during the redox reaction. |
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