Design,Synthesis Of Ferrocene Derivants And Appliacation In Non-aqueous Redox Flow Batteries

Since the new century,facing resource depletion and a series of ecological and environmental problems,people pay more and more attention to the research and application of green new energy.However,renewable new energy sources represented by solar and wind energy are always affected by uncertainties such as weather changes and geographic environment.Therefore,the research of low-cost,stable and efficient,and green renewable energy storage technology is the key to solve the current environmental problems.Compared with other energy storage methods,the redox flow batteries(RFBs)have independent capacity and power control unit,both in its own internal structure design and in the external geographical environment siting have more flexible use.RFBs are usually classified by the type of electrolyte used internally and are divided into two categories:aqueous redox flow batteries(ARFBs)and non-aqueous redox flow batteries(NARFBs).In ARFBs,the open circuit voltage of the battery is limited because of the narrow electrochemical window of water,which also affects the energy density of the battery.Conversely,NARFBs,organic solvents with a broaden electrochemical window are used internally as the electrolyte,so they are also widely considered to be a highly promising form of energy storage.Compared with traditional metal-based electrode active materials,organic molecules have a wide range of sources,low cost,safety and environmental protection,especially organic molecules can be modified to optimize their performance,so organic active materials have become the focus of public attention in the research of positive and negative electrode materials for NARFBs.In previous research of various electrode materials,ferrocene as a positive active material has many advantages such as low cost,stable structure and good reversibility.However,the low redox potential and poor solubility in the electrolyte severely limit the improvement of energy density of NARFBs.Therefore,the modification of ferrocene molecules was studied in terms of open circuit voltage and solubility in order to improve the energy density of batteries in this study.The specific results are as follows:1.In Chapter 3,we compared different electron-withdrawing groups and also analyzed both single and double substituted methods,in order to make up the defect of low ferrocene redox potential.After taking into account the potential and stability,the sulfonic acid group was chosen for the single substituted modification,and the methoxy that is a hydrophobic group was also added.The experimental results showed that compared to ferrocene with a redox potential of less than 0.3 V(vs.Ag/AgCl),the methyl benzenesulfonate(FSE)with sulfonic acid and methoxyl group had a redox potential of up to 0.81 V(vs.Ag/AgCl)and increased solubility from less than 0.1 M to 0.5 M.In addition,theoretical open circuit voltage and energy density were 2.8 V and 38 Wh L-1 in the full cell of cathode of FSE,respectively,when the quinoxaline with methoxy can be used as the negative electrode material.2.In Chapter 4,given the effect of electron-withdrawing groups on material stability,the intramolecular interaction that is a new method can be used to increase the redox potential of ferrocene.The 4,4-diferrocenyl-1-(2-methoxy-ethoxy)-pentane(DFDE)molecule with a two-electron structure was synthesized by joining two ferrocene molecules and adding an ether chain.Electrochemical characterizations suggest that the redox potential of DFDE is 0.12 and 0.08 V higher than ferrocene in the second oxidation step(vs.Ag/AgCl)and the solubility of DFDE are 1.0 and 4.5 M equivalent electron density in acetonitrile(ACN)and 1,2-dimethoxyethane(DME),respectively.The capacity was almost not decay after 150 cycles in half-cell test when DFDE was used as cathode.Then paired with an anode-active material,N-butylphthalimide(BuPh),the symmetric cell exhibits a high theoretical energy density exceeding 55 Wh L-1.3.In Chapter 5,we analyze the problem that the solubility of organic molecules,represented by ferrocene,decreases dramatically after changing from the initial state to the oxidized state.The strategy of preparing organic molecules and alkali metal salts as organic eutectic electrolytes(OEEs)is proposed to solve the problem,and the intrinsic mechanism is explained by combining theoretical simulations and experimental verification.After the OEE was simply prepared by mixed(1-methoxymethyl)ferrocene(Fc-1)and bistrifluoromethanesulfonimide lithium salt(LiTFSI),that the solubility of OEE is more than three times higher than that of a single molecule of Fc-1,at about 2.8 M.Moreover,the high actual discharge energy density of 188 WhL-1 was achieved and the capacity was almost not decay after 150 cycles in the Li hybrid cell when OEE was used as cathode.4.In Chapter 6,we designed and synthesized a different type of binary eutectics than before in order to have a higher concentration of active material and proposed a strategy for solvent-free liquid flow cells.Both ferrocene and amide molecules were first added alkyl chains and then mixed with the alkyl chain-containing ionic liquid tributylmethylammomium bis(trifluoromethanesulfonyl)imide(TBMA-TFSI)to obtain two binary eutectics,DDF/TBMA-TFSI and PHD/TBMA-TFSI,respectively.Because they have lower internal viscosity and weaker intermolecular interactions,their internal TBMA-TFSI molecules have higher ionization degree.Finally,they were used as positive and negative electrolytes respectively,and the battery without adding any solvent was able to charge/discharge stably for 15 cycles,which is the first time to realize solvent-free liquid flow battery in a real sense.