Preparation And Invenstigation On The High Performance Ion Exchange Membrane For Vanadium Battery

Conventional fuel is the nonrenewable energy, with the continuous consumption, it will be exhausted finally. Therefore, many countries in the world are focusing on the new energy such as the wind, the tidal, the solar and so on. Due to the shortcoming of the new energies, which can not be operated at all time in all-weather, consequently, the power needs the matched energy storage technology for continuous supply. The vanadium redox battery（VRB） is currently the research focus both at home and abroad due to its attractive features of long-life, reliability, safety and recyclability. Ion exchange membrane, is a key factor restricting the commercialization of VRB. It is crucial to develop the ion exchange membrane with substantial and high-performance feature.Sulfonated poly（ether ether ketone）（SPEEK）, possesses the properties of high conductivity and chemical stability, but it does not suitable for the long operation vanadium battery because of its poor mechanical performance. In order to improve the stability of the SPEEK, at the first part in this thesis, the polytetrafluoroethylene（PTFE） which has the good mechanical properties was used as the substrate to prepare the composite membrane by casting the SPEEK solution onto the surface of the PTFE. The results prove that the performance of the composite film is better than that of the SPEEK film. During the tests of the batteries at high current density, coulomb efficiency, voltage efficiency, and energy efficiency are 96%, 95% and 91% respectively, which are higher than that of the commercial Nafion212 membrane. The Vanadium resistance performance of the composite membrane enhanced significantly, and the self-discharge time reaches to 20000 min.The permeability of VO²⁺ for commercial Nafion membranes is severe and researchs adopt solution casting method to modify it. But the choices of the casting solvent in the research process were different. So in the second part of this work, the effects of different high-boiling solvent and temperature on recast Nafion membrane performances and the effects of different heat treatment temperature on the properties of recast film were studied. In this paper, three kinds of high boiling point including N,N-dimethylformamide（DMF）, N-methylpyrrolidone（NMP）, dimethylsulfoxide（DMSO） solvent as well as heat treatment temperatures 100 °C, 140 °C, 180 °C were chosen. The results showed that the performance of the recast film is the most outstanding prepared in the condition of DMF and 180 °C（DMF-180）. The vanadium permeability of DMF-180 is 2.9 × 10-7 cm2/min, which was the lowest among all the recast membranes. The film showed the 90% of coulomb efficiency which was closed to that of the commercial Nafion212 membrane at 80 m A/ cm2. The proton conductivity decreases slightly with the increase of the heat treatment temperature for the recasting film formed in the same solvent and different temperatures, while the vanadium ionblck abilitu increased. By comparison, the film recasted at heat treatment temperature of 180 °C had the best performance.In the third part of this thesis, in order to reduce the permeability of vanadium and enhance the battery performance, Nafion membrane was researched with different particle sizes and qualities of nano-SiO₂. Three particle sizes of 15 nm, 30 nm, 40 nm and three kinds of qualities of 3 wt.%, 5 wt.%, 10 wt.% were adopted in the expereiment. The results showed that the vanadium of recasted Nafion membrane increased after adding nano-SiO₂, while their conductivity decreased slightly. A slight agglomeration occurred when the amount of SiO₂ increased to 10 wt.%,which has an effect on all performance of the membrane. Recasting film modified with 30 nm and 5 wt.% of SiO₂ particle showed the best performance of 92% coulombic efficiency and 85% energy efficiency at high current densities.Finally, the market analysis of high-performance ion exchange membrane was done and the cost of PTFE/SPEEK（PS） composite film, recast Nafion membrane and Nafion membrane recasted with SiO₂ modified was estimated. It was found that the cost of PS composite membrane is less than that of commercia l Nafion film, recasted membrane makes the Nafion membrane reused and reduce the cost.