| The extensive use of tradit ional fossil energy sources has caused t he shortage of resources and serious pollution of the environment. In oreder to resolve these problems, people from all over the world are devoted in developing the high efficient and clean rene wable energy such as solar and wind. However, thoses new energy requires the corresponding energy storage technology. As a new energy storage technology, flow redox cell can not only be used as energy storage devices for power generation systems, but also it can be used as the power grid peak shaving device to improve the quality of output power. All- vanadium redox flow battery(vanadium battery, VRB) is one of the most promising flow redox batteries for large-scale energy storage. As a key component in vanadium battery, ion exchange membrane plays an important role in blocking the vanadium ion osmosis and transfering the hydrogen ions. N afion(Du Pont) is currently the most popular membranes being used in VRB, however, its high cost and serious vanadium permeability blocks the large- scale commercialization of vanadium battery. Consequently, it is necessary to develop new type of ion exchange membrane.Sulfonated poly(ether ether ketone)(SPEEK) ion exchange membrane possesses high conductivity, high temperature resistance and good chemical stability. But the conductivity and mechanical properties of SPEEK are antagonistic. In general, the higher the conductivity is, the worse the mechanical properties are. In oreder to overcome the shortcomings of the SPEEK membranes’ poor mechanical property at high conductivity, the PTFE/SPEEK(PS) composite membranes were prepared with the PTFE(Polytetrafluoroethylene) porous membrane in this paper. The influence of different solvents, the thickness of PTFE and the content of SPEEK on the properties of composite PS membrane were investigated. Results showed that the energy efficiency(EE) of PS composite membrane prepared by different solvents were higher than that of N afion212 membraene. At current density of 40 m A/cm2, the EE of PS composite membrane prepared by 1-Methyl-2-pyrrolidone(N MP), N,N-Dimethylacetamide(DMAC), N,N- Dimethylformamide(DMF) increased by 10.3%, 12.4% and 13.6% compared to that of Nafion212, respectively. Furthermore, the PS composite membrane prepared with the solvent of DMF showed the highest energy effic iency, the stability in the long cycles, and the lowest vanadium permeabiltiy among others. With the thickness increase of the PS membranes prepared with different contents of SPEEK, the PS composite membrane of 40 μm showed the best battery performances. Furthermore, the results showed that the PS composite membrane had the best battery performance when with the PTFE membrane of 20 μm was used.Despite the high cost and serious vanadium ion permeability of Nafion membran-e, it is still widely used in all vanadium redox battery due to its high stability. Therefore, the SPEEK membrane with sulfonation degree of 48% was immersed in Nafion solut ion to prepare the Nafion/SPEEK /Nafion(N SN) composite membrane. The N SN membrane prepared by the solut ion dipping method can not only improve the stability of SPEEK, but also can reduce the consumption of N afion. The chemical stability test showed that the NSN composite membrane was more stable than that of SPEEK membrane. Furthermore, the cell test indicated that the energy efficiency of NSN membrane was higher than that of SPEEK. Self-discharge performance further proved that the vanadium permeability of NSN membrane was better than that of SPEEK.At the last part of the paper, the market survey of vanadium battery and ion-exchange membrane were analyzed. It was estimated that the cost of PS and NSN composite were low and they were promising substitutes for Nafion membrane in VRB application. |
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