Preparation And Study On The Novel Nafion Composite Membranes For Vanadium Redox Flow Battery Application

All-vanadium redox flow battery (vanadium battery, VRB) has advantages ofrelatively independent power, high efficiency, stability, and so on. It is expected tobe applied in large-scale energy storage and power peaking. Ion-exchangemembrane is an important component of vanadium battery. The most widely usedseparator is Nafion membrane (the U.S. company, DuPont). Despite of the highchemical stability and good electrochemical perfromance, Nafion membrane suffersfrom serious vanadium infiltration and water penetration, which seriously affectsthe efficiency of the battery. Furthermore, the high price of Nafion limits thecommercialization of vanadium battery, so it is important to develop a new kind oflow-cost membrane.Our previous studies show that polytetrafluorethylene/Nafion (PN) compositemembrane is an excellent ion exchange membrane for VRB. To further reduce theconsumption of Nafion resin while still maintaining vanadium barrier properties ofthe PN, a25μm-PN membrane was first prepared. Then PTFE/Nafion/SiO2composite membrane (PNS composite membranes) was preapred through recastingand sol-gel method.The effects of SiO2content on the PNS membreans were studied and theconcentration of SiO2in PNS composite membrane is controlled to be1%,3%,5%,7%and9%. Physical and electrochemical tests show that, compared to PNmembrane, vanadium permeability of the3%-PNS composite membrane preparedby recasting method decreased by27%. At current density of80mA·cm-2, Coulombefficiency increased by6.4%, voltage efficiency decreased slightly, energyefficiency increased by3.6%.7%-PNS composite membrane prepared by sol-gelmethod shows better performance of vanadium-blocking performance compared tothat of the PN membrane. At the current density of80mA·cm-2, the Coulombefficiency increased by9.8%, the voltage efficiency increased by2.3%, and theenergy efficiency increased by11.9%.Non-fluoride ion exchange membrane, sulfonated polyether ether ketone(sPEEK), is one of the most promising candidate membrane for Nafion membrane. To improve the stability of sPEEK membrane, Nafion/sPEEK/Nafion compositemembranes (NSN membranes) were prepared by immersion into Nafion solution.The physical and electrochemical performance tests of NSN membrane showed thatswelling rate was reduced. At the current density of40mA·cm-2, the Coulombefficiency is improved by4%, the energy efficiency is improved by1.6%, and thedischarge time is much longer than that of sPEEK membrane.Finally, this paper analyzes the needs of energy storage market andestimatesthe cost of the vanadium battery. In the end, we estimate the cost of PNS compositemembrane and NSN composite membrane prepared in our laboratory.