Design And Performance Of Ion Exchange Membranes For Vanadium Redox Flow Battery Based On Sulfonated Polyethersulfone

Vanadium redox flow battery(VRFB)is a typical large-scale energy storage electrochemical device,which attracts growing attention because of its safety and flexible design.Ion exchange membrane,as an essential part of the flow battery,has a significant impact on the performance and cost of the battery.Considering the high price and high vanadium permeability of the perfluorosulfonic acid membrane,which is widely used in the VRFB,the development of high-performance and low-cost ion exchange membrane is of great significance for the popularization of all vanadium redox flow battery.Sulfonated polyethersulfone(SPES)is a good choice as a nonfluoropolymer material for ion exchange membrane because of its high chemical stability and low price.In order to further improve the chemical stability of ion exchange membrane and reduce the cost of resin material,sulfonated polyether sulfone with low sulfonation degree is used as the basic material of ion exchange membrane.Based on the effective construction of unique ion-conducting channels,the problem of insufficient proton conductivity of sulfonation degree SPES is solved,and three different SPES ion exchange membranes with high battery performance are successfully prepared:(1)Using polyethylene glycol(PEG)as template and 20% sulfonated SPES as base polymer material,microporous ion exchange membranes(SPES(PEG)are prepared via the template method.Benefiting from the unique property of PEG,abundant ion transportation channels are constructed in the polymer matrix,providing high proton conductivity and good H/V ion selectivity.(2)Using ionic liquid(IL)as a novel pore forming agent and 20% sulfonated SPES as base polymer material,microporous ion exchange membrane(SPES(IL))with asymmetric porous structure is successfully prepared.The dense layer effectively reduces the vanadium ion penetration,and the porous layer significantly improves the proton conductivity of SPEs membrane,which can increase the conductivity of SPES-SD20 by more than one magnitude.The asymmetric porous SPES ion exchange membrane has extremely low vanadium permeability and good proton conductivity.(3)For the first time,SPES ion exchange membrane with 5% sulfonation degree(SPES-SD5)was prepared by a novel method named controlled swelling method.By the controlled swelling method,a large number of ion-transport channels can be constructed even in nonionic polymer,and high proton conductivity can be obtained.By controlling the parameters,the size of the ion transport channel can be precisely controlled at the molecular scale,thus obtaining high H/V ion selectivity.Due to its very low sulfonation degree,SPES-SD5 shows improved chemical stability than SPES-SD20,which makes it more promising for the application in redox flow battery.