| As a large scale energy storage system,VRFB has the advantages of large energy storagecapacity,high energy efficiency and easy location.Ion exchange membrane is an important component of VRFB.It's properties directly affects the energy efficiency and cycle life of VRFB.At present,sulfonated aromatic polymer ion-exchange membranes have attracted extensive attention due to their low cost.However,the direct introduction of sulfonic groups to the main chain of polymers has prevented the membrane from forming a hydrophilic /hydrophobic microphase separation structure,and the proton conductivity of the membrane was low,which would affect the performance of the VRFB.In this paper,the sulfonic group was introduced into the side chain far away from the main chain of polyphenylene ether,and the sulfonated long side chain polyphenylene ether membrane was prepared,and its basic performance and battery performance were improved.In this thesis,S-L-PPOs with different sulfonation degrees were prepared by using PPO as the main chain.The hydrophilic / hydrophobic microphase separation of the membrane was improved because the hydrophilic sulfonic group was introduced into the side chain far from the main chain of the polyphenylene ether.The effects of different sulfonation degrees on the basic properties of the membrane and the performance of the battery were studied.When the sulfonation degree of the membrane is 51%,the vanadium ion permeability of S-L-PPO-51%membrane is 4.3 × 10-9cm2s-1lower than that of commercial Nafion 212 membrane(210 ×10-9 cm2 s-1).The results show that the energy efficiency of S-L-PPO-51% membrane is81.85% higher than that of commercial Nafion 212?78%?at 120 m A cm-2.However,with the increase of sulfonation degree,the water absorption of S-L-PPO membrane increases,the vanadium ion permeates the membrane more easily.In the chemical stability test of 0.1 M VO2+,the weight loss of the membrane was up to 13.9% after the test.The vanadium resistance and chemical stability of the S-L-PPO membrane with high sulfonation degree need to be further improved.The S-L-PPO / SiO2 hybrid membrane with various content of SiO2 was prepared by doping SiO2 nanoparticles as inorganic particles into S-L-PPO with sulfonation degree of 56%.The filling of SiO2 reduces the pore size of the membrane and inhibits the permeation of vanadium ions with larger particle size.The results show that the vanadium ion permeation rate of S-L-PPO / SiO2 hybrid membranes are lower than that of Nafion 212 membrane andunmodified S-L-PPO membrane?S-L-PPO / SiO2-0%?.When the current density is 120 m A cm-2,the EE of S-L-PPO / SiO2-2% membrane is 81.82% higher than that of Nafion 212.The weight loss of S-L-PPO / SiO2-2% hybrid membrane was 6.3% higher than that of S-L-PPO /SiO2-0% membrane after the chemical stability test.In order to further improve the vanadium resistance and chemical stability of S-L-PPO membranes with high sulfonation degree,the S-L-PPO / PBI blend membranes with different blending ratios were prepared by blending poly?benzimidazolium?with 56% S-L-PPO in this chapter.The addition of PBI in acidic condition resulted in the formation of positive charge and ion crosslinking network structure in the membrane,which prevented vanadium permeation more effectively through the repulsive effect of Donnan.The results show that the vanadium ion permeability of S-L-PPO / PBI membranes are lower than that of S-L-PPO /PBI-0%.The coulombic efficiency and the chemical stability of the blend membrane were improved to a great extent.When the current density is 120 m A cm-2,the energy efficiency of S-L-PPO / PBI-10% membrane?82.73% vs 78%?and the coulombic efficiency?97.6% vs89.82%?of S-L-PPO / PBI-10% membrane are higher than that of commercial Nafion 212.After the chemical stability test,the weight loss of the S-L-PPO / PBI-10% membrane was4.51% and the self-discharge time of the battery was 142 h,which was much higher than that of the Nafion 212?23 h?. |
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