| All-Vanadium Flow Battery?VFB?,a new kind of large scale energy storage system,which has the advantage of quick response,high efficiency,flexible scale design,long life and high security,can be applied to power grid peak clipping filling valley,emergency power and other fields.The ion exchange membrane is one of the core components of the VFB.Nafion?membranes are frequently used in VFBs,however,which suffers extremely serious vanadium ions migration and high cost.In this thesis,we prepared the ImPSf/SPEEK amphoteric blended membrane,and the Donnan exclusion effect of imidazolonium effectively reduces the vanadium permeability and improves the coulombic efficiency of battery.Based on this,we design the structure of the alkyl sulfonated imidazole and the contents of positive and negative groups can increase simultaneously,and then the heterocyclic polybenzimidazole is used as the main chain to obtain the amphoteric membranes with high selectivity and conductivity and good chemical stability.Firstly,the amphibolic ImPSf/SPEEK membranes were prepared by one-step process of the Menshutkin reaction and the membrane-forming process.With the increase of ImPSf content,the swelling degree of ImPSf/SPEEK membrane decreased gradually,and the permeability of vanadium ion also decreased gradually.The energy efficiency?EE?of ImPSf/SPEEK-18 membrane is the highest,77.3%under the 200 mAcm-2,when ImPSf content is 18%.The CE is 97.5%better than the Nafion membrane?EE=75.5%,CE=94%?.At the 80 mAcm-2 current density,the ImPSf/SPEEK-18 smoothly runs 50 cycles of charge and discharge,the CE of the battery is constant over 95%,the EE is above 85%and the capacity attenuation of battery is 0.6%per lap,which is better than the Nafion membrane and the SPEEK membrane.Secondly,alkyl sulfonated imidazole amphoteric group and different chloromethylation degree of chloromethylated polysulfone were synthesized,and then the PSf-MI-PS amphoteric membranes were prepared through the Menshutkin reaction.With the increase of the functionalization degree,the swelling degree of membrane and the permeability of vanadium ion increase slightly,but far below the Nafion membrane.Under the current densities from 40 to 200 mA cm-2,the coulombic efficiency?C E?of PSf-MI-PS 190%membrane is above 97%,and the voltage efficiency?VE?is equivalent to Nafion membrane.At the 200 mA cm-2,the C E is 99.0%,and the energy efficiency?EE?is 77.4%,which is better than the Nafion212 membrane?CE=93%,EE=73%?,but its capacity attenuation is serious?cut down 53.2%after 50 cycles?and the chemical stability is worse,which still need to further improve.In order to improve the chemical stability of ion exchange membrane,the polybenzimidazole membranes with alkyl sulfonate were prepared using the chain of heterocyclic aromatic polymer.And the membrane has good resistance performance of vanadium ion.Under the current densities of 40 to 200 mA cm-2,the CEs of each sulfonated membranes are more than 96%.When the degree of sulfonation is 200%,the VE of the PBI-PS 200%membrane is equivalent to that of Nafion membrane.At the 200 mA cm-2,the CE of PBI-PS 200%membrane is 98.9%,and the EE is 77.5%,which is superior to the Nafion212 membrane.Under 80 mA cm-2,PBI-PS 200%membrane can smoothly run 200times of charging and discharging circulation,the C E of the cell is constant over 98.3%,and the EE is over 87.5%.The capacity attenuation of PBI-PS 200%membrane is 0.52%each lap and the membrane structure remain unchanged after the cycling test,having good chemical stability.PBI-PS amphoteric membrane is one of the most promising choice for all-vanadium flow battery. |
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