Preparation Of Pyridinium-containing Poly(Phthalazinone Ether Ketone) Membrane For Vanadium Redox Flow Batteries

Vanadium batteries are a new type of energy storage device that can perform smart grid peak shaving and smooth grid output,thus solving the problem of discontinuous and unstable new energy generation.Diaphragms are a key component of vanadium batteries,and the Nafion series is the most commonly used diaphragm for vanadium batteries,which has high ionic conductivity and chemical stability,but has poor vanadium barrier properties and high manufacturing costs.Our groups have prepared pyridinium-containing poly（phthalazinone ether ketone）（Py BPPEK）anion-exchange membranes,which has excellent vanadium barrier properties and good battery performance in vanadium batteries,but its stability is not good.Therefore,in order to improve the membrane stability,and to ensure that the membrane has a high ion conduction rate,this paper uses the solution casting method to prepare a low-substitution pyridinium-containing poly（phthalazinone ether ketone）（Py-PPEK）porous anion exchange membrane.In this paper,dimethyl-containing poly（phthalazinone ether ketone）（DMPPEK）with 10%,20%and 30%dimethyl content was used as raw material,which was modified by bromination with N-bromosuccinimide to obtain brominated poly（phthalazinone ether ketone）（BPPEK）.Nuclear magnetic resonance hydrogen spectroscopy and infrared spectroscopy demonstrated that the expected structure of the polymer was obtained;the bromination of BPPEK ranged from 0.06 to 0.24;the solubility of Py-PPEK in the non-polar solvent chloroform gradually decreased with increasing pyridine group content and in the polar solvents N,N-dimethylacetamide,N,N-dimethylformamide and dimethyl sulfoxide gradually.The solubility of Py-PPEK was enhanced in NMP（N-methylpyrrolidone）,which met the requirements for the formulation of film casting solution;the pyridine group in Py-PPEK made its onset decomposition temperature at 190℃,both of which had good thermal stability.The effect of solvent evaporation time on the structure and properties of Py-PPEK membranes was investigated by using NMP as the solvent.The ion exchange capacity（IEC）of Py-PPEK membranes ranged from 0.08 to 0.41 mmol/g,and the effect of IEC on membrane performance was investigated.As the IEC increased,the surface resistance,water absorption and swelling rate of Py-PPEK membranes showed an increasing trend and the vanadium ion permeability coefficient and the stability in VO₂⁺solutions decreased.The current efficiency,voltage efficiency and energy efficiency of Py-PPEK membranes applied in vanadium batteries increased with IEC.At a current density of 40 m A/cm²,the Py-PPEK30 membrane achieves a single cell current efficiency of 95.5%,which is better than the Nafion115 membrane.At a current density of 80 m A/cm²,the Py-PPEK30 membrane showed high stability over 300charge/discharge cycles tested.