Research On Polyvinylidene Fluoride Based Porous Composite Membranes For Vanadium Flow Battery Application

Vanadium redox flow battery,a large energy storage system,can realize the effective storage and stable output of energy.As one of the key materials for all vanadium redox flow batteries,the membrane has a direct impact on the battery.Polyvinylidene fluoride?PVDF?membranes with its good thermodynamics,mechanical properties,chemical stability and low cost has always been the focus of attention.However,the vanadium flow battery assembled with Polyvinylidene fluoride?PVDF?membranes suffers a great polarization.In this paper,three modification measures,such as in situ filling,layer by layer self-assembly and addition surfactants,were taken to make the PVDF porous membranes service better for the vanadium redox flow battery.In addition,the effect of different modification methods on the properties of porous membranes was explored in details.The main contents of the paper are as follows:SiO₂/PWA composite particles was fabricated in the inner pores of PVDF porous membranes by in situ gel hydrolysis method.The SiO₂/PWA/PVDF composite membranes effectively released the contradiction between the vanadium ion selective and proton conductivity of porous membrane to a certain extent.The energy efficiency?EE?of battery assembled with the composite membranes increased by 17.6%at a current density of 40 mA cm^-2.Phosphotungstic acid?PWA?and poly?diallyl dimethylammonium chloride??PDDA?were deposited on the surface and pore wall of PVDF porous membrane by the layer by layer self-assembly method,respectively,which adjusted the proton conductivity and the vanadium ion selectivity of the porous membrane.At a current density of 80 mA cm^-2,the battery assembled with PVDF-?PWA/PDDA?₃ membrane attained a coulombic efficiency?CE?of94.8%and an EE of 77.9%,which is compared with the battery using a Nafion membrane?CE=96%,EE=76.6%?.After the 100 cycles test,the energy efficiency of the battery still maintained 77.9%,which demonstrated the good chemical stability and energy conversion rate.The high proton conductivity PVDF porous membrane with the interconnected pore structure was fabricated by the addition of CTAC.The battery assembled with PVDF?3wt%CTAC?porous membranes indicated an excellent charge-discharge performance whose CE and EE are 95%and 81%,respectively.The battery also showed a good cycling performance?100 cycles?at a current density of 80 mA cm^-2.