Rigidly and intrinsically microporous polymer reinforced sulfonated polyether ether ketone membrane for vanadium flow battery

Ion exchange membranes (IEMs) blending porous materials have shown great potential for the large-scale energy storage technologies, such as flow battery. However, it remains challenging to overcome the compatibility issue between polymer and porous fillers. In this work, the polymer of intrinsic microporosity (PIM) was successfully introduced into sulfonated polyether ether ketone with high degree of sulfonation (HDS-SPEEK) membrane. PIM exhibited desirable compatibility with HDS-SPEEK due to the natural polymer property. Meanwhile, the rigid skeleton structure of PIM effectively solved the problems of HDS-SPEEK involving poor mechanical property and low vanadium resistance. With increasing the doping of carboxyl grafting modified PIM, the tensile strength increased from 15.22 to 29.94 MPa and the vanadium permeability declined from 4.4 × 10⁻⁶ to 1.6 × 10⁻⁷ cm² min⁻¹. As a result, the vanadium flow battery equipped with the optimized blend membrane showed significantly enhanced coulombic efficiency from 55% to 99% at the current density of 20 mA cm⁻², and had good long-term stability. This work presents a new route to prepare high-performance IEMs based on porous PIM materials for flow battery.