Low-Cost and High-Performance Sulfonated Polyimide Membrane for Vanadium Redox Flow Battery Application

A novel sulfonated polyimide (SPI-PTDA) is synthesized by introducing low-cost and rigid perylene-3,4,9,10-tetracarboxylic dianhydride (PTDA) into the SPI backbone. A sequence of SPI-PTDA-X membranes with different sulfonation levels has been prepared and characterized. The stable retention time of the SPI-PTDA-75 membrane in aqueous solution at 80 °C is greater than 240 h; its tensile strength (25.83 MPa) is three times that of N212, and the results of the theoretical calculations of molecular ESP indicate the existence of certain interactions within the SPI-PTDA molecule, being responsible for the enhanced mechanical strength of the SPI-PTDA membrane. Additionally, the vanadium ion selectivity of the SPI-PTDA-75 membrane is approximately double that of the N212. The VRFB with the SPI-PTDA-75 membrane demonstrates a Coulombic efficiency (CE) of 97.59% and an energy efficiency (EE) of 80.47% at 120 mA cm–2. The results of 400 charge–discharge cycling tests reveal that the SPI-PTDA-75 membrane maintains strong long-term cycling stability.