Robust Polyaniline-silica@polypropylene for High-Performance, High-Capacity Retention All-Vanadium Redox Flow Battery

Abstract

The development of high-performance membranes to address the issue of vanadium ion crossover in vanadium redox flow batteries (VRFB) is a significant area of focus. Current commercial perfluorinated membranes suffer from economic impracticality, poor ion selectivity, and electrolyte leakage. In this report, we present a composite membrane called PANI-Si@PP, which exhibits exceptional selectivity for protons over vanadium ions due to Donnan exclusion by the positively charged polyaniline backbone and the presence of well-defined proton conductive channels. To begin, we successfully synthesized and characterized a composite of polyaniline and silica (PANI-Si). Subsequently, we coated a porous polypropylene (PP) film with the PANI-Si composite using the phase inversion technique followed by acid functionalization. We assessed the surface characteristics and extent of pore filling through microscopic analysis and water flux measurements. The resulting membrane displayed excellent electrochemical and physicochemical properties. In a single-cell commercial VRFB, the PANI-Si@PP membrane achieved a Coulombic efficiency and energy efficiency of approximately ∼99 and ∼70%, respectively, over 300 cycles at a current density of 200 mA cm −2 , while retaining a high capacity of ∼70%. Additionally, the membrane exhibited a peak power density of 322 mW cm −2 at a current density of 350 mA cm −2 . This work highlights that the synergy of effective material selection and proper fabrication techniques is a successful approach to develop cutting-edge separators for battery applications.