Robust Ion Highways in Vermiculite-Based Ultrathin Composite Network Membranes for High-Performance Flow Batteries

Rational design of ion-selective membranes is crucial for energy technologies. Herein, we developed a vermiculite nanosheet (VN)-enabled nanoconfined network membrane with ultrahigh ion selectivity. The complete infusion of VN-polymer composites into polypropylene network established a robust architecture featuring negatively charged VN-dispersed laminar channels. The optimal ultrathin composite network membrane (7 μm) exhibited exceptional tensile strength up to 310 MPa, an order of magnitude greater than that of commercial Nafion 212. Leveraging the synergistic effects of size exclusion and Donnan exclusion, the membrane achieved a proton conductivity of 78.5 mS cm–1, coupled with an outstanding K+/Fe(CN)63– selectivity of 260, approximately 3.0 times superior to Nafion 212. Ab initio molecular dynamics (AIMD) simulations revealed that the rapid proton transport within VN interlayers was achieved through the synergistic operation of the Grotthuss and vehicular mechanisms. In vanadium flow batteries, it achieved 80.1% energy efficiency at 200 mA cm–2 with 1000-cycle stability and ultralow capacity decay (0.08%/cycle vs Nafion’s 0.24%/cycle). Meanwhile, the membrane demonstrated an outstanding energy efficiency (EE) of 86.7% at 80 mA cm–2 in the zinc–iron flow battery system and effectively inhibited zinc dendrite penetration. This vermiculite-based composite membrane with robust nanoarchitectonics establishes a high-performance platform for advanced energy storage.