Electrospun polyacrylonitrile/bio-based polyurethane composite membranes filled with ZIF-8 and MXene as durable, thermally stable, and high-ionic-conductivity separators for aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) are promising energy storage systems owing to their safety and low cost. However, internal short circuit failure caused by uncontrolled zinc plating is a major challenge. Here, we developed a dual-filler co-modified polyacrylonitrile (PAN)/bio-based polyurethane (PU) nanofibrous separator in which MXene was incorporated together with zeolitic imidazolate framework-8 (ZIF-8) into an electrospun 75/25 PAN/PU matrix. The concurrent presence of ZIF-8 and MXene establishes a multi-interfacial ion-regulation mechanism that homogenizes zinc ion flux and suppresses localized zinc deposition, enabling cooperative ion-transport modulation over using single-filler modification. The optimized 10%ZIF-8/MXene/PAN/PU membrane exhibited high electrolyte uptake of 2273 ± 31%, porosity of 99.4 ± 0.1%, ionic conductivity of 10.55 mS cm−1, and a zinc ion transference number of 0.63, facilitating uniform ion transport and reduced polarization. In zinc||zinc symmetric cells, the membrane maintained stable charge-discharge profiles for over 500 hrs. Systematic studies further revealed that electrospinning parameters and filler content critically influenced fiber morphology, porosity, and electrochemical performance, highlighting the significance of design optimization. Notably, the dual-filler strategy enabled improving electrochemical characteristics, directly demonstrating that the observed performance enhancement originated from the co-modification effect of ZIF-8 and MXene. These results provide a new co-regulation design concept for high-safety separators that enhance the performance, reliability, and durability of AZIBs.