Bioinspired Triply Hierarchical Hydrogel Electrolyte for Wide-Temperature-Adaptive Flexible Al–Air Batteries

The practical application of hydrogel-based Al–air batteries is severely hampered by the intrinsic trade-off between mechanical robustness and ionic conductivity, along with uncontrolled water-induced parasitic reactions. In this study, we report a bioinspired triply hierarchical hydrogel electrolyte. Through the in situ polymerization of poly(acrylic acid) within a natural loofah sponge, macro-micro-nano hierarchical pores are developed, and a robust quasi-solid polymer electrolyte is obtained for high-performance flexible Al–air batteries. The composite hydrogel exhibits a remarkable mechanical enhancement, with a tensile strength ∼70.69 times greater than that of pure poly(acrylic acid). Simultaneously, a high ionic conductivity of 333.98 mS/cm is obtained, owing to the synergistic effect of efficient water retention and rapid ion transport within the triply hierarchical pores. Besides, the transport of free water molecules is regulated intelligently, suppressing the hydrogen evolution reaction of the Al anode with an impressive anticorrosion efficiency of 63.55%. Furthermore, the flexible Al–air battery using the proposed hydrogel delivers a specific capacity of 1805.98 mAh/g at 5 mA/cm² and a peak power density of 52.65 mW/cm². The cyclic discharge longevity of the battery reaches 2.05 times that of pure poly(acrylic acid). Remarkably, the battery maintains stable operation even at −20 °C, showcasing excellent adaptability to harsh environments. The composite hydrogel offers a green and sustainable strategy for developing robust hydrogel electrolytes for advanced flexible energy storage systems under extreme conditions.