Sodium‐Ion and Polyaniline Co‐Intercalation into Ammonium Vanadate Nanoarrays Induced Enlarged Interlayer Spacing as High‐Capacity and Stable Cathodes for Flexible Aqueous Zinc‐Ion Batteries

Abstract Vanadate oxides with low price and high theoretical capacity are competitive cathodes for aqueous zinc‐ion batteries (AZIBs). However, the existing problems such as sluggish Zn 2+ ion mobility, weak conductivity, and complicated flexible electrode preparation hinder the development of their practical applications in flexible AZIBs (FAZIBs). Herein, sodium‐ion and polyaniline are co‐inserted into ammonium vanadate (NaNVO‐PANI) nanoarrays, which can serve as the novel freestanding cathodes for FAZIBs. By virtue of synergistic pillar effect of sodium ions and polyaniline, the interplanar spacing of NaNVO‐PANI expands to ≈13.8 Å. Both experimental data and theoretical calculation confirm that the optimal spacing of NaNVO‐PANI can boost enhance the electronic conductivity and reduce Zn 2+ diffusion barrier. As expected, the resulting coin‐type AZIBs exhibit high capacity of 610.7 mAh g −1 at 0.5 A g −1 and remarkable capacity retention of 98% after 5000 cycles at 5 A g −1 . More encouragingly, quasi‐solid‐state FAZIBs with sandwich structure are assembled, achieving impressive energy density of 345.59 Wh kg −1 at a power density of 380.46 W kg −1 . This study is of great significance for developing high‐performance vanadium‐based electrode for wearable FAZIBs.