Flexible zinc-ion batteries promise safe, low-cost storage, yet hydrogel electrolytes force a three-way trade-off among high ionic conductivity, fast Zn²⁺ transport and suppressed water-induced side reactions. Now a CityU–Fuzhou University team led by Prof. Wenjun Zhang, Prof. Guo Hong and Prof. Chengkai Yang unveils PAPTMA, a cationic hydrogel whose quaternary-ammonium branches build repulsion-driven “express pathways” that deliver 28.7 mS cm^-1 conductivity and 0.79 Zn²⁺ transference number while locking water into a low-activity state—yielding > 6000 h reversible plating/stripping and 150-cycle pouch-cell stability under 0–360° bending.

Why PAPTMA Matters

• Triple-Breakthrough Design
  – Long –N⁺R₃side-chains create cationic express lanes: AIMD shows Zn²⁺–amide distance widens from 1.98 Å (PAM) to 3.84 Å, cutting hopping barriers.
  – SO₄^2- immobilisation (Zn–O distance 2.08 Å vs 1.32 Å in PAM) suppresses anion polarization, doubling t_Zn²⁺ to 0.79 while maintaining σ = 28.7 mS cm^-1.
  – Interfacial-bound water (92 % medium H-bond, 19 % strong H-bond) curbs HER: H₂ evolution 72 ppm vs 421 ppm in PAM; corrosion current 0.30 mA cm^-2 vs 3.36 mA cm^-2.
• Mechanical & Interfacial Robustness
  – Tensile strength 96 kPa @ 680 % strain; lap-shear adhesion to Zn 50 kPa (2× PAM), leaving gel residue after failure—mechanically pinning the metal surface.
  – In-situ optics at 10 mA cm^-2 show flat Zn deposits; nucleation overpotential only 23 mV vs 76 mV for PAM.
• Cell-Level Validation
  – Symmetric Zn|Zn: 6060 h @ 1 mA cm^-2, 1240 h @ 8 mA cm^-2, 1000 h @ 71 % DoD—3–6× lifespan of best literature hydrogels.
  – Full-cell vs δ-MnO₂: 127 mAh g^-1 after 1 000 cycles (0.5 A g^-1, 76 % retention); 4 × 4 cm² pouch delivers 206 Wh kg^-1 (MnO₂ basis) for 150 cycles with zero capacity loss under 360° bending.

Outlook

The team is now scaling 30 µm-thin PAPTMA membranes via roll-to-roll UV curing and validating −15 °C ↔ 60 °C operation for wearable and grid-storage modules. By turning ionic repulsion into a transport engine and bound water into a stability shield, the work offers a universal design rule for long-life, high-rate flexible aqueous batteries.