Article Highlight | 17-Dec-2025

Water‑restrained hydrogel electrolytes with repulsion‑driven cationic express pathways for durable zinc‑ion batteries

Shanghai Jiao Tong University Journal Center

Water‑Restrained Hydrogel Electrolytes with Repulsion‑Driven Cationic Express Pathways for Durable Zinc‑Ion Batteries

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  • A novel cationic hydrogel electrolyte is prepared to address a significant challenge of balancing the tripartite trade-offs of hydrogel properties.
  • Cationic express pathways enable fast and selective Zn2+ transport through dynamic ionic repulsion, achieving high ionic conductivity (28.7 mS cm−1) and Zn2+ transference number (0.79).
  • The hydrogel demonstrates exceptional cycling stability across − 15 to 60 °C, showcasing great potential for practical flexible battery applications.
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Credit: Dewu Lin, Yushuang Lin, Ruihong Pan, Jiapei Li, Anquan Zhu, Tian Zhang, Kai Liu, Dongyu Feng, Kunlun Liu, Yin Zhou, Chengkai Yang*, Guo Hong*, Wenjun Zhang*.

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⁺R3 side-chains create cationic express lanes: AIMD shows Zn2–amide distance widens from 1.98 Å (PAM) to 3.84 Å, cutting hopping barriers.
    – SO42- 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, 1 240 h @ 8 mA cm-2, 1 000 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.

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