Aqueous zinc-ion batteries (ZIBs) are a promising power source technology for portable and wearable electronic devices due to their high energy/power density, inherent safety, and environmental friendliness. The emergence of hydrogel electrolytes (HEs) has made the construction of flexible ZIBs possible, as they provide ion transport channels and can withstand various mechanical deformations, such as bending, shearing, or folding. However, polymer-based HEs typically contain a large amount of water (>80 wt%), leading to uncontrolled dendrite growth on the anode and unfavorable side reactions. Additionally, the ion conductivity of polymer-based HEs is low because the polymer matrix itself cannot transport ions, affecting the electrochemical performance of flexible batteries. Notably, the functional groups on HE polymer chains can interact with Zn²⁺, adjusting the solvation structure to suppress side reactions and providing shorter, faster pathways for Zn²⁺ transport. Moreover, dendrite growth can puncture the HEs, causing internal short circuits in flexible batteries. By endowing HEs with self-healing properties, the rate of dendrite penetration through HEs can be reduced. Therefore, developing novel HEs with high ionic conductivity, rapid ion transport mechanisms, and self-healing capabilities is essential for achieving a long-life zinc anode.
In light of this, Professor Yagang Yao's team at Nanjing University proposed a molecular engineering strategy that incorporates oxygen-rich polyurethane (OR-PUU) into polyacrylamide (PAM)-based HEs (OR-PUU/PAM). By utilizing an ion hopping migration mechanism to construct ion transport channels, rapid ion transfer is promoted, achieving uniform Zn²⁺ deposition. The abundant polar groups on OR-PUU molecules break the intrinsic hydrogen-bond network, modulate the solvation structure of hydrated Zn²⁺ ions, and suppress side reactions. Furthermore, the hierarchical hydrogen bond interactions within the OR-PUU/PAM HEs confer self-healing properties, enabling in-situ repair of cracks caused by plating/stripping. The long-chain OR-PUU polymer physically adsorbs and forms hydrogen bonds with the SEI layer on the zinc anode surface, establishing a direct ion transport pathway. Due to dipole moment formation, the carbonyl groups on these long-chain molecules are electronegative, providing a transition state for Zn²⁺ hopping. Subsequently, Zn²⁺ can rapidly shuttle along the direction of the long polymer chains, promoting ordered deposition while suppressing dendrite formation. The abundant polar groups on OR-PUU disrupt the inherent hydrogen-bond network in HEs, partially displacing active H₂O molecules from the solvation shell, modifying the Zn²⁺ solvation structure, and reducing the number of H₂O molecules coordinated with Zn²⁺, thereby inhibiting corrosion and hydrogen evolution reaction (HER). The six types of hydrogen bonds within OR-PUU form a hierarchical hydrogen-bond cross-linked network, enhancing the structural strength of the PAM gel. Additionally, this rich hierarchical hydrogen-bond interaction imparts excellent self-healing properties to the HEs without affecting electrolyte viscosity, facilitating in-situ repair of interfacial fatigue cracks while maintaining high ionic conductivity. This work provides valuable insights for achieving dendrite-free zinc metal anodes through molecular engineering of HEs.
This work, titled “Molecular Engineering Enables Hydrogel Electrolyte with Ionic Hopping Migration and Self-Healability toward Dendrite-Free Zinc Metal Anodes,” was published in *Advanced Materials*, a leading journal in the field of materials science. Kaiping Zhu and Dehe Zhang, Ph.D. students at the School of Modern Engineering and Applied Sciences at Nanjing University, along with postdoctoral researcher Jie Luo from the Suzhou Institute of Nano-Tech and Nano-Bionics, are the first authors of the paper. This research was supported by the National Key Research and Development Program, the Natural Science Foundation of Jiangsu Province, and also received substantial assistance from the National Laboratory of Solid State Microstructures.
