Double Network Gel\nElectrolyte with High Ionic Conductivity\nand Mechanical Strength for Zinc-Ion Batteries

Gel electrolytes hold promise for stabilizing zinc-ion\nbatteries\n(ZIBs), but achieving both high ionic conductivity and strong mechanical\nproperties remains challenging. This work presents a double network\ngel electrolyte based on poly(<i>N</i>-hydroxymethyl acrylamide)\n(PNMA) and sodium alginate (SA), overcoming this trade-off. The PNMA\nnetwork provides mechanical strength and water retention, while the\nSA network facilitates rapid zinc-ion (Zn<sup>2+</sup>) diffusion\nthrough tailored solvation. This double network gel exhibits a tensile\nstrength of up to 838 kPa, significantly higher than previous reports.\nThe SA network provides ion channels for rapid transport of hydrated\nZn<sup>2+</sup>, enhancing the ionic conductivity to a ground-breaking\n33.1 mS cm<sup>–1</sup>. This value is even higher than the\nliquid electrolytes. The growth of Zn dendrites is also suppressed\ndue to the mechanical constraint and rapid ion conduction. In symmetrical\ncells, the PNMA/SA gel demonstrates exceptional cycling stability\n(>2000 h). Characterizations show this is because of reduced free\nwater amount, hindering cathode material dissolution. The full cells\nwith sodium vanadate cathode manifest a high capacity (364.8 mA h\ng<sup>–1</sup> at 0.5 A g<sup>–1</sup>) and excellent\ncapacity retention (83% after 2500 cycles at 10 A g<sup>–1</sup>). This double network design offers a way to achieve high-performance\nand stable ZIBs.