Ultra-thin amphiphilic hydrogel electrolyte for flexible zinc-ion paper batteries

Hydrogel electrolytes are the ideal platform to construct flexible zinc-ion batteries. However, they usually require immersion in salt solutions to the swollen state for high ion transportation, resulting in a decreased energy density and poor interface adhesion. Herein, we developed a hydrophobic-hydrophilic dual phase stabilization strategy to crosslink polymer membranes into hydrogels based on solvent displacement. The hydrophobic and rigid polyacrylonitrile (PAN) network effectively restricts the swelling behavior of the hydrophilic polyvinyl alcohol (PVA) network, forming an interconnected amphiphilic hydrogel (C-PVA/PAN) with a thickness of only 20 mu m even after swelling. The Zn||C-PVA/PAN||Zn symmetric cell cycling tests demonstrate stable performance exceeding 3500 hours without zinc dendrite formation. Molecular dynamics (MD) simulations also corroborate the ability of the C-PVA/PAN hydrogel electrolyte to facilitate uniform zinc deposition. Additionally, paper-like Zn||C-PVA/PAN||NH4V4O10 batteries with a thickness of only 82 mu m exhibit remarkable cycling performance (180 mA h g-1 after 3000 cycles at 20 A g-1) and can be folded using the Miura folding technique, significantly enhancing areal energy density. This work presents a facile strategy for designing ultra-thin hydrogel electrolytes, paving the way for powering next-generation flexible electronics through paper-like batteries. The paper-like ZIBs can be folded and unfolded using the Miura folding technique, enhancing the areal energy density by a factor of 18.