Construction of zwitterionic osmolyte-based hydrogel electrolytes towards stable zinc anode for durable aqueous zinc ion storage and integrated electronics

Abstract

Progress towards extra stable Zn ion power supply systems is important for developing integrated electronics. However, deep-seated issues of severe Zn dendrite growth radically impede the rechargeability and utilization of Zn ion storage devices in these electronics. Herein, a tough zwitterionic osmolyte-based hydrogel electrolyte (denoted as SPS–Zn) with multiple network interactions was developed in this work to effectively modulate the Zn deposition behavior and suppress the dendrite growth. Through this approach, the original sodium alginate/polyacrylamide (denoted as SP) polymeric network can be optimized and it eventually enables strong mechanical strength (high tensile strength of 61.8 kPa at 310.2%), high ionic conductivity (2.50 S m⁻¹), large Zn²⁺ transference number (t_Zn²⁺ = 0.64), and low activation energy for Zn²⁺ ion desolvation. Additionally, the theoretical calculations further proved that the zwitterionic osmolytes promote the migration of solvated Zn²⁺ ions via the formation of ion-migration channels, possess a strong affinity to metallic Zn for increasing nucleation sites, and restrict the 2D diffusion of Zn²⁺ ions. Meanwhile, experimental results and the finite element simulation revealed that SPS–Zn can homogenize the electric field distribution and Zn²⁺ flux. Consequently, the asymmetry and symmetric batteries with SPS–Zn display enhanced cycling life and reversibility. The as-assembled zinc-ion hybrid supercapacitor (ZHSC) exhibits satisfactory capacity and long-term stability. A portable integrated device with the ionic skin (denoted as i-skin) and ZHSC was also assembled and it could steadily detect physiological signals. This work provides new insight into the design of functional hydrogels for highly stable ZHSCs and integrated i-skins.