A Hydrogel Electrolyte toward a Flexible Zinc-Ion Battery and Multifunctional Health Monitoring Electronics

The compact design of an environmentally adaptive battery and effectors forms the foundation for wearable electronics capable of time-resolved, long-term signal monitoring. Herein, we present a one-body strategy that utilizes a hydrogel as the ionic conductive medium for both flexible aqueous zinc-ion batteries and wearable strain sensors. The poly(vinyl alcohol) hydrogel network incorporates nano-SiO₂ and cellulose nanofibers (referred to as PSC) in an ethylene glycol/water mixed solvent, balancing the mechanical properties (tensile strength of 6 MPa) and ionic diffusivity at −20 °C (2 orders of magnitude higher than 2 M ZnCl₂ electrolyte). Meanwhile, cathode lattice breathing during the solvated Zn²⁺ intercalation and dendritic Zn protrusion at the anode interface are mitigated. Besides the robust cyclability of the Zn∥PSC∥V₂O₅ prototype within a wide temperature range (from −20 to 80 °C), this microdevice seamlessly integrates a zinc-ion battery with a strain sensor, enabling precise monitoring of the muscle response during dynamic body movement. By employing transmission-mode operando XRD, the self-powered sensor accurately documents the real-time phasic evolution of the layered cathode and synchronized strain change induced by Zn deposition, which presents a feasible solution of health monitoring by the miniaturized electronics.