Stretchable Zn‐Ion Hybrid Capacitor with Hydrogel Encapsulated 3D Interdigital Structure

To enhance the areal energy density of current flexible energy storage devices, hybrid capacitors combining the advantages of supercapacitors and batteries are proposed and further enhanced by incorporating the 3D interdigital structure design. However, uneven electric field distribution and hindered ion diffusion kinetics due to the non‐electroactive components in these devices limit the enhancement of areal electrochemical performances when expanding the electrodes longitudinally. Herein, hydrogels with high ionic conductivity and high mechanical stability are designed to accommodate Zn 2+ ‐containing electrolytes and integrated with Ti 3 C 2 T x ‐MXene electrodes to assemble flexible Zn‐ion hybrid capacitors (ZIHCs). Fully encapsulated by ionic conductive hydrogels, 3D interdigital electrodes enable omnidirectional ion transport and unimpeded ionic accessibility, facilitating adequate electrode reactions, rapid energy storage, and uniform energy distribution. Hence, the all‐hydrogel‐encapsulated ZIHC achieved a 50‐fold increase in capacitance with a quadrupled electrode thickness, exhibiting a large areal capacitance of 1432 mF cm −2 and an energy density of 389.7 µWh cm −2 without sacrificing power density and rate performance. Finite element simulations further illustrate the uniform distribution of potential, electric field intensity, and energy density in this structure. In addition, the device shows great stability under deformation, excellent adhesion, and underwater workability, demonstrating great promise for next‐generation wearable energy storage devices.