Embedding hydrogel electrodes into hydrogel Electrolyte: An 3D protecting strategy for stretchable High-Performance supercapacitor

Stretchable supercapacitors (SCs) are typically either sandwich or two-dimensional (2D) structure design. Single sandwich SC can offer high energy and power density even under large strain, but require complicated construction process. Furthermore, the integrated sandwich SCs in series strongly depend on external conducting wires, which limits the stretchability of SC devices. Two-dimensional (2D) SCs show exceptional integration, however, their strain tolerance, energy and power density are unsatisfactory. Here, we present an innovative structure design via embedding high-modulus hydrogel electrodes (elastic modulus of 342 kPa, tensile strain of 590 %) into a low-modulus hydrogel electrolyte (elastic modulus of 42 kPa, tensile strain of 1184 %). The resulting multiphase hydrogel with wrapped structure could protect the high-modulus hydrogel electrodes via dissipating the load stress on the surrounding electrolyte, and greatly improve the interfacial toughness between electrodes and electrolyte, giving rise to excellent stretchability (tensile strain of 834 %) and elastic modulus (173 kPa). This 3D protecting mechanism enables the multiphase hydrogel to synchronously hold the advantages of sandwich and 2D SCs. As a result, high areal capacitance of 1049.2 mF cm-2, 84.0 % capacitance retention under 360 % strain and effortlessly printable integration could be achieved for high-voltage output. We believe that this unique structure design of the multiphase hydrogel can not only fill the gap between conventional 2D and sandwich SCs, but also become a new paradigm for the creation of stretchable SCs with off-the-shelf availability.