2D reentrant auxetic structures of graphene/CNT networks for omnidirectionally stretchable supercapacitorsElectronic supplementary information (ESI) available: Additional technical details as a PDF file. See DOI: 10.1039/c7nr02869e

• Main Authors: Kim, Byoung Soo, Lee, Kangsuk, Kang, Seulki, Lee, Soyeon, Pyo, Jun Beom, Choi, In Suk, Char, Kookheon, Park, Jong Hyuk, Lee, Sang-Soo, Lee, Jonghwi, Son, Jeong Gon
• Format: Journal Article
• Language: English
• Published: 14.09.2017
• ISSN: 2040-3364; 2040-3372
• DOI: 10.1039/c7nr02869e

Stretchable energy storage systems are essential for the realization of implantable and epidermal electronics. However, high-performance stretchable supercapacitors have received less attention because currently available processing techniques and material structures are too limited to overcome the trade-off relationship among electrical conductivity, ion-accessible surface area, and stretchability of electrodes. Herein, we introduce novel 2D reentrant cellular structures of porous graphene/CNT networks for omnidirectionally stretchable supercapacitor electrodes. Reentrant structures, with inwardly protruded frameworks in porous networks, were fabricated by the radial compression of vertically aligned honeycomb-like rGO/CNT networks, which were prepared by a directional crystallization method. Unlike typical porous graphene structures, the reentrant structure provided structure-assisted stretchability, such as accordion and origami structures, to otherwise unstretchable materials. The 2D reentrant structures of graphene/CNT networks maintained excellent electrical conductivities under biaxial stretching conditions and showed a slightly negative or near-zero Poisson's ratio over a wide strain range because of their structural uniqueness. For practical applications, we fabricated all-solid-state supercapacitors based on 2D auxetic structures. A radial compression process up to 1/10 th densified the electrode, significantly increasing the areal and volumetric capacitances of the electrodes. Additionally, vertically aligned graphene/CNT networks provided a plentiful surface area and induced sufficient ion transport pathways for the electrodes. Therefore, they exhibited high gravimetric and areal capacitance values of 152.4 F g −1 and 2.9 F cm −2 , respectively, and had an excellent retention ratio of 88% under a biaxial strain of 100%. Auxetic cellular and vertically aligned structures provide a new strategy for the preparation of robust platforms for stretchable energy storage electrodes. Stretchable energy storage systems are essential for the realization of implantable and epidermal electronics.