A Highly Stretchable Supercapacitor Using Laser‐Induced Graphene Electrodes onto Elastomeric Substrate

DOI: 10.1002/aenm.201600050 (polyimide and polyetherimide) [ 20 ] that cannot provide the suitable mechanical properties required for stretchable energystorage devices. Herein we report a simple method to transfer the LIG porous layer obtained onto polyimide sheet to a transparent and elastomeric substrate such as PDMS (polydimethylsiloxane). Morphology and chemical-physical properties of the obtained material were deeply characterized by electron microscopy investigation, contact angle measurements and vibrational spectroscopy analysis. The as-fabricated electrodes were assembled into symmetric electrical double-layer supercapacitors and, thanks to the intrinsic mechanical properties of PDMS, the retention of energy-storage performance under bending and stretching conditions was demonstrated. The fabrication process of the LIG/PDMS electrodes is described in the experimental section (see also Supporting Information) and schematically represented in Figure 1 a–d: porous LIG pattern was obtained by a direct writing of polyimide sheet using a nanosecond CO 2 laser (a); afterward the PDMS was poured onto the written sample and the air was evacuated by a vacuum step in order to allow the full infi ltration of PDMS into the 3D network (b); after a thermal curing at 80 °C for 1 h the LIG/PDMS slide was manually peeled off from the polyimide sheet (c,d). The resulting composite material take advantage of the unique mechanical properties typical of elastomers (Figure 1 e) and of the good electrical conductivity and high surface area intrinsically present in LIG structures. Figure 1 f,g show the transparency of a logo pattern written on polyimide foil and then transferred onto PDMS slice respectively. The preservation of the electric conduction was tested by using LIG/PDMS composite to close a circuit (powering a green LED) as shown in Figure 1 h and by electrical measurements. Current–voltage characteristics shown in Figure S1 (Supporting Information) were recorded on the LIG/PDMS sample subjected to stretching in the range 0%–50%, confi rming the good maintenance of electrical properties. FESEM characterization was used to assess the morphology of the LIG sample before and after transfer onto PDMS substrate. Figure 2 a,b show the characteristic 3D foam-like structure of the laser-written LIG sample, which is composed of multilayer graphene walls. The holey foam-like structure, which is a result of the emission of gases during the irradiation process, [ 20,21 ] is actually well suited for both infi ltration with PDMS and impregnation with the electrolyte for supercapacitor application. Figure 2 c presents a cross-sectional view of a LIG sample after it is successfully transferred onto a PDMS substrate through the cast-and-peel process. Thanks to the effective infi ltration of PDMS, the LIG shows good adhesion to the underlying fl exible substrate. Moreover, as shown in Figure 2 d–f, a 3D structure of interconnected multilayer The fi eld of wearable electronics has been evolving very rapidly in the last few years due to the increasing demand for fl exible portable devices as alternatives to conventional rigid systems. [ 1 ] Indeed, contrary to the standard silicon-based electronics, stretchable devices allow easy conformal integration into deformable systems [ 2 ] and can adapt to different shapes and surfaces. Up to now, huge efforts have been devoted to developing fl exible devices for different applications, such as tactile sensors, [ 3,4 ] molecular sensors and pH sensors, [ 5,6 ] actuators, [ 7,8 ] photodetectors, [ 9,10 ] solar cells, [ 11,12 ] piezoelectric and triboelectric nanogenerators, [ 13,14 ] and other fl exible systems. [ 15 ]