Flexible Asymmetric Supercapacitors with Ultrahigh Energy Density through Synergistic Design of Electrodes

Despite being among the most researched energy storage devices, supercapacitors have often suffered from their relatively low operating voltage and energy density, which greatly limit their practical applications. In this work, asymmetric supercapacitors (ASCs) are developed by synergistically designing carbon nanotube composite electrodes with 3D porous structures. The resultant ASC devices exhibit an extended operating voltage of 1.8 V, much higher than that of symmetric supercapacitors (≤1.0 V). Significantly, the obtained ASC devices deliver ultrahigh volumetric energy density as high as 19.8 mWh cm(−3) (corresponding to an areal energy density of 198 µWh cm(−2)), which is the highest value among reported ASC devices. In addition, the ASC devices not only possess outstanding cycling stability and long self‐discharging time, but also exhibit excellent mechanical flexibility under any bending states, even over 5000 bending cycles. The demonstrated flexible ASC devices with high performance are promising to be used as power sources for next‐generation portable and wearable electronics.