Integration of ultrathin graphene/polyaniline composite nanosheets with a robust 3D graphene framework for highly flexible all-solid-state supercapacitors with superior energy density and exceptional cycling stability

Here we report a unique hierarchical free-standing graphene/polyaniline (G/PANI) composite electrode with ultrathin G/PANI composite nanosheets embedded in the skeleton of a three-dimensional (3D) graphene framework. Due to the intrinsic structural advantage of ultrathin G/PANI composite nanosheets and their synergetic interaction with the 3D graphene network, the 3D-G/PANI composite electrode can deliver a high specific capacitance of 777 F g(-1) and 990 F cm(-3) at 1 A g(-1) and an exceptional cycling stability with 85% capacitance retention after 60 000 deep cycles in a three-electrode cell configuration. The further assembled all-solid-state supercapacitor based on the 3D-G/PANI composite electrode can not only show extraordinary mechanical flexibility allowing bending, twisting and folding, but also demonstrate remarkable electrochemical performance under its folded state, including an ultrahigh specific capacitance of 665 F g(-1) and 847 F cm(-3) for the 3D-G/PANI composite electrode, excellent rate capability with a capacitance retention of 86% at 20 A g(-1) and superior cycling stability with no capacitance decay after 10 000 cycles, as well as ultralow self-discharge characteristics. Furthermore, the entire ultrathin device (similar to 45 mu m, much thinner than a commercial standard A4 paper) can deliver volumetric, gravimetric and areal energy densities up to 14.2 mW h cm(-3), 10.9 W h kg(-1) and 64 mW h cm(-2), respectively, which are much higher than those of current high-level commercial supercapacitors (similar to 5 W h kg(-1)) and even lithium thin-film batteries (similar to 8 mW h cm(-3), 4 V/500 mu A h).