Multi-dimensional graded electrodes with enhanced capacitance and superior cyclic stability

Even though electrode materials are widely explored for supercapacitive applications, the basic methods of electrode design are rarely explored to enhance capacitive performance and improve cyclic stability. Herein, multi-dimensional graded electrodes, with gradient polytetrafluoroethylene (PTFE) distribution, are fabricated by a simple recut-reassemble method. At the current density of 1 A g−1, the conventional homogeneous electrode with 5% PTFE concentration renders a specific capacitance of 182 F g−1, whereas the capacitance of multi-dimensional (215 F g−1) and radially-graded (208 F g−1) electrodes are increased by 15.3% and 13.7%, respectively. The enhanced capacitance can be ascribed to lower PTFE content without compromising the structural stability. One should note that the higher PTFE content blocks micropores and reduces the specific surface area of activated carbon (AC) electrode. Moreover, multi-dimensional graded electrode exhibits superior capacitance retention of 99%, which can be attributed to high PTFE concentration in the outer layer, inhibiting the volumetric expansion and reducing the electrode pulverization during charge/discharge process. Furthermore, finite element analysis and post-electrochemical scanning electron microscopy (SEM) observation reveal that multi-dimensional graded electrodes effectively inhibit electrode expansion during the charge/discharge process. Hence, multi-dimensional graded electrodes are promising candidates for next-generation energy storage devices.