Decoupling and correlating the ion transport by engineering 2D carbon nanosheets for enhanced charge storage

Abstract The high aspect ratio of two-dimensional (2D) carbon materials feature unique superiorities and great potential in supercapacitors. The transport of electrolyte ions inside the 2D carbon electrode that can directly affect the overall electrochemical performance, is a key issue that need to be concerned. Nevertheless, the research regarding this process always lags far behind the material concerns and the intrinsic factors to affect ion transport remain obscure. Here we for the first time focus on and correlate the potential and possible factors for addressing this issue using 2D porous carbon nanosheets with tunable thickness as representative demos. A compromise balance between the thickness and ion transport behavior is presented and investigated. The optimal thickness of nanosheets can effectively avoid curling and stacking of ultrathin nanosheets, shorten the distance of ion transport and accelerate the ion diffusion, which render the material with the low resistance corresponding to minimum Warburg coefficient and maximum ion diffusion coefficient for fast transport of electrolyte. A superior capacitance value of 280 F g −1 can be obtained at 0.5 A g −1 , with a retention rate of 81% even at a large current density of 100 A g −1 . Besides, the symmetric supercapacitor with 1-ethyl-3-methylimidazolium tetrafluoroborate electrolyte (EMIMBF 4 ) delivers an energy density of 94 Wh kg −1 at 1.8 kW kg −1 . This work illustrates the importance for transferring the focus from carbon materials to electrolyte ion transport behavior within electrode and provides a guidance for regulating the ion transport by engineering the microscopic thickness of advanced materials in energy-related fields.