Extraordinary Thickness-Independent Electrochemical Energy Storage Enabled by Cross-Linked Microporous Carbon Nanosheets.

Two-dimensional carbon-based nanomaterials have demonstrated great promise as electrode materials for electrochemical energy storage. However, there is a trade-off relationship between energy storage and rate capability for carbon-based energy storage devices because of the incrementing ion diffusion limitations, especially for thick electrodes with high mass loading. Herein, we report the cross-linked microporous carbon nanosheets enabling high-energy and high-rate supercapacitors. The as-fabricated microporous carbon nanosheets exhibit an extraordinary thickness-independent electrochemical performance. With the thickness of 15 μm, the as-fabricated carbon nanosheet electrode possesses areal/volumetric/gravimetric capacitance of 895 mF cm-2/596 F cm-3/358 F g-1. Even at a high electrode thickness of 125 μm, the as-fabricated thick electrode presents an ultrahigh areal/volumetric/gravimetric capacitance of 4102 mF cm-2/328 F cm-3/328 F g-1. Furthermore, the as-assembled symmetric supercapacitor delivers an outstanding energy density of 19.2 W h kg-1 at a power density of 135 W kg-1 and ultralong cycling stability (capacitance retention of 95% after 180 000 charge/discharge cycles) in an alkaline electrolyte. This work not only provides a facile method for low-cost preparation of carbon nanostructures and high-value utilization of biomass wastes but also offers new insights into rational design and fabrication of advanced electrode materials for high-performance electrochemical energy storage.