▎ 摘　　要

With the ever-growing demand of miniaturized electric double-layer capacitors (EDLCs), it is still a big challenge to well-balance the competing relationships between high specific surface area (SSA) and high packing density in porous carbons. Herein, 2D porous carbon nanosheet (PCN) with high carbon yield is synthesized by a simple interface self-assembly and subsequent activation strategy from industrial sulfonated pitch by-product, which is composed of graphene quantum dots. It is bestowed with ultrathin thickness of 20 nm, adequate SSA of 2429 m(2) g(-1), high packing density of 0.562 g cm(-3), high e-conductivity of 89 S m(1) and high mechanical flexibility all in one, giving full play to the synergistic effect of electrons and ions. Based on the structure advantages, this PCN can be used as high-performance EDLC electrode. In pure EMIMBF4 electrolyte, it achieves high volumetric capacitances of 90.1 F cm(-3) at 0.5 A g(-1), excellent rate capability C-20/0.05 of 71% and good high-voltage endurance lifetime of 88% after 5000 cycles at 1 A g(-1). Satisfactorily, the maximum volumetric energy density can come up to 39 Wh L-1. More significantly, this work can also provide a new perspective on the architectural conception of other 2D carbon materials.