Core-shell hierarchical porous carbon spheres with N/O doping for efficient energy storage

Abstract

Cost-effective synthesis of core-shell carbon spheres for supercapacitor applications remains a challenge. N/O codoped hierarchical porous carbon spheres with the core-shell architecture (MPG2) are fabricated based on the dynamic Schiff-base chemistry free from any templates or complicated procedures. The nanoarchitectures of carbon materials are strongly determined by the addition of glyoxal which not only plays a key role in guiding the reassembly of dynamic imine intermediates to construct a stable core-shell architecture, but also endows carbon spheres with high mechanical strength/stability for the pyrolysis/hybrid modification due to the compact π-conjugated polymer shell. Benefiting from diffusion highways in hierarchical porous structure, a high ion-matching/adsorbing shell surface (1514 m2 g–1) with abundant micropores (0.5–0.8 nm) and N/O functionalities, the resultant MPG2-based symmetric supercapacitor using the lithium bis(trifluoromethane sulfonyl)imide electrolyte (the size of Li+/TFSI– is 0.069/0.79 nm) yields the large energy storage of 31.6 Wh kg–1 at 550 W kg–1 under the high aqueous voltage of 2.25 V, accompanied with a well-behaved cycling stability (capacitance retention of 86.2% over 10,000 rounds at 1 A g−1) and broad temperature applicability from 20 to 80 °C. Furthermore, MnO2 is further deposited on the robust MPG2 architecture to obtain the MPG2/MnO2 composite as a positive electrode in the asymmetric device, and the overlapped voltage window of the MPG2/MnO2 composite and the capacitive MPG2 paves another efficient avenue toward a high energy-power aqueous device of 43.74 Wh kg–1 at 450 W kg–1.