Revealing the “double-layer ionic monotonic adsorption” electrochemical ion storage mechanism of nano-confined porous carbon

Abstract

High voltage carbon-based capacitors used organic electrolytes show great potential due to high energy density, wide operating voltage, and long cycle stability. However, oxygen groups in carbon-based materials will undergo oxygen evolution reaction at high potential, leading to failure of the electrode material and triggering the decline of the capacitor. In addition, the ion storage mechanism of carbon-based materials in high voltage ionic liquids is unclear. Herein, we present a scalable method to synthesize three-dimensional porous flower-like carbon (3DPFC) composed of interconnected carbon sheets, highly interconnected pores, large specific surface area, low oxygen content from coconut shells using a simple bicarbonate activation method. Furthermore, combining in situ spectroscopy and theoretical calculations, a new “double-layer ionic monotonic adsorption” ion storage mechanism is revealed to be different from the conventional one, and the relationship between the pore structure and the ion storage behavior has been sublimely understood. As a result, the symmetrical supercapacitors using 3DPFC deliver an ultrahigh energy density (109 Wh kg⁻¹) and high-power density (71 kW kg⁻¹), retaining 94.1 % after 10,000 cycles at 10 A g⁻¹. This study highlights the scalable production of high-capacity and low-oxygen-content carbon materials and offers insights into ion storage mechanisms for developing high-energy-density supercapacitors.