Control of Nano Grains and Wide Carbocyclic Layer Space of Forming Active Carbon with Extraordinary Capacitance Characteristics in Supercapacitors

Abstract

Improving the properties of activated carbon (AC) electrodes for enhancing the electrochemical performance of commercial supercapacitors is still a great challenge. In this work, a coconut shell carbonized raw material is used to successfully manufacture AC by the traditional steam activation method followed by further calcination in CO2. Results showed that a skeleton mesh wall was formed in AC, the thickness of the mesh wall was around 1.5 nm, and the crystalline phase of grain size of 1.13 nm was controlled to form independently in the wall of AC after calcination in CO2 for 4 h. The carbocyclic layer space of the grain phase ranges from 0.381 to 0.392 nm in AC, which is 17% wider than that of 0.335 nm of graphite. The AC shows a high specific surface area (1782 m2/g), and the supercapacitor prepared by AC shows a high specific capacitance (112.5 F·g–1 at 0.1 A·g–1), a high capacitance retention rate (retains 89.06% after 10,000 charge/discharge cycles), a high rate performance (specific capacitance going down from 111.2 to 65.1 F·g–1 under current density from 0.1 to 10 A·g–1), low internal resistance, and a power and energy capacity (energy density, 28.83 W h·kg–1; power density, 9.89 kW·kg–1). It is worth comparing with the typical commercial YP-50 of Kuraray, Japan.