Super long-life supercapacitor electrode materials based on hierarchical porous hollow carbon microcapsules

Remarkable supercapacitor electrodes with a high specific supercapacitance and a super long cycle life were achieved by using hierarchical porous hollow carbon microcapsules (HPHCMs) as active materials. HPHCMs were prepared by a facile chemical route based on pyrolysis of a soft sacrificial template involving a non-crosslinked core of poly(styrene-r-methylacrylic acid) and a crosslinked shell of poly(styrene-r-divinylbenzene-r-methylacrylic acid), which were synthesized by using traditional radical polymerization and emulsion polymerization. The results of scanning electron microscopy, transmission electron microscopy and Brunauer-Emmett-Teller characterizations revealed that HPHCM possessed the desired pore structure with apparent macro-/meso- and micropores, which not only provided a continuous electron-transfer pathway to ensure good electrical contact, but also facilitated ion transport by shortening diffusion pathways. As electrode materials for supercapacitor, a high specific capacitance of 278.0 F g(-1) was obtained at the current density of 5 mA cm(-2). Importantly, after 5000 potential cycles in 2 M KOH electrolyte at the discharge current density of 20 mA cm(-2), the capacitance actually increased from 125 to 160 F g(-1) and then remained 151 F g(-1), corresponding to a capacitance retention of 120%, likely due to electrochemical self-activation.