Electrochemical energy storage devices with high working efficiency and low cost are the goal that researchers are working towards. The traditional wet-chemistry method leads to agglomeration and hinders its conductivity. Graphene, with high surface area, chemical stability, and excellent electric and thermal conductivity, is among the most promising materials being applied in energy devices.  

Prof. ZHU Yanwu and Prof. JI Hengxing at University of Science & Technology of China of Chinese Academy of Sciences reported their achievements in avoiding agglomeration and improving the device’s capacitance to 401 F g^-1 in aqueous electrolytes on Advanced Materials. 

Researchers fabricated a 3D hierarchical porous carbon by the aid of sponge-templates. The sponge templates suck potassium hydroxide (KOH) into its backbone and simultaneously assemble graphene oxide (GO) platelets into a 3D structure. After these process, the templates display in honeycomb-like meso- and micropores covered by a chiffon-like 3D graphene membrane. The mesopores and macropores could provide electrolyte ion transportation and diffusion channels in 3D. The reduced GO platelets on the surface of skeleton offer highly conductive channels for electron transport and lower the square resistance of the prepared electrodes. 

All these essentials result in a high energy and power density device whose capacitance is up to 401 F g^-1 in aqueous electrolytes measured in three-electrode configuration, 207 F g⁻¹ and 149 F cm⁻³ in organic electrolytes measured in two-electrode configuration. 

According to the electrochemical impedance spectroscopy (EIS) tests, the electrode demonstrates a nearly ideal capacitance behavior with a vertical slope at the low-frequency region and an ionic resistance of 3.16Ω. Moreover, it still has 93% retention in capacitance after 4000 times charging/discharging in BMIMPF/AN. 

This work was financially supported by China Government 1000 Plan Talent Program, China MOE NCET Program, Natural Science Foundation of China, the Fundamental Research Funds for the Central Universities, the External Cooperation Program of BIC, Chinese Academy of Sciences, and the 100 Talents Program of the Chinese Academy of Sciences.