Facile Preparation of Cobalt Hydroxide Based Supercapacitor with High Volumetric Energy Density at High Volumetric Power Density

Developing supercapacitor electrodes with an ultra-high specific energy density at high power density and long cycle life is critical to future energy storage devices. However, it is still challenging to fabricate highperformance supercapacitors in a facile and scalable process. In this work, the cobalt nanocone arrays (CNAs) were plated on the copper foil (CF) within 40-second electrodeposition and were transferred into cobalt (Co)/cobalt hydroxide [Co(OH) 2 ] in the alkaline solution after activation of several CV cycles. The flexible Co/Co(OH) 2 @CF electrode can deliver an ultrahigh specific capacitance of 1043 F cm−3 at 1 mA cm−2 and excellent cycle stability with a retention of 98% after 20000 cycles in the three-electrode test. Co/Co(OH) 2 @CF and active carbon were used as the cathode and anode to assemble asymmetric supercapacitors, respectively, in the form of coin and soft package. The soft-package supercapacitor shows an energy density of 28 mWh cm−3 at 62 W cm−3 with 82 % retention after 5000 cycles. And the coin supercapacitor shows a larger energy density of 69 mWh cm−3 at 100 W cm−3 with retention of 123% after 10000 cycles. Good electrical and mass transport and stable structure contribute to its excellent electrochemical performance. Considering the advantages of the facile and scalable preparation process, low cost, flexibility, and excellent capacitance and stability, this electrode is promising in application to high-performance flexible supercapacitors.