Fluorine-activation driving surface reconstruction on CoNi nanoparticles for high-energy supercapacitors

Maximizing the effective surface area with high reactivity is vital but still a challenge to electrode materials for high-energy supercapacitors. Herein, we demonstrate a fluorine-driving reconstruction strategy to synthesize ultrathin nanosheets on the CoNi nanoparticles with abundant M-F bonds by a simple molten-salt method. Ex-situ surface characterizations reveal that M-F bonds can trigger the surface transformation to generate abundant M-OH groups during electrochemical activation, endowing with greatly enhanced surface reactivity. The resultant activated sample (F-CoNi-A) can deliver an ultrahigh specific capacitance of 2476 F g(-1) at 1 A g(-1) and a capacitance retention of 86.8% after 10,000 cycles at 10 A g(-1), which is almost the best results for the pesudocapacitance-dominated electrode materials to date. After assembling into an asymmetric supercapacitor with active carbon, an energy density of up to 75.2 Wh kg(-1) is achieved at a power density of 0.8 kW kg(-1). (C) 2021 Elsevier Ltd. All rights reserved.