Effect of fluorine doping and sulfur vacancies of CuCo₂S₄ on its electrochemical performance in supercapacitors

The intriguing features of copper cobalt sulfide (CuCo₂S₄), such as multiple Faradaic reactions and abundant valance states, enable it a promising electrode material for supercapacitors. However, the sluggish transfer kinetics of charges and the insufficient number of active sites hamper its practical application. Herein, an efficient strategy was proposed to boost the electrochemical performance of CuCo₂S₄ through a synergetic incorporation of F dopants and S vacancies. The induced effects of F dopant and S vacancy of CuCo₂S₄ (denoted as F-CuCo₂S_4−x) on the physical characteristics and the electrochemical behaviors were investigated systemically. Experimental results reveal that through introduction of F dopants and S vacancies in dominant lattice, the low oxidation state concentrations of Cu and Co species are boosted remarkably, which lead to the improved electric conductivity and the enhanced interfacial activities of F-CuCo₂S_4−x, and facilitate the reaction kinetics. The as-synthesized F-CuCo₂S_4−x exhibits the ultrahigh specific capacity of 2202.7 C g⁻¹ at 1 A g⁻¹, and the excellent capacity retention of 96.7% after 5000 cycles at 20 A g⁻¹. An asymmetric supercapacitor assembled with F-CuCo₂S_4−x and activated carbon as the positive and the negative electrodes, respectively, delivers the favorable energy density of 49.8 W h kg⁻¹ at 897.39 W kg⁻¹, as well as the long-term cycling lifetime. This study offers an effective strategy to optimize the transition metal compounds for electrochemical energy-storage devices.