AUTHOR=Dong Mingxia , Wang Zhixing , Wang Jiexi , Guo Huajun , Li Xinhai , Yan Guochun TITLE=Controlled Synthesis of NixCoyS4/rGO Composites for Constructing High-Performance Asymmetric Supercapacitor JOURNAL=Frontiers in Materials VOLUME=6 YEAR=2019 URL=https://www.frontiersin.org/journals/materials/articles/10.3389/fmats.2019.00176 DOI=10.3389/fmats.2019.00176 ISSN=2296-8016 ABSTRACT=

Nickel-cobalt sulfides (Ni_xCo_yS₄) are promising supercapacitor materials due to their high capacitance, while the sluggish kinetics in terms of charge transfer limits their energy density. To achieve both high energy and power density for the Ni_xCo_yS₄–based supercapacitor, sulfur-doped reduced graphene oxide (rGO) is incorporated into Ni_xCo_yS₄ by an in situ growth—ion exchange strategy to synthesize Ni_xCo_yS₄/rGO composites. Profited from the synergetic effect between rGO and Ni_xCo_yS₄, the Ni_1.64Co_2.40S₄/rGO electrode delivers high specific capacitance of 1,089 F g⁻¹ at 1 A g⁻¹, and remains 92.6% of its original capacitance at 20 A g⁻¹ (1,008 F g⁻¹). Asymmetric supercapacitors assembled with active carbon (AC) and Ni_1.64Co_2.40S₄/rGO (Ni_1.64Co_2.40S₄/rGO//AC) offer both high specific capacitance (265.5 F g⁻¹ at 1 A g⁻¹) and superior rate capability at 50 A g⁻¹ (recovering 63.6% of the capacitance determined at 1 A g⁻¹). In addition, the assembled device exhibits a high capacitance retention of 92.6% after 10,000 cycles at 10 A g⁻¹, which implies an excellent cyclic stability. Ragone plot reveals that the energy density of Ni_1.64Co_2.40S₄/rGO//AC asymmetric supercapacitor do not vanish as it delivers 30.4 Wh kg⁻¹ at 10 kW kg⁻¹, demonstrating its promising application.