Nitrogen-doped graphene encapsulated cobalt iron sulfide as an advanced electrode for high-performance asymmetric supercapacitors

Abstract

To develop supercapacitors (SCs) with high energy and power densities, a new type of electrode material with unique properties is strongly required. Metal sulfides (MSs) have been recently studied as promising electrode materials for high-performance SCs because they have excellent redox properties, outstanding electrical conductivity, exceptional catalytic activity, and ultra-high specific capacity. However, their large volume changes and poor rate performances seriously hinder their commercial applications. Herein, a novel nitrogen-doped graphene encapsulated cobalt iron sulfide core–shell (Co₈FeS₈@NG) hybrid was successfully synthesized through a facile, scalable, and single-step in situ hydrothermal technique. The hierarchical core–shell Co₈FeS₈@NG hybrid was employed as an advanced electrode material for high-performance solid-state asymmetric SCs (ASCs). The Co₈FeS₈@NG electrode delivers an ultra-high specific capacitance of ∼1374 F g⁻¹ at a current density of 2 A g⁻¹, with tremendous rate capability (∼71.69% of capacitance retention at 40 A g⁻¹) and excellent cycling stability (∼96.1% of capacitance retention after 10 000 cycles). Furthermore, the assembled Co₈FeS₈@NG//FeS@NG ASC device exhibits an ultra-high energy density of ∼70.4 W h kg⁻¹ at a power density of 0.598 kW kg⁻¹, exceptional power density (∼22.55 kW h kg⁻¹ at 49.5 W h kg⁻¹), and outstanding cycling stability (∼93.7% of initial capacitance after 10 000 cycles). Therefore, these results demonstrate a simple and cost-effective route for the development of new types of NG encapsulated ternary MSs for future electronics.