Ultrathin and Porous Ni3S2/CoNi2S4 3D‐Network Structure for Superhigh Energy Density Asymmetric Supercapacitors

Abstract 3D‐networked, ultrathin, and porous Ni 3 S 2 /CoNi 2 S 4 on Ni foam (NF) is successfully designed and synthesized by a simple sulfidation process from 3D Ni–Co precursors. Interestingly, the edge site‐enriched Ni 3 S 2 /CoNi 2 S 4 /NF 3D‐network is realized by the etching‐like effect of S 2− ions, which made the surfaces of Ni 3 S 2 /CoNi 2 S 4 /NF with a ridge‐like feature. The intriguing structural/compositional/componental advantages endow 3D‐networked‐free‐standing Ni 3 S 2 /CoNi 2 S 4 /NF electrodes better electrochemical performance with specific capacitance of 2435 F g −1 at a current density of 2 A g −1 and an excellent rate capability of 80% at 20 A g −1 . The corresponding asymmetric supercapacitor achieves a high energy density of 40.0 W h kg −1 at an superhigh power density of 17.3 kW kg −1 , excellent specific capacitance (175 F g −1 at 1A g −1 ), and electrochemical cycling stability (92.8% retention after 6000 cycles) with Ni 3 S 2 /CoNi 2 S 4 /NF as the positive electrode and activated carbon/NF as the negative electrode. Moreover, the temperature dependences of cyclic voltammetry curve polarization and specific capacitances are carefully investigated, and become more obvious and higher, respectively, with the increase of test temperature. These can be attributed to the components' synergetic effect assuring rich redox reactions, high conductivity as well as highly porous but robust architectures. This work provides a general, low‐cost route to produce high performance electrode materials for portable supercapacitor applications on a large scale.