In-situ growth of series-connected CoNi2S4 hollow nanocages strung by carbon nanotubes for high-performance hybrid supercapacitors

Abstract

For supercapacitors (SCs), there is an urgent need to develop positive materials with excellent electrochemical performance. In this work, in-situ growth of series-connected CoNi₂S₄ hollow nanocages derived from zeolitic imidazolate framework-67 (ZIF-67) and strung by carboxylated carbon nanotubes (C-CNTs) were successfully synthesized through a two-step ordered ion etching/exchange procedure. The special connection structure and synergistic effect between CoNi₂S₄ nanocages and C-CNTs greatly improve the electrochemical performance of the hybrid (CoNi₂S₄/C-CNTs), in which porous CoNi₂S₄ hollow nanocages offer electrochemical active sites and fast ion diffusion channels, while C-CNTs provide electron transport paths. The optimized hybrid, CoNi₂S₄/C-CNTs20, exhibits excellent electrochemical performance with a high specific capacity (1314.6C g⁻¹ at 1 A g⁻¹) and an impressive rate capability (72.1 % retention at 20 A g⁻¹). Furthermore, the hybrid supercapacitor (HSC) using CoNi₂S₄/C-CNTs20 and active rice husk carbon (ARHC) as the positive and negative electrodes, respectively, demonstrates an outstanding energy density of 47.9 Wh kg⁻¹ at a power density of 800 W kg⁻¹ and remarkable cycling stability of 90 % at 5 A g⁻¹ after 8500 cycles. Our work will open up a brand-new strategy to oriented design electrode materials for various energy storage devices.