Necklace-like CNT-Co9S8@C-CNT for high-performance zinc-ion batteries

Abstract

Metal sulfide-based cathode materials for aqueous zinc ion batteries (AZIBs) suffer from high Zn²⁺ diffusion energy barrier and sluggish diffusion kinetics issues, leading to poor rate capability and cycle life. Herein, we have designed a “jeweled necklace”-like hybrid composite comprising cobalt sulfide encapsulated within carbon as “beads” and a carbon nanotube (CNT) as the “string” to form an open-ended porous CNT-Co₉S₈@C-CNT composite as a high-performance ZIB cathode. The open-ended hierarchical porous CNT possesses high surface area and porosity, which endow the CNT-Co₉S₈@C-CNT composite with good electronic and ionic conductivity. Moreover, the CNT-Co₉S₈@C-CNT cathode exhibits superior control over the structural strain that occurred during the repeated fast Zn²⁺ (ex)insertion, thereby maintaining structural stability. Therefore, CNT-Co₉S₈@C-CNT exhibits an inspiring high discharge specific capacity of 302.7 mA h g⁻¹ and a coulombic efficiency (CE) close to 100% after 5000 cycles. Furthermore, the zinc ion storage mechanism in the CNT-Co₉S₈@C-CNT cathode is investigated through multiple ex situ characterization experiments and density functional theory (DFT) calculations. The assembled flexible AZIB also exhibits excellent flexibility and thermostability. This study provides new insights for the design of advanced cathode materials for AZIBs.