Large-scale Co9S8@C hybrids with tunable carbon thickness for high-rate and long-term performances of an aqueous battery

Abstract

To realize high-rate and long-term performances of an aqueous rechargeable battery, the most effective approach is to build electrode materials with more reaction active sites and stable structures. Transition metal sulfides have become up-and-coming electrodes due to their high conductivity. Herein, we demonstrated the in situ construction of core–shell Co₉S₈@C materials with controlled carbon content and thickness. Nanorod-like cobalt–organic chelates were used as the precursors. The cobalt in cobalt–organic chelates reacted with sublimed sulfur to generate the Co₉S₈ core in situ; meanwhile, the organic chelates were converted into carbon shells, which coated the Co₉S₈ core and connected with each other to maintain the whole rod shape. Moreover, tunable thickness and content of the carbon shell in the Co₉S₈@C composite could be achieved by regulating the composition of the reaction solvent. In addition, when 20 mL of dimethylcarbinol was used, the obtained Co₉S₈@C composite (H1) exhibited the most excellent electrochemical performances, in particular outstanding cycling stability. When assembled with a treated iron powder (TIP) electrode, the Co₉S₈@C//TIP aqueous rechargeable battery delivered 220.7 mA h g⁻¹ discharge capacity at 1 A g⁻¹, which decreased to 152.8 mA h g⁻¹ even when the current density was increased by a factor of ten (10 A g⁻¹), indicating surprising high-rate performance. Also, after 5000 cycles at 10 A g⁻¹, 74.8% of capacity retention was obtained, further illustrating its excellent long-term cycling stability. Suitable electrode materials with a tunable carbon content have direct impact on the overall performance of an aqueous rechargeable battery, which will guide us for obtaining high-rate and long-term aqueous batteries.