关键词: 二氧化锰, 碳纳米纤维, 锌离子电池, 水热法, 阴极

Abstract: The growing environmental concerns and energy consumption are driving an ever-increasing pursuit for advanced energy storage system with high energy density, environmental friendliness, and high safety. Although lithium-ion batteries (LIBs) dominate the battery market due to their light weight, high energy density, and long cycle life, the application of LIBs as large-scale energy storage systems has been plagued by the safety issues and environmental problems associated with flammable organic electrolytes. In recent years, aqueous rechargeable batteries, which feature high safety, eco-friendliness, and high ion conductivity of water-based electrolyte have been considered as promising alternatives to overcome these dilemmas. Rechargeable zinc-ion batteries (ZIBs) are in the spotlight of grid-scale electrical energy storage owing to the advantages of aqueous electrolyte and Zn metal anode. Manganese-based materials are often used as cathode materials for zinc ion batteries (ZIBs), which have the advantages of high theoretical capacity, low cost, low toxicity and various valence states. However, inherent poor conductivity, sluggish zinc ion diffusion kinetics and terrible rate performance limit their practical application.
MnO2 was combined with carbon nanofibers to improve its electrical conductivity. The dissolution of MnO2 in charge and discharge process is alleviated by designing the microcore-shell structure. Carbon nanofibers were successfully prepared by electrospinning and annealing, and then KMnO4 was reduced to MnO2 on the surface of carbon nanofibers by wet chemical method. At the current density of 0.1 A/g, the prepared C@MnO2 still has a capacity retention rate of 83% after 100 cycles, and can provide respectable specific capacity of 163.89 mAh/g. The excellent long cycle performance of this material is attributed to the synergistic action of carbon nanofibers and MnO2. The conductive carbon nanofibers act as the skeleton to promote the electron transfer kinetics, while the MnO2 nanosheets improve the contact area between the active material and the electrolyte, promoting the Zn2+ diffusion. In addition, MnO2 is closely connected with carbon nanofibers, forming a complete and uniform structure and alleviating the volume change and dissolution of MnO2 in the charging and discharging process to the greatest extent.
In summary, MnO2 was successfully grown on the surface of carbon nanofibers by hydrothermal method as the cathode for rechargeable aqueous zinc-ion batteries. The results of this experiment show that this structure is conducive to the charge transfer dynamics and cycle stability of zinc ion batteries. Considering the simplicity of fabrication, rational design of hierarchical core–shell architecture for synergism and exceptional electrochemical performance, the C@MnO2 will be a highly promising cathode candidate for low-cost and high-performance aqueous rechargeable aqueous zinc-ion batteries.

Key words: MnO2, carbon nanofiber, zinc-ion batteries, hydrothermal method, cathode