Vanadium-Based Oxides/Carbon Composite As The Cathodes For Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries（ZIBs）stand out among many univalent or multivalent metal ion batteries because of their advantages including high safety,low cost,and environment friendliness,and which has been one of the most promising prospective energy storage devices.Vanadium-based oxides possess the large layer spacing and different oxidation states,which has been considered as a potential cathode for aqueous ZIBs.However,the electrochemical performance of vanadium-based oxides cathodes is still limited by the inherent issues,such as poor conductivity,structural degradation,and vanadium dissolution.The combination of carbon materials and vanadium-based oxides composites has proven an effective strategy by improving the electrical conductivity and alleviative structural degradation.In such cases,this thesis demonstrates the fabrication of vanadium-based oxides and nano-carbon composites via using different synthetic methods,and which as the cathodes for ZIBs exhibit the enhanced electrochemical performance owing to the improved electrical conductivity and the alleviative structural degradation.Its contents are as follows:（1）Carbon nanotubes intertwined porous vanadium oxide heterostructured microfibers（VMF/CNT）was constructed by employing a facile template strategy.Upon using as the cathode for ZIBs,the specific capacities of 435.4 mA h g^-1at 0.2 A g^-1 and 167.5 mA h g^-1 at 10 A g^-1 are achieved.In addition,the as-obtained VMF/CNT electrode exhibits a stable cyclic performance with a retention of 84%at a current density of 10 A g^-1after 1500 cycles.Various characterizations showed that the excellent electrochemical performance of the VMF/CNT composites can be attributed to the porous heterogeneous structure,the high electrical conductivity of CNTs,and the strong interaction between CNTs and VO₂-V₂O₅ microfibers.It can effectively promote the charge transfer kinetics during the activation and subsequent Zn²⁺insertion/desertion processes by improving the electrical conductivity and providing abundant sites.This work provides a simple and feasible method for the design and development of high-performance V₂O₅ cathodes for aqueous ZIBs.（2）The composite containing nitrogen-doped carbon dots and vanadium oxide（N-CDs/V₂O₃/NVO）was constructed by employing the rapid Joule heating method.When using as the cathode for ZIBs,the as-obtained N-CDs/V₂O₃/NVO composites yield a high specific capacity of 320 mAh g^-1 after 1000 cycles at 1 A g^-1.More notable,the specific capacity can be maintained at 138 mAh g^-1 after 5000 cycles at the high current density of 10 A g^-1.The excellent electrochemical performance of N-CDs/V₂O₃/NVO can be assigned to the incorporation of N-CDs,which can not only improve the conductivity of composites but also provide more active sites via increasing the specific surface area,consequently improving the specific capacity and cycling performance.This work provides a practical method for the rapid synthesis of carbon dots modified vanadium-based cathodes for the high performance aqueous ZIBs.（3）The composite of graphene/vanadium oxides（G/VO₂-V₂O₅）was synthesized through the carbothermal reduction reaction through the rapid Joule heat method.It shows that the as-obtained G/VO₂-V₂O₅composite obtains a specific capacity of 356.3 mAh g^-1 after 2500 cycles at the current density of 1 A g^-1,and even at the current density of 10 A g^-1,a high specific capacity of 169.5m Ah g^-1 after 10000 cycles can still be reached.The electrochemical characterizations unveil that the improved electrochemical performance can be attributed to the high conductivity and large specific surface area of graphene,which can effectively promote the charge transfer and simultaneously improve the structural stability of the composite.In addition,the mixed valence states of vanadium oxides in the composite can also provide a multi-electron reaction for Zn²⁺insertion/desertion,thus achieving an enhanced electrochemical performance.This work lays a foundation for the application of flash Joule heat technology in the field of ZIBs.