The Modification Of Vanadium-based Layered Oxides And Their Application In Aqueous Zinc Ion Battery

As a response to the national"carbon peaking and carbon neutrality goals",it is essential to develop new and efficient energy storage systems to match clean energy generation,and electrochemical energy storage systems are widely preferred because of their high flexibility and high specific energy.The aqueous zinc-ion battery is an alternative to the Li-ion battery in existing electrochemical energy storage systems due to its eco-friendliness,affordability,safety,and ultra-high adaptability to aqueous electrolyte.However,the insertion and extraction process of Zn²⁺in the cathode material is greatly affected by electrostatic interactions,and high capacity and long cycle time cannot be achieved.Therefore,the main problem facing aqueous Zn-ion batteries now is the development of suitable cathode materials.Vanadium-based oxides have attracted the attention of researchers due to their oxidation-reduction valence diversity,stable layered structure for easy de-embedding of zinc ions and high theoretical specific capacity,as well as the abundance of vanadium metal in the natural environment.However,conventional vanadium-based oxides suffer from low electrical conductivity,poor reversibility,and slow diffusion kinetics,which cannot meet the high requirements of aqueous zinc ion batteries.In order to solve the above intrinsic defects of vanadium oxides,this paper aims to improve the practical application of vanadium-based oxides in aqueous zinc ion batteries by improving the material phase composition and crystal structure,and regulating the microscopic morphology through a multi-faceted synergy based on vanadium pentoxide with a stable layered structure,and addressing the problems that arise in the electrochemical reaction stage.Physical phase characterization,morphological analysis,electrochemical testing,and theoretical calculations are used to gain a deep understanding of the material zinc storage mechanism.The main work of this paper is as follows:1.To overcome the problem that the tightly packed layer structure of vanadium pentoxide is not conducive to zinc ion de-embedding,electrochemical lithium insertion is achieved by pre-discharging V₂O₅ in lithium-ion batteries to obtain lithium-ion pre-embedded vanadium oxide（LVO）with a tunable phase structure.By combining the reversibility of the LVO phase during the discharge process,the depth of discharge can be adjusted to vary the amount of lithium ions embedded to obtain a lithium-inserted vanadium oxide material with a reversible structure and optimal layer spacing.This LVO phase has a larger layer spacing,which facilitates the reversible de-embedding of zinc ions in the layer structure and allows for improved diffusion kinetics of zinc ions in the cathode material.2.In order to overcome the effects of electrostatic interactions on the unembedding of zinc ions in the interlayer structure of vanadium pentoxide,potassium ion-inserted vanadium oxide（KVO）materials with different amounts of potassium ion insertion were synthesised by a simple one-step hydrothermal method.The layer spacing（9.35（?））of the KVO material is significantly increased compared to the conventional vanadium oxide（5.77（?））,which is more suitable for the interlayer transport of zinc ions.The reconstructed KVO material tends to have a short nanorod-like morphology in contrast to the vanadium pentoxide with large stacked morphology,and this short nanorod-like structure can provide more abundant reaction sites for zinc ion insertion/extraction,in addition to the nanostructure can provide a shorter ion transport path.Meanwhile,the low desolvation energy of K can easily leave the interlayer space during the reaction,providing additional active sites for the electrochemical reaction.As a result,this KVO cathode with larger interlayer spacing and better morphology structure has a specific capacity of more than 400m Ah g^-1 at a current density of 0.1 A g^-1 and a stable cycle life of more than 4000 cycles at10 A g^-1.3.The one-dimensionality and planarization of the electrode materials lead to insufficient overall material utilization and the vanadium-based materials are prone to dissolve in the electrolyte,resulting in lower capacity and poorer cycle life of the material.For this reason,a new type of three-dimensional V₆O₁₃ nanoflower-like material（VONs）with large specific surface area were synthesized by a solvent thermal combined with carbon reduction method.The solubility of V₆O₁₃ in the electrolyte is greatly suppressed thanks to the reduction of orthorhombic V₂O₅ to monoclinic crystal system V₆O₁₃ during the reaction of carbon.The inherent open structure and mixed multivalent states of tunneled V₆O₁₃ are the main advantages to achieve rapid Zn²⁺diffusion and increased electronic conductivity.Meanwhile,the large specific surface area is more favorable for the contact between the electrode material and electrolyte,while providing more Zn ion diffusion paths and reactive sites.In addition,the mechanism and kinetics of Zn²⁺storage and diffusion in VONs were investigated by combining density flooding theory（DFT）calculations with experimental data.This in-situ phase transition preparation strategy provides a new idea to inhibit vanadium oxide dissolution and improve its performance in AZIBs.