Structural Regulation Of Vanadium Oxide For Aqueous Zinc Hybrid-Ion Battery

With the gradual increase of human demand for energy,the disadvantages of traditional energy are gradually exposed.Resource problem,environmental pollution,energy efficiency and cost limit the use of traditional energy sources.In order to find alternatives to traditional energy,research and development of new energy has become the common goal of all countries.The widespread use of lithium batteries has made battery storage the key to the large-scale development of renewable energy.Polyvalent ion batteries,represented by water-based zinc ion batteries,have become the focus of secondary battery research in recent years because of their rich resources,low cost,simple operation,high energy density and safety and no pollution.As an important part of the battery,the selection of electrode materials determines the energy storage performance of the battery to a great extent.However,one of the major obstacles hindering the development of water Zn²⁺batteries is the lack of cathode materials capable of reversible Zn²⁺embedding/deembedding.Due to its advantages of large theoretical capacity,diverse crystal structure,abundant resources and low cost,vanadium-based oxides have become the focus of research on electrode materials for water zinc ion batteries.Although most vanadium-based compounds have poor electrical conductivity,their properties can be regulated by effective engineering strategies.In this paper,three vanadium based materials（NH₄）₂V₇O₁₆,PANI-V₂O₅ and V₃O₅ were prepared,and their zinc ion storage properties were studied respectively.The（NH₄）₂V₇O₁₆ material has a two-dimensional layered structure,and the layer spacing is 0.91 nm.The larger layer spacing can effectively improve the diffusion coefficient of Zn²⁺.Meanwhile,the mixed valence vanadium can improve the electrical conductivity of the material.The（NH₄）₂V₇O₁₆ material was synthesized by hydrothermal method in one step and applied to water zinc ion cathode material.At the current density of 0.1 A g^-1,the specific capacity was 452.4 m Ah g^-1,and at the high current density of 5 A g^-1,the capacity retention rate was 91%after 1500 cycles.GITT and DFT calculations demonstrate the rapid diffusion kinetics of Zn²⁺.Due to the dissolution of vanadium,the stability of vanadium compounds is poor,while organic compounds are relatively stable.Based on the above problems,polyaniline intercalated vanadium pentoxide was synthesized by hydrothermal method and its zinc storage performance was studied.V₂O₅ shows a specific capacity of 110.9m Ah g^-1 at the current density of 0.1 A g^-1,while the specific capacity after PANI intercalation can reach 319.6 m Ah g^-1.The significant improvement of performance is mainly attributed to the fact that the intercalation of PANI expands the V₂O₅ layer spacing,improves the diffusion kinetics process of Zn²⁺,alleviates the volume change of Zn²⁺embedding/deembedding process,and increases the stability of the material.On the other hand,EIS results show that the intercalation of polyaniline improves the electrical conductivity of V₂O₅ and promotes electron transfer.In the process of charge and discharge,the ion embedding/deembedding and electrolyte often react partly,which results in the transformation of electrode material structure,especially in the water system electrolyte.In general,the by-products generally do not have electrochemical activity,and some of the by-products are even better than raw materials in electrochemical performance.According to this phenomenon,V₃O₅ material was synthesized by solid phase sintering.The crystal structure of V₃O₅ is not suitable for use as electrode material.As the electrode material,the capacity of V₃O₅ is only 60 m Ah g^-1 at the current density of 0.1 A g^-1,and the damage occurs after 90 cycles at low current density.However,its capacity increases sharply(436.5 m Ah g^-1)after phase transition under high voltage,and its cycling stability is greatly improved.The phase change materials(Zn₃（OH）₂V₃O₇·2H₂O,V₁₀O₂₄·12H₂O)have better zinc storage performance,which expands the voltage window of the battery from the side and is more conducive to the storage of zinc ions.