Preparation And Zinc Ion Storage Mechanism Study Of Vanadium Oxide/Sulfide Cathodes

With the development of renewable energies,including wind,solar,tidal,and geothermal energies,there is an urgent need for electrochemical energy storage devices to meet their requirements.Aqueous zinc ion batteries have attracted wide attention due to their advantages of high safety,environmental friendly,and high theoretical specific capacity of zinc(820 m Ah g^-1 and 5855 m Ah cm^-3).Compared with zinc anode,the development of high-performance cathode materials plays an important role in improving zinc storage performance.Among different types of cathode materials,vanadium-based cathode materials are favored by researchers because of their various vanadium valence states,diverse crystal structures and low cost.In this paper,we firstly take VO₂（B）as the research object and improve zinc storage performances through two strategies of in-situ electrochemical conversion under high potential and metal-oxygen bond pre-introduction.Furthermore,the heterostructure is constructed in situ by using the VS₄ precursor externally adsorbed oxygen to realize the obvious enhancement of the zinc storage cathodes.The details are as follows:（1）Firstly,the VO₂（B）nanorods with an aspect ratio of about 4.5 were prepared by solvothermal method.The electrochemical performance of VO₂（B）nanorods was tested in different voltage ranges,and it was found that the batteries had a good zinc storage performance in the large voltage range（0.3-1.8 V）.In order to study its zinc storage mechanism,X-ray diffraction,scanning electron microscopy,transmission electron microscopy,and X-ray photoelectron spectroscopy analysis were used.The results indicate that VO₂（B）is in situ converted to zinc vanadate hydrate（Zn₃（OH）₂V₂O₇·2H₂O）during the first charging process in the large voltage range.With the help of the in situ conversion mechanism,the battery has a zinc storage capacity of 330 m Ah g^-1(0.1 A g^-1)and high rate performance(10 A g^-1).（2）The tunnel structure of VO₂（B）can be directly used as the active sites for zinc ion storage,but the strong charge repulsion inhibits the Zn²⁺rapid diffusion.Under the conditions of similar ionic radii of W⁶⁺（0.06 nm）and V⁴⁺（0.058 nm）,the proposed tungsten-oxygen bonds pre-introduction strategy is used to regulate the tunnel structure of VO₂（B）to achieve fast and stable zinc ion storage.Then,VO₂（B）with different tungsten-oxygen bond content（0.5 at%,1.5 at%,and 3 at%）were synthesized by controlling the ratio of elements.Electrochemical test results showed that 1.5 at%tungsten-oxygen bond pre-introduced VO₂（B）exhibited excellent zinc storage capacity(265m Ah g^-1 at 0.1 A g^-1),rate performance(10 A g^-1),and cyclic stability(cycling for 2000cycles with 118 m Ah g^-1).Furthermore,structural and electrochemical analyses show that the tungsten-oxygen bond pre-introduced VO₂（B）can increase spacing layers and help stabilize the tunnel structure of VO₂（B）,which accelerate zinc ion diffusion,increase zinc storage capacity and cycle stability.The research on zinc storage mechanism shows that tungsten-oxygen bond pre-introduced VO₂（B）have a pseudocapacitance reversible Zn²⁺intercalation/de-intercalation mechanism.（3）Based on the exposure of vanadium sulfide to air,a nano-depth heterostructure layer will be formed on the surface.However,the near-surface heterostructure layer cannot change the zinc storage activity of the vanadium sulfide.In this work,VS₄/V₂O₃heterostructures were constructed through a facile operando heat treatment approach by the VS₄ extrinsic adsorbed oxygen.The VS₄/V₂O₃ heterostructure with high conductivity and the high chemical stability can improve the zinc storage activity,providing a zinc storage capacity of 164 m Ah g^-1 at 0.1 A g^-1.At the same time,through analyzing the kinetic testing,it is confirmed that the VS₄/V₂O₃ heterostructures have a Zn²⁺reversible intercalation/de-intercalation storage mechanism.