Study On Vanadate As Anode Materials For Aqueous Zinc Ion Batteries

Aqueous battery refers to the secondary battery with aqueous solution as electrolyte,which has attracted extensive attention from researchers because of its low cost,high safety factor,excellent electrochemical performance,and environmental friendliness.According to the classification of ions migrated during the working process of the battery,aqueous batteries can be divided into aqueous monovalent ion batteries and aqueous multivalent ion batteries,which have become a research hotspot due to the large number of charges transferred by polyvalent ions and higher energy density.Compared with water-based magnesium-ion batteries and water-based aluminum-ion batteries,which are easy to produce passivation films,aqueous calcium-ion batteries have too large calcium ion radius,which is suitable for less intercalation materials,aqueous zinc-ion batteries stand out in aqueous polyvalent ions.However,the current research on aqueous zinc-ion batteries mainly focuses on cathode materials,and reports on anode materials are relatively limited.Therefore,this paper takes the negative electrode material as the research content,prepares vanadate anode materials with different ion intercalation,investigates its electrochemical performance,combines characterization methods and electrochemical tests,explores the optimal synthesis conditions and electrolyte,and studies the reaction mechanism of the electrode in the working process.The main research contents of this paper are as follows:Using Na₃VO₄ as raw material,Na₂V_6.5O₁₆·3H₂O nanosheets were synthesized by one-step hydrothermal method,and it was found that the material morphology obtained by the reaction for 24 h at 120°C temperature is uniform,the nanosheets were thin and no agglomeration,the specific surface area of the material was large,and the contact with the electrolyte is sufficient,which was conducive to Zn²⁺intercalation and had excellent electrochemical performance.In the electrochemical test of 2 mol L^-1 Zn SO₄ electrolyte,when the current density is 1000 m A g^-1,the specific discharge capacity of the first turn is265.9 m Ah g^-1,and after 240 cycles,the discharge specific capacity can still reach 263.4 m Ah g^-1.The rate performance under different current densities is tested,and when the large current density returns to the small current again,the discharge specific capacity can almost return to the original size,indicating that the material has excellent rate performance.Combined with kinetic testing,XRD and XPS analysis,the intercalation mechanism of Zn²⁺in the material was obtained,and the Zn²⁺intercalation was accompanied by the valence changes of V⁵⁺/V⁴⁺and V⁴⁺/V⁵⁺.Combined with the structural characteristics of vanadate,the vanadate of Na⁺and H⁺co-intercalation is designed by adjusting p H,and the layered structure of vanadate adjusted by metal ion and non-metal ion coinsertion synergy and the support of water combined with water was used to improve the stability and electrochemical performance of the material.Among them,when the reaction temperature is 200°C and the reaction time is 24 h,the XRD diffraction peak of Na HV₆O₁₆·4H₂O is the sharpest and strongest,the crystallinity is the best,the degree of agglomeration between nanosheets is the smallest,and there are large voids,showing excellent cycling performance and rate performance.The specific discharge capacity of the material is 509.8 m Ah g^-1 for the first time,and the discharge specific capacity is 411.6m Ah g^-1 when cycling to 300 cycles.Combined with the analysis of XPS and XRD results,the Zn²⁺embedding removal process is accompanied by the conversion between the three valence states of V⁵⁺,V⁴⁺,and V³⁺.