Study On Interlayer Regulation Of Vanadium Oxide Cathode Of Aqueous Zinc Ion Batteries

Aqueous zinc ion batteries（AZIBs）have become a new energy storage due to the advantages of high zinc abundance,low cost,high theoretical volume capacity and low oxidation reduction potential.Vanadium based oxides have become promising positive electrode materials for AZIBs due to their high theoretical mass specific capacity,high magnification,open layered skeleton structure,and excellent high current and long cycle stability.However,due to its low conductivity,the reaction kinetics are delayed,which reduces the rate performance.The unstable skeleton structure makes the positive electrode easy to collapse and dissolve,reducing its cycling stability.Based on this issue,the research work in this paper has improved the rate performance and cycling stability of vanadium oxide cathode materials through interlayer regulation strategies.The corresponding research results are as follows:（1）By introducing Na⁺ions（NVO）between the layers of hydrated vanadium oxide,the dissolution of the vanadium oxide positive electrode during the Zn²⁺insertion/removal process is effectively suppressed through the"pillar effect"of Na⁺ions,and increased the proportion of V⁴⁺through the introduction of Na⁺ions,thereby enhancing the conductivity of the material and improving the rate performance.NVO exhibit high rate performance(40 A g^-1,204 m Ah g^-1)and good cycle stability(10 A g^-1,358 m Ah g^-1 retains 72.1%capacity after 1500 cycles)as positive electrode materials for aqueous zinc ion batteries.Na⁺ion pre embedding has some effect on the electrochemical reaction kinetics of V₂O₅·n H₂O electrode materials.On the one hand,due to the removal of some structural water,the interlayer space of NVO decreases（1.08 nm）.However,during the Zn²⁺embedding process,water molecules from the electrolyte will enter the interlayer of NVO.The fully activated NVO interlayer spacing（1.30 nm）is actually greater than that of HVO（1.25 nm）.This portion of interlayer water is constrained by pre embedded Na⁺and exists in the form of Na（H₂O）_n⁺between vanadium oxide layers.The Na（H₂O）_n⁺support layer provides additional ion diffusion channels for Zn²⁺,allowing more Zn²⁺to diffuse into the internal structure.In addition,a large amount of interlayer water plays a"lubricating role"in the migration process of Zn²⁺ions,shielding the effective charge of Zn²⁺and establishing a smoother electrostatic environment.（2）The hydrated potassium vanadate（KVO）with similar crystal structure but lower interlayer water content was obtained by pre embedding K⁺ions which belong to the same alkali metal but have smaller hydration ionic radius and hydration enthalpy than Na⁺ions.By comparing the interlayer water content and structural changes of NVO and KVO,and the resulting electrochemical performance,we systematically explore the effect of interlayer water content on the electrochemical performance of layered vanadium oxide in the positive electrode of water-based zinc ion batteries.KVO has a capacity of 430 m Ah g^-1 at a current density of 0.2 A g^-1,and still maintains a capacity of 337 m Ah g^-1 after 100 cycles,with a capacity retention rate of 78%.After4000 cycles at a high current of 10 A g^-1,it still maintains a capacity of 203 m Ah g^-1,retaining 73.6%of the capacity.Obviously,KVO exhibits better cyclic stability than HVO and NVO.The interlayer water molecules have a certain impact on the electrochemical performance of hydrated vanadate（MVOH）.On the one hand,interlayer water expands the interlayer spacing of vanadium oxide and plays a role in shielding the effective charge of Zn²⁺,which is conducive to the rapid migration of Zn²⁺and significantly improves the rate performance of MVOH.On the other hand,after being filled with a large amount of interlayer water,MVOH with larger interlayer spacing will dissolve and collapse during the migration of Zn²⁺.Moreover,excessive interlayer water content will reduce the thermodynamic generation energy of water molecules and vanadium oxide layers,and some interlayer water will be irreversibly replaced by Zn²⁺,causing lattice distortion of vanadium oxide and blocking the migration channel of Zn²⁺.In addition,a large amount of interlayer water not only blocks the effective charge of Zn²⁺,but also blocks the effective charge of preembedded metal ions,weakening the electrostatic interaction between preembedded metal ions and vanadium oxide layers.These have caused irreversible decay in the cyclic life of MVOH.