Fabrication And Modification Of Vanadate Homogeneous Interfacial Nanosheets For The Study Of Their Performance In Zinc Ion Batteries

A new challenge is being posed to the new energy system as the sales and ownership of new energy vehicles continue to soar,with"charging difficulties"becoming the focus.After years of development,the charging system has been basically built but not perfect,and the long charging time is still the main technical problem that needs to be solved.Aqueous zinc ion batteries（AZIBs）are an emerging type of energy storage battery.Because they use an aqueous electrolyte,which has a conductivity several orders of magnitude higher and higher safety than organic electrolytes,and use zinc as the negative electrode,they are inexpensive and require less assembly of energy materials,and therefore have great potential for rapid charge and discharge applications.Vanadium-based materials are expected to achieve high energy density fast charging capability in zinc ion batteries（ZIBs）due to their layered crystal structure and multi-electron redox mechanism.However,the fast charging capability is usually limited by surface-controlled pseudo-capacitance due to the poor diffusion kinetics of Zn²⁺within the material.To address these issues,we have worked to further enhance the conductivity and fast kinetics of vanadium-based materials in the following ways:（1）Firstly,we perform microstructural tuning by designing interfacial reactions to finally obtain sodium vanadate nanosheet arrays(Na V₈O₂₀·1.92H₂O)with homogeneous interfaces.The designed nanosheet structure allows the material to have open ion storage space,providing abundant active sites for electrochemical reactions while also allowing open migration paths for ion transport,thus improving the theoretical specific capacity and electrochemical reaction kinetics of the material;moreover,the nanosheets are easy to modulate in terms of surface modification,doping and defects,which is very beneficial for designing and improving the material properties.It has been shown that the homogeneous interface is easier to embed/detach ions than the surface,so that the homogeneous interface will first enrich a large amount of Zn²⁺during discharge,and the resulting difference in Zn²⁺concentration allows for rapid diffusion of Zn²⁺from the homogeneous interface to the interior.This allows the material to maintain its structural stability at large charge/discharge rates.Based on these advantages,the material was used as an anode material for ZIBs and showed excellent electrochemical performance.At 0.1 A g^-1 this electrode material provides a specific capacity of 370 m Ah g-1and at 0.5 A g^-1 it provides 335 m Ah g^-1.After 140 cycles the specific capacity of the cell is maintained at 327 m Ah g^-1 with a capacity retention rate of 97.6%.The battery also exhibits an initial specific capacity of 100 m Ah g^-1 and a capacity retention of 94.3%for 1550 cycles at a high current density of 10 A g^-1.This is superior to many of the V-based AZIBs that have been reported.To verify the generality of the preparation method,we also used Mn SO₄,Ca Cl₂,Co SO₄,Ni SO₄ and KCl as interfacial reaction substrates to prepare vanadate nanosheets with homogeneous interfaces.The preliminary characterisation of the physical and morphological features was carried out by SEM and XRD.The results show that the homogeneous interfacial vanadate nanosheets can be prepared by controlling the reaction temperature and time.Furthermore,the electrochemical properties of the vanadate nanosheets with homogeneous interfaces were compared and confirmed to exhibit better electrochemical properties.（2）Secondly,the two-dimensional structure with a homogeneous interface is easy to modulate in terms of surface modification,doping and defects,and to address this property,we have plasma etched the material to obtain an array of sodium vanadate nanosheets with graded N doping.As the homogeneous interface has a lower defect formation energy than the surface^[1],etching increases the number of accessible active sites while creating a gradient of N doping from the homogeneous interface to the surface,from high to low concentrations,which induces the formation of microelectric fields that further promote the electrical conductivity of the material;moreover,etching is accompanied by the creation of a large number of micropores that establish a shorter ion transport pathway,and these micropores are associated with the gradient N doping concentration induced microelectric fields,accelerating ion transfer in the shortened pathway.The synergistic effect of the homogeneous interface,gradient doping and mesoporous micropores greatly enhances the fast charge/discharge capability of the material.The modified material was used as a cathode material for ZIBs,providing a high specific capacity of 417 m Ah g^-1 at 0.1 A g^-1,maintaining a reversible capacity of 111 m Ah g^-1 in the 100 A g^-1 mega-current density multiplication test,and still recovering to 404 m Ah g-1 when returning to 0.1 A g^-1,showing excellent multiplication performance;and In the long cycle test at 100 A g^-1,a reversible capacity of 111 m Ah g^-1 was achieved,with a capacity retention rate of 68.4%at 50000 cycles of stability.The demonstrated electrochemical performance in the fast-charging area is superior to all reported vanadium-based zinc ion batteries.