Design And Construction Of Vanadium Based Materials And Their Application In Secondary Batteries

The vanadium element in the vanadium-based material has a variety of valence in the chemical reaction process,which can realize the redox reaction with multielectrons transfer.At the same time,vanadium-based compounds have rich crystal structures,which can be embedded in guest ions without damaging the main structure of the material.Recently,vanadium-based materials have been extensively studied in various battery systems for lithium-ion batteries and polyvalent ion batteries.However,vanadium-based materials still have problems such as low ion conductivity and unclear reaction mechanism in the electrochemical process.In this paper,vanadate and vanadium oxide materials are selected as the sugjects.The lithium storage performance of vanadate materials is improved by carbon coating,phosphating and other modification methods,and the lithium storage mechanism is explored;the electrochemical method is used for the in-situ structure transformation of vanadium oxides,which could improve its zinc storage performance.Meanwhile,the transformation mechanism and electrochemical reaction mechanism are also studied.The specific research contents of this paper are as follows:1.Phosphorous containing Fe₂VO₄ nitrogen-doped carbon coated mesoporous nanowires are synthesized by a multi-step method with hydrothermal reaction,in-situ polymerization of dopamine,and phosphating process.The phosphorus doping not only alleviates the overall charge transfer reaction kientics of active material,but also covalently“bridge”the carbon layer and Fe₂VO₄ through P-C and Fe-O-P bondings.Density functional theory（DFT）calculations indicate that the P dopant enables the favorable electronic structure of the active material.With the combined advantages of highly accessible surface(hierarchical mesoporous nanowire with a high surface area of97 m² g^-1),highly conductive network（N,P-codoped carbon coating）,reduced charge transfer resistance（P doping and one dimensional nanostructure）,and robust structure stability.P-Fe₂VO₄/NCMNWS material shows excellent electrochemical performance of lithium storage:The electrode materials have discharge specific capacities of 550,486and 282 m A h g^-1 at 0.5,5 and 10 A g^-1,respectively,and maintain 1002,533 and 364m A h g^-1 after 250,500 and 1000 cycles.All of the results revealed that the strategy reported here may pave a new way for realizing an improvement in energy storage field.2.The flexible hydrated zinc vanadium oxide/carbon cloth（Zn VOH/CC）was obtained by the in-situ transformation of hydrated zinc vanadium oxide/carbon cloth（VOH/CC）during the electrochemical process.The H⁺and Zn²⁺co-insertion reaction mechanism is observed for the active materials,which finally lead to the phase transition from VOH to Zn VOH.The unique advantage for the structure could be principally demonstrated as follows:（I）the porous texture of CC and 2D nanosheet morphology of the active materials allows the sufficient penetration of electrolyte and rapid transfer of electron/ionic;（II）the existence of structural water and lattice defects increases the conductivity and reaction sites of the active materials,realizing the high intercalation pseudocapacitive charge storage;and（III）the binding force between active materials and CC is strong,reducing the aggregation and dissolution of the active materials.Based on these synergetic effects,the Zn VOH/CC exhibits a high discharge capacity of 337 m A h g^-1 at 1.0 A g^-1,as well as an ultra-stable reversible capacity of 135 m A h g^-1 at 20 A g^-1after 5000 cycles.Particularly,when the Zn VOH/CC was assembled with Zn/CC anode,this flexible device also presents superior rate capability and cycling durability(184 m A h g^-1 at 10 A g^-1 after 170 cycles).The battery could also work normally under folded and punched condition,indicating its superior flexibility and safety.This work reports a reliable in-situ electrochemical conversion strategy to construct novel flexible electrode as ZIBs cathode,which could guide the electrode material design for next generation ZIBs.