Preparation Of Vanadium Oxide And Nitride And Its Application In Aqueous Zinc Ion Batteries

Aqueous zinc ion batteries has broad application prospect in large-scale energy storage field in the future.Vanadium-based materials as cathode materials of zinc ion battery has advantages in theoretical specific capacity and structural characteristics,but there are still many problems to be solved in practical application.In this paper,aiming at the current problems of vanadium-based materials with low actual specific capacity,poor electrical conductivity,poor cycle stability and controversial zinc storage mechanism,the methods of synergistic effect between vanadium oxides,composite of vanadium oxides or nitrides and carbon-based materials,and N-doped technology are used to improve the zinc storage performance of vanadium-based materials.In addition,the zinc storage mechanisms of electrodes are studied by ex-situ characterization techniques to provide theoretical basis for the design and optimization of electrode materials.The details are as follows.（1）Based on V₃O₇/V₂O₅ composite materials,it is demonstrated that Zn_xV（H₂O）₆（H₅O₂）（CF₃SO₃）₄ is formed when Zn²⁺inserted into vanadium oxide in Zn（CF₃SO₃）₂ electrolyte.In addition,the synergistic action of V₃O₇ and V₂O₅ can promote the reduction of vanadium（Ⅳ）and vanadium（Ⅴ）to vanadium（Ⅲ）,thus significantly increasing the specific capacity of the electrode.The V₃O₇/V₂O₅ electrode has 96.2%capacity retention and225 m A h g^-1 specific capacity at 2 A g^-1 after 1120 cycles,and 82.6%capacity retention and 176 m A h g^-1 specific capacity at 5 A g^-1 after 6500cycles.（2）V₂O₃@amorphous carbon（V₂O₃@AC）is used as the cathode materials of zinc ion battery in ZnSO₄ electrolyte system.Amorphous carbon improves the conductivity of V₂O₃@AC materials,and provides good electron and ion channels for V₂O₃@AC electrode.By studying the zinc storage mechanism of V₂O₃@AC electrode,it is found that V₂O₃ is oxidized to V₁₀O₂₄·12H₂O when the electrode is charged for the first time,and then V₁₀O₂₄·12H₂O is used as the active material for zinc storage.In addition,the insertion of zinc ion is accompanied by zinc salt deposition,and amorphous carbon can provide more space for the deposition process to maintain the electrode structural stability.The V₂O₃@AC electrode can maintain 94.8%capacity retention and 217 m A h g^-1 specific capacity after180 cycles at 0.1 A g^-1 current density,and 90.7%capacity retention and116 m A h g^-1 specific capacity after 1600 cycles at 1 A g^-1 current density.（3）V₂O₃@C-PE is prepared by reducing ammonium metavanadate（NH₄VO₃）with polyethylene（PE）.A large number of pore structures is produced during PE pyrolysis,and the V₂O₃ agglomeration is inhibited by the combination of reduced V₂O₃ and PE carbon.In ZnSO₄ electrolyte,the specific capacity of V₂O₃@C-PE electrode reaches 393 m A h g^-1 at current density of 0.1 A g^-1.After 1600 cycles at 20 A g^-1,the capacity retention is97.3%and the specific capacity is 223 m A h g^-1.In addition,the V₂O₃@C-PE electrode is oxidized to V₅O₁₂·6H₂O when first charged and subsequently stores zinc in this form.（4）Nitrogen doped aluminum-vanadium oxide（AlVO-N）is prepared by using ammonia（NH₃）as reducing agent and nitrogen source.The addition of N atom inhibits the agglomeration of AlVO-N in the reduction process and maintains the diffusion of zinc ions at a high level.The AlVO-N electrode stores zinc in the form of Zn_xV₅O₁₂·6H₂O.At the current density of 1 A g^-1,the specific discharge capacity of the AlVO-N electrode is 224 m A h g^-1 and the capacity retention is 94.5%after 350 cycles.At the current density of 20 A g^-1,the capacity retention of the electrode remains above 90%after 9000 cycles.（5）VN@rGO composite is prepared by modifying industrial vanadium nitride（VN）with reduced graphene oxide（rGO）.The rGO significantly improves the electron and ion transport characteristic of VN,which enables VN@rGO electrode to have higher capacitance contribution and more stable zinc ion diffusion coefficient.The specific capacity of VN@rGO electrode is 267.0 m A h g^-1 and the capacity retention is 94.68%after 585 cycles at 1 A g^-1 current density.And at 20 A g^-1 current density,the specific capacity of 125.6 m A h g^-1 and the capacity retention of 91.24%is obtained after 10900 cycles.When the VN@rGO electrode is first charged,VN is oxidized to V₅O₁₂·6H₂O,and zinc is stored in this form thereafter.（6）Vanadium nitride@nitrogen doped graphite（VN@NGr）is prepared by using dicyandiamide（DCDA）as nitrogen source and glucose as carbon source in nitrogen（N₂）atmosphere.NGr improves the electron and ion transport characteristic of VN,and alleviates the volume expansion when zinc ions inserted into the active materials.Hence,VN@NGr electrode has excellent rate performance.It has～100%capacity retention after 1000 cycles at 1 A g^-1 current density after the rate test,and above 70%capacity retention after 26000 cycles at 20 A g^-1.After the first cycle of VN@NGr electrode,VN is converted to Zn₃（OH）₂V₂O₇·2H₂O,and zinc is stored in this form.