Preparation Of Vanadium-based Cathode Materials And Their Application In Aqueous Batterie

Because of the advantages of high security,low cost and environmental protection,as well as the unique advantages of hydrogen ion carrier in small ionic radius and high ionic conductivity,the aqueous hydrogen-ion battery is one of the promising aqueous battery systems.At present,the research of aqueous hydrogen-ion batteries is still in a relatively early stage,and there are few positive electrode materials for hydrogen storage.Vanad-based oxides have many attractive properties,such as abundant valence states,abundant ion storage sites and diverse crystal structures.However,the microsolubility of vanad-based oxides,especially V₂O₅,leads to the collapse of crystal structures during charge/discharge process,which leads to the decline of reversible capacity and cyclic stability of the material.In order to overcome this problem,three vanad-based cathode materials were prepared by pre-embedding guest ions（K⁺,NH₄⁺,etc.）or structural water molecules in the electrode materials,and their electrochemical performance and energy storage mechanism were studied.The main research contents of this dissertation are as follows:（1）K⁺is preembedded between the V₂O₅ bilayer by hydrothermal method,and the"sandwich"structure of K_0.48V₂O₅ electrode material is obtained.The nanorod structure of K_0.48V₂O₅provides abundant active sites for the adsorption and reaction of H₃O⁺,and can work well in low concentration acidic electrolyte(0.01 mol L^-1 H₂SO₄).At a current density of 50 m A g^-1,K_0.48V₂O₅ provides high proton storage capacity of approximately 129 m Ah g^-1 and impressive cyclic stability in 0.01 mol L^-1 H₂SO₄ electrolyte.After 50000 cycles of 1 A g^-1,the capacity retention rate can still reach 53%.More importantly,the K_0.48V₂O₅ battery system shows the insertion/extraction mechanism of H₃O⁺.（2）The（NH₄）_0.5V₂O₅·0.75H₂O electrode material with large layer spacing was obtained by preembedding NH₄⁺and water molecules between the V₂O₅ bilayer simultaneously.The nanosheet structure of（NH₄）_0.5V₂O₅·0.75H₂O electrode material also provided abundant active sites for the adsorption and reaction of H₃O⁺,which endowed the active material with large pseudo capacitance charge storage characteristics.It can work normally in ultra-low concentration(0.001 mol L^-1 H₂SO₄)aqueous hydrogen-ion battery and has good performance.In 0.001 mol L^-1 H₂SO₄ electrolyte,（NH₄）_0.5V₂O₅·0.75H₂O cathode material can provide a high reversible capacity of about 150 m Ah g^-1 at 50 m A g^-1 current density.At the same time,it has a surprisingly long cycle performance,and can maintain up to 80%capacity retention rate after70000 cycles with a current density of 1 A g^-1.In addition,the mechanism of H₃O⁺reaction was also studied by ex-situ characterization.（3）The V₁₀O₂₄·12H₂O electrode material with large layer spacing was obtained by preembedding plenty of water molecules between the V₂O₅ bilayer.The V₁₀O₂₄·12H₂O electrode not only has a specific capacity of up to 140 m Ah g^-1 in 0.01 M H₂SO₄ electrolyte,but also has good rate performance.More importantly,V₁₀O₂₄·12H₂O provides A highly reversible capacity of approximately 160.3 m Ah g^-1(current density 0.1 A g^-1)in 1 M（NH₄）₂SO₄ electrolyte.The reverse dual-ion battery prepared by using V₁₀O₂₄·12H₂O as the cathode material has excellent electrochemical performance because both the cationic and cationic ions in（NH₄）₂SO₄ electrolyte participate in the reaction.The specific discharge capacity of the full battery is about 225 m Ah g^-1 at 0.1 A g^-1 current density.It can continue to operate even at a high current density of 10 A g^-1,with a specific capacity of about 50 m Ah g^-1.The excellent electrochemical performance of the whole cell is mainly attributed to the unique reverse ion conduction inside the cell.During discharge,the cation NH₄⁺in 1 M（NH₄）₂SO₄electrolyte is transferred to the positive electrode,while the anion SO₄^2-is transferred to the negative electrode.The research results of this paper provide a new idea for the development of high performance vanad-based cathode materials used in aqueous hydrogen-ion battery,and deepen the understanding of vanad-based oxide energy storage mechanism.