Preparation Of High-performance Electrode Materilas For Vanadium Redox Flow Battery And Construction Of Asymmetrical Battery Structure

With the renewable energy developing rapidly,the supportive large-scale energy storage technology has also received extensive attention.As one of the most industrialized large-scale energy storage technologies,all-vanadium redox flow battery(VRFB)takes the advantages of easy expansion,long cycle life,high safety,fast response speed and large capacity,which has always been a research hotspot in energy storage field.However,the high energy storage cost limits its large-scale application,and improving battery performance is a major indirect route to reduce the energy storage cost of VRFB.Electrode is one of the key materials of VRFB,which has a crucial influence on the battery performance.The kinetics of the positive and negative reactions in VRFB are mismatched,thus using the same electrode material may adversely affect the electrolyte utilization and cycle stability.By optimizing and designing the positive and negative electrode materials respectively,this mismatch can be effectively reduced and the battery performance may be further improved.In this paper,a series of high-performance positive and negative electrode materials have been constructed,and the asymmetric VRFB structure is assembled finally to further improve the battery performance.The reactive specific surface area is one of the most critical indicators affecting the electrode activity.In the second chapter,a porous carbon nanofiber electrode material with high reactive surface area has been prepared by electrospinning technology and high temperature water etching method.Due to the large electrochemical specific surface area,the reaction activity of the negative electrode is significantly improved,thus effectively narrowing the gap between the positive and negative electrode reaction kinetics.The surface morphology,structural characteristics and hydrophilic properties of the materials are investigated by SEM,TEM,contact angle test,infrared spectroscopy,Raman spectroscopy,XPS and etc..The electrochemical performance of the electrodes are investigated by CV,EIS and constant current step.The single batteries are assembled finally with P-ECNFs and W-WECNFs respectively to study the effect of water etching electrode on the battery performance.The electrocatalytic performance of electrode materials directly affects the redox kinetics of vanadium ions.In the third chapter,ionic liquid and hydrochloric acid is used as a new etchant system and combined with a simple and green microwave-assisted method to prepare a layered“ion-electron”coupled Ti₃C₂T_XIL-MW-MXene material with rich active functional groups,which can be used as an excellent electrocatalyst for the V³⁺/V²⁺redox couples and loaded on the carbon felt to construct the high-performance IL-MW-MXene/CF negative electrode material.SEM,TEM,contact angle test,XPS and XRD have been used to investigate the morphology,hydrophilicity,structure and composition of the prepared materials.The electrochemical properties of the electrode material are studied by CV and EIS.A single cell with IL-MW-MXene/CF as the negative electrode is assembled and tested for charge and discharge to inspect the effect of the new composite electrode on the VRFB performance.Designing the positive and negative electrodes separately and assembling an asymmetric battery is an effective way to further improve the VRFB performance.In chapter four,the positive and negative electrode materials have been designed and prepared respectively by electrospinning technology and the subsequent thermal treatments based on the electrochemical reaction characteristics in VRFB.As a result,tungsten and antimony-based nanoparticles have been introduced into the carbon nanofibers,and the obtained HPW-ECNFs and Sb-ECNFs shows excellent electrochemical property towards the positive and negative electrode reactions respectively,and the gap between positive and negative redox kinetics reduced effectively.The structure and surface characteristics of these carbon nanofibers elecrodes are investigated by SEM,TEM,contact angle test,BET,XPS,IR and Raman.The electrochemical performance of the electrodes are studied by CV and EIS.Finally,a series of asymmetric single cells are constructed,that is,the positive/negative electrodes are HPW-ECNFs/P-ECNFs,P-ECNFs/Sb-ECNFs and HPW-ECNFs/Sb-ECNFs respectively,and the charging and discharging performance of these VRFBs are carried out and analyzed.The results showed that the asymmetrical VRFB with HPW-ECNFs and Sb-ECNFs as the cathode and anode respectively exhibited the highest battery efficiencies.