The Research Of Electrochemical Energy Storage In Tantalum Pentoxide

Metal oxides from VB group such as niobium pentoxide(Nb2O5)and tantalum pentoxide(Ta2O5)have captured much attention as electrode materials for electrochemical energy storage.Ta2O5 shares similar physical and chemical properties with Nb2O5,but the theoretical capacity of Ta2O5 is 482 m Ah g-1 and much higher than that of Nb2O5(~200 m Ah g-1).Therefore,Ta2O5 has huge potential in the application of electrochemical energy storage devices.However,it suffers from a low conductivity and poor activity as a result of the large bandgap(4.2 e V).In order to solve the problem mentioned above,we designed the three-dimensional self-supported Ta2O5 thin films in this work.In addition,the application in electrode material of lithium ion batteries and sodium ion batteries has been studied systematically and some meaningful results have been obtained.Works conducted can be summarized as follows:1)As a control,self-supported Nb2O5 film was first studied.The focus of this study was using the method of electrochemical anodization to synthesize the ordered three-dimensional self-supported nanopore arrays on the metallic Nb foils and explore the different experimental conditions on the influence of niobium oxide film morphology to determine the best synthetic conditions eventually.Then the samples were treated with high temperature and the subsequent characterization and electrochemical test were carried out.The electrochemical properties of the post-processing self-supported Nb2O5 thin films as the cathode materials of supercapacitors show the typical pseudocapacitive character and good stability.2)Ta2O5 thin films with the ordered nanostructure was then explored.Finally the thin films were used in electrode materials of electrochemical energy storage devices.Three-dimensional self-supported structure ensures the solid phase of ion transport in nanoscale.Furthermore,current collectors and binder are unnecessary when the Ta2O5 thin films are used as the electrode materials of electrochemical energy storage devices.This will enhance the diffusive rate of ions.Annealing at high temperature in the argon atmosphere can fully remove the residual water in the process of synthesis and produce oxygen vacancies.The band gap of Ta2O5 will be reduced and the conductivity will be enhanced.The electrochemical energy storage property and the cycling stability of Ta2O5 thin films will be improved eventually.First,the treated samples were electrochemical tested as cathode materials of lithium ion batteries.Samples annealed at 450 oC in the argon atmosphere(Ta2O5-450)maintains the capacity of 402 m Ah g-1 at the current density of 96.4 m A g-1(0.2 C,1 C is equal to 8 Li+ ions insertion into Ta2O5 in 1 h,= 482 m A g-1)and keeps the capacity of 209 m Ah g-1 at the larger current density of 2410 m A g-1(5 C)after 10000 charge and discharge cycles.The rate and cycling performance are better than the current literature reports.The mechanism of lithium storage in Ta2O5 thin films was studied subsequently.3)Finally,Ta2O5 thin filmsin sodium storage has been studied.The Ta2O5 thin films after anodization and annealing exhibit typical pseudocapacitive property and good stability.In order to improve the storage capacity,we are exploring a new method of anodization to synthesize the nanostructure Ta2O5 thin films.