| Aqueous batteries have-been investigated due to their low cost,environmental friendliness and safety.However,the development of anode materials is still in their infancy,which is the core task for building excellent aqueous batteries.Bi-based anode materials are the most promising candidates due to their wide potential window,high theoretical capacities and non-toxicity.However,there is lack of systematic studies on the relationships between the structure of and electrochemical performance and energy storage mechanism for Bi-based material.These relationships play key roles in the synthesis and electrochemical modification.In this disertation,we will explore the electrochemical performance and electrochemical reaction mechanism for Bi-based anode on the basis of their structures.The primary contents and conclusions in this desertation,focusing on Bi2O3,Bi-Bi2O3 and Bi electrodes,are summarized as follows:1.Expoloring the influence of oxygen vacancies of Bi2O3 on its electrochemical properties and energy storage mechanism.δandα-Bi2O3 electrodes were prepared by simple solvothermal reaction and annealing treatment.δ-Bi2O3exhibited excellent rate performance and ultra-high specific capacity due to its aboundant oxygen vacancies.Positively charged oxygen vacancies can not only adsorb OH-to promote ion diffusion,but also improve electronic conductivity.However,the existence of oxygen vacancies could cause the instability ofδphase structure,which is an unfavorable factor to cycling stability.2.Investigating the effect of Bi on electrochemical performance and energy storage mechamism of Bi-Bi2O3 electrode.Bi was precipitated fromδ-Bi2O3 through simple annealing treatment.Two self-derived Bi species,interstitial-Bi liberated from Bi2O3 unit cell and colonized surface nano-Bi were observed combining structure characterization and First principles calculation.Bi had made great contribution to the electrochemical performance of Bi-Bi2O3 electrode.On the one hand,Bi metal could play a role as electrochemical energy storage sites.On the other hand,interstitial-Bi created a new electronic level in the energy gap to boost electrical conductivity,and nano-Bi on the surface can tune the Bi/Bi2O3 interface coordination which is conducive to ion diffusion and mechanical stress release.Thus,Bi-Bi2O3electrode endowed with outstanding rate performance,high specific capacity and cycling stability.3.Revealing the energy storage mechanism of Bi anode for aqueous potassium ion battery.Bi electrode was prepared delicately by using a simple reduction.In-situ XPS,ex-situ XRD,Raman,XPS,TEM characterization were used to characterize the electrochemical behavior through following the evolution of structure,bondings,valence states and phase transition of Bi anode in a reaction process.It indicated that Bi is alloyed with K+occurred,instead of the assumed redox reaction（with OH-）,and the alloyed product is Bi K3.The excellent electrochemical performance of Bi electrode was attributed to its unique layered structure,which could provide efficient ion diffusion channels and storage sites.4.Studing the electrochemical behaviors and energy storage mechanism of Bi electrode in aqueous Li+/Na+/K+electrolyte.The electrochemical behaviors,reaction kinetics and electrochemical performance of Bi electrode in Li OH/Na OH/KOH were analyzed.Then we also characterized the evolution process of bondings and valence states for Bi electrode by in-situ XPS in different electrolytes.The conclusions were as follows:The electrochemical energy storage mechanism of Bi in Li OH and Na OH electrolytes was similar to that of KOH based on the mechanism of alloying/dealloying reaction;Bi electrode in Na OH electrolyte showed the best rate performance and specific capacity,but the worst in Li OH;The performance differences in different electrolytes were related to reaction kinetics,and the poor performance in Li OH was mainly due to serious polarization and difficult charge transfer. |
