Synthesis And Electrochemical Performance Investigation Of Alkali Metal Copper-based Vanadate Anodes

Rechargeable lithium ion batteries（LIBs）have been widely applied in the field of high energy storage applications because of the merits such as high energy density,high security and environmental benignity.In addition,sodium and lithium both belong to the alkali metal elements,which possess similar physical and chemical properties,and sodium has advantages of abundant resources,uniform distribution and low cost.Thus,sodium ion battery has become another important direction for the future development of energy storage system.Metal vanadates are important groups of vanadium oxides,in which lithium ion intercalation and deintercalation reaction can be reversible.They have been widely studied in the field of energy storage due to their abundant changeable structure and high theoretical capacity in recent years.However,during the cycling process,structural deterioration and collapse phenomenon exist.To further promote the large-scale application of vanadate,these problems must be solved.In this paper,we chose two kinds of alkali metal vanadate materials（LiCuVO₄ and NaCuVO₄）as the research objects and successfully constructed the nanoscale interconnected networks for the first time.A variety of modern testing technologies were utilized to characterize the structure,morphology,phase and electrochemical performances of the nanomaterials.The electrochemical reaction mechanism of LiCuVO₄ was further analyzed through testing the electode materials before and after cycling.The main results are summarized as follows:（1）The nanoscale interconnected LiCuVO₄ networks were successfully constructed.The resulting samples were characterized by XRD,SEM,TEM and BET to analyze its morphology,phase,structure and component.As an anode material for lithium ion batteries,the nanoscale interconnected LiCuVO₄ networks deliver excellent cycling stability and rate performance.The capacity retention is 98%after 50 cycles at a current density of 0.1 A g^-1.It can provide a capacity of 253mA h g^-11 at a high current density of 5 A g^-1,remaining 85%after 5000 cycles.In addition,it exhibits extraordinary rate performance,showing a capacity of 216mA h g^-11 at 10 A g^-1.Lithium ion full cells were assembled based on the nanoscale interconnected LiCuVO₄ network anode and commercial LiFePO₄cathode.The LiCuVO₄ delivers a capacity of 161 mA h g^-1after 50 cycles at the current density of 1 A g^-1,with a Coulombic efficiency of 98%.（2）The reaction mechanism was elucidated.The LiCuVO₄ decomposes into Cu and Li₃VO₄ in the first discharge process.After that,metallic Cu is no longer involved in the reaction,and lithium ions can insert and extract in Li₃VO₄reversibly to complete the storage and conversion of energy.The capacity analysis results show that capacitive proportion occupies a large part of the total capacity.The predominant capacitive charge storage endows the material rapid discharge/charge capability.（3）By adding surfactant CTAB and adjusting the sintering temperature,the nanoscale interconnected NaCuVO₄ networks were successfully constructed.The morphology,phase and structure of NaCuVO₄ were characterized by modern testing techniques.When evaluated as an anode of sodium ion batteries（SIBs）,under the current density of 0.1 A g^-1,NaCuVO₄ can deliver a capacity of 443 mA h g^-1,and the capacity retention is as high as 96%after 50 cycles.In addition,at a high current density of 2 A g^-1,it exhibits a capacity of 305 mA h g^-1after 1000 cycles.In the rate test,the capacity can still be well maintained after the large current impact,manifesting its good cycling performance.