Design,Synthesis And Electrochemical Performance Of Transition Metal Vanadate Anodes

Nowadays,the ever-increasing energy demand for novel,sustainable,and environmentally friendly energy sources has been a vital and challenging issue.Among various available energy storage technologies,rechargeable lithium ion batteries?LIBs?with high capacity,long lifespan,no memory effect,and environmental benignity have been extensively applied in high-end consumer electronic devices.However,conventional commercial graphite with relatively low theoretical capacity(372 mA h g^-1)may be hard to meet the tremendous demands of high-energy applications.Therefore,it is vital to explore new materials with high specific capacity,excellent rate capability,and long cycle life.Metal oxides have been considered as promising electrodes for the development of LIBs because of their high specific/volumetric capacity,low cost and toxicity.Among them,transition metal vanadates have gradually attracted researchers'attention due to their high capacity,good ion conductivity,high chemical stability and special lithium storage mechanism.In this article,we chose two kinds of transition metal vanadates as the research objects to construct zinc pyrovanadate nanoplates embedded in graphene networks and iron vanadate nanorods via a one-pot hydrothermal method.Modern testing technologies were utilized to characterize the nanomaterials which are used as the anode materials to test the electrochemical performance.The main results are as follows:?1?Zinc pyrovanadate nanoplates embedded in graphene networks were synthesized by a simple one-pot hydrothermal method using zinc nitrate,vanadium pentoxide and graphene oxide,etc.The resulting samples were characterized by XRD,SEM,Raman,BET,TG,CHNS elements analysis to analyze the morphology,phase,structure and component,then the formation and growth mechanism of the composite is clarified.?2?We test the battery assembled with zinc pyrovanadate nanoplates embedded in graphene networks as the anodes in LIBs in the voltage range of 0.01-3.0 V.The results indicate that the composite shows excellent cyclability and rate capability superior to bare zinc pyrovanadate nanoplates.The nanocomposite still exhibits a high specific discharge capacity as 854 mA h g^-1 at a current density of 500 mA g^-1after 400 cycles with the capacity retention of 95%.In addition,we carry out ex-situ XPS measurement to clarify the electrochemical reaction mechanism of zinc pyrovanadate and investigate other factors that affect the electrochemical performance of zinc pyrovanadate.The graphene netoworks in nanocomposite not only enhance the whole conductivity,but also improve the structural integrity of electrodes.Such design and construction could effectively buffer the strain from volumetric expansion of active materials during repeated lithiation/delithiation and prevent active materials from pulverization.?3?Iron vanadate nanorods were synthesized via a one-pot hydrothermal method using ammonium ferric sulfate and ammonium metavanadate.We test the battery assembled with iron vanadate nanorods as the anodes in LIBs in the voltage range of 0.01-3.0 V.The results indicate that iron vanadate nanorods exhibit a first discharge specific capacity as 1099 mA h g^-1 at the current density of 500 mA g^-1,with the first coulombic efficiency of 77%.After 400 cycles,the capacity remains534 mA h g^-1.The electrochemical performance of iron vanadate nanorods is superior to that of dehydrate iron vanadate nanorods after calcination,which can be ascribed to two factors:Firstly,lithium ions partially reversibly react with the crystal water to provide extra capacity.Secondly,the obtained dehydrate iron vanadate nanorods through calcination agglomerate obviously,which is not beneficial for the material to release the capacity.