The Synthesis And Electrochemical Performance Of An Iron Vanadate Cathode Materials

As the mainstream product on second battery market,lithium ion battery still suffers from drawbacks like high price and poor safety.For long-term development,researchers have been looking for its substitute.The aqueous zinc ion battery is a kind of second battery which is safe,eco-friendly,cheap and has no strict need for assembly environment.These advantages make it a promising battery system for application.Now the studies on zinc ion battery are mostly focusing on cathode materials.This work has investigated the ability to storage zinc ions of an iron vanadate Fe₅V₁₅O₃₉?OH?₉·9H₂O.It has a nanosheet morphology and layered structure.The synthesis process of Fe₅V₁₅O₃₉?OH?₉·9H₂O nanosheet is simple and quick,with cheap ingredients.This cathode material also shows superior electrochemical performance in zinc ion battery.The main content and results of this work are as follows:?1?The Fe₅V₁₅O₃₉?OH?₉·9H₂O nanosheet was synthesized by water bath in atmospheric pressure.We used XRD,IR,TG-DSC,SEM and TEM to characterize the product.The results demonstrate a stable layered structure in which the H₂O molecules act as“pillars”.This structure is beneficial for intercalation and de-intercalation of Zn²⁺ions.?2?Microwave irradiation method was used to synthesize the same Fe₅V₁₅O₃₉?OH?₉·9H₂O nanosheet.Thanks to the advanced temperature and pressure sensors of microwave reactor,we managed to accurately control and observe the parameters during reaction process.By carrying out gradient experiments,we investigated the different influences to reaction of different parameters,which reveal the kinetic of this reaction.The results indicate that this reaction is sensitive to temperature and spontaneous in room temperature.?3?A aqueous zinc ion battery was assembled utilizing Fe₅V₁₅O₃₉?OH?₉·9H₂O as active material in cathode,and Zn?TFSI?₂?zinc?II?bis?trifluoromethanesulfonyl?imide?solution as electrolyte.Various electrochemical tests were conducted on this battery system.It delivers a high capacity of 385 mAh g^-1 at 0.1 A g^-1 and remarkable cycling performance at high current density(over 80%capacity retention after 300 cycles at 5A g^-1).?4?The zinc ion storage mechanism of Fe₅V₁₅O₃₉?OH?₉·9H₂O was investigated by ex-situ XRD and in-situ XRD tests on electrodes.Also,the XPS result of electrolyte collected during cycling shows the change inside cell.?5?The ICP?Inductive Coupled Plasma?result of electrolyte during charge and discharge process reveals the loss of elements in cathode material.We managed to figure out the different characters of Fe and V in construction of Fe5V15O39?OH?9·9H2O by analyzing the concentration variation of elements in electrolyte and the change of capacity.Based on the principle of dissolution equilibrium,we tried to add compounds containing Fe and V elements into electrolyte to suppress the loss of Fe and V,and also tried a“recycled”electrolyte from electrolytic cell,and achieved certain effects.