Synthesis And Electrochemical Performance Of Transition Metal Molybdates

In the past few decades,heavy consumption of fossil fuels and continuous increase of energy demands have compelled researchers to seek renewable clean energy and develop related energy storage technologies.Among the numerous energy storage technologies,lithium-ion batteries（LIBs）are widely utilized in electronic devices,electric vehicles and other fields because of their high energy and power density,long cycle life.Sodium-ion batteries（SIBs）have attracted much attention in the large-scale energy storage owing to the abundance and low cost of sodium.However,the current developments of LIBs and SIBs can’t meet the demand of the society.It is crucial to develop high-performance electrode materials for LIBs and SIBs.Transition metal molybdates have been investigated as anode materials for high-performance LIBs and SIBs due to their high theoretical capacity,low cost,and rich oxidation states of molybdenum,but their poor conductivity and large volume change impede their electrochemical performance.In this article,we chose transition metal molybdates as the research object and prepared two kinds of metal molybdates nanomaterials.Some technologies were used to investigate their structure,electrochemical performances and sodium storage mechanism,which can provide a reference for other researches.The main conclusions are as follows:（1）The three-dimensional（3D）graphene oxide decorated Fe₂（MoO₄）₃microflowers（FMO/GO）were synthesized by a one-pot water bathing method.The obtained FMO microflowers,which constructed by numerous nanosheets with the diameter of 2–3μm and the thickness of 100 nm,are uniformly embedded in a 3D GO network.（2）When used as the anode material of LIBs,the FMO/GO delivered a high capacity,good cycling stability and excellent rate performance(1220 mAhg^-1 after50 cycles at 200 mAg^-1,as high as 685 mAhg^-1 at 10 Ag^-1).When used as the anode material of SIBs,the FMO/GO demonstrated good cycling stability and rate capability(188 mA h g^-1 after 1000 cycles at 1 Ag^-1,107 mAhg^-1 at 10 A g^-1).The excellent electrochemical properties can be attributed to the combination of FMO microflowers and conductive graphene oxide,which provides a pathway for electron transport and buffers the volume changes during the discharge/charge processes.（3）The sodium storage mechanism of FMO was investigated by ex-situ XRD,TEM and XPS.The results showed that the electrochemical process is the combination of conversion and insertion reactions.（4）The nickel molybdate nanorods（NMO-600）were prepared by a hydrothermal method and subsequent calcination process,which are around 200 nm in width and 5–10μm in length.When used as the anode material of SIBs,the NMO-600 delivered good electrochemical performance(250 mAhg^-1 after 100cycles at 100 mA g^-1,as high as 103 mA h g^-1 at 10 Ag^-1),which is better than that of FMO.