LiY（MO₄）₂（M=MO,W）as Anode Material Of Lithium Battery

The growing demand for energy storage has aroused great interest in the research of lithium-ion batteries.Lithium-ion batteries are one of the most promising systems that can effectively transfer energy,reduce weight and reduce environmental hazards.Existing lithium-ion batteries with graphite as the anode electrode have been widely used in mobile applications.However,the development of lithium-ion batteries with larger specific capacity and higher power density for use in mobile devices,hybrid vehicles（HEV）and plug-in hybrid vehicles（PHEV）is still urgent and important.In recent years,mixed binary transition metal oxides have attracted worldwide attention due to their higher electrochemical performance and stronger electrical conductivity than single-component metal oxides.Especially metal molybdate（MMo_xO_y,M=Sr,Zn,Co,Mn,Ba,Mg,Cu,Ni,Pb,Sn,Ca,Cd,etc.）is one of the important series of inorganic materials widely used in energy storage equipment.Molybdenum can accept oxidation states from 0 to+6 and is considered to be one of the promising anode elements.Similar to molybdate,a tungstate containing a similar polyanionic group（WO₄）^2-should also exhibit a strong redox activity similar to（Mo O₄）^2-.Therefore,this paper has carried out in-depth and detailed research on LiY（WO₄）₂ and LiY（MoO₄）₂.The traditional solid-phase method and electrostatic spinning technology have been used to synthesize LiY（WO₄）₂ and LiY（MoO₄）₂ as anode materials for lithium-ion batteries.We analyze its electrochemical performance,explore the influence of morphology on electrochemical performance,and the lithium storage mechanism and kinetics of intercalation/delithium.The details are as follows:First,because molybdenum has a lighter atomic mass than tungsten,replacing tungsten with molybdenum can provide a higher theoretical capacity.Therefore,a new type of zero-strain anode material LiY（MoO₄）₂ nanotubes was prepared by a simple electrostatic spinning method,which showed excellent rate performance and cycle performance.After 580 cycles,the capacity retention of LiY（MoO₄）₂ nanotubes was as high as 94%,while bulk LiY（MoO₄）₂ synthesized by the solid-state method was only 30%.This enhancement can be attributed to the hollow structure of the nanotubes.More importantly,the in-situ X-ray diffraction（XRD）technique was used for the first time to explore the Li ion insertion/extraction mechanism of LiY（MoO₄）₂ nanotubes.It can be concluded that lithium ions initially occupied a free 8c site through a tunnel built by Mo-O tetrahedron to store energy.With repeated lithiation,the Y（Li）O₈ polyhedron gradually distorted.The deformation of the Y（Li）O₈ polyhedron can not only reduce the volume expansion caused by lithiation,but also induce the 8d site to be opened,allowing more lithium ions to be inserted.In addition,in-situ XRD and ex-situ transmission electron microscope（TEM）studies show that LiY（MoO₄）₂ nanotubes have excellent structural stability,and the maximum volume expansion rate of LiY（MoO₄）₂ nanotubes is only0.53%,indicating like Li₄Ti₅O₁₂,LiY（MoO₄）₂ nanotubes are zero-strain insertion materials.These advantages indicate that LiY（MoO₄）₂ nanotubes are ideal anode materials.Secondly,we all know that nanomaterials have a great impact on electrochemical performance,so we also prepared LiY（WO₄）₂ nanotubes by a simple electrostatic spinning technique.This new type of anode material has good electrochemical performance.The capacity loss of LiY（WO₄）₂ nanotubes after 156 cycles is 6.9%,while the capacity loss of bulk LiY（WO₄）₂ is higher than 55.0%.Even after 600 long life cycles,the capacity loss of nanotubes is only 9%.It can be seen that the hollow structure with rough surface and porous morphology helps to improve the electrochemical performance.In addition,the in-situ XRD method was used for the first time to study the insertion/extraction mechanism of lithium ions in LiY（WO₄）₂ nanotubes.It can be considered as an asymmetric two-phase reaction.The phase transition of LiY（WO₄）₂ to Li₃Y（WO₄）₂ can be clearly seen by in-situ XRD during discharge.In the opposite charging process,the mesophase Li₃Y（WO₄）₂ appears.In addition,in situ XRD also showed that LiY（WO₄）₂nanotubes have good electrochemical reversibility.The above results indicate that this material is expected to become a candidate material for negative electrodes of lithium ion batteries.