Synthesis And Electrochemical Properties For Tungstate And Tungsten Trioxide As Lithium-ion Battery Anode Materials

In this paper,tungstates Sb₂WO₆,Fe WO₄ and tungsten oxide WO₃ were used as research objects.Pure compounds were synthesized by appropriate synthesis methods,and they were used as anode materials for lithium ion batteries.Then we explored their electrochemical properties and improved their shortcomings.A series of important conclusions were reached,the specific conclusions were as follows:（1）Sb₂WO₆ microspheres were synthesized by solvothermal method,Na₂WO₄·2H₂O and Sb Cl₃ were used as raw materials,1:1 ratio of ethanol and water as solvents,reaction condition was 180°C for 24h.Then the in-situ polymerization method was used to synthesize the target product as Sb₂WO₆@PPy microsphere complex.The structures of Sb₂WO₆ and Sb₂WO₆@PPy were characterized by X-ray diffraction（XRD）.The morphologies of Sb₂WO₆and Sb₂WO₆@PPy were observed by scanning electron microscopy（SEM）technology.It was found that Sb₂WO₆ was a multi-dimensional layered microsphere structure composed of two-dimensional nanosheets.However,the Sb₂WO₆@PPy complex coated with pyrrole polymerization could not observe a multi-dimensional layered structure,which showed a smooth micro-spherical surface.The two products were tested by infrared spectroscopy（IR）,that further proved that PPy was successfully coated on the surface of Sb₂WO₆.The content of PPy in Sb₂WO₆@PPy was determined by thermogravimetric analysis（TGA）to be 24%.The electrochemical performance test was performed under the conditions of a current density of 100 m A·g^-1 and a voltage range of 0.01 to 3 V.It was found that after 100 charge and discharge cycles,the charging voltage platforms of the Sb₂WO₆ electrode and Sb₂WO₆@PPy electrode were respectively2.5 V and 1.0 V.After 200 cycles,the specific discharge capacities of the Sb₂WO₆ electrode and Sb₂WO₆@PPy electrode were 304 m A·h·g^-1 and 557m A·h·g^-1respectively,and their capacity retention rates were 46.8%and 73.0%respectively.And under the same test conditions,the Sb₂WO₆@PPy composite material exhibits better rate performance,which was due to the material’s smaller charge transfer resistance and larger lithium ion diffusion coefficient.It could be seen that the surface coating of polypyrrole and the three-dimensional layered microsphere structure could effectively improve the electrochemical performance of the Sb₂WO₆ electrode.The Sb₂WO₆@PPy microsphere material prepared by this method is a promising anode material for lithium ion batteries and is expected to be applied to lithium ion battery system.（2）Using Na₂WO₄·2H₂O,Fe SO₄·7H₂O,and Co SO₄·7H₂O as raw materials,different proportions of Co-doped Fe WO₄ products were obtained by solvothermal method combined with high temperature annealing treatment,namely Fe_1-xCo_xWO₄（x=0,0.05,0.1,0.2,0.3）.The structure of the synthesized compounds was characterized by X-ray diffraction（XRD）.It was found that these doped compounds have the same crystal structure as Fe WO4.Fe_0.9Co_0.1WO₄ has the best crystallinity among the all compounds.By scanning electron microscopy（SEM）technology to observe the compound,it was found that Fe_0.9Co_0.1WO₄showed the most regular micron spherical appearance.X-ray photoelectron spectroscopy（XPS）was used to test and analysis of Fe_0.9Co_0.1WO₄ to confirmed the existence of Fe,Co,W,and O elements and their valence states.Through the electrochemical performance test of each product,when the current density was 100 m A·g^-1 and the voltage range was 0.01～3V,after 100 charge/discharge cycles,the discharge specific capacity of Fe_0.9Co_0.1WO₄ was the highest and its value was 1008.2 m Ah·g^-1.In addition,Fe_0.9Co_0.1WO₄ also showed the most excellent rate performance.The experimental results showed that proper amount of cobalt ion doping can effectively improve the electrochemical performance of Fe WO₄.Therefore,Fe_0.9Co_0.1WO₄ is a promising anode material for lithium ion batteries and is expected to be applied.（3）Using Na₂WO₄·2H₂O and Na Cl as raw materials,WO₃ was successfully prepared by hydrothermal method,and the target product WO₃/Ge O₂ composite was synthesized by the high-temperature solid-phase method using the prepared WO₃ and Ge O₂.X-ray diffraction（XRD）was used to characterize the obtained products,which proved the synthesis of the target products.The products were tested by scanning electron microscopy（SEM）technology.WO₃ showed lamellar agglomeration morphology,and Ge O₂ was irregular spherical and granular agglomerates.When the two were combined,a WO₃/Ge O₂ composite was formed,the morphology of WO₃/Ge O₂ revealed a polymerized of two-dimensional sheet layered structure.After the electrochemical performance test,when the current density was100m A·g^-1 and the voltage range was 0.01～3 V,the WO₃/Ge O₂ composite combines the advantages of pure WO₃ and Ge O₂,and had the same low charge voltage platform of Ge O₂（about 0.3V）and same high cycle stability of WO₃(after 100 charge/discharge cycles,the discharge specific capacity can be maintained at 557.6 m Ah·g^-1),and WO₃/Ge O₂ also had good rate performance.Therefore,WO₃/Ge O₂ composite is a kind of potential lithium ion battery anode material,which is expected to be applied to lithium ion battery system.