Preparation And Electrochemical Performance Of Nanostructrued Tetravalent Metal Oxide And Its Composite Material

Nowadays, lithium-ion battery has played an important role in people’s study,life and work. Therefore, lithium-ion battery （LIB） with high performance is required.To explore LIB electrode material with high capability and excellent cyclability is oneof the focuses of the current scientific researches. Tetravalent metal oxide attractsincreasing attention due to its high capacitance, safe and no-toxic,environment-friendly and low cost. However, the poor conductivity and changedvolume of materials for tetravalent metal oxide restrict its electrochemicalperformance. Herein the electrochemical performance of tetravalent metal oxide isexpected to be improved with help of doping and combination with other conductivematerials. The tin oxide nanocrystal and titanium dioxide-graphene composite wereprepared via a solvothermal method, and characterized by various electrochemicalmethods including XRD, EDX, SEM, TEM, Raman, FT-IR, UV-vis and BET. Thelithium-ion batteries were assembled in an Ar-filled glove box and tested on anelectrochemical workstation and a battery tester. The results are shown as thefollowing:Colloidal SnO₂nanocrystals were prepared via a solvothermal method using tintetrachloride as tin precursor, Gd³⁺ions as doped ions and oleic acid as stabilizingagent. The XRD，TEM，Raman，UV-Vis results of SnO₂nanocrystals with differentdoping concentrations indicate that the as-synthesized samples are tetragonal rutileSnO₂and Gd³⁺ions exist as the formation of substituting Sn4+ion. Pure SnO₂nanoparticles with quasi-sphere shape are converted to nanorods due to Gd³⁺ionsdoping. In addition, with increasing Gd³⁺doping concentration, the size of SnO₂nanorods decreases from6.2to4.2nm. The growth mechanism of SnO₂nanocrystalswas explained through surface free energy principle. The electrochemical propertiesof as-synthesized samples show that the initial discharge and charge capacities, cycleperformance and coulombic efficiency of SnO₂nanorods are better than those of SnO₂nanopaticles. Moreover, SnO₂nanorods show a reversible capacity of370mAh/gafter50cycles. The results demonstrate as Gd³⁺ions are introduced, the shape andsize of SnO₂nanocystals can be changed and the electrochemical property beimproved.3D TiO₂-Graphene composites were prepared via a solvothermal method usingamorphous TiO₂with sphere shape and graphene oxide as precursor. The structure, morphology, size and component of the TiO₂-Graphene composites were studied.The results indicate that anatase TiO₂microspheres are well dispersed on the graphenesheets. The composites show a high surface area of about155m²/g and pore size of3.8nm. The electrochemical properties of TiO₂-Graphene composites show excellentcyclability and rate capability, which display a reversible capacity of203,183,153,140and123mAh/g at0.5C,1C,5C,10C and20C rate, respectively. As3DTiO₂-Graphene composites have well-dispersed mesoporous TiO₂microspheres，excellent conductivity and stabilized structure, volume strain and agglomeration ofTiO₂can be suppressed during the discharge and charge process, which results in anexcellent electrochemical property.