Nanostructural Titanates:Synthesis And Its Electrochemical Properties

Ti-based materials (such as Li-Ti-O, TiO2, Zn-Ti-O and so on) have been considered as potential alternative materials for replacing traditional carbon-based anodes, since theses materials exhibited excellent Li-ion insertion/extraction reversibility with a small structural change and a much higher operating voltage ranging from 3 to 1 V (vs. Li/Li+) ensuring a better safety of the battery by avoiding the problem of lithium dendrites. Despite these advantages, the rate capability of Ti-based materials is relatively low because of a large polarization at high charge-discharge rates resulting from the poor electrical conductivity and sluggish lithium-ion diffusion. In an attempt to overcome these drawbacks, many approaches have been developed for enhancing the battery performances:(1) synthesis of nanostructured Ti-based materials; (2) surface modification of Ti-based materials; (3) ion doping of Ti-based materials. All of the approaches above will improve the ionic diffusion and electronic conductivity of Ti-based materials for enhancing their electrochemical performances for lithium ion storage.In the present work, a series of Li2ZnTi3O8/C nanocomposite, Li2MTi3O8/C(M Mg,Mgo.5Zno.5) nanocomposites were successfully synthesized, and then were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM), Transmission electron microscope (TEM), Thermo gravimetric analysis (TGA), N2 Physisorption, etc. Furthermore, these materials were used as the anode materials in lithium-ion batteries, and their electrochemical properties were investigated in detail.The main contents and results are as following:(1) Nanorods of Li2ZnTi3O8/C composite were synthesized using hydrogen titanate nanowires as a precursor and their size was found to be ca. several micrometers. Anode materials composed of these Li2ZnTi3O8/C nanocomposites exhibited good cycling performance and rate capability. The Li2ZnTi3O8/C nanocomposites which the content of carbon was 3.5% showed a capacity of 247.6 mAh g-1 at 0.2 A g-1 after 200 cycles.(2) One step sol-gel route was developed for synthesizing Li2ZnTi3O8/C nanocomposite, in which a thin layer of carbon was coated on the surface of Li2ZnTi3O8 nanoparticles. These nanoparticles were high crystalline and their size was found to be ca.20-30 nm. The synthesized Li2ZnTi3O8/C nanocomposite was used as an anode for rechargeable lithium-ion batteries and exhibited a high reversible charge-discharge capacity, excellent cycling stability and high rate performance. A large capacity of 284 mAh g-1 can be kept after 200 cycles at a current density of 0.2 A g-1. These results can be attributed to the intrinsic characteristics of Li2ZnTi3O8/C nanocomposite. A thin layer of carbon on the surface of Li2ZnTi3O8 nanoparticles could improve significantly the conductivity and the anode made of nanoparticles greatly decreased the diffusion distance for lithium ions and electrons in the solid state.(3) Li2MTi3O8/C (M=Mg, Mg0.5Zn0.5) nanocomposite were successfully prepared by using one-step sol-gel route. It was found that the as-prepared products were composed of nanoparticles with a size of several tens to several hundreds of nanometers. Furthermore, these materials were used as the anode materials for lithium-ion batteries and showed a higher capacity. The capacity of Li2Mgo.5Zno.5Ti30g/C nanocomposite was 185 mAh g-1 at 0.2 A g-1 after 50 cycles, while Li2MgTi3O8/C nanocomposite only exhibited a capacity of 154.9 mAh g-1.