Preparation And Properties Of Cathode Materials For Lithium Ion Batteries Based On Spherical Titanium Titanate

Spinel Li4Ti5O12 (LTO) is a promising negative electrode materials for lithium-ion batteries due to its excellent cycle performance and low volume change. This material has excellent characteristic such as " zero strain " of the framework structure. However, the poor conductivity and low specific capacity of LTO leads to its poor rate capacity and further limits its practical application. By synthesizing nano-LTO and its highly conductive composite materials, the rate capability and specific capability of LTO can be improved significantly.(1) Li4Ti5O12 hollow spheres were prepared by a facile two-step method. TiO2 nanoparticles were firstly be uniformly coated on the SiO2 template through a facile sol-gel process. Chemical lithiation of the TiO2 shell and dissolution of the SiO2 core were carried out simultaneously through a one-step hydrothermal reaction in LiOH solution, and followed by an annealing process at 500 and 700℃. The resultant Li4Ti5O12 hollow spheres showed different microstructures and crystal structures under different reaction conditions, which were characterized using various means such as TEM, FE-SEM and XRD. Nanoparticles assembling Li4Ti5O12 hollow spheres calcined at 700℃ is more dense than that calcined at 500℃ and showed better crystal structures. Moreover, Li4Ti5O12 hollow spheres (at 700℃) exhibited better cycle performance compared with the spheres calcined at 500℃ at the rate of 0.2 C.After 250 cycles, the capacity retentions of hollow spheres (at 700℃) are 91.42%.(2) Li4Ti5O12 hollow spheres/graphene composite materials were prepared by one-step process. Graphene oxide was firstly dispersed in Li4Ti5O12 hollow spheres suspension with sonication at room temperature, and then followed by an annealing process. X-ray diffraction measurement showed that with the increasing amount of graphene, the crystal structures of the LTO hollow spheres/rGO composite becoming poor. However, LTO hollow spheres/rGO composite with 9.09wt% rGO exhibited excellent specific capability with discharge capacities of 115 mA h/g at 20 C.Moreover, LTO hollow spheres/rGO composite with 9.09wt % rGO shows superior cycle performance than that with 16.67wt%rGO.(3) The Co3O4/Li4Ti5O12 hollow spheres/rGO composite were prepared by two step synthesis. Cobalt acetate were dispersed on the surface of GO. And the composite were further dispersed in Li4Ti5O12 hollow spheres suspension with sonication at room temperature, and than followed by an annealing process. The resultant Co3O4/Li4Ti5O12 hollow spheres/GO composite showed different microstructures and crystal structures under different reaction conditions, which were characterized using various means such as TEM, FE-SEM and XRD.Co3O4/Li4Ti5O12 hollow spheres/rGO composite with 32.3wt% showed excellent cycle performance, with discharge specific capacities of 553 mA h/g at a constant current density of 50mA/g after 50 cycles and discharge specific capacities of 385 mA h/g at a constant current density of 400 mA/g.