Synthesis And Electrochemical Properties Of Ti-based Compound Nanocomposites

Energy consumption and serious environmental deterioration has been subject to widespread concern. Therefore, it is necessary to develop new clean energy in order to solve the two problems. Lithium ion batteries with high energy density and good cycle performance are widely used in mobile phones, notebook computers, digital cameras and other portable electronic devices. To make lithium ion batteries are more widely used in electric vehicles and large energy storages and conversion devices, it is necessary to improve the performance of lithium ion batteries, especially high rate performance, safety performance and long-cycle performance.Titanium oxide has become the most promising anode material for lithium ion batteries due to its good cycle stability and safety. However, the conductivity of titanium oxide itself severely limits its application in high rate. In order to solve the poor conductivity of titanium oxide, we hope to improve the overall conductivity of titanium oxide through the preparation of niobium doped Li₄Ti₅O₁₂-TiO₂ core-shell microspheres, Li₄Ti₅O₁₂/graphene nanocomposites, and niobium doped TiO₂（B） nanostructures in this paper. The experimental results show that the prepared materials have a certain improvement in capacity, rate performance and cycle stability. The main results are as follows:（1） Nb doped Li₄Ti₅O₁₂-TiO₂ core-shell microspheres: Nb doped Li₄Ti₅O₁₂-TiO₂（Nb-LTO-TO） core-shell microspheres have been synthesized by a facile hydrothermal method combined with calcination. The obtained core-shell microspheres show uniform and hierarchical morphology with a diameter of about 1 μm, which are further constructed by primary nanosheets with a thickness of 10²0 nm and width of 30⁴0 nm, respectively. Nb doped Li₄Ti₅O₁₂-TiO₂ core-shell microspheres used for electrode of lithium ion batteries show high rate capability and good cycling performance. When evaluated for lithium storage capacity, the Nb-LTO-TO core-shell microspheres display enhanced electrochemical energy storage performances compared to the pristine Li₄Ti₅O₁₂-TiO₂ core-shell microspheres（LTO-TO）, including high capacity（176.9 mAh g-1 at 0.5 C）, excellent rate capability（141 mAh g-1 at 20 C）, and good cyclic stability（87.8% capacity retention after 100 cycles at 2 C）. The improvement of electrochemical performance is attributed to the increase of the number of carriers which are supplied by Nb element, resulting in better electronic conductivity of the materials.（2） Li₄Ti₅O₁₂/grapheme（LTO-G） nanocomposites: LTO-G nanocomposites have been synthesized by using the amorphous TiO₂ synthesized by sol-gel method, lithium hydroxide and graphite oxide as reactants with the help of hydrothermal method and calcination. The obtained LTO-G nanocomposites used for electrode of lithium ion batteries show high rate capability. When evaluated for lithium storage capacity, the LTO-G nanocomposites display enhanced electrochemical energy storage performance, including high capacity（194.9 mAh g-1 at 0.2 C） and good rate capability（68.4 mAh g-1 at 10 C）. The improvement of electrochemical performance is attributed to the excellent conductivity of graphene, which is conducive to transpertation of electrons, resulting in high rate performance of the materials.（3） Nb doped TiO₂（B） nanostructures [Nb-TiO₂（B）]: Nb doped Ti O2（B） nanostructures have been synthesized via a facile solvothermal approach combined with calcinating treatment. The obtained Nb doped TiO₂（B） nanostructures constructed by primary nanosheets with a thickness of several nanometers. When used as electrode of lithium ion batteries, Nb-TiO₂（B） nanostructures show good rate capability, including 315 mAh g-1 mAh g-1 at 0.2 C and 129.9 mAh g-1 at 1 C. The improvement of electrochemical performance is attributed to the nanostructures which greatly increase the surface area and is beneficial to contact with electrolyte. Doping niobium element can increase the number of carriers and improve the electronic conductivity of the materials.