Synthesis And Electrochemical Properties Of Ti-Based Oxide Nanosturctures

Rechargeable lithium ion batteries with multiple properties, such as high power density, high energy density and high safety, are excellent power sources for portable electronic devices, electric vehicles and stationary energy storage systems. Ti-based compound nanostructures exhibit excellent cycling reversibility owing to their unique zero-strain insertion crystal structure. Their high working potential ensures the high security for lithium ion batteries application. However, their intrinsic electrical conductivity (ca.10-13 S cm-1) and lithium ion diffusion coefficient (ca.10-9-10-13 cm2 s-1) are relatively low, which severely prohibit their application for achieving high rate performance. In our work,(1) Ti3+ self-doped Li4Ti5O12 (S-LTO) nanosheets:Ti3+ self-doped Li4Ti5O12 (S-LTO) nanosheets have been synthesized via a facile solvothermal approach combined with hydrogenation treatment. The thickness and lateral dimension of Li4Ti5O12 nanosheets are 10-20 nm and 100-400 nm, respectively. The Ti3+ species and/or oxygen vacancies are well introduced into the crystal structures of Li4Ti5O12 after hydrogen reduction, resulting into an enhancement in the electronic conductivity and the modified surface electrochemical activity. When evaluated for lithium storage capacity, the S-LTO nanosheets exhibit enhanced electrochemical energy storage performances compared to the pristine Li4Ti5O12 (P-LTO) nanosheets, including high capacity (165.6 mA h/g at 0.5 C), excellent rate capability (119.6 mA h/g at 20 C), and good cyclic stability (95.3% capacity retention after 100 cycles at 10 C). The improvement of lithium storage performances is ascribed to the increased electronic conductivity and the shortened lithium ion diffusion paths arising from the introduction of Ti3+ species and the ultrathin thickness of S-LTO.(2) Hydrogenated Li4Ti5O12 hollow microspheres:Hydrogenated hollow microspheres composed of Li4Ti5O12 nanosheets have been synthesized on a large scale by a facile low-temperature solution-based approach combined with high temperature calcination. When evaluated for lithium storage capacity, the H-LTO hollow microspheres display enhanced electrochemical energy storage performances compared to the pristine hollow microspheres composed of Li4Ti5O12 nanosheets (A-LTO), including high capacity (188.6 mAh g-1 at 0.5 C), excellent rate capability (123.7 mAh/g at 20 C), and good cyclic stability (95.8% capacity loss after 100 cycles at 20 C). The reasons for these improvements are explored in terms of the increased electronic conductivity and the facilitation of lithium ion transport arising from the introduction of oxygen vacancies and the unique Hierarchical hollow microspheres.