Synthesis And Electrochemical Performance Of Nano-sized TiO₂ Anode Materials

Titanium dioxide?TiO₂?as a very promising anode material of lithium-ion battery?LIB?and sodium ion battery?SIB?,is not only abundant,low cost and stable,but also has small volume change in the process of charge?less than 4%?and discharge as well as high lithium ion insertion/extraction potential?1.7 V vs Li⁺/Li?.Thus,the TiO₂anode materials have very excellent cycle reversibility,safety and charge/discharge performance.However,the ionic conductivity and electronic conductivity of TiO₂ anode materials are relatively lower,which cannot meet the requirements of high-energy density batteries.In this paper,three kinds of TiO₂ nanomaterials with different morphologies were synthesized by simple methods?hydrothermal and hydrolysis?,and their transportation and storage properties for lithium ions and sodium ions were investigated.Firstly,anatase TiO₂ spheres with high tap density?1.06 g/cm³?were prepared by a simple hydrolysis process of titanium nitride.It was found that the size and pore size distribution of this TiO₂ spheres could be regulated and the TiO₂ spheres present excellent lithium ion and sodium ion storage properties.More importantly,the size and pore distribution of TiO₂ spheres have an extremely important effect on their lithium ion and sodium ion storage behavior.The storage and transportation properties of lithium ions mainly depend on the size and the distribution and volume of the micropores of the TiO₂ spheres.In contrast,the storage and transport properties of sodium ions primarily depend on the loose structure of smaller TiO₂ spheres with large macropore volumes because the loose structure can greatly reduce the diffusion length of sodium ions.The lithium ion storage capacity of high tap density TiO₂ spheres is 189 mAh/g at 1 C and the capacity retention is 88.1%after 83 cycles for rate test and 100 cycles for cycle test.The storage capacity is 184 mAh/g at 1 C for sodium ion battery and the capacity retention is 90.5%after 200 cycles.Secondly,in order to further reduce the preparation cost of TiO₂ nanomaterials,a crystalline TiO₂ mesocrystals was prepared at low temperature of 80 ^oC.It is found that during the a facile hydrolysis and evolution process induced by acetic acid?HAc?solution using TiN as starting material without subsequent heat treatment at high temperature.The size and crystallinity of the TiO₂ mesocrystals can be easily adjusted by changing the content of HAc and the reaction time.The TiO₂ mesocrystals also exhibit excellent lithium ion storage performance,which specific capacity is 180 mAh/g at 1 C and the capacity retention is 92.9%after 100 cycles.Finally,rutile TiO₂ nanorods with nitrogen self-doping was obtained using titanium nitride?TiN?nanopowder by hydrothermal method.The length and thickness of the TiO₂ nanorods could be controlled by the composition ratio in the hydrothermal solution.When the hydrochloric acid concentration is 2.4 mol/L,the electrochemical performance of the TiO₂ nanorod anode material is the best and the capacity is almost no obvious loss after 400 cycles.At the same time,the introduction of multi-walled carbon nanotubes into the preparation of TiO₂ nanorods can improve the its specific capacity during the long cycle.