Preparation Of Carbon-Nitrogen-Doped TiO₂ Nanotube-Based Materials And Their Electrochemical Properties In A Wide Temperature Range

As a semiconductor material,titanium dioxide?TiO₂?has great potential as a negative electrode material for lithium ion batteries due to its good structural stability,high specific capacity,good cycle stability and high safety.However,its low electronic conductivity and poor ion diffusion ability limit the practical application of titanium dioxide in lithium ion batteries.Moreover,the intrinsic conductivity of the TiO₂ electrode material decreases as the temperature decreases,further limiting the application of titanium dioxide in low temperature lithium ion batteries.In this paper,the combination of conductive materials,doped heterogeneous atoms and material nanocrystallization to improve the ion and electronic conductivity of titanium dioxide,and improve the electrochemical performance of TiO₂ as a negative electrode material for lithium ion batteries at room temperature and low temperature?0-minus 20°C?.The main research contents are as follows:Oxidation of TiN into titanium dioxide?TiO₂?as precursor,MXene?Ti₃C₂?as a synergistic titanium source and carbon source,C/N co-doped TiO₂ nanotubes were prepared by hydrothermal and heat treatment.It can be observed that TiO₂ as raw material is obtained by oxidation of TiN and oxidation of MXene during hydrothermal and heat treatment.In this process,the carbon-nitrogen co-doping of TiO₂ was realized in a simple way.The properties of the material as a negative electrode material for lithium ion batteries at room temperature and low temperature were investigated.The sample prepared by the ratio of TiO₂ and MXene to 20:1 has a reversible discharge capacity of 128.9 mAh/g at a current density of 20 A/g and after circulating for 500 cycles at a current density of 2 A/g,the capacity was maintained at 180.4 mAh/g at room temperature.At-20?,the sample showed a specific capacity of 188.5 mAh/g at 0.1 A/g,while at this temperature,a reversible capacity of 134.6 mAh/g was maintained for 500 cycles with a current density of 1 A/g.Incompletely oxidized TiN as precursor and multi-layer graphene oxide?GO?as the source of graphene nanosheets,multiphase N-doped TiO₂ nanotubes/TiN/graphene nanocomposites were synthesized by hydrothermal synthesis under high concentration of sodium hydroxide and heat treatment.Graphene connects N-doped TiO₂ nanotubes together to form a conductive network,improving their electrochemical performance at room temperature and low temperature.The nanocomposite sample prepared by heat treatment at400°C had a reversible capacity of 154.3 mAh/g at a current density of 20 A/g,and a capacity retention rate of 86%after 500 cycles at a current density of 2 A/g at room temperature.At-20?,the reversible capacity of the sample at 2 A/g is 123.2 mAh/g.Current density 1 A/g maintained a reversible capacity of over 93%after 500 cycles.