Preparation Of N,S Or P Modified Ti₃C₂T_x MXene Material And Its Performance As A Negative Electrode For Alkaline Metal Batteries

Alkali metal ion（Li,Na,and K）batteries have become the most promising energy storage devices.Exploring high-performance electrode materials for alkali metal ion batteries attracts lots of attention.Ti₃C₂T_x MXene materials as a new type of two-dimensional layered material show their potential application as anode materials for alkali metal ion batteries due to their high surface area and good electronic conductivity.In this thesis,the Ti₃C₂T_x MXene is employed as an anode material for the alkali metal ion batteries,and its electrochemical performance is investigated.Moreover,its electrochemical performance is further improved by heteroatom modification technology.The research mainly contains the following three parts:Firstly,the electrochemical performance of the few-layer Ti₃C₂T_x MXene material is synthesized and employed as the anode material for the alkali metal（lithium,sodium,potassium）ion battery.After 200 cycles m A g^-1,few-layer Ti₃C₂T_x MXene presents a capacity of 209.2,86.0,and 53.9 m Ah g^-1 at a current density of 100 in lithium,sodium,and potassium ion batteries,respectively.Ti₃C₂T_x displays a good cycling performance but low capacity and unsatisfied rate performance.Then,nitrogen（N）modified few-layer Ti₃C₂T_x MXene is synthesized via a hydrothermal method following the calcination process.The N modification enlarges the interlayer spacing of Ti₃C₂T_x material,and the Ti-N bond is formed.Moreover,the F-containing functional groups on the Ti₃C₂T_x surface are reduced.When N-Ti₃C₂T_xmaterial serves as anode materials for lithium,sodium,and potassium ion batteries,a capacity of 308.9,165.6,and 95.6 m Ah g^-1 is obtained at a current density of 100 m A g^-1after 200 cycles of cycles,respectively.Meanwhile,the rate performance is improved.The N-Ti₃C₂T_x displays a lower charge transfer resistance than that of the original material,indicating enhanced conductivity of the N-Ti₃C₂T_x material.The kinetic analyses suggest a capacitor-dominated metal-ion storage process in the N-Ti₃C₂T_x electrodes,which promises a good rate performance and cycling stability.Finally,sulfur（S）or phosphorus（P）modified Ti₃C₂T_x material is prepared by a high-temperature calcination process.When S-Ti₃C₂T_x material is used as the anode material for lithium,sodium,and potassium ion batteries,a discharge capacity of 293.9,150.9,and 101.1 m Ah g^-1 is obtained,respectively,at a current density of 100 m A g^-1 after200 cycles.The Ti-S bond is formed between S and Ti₃C₂T_x,and the content of-F functional groups is reduced,which could improve the electrochemical performance of the electrode material.When P-Ti₃C₂T_x material is used as the negative electrode material of lithium,sodium,and potassium ion battery,a discharge capacity of 246.2,107.6,and 87.7m Ah g^-1 is obtained,respectively,at a current density of 100 m A g^-1 after 200 cycles.The Ti-O-P bond is formed between P and Ti₃C₂T_x,which enhances the stability of the P-Ti₃C₂T_x structure.The kinetic analyses suggest a capacitor-dominated metal-ion storage process in the S-Ti₃C₂T_x and P-Ti₃C₂T_x electrodes,which promises a good rate performance and cycling stability.In short,N,P,or S modified Ti₃C₂T_x materials present enhanced interlayer spacing,adjusted surface functional groups,reduced charge transfer resistance,and the rapid alkali metal ion storage behavior,which leads to high specific capacity,stable cycling performance,and good rate ability.