The Modification Of Ti₃SiC₂ And Ti₃C₂-based Materials And Their Performance Of Lithium Ion Batteries

With changes in power consumption and energy storage methods,lithium-ion batteries have become a hot topic in energy research.New MAX and MXenes materials become promising anode materials for Li-ion batteries.In order to solve the problem that MAX and MXenes materials have small specific capacity and tend to re-stack,this thesis modified the materials by heteroatom doping,liquid phase exfoliation,compounding and column support,and characterized the components,morphology and structure and tested the lithium-ion battery performance.The details of the study and the results are as follows:（1）Oxygen-doped Ti₃SiC₂ was prepared by a simple high-temperature calcination method.When some carbon atoms in Ti₃SiC₂ were replaced by oxygen atoms,many structural defects would be generated,resulting in more electrochemically active sites.Oxygen atoms were larger in size,and doping was more beneficial to increase the interlayer spacing and conductivity,further improving the reversible capacitance and cycling stability of the electrode material.Electrochemical tests were performed on the as-synthesized materials,and Ti₃SiC₂-800 exhibited the best rate and long-cycle stability.At 2 A g^-1,there was a reversible capacity of 88.2 m Ah g^-1 and a specific capacity of 175.0 m Ah g^-1 after3000 cycles at a current density of 1 A g^-1.This work provides a new design idea for improving the performance of Ti₃SiC₂ lithium-ion battery anode materials.（2）Multilayer Ti₃C₂ was prepared by selective etching of Ti₃AlC₂ by HF,and then it was combined with Mo S₂ to prepare Mo S₂-0.6@M-Ti₃C₂ composite material by hydrothermal method and high temperature annealing.When assembled into a Li-ion battery,it exhibited the best rate and long-cycle stability,with a specific capacity of 241.1 m Ah g^-1at a current density of 2 A g^-1,after 1200 cycles at 1 A g^-1,the specific capacity of nearly355.0 m Ah g^-1 was obtained.Mo S₂ provided a high capacity for the composite material,and the interlayer spacing of M-Ti₃C₂ was improved by inserting into the M-Ti₃C₂ layer,and the increased interlayer spacing was beneficial to the migration of Li⁺.The interlayer confinement effect of M-Ti₃C₂ and the buffering effect of the matrix could effectively alleviate the volume expansion of Mo S₂ during the charge-discharge reaction,and improve the cycle stability of the composite.（3）Based on the above experiments,this thesis made further improvements to the electrode materials by etching Ti₃AlC₂ with HCl+Li F to obtain multilayer Ti₃C₂,then ultrasonically exfoliating to obtain few layers of F-Ti₃C₂,and finally the Mo S₂@F-Ti₃C₂composite was successfully prepared by hydrothermal method.The Mo S₂ nanoflowers were uniformly grown on the layers of F-Ti₃C₂,and the F-Ti₃C₂ nanoflakes not only provided fast transport channels for Li⁺and electrons,but also alleviated the volume expansion of Mo S₂during the reaction process.In addition,the F-Ti₃C₂ nanoflakes with abundant surface groups could generate strong interfacial interactions and pseudocapacitive behaviors with Mo S₂,which were conducive to fast and stable lithium storage.When used as an anode material for lithium-ion batteries,it exhibited the best rate and long-cycle stability,with a specific capacity of up to 568.4 m Ah g^-1 at 2 A g^-1 and nearly 530 m Ah g^-1 after 1200 cycles at 1 A g^-1.Compared with the Mo S₂@M-Ti₃C₂ composite and other anode materials in the literature,its specific capacity and cycle life had great advantages.（4）Ti₃C₂ was prepared by etching Ti₃AlC₂ with HF,and then cetyltrimethylammonium bromide was intercalated into Ti₃C₂ by electrostatic interaction to obtain the prepillared Ti₃C₂,finally,Fe³⁺was intercalated by ion exchange interaction.The iron nanocomposite pillared CTAB-Fe（III）@Ti₃C₂ was obtained.The pillaring effect of Fe³⁺between Ti₃C₂layers could expand the interlayer spacing,expose more active sites,and provide open ion transfer channels.When applied to Li-ion batteries,it exhibited the best rate and long-cycle stability,with a specific capacity of 315.2 m Ah g^-1 at a high current density of 2 A g^-1 and1017.5 m Ah g^-1 after 1300 cycles at 1 A g^-1.This work provides ideas for designing other2D energy storage materials with large interlayer spacing,high rate and cycling performance.