Preparation And Electrochemical Properties Of Multi-ion Intercalated Anode Materials Based On Ti₃C₂ MXene

In recent years,lithium-ion batteries have become the mainstream of the power battery and portable electronic products market due to their advantages such as high energy density,good cycle stability,and low environmental pollution.In 2011,Drexel university in the United States reported a two-dimensional layered carbide and/or nitrite?MXene?obtained by etching ternary layered material MAX phase with HF,which showed graphene-like conductivity and large specific surface area,and was regarded as an ideal raw material for anode materials of lithium ion batteries.However,the spontaneous agglomeration and collapse problems of the MXene sheets during the charge and discharge process limit its application in lithium ion batteries.Research shows that intercalation modification can increase the active sites of lithium ion transport.At the same time,the introduction of intercalated materials can reduce self-stacking and collapse through the"pillar"effect.Therefore,it is of great significance to improve the electrochemical performance.In this paper,the MAX phase?Ti₃AlC₂?was selected as the precursor,and the Ti₃C₂MXene material was prepared by the conventional HF liquid etching method.The influences of HF concentration,etching reaction time and temperature on the phase composition,microstructure and valence distribution of Ti₃C₂ MXene were studied.At the same time,three cations of Li⁺,Na⁺and Sn⁴⁺were selected to study the intercalation modification of Ti₃C₂ MXene.In the experiment,the effects of"two-step intercalation method"?intercalation followed by HF etching?and"one-step intercalation method"?etching and intercalation simultaneously?on Ti₃C₂ MXene lamellar structure were compared.The influence of four cationic surfactants with different chain length,DTAB,TTAB,CTAB and STAB,on the delamination of Ti₃C₂ MXene material was investigated.The influence of cationic intercalation on the structure and electrochemical properties of Ti₃C₂ MXene materials in"one-step intercalation method"was analyzed,and the mechanism of cationic intercalation agent improving MXene layer spacing and reducing self-agglomeration and collapse was revealed.The following conclusions were obtained:?1?HF concentration,temperature and etching time affect the phase and microstructure of Ti₃C₂ MXene.As the concentration of etching agent HF increases,the interlayer spacing of MXene increases.With the increase of etching time,the interlayer spacing of MXene increases.When the etching time is extended to 24h and the etching reaction continues,the interlayer spacing of MXene tends to decrease due to the secondary stacking of layers.The increase of etching temperature can promote the process of etching reaction,but the excessively high reaction temperature?>40??and the local high temperature generated in the process of acid etching will lead to the destruction of MXene structure and the formation of holes in the lamella.?2?The CTAB intercalated into Ti₃C₂ MXene?CTAB@Ti₃C₂-??can be prepared by the"one-step intercalation method",compared with the intercalated product?CTAB@Ti₃C₂-??prepared by the"two-step intercalation method",the interlayer spacing has increased by 1.03?,the layers showed fluffy,and there are obvious signs of delamination;through ultrasonic treatment for 8h,a thin layer of Ti₃C₂ MXene can be obtained.At the same time,MXene with different chain lengths was prepared by the"one-step intercalation method".The study showed that when the number of carbon atoms in the alkyl chain was lower than 16,the interlayer spacing of MXene increased with the increase of the number of carbon atoms in the alkyl chain,and the layers became more bouffant.When the number of carbon atoms exceeds 16,the interlayer spacing decreases and thicker sheets were formed.?3?The“one-step intercalation method”can be used to achieve Na⁺,Li⁺,and Sn⁴⁺intercalation.The cationic intercalated Ti₃C₂ MXene material provides more active sites for lithium ion transport during charging and discharging due to the increased layer spacing and"pillar"effect,which significantly improves its electrochemical performance.Among them,when the concentration of SnCl₄·5H₂O solution is 0.25M,the interlayer spacing of the prepared MXene intercalation material?Sn@Ti₃C₂?is increased from9.93?to 11.52?,and the intercalation product has few and thin layers,with good cyclic stability and multiplier performance.